EPA-600/9-76-030
December 1976
TRANSLATION OF
REPORTS ON SPECIAL PROBLEMS
OF WATER TECHNOLOGY
Volume 9—Adsorption
CONFERENCE HELD IN
KARLSRUHE, FEDERAL REPUBLIC OF GERMANY
1975
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH & DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
EPA-600/9-76-030
December 1976
Publications of the Department of Water Chemistry
Engler-Bunte-Institute
University of Karlsruhe
TRANSLATION OF
REPORTS ON SPECIAL PROBLEMS
OF WATER TECHNOLOGY
Volume 9 - Adsorption
Edited by
H. Sontheimer
University of Karlsruhe
Conference Held in
Karlsruhe, Federal Republic of Germany
1975
WATER SUPPLY RESEARCH DIVISION
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not
constitute endorsement or recommendation for use. This report was printed
as received from the Engler-Bunte-Institute, Karlsruhe, Federal Republic
of Germany.
11
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem
solution and it involves defining the problem, measuring its impact, and
searching for solutions. The Municipal Environmental Resarch Laboratory
develops new and improved technology and systems for the prevention,
treatment and management of wastewater and solid and hazardous waste
pollutant discharges from municipal and community sources, for the
preservation and treatment of public drinking water supplies, and to
minimize the adverse economic, social, health and aesthetic effects of
pollution. This publication is one of the products of that research;
a most vital communications link between the researcher and the user
community.
In the summer of 1975 a Conference was held at the Engler-Bunte-
Institute in Karlsruhe, Federal Republic of Germany on the subject of
adsorption and reactivation as a water treatment unit process. Twenty-
four papers were presented by the leading scientists and engineers in
Western Europe. The Proceedings of this Conference have been translated
and are presented herein. The information of the adsorption process
formerly available only in German is now available in English and this
should help those in the United States attempting to provide safe drinking
water. Copies of the previous 8 volumes are available in German from the
Engler-Bunte-Institute.
Francis T. Mayo
Director
Municipal Environmental Research
Laboratory
111
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PREFACE
When I visited the Engler-Bunte-Institute in Karlsruhe, Federal
Republic of Germany in the fall of 1975 Professor Sontheimer showed me the
program of a recent conference on the treatment of drinking water for the
removal of organic matter. As we discussed the various papers I realized
that most of the European technology we had been seeking over the past
few years was summarized at this Conference. We then dicussed how best to
share this information with our United States colleagues. Translation
of the Proceedings of the Conference seemed the best method.
After many hours of effort by Professor Sontheimer and his colleagues
Dr. C.N.S. McLachlan, Dr. W. Kuhn and Mrs. I. Hein, as well as by
Dr. James M. Symons of my staff, the translation was completed and I
am pleased to make it available. I am sure that all will agree that it
represents a significant contribution to our literature.
Gordon G. Robeck
Coordinator, Water Supply Research
U.S. Environmental Protection Agency
Cincinnati, Ohio
November 1976
This publication was compiled in cooperation with many scientists.
To all of them who have helped towards its completion I express my cordial
thanks. I hope that this publication will contribute to the further
development of adsorption processes and their optimum application. This,
in turn, would be an important contribution towards ensuring the supply
of drinking water of high quality at any time.
Thanks are due to all authors for agreeing to the translation of
their papers and for their support to Mrs. I. Hein, Dr. C.N.S. McLachlan
and Dr. W. Kuhn for their valuable help in translating.
Prof. Dr. H. Sontheimer
Engler-Bunte-Institute
Karlsruhe, Federal Republic of Germany
August 1976
IV
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CONTENTS
Foreword
Preface iv
List of authors vii
Conversion Factors ix
Sontheimer, H. 1
The importance of adsorption processes in
drinking water treatment
Jiintgen, H. 16
Manufacture and properties of activated carbon
Sontheimer, H. 29
Basic principles of adsorption process techniques
Sontheimer, H. 67
The use of powdered activated carbon
Poggenburg, W. 74
Activated carbon filters in water treatment plants
Processing techniques - Engineering - Operation
Scheidtmann, W.
Investigatio
when using ozone
Investigations of the optimization of pretreatment "°
Heymann, E.
Practical experience in the use of flocculation 112
filtration connected in series to granular activated
carbon filters
Schalekamp, M. 128
Use of activated carbon in the treatment of
lake water
van Lier, W.C., Graveland, A., Rook, J.J., Schultink, L.J. 160
Experiences with pilot plant activated carbon filters
in Dutch waterworks
182
Fuchs , F. , Ku'hn , W.
The use of activated carbon to analyse natural waters
with regard to their behaviour in waterworks filters
Sontheimer, H. 208
Considerations on the optimization of activated carbon
use in waterworks
-------
Klein, J. 215
Comparative assessment of adsorbents
Janata, W.
Investigations into the control of activated carbon
filters at waterworks
O O Q
Weissenhorn, F.J.
Testing of activated carbon filters in waterworks
Sontheimer, H.
Realistic laboratory test methods for the
evaluation of activated carbon
Juntgen, H.
Phenomena of activated carbon regeneration
Strack, B. 284
Operation, problems and economy of activated
carbon regeneration
01 9
Klotz, M. , Werner, P., Schweisfurth, R.
Investigations concerning the microbiology of
activated carbon filters
Eberhardt, M. ' 331
Experience with the use of biologically effective
activated carbon
van der Kooi j , D. 348
Some investigations into the presence and behaviour
of bacteria in activated carbon filters
Albert, G. 355
The influence of dissolved organic compounds on
flocculation
Eberle, S.H., Stober, H., Donnert, D. 380
Study on the adsorption properties of aluminium oxide
and its application for the purification of ground water
containing humic substances
Kolle, W. 405
Use of macroporous ion exchangers for drinking water
purification
Sontheimer, H. 414
Theory and practice in the use of adsorption processes
Literature references
vi
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AUTHORS
Dr. G.ALBERT
Dr. D.DONNERT
Dr. M.EEERHARDT
Dr. S.H.EBERLE
Dipl.Chem. F.FUCHS
Dr. Ir.A.GRAVELAND
Dr. E.HEYMAMN
Chem.Ing.(grad.) W.JANATA
Prof.Dr.rer.nat. H.JONTGEN
Dr. J.KLEIN
M.KLOTZ
Dr. W.Kdlle
Dr. D.van der KOOIJ
Dr. W.KOHN
Dr. W.C. van LIER
Engler-Bunte-Institut, Bereich Wasser-
chenn'e, Uni Karlsruhe, Postfach 6380,
75 Karlsruhe 1
Institut fur Radiochernie, Bereich PTW,
Kernforschungszentrum Karlsruhe
Stadtwerke Bremen AG, Postfach 107303,
28 Bremen 1
Institut fur Radiochernie, Bereich PTW,
Kernforschungszentrum Karlsruhe
Engler-Bunte-Institut, Bereich Wass.er-
chemie, Uni Karlsruhe, Postfach 6380,
75 Karlsruhe 1
Gemeentewaterleiding Amsterdam,
Amsterdam-Sioterdijk, Condensatorweg 54,
Niederlande
Nicderrheinische Gas- und Wasserwerke GmbH,
Postfach 45, 41 Duisburg 11
GEW-Werke Kbln AG, RosenstraBe 30,
5 Kbln 1
Bergbau-Forschung GmbH, Forschungsinstitut
des SteinkohlenbergbauvereinSj Postfach,
43 Essen 13
Bergbau-Forschung GmbH, Forschungsinstitut
des Steinkohlenbergbauvereins, Postfach,
43 Essen 13
Fachbereich 4 der Universitat des Saarlandes
- Fachrichtung 4.18 - Hygiene und Mikrobio-
logie - Med. Fak. Bau 43,
665 Homburg/Saar
Stadtwerke Hannover AG, Postfach 5747,
5 Hannover 1
Keuringsinstitut voor Waterleidingsbedrijven
(KIWA), Rijswijk/Niederlande
Engler-Bunte-Institut, Bereich Wasser-
chemie, Uni Karlsruhe, Postfach 6380,
75 Karlsruhe 1
Norit - Research
Textielweg 15, Amersfoort/Niederlande
Vll
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Direktor W.POGGENBURG
Dr. O.J.ROOK
Direktor M.SCHALEKAMP
OIng. W,SCHEIDTMANN
Dr. L.J.SCHULTINK
Prof.Dr.rer.nat. R.SCHWEISFURTH
Prof.Dr.rer.nat. H.Sontheimer
Dr. H.STDBER
Direktor Dr. B.STRACK
Dr. F.J.WEISSENHORN
P.WERNER
Stadtwe^ke Dusseldorf AG
Postfach 1136, 4 Dusseldorf 1
Drinkwaterlei ding Rotterdam
Postfach 1166, Rotterciain/Niedcrlande
Wasserversorgung Zurich
Bahnhofsquai 53 CH-3023 Zurich
Stadtwerke Duisburg AG, Postfach 89,
4100 Duisburg
Provinciaal Waterleidingsbedrijf van
Noord-Ho 11 and,
Bloentendaal/Niederlande
Fachbereich 4 der Universitat des Saarlandes,
- Fachrichtung 4.18 - Hygiene und Mikrobic-
logie - Med. Fak. Bau 43,
665 Homburq/Saar
Engler-Bunte-Institut, Lehrstiihl und Bereich
fiir Wasserchemie, Uni Karlsruhe,
Postfach 6380, 75 Karlsruhe 1
Institut fur Radiochemie, Bereich PTW,
Kernforschungszep.trum Karl sruhe
Stadtv^erke Wuppertal AG,
Postfach 201616, 56 Wuppertal 2
Stadtv;erke Dusseldorf AG,
Postfach 1136, 4 Dusseldorf 1
Fachbereich 4 der Universitat dss Saarlandes,
- Fachrichtung 4.18 - Hygiene und Mikrobio-
logie - Med. Fak. Bau 43,
665 Homburg/Saar
viii
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CONVERSIONS FACTORS
1) AE (Angstrom) x 0.0001 = ymeter
2) Bar x 33.3 = feet of water
x 14.5 = pounds per square inch
3) cm x 0.39 = inches
4) Dates are Day/Month/Year
5) DMarks x 0.39 = Dollars
6) DMarks/kg x 0.18 = Dollars/pound
7) DMarks/m x 1.1 = cents/cubic foot
x 147.7 = cents/1000 gallons
8) DMarks/t (metric) x 0.022 Cents/pound
9) Dollars/m x 379 = cents/1000 gallons
10) Dollars/m3/day x 3800 = Dollars/mgd
11) Dutch id/m3 x 1.42 = cents/1000 gallons
2
12) g/cm x 62.3 = pounds/cubic foot
3
13) g/m x 1 =- milligrams/liter (ppm)
14) Kcal/kg x 1.80 = BTU/pound
15) kg x 2.2 = pounds
3
16) kg/m x 0.063 = pounds/cubic foot
17) kg/sec x 190,480 = pounds/day
18) km x 0.62 = miles
19) m x 3.28 = feet
20) m x 10.79 = square feet
21) m3 x 264 = gallons
x 35.3 = cubic feet
22) mbar x 0.0333 = feet of water
x 0.0145 = pounds per square inch
IX
-------
3
23) m /d x 0.000264 = million gallons/day
24) mg/m x 0.000063 = pounds/cubic foot
25) m/hr x 0.4 = gpm/sq ft
x 0.055 = feet/second
3
26) m /hr x 4.4 = gallons per minute
x 0.0063 = million gallons/day
27) m3H20/kgGAC x 120 = gallons/pound GAG
28) mm x 0.039 = inches
3
29) mmole/m x 0.001 = mmole/liter
30) mole/kg x 0.454 = mole/pound
31) m/sec x 3.28 = feet/second
3
32) m /sec x 22.8 = million gallons/day
x 35.3 = cubic feet/second
33) t(metric) x 0.91 = U.S. Ton
x
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THE IMPORTANCE OF ADSORPTION PROCESSES IN DRINKING WATER
TREATMENT
by H. Sontheimer
The use of adsorption as a purification process has become
increasingly important for drinking water treatment in recent
years. However, it is by no means a new technique, as may be
seen in the following recommendation in a Sanskrit text from
about 20O B.C.: "It is good to keep water in copper vessels,
to expose it to sunlight, and filter it through charcoal"
(MANTELL 1951) .
Many centuries later NICHOLSON (18O6) gave an exact description
for using powdered charcoal and barrels with a charred inner
surface for keeping water fresh on ships. At the same time
the first carbon filters in waterworks were installed, using
wood charcoal and bone charcoal. This kind of treatment was
discontinued later because of the poor effectiveness of the
filters (KIRK 1964).
With the development of processes for manufacturing suitable
activated carbons, the importance of adsorption techniques for
water treatment increased again. The removal of taste and odour
and dechlorination were the most important aims during this
period (HOLLUTA 1954, BAUER and SNOEINK 1973, SONTHEIMER 1975).
In recent years, there has been an increased use of adsorption
processes, mainly due to the rise in chemical water pollution
(SONTHEIMER 1975). Adsorption plants such as activated carbon
filters are no longer used for the removal of taste and odour
but also for the reduction of the total load of organic sub-
stances, and especially of organic contaminants which are
hazardous to health.
-------
However, adsorption is only one possibility for the removal of
dissolved organics in water treatment. It must compete with
other treatment techniques which have the same objectives.
These techniques are the following:
biological oxidation
chemical oxidation
precipitation and flocculation
ion exchange
membrane processes
One can distinguish between treatment methods based on chemical
reactions, like oxidation processes and ion exchange, and those
where accummulation of material on a solid surface takes place,
like adsorption and flocculation. The latter two processes are
the subject of this book.
All these processes have one thing in common; they are of
limited effectiveness. Of the great variety of organic substances
present in the water to be treated, only a certain fraction can
be removed by such processes. Thus biological treatment in
general removes only biodegradable material and, similarly,
chemical oxidation cannot completely remove all organics.
This is also the case in all the other treatment processes,
including adsorption.
Therefore it is necessary to check for each water which treatment
process is most essential,and the advantages and disadvantages
of each process must be considered. Adsorption processes have
the following advantages:
1. Specific removal of the least desirable organics,
because they are usually strongly adsorbed.
-------
2. Highly effective purification, especially while using
activated carbon filters.
3. Favourable economics and simple application.
Of the points mentioned above, the specific adsorption
characteristics of the undesirable organics are of special
importance, since they are the main reason for the high treat-
ment results and the reasonable economics. The question then
arises which contaminants need to be removed in drinking water
treatment and what specific characteristics the adsorbants need
to have. Some papers in this book will deal with this problem
because it is evident and of increasing importance for all
waterworks. However, first of all a general view is given of
the problems facing waterworks, starting with the discussion
of analytical results obtained by the Engler-Bunte-Institut
for the waterworks along the Rhine.
The most simple parameter to determine is the overall concen-
tration of dissolved organics. Such measurements have been made
along the Rhine at many sampling stations for some years. The
values obtained are reported in the papers of the Association
of the River Rhine Waterworks (ARW 197O-1971) and the Association
of Waterworks at the Lake of Constance and the Rhine (AWBR
197O-1974). Fig. 1 shows the geometric mean data for three
typical points along the Rhine.
Fig. 1; Organics in Rhine water.
Comparison of the geometric mean data for
1970-1974
The following sum parameters are shown: DOC (Dissolved Organic
Carbon), COD (Chemical Oxygen Demand) and UV extinction. The
total load of organic carbon may be obtained by measuring the
DOC, COD or the UV extinction. The level of these values and
thus the concentration of dissolved organic material in the
-------
fi. DOC COD UV
in m3/sec ingC/m inmg02/l in nV'
2000- :
2000-
1000-
IT
- ' \
10-
5-:
30
x s 15
•
35,0-
p
1^5- ;
'-
Oberrhein, Strom-km 354
Karlsruhe
Mittelrhein, Strom-km 507
Wiesbaden
g 1970
0 1971
Q1972
| 1973
1974
Niederrhein, Strom-km 730
Dusseldorf
Fig. 1:
Oberrhein, Strom km 354: Upper Rhine at km 354 of the river
Mittelrhein : Middle Rhine
Niederrhein : Lower Rhine
-------
5
river Rhine changes, as these data show, with flow rate and
flow distance. However, it may be seen that the changes in the
three parameters are not parallel.
Fig. 2; Comparison between DOC discharge and flow rate
for some places along the Rhine (averaged
curves 197O-1974)
Figure 2 shows particularly clearly how strongly the change in
organic loading depends on the two parameters flow rate and
flow distance. It may be seen that the DOC load increases both
with increasing flow rate and with increasing flow distance.
Conversely, the concentration shows the reverse tendency, that
is to say, the highest concentrations are found at low flow
rates.
Relationships such as shown in Figure 2 can be taken in con-
junction with suitable theoretical models to give some infor-
mation on the fraction of bioresistant compounds in the Rhine
river water. These compounds are of special interest because
they are not retained by the river bank filtration. Since most
German waterworks at the Rhine do not take their raw water
directly out of the river, these compounds have to be removed
on the activated carbon filters.
Fig. 3; Change of load with bioresistant compounds
with the flow distance
The increase in the load of bioresistant compounds with the
flow distance is much higher than the increase of the water
flow. Therefore, at the middle and lower Rhine river a high
concentration of organic material has to be removed by ad-
sorption. The chemical composition of these organics and the
change in their relative fractions with flow rate is shown
in Figure 4, using different group parameters and the data
of 1974 (SONTHEIMER 1974).
-------
20-
P. . JQOO 2000 3 300C
Wasserfuhrung in m /sec
4000
Fig. 2:
DOC-Fraclvt in kg/sec: DOC loading in kg/sec
3 3
Wasserfuhrung in m /sec: flow rate in m /sec
-------
o
0>
I/)
en
6
4
-C
g
ul
0>
L~
a
_a
z>
a
JD
J3
a
$8
0,6
0,4
0,2
0,1
200
I i
400 600
Flufistrecke in km
800
Fig. 3;
Schwerabbaubare Fracht in kg/sec: bioresistant load in kg/sec
FluBstrecke in km: flow distance in km
-------
8
Fig. 4; Variation of the main components of the
dissolved organic material with river flow
rate in the lower Rhine
During ground passage, i.e. sand bank filtration, the bio-
degradable compounds and also part of the humic acids are
removed. The substances remaining for the adsorption treatment
belong mostly to the group of sulphonic and lignin sulphonic
acids, which are only partly removed in sand bank filtration*
and the organo-chloro compounds. These amount from 5 to 12 per
cent of the total load and many of them are health hazards.
That they can be adsorbed by activated carbon is shown in
Figure 5, where a gas-chromatrogram of an extract of a loaded
activated carbon from a waterworks filter is shown.
Fig. 5; Gas-chromatogram of an activated carbon extract
This figure, which is representative of many similar results,
shows why adsorption techniques have become of such increasing
importance. Many of the identified compounds which were removed
in the activated carbon filter mentioned above are undesirable
in drinking water. Only activated carbon filters are able to
achieve the degree of removal required, at present.
When discussing organo-chloro compounds, it is necessary to
remember that when waters with a high concentration of organics
are chlorinated, organo-chloro compounds are also produced
(ROOK 1974). As Figure 6 shows, fairly high concentrations of
organo-chloro compounds can be observed (SYMONS 1975).
-------
100
a so
o1
1000
2000 3000
Wasserfuhrung in m /sec
4000
Fig. 4:
Geloste organische Substanz in %: dissolved organics in per cent
abbaubare Stoffe: degradable substances
Huminsaure: humic acids
org. Chlorverbindungen: organo-chloro compounds
Sulfonsauren auBer LS: sulphonic acids except LS
Ligninsulfonsaure: lignin sulphonic acid (LS)
3 3
Wasserfuhrung in m /sec: flow rate in rn /sec
-------
10
Tempcraturprogramrr
Fig. 5:
Intensitat: intensity
unbekannt: unknown
-------
11
Fig. 6; Frequency distribution of different trihalogen
methanes in chlorinated USA drinking waters
(SYMONS)
According to the data in Figure 6, chloroform concentrations
of up to 0.1 mg/1 have been measured. Furthermore, there is a
relationship between the concentration of dissolved organic
carbon in the treated water and the concentration of organo-
chloro compounds (see Fig. 7). This topic is of special impor-
tance.
Fig. 7; Dependence of the medium concentration of
trihalomethane compounds on the concentration
of dissolved carbon (SYMONS)
Although taking into consideration the relatively high chlorine
dosages used in the USA, it may be deduced from these results
that it is not only important to remove the existing organo-
chloro compounds from the raw water during drinking water treat-
ment but that one should also lower the total concentration of
organic materials. Otherwise, organo-chloro compounds will be
produced during chlorination, which is necessary for disin-
fection before distribution.
However, it should be mentioned too that dissolved organics,
especially fulvic acids, act as corrosion inhibitors (SONTHEIMER
1969, RUDEK 1975). Therefore, it is not advisable to remove too
much of these organic substances.
Considering that all raw waters contain a great amount of
different substances and that competitive and selective ad-
sorption may cause an increase in the concentration of certain
compounds - as can be seen from gas- or liquid chromatography
analyses - it becomes clear how difficult it is to produce a
common evaluation for the adsorbent quality and the running time
of an activated carbon filter. Additional difficulties arise
due to the different operation conditions at each waterworks.
In addition, process and technological points of view, as well
as security in treatment effectiveness with changing water
quality, have to be considered.
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12
0,1 2 5 10 20 50 80 9095 98
Percent equal to or less than
given concentration
Figure 6
Note- 1pM/l Total
Trihalomethane =
119pg/l Chloroform
if only Chloroform
was present
No - Number of locations in
Non-Volatilz Total Organic
Carbon cell
_L
_L
"0 12 3 i, 5
Finished Water, Non - Volatile Total Organic
Carbon mg/l
Jlgure 7
-------
13
To sum up all these aspects for the control of adsorption
processes - despite all the difficulties - the following
recommendations, set out in Table 1, can be made:
Table 1; Recommendations for controlling adsorption processes
(activated carbon filters) for drinking water
treatment
1) Evaluation of activated carbon with several parameters
a) Examination of adsorption equilibria for adsorptive
mixtures;
b) Selection of adsorptive mixtures in respect of the
practical problems;
c) Examination of adsorption kinetics.
2) Evaluation of running time with different parameters
a) Reduction of UV extinction;
b) Loading with non-polar and polar organo-chloro
compounds at different filter layers;
c) Removal of odour substances;
d) Measurement of biological effectiveness;
e) Comparison with laboratory testing methods.
3) Periodic control of the effectiveness of the activated
carbon filters
4) Coordination of the additional treatment steps with the
effectiveness of the activated carbon filters
-------
Because more detailed explanations are made on the topics
mentioned above in other papers, only some general remarks
are made here. From the experience available to date, it can
definitely be concluded that parameters such as phenol loading
or phenol value, iodine number etc., give no relevant informa-
tion for the evaluation of activated carbon used in waterworks.
Here the displacement of adsorbed material caused by competitive
adsorption is nearly always of such importance that only measure-
ments of the adsorption equilibria with mixtures of substances,
which show some correlation with the pratical problem, are worth-
while carrying out. Furthermore, in addition to the adsorption
equilibria - to avoid misinterpretation - kinetic studies are
always necessary.
Similar aspects have to be considered for the regular control
of the carbon filters. Although the control of the reduction
in UV extinction is easy and useful, and although these results
correlate well with other sum parameters such as DOC, this
value alone provides little information about the effectiveness
of an activated carbon filter.
On the one hand, it can be concluded that an extensive removal
of organics would inevitably result in the removal of all
undesired and hazardous material.-However, according to results
available so far, this is only valid when more than 8O per cent
of the total dissolved organics are removed. - On the other hand,
such a high degree of removal is not always required. It is
therefore necessary to carry out additional investigations on
the loading of activated carbon with organo-chloro compounds
and also on the removal of taste and odour, together with
investigations on the biological effectiveness of the filters.
The results obtained from the large filters should also be
compared with the laboratory tests.
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15
If such a control of the filters is carried out regularly,
and the other treatment steps are optimized at the same time,
the necessary informations will be obtained for each individual
case to decide on the running time before regeneration, the
choice of the proper carbon quality and on the optimum process
data.
It is quite possible that this kind of procedure will lead to
different conclusions on the optimum running conditions in
activated carbon plants at different waterworks. Nevertheless,
important conclusions on the optimum application of adsorption
techniques can be drawn from the experiences at different places.
Therefore, the results obtained at different waterworks are
discussed in detail in a number of the following papers.
However, experience alone, without an understanding of the
process itself, may lead to misinterpretations. Therefore,
reports of practical work are supplemented by papers dealing
with basic aspects of these processes. The research work for
these was supported by grants given by the Federal Ministry
of Research and Technology in a programme called "New tech-
nologies of water treatment" and by the German Research
Association in the Special Research Group 62 entitled "Basic
processes in water and gas purification". In addition, the
research work carried out at the Engler-Bunte-Institut was
supported by different German waterworks.
This support deserves recognition and appreciation, as do the
intensive activities of the waterworks in solving their own
problems in the use of activated carbon filters. This shows
^he importance of adsorption techniques in the field of drinking
water, where they are indispensable in solving many problems
on quality control.
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16
MANUFACTURE AND PROPERTIES OF ACTIVATED CARBON
by
H. Juntgen, Essen
1. Introduction
An adsorbent consisting mainly of carbon having a distinct structure
of pores is called activated carbon. The general scheme of the
highly ramified pore system is shown in Fig. 1 ,
Diffusion pores Micro- und submicropores
Fig. 1; Scheme of the pore structure of activated carbon
The particle of activated carbon as shown on Fig. 1 exhibits
macropores of a diameter = 500 AE/which extend all through it. The
transport of the adsorptives from the outer particle limit to the
pore system is effected rapidly; thus, these macropores are also
called "admission pores" or "diffusion pores". From these macro-
pores numerous finely ramified meso-, micro- und submicropores
branch off, the diameters of which are *500, •£ 2o and
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17
the load of a medium-quality activated carbon at full saturation
of the surface may be estimated to be 5o to 7o % (by weight) of
organic matter.
As a characteristic feature for the carbon structure of activated
carbon the adsorption heat at adsorption of non-polar organic
matter is considerably higher than the one of adsorption of
polar-organic matter or of water. This behaviour, also called
hydrophobia, means that in contrast to other adsorbents activated
carbon adsorbs selectively the non-polar organic matters. Due to
its hydrophobic surface activated carbon is especially suitable
to adsorb organic pollutents contained in low concentration in
waste waters of all kind. Since recently the use of grain-sized
activated carbon became more and more widespread for those
purposes, the present note shall deal exclusively with the
manufacture of grain-sized activated carbon. A detailed descriptior
of all manufacturing processes has been set up by ¥. Aehnelt
(Ullmanns Encyklopadie der technischen Chemie, 3. Auflage, Bd. 9,
S. 800).
Basic principles for the manufacture of activated carbon
The manufacturing principle consists in selective removal of
certain components of suitable carbon-containing ma-
terial by a subtraction without shrinkage of the grain so that
defined hollow spaces remain instead of the removed components.
The most simple process,applied since more than 2ooyears consists
in the pyrolysis of wood or other organic material. In the course
of this pyrolysis volatile matter is removed and the remaining
carbon-containing residue exhibits already a certain porosity.
The pyrolysis of organic matter consisting of carbon hydrates
or cellulose can be controlled by use of water-separating
additives as e.g. zinc chloride or phosphoric acide in a way that
a considerably greater pore system is obtained than in case of
a pyrolysis without use of such additives. The method described
is also referred to as "chemical activation". The pore system of
-------
18
a pyrolysis residue - sometimes also called "coke" - may in many
cases be systematically enlarged and modified by reaction of a
coke at higher temperature with oxidation agents as e.g. steam
or COp which transfer selectively a part of the carbon substance
into the gaseous phase thus leaving hollow spaces. Table 1 shows
a selection of carbon-containing raw materials, predominantly
used nowadays for manufacture of activated carbon by means of
chemical activation and gas activation processes. Whereas the
chemical activation process is confined to cellulose-containing
raw materials - here called wood - the number of raw material
for the gas activation process is considerably greater and ranges
from wood and peat to hard coal and petroleum coke.
Process
Raw material
Activation agent
Chemical
activation
Gas acti-
vation
Wood
Wood
Peat
Lignite
Hard coal
Petroleum
coke
ZnCl9, H^PO/, etc.
H2°D
ro
Table 1: Manufacture of activated carbon -
Process and raw materials
Before activation, the basic material used for activated carbon
production has to be brought to uniform size. Several methods
are available for this purpose which are shown on Table 2. By
extrusion of a blend of fine basic material and binder, several very
solid cylindrically shaped pieces with a smooth surface can be
obtained in a range of graine size between 1 and 9 mm. The grains
are fairly uniform in size.
Generally, the diameter of the cylinder varies only within very
tight tolerances, whereas the length of the individually shaped
particles is somewhat non-uniform. By this process, also particles
of a length equal to their diameter can be produced. Pelletisation
-------
19
constitutes another method of shaping. By this method ball-shaped
particles of satisfactory hardness are obtained, however, the
range of sizes is considerably greater than for extrusion pro-
ducts. For adsorption purposes, pellets of 4 to 9 mm in size
may be produced. Another method for shaping small-particle basic
material consists in agglomateration with subsequent crushing and
screening which can be carried out after pyrolysis or after activ-
ation. Due to the crushing, the shaping of individual particles
is irregular and the surface of the particles is rough. The hard-
ness of these particles may be good or even very good . The range
of grain sizes is wide. Eventually, also basic material of natural
granularity may be used for manufacture of activated carbon in
the course of which it is crushed either before or after activ-
ation. Also in that case the particles are of irregular shape
and rough surface, but the hardness is generally inferior to the
one of the products obtained by the shaping processes (H. Dratwa,
H. Juntgen, Staub-Reinhaltung der Luft, 27 (1967), p. 3ol/3o7).
Shaping
Extrusion
Pelletis-
ation
Agglomer-
ation and
crushing
Crushing
Grain size
1-9
4 - 9
o -lo
o -lo
[
Range of
sizes
narrow
wide
wide
wide
Grain shape
cylindrical
round
irregular
irregular
Grain sur-
face
smooth
nearly
smooth
rough
rough
Hardness
very
good
satis-
factory
very good
to good
satis-
factory
Table 2: Manufacture of activated carbon - Shaping process
Description of chemical activation process
On Figure 2 a schematic representation of the individual process
phases for chemical activation of activated carbon is shown
(M. Smisek and S. Cerny, Active Carbon, Elsevier Pub., Amsterdam
097o)). The raw material is first ground to fine grain size and
then blended to a certain ratio with an activation reagent, e.g.
-------
20
zinc chloride or phosphoric acid. The paste thus obtained is then
brought to shape by the processes described in the previous
chapter, extrusion being preferred. After shaping the products
obtained must be dried according to a clearly defined process.
Then, calcination is carried out in rotary kilns at temperatures
ranging from 7oo to 9oo °C, the activation agent being partly
removed by distillation and subsequently recovered. After cooling
a wet extraction is carried out in order to remove the quantity
of activation agents still contained in the pore system. Again,
the removed residual activation agent is recovered from the
aqueous solution. After chemical activation wet treatment with
steam at 5oo °C may be practised in order to make the surface
hydrophobic.
Raw material
4'
Grinding
Activated
carbon
ZnClQ, H,P(
42 3
Blending
H20
After- treat-
ment ^~
}4 etc.
Gas
^
. Shaping . Preliminary drying
Wet extraction^
I < —
I
R p n n'v/'o'pir —,....
Gas
4^ v*
Calcination
— i
1
Figure 2: Manufacture of activated carbon - chemical activation -
Process description of gas activation of activated carbon
Figure 3 gives a schematic view on the process phases for gas
activation (H. Juntgen, Ber. Bunsenges. Phys.Chem. 1975)- In
this case, too, the raw material is ground to fine granular sizes
and, if necessary, subjected to preliminary treatment. In case
of e.g. hardcoal used as raw material this preliminary treatment
consists of an oxidation in atmospheric air at temperatures be-
low 3oo °C. After this pre-treatment the fine dust is blended
with binder and brought to cylindrical shape. The shaped products
are subjected to pyrolysis at temperatures between 600 and 9oo °C
in ambiance of inert gas. During this pyrolysis a residue is
produced which subsequently is treated at temperatures between
7oo and 9oo °C with oxidizing agents, as e.g. steam or C02>
-------
21
Raw material
4
Grinding #• Pre-treatment
Activated
carbon
Cooling
Binding agent
Blending
Shaping
co2,
4-
etc.
Activation
\s
Pyrolysis
Figure 3: Manufacture of activated carbon - Gas activation -
The steam reaction or Boudouard reaction respectively/ which
takes place has been examined very carefully under various
points of view. Especially the mechanism and the kinetics of
these reactions are well known (K. Hedden.Ullmanris Encyklopadie
der technischen Chemie, 3. edition, Vol. lo, p. 362). Due to this
knowledge the reaction can be controlled so that a well-defined
pore system can be obtained. After activation the product is
cooled and packed.
Properties of activated carbon obtained by gas activation
The properties of activated carbons depend in a fairly complex
manner on the raw material used and on the activation process
applied. Within the framework of the present note a comprehensive
view on this cannot be given. Therefore, some observations per-
taining to the properties of gas-activated carbons in function of
different parameters of the manufacturing process shall be
quoted as examples.
Detailed investigations carried out by Bergbau-Forschung have
shown that the macropore system of activated carbon is pre-de-
termined already during the shaping process and definitely fixed ,
by the subsequent pyrolysis (H. Juntgen's inaugural dissertation).'
It is easily imaginable that during extrusion the original void
volume between the individual grains of carbon is filled up by
*) Heidelberg, 1966
-------
22
the binder, the individual grains being agglomerated under the
pressure applied. During the subsequent pyrolysis mostly macro-
pores are created in the void volume filled up by the binder, by
disintegration of the latter, since the coke residue of the
binder is comparably small. It is, therefore, to be expected
that the inacropore volume of the formed grains depends not only
on the forming pressure but also on the grain size and grain
distribution of the carbon dust used, since the latter data have
a decisive influence on the void volume. For illustration Fig. 4
shows the integral pore distribution of the macropore system
- measured by mercury porosimetry - within shaped products
immediately after pyrolysis, three carbon-containing raw material
qualities of different grain size having been used. A material
containing a relatively high proportion of coarse grains and a very
heterogeneous grain distribution results in a macropore system
/, g
with a range of pore radii from lo to lo AE. This range is
obviously very wide. When using a feed stock containing a smaller
share of coarse grains, this range may be keut narrower and the
4 5
most frequent pore radii are lo to lo AE. Furthermore, the
total volume of macropores is reduced. A very fine dust with a
relatively narrow grain size distribution eventually results in
a macropore system with a very narrow range of radii, mostly of
L^
approx. lo AE. Again, the total volume of macropores is further
decreased.
Admission r>ore volume
CcmJ/}OOg]
—^
40
30
0/1
2U
10 -
0
1
Fig. L
&•&.
'- ,*-*± .
,-.-.%>:-
' V ;*iV •
'•*'*'*•'«
^fe--
4^?'J
T^»
/
1/ /
1
PC
l/^-
/
W
#fc.
«• • . i \ •
4
*
\
~7
Q2 5 103 5 JO4 5 tO5 5 101
t- Manufacture of activated carbon - Ini
radius
-------
23
The control of the activation process is of particularly decisive
influence on the micropore system and, thus, on the properties
of the activated carbon. In case of very short treatment periods
in activating gas atmosphere only a small share of the carbon is
partly gasified and, consequently, the micropore system obtained
is small. V/ith increasing activation time the micropore system
may purposely be increased. The degree of activation may pre-
ferably be defined by the recorded portion of the carbon origin-
ally contained which partly gasified by the activation process.
Fig. 5 shows the most important properties of activated carbon
in function of the degree ol activation represented schematically
in the abscissa. First, it is noted that the bulk density
decreases nearly linearly with increasing degree of activation.
The decrease of bulk density is due to the pore system becoming
larger with increasing degree of activation, i.e. due to the
decreasing apparent density and the constant real density of the
material. The development of the micropore volume is different
from the one of the macropore volume. These developments are not
related to grams of activated carbon but to loo ml bulk volume
of activated carbon. The micropore volume increases nearly
linearly with increasing degree of combustion. This strong increase
may be explained by the gasification reaction taking place pre-
dominantly on the total inner surface of the coke and, thus, forms
mostly very fine micropores.The macropore volume increases re-
latively moderately in the course of activation. Furthermore,
it was found - not illustrated here - that the pore distrib-
ution of the macropore volume is not significantly influenced
by the activation process.
In Fig. 5 it is shown that the average adsorption pore diameter
increases sharply with increasing activation, viz. by the
factor 2.5, i.e. with increasing activation activated carbon
becomes increasingly wide-pored. As expected, the inner surface
does not increase uniformly over the whole activation process. It
is even to be noted that after a sharp increase and a maximum
period a slight decrease follows. The reason is that at the
-------
g/i Schuttdichte
8001
cm3/100 ml Mokroporenvolumen
30-1 MOOAE
15-
Gew %=-0.5mm StoHhorte
100-1
50
cm/100ml Mikroporenvolumen
304 r-=«OAE
15-
AE mittlerer Adsorptionsporen- m/100ml BET-Oberflache
20idurchmesser + «103
4U-
0
Fig. 5
— Aktivierungsgrod —-
Manufacture of activated carbon - Influence of the
degree of activation -
Schlittdichte = bulk density
Makroporenvolumen = macropore volume
Gew.-Jo = % (by weight)
Mikroporenvolumen = micropore volume
Stoflhorte
impact hardness
^orption pore diameter
BET Oberflache = surface as per BET
Aktivierungsgrad = degree of activation
beginning of activation mostly narrow pores are formed, the
surface of which contributes largely to the total inner surface.
Later on, activation predominantly causes a growth of the smaller
pores so that the increase of the specific inner surface is slowed
down and later on even turns into decrease. With increasing
micropore volume and macropore volume the carbon structure
necessarily becomes more fragile, i.e. the so-called impact
hardness decreases, firstly fairly slightly, however more
pronounced beyond the medium values of degree of activation.
The changes in pore distribution within the micropore volume are
shown on Fig. 6. Here, the differential pore distribution of
activated carbon withdifferent degree of activation values is
shown. The respective values have been established by measuring
-------
25
benzene adsorption and subsequent assessment according to
Dubinin-Radushkevich using Thomson's equation (H. Juntgen,
H. Seewald, Ber. Bunsenges. Phys.Chem., 1975). The differential
pore volume dV/dR is plotted against the pore radius.
0
Fig. 6
WrtAEJ
Volume distribution of adsorption pore system of
different activated carbon qualities
From these curves the average pore radii, i.e. the average pore
diameters shown in Fig. 5 are determined by separating the
surfaces under the curves into two equal shares. From the
graphical representation it may be noted that with increasing
degree of activation the pore volume - integral below the total
curve - as well as the most frequent and the average pore radius -
increases. The average pore radius is approx. twice as large as
the most frequent one. The micropore distribution depends not only
on the degree of activation but also on the raw material. This
fact may be exemplified by Fig. 7 showing the differential pore
distributions of two activated carbon qualities exhibiting the
same degree of activation,but being made from different raw
materials. Also in this way the pore distribution can be con-
siderably influenced. Thus, both curves shown exhibit a ratio
of 1:2 when comparing the most frequent pore radii.
-------
dr
-AW2-50
-TK 20/80-50
01 2 3 4 5 6 7 8 9 10 n 12 13 14 15 16 17 18 19
rlAEl
Fig. 7 Differential pore radii distribution of activated carbon
Even though the specialist may draw certain conclusions from the
properties discussed - pore volume and pore distribution - the
requirement for thorough examination continues to exist for the
assessment of the applicability of activated carbon coming from
different manufacturing processes. This point of view is so
complex that it should not be discussed within the framework of
the present lecture. Nevertheless, it should perhaps be pointed
out that the adsorption of organic matter from aqueous solutions
also depends on the relation of molecule size to micropore diameter
In Fig. 8 the adsorption of different organic matter from an
aqueous phase is plotted against activated carbon qualities of
different degree of activation, based on a residual concentration
of 5o mg/1. These organic matters are different by their molecular
weight. In particular, these matters are: phenol (molecular weight
94), Na-salt of p-n-dezylbenzenesulfanate (molecular weight 32o)
and p-n-nonylphenolnonaglykolether (molecular weight 612). It is
to be noted that the phenol adsorption first increases with in-
creasing degree of activation, then passes through a maximum and
subsequently decreases, whereas the adsorption of the two other
materials is completely insufficient at small degree of activation.
however sharply increases with increasing degree of activation
-------
27
and eventually is higher than the phenol adsorption at high degree
of activation. A detailed explanation for this complex behaviour
cannot be given within the framework of the present lecture.
loading (g/£)
80
-OH
60'
50
30
20
10
0
. _
10H21-S03Na
= 320
degree of activation, %
Fig. 6 Characterization of adsorption capacity in aqueous
solution
The ratio molecular diameter/pore diameter is one of the
essential features: whereas phenol adsorption at medium degree
of activation seems optimum, the high-molecular materials are
only adsorbed satisfactorily by wide-pored activated carbon,
the difference between the two high-molecular materials mentioned
before being not too significant. The last-mentioned fact may be
due to the oblong molecular shape, the steric behaviour of which
may be comparable in case of diffusion in relatively narrow pores.
Of course, in this context, the polar character and the solubility
of the materials may be of certain importance for the adsorption
behaviour.This example may, however, show that it is impossible
to find an activated carbon quality which exhibits optimum ad-
sorption properties for all materials. Thus, it is obviously ne-
cessary to adapt the activated carbon quality to the specific
adsorption problems.
-------
28
6. Conclusions
This more general lecture is supposed to discuss only some
essential points of view for activated carbon production. It was
intended to show that by choice of activation process of the
feed stock and by the adjustment of certain activation
conditions the properties of activated carbon may be changed
nearly at will. Thus, it will always be possible to make
activated carbon with optimum properties for specific applic-
ation on the basis of appropriate development work.
-------
29
BASIC PRINCIPLES OF ADSORPTION PROCESS TECHNIQUES
by H. Sontheimer
Introduction
During adsorption, organic molecules are removed from the water
by being attached at the large inner surface of the adsorbent
which, in the case of activated carbon, may be as large as
1OOO m /g. To describe the adsorption process mathematically,
which is necessary to design adsorption plants, knowledge of
the adsorption kinetics and adsorption equilibrium is required.
The literature references at the end of this book give a survey
of some of the most important work in this field.
Although many investigations and theoretical calculations have
been made in order to describe the adsorption equilibrium and
the kinetics, the design and optimization of adsorption plants
in waterworks still have to be made empirically in most cases.
This is mainly due to the following:
1) Activated carbon used for water purification is nearly
always made from natural products and can be characterized
by empirical data only. This makes it difficult to describe
activated carbon qualities and the processes taking place
during adsorption.
2) The raw water always contains a large number of organic
substances which interfere with each other during adsorption.
The complex nature of these problems makes it difficult to
design an adsorption plant for water treatment. Nevertheless,
knowledge of the unit operations used by adsorption techniques,
as given in Vol. 8 of the Engler-Bunte-Institut series, provides
a valuable guide on the effective application of adsorption
processes in drinking-water treatment. This paper is intended,
in the main, to take a more detailed look at these relationships,
based on the knowledge of the adsorption behaviour of single
substances.
-------
30
Adsorption equilibria
In an aqueous solution of organic substances, the adsorption
isotherm describes the final state of the adsorption process.
The loading q of the activated carbon is specified in g or mol
of organic substance per kg of activated carbon as a function
of the residual concentration c in g/m or mol/m . The Langmuir
isotherm, one of the best known relations for the description
of the adsorption equilibria, is shown in Fig. 1.
Fig. 1; Langmuir isotherm
The Langmuir isotherm can be deduced from a simple mathematical
model. A characteristic of this isotherm is the fact that the
loading of the carbon approaches a limiting value q as the
concentration increases, corresponding to a monomolecular
coverage of the surface.
The two parameters of the Langmuir isotherm can be determined
from the measured adsorption equilibria. A linearization of the
relationship can be obtained by plotting the reciprocal values
of q and c (Engler-Bunte-Institut, Vol.8,1975). When c is
related to c , the initial concentration, a dimensionless
representation is also possible. Using this method of des-
cription, there is only one parameter R, the separation factor.
If R is < 1 , as is the case in Fig. 1, then one speaks of a
favourable equilibrium. If the curve lies below the y = x
line, then R is > 1 and the equilibrium is said to be un-
favourable.
However, whereas the Langmuir isotherm can only be applied in
rare cases for adsorption from the aqueous phase, the Freundlich
adsorption isotherm provides in most instances a better des-
cription of the adsorption equilibrium, as shown in Fig. 2
FRITZ 1975).
Fig. 2; Adsorption isotherms of p-nitrophenol (1)
and phenol (2)
Comparison: Langmuir-Freundlich-isotherms
-------
31
p bzw c
a) normal
l/q
"«„
l/p
b) linearisiert
c) dimensionslos
Fig. 1
linearisiert: linearized
dimensionslos: dimensionless
3h
-o
a
0,U
Phenol (2)
FREUNDUCH-Isotherme q. = 3,23 c.
LANGMUIR-lsotherme q. = 20cl
1 USc,
FREUNDUCH-Isotherme q = 2,16 c °'231
LANGMUIR-lsotherme q,
7,65 c 2
U2,3c2
345
Konzentration c in mol/m
Fig. 2: Beladung q in mol/kg: loading q in mol/kg
-------
32
Here the adsorption of phenol and p-nitrophenol onto an acti-
vated carbon, B 1O, are described using Langmuir and Freundlich
isotherms. One can easily see the better fit of the values ob-
tained using the Freundlich isotherm. A plotting of this isotherm,
its linearization, using a double logarithmic plotting, and the
corresponding dimensionless representation are shown in Fig. 3.
n = 0,2
logjq|
= 0,2
= 2
a) normal
logic)
b)
linearized
"0
c)
1
dimensionless
Fig. 3; Freundlich isotherms
In Fig. 3 two representative isotherms are shown which describe
completely different adsorption behaviours. They are referred to
(Fig. 3 b) as flat (n = O.2) and steep (n = 2) isotherms. When
considering the behaviour of activated carbon filters, it is
important to remember that gradients greater than 1 (n = > 1)
lead to an unfavourable equilibrium. Under such circumstances
one can expect that the complete removal of the substances in
a filter will be difficult to obtain. Such isotherms are found
fairly frequently in drinking water treatment, for instance with
humic acids.
In contrast, gradients less than 1 (n = < 1) are nearly always
obtained for defined single substances, as for instance non-
polar organo-chloro compounds. Due to the favourable equilibrium,
such substances can nearly always be easily removed with a
carbon filter.
It is important for all practical considerations to bear in mind
that the Freundlich isotherm describes the adsorption behaviour
only over a limited concentration range, so that every investi-
gation of adsorption equilibria should be made in the concen-
tration range for which the activated carbon treatment is
intended. Investigations at higher concentrations, which are
often made because of the greater accuracy of measurement,
cannot therefore be transferred directly to other concentration
ranges. This applies even to pure substances, as can be seen
in Fig. 4 for p-nitrophenol and phenol isotherms (FRITZ 1975).
-------
33
Fig. 4; Freundlich isotherms of p-nitrophenol and
phenol over a wide concentration range
The illustrated equations for the various ranges show that the
isotherms increase in gradient at lower concentrations, with a
corresponding increase in the two constants K and n.
Data can be correlated over a wide range, using a single
relationship such as that of RADKE and PRAUSNITZ (1972); however,
a third parameter is then necessary. Because of this complication
such an equation is therefore seldom used. It is only mentioned
here for the sake of completeness and because it has the ad-
vantage that it can be applied in most cases of practical
interest in adsorption from liquids since it includes as
limiting cases the pure Langmuir and Freundlich isotherms
(FRITZ 1974). The application of the Freundlich isotherm has
the advantage in practical problems in water treatment that
group parameters such as DOC or UV extinction can be used for
the determination of an isotherm, and that nearly always
reasonable straight line double logarithmic plots are obtained.
Even adsorption isotherms where only odour threshold numbers are
used instead of concentrations can be described in this way,
as shown in Fig. 5 (Engler-Bunte-Institut, Vol. 2, 1967).
Fig. 5; Adsorption tests with water from the Lake of
Constance (sampling station Sipplingen)
One can see quite well from this illustration that, despite
the difficulties to obtain exact measurements of odour
threshold numbers, they can be quite well described by a
Freundlich isotherm.
However, it is also obvious that the isotherm gradients may
differ widely and that values greater than 1 are possible.
This indicates, however, as already mentioned, that a com-
plete removal of the particular material is difficult to
obtain. Nevertheless, attention must be paid not only to the
slope of the gradient but to the position of the isotherm.
The description of the adsorption equilibrium becomes even
-------
3
-------
35
more complicated when several organic substances are present
in the solution. This can be seen especially well with the
combination phenol - p-nitrophenol. The measured adsorption
isotherms for this system are shown in Fig. 6 (FRITZ 1974).
Fig. 6: Adsorption isotherms, at 2O °C, of p-nitrophenol
(1) and phenol (2) on B 1O
In the upper part of this figure the isotherms for p-nitrophenol
are plotted in the presence of different amounts of phenol;
it may be seen that this has little influence on the adsorption
of p-nitrophenol. In contrast, as may be seen in the lower part
of this figure, the presence of p-nitrophenol has a strong
influence on the adsorption of phenol. According to these
measurements, p-nitrophenol is very much better adsorbed than
phenol and displaces it from the activated carbon.
In this case the different solubilities of the two substances
play an important role, as may be seen in Fig. 7 (BALDAUF 1975).
Fig. 7; Isotherms of phenol and p-nitrophenol
with different methods of plotting
In the upper part of this figure the normal isotherms are
plotted, whilst in the lower part the results are plotted
with the ratio residual concentration to saturation concen-
tration (solubility) as abscissa.
With this type of presentation the two isotherms practically
coincide because phenol is much more soluble than p-nitrophenol.
This difference also explains to a great extent the behaviour
of both substances during mixed adsorption.
However, this is not always the case, as can be seen in Fig. 8,
where adsorption data of the mixture benzoic acid - p-nitrophenol
are shown (FRITZ 1975).
-------
36
Figure 6
= KFcnl ° P-Nitrophenol
' • Phenol
Kp =1,65 n = 0,18
10°
_c_j | "P- Nitrophenol
ff j • Phenol
Figure 7 c /Cs
-------
37
Fig. 8; Adsorption isotherms, 2O C, for p-nitrophenol C\,
and benzoic acid (2) on B 10
Here, the two substances displace one another almost equally
strongly, despite large differences in solubility. From this
and other results it can be deduced that for the mutual dis-
placement on the carbon and the resulting hindrance of the
adsorption of a substance chemical parameters are also important,
in addition to the solubility.
The behaviour of adsorption mixtures can be well described
by an empirical equation, provided the individual substances
have Freundlich isotherms (FRITZ 1974). The relations deduced
from some adsorption mixtures can be used to predict how two
different adsorbents behave during combined adsorption. From
these calculations one comes to the conclusion, in a number
of cases involving mixtures, that better results can be ob-
tained with a suitable choice of adsorbents than when each
is adsorbed alone, as is shown in Fig. 9 (BALDAUF 1975).
Fig. 9; Calculated adsorption isotherms
It can be seen that, at least theoretically, better results
can be obtained with mixtures of adsorbents than with indi-
vidual adsorbents.
Fig. 1O: Break-through curves in large filters with
different types of activated carbon
(RWW Miilheim)
That such considerations can also have practical consequences
is shown in Fig. 1O (VOLLMER, NOLTE 1974), in which break-
through curves for a large filter are shown with three different
types of carbon. Also included is a break-through curve for a
mixture of equal quantities of two carbons. Better results
were obtained in the first month of running time with the
mixed carbons than with the two individual carbons, especially
-------
38
0,1
0,01
0,05 0,1 0,5 1
C,in mmol/1
0,001
Figure 9
0,005 0,01 0,05 0,1
C2in mmol/l
0,5 1
Filterbelostung . 0,18 m3/kg.d IF 300)
0,19 m3/kg.d (LSS)
0,22m3/ kg-d (BD)
10 20
30
40 50 60
Zeit t in Tagen
70 80
90
Fig. 1O
Filterbelastung: filter loading
Zeit in Tagen: time t in days
-------
39
in the case of organo-chloro loading. Although the effect
is not very pronounced, considering the total filter running
time, it is nevertheless quite interesting and may be worth-
while pursuing further. In this connection, adsorption kinetics
also play an important part. Before examining this in further
detail, it is advisable to point out the consequences of ad-
sorption equilibria which are important in practice. They
are summarized in Table 1.
Table 1; Practical significance of adsorption
equilibria measurements
1) Evaluation of results using the Freundlich isotherm
(double logarithmic plotting)
q = Kp • cn
Important numerical values;
a) q = q for c = c
A high q leads to a high loading in the filter.
b) n = adsorption exponent (slope of the double
logarithmic plot)
Precondition for an efficient removal of organic
substances in the filter: n < 1.
2) Carbon evaluation, because of competitive adsorption
only using adsorptive mixtures
3) Use of adsorbent mixtures
Prediction of the suitability by isotherm measurements,
The table shows that it is important for the practical evalua-
tion of carbons that the values for q and n are determined
-------
from experimentally measured isotherm data, because these
numerical values provide a direct indication of t 5 behaviour
of the carbon in the filter. It is therefore adv.i >le to
always determine these two numerical values from ilibrium
measurements.
Also of great importance is to note the behaviour of the
competing adsorption for the evaluation pf the effectiveness
of certain types of activated carbon. Although this reduces
the choice of suitable test methods quite considerably, it is,
according to current experience, absolutely essential.
Such measurements can also provide an indication of the
possible advantage of using adsorbent mixtures. The advantages
of such a method of operation are only small because of the
activated carbon qualities on the market at the moment, but
the advantages of a flocculation prior to adsorption, reported
by HEYMANN and SCHEIDTMANN (1975) show clearly that all the
optimization possibilities have not been utilized by any means
yet.
That this is often not possible must be put down to strongly
differing adsorption kinetics of the various carbon types,
which are discussed in more detail in the following chapters.
Adsorption kinetics
A mathematical description of the adsorption kinetics requires
as a prerequisite a suitable model of the process and the
rate-determining mechanisms (HEIL 1971). However, the diffi-
culties involved in producing a general description /ecome
apparent when one examines electron-micrographs of different
types of carbon, remembering that the pore structure is of
great importance to the mass transport (BRAUCH 1974,
HOLZEL 1975).
-------
1*1
Fig. 11; Surface structure of an activated carbon
In Fig. 11 the pore structure of an activated carbon produced
from charcoal is shown. One can see that the wood-derived
structure is very regular and that the pores are easily
accessible. However, it appears that the residual carbon
volume is insufficient for the micropores, so that the
carbon has only a small capacity.
A completely different appearance is shown by the pressed
(extruded) carbon in Fig. 12.
Fig. 12; Surface structure of a pressed carbon
The area illustrated in the figure has a linear dimension
of O.2 mm. It appears that there are no large pores, and
if the dark areas represent the position of macropores, they
are uniformly distributed and must have a diameter of less
than 1 ym.
Again, a totally different picture is obtained of an activated
carbon produced from crushed carbonized raw material, as is
shown in Figures 13 and 14 (HOLZEL 1975).
The carbon in Fig. 13 contains a mixture of large and small
macropores, while that in Fig. 14 appears to have an almost
smooth sintered surface, which is traversed by deep cracks,
so that only a limited part of the outer surface is accessible.
Thus all the organic material must be transported through the
few cracks into the inside.
Fig. 13; Pore structure of a granular activated carbon
made of coal
Fig. 14; Pore structure of a higher activated granular carbon
made of coal
-------
1*2
Abb.11
Abb.12
-------
Abb.13
Abb. 14
-------
These structural differences make it already clear that major
simplifications will be necessary to satisfactorily describe
the mass transport during the adsorption process. It is not
possible within the scope of these discussions to describe
the development of models and their associated mass transport
equations. However, it will be tried to clearly set out the
information available of the different transport steps. These
transport mechanisms are shown in Table 2.
Table 2; Mechanisms of the mass transport during the
adsorption of activated carbon
1) Transport in the free liquid
Insignificant in most cases.
2) Film diffusion
The concentration gradient in the liquid film
around the granule is the driving force. The
transport in the beginning is always rate-
determining.
3) Pore diffusion
The concentration gradient in the water-filled
pores is the driving force. The concentration in
the water enclosed by the pore walls is permanently
in equilibrium with the concentration in the carbon
phase. This is rate-determining for the mass trans-
port in the easily accessible pores.
4) Surface diffusion
The concentration gradient at the pore surface is
the driving force. Rate-determining for the mass
transport in the less accessible pores.
5) Adsorption onto the active sites
Very fast in comparison to the diffusional mass
transport.
-------
1*5
When one considers the adsorption process, it is clear that
transport within the bulk liquid to the vicinity of the
granule surface must occur before any other step. However,
under conditions of practical importance this step is very
rapid in a well mixed system. This is followed by the mass
transport process through the liquid film surrounding the
granule, which initially is rate-determining. The mass trans-
fer coefficient for the film diffusion can therefore be esti-
mated from the limiting slope at time zero (HEIL 1971, SPAHN 1974;
Fig. 15; Film diffusion
Figures 15 and 16 show experimental data and a curve calculated
on the assumption that the process is film-diffusion controlled
(HEIL 1971). In Fig. 15, even after long times, the process is
well described by the film diffusion model. However, in Fig. 16,
where a relatively large molecule is being adsorbed, the film-
diffusional model is clearly inadequate to describe the mass
transfer process.
Fig. 16; Comparison between the measured concentration
reduction and that calculated with the aid of
the film diffusion model
Today numerous analogous investigations have been carried out
under a variety of conditions (see references). In the carbon
filters used in waterworks, film diffusion during the first
phase of the filter time has an important influence (WEBER 1972).
Initially a high flow velocity and a deep layer of carbon would
be most effective, that is to say, for a fixed quantity of
carbon and a fixed flow rate a narrow high filter would be more
effective than a broad shallow filter with a suitable lower
flow velocity.
-------
Capronsaure
100 t(min)
Fig. 15
Capronsaure: caproic acid
10
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Badkonzentration
. (mMol/l)
Adsorptiv: Kristallviolett
gemessene Werte
nach Filmdiffussion-
Adsorption berechnet
20
60
80
t (min)
Fig. 16
Badkonzentration: bath concentration
gemessene Werte: measured values
nach Filmdiffusion-Adsorption berechnet: calculated for
film diffusion
-------
The influence of film diffusion becomes less important as the
carbon is loaded and diffusion within the granule becomes more
and more rate-determining. As shown in Table 2, under these
conditions it is necessary to distinguish between two mecha-
nisms. In the case of the pore diffusion the driving force
is provided by the concentration gradient within the pores.
Under these conditions we must remember that the concentration
in the pores is permanently in equilibrium with the concen-
tration in the carbon phase. Under comparable conditions a
inore favourable behaviour should be obtained when the material
being adsorbed possesses a favourable isotherm.
Proof of the existence of pore diffusion has been shown in
various ways. However, the observation of a moving concen-
tration front, using radioactive-marked organic substances,
provides a very clear demonstration (BRAUCH 1974). The results
of such an experiment are shown in Fig. 17.
Fig. 17: Experimental proof of irreversible adsorption
Plotted are the test results with radioactive-marked phenyl-
acetic acid on B 1O carbon at different adsorption times.
After a loading with marked acid, a further loading with un-
marked phenylacetic acid followed, which did not lead to any
change of the position of the marked acid.
The sharp loading fronts can vividly be seen in Fig. 17.
Other measurements show, however, that there is always an
additional transport through surface diffusion too, and that
here for example also chemical parameters, especially the
affinity between organic substance and activated carbon, can
be important. This incident can be recognized very clearly
by calculating break-through curves, assuming that there is
only pore diffusion (MERK 1975).
Fig. 18; Comparison of measured and calculated
break-through curves
-------
t [mm] unmarkiert
2 5 W 20
Fig. 17: markiert: marked; unrnarkiert: not marked
Phenol c20 = 10mmol/l
0 WO 200 300 400 1 [mm ] 600
p-Nitrophenol clo=10mmol/l
100 200 300 400 t[mm] 600
Rechnung: calculated curve
-------
Calculation and measuring still agree fairly well if one
chooses phenol as solute, while the calculation still can be
improved by assuming a Freundlich isotherm, as shown in Fig.18.
With nitrophenol, however, the deviations become so high that
they have to be considered. This can be explained by the fact
that the influence of surface diffusion is bigger. It can
clearly be imagined that surface diffusion will take place
more slowly with a substance of higher affinity to the carbon
surface, for this substance is held tight stronger there and is
therefore less flexible. A model with which all made obser-
vations can be explained can be seen in Fig. 19. Here schema-
tically, with strong magnification, a single transporting
pore within an activated carbon granule of a size of about
1 pm in diameter can be seen. The transport to the inside
happens within such pores, while a concentration gradient
occurs in the pore water. This pore diffusion is coupled with
a loading of the adsorption pores within the region of the
transporting pores, which are easily accessible. Here primarily
a pure pore diffusion appears leading inevitably to building up
a sharp front.
Fig. 19; Schematical loading process in an
activated carbon pore
Now, not all adsorption pores are that easily accessible.
It can rather be expected that certain adsorption fields are
situated within the easier accessible regions and hardly opened
through transport pores. The organic substances must therefore
migrate into these regions along the inner surface of the
activated carbon. Through that easier accessible pores become
free again and this event brings an additional decrease im-
proving the pore diffusion too. This kind of transport into
the hardly accessible pores occurs after the pore diffusion
and therefore determines the adsorption kinetics especially
at the end of the loading very strongly. Without taking further
details into consideration, it will be tried to get some con-
clusions out of this model. -
-------
50
-------
51
1) Different kinds of carbon have different degrees of
easy and hard accessible pores. These differences take
effect especially during the second part of the usual
filtering time and are especially important for the
removal of the better adsorbable substances such as the
organo-chloro-and the nitro-compounds. This relationship
has to be considered during every way of testing acti-
vated carbon.
2) A higher portion of poorly accessible pores will be more
important at lower concentrations and with that also
at lower equilibrium loadings than at high initial
concentrations in the water. That explains the statement
that certain kinds of activated carbon can be of advantage
at high initial concentrations, whilst others have to be
preferred at lower concentrations. Therefore carbon tests
should always be done under conditions corresponding to
the practical conditions. This is at least necessary as
long as there are no common test methods known that would
allow a precalculation starting from a general description
of the carbon geometry. The measurement of the pore
distribution after BET does not bring sufficient infor-
mation for this.
Behaviour of activated carbon filters
The exact description of the adsorption kinetics on the
single granule allows the calculation of the behaviour of
filters (BRAUCH et al 1974). Corresponding methods have
nearly only been applied successfully for the adsorption of
defined single substances. Such an example of calculated
break-through curves of phenol and nitrophenol is shown in
Fig. 18. Out of this it can be seen that a very exact des-
cription of the mass transport in the carbon granule is
necessary if one does not want to have strong deviations
between calculated and measured break-through curves.
-------
52
In practice, however, such calculating methods are unimportant
because the treated waters always contain mixtures of different
substances which are hard to be defined and analysed. Therefore,
in the following it is done so that first the basic behaviour
of activated carbon will be discussed, and after that the dis-
placement effects at the adsorption of mixed substances shall
be examined. Even though no direct consequences for the calcu-
lation of the waterworks filters can be taken, such considera-
tions give important indications for the interpretation of
practical observations.
One has to take into account that there are two basically
different kinds of "break-through" behaviour of activated
carbon filters; the constant and the proportional pattern
(SPINDLER 1973, Engler-Bunte-Institut Vol. 8, 1975). The
corresponding break-through curves are shown in Fig. 2O.
Fig. 2O: Loading pattern
Most common is the constant pattern which is always achieved
if there is a favourable equilibrium. Here the break-through
curve has, after a transition region, always the same shape
and is estimated through the adsorption equilibrium and
through the kinetics.
Entirely different is the filter behaviour at the proportional
pattern; this, however, is especially important in the practice
of drinking water support. Here a steady extension of the
front length occurs with time. The length of the front will be
proportional to the way covered, and this means a proportional
pattern. Theoretically, such a behaviour is to be expected if
a so-called unfavourable equilibrium occurs, meaning the separa-
ting factor and the exponent in the Freundlich isotherm are
bigger than 1. But that is often observed in practice, as one
can see from the isotherms in Fig. 5. In such a case the working
-------
53
LL
E
..konstemtes Muster
„proportionates Muster
Fig. 20
Schichttiefe im Filter: bed depth of filter
konstantes Muster: constant pattern
Frontbreite: front width
proportionales Muster: proportional pattern
-------
zone of a filter becomes so long that not the adsorption
kinetics but the equilibrium data alone become determining
for the effectiveness of the filter. Knowing the isotherm
one can precalculate the break-through curve for every filter
in a very simple way (DE VAULT 1943, PERRY 1974).
Considering the practical use, it is not quite as simple
because for large organic molecules there is always still
the influence of the adsorption kinetics. Besides that steep
isotherms with exponents over 1 are only achieved if one uses
sum parameters, so that the steep isotherm is caused through
the different ability of adsorption of different substances.
It is quite helpful anyway if in such cases one calculates
as if one had only one substance which behaves according to
the isotherm. With that one can make helpful comparisons
between different activated carbons, leading to results which
can be observed in practice too.
For the practice of waterworks, however, the constant pattern
is important too. For example, the adsorption behaviour of
especially well-adsorbable organo-chloro compounds can be
described in this way. Here one can precalculate fairly
exactly by using the measurements in the upper layer of a
filter, when a break-through at the end of a filter can be
expected. One of the methods used for this is the LUB method,
whose principle can be observed in Fig. 21 (COLLINS 1967).
Fig. 21; Break-through behaviour of a filter
Definition by LUB
Here such a constant shape of the front is assumed, which goes
through the filter with a constant speed. The measuring of a
break-through curve at a given speed allows an exact filter
calculation, which will not be discussed in further detail
here. There are still a number of similar calculating methods
(PERRY 1974).
-------
55
Luel
T T T T T T
Abb.21
-------
56
On the other hand, the front form, meaning the shape of the
break-through curve, is seldom as S-shaped as it is shown in
Fig. 21. Generally, in practice one can distinguish between
two cases. The case with mainly film diffusion and the one
when the adsorption kinetics is determined by the diffusion
within the grain. Then one achieves different shapes of a
break-through curve, as shown in Fig. 22.
Fig. 22; Break-through curves
In the first case we have an early break-through of low
concentration, while then, if the grain diffusion is rate-
determining, a so-called tail formation occurs. The latter
will occur remarkably more often.
Such influences on the tail shape can also be calculated,
as shown in Fig. 23 (MERK 1975).
Fig. 23; Progress of water loading
In the upper part of this figure one can see how an increasing
film diffusion coefficient, meaning a decreasing resistance
in the film, leads to sharper tails. A similar behaviour can
also be observed at higher diffusion coefficients within the
granule, because a faster transport of the organic substance
will occur.
Apart from this, the steepness of the isotherm or the size of
the separating factor influences the shape of the break-through
curves, as it can be observed in Fig. 24 (MERK 1975).
Fig. 24; Progress of water loading at different
adsorption exponents
-------
57
t,bzw.V
Bi
-------
58
* 0.5|
Abb.24
-------
59
The more flat the isotherm, i.e. the smaller the adsorption
exponent, the steeper is the break-through curve and the
more favourable is the behaviour of the filter.
These remarks show how difficult it will be to make relevant
predictions for practice even if the loading curves for
5 different substances of wastewate.r, depending on the bed
length, look almost like theoretical curves (KdLLE et al 1975).
Fig. 25 shows that the most favourable adsorbable dichlarphenol
has the smallest break-through pattern, while this is nearly
3 m long for the two polar chlorine compounds. Contrary to all
other substances one gets also the typical S-shape, where a
tail formation, meaning a strong influence of grain diffusion,
appears.
But this picture changes dramatically if one observes the
analogous curves for a stronger polar substance such as
chlorisopropyl ether at other carbon qualities (KC5LLE et al
1975).
Fig. 25; Adsorption of organo-chloro compounds i^n an
activated carbon filter (KOLLE)
In Fig. 26 a re-increase of the loadings at the filter end,
and in one case even a clear maximum of carbon loading in
the middle of the filter, can be observed. Such a behaviour
can only be explained if displacement effects occur within the
filter because of competitive adsorption.
Fig. 26; Adsorption of organo-chloro compounds onto
activated carbon (KOLLE)
-------
GO
o i
Schichthohe.m
500 h
Schichthohe.m
Figs. 25 and 26:
Schichthohe: filter height
-------
61
The meaning of such effects can be noticed best out of
investigations with the already discussed phenol-nitrophenol
system, in which the nitrophenol is able to displace the
phenol out of the activated carbon. By leading such a mixture
through an activated carbon filter one can observe a behaviour
of the break-through curves in different bed lengths, as shown
in Fig. 27 (MERK 1975) .
Fig. 27; Measured break-through profiles at competing
adsorption of p-nitrophenol (1) and phenol (2)
While the break-through curves for nitrophenol have a habitual
S-shaped course, at phenol a higher concentration at the filter
end occurs than in the entrance after some time, attributed to
the displacement effects. Even within the single granule, as
FRITZ (1975) could show through his calculations, such dis-
placement effects occur. That can be seen in Fig. 28.
Fig. 28; Concentration profiles in the granule
at competing adsorption of p-nitrophenol (1)
and phenol (2)
Here the loading scales are drawn in as they move from the
right to the left into the center of the granule. The conti-
nuous curve stands for nitrophenol, the interrupted one for
phenol. The latter substance, as can be noticed, will be
displaced from the outside to the inside during the adsorption.
As soon as the nitrophenol has also moved inwards, the phenol
is displaced again out of the carbon.
This displacement effect can also be proved in the batch test
if a phenol-preloaded carbon is put into a nitrophenol solution
(FRITZ 1975) .
Fig. 29; Investigation of the displacement phenomena
on activated carbon in a beaker test
-------
62
CjQ=5mmol/l
tOO 500 ~t[mnl 700
S00~
'tlrrinl TOO
Abb.27
y
r, = 0.0.? r, -- 0,1 r, = 0,75 r, = 0,4 r, = 0.8
Biotzahlen
Diffusionskoeffizienten
Anfangskonzentrationen
Bi, - B/? 7
Deff , =Deff2
c,0 = C20
5 mmo/ll
Losungsmenge/Kohlemenge LJS^ 0,5 II g
P-NPh
---- Ph
Fig. 28
Biotzahlen: biot numbers
Diffusionskoeffizienten: diffusion coefficients
Anfangskonzentrationen: initial concentrations
Losungsmenge/Kohlemenge: amount of solution/amount of carbon
-------
63
Umsatg - Zeitkurven
p-Nitrophenolfe) * Phenol^) I BIO
S gleichzeitige Adsorption
S Vorbeladen mit Phenol
* Vorbeladen mit p-Nitrophenol
7500
2000 2500
Zeit —~t frwnj
JOOO
Fig. 29
Umsatz - Zeitkurven: change of concentration with time
gleichzeitige Adsorption: simultaneous adsorption
Vorbeladen mit Phenol: preloading with phenol
Vorbeladen m-it p-Nitrophenol: preloading with p-nitrophenol
Wasserbeladung: concentration in water
Zeit: time
-------
Then, as shown in Fig. 29, the concentration of nitrophenol
within the solution decreases, while at the same time the
phenol concentration increases, because it is displaced out
of the carbon into the solution. Such a displacement of
already adsorbed phenol occurs within the filter too and
causes the concentrations at the filter end to be higher
after a certain time than at the entrance.
If the loading of phenol is plotted versus the filter bed
length, one will achieve curves as shown in Fig. 3O.
Fig. 3O; Process of carbon loading with phenol
in an activated carbon filter
Here it can be noticed very clearly that for phenol a
maximum of loading in the middle of the filter is observed
after a certain time, exactly the same behaviour as was ob-
served at one of the test filters in practice for chlor-
isopropyl ether (see Fig. 26).
These effects show that in practice of drinking water support
such displacement effects happen effectively, and wanting to
avoid that the concentration of any harmful substance is
higher at the filter outlet than at the entrance, those
effects have to be taken into consideration.
But this is easier said than done. One of the main problems
in registering and taking into account such effects is within
the problems corresponding to the analytics, as much as the
question of the importance of certain concentrations of harmful
substances. Additionally, the concentration and the kind of
organic substances within the water can change during a filter
run.
Because of this reason one had to rely so far on the use
of sum and group parameters in order to predict the working-
time of a filter and with that to rely on indirect conclusions
for the effectiveness of the filter. Additional single-
substance measurements, as they are done at different places
-------
65
1.5 3.5 - zjcm] 75
Cleichgewich tsbeladung
t(min]
50 c,0= 5mmol/l
150 c20 = 3mmotll
Fig. 30;
Gleichgewichtsbeladung: equilibrium loading
-------
66
now, can help to improve the models used so far and to
optimize the use of adsorption plants.
This task requires solid knowledge about the unit operations
of adsorption and their use for the interpretation of practical
observations. In this way theory and practice complement each
other for the benefit of drinking water treatment.
-------
67
THE USE OF POWDERED ACTIVATED CARBON
by H. Sontheimer
The use of powdered activated carbon in drinking water treatment
is far more common than the use of activated carbon filters.
It may be estimated that about 9O per cent of the waterworks
all over the world which use activated carbon use it in the
form of powder (HANSEN 1975). However, in the Federal Republic
of Germany the situation is exactly the opposite; a number of
factors are responsible for this development.
Nevertheless, before going into further detail, some remarks
should be made on the treatment procedure for using powdered
carbon and the problems resulting from it. For this purpose,
it is helpful to look at the schematic layout of a normal
drinking-water treatment plant using surface water.
Fig. 1; Possibilities for the use of powdered carbon
in the treatment of surface waters
The treatment process illustrated in Fig. 1 includes floccu-
lation and sedimentation, followed by filtration. There are
two stages at which the carbon can be added for removing
taste and odour substances. These stages are indicated by A
and B. Both methods are of some importance for practical use.
The big advantage of adding the carbon at stage A is that,
apart from the dosage equipment, no additional equipment is
necessary. Furthermore, the length of time required for
flocculation is nearly always sufficient for adsorption.
Using this method, there are no particular problems in
separating the extremely small carbon particles because these
are embedded within the floes.
However, the advantage of this method implies, at the same
time, a considerable disadvantage. For one thing, the encase-
ment of the carbon particles will impede the adsorption
kinetics, and it will therefore take much longer until the
-------
88
Fig. 1
Activated
Carbon
Activated
Carbon B
Single-step dosing'of powdered carbon;
Dosage at A : lengthy reaction time; no additional equipment
required; interrupted adsorption caused by a
coating and by the floes
Dosage at B
additional reaction vessel required;
problems with filtration; better efficiency
because of extensive preliminary purification.
Consecutive multistage treatment:
Dosage at A and B: lower consumption of activated carbon;
higher investment costs.
-------
69
final equilibrium is reached. Another point is that by this
method a number of substances are adsorbed which v,'ould have
been removed by flocculation alone. Therefore, more activated
carbon is needed. Nevertheless, there have been cases where
this disadvantage was compensated by the fact that, due to
the presence of activated carbon, flocculation was improved,
so that the use of activated carbon leads to a saving of
flocculants.
If the activated carbon is added at stage B, it has only to
adsorb those substances not removed by flocculation and preci-
pitation. Thus it is possible to choose a specific carbon
type with high efficiency. But an additional reaction vessel
will be required if the carbon is to be utilized completely.
Also, in some cases, the minute carbon particles are not
sufficiently retained by the filter. The simplest remedy for
this defect is to add a small amount of flocculant before the
filter. Today,polyelectrolytes are preferably used for this
purpose.
It is also possible, in principle, to divide the activated
carbon and to add one half at stage A and the other half at
stage B. By this method the amount of activated carbon needed
to obtain the same residual concentration is smaller, which
can be seen from the diagram shovvn in Fly. 2.
Fig. 2; Comparison of operational charts for single-step
and two-step use of powdered carbon
The diagram on the left illustrates the change in residual
concentration and loading when activated carbon is added to
the water. The system follows the operating line until it
reaches equilibrium (EBI 1974).
It can be seen from the diagram that the load q_, in equi-
librium with the desired low residual concentration c_, is
comparatively small. This is the main drawback of using
-------
70
= 2
S>S1+S2
L (c0-c2) = S-q2
L(c0-c2) L(c0-c2)
q2 = KF-c2n
(C]/c2)-n-Co/C|
Fig. 2:
einstufig: single-step
2 Stufen bintereinander : two-step, consecutive
S
q
L
c
c
(kg)
(g/kg)
(m3)
amount of carbon
carbon load
volume of water
concentration of substances to be removed (g/m )
initial concentration
-\rnax =
load at equilibrium - the equilibrium concentration
being equal to the initial concentration
-------
71
powdered carbon because in most cases the highest maximum load
possible - which may be attained in a sufficiently large carbon
filter - is almost three times as high. Thus, quite often the
consumption of powdered carbon is twice as high than if granular
activated carbon is used in filters.
Some improvement can be made by a two-step dosing, as shown
in the diagram of Fig. 2. Here the amount of carbon is divided
and added in two consecutive doses. By this type of process
one half of the carbon is more heavily loaded and, corresponding
to the relation of q? to q , carbon consumption can be reduced;
but, at the same time, more equipment is necessary. The amount
of carbon required for each stage can be calculated from the
formulas listed in Fig. 2. However, when put into practice,
this method does not seem worth-while because in most cases
the advantage is too small. Nevertheless, in some special
cases it may be interesting to use a different type of carbon
at either stage, thus having the advantage of a carbon mixture
(BALDAUF 1974).
For the sake of completeness, mention should be made of
another technical possibility for the use of powdered carbon,
i.e. the depositing of the carbon, usually together with
(diatomaceous earth)
kieselguhr,/in a filter cake through which the water to be
treated is filtered. In addition to the deposited material
there is nearly always a continual dosing of carbon (VOSTRCIL
1971, KURAPKAT 1963). This treatment process has some similarity
to the effectiveness of an activated carbon filter. In recent
years this process has frequently been used for drinking water
treatment, especially in those cases where the water contained
coloured substances. Particularly good results were obtained
with raw waters from lakes, which only required an occasional
treatment with activated carbon (SYMONS 1975).
-------
72
The pros and cans of using powdered activated carbon, based!
on experience and information available so far, are listed'
in Table 1.
Table T. r Advantages and disadvantages of using;
powdered activated carbon
Advantages: 1) Easy adaptation to> changes in
water quality
2) Low investment costs
Disadvantages:
1) High operating costs
2) Bra regeneration of the activated carbon.
3) Poor efficiency for DOC removal
4) Additional sludge problems
5) Problems of complete removal of
minute carbon particles
It would therefore seem that the use of powdered, activated
carbon is most advantageous in those cases where an adsorbent
is required only occasionally or where the demand of acti-
vated carbon varies considerably. Activated carbon filters most
be designed for the poorest quality of raw water, which means
that investment costs are high. Treatment with powdered carbon,
on the other hand, merely requires stocking a certain amount
of carbon. It is possible to start or stop the dosing at very
short notice, and also to lower or to increase it. Carbon
filters, on the other hand, will rise problems of bacterial
growth etc. when the filters are left to stand without water
flow.
-------
73
For this reason, powdered carbon is recommended in those
cases where an occasional use of adsorbents is required.
The disadvantages listed in Table 1 will be of less impor-
tance or, rather, remedial measures can be taken.
However, the above does not apply when activated carbon is
required constantly as, for instance, at many places along
the Lower Rhine, due to the chemical pollution of the water.
For this reason, most waterworks in Western Germany are now
using activated carbon filters. However, investigations are
being made in some places on whether suspended powdered carbon
might be used in a cycle with a cascade system. However, no
detailed practical results are available as yet.
-------
ACTIVATED CARBON FILTERS IN WATER TREATMENT PLANTS
PROCESSING TECHNIQUES - ENGINEERING - OPERATION
by W. Poggenburg, Diisseldorf
The general processing techniques developed for the treatment
of Rhine-bank-filtrate, the construction and the knowledge
and experience gained from running activated carbon filter plants
are well illustrated by the Diisseldorf drinking water supply.
Since 1961 the city of Diisseldorf has processed natural ground
water, which is influenced by the condition of the Rhine water,
using ozone and activated carbon to produce drinking water. The
producing plants Flehe, Staad and the Wuppertal and Lower Rhine-
Bergische waterworks are all situated on the Rhine, with well
centers 5O m to 250 m from the bank.
Fig. 1; Bank filtration
The bank filtration
The ground water is extracted in vertical and horizontal wells
from large 1O m to 3O m water-bearing diluvial gravel and sand
sediments. The raw water consists mainly of bank filtrate,
together with a small amount of ground water inflow from the
Bergische Land.
Normally, the ratio of bank filtrate to ground water is about
3 to 2, but it varies with the water level of the river and
changes in the water-table. The natural treatment effect of
ground passage on the bank filtrate between the Rhine and the
well should not be underestimated. During ground passage there
occur numerous mechanical, biological and chemical processes.
Turbidity and, included with it, associated organic and inorganic
susbstances such as pesticides, heavy metals and bacteria are
retained in the gravel and the sandstone sediment. The combined
bank filtrate and ground water in the wells is clear and almost
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75
1 HOCHSTER RHEINWASSERSTANO
.1 *BG£SENKTER_GHUNDWASS|RSPIEGEL_8 3J[_'HEBEfiROHR_LEITUNG_
10WASSEHFOHRENDE SCHICHTEN
1 2 WASSERTRAGENDE SOHLE
Fig. 1
i Hochster Rheinwasserstand: maximum water level of the river Rhine
»Mittlerer " : medium
3 Mutterboden mit Rasennarbe: top soil with grass cover
4Deckende Lehmschicht: covering clay layer
sBrunnen: well
6Pumpendruckleitung: pressure pipe
/Ortspegel: level control
aAbgesenkter Grundwasserspiegel: reduced ground-water level
9Heberohrleitung: siphoning installation
10 wasserfiihrende Schichten: ground-water transporting layers
11Pumpe: pump
uWassertragende Sohle: water-bearing layer
i3Sammelbrummen: collecting well
nTertiare Sande: tertiary soil
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76
always bacteriologically acceptable. It contains, however,
soluble iron, manganese and other inorganic and organic com-
pounds which are not removed during ground passage. These
substances', either because of their bad taste and odour
characteristics, or due to their possible harmfulness to human
lifev Jhave to be removed as far as possible in the water
treatment plant.
The treatment process
The treatment processes used by the Rhine waterworks have been
developed as the result of a close interchange of information
betwe'en the waterworks in cooperation with the Engler-Bunte-
Institute at Karlsruhe, and have been adapted to meet the
conditions existing at present.
Fig. 2; The treatment process
In Dusseldorf the treatment of the raw water obtained in the
wells takes place in four processing steps.
Step 1 ;
Oxydation of the impurities by ozonization.
Step 2, upper activated carbon layer:
Reduction of permanganate to manganese dioxyde,
filtration, operation of biological processes.
Step 3, lower activated carbon layer:
Adsorption and operation of biological processes.
Step 4;
Removal of aggressive carbon dioxyde in the main distribution
pipes by addition of sodium hydroxide.
Fig. 3; The first processing step
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77
AKTIVKOHLE-FILTER
2 REINWASSER
INS NETZ
- -OBERE SCHICHT
7 BEGASUNGS-BEHALTER
HT
• —
8 OZONHALTI6E LUFT
VON DER OZONANLAGE
I
9INIEKTOR
TREIBWASSER
to
_J
ROHWASSER-ZULAUF
* ZWISCHEN-BEHALTER
7 Begasungs-Behalte
8 Ozonhalhge Lull
von der Ozonanlage
9 ln|ektor
10 Treibwasser —I
1' Rohwasser- I
Zulaul
4 Zwischenbehalter
Fig. 2 and 3
i Aktivkohle-Filter: activated carbon filter
2 Reinwasser ins Netz: treated water
3Obere Schicht: upper layer
4Untere Schicht: bottom layer
s Pumpe: pump
*Zwischen-Behalter: intermediate container
7 Begasungs-Behalter: gassing tank
aOzonhaltige Luft von der Ozonanlage: ozone-containing gas from
ozone generator
»Injektor: injector
10 Treibwasser: carrier water
11 Rohwasser-Zulauf: raw water inlet
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78
Only a short description of the first processing step is given,
as it gives a better overall view. However, some particular
details are of general interest.
Water-jet injectors introduce the ozone-containing air into
the pipes leading to the gas adsorption tank. Using this
technique, good mixing and an intimate contact of the gas and
the raw water is obtained.
The ozone, which is produced from air in tube ozonizers having
a potential of 16,000 volts, is used to oxidize organic and
inorganic compounds in the water, part of which may be removed
as a filterable suspension. The gas mixture contains 35 g/m
ozone, at a pressure of 1 bar, and has a contact time of 5 min.
To achieve an adequate degree of oxidation, as the amount of
harmful material increases, up to 3 g ozone/m water have to
be added today, whereas previously 1 g/m was sufficient.
This method used at Diisseldorf is not practised everywhere,
hov/ever. Ozone can also be obtained from pure oxygen. It is
also possible to dissolve the gas countercurrently in washing-
or mixing tanks using the pressure in the water supply pipe.
If the ozone is added in a closed process immediately before
the activ* carbon plant, which is under supply water pressure,
the production of oxygen is unavoidable. The undissolved gases
are dried and recycled.
After ozone, potassium permanganate or chlorine may be applied.
Fig. 3 a: Tube ozone generator
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79
"»~# * •
* • » »
.v.v
v.v
:•:•:•:• OZON
W® LUFT
KOHLWASSER
HOCHSPANNUNG -
3a
Ozon : ozone
Luft: air
Kuhlwasser: cooling water
Hochspannung : high voltage
-------
80
At Dusseldorf, the v/ater flows from the gas adsorption tank
to two large intermediate storage containers where after-
reaction and degasification occur. The retention time of the
water in the container is at least half-an-hour. The residual
ozone-containing air is discharged to the atmosphere through
special treatment plants. Originally, the residual ozone was
removed by contacting it with loaded activated carbon. As a
result of operating disturbances on higher ozone dosages,
larger amounts of exhaust air are discharged, which ,may result
in ozone break-through. For the past few months special catalysts
have been tested at the treatment plant at Staad to remove the
ozone from the exhaust air. The results obtained so far show
that the catalysts are effective even under the most unfavourable
conditions. However, still unknown is the effective life of the
catalyst.
The residual ozone content of the exhaust air is at a maximum
3 per cent of the generated ozone, giving an efficiency of ozone
consumption of more than 97 per cent.
The activated carbon filter plant - processing steps 2 and 3
Operation and construction of the activated carbon filters
From the surge tanks the water is pumped, using centrifugal
pumps, at full supply pressure - 6 to 7 bar - into the two-stage
activated carbon filters. The filters are constructed of steel
and are 8 m high, with a diameter of 5 m. The water enters at
the top of the filter through distributors and passes through
two layers of carbon. Each layer rests on a support plate which
contains 632 plastic jets, about 31 per m .
A layer of gravel of various size fraction lies between the
support plate and the activated carbon. The medium velocity
in the filter at present is 22 m/h. However, to obtain a better
filtrate, as a result of a longer contact time with the activated
carbon, the plant has been enlarged and the velocity reduced
to 12 m/h.
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81
Operations of the plant at 2O m/h also produced problems in
running the filters in that an even layer of carbon in the
upper sections was not always obtained. Scouring of up to
7O cm was noticed. This was eliminated by modifying the
distribution system and reducing the entry velocity of the
water.
Fig. 4; Protection of the upper jet support plates
'J.nhe support plates are designed for a working pressure
differential of 1 bar, while new plants are designed for a
pressure differential of 2 bar. To protect the upper plate,
which is most likely to be overloaded, bypass pipes with
rupture disks are installed. The failure of a rupture disk
is signalled to the filter control panel and the corresponding
filter is then immediately removed from service.
To minimize corrosion in the inner parts of the steel filter,
it is coated with a physiologically inert two-component material.
The coating thickness varies between 0.4 mm and 1.O ran. To ensure
good durability, the steel surface must be sand-blasted and
treated according to DIN 28051 before the application of the
coating. The first activated carbon filters were put into service
in 1961. Up to the present time none of the filter coatings have
had to be renewed, except on parts which were damaged by mechanical
wear. This was the case, after ten years of operation, with the
carbon filling- and flushing connecting pipe.
Activated carbon filters are not only produced as steel pressure
filters but also from reinforced concrete, in rectangular form,
and also as open filters for pressureless running. The type of
filter and materials of construction may be determined on economic
and technical grounds. At high operating pressure, steel filters
are used exclusively. With open filters and at low operating
pressure, construction of steel or reinforced concrete is possible.
Reinforced concrete filters do not require any special coating
but must be made waterproof following DIN 1O45 and, to insure
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82
>&$$$$& Dusenboden
Berstscheibe
Spulwasser
Fig. 4
A-Kohle: activated carbon
Dusenboden: jet support plate
Berstscheibe: safety disk
Spulwasser: backwash water
-------
83
the protection of the reinforcing steel, the concrete should
cover it to at least 5 cm, according to DVGW paper W 111.
Large stainless steel filters are unlikely to be installed
because of the high cost of construction. However, an internal
coating is also recommended in stainless steel filters to
eliminate the possibility of corrosion, even though it may not
be strictly necessary.
The second processing step
In the second processing step the manganese,which has been con-
verted to pyrolusite, and other suspended material produced in
the oxidation process are removed in the upper layer of the
activated carbon by filtration.
Fig. 5: Second and third processing step
Until recently, the filter material was an activated charcoal
with a granule size of between O.5 and 2.5 mm. The height of the
layer was 1 m. It was found over the years that the charcoal was
inadequate as a filter material as well as for the separation of
ammonia. A considerable fraction of the suspended material
passed through the upper layer to the lower layer, which is used
for the adsorption of organic material.
Extensive experiments have been undertaken to improve the
effectiveness of this processing step. Experiments in which a
prior flocculation was carried out produced no worth-while im-
provement. Numerous filter materials, both alone and in various
combinations, were tested in small and large filters to produce
a both technical and economical solution. The problem appeared
to be to find a filter material which in its granulation and
pore-size distribution would suit the conditions existing in the
filter.
It was found that either, when good-quality filtrate was obtained,
the operating times were very short or the pressure differential
was unacceptably high. The quality of the filter material was
judged on turbidity measurements, running time, the pressure drop
dependence on flow velocity as well as the determination of the
behaviour of the start-up, operation and flushing. The pressure
drop was measured at various depths in the layer of the activated
carbon. The presupposed limiting conditions for the filtration
were:
-------
Aktivkohlefilter
_Trinkwasser
ins Netz
Obere
Schicht
Untere
Schicht
Pumpe
Fig. 5
Aktivkohlefilter: activated carbon filter
Trinkwasser ins Netz: drinking water to the supply system
Obere Schicht: top layer
Untere Schicht: bottom layer
Pumpe: pump
-------
85
Removal of
manganese to O.5 g/m ozonized water
iron to O.1 g/m ozonized water
filter velocity 2O rn/h
maximum pressure drop 6OO mbar
layer height 1.8m
The values aimed at v/ere:
manganese not detectable
iron not detectable
running time 48 hours
surface loading 1OOO m /m
Although not all the problems, especially the theoretically
interesting ones, have been solved, it can be said already
now that the tests have been successful.
The desired values were best obtained with an intermediate
product of activated carbon production, a so-called pre-activate.
Characteristic properties of this material:
granule size: O.9 - 2.5 mm
mean granule diameter: 1.7 mm
bulk weight: 58O kg/m3
The use of the pre-activate provides a number of advantages
at a filter layer height of 1.5 m. They are:
1. Considerable improvement of the filtrate quality and
the start-up process.
There are now no noticeable amounts of filterable
material on the lower adsorption layer at reasonable
filter running times.
2. The degradation of ammonia which may be present by
biological processes (nitrification) is moved from
the lower to the upper filtration layer of the filter.
3. Due to the good filtration in the upper layer the
adsorption process is necessarily improved in the
lower layer.
-------
Because of the pressure drop measurements a layer thickness
of O.5 m would be sufficient for filtration. Most of the
filterable substances are retained in the upper O.5 meters
of the carbon layer, Figure 6.
However, the turbidity measurements show that a layer thickness
of at least 1.5 m is necessary for the filtration of the finest
particles, and to obtain optimum conditions, Figure 7.
The third processing step
In this process step organic compounds are removed in the
lower activated carbon layer by adsorption. The activated carbon
quality,originally mainly chosen according to its phenol loading
to improve taste and odour in the water, has been shown not to
meet modern requirements in almost any way.
The further increase in organic load of the mixed ground water,
which depends on the quality of the Rhine water, especially of
organo-chloro-compounds, was at first balanced by increasing
the ozone dosage from initially 1 g to 3 g/m , and the activated
carbon from 3 g to 1O g/m water. In long-term tests, in co-
operation with the Engler-Bunte-Institute and other waterworks,
the behaviour of different carbon qualities under different
conditions was investigated, especially regarding adsorption
capacity and adsorption velocity. The information obtained and
more sensitive analytical methods made it possible to get the
activated carbon manufacturers to supply carbons of a better and
more uniform quality, with higher activity, although they are
not quite satisfactory yet.
By this, a further optimization of the third processing step
has been achieved. The activated carbons "LS Supra" and "F 3OO"
are mainly used, chiefly as a mixture, with a granule size between
0.5 mm and 2.5 mm, at the Diisseldorf plants. The mean diameter
of the carbon granules is 1.4 to 1.6 mm. The carbons are about
4O % heavier than those previously used. No disadvantages were
noticed in the operation of the filters, due to the higher
particle density.
-------
87
1 m bar]
10 20 30 40 h 50
0.5-
10 20 30 40 h 50
Figure 6. Pressure Differential Figure 7. Turbidity in the Upper
in the Upper Filter Layer
Filter Layer
Figs, b and 7
Schichttiefe: filter bed depth
Differenzdruck: differential pressure
Trtibung: turbidity
Zeit: time
-------
Apart from the two carbon types mentioned above, there are
other good materials on the market.
Using the better-quality activated carbons, it was possible to
achieve a greatly increased removal of organic compounds in
the adsorption layer by reducing the operating velocity by
about 50 % and by increasing the layer height from 2 m to 2.5 m.
In order to make a valid statement on the influence of the
mechanical properties of activated carbon, further investigations
have to be made.
A process control procedure, introduced at Diisseldorf, has
proved to be very satisfactory. The total dissolved organic
content of the water is defined by measuring the UV extinction.
For a reliable evaluation, an investigation period of about
8 days is required. However, it is necessary to find a method
which makes it possible to detect very rapidly the degree of
exhaustion of activated carbon and also the harmful substances
in drinking water. This problem has been worked at for a long
time. It is hoped that it will be solved shortly in a manner
acceptable to the waterworks. This would certainly be an enormous
advance.
The effectiveness of bank filtration and of the individual
processing steps in water treatment are illustrated in Figs.
8 and 9. In evaluating the effectiveness, it is to be remembered
that in the treatment processing steps mainly the organic com-
pounds which are present in small amounts in the water, which
are non-biodegradable but which are harmful or even dangerous,
are oxidized, altered, filtered out and adsorbed.
Fig. 8; Relative treatment effectivity
referred to DOC, COD and UV in 1974
Fig. 9; Mean values of important substances
in Diisseldorf drinking water
-------
89
Rheinwosser \-
Brunnenwasser
Ozonung
Aktivkohle E
1 — 1
T"
;.
-
pr-^T
;
'
'
1
1
00%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0
DOC
COD
UV
Fig. 8
Rheinwasser: water from the river Rhine
Brunnenwasser: water from the well after bank filtration
Ozonung: ozonization
Aktivkohle: activated carbon
-------
90
Rhein Brunnen Aufbereitung
~T~ A-Kohle- Na OH-
[Ozonung Filtration Dosierung
Trink-
wasser
Img/ll C g
10
Fig. 9
Rhein: river Rhine
Brunnen: well
Ozonung: ozonization
Aufbereitung: treatment
A-Kohle-Filtration: activated carbon filtration
Na OH-Dosierung: Na OH-dosage rate
Trinkwasser: drinking water
-------
91
backwashing of activated carbon layers
After a certain amount of throughput the filters have to be
backwashed. This is the case for the upper filter layer after a
water throughput of about 20,000 m , v/hich means a running time
of 50 hours at an operating velocity of 20 m/h.
The running time of the adsorption layer is considerably longer
because filterable substances, as already mentioned1, do not reach
this layer in any appreciable quantity.
By special measures it was possible to reduce the amount of
backwash water and the backwashing velocity, although an activated
carbon with a higher density was used. The freeboard height,
v/hich is the distance of the upper layer of carbon and the
backwash discharge pipe, was reduced amongst other things. For
backwashing air was used, and .then water. The initial resistance
of the unsoiled carbon are abotit 8O mbar in the upper filtration
layer and about 120 mbar in the lower adsorption layer.
The measures applied made it possible to reduce the backwash
velocity from 3O m/h to about 15 m/h, and the backwash time, using
water, from 2O min to about 5 min. Limiting values for the back-
washing process are a filter resistance ' of GOO mbar in the upper
layer and 3OO mbar in the lower layer at a filter velocity of
20 m/h. The volume of backwashing water is today about 5O m
as against 15O m v/ith the previous backwash technique.
The treatment of the backwash water is carried out in special
plants. The water is passed from the filters to sedimentation
tanks, made of reinforced concrete, the lower parts of which
are funnel-shaped. The filtered substances settle rapidly.
After a sedimentation time of about 2O min the clear water is
drawn off and discharged into a sewer. The settled sludge is
pumped to drying beds once a week, and then later incinerated.
Fig.10; Schematic layout of a filter in operation
and during backwashing
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92
Spulung 3 Bftritb
s Spu/wossrr-
'
Spullufl 9
9
-7-
1
,
"g
'Sputwast
Fig. 10
iSpulung: backwashing
2A-Kohle: activated carbon
aBetrieb: filtration operation
4 Dusen: j ets
sSpulwasseraustritt: outlet for backwashing
6Spulwassereintritt: inlet for backwashing
JRohwasser: raw water
sReinwasser:treated water
'Spulluft :air for backwashing
-------
93
Reactivation of the activated carbon
Whilst the upper activated carbon layer does not need changing,
or mayte only very seldom, the lower adsorption layer is ex-
changed regularly twice a year - previously it was once a year.
According to the present evaluation methods - determination of
the total organic components by UV extinction - the adsorption
capacity is only 2O % after a throughput of between 400 ,OOO m
and 6OO,OOO m water per filter ana an activated carbon amount
of 4O in . The adsorption capacity of new or freshly reactivated
carbon lies generally between 70 % and 8O %. Taking as a basis
this degree of loading and a mean operating velocity of 12 m/h,
the activated carbon has to be reactivated or replaced by fresh
carbon in each filter four or five times a year.
Due to the problems associated with the reactivation of spent
activated carbon at outside firms, it seems advisable that the
waterworks had its own plant. Apart from the economy, this
contributes substantially towards securing a constant water
quality. It is thus possible to adjust the carbon quality to
any special requirements at any time, and to have newly re-
activated carbon available at short notice in the event of a
sudden concentration of harmful substances in the raw water.
A reactivation plant with a fluidizec bed furnace with a daily
capacity of 6 t will therefore be put into operation at the
Diisseldorf waterworks. The plant can be extended to a daily
capacity of 18 t.
Of course, losses of carbon are incurred in the running of
activated carbon plants and the thermal reactivation of
activated carbon. The carbon loss in backwashing, operation,
transport and reactivation is at present reported to be between
14 % and 15 %. The highest losses are incurred in transport.
They are in the range of 1O %. These losses can surely be
substantially decreased by on-site reactivation.
-------
Input, extraction and transport of activated carbon
Since 1969, the transport of all activated carbons has been
made exclusively in silo transporters.
The carbon is washed into the carbon filter from, the silo
transporter with the aid of an injector and pressurized water
through a transportable steel pipeline ot flexible pipes.
The tank of the silo transporter is first lifted and inclined
by about 6O°. If the carbon in the transporter is dry, water
is added with a hose pipe until the carbon has the consistency
of dough. This has the advantage, anongst others, that the
carbon is wetted with water already at this stage and that the
degassing period of 24 hours, which may be necessary in some
instances, can be considerably reduced.
The filling process can be observed and controlled through a
sight glass. In order to prevent the carbon from piling up in
the filter, it is necessary to flush with water or air several
times during filling. The time required to transport 4O m
activated carbon over a distance of 5O m and a filling height
of 8 m is about 4 hours, at a bulk weight of about 420 kg/rn .
The preparation periods for transport, pipelines etc. are
contained herein. The ratio of pressurized water to activated
carbon is 3 to 1.
When the carbon is flushed from the filters, the filters are
kept filled with water and are put under pressure. The silo-
transporter is connected by a pipeline system with the appropriate
filter.
In order to keep the carbon from settling during the flushing-out
process, about 30O m /h to 5OO m /h water is added continuously.
Thus it is possible to rinse out even the last remains of carbon.
-------
95
There are no significant amounts of gravel washed out during
this process from the supporting layers into the flushed-out
carbon. If a certain amount of gravel is contained in the
activated carbon, reactivation is disturbed.
The time necessary for flushing out 40 m activated carbon,
including preparation time, is three hours. The actual
flushing-out period is about 4O minutes. The filling and
flushing-out of the carbon can easily be done by two persons.
After the flushing-out process an after-dehydration of 2 to 3
hours of the activated carbon is required to avoid overloading
the silo transporter. The silo has to be inclined for this
purpose.
Since the installation of the reactivation plant at the
Holthausen waterworks, the filling and flushing-out of
the activated carbon between filter and storage tank has been
made through a fixed pipeline system made of synthetic material.
The transport of the activated carbon between the works at
Flehe or Staad and the reactivation plant is carried out, as
usual, with silo transporters.
In order to save costs, investigations are made at present
to reduce.thfe demand of water required for filling and
flushing-out.
Because of the frequent changing of the activated carbon
underlayers, the filling-and flushing-out nozzles of the
steel filters are subjected to heavy mechanical stress.
The pipes, which were originally welded into place, have been
replaced by exchangeable ones.
Supervision and controlling of the plants
The pump station and treatment plants are operated and
supervised by remote control from a central switchboard.. The
operation is partly automatic. The distribution of the
ozone/air mixture on the gassing containers is done automatically,
according to the water throughput.
-------
At present, plants for the automation of the flushing process
for the two-layer activated carbon filters are being installed.
The flushing process is to be initiated depending on the amount
of throughput and on the filter resistance, and will then
proceed automatically. Freely programmable controls are planned
which can analyze analogous and digital signals and which can
be used as a reference input for control purposes. This requires
using a process computer.
The computer consists of input and output facilities, a central
computer, a central memory unit with a maximum storage volume
of 32 K. The computer output is recorded on a page printer
which may be used to supervise the programme and to record
the operation data. It is also intended for danger warning and
recording primary data, so that it will be possible to record
all disturbances in the operation of the plant according to
their location and time.
In order that the computer will not be blocked excessively
in times of disturbances, a line writer is to be installed.
Disturbances within the computer up to the periphery are
signalled independently. Any disorder in the computer is
signalled to a video screen. The computer is designed to
take over additional arithmetical-, operational- and
automational tasks for all activities within each working
group.
Expansion of an activated carbon plant
The activated carbon plant at Holthausen is presently being
extended by 12 filters. From a technical point of view, the
transport and installation of the filters ought to be of
interest. The transport of the steel containers, weighing
30 t and with a diameter of 5 m and a height of 8 m, was
made by ship on the Rhine from the manufacturer to the ship-
yard Reisholz in Diisseldorf. They were then loaded onto a special
transporter and carried by road to the building site. The
-------
97
containers were then rolled with tank rollers, as used by army
vehicles, via guiding rails to the finished concrete foundations
in the pre-fabricated filter hall made of reinforced concrete.
This was the first use of such a procedure for a container of
this size.
Many experts are of the opinion that a water treatment plant
has to be designed individually to fit the circumstances
existing in each individual case. This is correct to a certain
extent. Nevertheless, the aim should be to standardize the
design of treatment plants and treatment steps for drinking
water as far as possible. New processes are generally very
expensive and not necessarily fully developed. An even greater
exchange of experience between the operators of waterworks
than has been the case so far would be most useful in this
connection.
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98
INVESTIGATIONS OF THE OPTIMIZATION OF PRETREATMENT WHEN USING
OZONE
by W. Scheidtmann, Duisburg
Like many other Rhine waterworks, a combined ozone-activated
carbon treatment for processing highly loaded bank filtrate is
used by the city of Duisburg's waterworks. Similarly, it was
shown at Wittlaer at the end of the 1950s that in addition to
disinfection of the water, ozone also provided a good pretreatment.
The high consumption of activated carbon caused by the increased
pollution of the Rhine was considerably reduced by using ozone,
and at the same time the performance of the filter plant, in use
since 1957, was improved.
The process of ozone from oxygen, and its injection into the
raw water in a closed pressure system, as was used at Wittlaer,
have been reported previously (SIMON, 1968). Therefore, only a
schematic layout of the Wittlaer procedure is shown in Fig. 1.
Technical grade oxygen is taken from a liquid oxygen storage
tank and passed to a 4-tube ozone generator. The ozone/oxygen
mixture produced, containing up to 6O g 0-. per ,m oxygen is
pumped,using water-ring pumps,to two washers. Here gas is dissolved,
countercurrently, in part of the total flow.
-------
99
The undissolved gas mixture is returned to the ozone generator
via a drying plant. After an increase of pressure the highly
concentrated ozone mixture of about 20 g ozone per m of water
is conveyed with the raw water by a distributor tray to a
mixing and reaction tank which is filled with Raschig rings,
similar to the washers.
Fig. 1; Diagram of an ozone plant at the waterworks III
in Wittlaer
After a 4-minute retention in the reactor , the water, containing
an ozone surplus of about O.3 mg/1, reaches a two-stage filter
plant. The top stage has a multi-layer filter, the lower stage
high-grade activated carbon (see Fig. 2).
Fig. 2; Two-stage filter
The investigations of the optimization of flocculation-fj,ltration
at the Wittlaer treatment plant have been published (SCHEIDTMANN,
1973) and reported during the discussion meeting of the German
Association of Gas and Water Engineers (DVGU) in 1974 at Duisburg
The following brief report covers further investigations at
Wittlaer on the optimization of the oxidation step.
-------
18 Ozon-Wascher "Misch- und Reaktionsbehalter
7Trocknungsanlage
«Gas-
I ,«Gas- |~~
fl hi RUckfLihrung
"
20Raschig-Ringe
P
- "Ozoneur WassWing-
geblase
Ozon-Sauerstoff-Gas
uFilteranlage
Rascnig-Ringe
Druckerhbhungs-
pumpe 10
&—i
Ozon-Starkwasser
Entleerung
Verdampfer
*—i FlUssigsauerstoff-Behalter
Fig. 1 and 2
i Flussigsauerstoff-Behalter: liquid oxygen tank
jVerdampfer: evaporator
sOzon-Sauerstoff-Gas: ozone-containing oxygen
4OzOneur: ozone generator
sWasserringgeblase: v;ater ring blov;er
6 Gas-Ruckf iihrung : gas recycling
7Trocknungsanlage: drying plant
8Entleerung: discharge
»Ozon—Starkv^asser: water with high ozone concen
14
Mehrschicht-Filter
Aktivkohle-Filter
zum Verbraucher
O
o
'^Rohwasser
i-o Druckerhohungspurr.pe: pump for increase of pressure
nMisch- und Reaktionsbehalter: mixing and reaction
12Entluftung: ventilation vessel
i3Filteranlage: filter plant
KMehrschichtfliter: multi-layer filter
'sTeilstrom: recycling fraction
i«zum Verbraucher: to the consumer
irRohwasser: ravi water
iBOzon-Wascher: ozone washer;zoRaschig-Ringe: Raschig
i»Aktivkohle-Filter: activated carbon filter
rings
tration
-------
101
Entlliftung
Hydrofilt
Quarzsand
' Stiitzkies
6 Aktivkohle
9 Rohwasser
sEntlliftung
Spiniuft-Eintritt
A-Kohle-Einflillstutzen
7Splilwasser
Stlitzkies
A-Kohl e-Ausf lil 1 stutzen
s Reinwasser
Fig. 2:
'Stiitzkies: supporting gravel ; 6AI
-------
102
After being in operation for some years, it was found that the
Raschig rings in the mixing and reaction tanks of the ozone plant,
installed in 1966, were becoming increasingly clogged. Clearly, a
significant amount of the manganese had precipitated out as pyrolusite.
The one advantange of the removal of manganese, and other undesirable
components, in the reactors is that they reduce the load on the
succeeding multi-layer- and activated carbon filters.
But, as the reactors cannot be backwashed, there are increased pressure
losses because of the degree of clogging, which also results in
increased maintenance and repair costs. However, if one alters the
functioning of the reactors by filling them with filter material
instead of Raschig rings, and makes provision for backwashing then
the reactor acts simultaneously as a pre-filter, whose filter capacity
can be controlled by the adequate aoHLtion of ozone.
In line with these considerations, the following test programme was
set up in conjunction with the Engler-Bunte-Institute of the
University of Karlsruhe:
1) Determination of a suitable filter material.
2) Application of different ozone additions before the reaction filter
and the multi-layer filter.
3) Determination of the optimum filter velocities and filter running
times.
4} Additional use of flocculants and flocculant aids.
Preliminary tests have shown that the very porous Hydrofilt, which
has been in successful use for some time in multi-layer filters, is
also suitable for use in a pre-filter. This material yielded the best
results with regard to good filter volume effectiveness and running time.
-------
103
First of all, four different granule sizes, 2.5- 3.5 mm, 3-5 mm,
5-8 mm, 8-1O ram were examined. Plexiglass filters of 150 mm diameter
and filter layer height of 1 ra were used for the tests; the experi-
mental layout of which is shown in Figure 3.
All four filters were run at a filter velocity of 7O m/h and with
an ozone dosage of 2.5 - 3.O g/m of water.
The 2.5-3.5 mm and 3-5 mm granules were excluded from subsequent
tests because the pressure drop increased too rapidly compared with
the other granule sizes.
The subsequent tests using 5-8 mm and 8-1O mm granules gave almost
the same degree of purification, with the 8-1O mm granules having the
lowest rate of increase in pressure drop.
The most significant results with ozone additions before the reaction
filter and before the multi-layer filter of 1.5 g/m and 2 g/m
are set out in Table 1. It should be noted that with the poorer
raw water larger additions of ozone were required.
Running times of at least 8 days should be obtained with the pre--
filter and a maximum pressure drop of 5 m. For this reason, only
8-1O mm Hydrofilt granules were used in further tests.
Fig. 3: Reaction filter tests with 4 different granule sizes
Table 1; Reaction- and multi-layer filter tests with ozone
addition before and after the reaction filters.
Fig. 4; Layout of the reaction- and multi-layer filter tests
with ozone and flocculant dosing
In the next test series aluminium sulphate, ferric chloride and
a polyelectrolyte flocculants and flocculant aid were also used.
The test layout is shown in Fig. 4.
-------
Reaktions-Filter
ft
Rohwasser 03-Starkwasser
,, , ....
Hydrofilt
•N-. 2
,_,
Probeentnahmestellen
Filter 1
Filter 2
Filter 3
Filter 4
Kbrnung
2,5 - 3,5 mm
3 - 5 mm
5 - 8 mm
8 - 10 mm
3
-txh
4
Filtrat
Fig. 3
Probeentnahmestellen: sampling points
Kornung : grain size
Rohwasser: raw water
Cu-Starkwasser : water with high Cu concentration
Reaktions-Filter : reaction filter
Filtrat: filtrate
-------
105
Pilt.r ! Reaction Filter ffllt.r
Filter 2 Multi-Layer Filter
filter height 600 mm Hydrofilt
2.5-3.5 mm
400 mm quartz sand
O.9-1.2 mm
filter velocity 17 m/h
UV = UV extinction (240 nm)
Granulation ,
!
Dosage
UV
inlet
Filtrate
Inlet
Filtrate
Filter 1
5-dmm
1,5 g th/m3
0,127
0,100
OJ90
0,70
Filter!
1,Sg Oj/m1
0,100
0.072
0,70
0,01
Filter 1
5-Smm
?:0g03/m3
0,135
0,102
1.25
1.10
Filter2
WgOj/m3
0,102
0,077
VO
0,03
Filter 1
S-IOmm
!.5g 03/m3
a/27
0.102
0.90
0.75
Filter?
1,Sg03/nf
0,102
0.067
0.75
0,01
Filter 1
S-fOmm
2,0g03/m3
0.135
OJ03
1.25
1.13
Filter?
2,0g03/m3
0,103
0.070
W
0.03
-------
03-Starkwasser
Reaktions-Filter
Mehrschicht-Fil ter
Rohwasser
\
t.
VI
k ^v
&
i7|O 1
n
ol
o
LO
' CM
CD
J LD
,~
1
hnri
"//:<
M
'/-x
^
1
Hydrofilt
8-10 mm
Schichthohe
1000 mm
1 r I LN-NUnybiii 1 uue I -uub i cr uriy
1 N j* ^,
^
I
I
' r-H
1
J2
\\
^
I
N
:
^
/
r i
J0
1
j
te=s!
y^
,1,
^Sc
- 6C
i
OWM
'drofilt
5-3,5 mm
hichthohe L
0 mm .
Quarzsand 0,9-1,2 mm
0,9-1,2 mm
Schichthohe
400 mm
i
\N
^§\^
i
b
I S
O
O
0
f — 1
r2
1 1
CO
Probeentnahmestellen: sampling points
Kornung: grain size
Rohwasser: raw water
Cu-Starkwasser: water with high 0-, concentration
Reaktions-Filter: reaction filter
Filtrat: filtrate
Mehrschicht—Filter: multi-layer filter
Flockungsmittel-Dosierung: flocculant dosage
Schichthohe: filter height
Quarzsand : quartz sand
-------
107
In order to achieve a more effective treatment, by extending the
retention time in the filter, the filter velocity was reduced to
50 m/h.
Different ozone amounts were added with the aim of complete oxidation
of the Mn in the raw water to Mn . This would also result in the
removal of part of the dissolved organics in the pre-filter.
To begin, both large and small ozone dosages were added before and
after the reaction filter. The velocity in the multi-layer filter is
kept constant at 17 m/h because this velocity is used in industrial
filters using activated carbon.
The dosage before and after the filter was then varied.
It was found,satisfactory results were obtained with ozone additions
of 1.5 and 2.O g/m before the reaction filter, and 2 and 3 g/m
before the multi-layer filter, as can be- seen in Table 2.
Flocculants and a small amount of polyelectrolytes were again added
to a multi-layer filter, operated in parallel.
From the table one can see that there is a reasonable degree of
purification in the reaction filter with an ozone addition of
1.5 g/m . A further addition of 2 and 3 g/m ozone before the multi-
layer filter resulted in a considerable decrease in the concentration
of dissolved organics and manganese. Even more pronounced was the
improvement in the degree of purification when, in addition to this,
flocculants were added.
Table 2; Reaction- and multi-layer filtration tests with ozone
and flocculant dosing
A sufficiently long, baffled, contact path was arranged between
the point of flocculant addition and the multi-layer filter, which
obviously had a good influence on floe formation.
The final tests were run under the following conditions:
-------
108
Table 2: Reaction and multi-layer filtration tests
with ozone and flocculant dosing
Filter 1 = Reaction Filter filter height 1OOO mm Hydrofilt
8-10 mm
filter velocity 5O m/h
Filter 2 = Multi-Layer Filter
filter height 6OO mm Hydrofilt
2.5-3.5 mm
400 mm quartz sand
O.9-1.2 mm
filter velocity 17 m/h
Pr.= praestol as flocculant aid, UV=UV extinction (24O nm) ,
Tr.= turbidity
Ozone
Dosing
Flocc.
Aid
Dosing
UV
Inlet
Filtrate
Mn
Inlet
Filtrate
Tr.
Filtrate
Filter 1 Filter 2
1.5 g/m3
_
0.120
O.O91
1.03
0.75
—
3.O g/m3
_
0.091
O.O6O
0.75
0.07
O.4O
0 . Sg/h^Fe
0.1 g/m Pr.
0.091
0.050
0.75
O.O5
O.30
Filter 1 Filter 2
2.0 g/n
_
0.118
0.090
0.92
0.75
-
2 . o g/m
O.O9O
0.066
0.75
0.08
O.5O
O.5 g/rru Fe
0.5 g/m:; Al
0.1 g/m Pr.
0.090
0.055
0.75
O.05
0.30
-------
109
1) Ozone addition of 2 g/m , each, before the reaction filter
and the multi-layer filter.
2) Flocculant addition of 2 g Al/m and O.1 g Praestol/m .
3) Contact paths of the same length were used before the multi-
layer filter when using both ozone and ozone and flocculant,
4) The velocity in the reaction filter was 50 m/h and in the
multi-layer filter 17 m/h.
The most important results of this test series are set out in
Table 3.
Table 3; Reaction and multi-layer filtration tests with ozone
and flocculant dosing, using a constant contact path.
In conclusion, the following can be said:
The reduction in concentration of dissolved organics, measured by
UV extinction, are quite favourable at these ozone additions, in
the filtrate from the multi-layer filter. Also, the turbidity data
are so good that it can be confidently expected that the following
activated carbon will remove the remaining substances in the water,
especially the organo-chloro compounds.
A suitable contact path, after the second ozone addition, is also
then necessary in those cases where no further addition of flocculant
is made. Obviously, this strongly influences the effectiveness of
the treatment. The addition of flocculant showed no notable improve-
ment in the test series. However, it may be necessary if the quality
of the bank filtrate were to be extremely poor, for instance, after
a long drought and lowered water levels in the Rhine. For this reason,
an additional flocculation step was not included during the subsequent
extention of the treatment plant at Wittlaer.
-------
110
Table 3: Reaction and multi-layer filtration tests with ozone
and flocculant dosing, using a constant contact path
Filter 1 = Reaction Filter filter height: 1000 mm Hydrofilt
8-1O mm
filter velocity: 5O m/h
Filter 2 = Multi-Layer Filter
filter height: 6OO mm Hydrofilt
2.5-3.5 mm
4OO mm quartz sand
0.9-1.2 mm
filter velocity: 17 m/h
flocculant : Al = aluminum su]phate
Pr = praestol
iOzone
j Dosing
jFloccul.
JAid Dos.
(Contact
| Path
Filter 1
o / 3 f
2g/m
j\Uter__2 Filter 1
2 g/m3 1
no
Filter 2
3
no
yes
no
yes
2 g/m
Al , Pr. _
2g/m + O.lg/m
yes
lUV-Ext.
[(250 nm)
Inlet
Filtrate j
Mn(mg/1)
Inlet
Filtrate
Turbidity
(JTU)
Filtrate
O.085
0.057
O.O57 O.039
1.02
0.94
i O.9O
i 0.17
i
O.60
0.057
O.030
O.90
0.04
0.15
0.102 0.069 0.069
0.069 •0.040 I 0.031
1.24 JO.93
1.08 io.04
0.93
n.n.
7.0
O.14 0.10
-------
Ill
Finally, it should be mentioned that the double addition of ozone
is of advantage, especially at an increased ammonia content in the
1£
,4+
4+
bank filtrate. One has then - also at very high NH concentrations -
sufficient oxygen available for the biological oxidation of the NH
Also, it is possible to adjust the oxygen content in the treated
water, to a desired value, by a suitable choice of the ozone additions
before and after the reaction filter.
The described method of an optimum pretreatment of Rhine bank
filtrate provides an important contribution to obtaining a good
quality drinking water, even with poor quality rawvater, as is
occasionally the case along the lower Rhine.
-------
112
PRACTICAL EXPERIENCE IN THE USE OF FLOCCULATION FILTRATION
CONNECTED IN SERIES TO GRANULAR ACTIVATED CARBON FILTERS
by E. Heymann, Duisburg
Since it has already been described in more detail elsewhere
(HEYMANN 1974), the purification process will be discussed only
briefly here by means of the flow scheme shown in Fig. 1.
Fig. 1: Flow Scheme, waterworks No. 1
Purpose of the water purification process is the complete removal
of undesirable water impurities. Our raw water has virtually no
oxygen, consisting almost entirely of bankfiltrate from the river
Rhine. The water flows under pipe pressure (6 bar) to the purifi-
cation plant. The first step of the purification process is the
addition of a sodium hypochlorite solution in order to oxidize
ammonium ions followed immediately by the addition of a solution
of pottassium permanganate and aluminum chloride. The permanganate
is intended to oxidize nothing but the iron and manganese salts
dissolved in the raw water. The mixture of hydrated iron and
manganese oxide floe. formed thereby is already capable to adsorb
small amounts of organic water impurities. This effect is intensi-
fied by the floe formed due to hydrolysis of the aluminium
chloride added simultaneously.
In order to stabilize the floe an organic polyelectrolyte is
added at the inlet of the two-stage filters. After at least 10
minutes the water reaches the prefilter stage which consists of
three layers: activated carbon, anthracite and sand. The floccu-
lation stage is so adjusted that small shear-resistant floe
with large surface areas are formed.
Next in flow direction follows a 2 m-layer of granular activated
carbon. The brand in use is NORIT ROW O.8 supra which is rod-shaped
and has been reactivated at least four times so far. In contrast to
other reports the uniformity of the rods is so poor that they settle
in an identical manner after each filter backwash. The average
filter rate is 10 m/h. It varies between 5 and 2O m/h.
-------
113
Fig,
1) well for bank-filtered water
2) collecting well
3) pumping station
4) automation control
5) sodium hypochlorite
6) break-point chlorination
7) flocculant
8) mixer
9) flocculant aid
10) first filter
11) second filter
12) sodium hydroxide
13) safety chlorination
14) water meter
15) pressure control/distribution system
-------
The purified water is treated with sodium hydroxide for pH control
and once more with sodium hypochlorite as disinfectant. The auto-
matically working purification plant has now been in operation for
4 years.
Table 1; Effectiveness of various process steps
mg C/L %removal COD(mgQ/l) %removal
1) raw water 2.63 - 9.2 -
2) raw water + 0.45,u filtered 2.62 - 9.3
3) raw water + 2 rng Clp/1 +
0.45 ,u filtered 2.65 - 9.1
4) raw water + 2 mg Cl?/l +
2 mg KMnO./l (floe! • in
NaNO- + H?S04 dissolved) +
O.45 ,u filtered 2.62 - 9.0
5) raw water + 2 mg C1-/1 +
2 mg KMn04/l + 0.45 ,u filt. 2.45 6.8 8.0 13.O
6) raw water + 2 mg C1-/1 +
2 mg KMnO,/l + 5 mg Al /I
+ O.45 ,u filtered 1.58 39.9 5.1 44.6
7) raw water + 2 mg Cl~/l +
2 mg KMn04/l + 5 mg A13+/1
+ 0.45,u filtered + 2O mg
ROW supr.+ 0.45 u filtered O.42 84.O 1.3 85.9
Table 1, showing the effect of each individual step of the
purification process, clearly demonstrates that,up to step 5,
DOC and COD values remain unchanged. This means that without the
flocculation effects of the hydrated manganese oxide the COD and
DOC values are not influenced by break-point chlorination and
addition of potassium permanganate. It should be pointed out that
the DOC variation is very low.
Integration of the flocculation efffect by the hydrated manganese
oxide into the purification process causes for the first time a
pronounced reduction of the DOC values.
-------
115
Step 6 shows a substantial decrease of DOC- and COD values due
to the adsorption by aluminum hydroxide. The 5 mg Al /I added
are the optimum cost effectiveness. Step 7 shows the effect of
the activated carbon. It should be mentioned, however, that the
results of steps 6 and 7 could be very different. Not all of the
compounds which are adsorbed onto activated carbon can be elimi-
nated by precipitation. Due to the change of the water level of
the Rhine the composition of the raw water varies. Because of
this, the effect of precipitation can exceed the effect of the
activated carbon in the removal of DOC. Thus, it is clearly
demonstrated that the precipitation step cannot replace the
activated carbon despite of DOC removals exceeding 75 %.
Generally, the process is controlled in such a way that the
DOC content of the filter effluent is always below 1 mg/1. The
results shown in Table 1 are based on values obtained in the
summer of 1975 when the raw water was of good quality.
To understand the meaning of these results with respect to
quality and quantity, liquid-liquid extraction followed by GC
was used.
The gaschromatograms shown in Figs. 2 to 5 and 7 to 10 demonstrate
typical methodical errors resulting from differences in stability
and volatility of the organic substances under investigation.
For the purpose of this analysis these substances have not been
identified.
Fig. 2: Comparison of gaschromatographic test results
of pentane extracts
Substantially decreased are number and quantity of non-polar
substances extractable with pentane after the precipitation step
(Fig. 2). Interestingly, additional peaks occur in the effluent
of a freshly filled activated carbon filter. These peaks appear
neither after the precipitation step nor after exhaustion of the
activated carbon.
-------
ne
25 -I
20 -
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E 10 •
5 -
Rohwasser
o
o
*
O
0 * 0
? ? ? ?
1 1 1
0 10 20 30 40 50 60 70 76Min
25 •
20 •
^ 15 '
E
E 10 •
5 •
C
25 •
20 •
"^ 15 •
E
e 10 •
5 •
nach der FLockung
0
*
0
o
0
i- O x
"ll I
10 20 30 40 50 60 70 76Min
im Ablauf eines frisch gefiillten Aktivkohlefilters
""? 9" ° I
"
ll
0 "
0 10 20 30 40 50 60 70 76 Min
25
20
~ 15
E
E 10 •
5 •
0 •
im Ablauf eines erschbpften AktivkohlefiLters
0 g
f
0
1 ....
0 10 20 30 40 50 60 70 76Mm
Fig . 2
Rohwasser: raw water
nach der Flockung: after flocculation
im Ablauf eines frisch gefullten Aktivkohlefliters
outlet of a filter with fresh activated carbon
im Ablauf eines erschopften Aktivkohlefliters:
outlet of a filter with exhausted carbon
-------
117
Fig. 3: Comparison of gaschromatographic test results
of i-butanol extracts at pH 1
Fig. 4: Comparison of gaschromatographic test results
of i-butanol extracts at pH 4
Fig. 5; Comparison of gaschromatographic test results
of i-butanol extracts at pH 9
Figures 3 to 5 show gaschromatograms of the polar organic water
impurities. These substances have been extracted from the water
with i-butanol at varying pH values. As in the case of non-polar
substances, concentration and chromatographic effects can be seen:
the effluent of exhausted activated carbon filters shows more and
higher peaks than the effluent of the precipitation step or fresh
activated carbon.
The effect of the thickness of the carbon layers and the length
of the MTZ, and thus the minimum thickness of the carbon bed at
a constant filtration rate, can be seen from the diagrams in
Fig. 6. The limits of water purification by activated carbon are
evident: the water contains impurities which cannot be adsorbed
by activated carbon.
Fig. 6: Break-through curves of activated carbon at
different layer heights
Another result of our investigations is demonstrated in Figs. 7
to 1O. Here the contents of water impurities of pilot filter
effluents without preceding precipitation are shown. In each
case the activated carbon of the filters was exhausted. The
result is that high-boiling non-polar products, which can be
degraded biologically, are changed to lower-boiling polar sub-
stances in the carbon bed. It can be concluded that biologically-
operating carbon filters do not degrade organic substances to COp
completely. Apparently, the structure of large amounts of organic
compounds is changed only slightly, or not at all.
-------
118
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-------
119
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111 l" - III
30 40 50 60 70 76Min.
nach der Flockung
S
o
0 0 7
^ 0
a o *><
K X
20 30 40 50 60 70 76Min.
Ablaut eines frisch get iillten Aktivkohlefilters
''
0
m
20
o
0
S 7 0 °
l" 1
30 £0 50 60 70 76 Min.
Ablauf eines erschopften Aktivkohlefilters
0 0
7 «
o
£ "~~
X °
" 1
3 °
3 "^
C3
*)( °
* *K
.. 1 1 . -
10 20 30 40 50 60 70 76Min.
Fiq 4
Rohwasser: raw water
nach der Flockung: after flocculation
im Ablauf eines frisch gefullten Aktivkohlefilters
outlet of a filter with fresh activated carbon
im Ablauf eines erschopften Aktivkohlefilters:
outlet of a filter with exhausted carbon
-------
120
25 •
20 •
™ 15 .
E 10 •
5 •
0 •
C
25 -I
20 •
- 15-
E 10 •
5 •
0 •
C
25 •
20 •
-15.
6 10 -
5 •
0 •
C
25 •
20 -
-E15'
E 10 •
5
0 •
0 Rohwasser
f 0
§
j
B
0
II I
0 i
§ 5
0
CD
ooo
If
I
3
i
10 20
g
o '
0
J
0
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o
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1 1
g
C
(
10 20
im AbLauf
0
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;
C
c
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10 20
im AbLauf
o
o o
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a
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30
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3
1
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f
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30
-
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3
0
*
o
0
o TT i-
1
»
40 50 SO 70
nach der Flockung
o
0
i r
s
=
40 50 60
eines frisch gefuUten
c
1 r
•3
30
C
O
O
- t 1
I 1 1
!
76Min
0
70 76Min.
AktivkohlefiHers
40 50 60
1
2
70 76 Win.
eines erschopften AktivkohLef iltars
°
0 *
0
1
O
1
0
-J
M
0
1 7
c
1
C
10 20 30 40 50 60 70 76Min
Rohwasser: raw water
nach der Flockung: after flocculation
im Ablauf eines frisch gefiillten Aktivkohlef liters;
outlet of a filter with fresh activated carbon
im Ablauf eines erschopften Aktivkohlefliters:
outlet of a filter with exhausted carbon
-------
OJOC I
i
t
I
CM CM CM CM
-------
122
Fig. 7: Comparison of gaschromatographic test results
of pentane extracts
Fig. 8: Comparison of gaschromatographic test results
of i-butanol extracts at pH 1
Fig. 9: Comparison of gaschromatographic test results
of i-butanol extracts at pH 4
Fig. 1O: Comparison of gaschromatographic test results
of i-butanol extracts at pH 9
What are the criteria for operating the activated carbon stage
of the purification plant?
As a reference figure, the COD value was taken, and a reduction
of this value by at least 5O per cent in the activated carbon
filter bed was aimed at. Samples taken during one week of each
filter led to the results shown in Table 2.
Table 2: Drinking water treatment plant, waterworks No. 1
Loading of activated carbon filters
19th week
Filter
• ~"* — ~ — j~ —
Throughput
3
1000 m
1 18.2
i
Q £
., :
100O m :
t - - -J
130.1
2 ! 22.1 69.9
1
3 ! 25.5 j 49.7
4
5
33.4
29.3
437.0
372.8
Inlet
mg/1
"~ '
Outlet
mg/1
I
5.45 1.60
5.50
5.OO
1.12
O.7O
5.25 j 3.70
5.45 I, 3.70
i
Relative Loading
Residual i
Amount j kg
I
0.293
645.2
O.203 1 330.0
1
0. 14O
O.7O4
0.678
208.8
1326.1
1073.2
Table 3 shows the likely life span of a filter, computed from
values obtained from each filter.
-------
123
2b -
20
SJ
£
£ 15 - =
10 -
5 -
0 • •
0
D
sauerstofff reies Wasser
o
0 0
O
*
0
0
0
O
*
0
0
o
o
X
c
0
o ° o°
1* ° " 7 *
II III II
0 10 20 30 40 50
60 70 76
Minuten
20 •
15 -
10 -
5 -
sauerstof f haltiges Wasse
0
I
o
e
ii
II
a
X
6mg 02/L
o
o
o
o
I
o
o
3
0 10 20 30 40 50 60 70 76
Minuten
Fig . 1
sauerstofffreies Wasser: water containing no oxygen
sauerstoffhaltiges Wasser: water containing oxygen
Minuten: minutes
-------
25 ,
20 4
10
sauerstofffreies Wasser < 0,1 mg 02A
0 10 20 30 40 50 60 70 76
Minuter
25 ,
20 1
CM
i 15
10
sauerstoffhaltiges Wasser ~ 6mg
10 20 30 40 50
60 70 76
Minuten
Fig 8
sauerstofffreies Wasser: water containing no oxygen
sauerstoffhaltiges Wasser: water containing oxygen
Minuten: minutes
-------
125
i J
20
15 -
10
5 •
n -
souerstofff reies Wasser < 0,1 mg 0 j/ L
o
7 '"a
0-
C
s
'
3 2
i O
> ^
II
D
)( '
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3
0
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I
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o
0
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o
3
0
'
0
0
o
o
25
20
15 -
10 -
10
20 30 40 50 60 70 76
Minuten
sauerstoffhaltiges Wasser ~ 6mg 0 2 /I
10
20 30 40 50 60 70 76
Minuten
Fiq 9
sauerstofffreies Wasser: water containing no oxygen
sauerstoffhaltiges Wasser: water containing oxygen
Minuten: minutes
-------
126
25
20 -
XI
10
5 •
n - -
sauerstofffreies Wasser < 0,1 mgOj/l
\
O
^C"
C
'
if
3
3
i
W
3
O
0
C
0
f
C
o '
i
D
3
i
3
C
40 50 60 70 76
Minuter
'
20 •
10 •
5 •
0 -
sauerstoffhaltiges
C
o
o
°
o
i
3
T c
o
O
O
,f
ill
1
O
o
3
3
1
^
|
3
1
0
3
C3
"
C
i
Wasser ^ 6 mg 02/L
C
0
Q
3
C
0 10 20
30 40 50 60 70 76
Minuten
Fiq 1O
sauerstofffreies Wasser: water containing no oxygen
sauerstoffhaltiges Wasser: water containing oxygen
Minuten: minutes
-------
127
Table 3: Drink ing-Water Treatment Plant, waterworks No. 1
Running time of activated carbon filter No. 1
Calculated Data
Running time
(weeks )
17
22
27
shortest running time
medium running time
longest running time
Loading
(JisJ
1198
1530
1863
The filter efficiency will be obtained with a statistical
certainty of 99 per cent
Starting date: 12th week
34th week
Assumed
of filter run:
-------
128
USE OF ACTIVATED CARBON IN THE TREATMENT OP LAKE WATER
Maarten Schalckamp, Zurich
General DIscussi'on
First it is necessary to ansvjer the question, why the lake
waterworks in Sv;itzerland use the activated carbon filtration
method. There are several reasons for this:
For example, the oil-pipeline Genoa-Ingolstadt was laid direct-
ly adjacent to the lake of Constance and its surroundings. The
best possible safety precautions were observed during the
construction, and for the subsequent operation, since the
possibility of a pipe break must be taken into account. The
results of such a break occurring in a drinking water storage
basin of this sort could be disastrous. As a result of
efforts taken by several v/ater works, the Energia Nationals
Italiana (EN!) was willing to finance the costs of building an
ozone- or activated carbon filtration system, for all the
works lying within the danger area. In this manner, water
contaminated by slight amounts of oil can be purified into
drinking water.
Another reason was the phenol spill in the cities of St.Gallen
(1957) and Zurich (1967). During these times, large areas of
the respective drinking water supplies were highly contaminat-
ed and the occurrence of odours and flavours disturbed the area.
These two reasons were the determining factors which led to
the installation of an activated carbon filtration system
for the water works of the city of St.Gallen, which lie at
the Lake of Constance. The phenol spill which occurred in Zurich
-------
129
had such heavy consequences that sufficient impetus was pro-
vided for the construction of an additional activated carbon
filtration step in the treatment plants of Lengg and Moos.
For most of the other lake water works in Switzerland, how-
ever, the sudden appearance of the floating mussel "Dreissena
Polymorpha Pallas1' (DPP) was the main reason to use the acti-
vated carbon filtration system in their lake water works -
namely, for the dechlorination,
The consumption of energy, i.e. the use of oil and gasoline,
increased six fold during the past few years. Therefore, the
organic load of the rivers increased also. K. and G.Grob re-
ported that many organic substances are found on the surface
waters but are almost completely absent in pure well water
(Fig.1). Investigations carried out in the laboratories of the
Zurich water supply confirmed this condition. It is the duty
of every water supply to ensure that the quality of the drink-
ing water derived from surface water is in no way inferior to
the unobjectionable quality of water found in well - and
ground water, particularly with respect to the load of organic
substances. Therefore, the conditioning of surface water with
activated carbon filtration can no longer be omitted today
in Switzerland.
Dechlorination Efficiency of Activated Carbon
Several waterworks in Switzerland use chlorine to prevent the
DPP from attacking the raw water pipelines. The chlorine is then
removed through activated carbon filtration. Experiments have
shown that a concentration oflmg/1 remains, e.g., upon addi-
tion of 1.5 mg/1 C3-2 into the raw water catchment installa-
tion, which is 100& effective in eliminating DPP larvae after
11 days (Fig.2).
-------
130
3 1
n
Well water Dolder, July 5th 1973
.X-^fcjL^
1
23 21
20
19 18 15,1412,11 90 7 6,5 "4,3,2 1
Surface water of the Lake of Zurich, July 7th 1973
Fig. 1 Organic substances in well- and Zurich Lake water
(based on K. and G. Grob)
I.Omg CI2/I
Elimination m%
12
Fig. 2 Elimination of Lake of Constance-DDP-larvae in raw
water from the Lake of Zurich using 0.5 and l.O mg
of C12 per liter as a function of time
(based on Dr Siessegger)
-------
131
This amount of chlorine is sufficient since it has been shown
that the larvae are retained in the rapid filter for up to
15 days. As the normal treatment requires less than 1.5 mg/1
chlorine, investigations were undertaken to determine if an
effective killing of the DPP larvae could be attained
with a residual chlorine concentration of 0.5 mg/1, e.g.,
with a feed concentration of 0.8-1.0 rng/1 at the catchment
point on the lake. With this dose (Fig. 2), 13-14 days are required
to eliminate the DPP larvae. This value lies on the tolerance
limit, but may be considered as acceptable. Furthermore, the
results obtained by London's water-works showed that
a residual concentration of 0.5 mg/1 is sufficient. Here in
Switzerland, a residual chlorine concentration of only 0.05
mg/1 drinking water is permitted, the surplus chlorine must
be removed from the water.
Although neutralization with thiosulfate could be considered,
activated carbon is used instead as a safety measure by the
lake water treatment works. The activated carbon is applied
either as a second upper layer in the rapid filters, as a
5-10 cm thick layer above the sand in the slow filters, or
as a second top layer again in activated carbon filters.
In order to select the most applicable type, dechlorination
experiments were carried out with different activated carbons.
These were done for the velocities of the slow - as well as
for the rapid filters. With the exception of Hydraffin LW
and Pittsburgh 200, all the other carbon types were suitable
for the slow filters, such as Norit PKST, Norit 07, Sutcliffe,
and Hydraffin LW extra. For the rapid filters, however, the
activated carbons of Hydraffin LW extra, Sutcliffe, Norit 07,
and Pittsburgh 200 were most suitable (Fig.3)• As the effective-
ness of dechlorination decreases with time, experiments with
different activated carbons were carried out lasting for several
months using different velocities (Fig.4,5,6) . It is interesting to note
how the decrease in efficiency of dechior-ination appeal's for
-------
132
o
_c
to
o>
"o
I
M—
o
JC
o
"o
o
0)
Q
0
Hydroffin LW
Norit PKST
Pittsburgh 200
Norit 0,7
Sutcliffe
Hydroff in LWextra
100 300 500 700 900
Filtration rate cm/h
Fig. 3 Dechloririation half-values of various activated
carbon types at different filtration rates
— AC with raw water after
3 months* Cl
— AC with rapid filtrate
+ CVO:
u_ s
v=7m/h
v=5m/h
234
months
=3m/h
5 6
Fig. 4 Decrease in dechlorination efficiency of Norit 07
activated carbon per month at different rates
-------
133
Fig. 5
Fig. 6
AC with raw water after
3 months+C^
AC with rapid filtrate
I 23456
months
Decrease in dechlorinatiori efficiency of Lurgi LW Extra
activated carbon per month at different rates
—— AC with raw water after
3 months*
= 30m/h
v= 20m/h
v=IOm/h
Decrease in dechlorination efficiency of Norit PKST
activated carbon per month at different rates
-------
13*4
the activated carbons conveying either raw water or rapid
filtrate. As can be seen from Fig. 7.. the best results are
obtained with Pittsburgh 'iOO, Lurgi LW extra, and Norit 07.
A further result from these studies v,
-------
£
o
co
CD
_Z3
0
I
c
o
"o
c
o
CD
O
raw
100
90
80
70
60
50
40
30
20
10
0
135
water rapid filtrate
/-- - Pittsburgh 400
Lurgi LW extra
Norit 0,7
— Lurgi LW
Norit PKST
•— Sutcliffe
357 10
20
30
Vin m/h
Fig. 7 Dechlorination half values of various types of activated
carbon after 5 months at different rates
Fig. 8 Two-layer rapid filter no. 14 with 6O cm of
quartz nand (O.4 - l.O mm) and 2O cm of Norit PKST
activated carbon (O.r> -• 2.5 nun)
-------
135
Fig. 9 Two-layer rapid filter no. 20 with 60 cm of quartz sand
(O.4 - l.O mm) and 20 cm of Lurgi LW Extra Hydrafin
activated carbon
150
V=3,75m
0
SF12 Sand
SF14 PKST
20cm
SF16 PKST
40cm
SFl8 NoritO,7
SF20 Lurgi
Fig.lO Operating time of single-and double-layer activated
carbon rapid filters as a function of Pressure loss
-------
137
by 46 cm. This increase for the double-layer filter appeared
to be primarily due to the presence of the activated carbon
layer (Fig.11). The longer or shorter operating time for
the double-layer filter is, of course, also dependent upon
the grain size of the AC. Following intensive air rinsing,
it was possible to rigorously separate the quartz sand
and the AC with a back-wash water velocity of only 15ni/h.
Most of the lake water-works on the lake of Zurich impreg-
nate their rapid filters with activated carbon for the
purpose of dechlorination. At the water supply for Zurich,
the dechlorination was carried out with the slow filter
until the completion of the Ac filter, which covered the
original filter with an Ac layer of about 10 cm (Fir,.12).
It was seen that the operating times were at least five
times better than with the one-layer slow filters due to
this modification (Fig.13).
A new cleaning process was developed (Fig. I1!) which made
it no longer necessary to remove the AC during the rinsing
process. This is a. big advantage since the slow filters no
longer need to be closed down.
The top layer of the slow filter is backwashed with water,
through nozzles which penetrate 20 cm into the Ac layer
and sand surface. The polluted water is then channelled
into the sewage recycling system. This newly developed
machine can clean an area of 1000 m2 within 30-40 hours.
The operation requires only one man.
4. The Removal of Organic Substances by the Ac filter
According to K. and G.Grob( at least 186 kinds of organic
substances are found in the lake of Zurich. The ones with
the highest concentrations are:
-------
138
60
50
Q
Q=5t>00m3/h V 5,6m/Day Test I
overall pressure loss
28 30
August
back-washing
overall pressure loss
140cm
4 6 6 10 12 14 16
Date
September
Fig.11 Pressure loss in each layer of a double-layer
activated carbon rapid filter
Fig.12 Double-layer slow filter using river sand and
1O cm of Norit PKST activated carbon (O.5 - 2.5 cm)
-------
139
as a function of loss of pressure V= 15m/day
E
o
c
a>
3
U>
tn
a>
tn
V)
O
240
200
/ 9 months
'42 months
SF2 90cm sand
90 cm sand
* 9 cm AC
PKST Norit
5 10 15 20 25 30 35 40 45
months
Fig.13 Operating time of single-and double-layer slow filters
Back - washing water air
20cm long jets
':::::::::-:-:':':-x&^
sand
Fig.14 Slow filter cleaning machine
-------
1. benzene
2, tetrachloroethane
3. toluene
4 . dimethyldisulfide
5. 1. il-dimethylbenzene
6. 1.3- "
7 i p_ " " "
8. A-ethyltoluene
9. 3-ethyltoluene
10 . cineol
11. 2-ethyltoluene
12. 1.2.ij-trimethylbenzene
13. dimethyltrisulfide
14 . propyltoluene
15. 1.2 . 3-trimethylberujene
16. isobutylbenzene
17. dimethylethylbenzene
18. methylisopropylbensene
19. 1.2.4.5-tetramethylbenzene
20. alkane C,j-
21. molecular weight 182
22. dimethylnaphthalene
23. alkane C.,,-,
24. diphenyl
25. alkane C,„
26. diphenylether
From Fig.15 can be seen the amount of organic substances
which can be removed from water by 9g of Ac. Experiments
in Zurich showed that up to 80g of organic substances can
be removed from water per kg of Ac. These substances are
labelled as DMF-extract (DMF = dimethylformarnide).
Several types of Ac were investigated in Zurich with regard
to the removal of organic substances. The order concerning
the types of Ac tested and the amount of removed organic
substances from the raw water of the lake of Zurich are
as follows:
Experiment 1 -Duration 9 months Experiment 2 -Duration 3 months
Pittsburgh 40O
Norit
Lurgi
Lurgi
Norit
T7
PKST
LS-Supra
LW
07
61
41
34
28
21
g/kg
g/kg
g/kg
g/kg
g/kg
Pittsburgh
400
Lurgi LS-Supra
PKST
Pittsburgh
Norit 08
Norit O7
Zetclef
30O
61
49
41
38
34
28
26
g/kg
g/kg
g/kg
g/kg
g/kg
g/kg
g/kg
Fig.15
Organic residue from 9 grams of Pittsburgh activated
carbon
-------
11*1
The best ACs, which additionally demonstrated good reactiva-
tion, v/ere Pittsburgh '100, Lurgi LS-Supra, Pittsburgh 300
and Norit 08. The new carbon ROW 08 Supra from Norit was
tested and compared with the best suitable carbon, the
Pittsburgh '400. Experiments in larger plants already con-
firmed after one month that it was equal to the Pittsburgh
400. This was further substantiated by longer-termed exa-
minations (_Fig.l6) .
The carbon Pittsburgh 400, v,ras later on used in the AC
filtration process of the Lengg lake water-works, while
the ROW 08 found its application in the works"Koos". After
a two-month operating period in the lake water-works of
Lengg a load of 37 g/kg was determined
for the Pittsburgh 400 carbon. In the beginning, the new
carbon showed a load of 4g/kg(DMF-extract).
But the capacity increased already after 3 months operat-
ing time to 63.5 g and attained the highest capacity with
68.5 e/kg after seven months (Fig.17). Unfortunately, the
top as well as the lowest layer showed an equal capacity
after seven months. Theoretically the AC had to be changed.
But the efficiency with regard to the reduction of organic
substances was still as good as at the beginning, as dissolv-
ed organic carbon (DOC) and UV proved (Fig.18 and 19).
Even if the AC is completely loaded, as the parameter DMF
shows, the efficiency still practically corresponds to the
value of new carbon. This could be a result of the biolo-
gical processes at the AC filter. The exchange of the car-
bons takes place, therefore, only when the DOC and UV re-
duction-values fall under a certain limit.
The slow filter in the lake waterworks "Moos" was fitted
with a 5 cm layer of the AC PKST. The new carbon showed
a load of 5g/kg at the beginning. After three years,
the load was 29,2 g/kg (Fig.20). The efficiency of
-------
! ROW 0,8
supra
'ROW 0,8
supra M
Pittsburgh
JF400
DMF extract
g/kg AC
total
load
5,5
4,1
6,1
new
1,6
1,6
3,7
effective
load
3,9
2,5
2,4
DMF extract
extinction at
300 nm d=1cm
total
load
0,062
0,093
0,I2I
new
0,044
0,044
0,109
effective
load
0,018
0,049
0,012
Fig.16 Test 3; Load comparison of various activated carbons
34 days (1974), Water throughput of 4,5 m3 per
kilogram of carbon
-------
68,5 g/kg
63,5 g/kg
370g/kg
4,0g/kg
300 350 400
wave length in nm
Fig. 17 Activated carbon loo.d;new carbon as well as after
2,3 and 7 months of operation; UV-spectra of DMF
extracts
-— rapid filter
-«-»-» activated carbon
COD
4,0
3,0 -•-
2,0
0
->- t
35
th
40
th
week 1974
45
th
50
th
Fig. 18 Lengg lake-waterworks; COD in mg O,/! in rapid and
activated 'carbon filtrate
-------
rujjiu niier
-«-*-« activated carbon
40
30
20
10
n
>..
N4
V
'•-,-,.
s\t
.,---
''•--.
—
—
.,-.--
—
,-..,.
,_>-"•
X's,
.,.--"
--..
*\
'x
-.,.''''
-.-•"'
—
351
40'
451
50'
week 1974
Fig. 19 Lengg lake^aterv/orks; UV = 254nm; d = 1 cm. 1O-3
UV ,DMF
g/kg
1,982
29,2
0,037 5
Fig.2O
300 350 400
wave length in nm
Activated carbon load from the slow filter; new
carbon after a filter operating time of 1,2 and 3 years;
UV-spectra of the DMF extracts
-------
11*5
this carbon with respect to the removal of organic substan-
ces, for example, COD (chemical oxygen demand) was equally
good for three years. (Fig.21)
Therefore the construction of a separate AC filter, for
the recharge of ground water at the ground water-works
"Hardhof" for the water supply of Zurich, can be renounced
after the recharge basins showed an equal efficiency when
they were fed with AC. In addition , the operating time
of the recharge basins increases by five, tirces.
Reinfection
It is known that AC leads to reinfection. Experiments in
pilot plants proved this in Zurich. Fig.22 shows that the
highest bacterial count was found for the Norit PKST carbons
at the beginning. The number of germs of the Pittsburgh 400
was about half that for Norit PKST and the value of Lurgi
LS-Supra was even a little bit lower. The Sutcliffe-carbon
showed the best results. At the end, practically the counts
for all of the mentioned Ac types were equally high except
for the value of the Sutcliffe-carbon. Its value was only
a third of the others, namely, 3^3 germs per cubic centi-
meter .
It is obvious that there is a clos-e relationship between
the reduction of the organic substances and the reinfec-
tion, specially true for the Ac PKST. At the beginning it
was the most effective with respect to the removal of orga-
nic substances, but it showed also the highest reinfection
number for the same time. As experiment 2(Fig.23) striking-
ly shows, all monthly backwashing carbon types exhibit a bacterial
count of 5 digits already after an operating time of one
month. The weekly backwashing carbons Sutcliffe 2O6A and Norit
PKST showed only a number of four digits, and already
-------
rapid filtrate
slow activated carbon filtrate
1972
1973
1974
1975
Fig.21 Moos lakewaterworks; COD in mg O2/l in rapid and
slow filtrate
-------
1V7
I05
I04
I03
I02
10'
v--"^.'
PKST
LS supra
— Norit 07
— Sutcliffe "
—F400
May
July 1971 Sept.
Nov.
Fig.22 Test I; bacterial count after 3 days at 20 C in 1 ml
of chlorinated rapid filtrate and various activated
carbon filtrates (59 samples)
I04
I03
I02
10'
f"
/
s?\
s'.^
S^S^
\^"" •—
11
Back-washing mont
^^,
~sf
•L
hly
\.
K<
'\
'^^.
/
, " ~^~
/ ~
/
/
s.
X
Back-\
^.^•^
A/ash
SF2
PKS
•LS
^».~._^
"^^•^.
ng we
^03
T
supra
F400
\ Sutcliffe/
2kly
29. 4.
March
7
14. 18. 21.
April
25. 28. 2.
May
Fig.23 Test 2; bacterial count after 3 days at 2O°C in 1 ml
of ozonised slow filtrate and various activated carbon
filtrates (1O samples)
-------
11*8
after 5 weeks were shown to have a recurrent tendency
for these carbon types, e.g. about 60% . Hence, it must
be concluded that the carbons have a significantly lower
tendency towards reinfection upon backwashing the AC filter
rnore often. Full-scale tests with rapid filters of the works
"Lengg1^ charged with AC, confirmed this assertion.
In past experiments the Ac Lurgi LS-Supra and Norit PKST
did not lead at all to reinfection; however, they were
fed with chlorinated water. The new Ac-filter in "Lengg"
-they are backwashing twice a week- never exhibited a value of
more than 10 to 50 germs per cubic centimeter. These are
extraordinary results (Fig.2^).
6. Reactivation
Fig.25 shows the reactivation-oven installed in the water
works. The reactivation is done by the so-called "fluid-
u
bed process from Norit. It'is assumed that the AC must be
either replaced or reactivated every one-or two years. The
fluid-bed process was chosen because it shows the lowest
loss of carbon of all processes available on the market.
The efficiency of the reactivation can be seen in Fig.26.
The author was present when Norit ROW 08 Supra from Duis-
burg and PKST 1-3 from the work Zurich were reactivated.
Later, they reactivated another charge of soft carbon,
Norit PKST 1-2, i.e., a light 1C in the same oven. Although
this carbon is not usually suitable for reactivation, the
losses were only 50$ in comparison with common processes.
The effectiveness of the reactivation is excellent. The
PKST-carbon had only a small load of 28 g/kg.
Whereas fresh carbon had a load of 5 g/kg, the value
for the reactivated carbon was slightly higher, namely,
8 g/kg (Fig.27)• Such a reactivation plant is now installed
in the lake water-works"Lengg" and was set in operation
at the beginning of 1976, i.e. when the reactivation of
-------
50
40
30
20
10
0
Dec Jan
Fig.24 Lengg lakeLaterworks; bacterial count after 3 days at
2O°C in 1 ml of activated carbon filtrate of the "South'
installation
-------
150
Fig.25 Norit reactivation furnace, fluidized-bed process
-------
151
-
Duisburg
ROW 0,8 supra
Water throughput
per kg AC
unknown
Zurich
PKST 1-3
Water throughput
per kg AC of
3800m3
DMF extract
g/kg AC
total
load
28,5
20,9
new
1, 6
2,2
regene-
rated
3,l
4,5
DMFexract
extinction at
300 nm d=1cm
total
load
1,576
1,055
new
0,044
0,045
regene-
rated
0,066
0,057
Fig.26 Reactivation efficiency of various activated carbon
types, reactivated, in the Norit installation on
March 26th 1974
-------
152
new AC ca.5g
loaded AC ca. 28g
regenerated ACca.Sg
2 loaded carbon
3 regenerated
carbon
1 new carbon
300 350 400
wave length in nm
450
Fig.27 Results of the activated carbon reactivation;
UV-spectra of the DMF-extracts
-------
153
the used Fittsburg-'iOO-carbon v/as necessary. Further
results therefore can only be published later. The plant
is usually operated with natural gas which is environmentally
sound.
Construction of the..AC_f_il_ters in Zurich
In Lengg there are a total of twelve AC filters in use,
specifically, six on each side of the pumping station.
these are closed pressure filters of smooth-faced concrete
p
with an area of ^ irr each (Fig.28). They have a bottom
2
with 75 plastic nozzles per m". The filters are charged
with a. layer of quartz sand, 50 cm thick,- grain size
0.7-1 mm, and above with a layer of Pittsburgh F '!00 Ac
of 1.2 m thickness. As this carbon shows a very high
filtration resistance , it is replaced during the reacti-
vation by the very good AC Norit ROW 08 supra. With the
latter, there is a considerably smaller pressure loss.
Nevertheless, the Pittsburgh carbon has very good charac-
teristics and it is therefore still used in the lake water-
worksKoos, where pressure losses cause no problem.
The cleaning of the AC filter is accomplished by backwashing
with pure water, that is, with water of the same
which is used for the rapid filters. The back-washing velocity
is 25 m/hj if necessary it can be increased to 50 m/h.
The back-washing can also be done with air. The normal
velocity of the filter is 21.5 m/h if one of the twelve
AC filters is backwashing. For reactivation the AC can
be transported hydraulically to their respective reactiva-
tion plant silos. In the construction of the filters, mea-
sures must therefore be taken to ensure that enough free
space is available for the swelling of the carbons, which
is often greater than stated by the supplier (Fig.29).
The construction of recharge basins as two-layer filters.
h 10 era Ac, can be seen from Fig. 30.
-------
15*4
channel to ACF carrier water channel
9,7m x 4,5m-44,0m
pressure release
jjne
carrier water gutter
feed pipe
nozzles plate
rinsing air line -quartz sand-
channel from washing water —activated—
ACF channel carbon
Fig.28 Lengg lakewaterworks;Profile and cross-section of an
activated carbon filter
o/
/o
200
150
100
50
layer thickness:l6cm LW-extra
46cm PKST
77cm
measured
calculated on
data from the
supply works
m/h
25
50
75
Fig.29
Multi-layer activated carbon filter; expansion of the
activated carbon layers in % as a function of the
flushing rate
-------
155
-drainage well
ground-water carrier
activated carbon 10cm
filter sand 100cm
support layer 25cm
(gravel)
distributor layer made
of shingle 50cm
Fig.BO Composition of the enrichment basin at Hardhof,
10 cm of activcited carbon are placed above the
slow sand filter
-------
156
8. The Costs _of^ AC filbratiori
The construction costs for the 12 AC filters with a total
area of 528 m2 and a daily output of 250'000 jn-3 are as
follows:
Buildings $ 1'912'480
Technical installations $ 2'26O'52O
Consolidation of the
filter $, 90'280
Total $ 4'263'280
The costs of the reactivation plant are not included in this
list. The capital costs per cubic meter daily capacity are
therefore $ 17.—-The whole lake water treatment in "Lengg"
including pumping station, will cost $ 17O.— daily/cubic
meter, i.e., for the AC filtration 1O% of the capital costs
must be spent. The operating costs for interest and amorti-
zation (25 yearsr6£ interest)are $ 4OO'OOO.-- each year.
$ SO'OOO.— should be included as annual maintenance
costs. With an annual output of the worksof 40 million ms
the capital investment costs are therefore O/°l ?/m .
The operating costs for the annual reactivation result in the
following figures:
Construction costs of the reactivation plant and transfer
installations ($ 4OO'OOO.—) (1O% amortization, 6% interest)
capital costs $ BO'OOO.—
maintenance $ 2O'OOO.—
heating $ 16'OGO.—
service $ 16'OOQ.—
loss AC ca. 5% $ 28'000.—
annual total operation costs $ 16O'OOO.—
With a water output of '40 million nr per year the operation
costs for the reactivation including loss of AC
are O.004 $ per m5. The total costs will be O.016 $ per
3 o
m . '/'itn an annual ouLpuL oi 40 idiilion in the treatment
* includ-ing S 640!OOO,-- for the AC
-------
157
costs of the works at Lengf; total $ 0.13 per iv^. Thus
the costs for AC filtration come to only 12.5$ of the
total operating costs.
As the quality of the drinking water derived from surface-
water must not be inferior to that of perfect well - or
ground water, the AC filtration is indispensable. The
expenses for it arey8 of the total treatment costs,
so the use of AC is also economically feasible.
-------
158
Summary
ACs are principally available in Switzerland for the removal of
organic substances as well as for the removal of oxidizing agents,
sufih as chlorine.
The dechlorination efficiency of most ACs is goodj however;
it is decreased with time, so the ACs must be reactivated
or replaced for this reason. The finer the grain size of the
ACs the higher the dechlorination efficiency,
ACs can be used very well as a second layer for the rapid
and the slow filtration systems. As a results the duration
of-the operating time is increased by at least five .times
keeping the same cleaning efficiency. The
load of AC with organic substances can reach a level of
about 80 g/kg (DMF-extract). Even with this charge, the re-
duction of the parameters, as determined by DOC and UV, re-
mains good over a longer period, this for the ACs of the
rapid filters as well as for the slow filters. The DMF-ex-
tracticn-capacity is therefore not necessarily a criterion
for changing the ACs.
AC can lead to reinfection, too. This is among other reasons^
a result of poor backwashing or of intervals between backwashing,
which are too long. By backwashing the ACs twice a week, the number
of bacteria in the lake waterworks at Lengg did not exceed 50/cm .
Suitable Acs such
as Pittsburgh ^00, Lurgi LS Supra and Norit ROW 08 are well
suited for reactivation.
It must be considered for the construction of the AC filters
that enough free space is provided, as the swelling of the
AC during the backwashing is sometimes higher than reported
by the supplier.
-------
159
The total operating costs of the AC filtration are $ O.O16 per
meter cube in Zurich; this corresponds to 12.5 % of the total
operating costs of the lake v/ater-works Lengg. As treated sur-
face water must not be inferior to unobjectionable v/eli-
or ground water, an tc filtration system is necessary.
Economically, it is feasible.
-------
160
EXPERIENCES WITH PILOT PLANT ACTIVATED CARBON FILTERS
IN DUTCH WATERWORKS
by W.C. van Lier (Amersfoort), A. Graveland (Amsterdam)
J.J. Rook (Rotterdam) and L.J. Schultink (Bloemendaal)
In the near future several Dutch waterworks will use granular
activated carbon for water treatment. During the past few
years these waterworks have been carrying out experiments in
pilot plants. The results reported here were obtained at
Amsterdam-Leiduin (Municipal Waterworks)
Andijk (Provincial Waterworks of North-Holland)
Rotterdam (Waterworks)
all of which have quite different raw waters. In Fig. 1
the treatment steps which the raw (surface) waters were
subjected to prior to the carbon treatment are shown.
In the Rotterdam and Andijk pilot plants an analysis of the
activated carbon system itself was carried out. The influence
of (apparent) linear velocity, height of the carbon layer and
(apparent) contact time on the service time of the carbon
(i.e. the time between two consecutive reactivations) were
examined. The range of the variables investigated are shown
in Tables I and II.
In Amsterdam three different treatment sequences were investi-
gated parallel to each other. The (apparent) linear velocity
•} O -1
was 8 m .m .hr , height of the carbon layer 2 m.
Whereas in Andijk and Rotterdam the pilot plants were supplied
with drinking water (i.e. finished-water quality), the carbon
in the Amsterdam pilot plants formed part of a whole treatment
sequence. The water quality is expressed in parameters as
UV-absorption (\ = 24O nm, 1=4 cm, nitrate correction), DOC
(dissolved organic carbon), KMnO. consumption, colour and
taste. Determination of the DOC1 (dissolved organic chlorine),
-------
161
RIVER :iAAS
BIESEORCH
NaOH-dosing
Softening and
phosphate removal
Storage; in
reservoir
Superch.lorination
Transport
HONINGSRPr.I JIC
Storage reservoir
Chlorination
Coagulation (iron)
Rapid sand filtr.
PILOT PIAWT
ACTIVATED CARBON
I
Resorvoi;
Micro-straining
Chlorination
Powdered activ.
i
I carbon
I
I Coagrlation (iron)
i Rapid sand filtr.
I
PILOT PLANT
ACTIVATED GAFBON
GV?A AMSTERDAM
Ai'lSTE RDAi-i- KHINE- CH AKNE L
Coagulation (iron)
Rapid sand filtr.
' Transport chlorin.
1
1
I-
Ozonation
Rapid sand
filtration
Activ. carbon
Slow sand
f i Itrat ! on
Trc
msport
—
y
Rapid sand
filtration
Activ. carbon
Slow sand
filtration
>
i
Activ. c ?.-"•: on
Slov; scii'.d
filtration
Fig. 1
rftiL-.rr.-ant of the vrater supplied to the activated carbon
-------
162
h (m)
. 3 -2 , -1.
v ( n . IT. . hr )
7.5
15.0
30.0
0.5
4
2
1
1.0
8
4
2
1.5
12
6
3
J
Table I
2.0
16
8
4
2.5
20
10
5
3.0
24
12
6
Pilot plant Rotterdam. Values of the (apparent) contact tin:!
(rain.) as a function of height of the carbon layer (m) arid
the (apparent) linear velocity (v).
T
(rain. )
7.5
7.5
15
15
22.5
30
30
30
h
(m)
1.25
2.5
1.25
2.5
3.75
1.25
2
5
v
.3 -2 v -1.
lm .m .hr )
10
20
5
10
10
2.5
4
10
i
Table II : Pilot plant Andijk. Values of (apparent) contact tiir.e (T)
height of the carbon layer (h) and (apparent) linear
velocity (v).
-------
1G3
according to the method developed by SONTKEIMER and coworkers,
was made on several occasions. However, due to the limited
number of measurements they are not reported here.
All the experiments described here were performed with the
same carbon, ROW O.8 Supra, a NORIT product.
Results obtained at Amsterdam
The results obtained at the three pilot plant installations
in Amsterdam are given in Fig. 2. This Figure shows the
quarterly averages of a number of quality parameters after
each treatment step. In addition to these, the average values
over the whole testing period are given for turbidity, taste
and the frequency of cleaning of the slow sand-filters.
The following conclusions may be drawn:
1. Ozonation considerably increases bacterial count after
rapid and slow sand filtration.
2. With regard to colour, UV absorption and KMnO. consumption
the final quality of the first system (ozonation etc.)
is better than that of the two systems without ozonation.
3. Whereas the final water quality for the two systems
without ozonation does not show a great difference, there
exists a very important difference between the cleaning
frequency of the slow sand filters. In this particular
case, the replacement of the sand in the rapid filters
by activated carbon does not seem to be attractive.
4. Slow sand filtration reduces bacterial count, colour
and KMnO. consumption in all three systems.
-------
16**
SF + AK + LF
0, + SF + AK «• LF
TRUBUNG
(J.T.U.)
GESCHMACKSZAHL
REINIGUNGSFREQUENZ ,
LANGSAMF ILTER J
Ozonierung, SF= Schnellfiltration. AK= Aktivkohlefiltration , LF= Langsamfiltration
Figure 2. -
Kelmzahl: countings
3 Tagen 22°C: 3 days 22°C
auf Peptonagar: on peptone-agar
nach: after
Rohwasser: raw water
Farbe: color
KMnO.-Zahl: KMnO. number
A it
Vierteljahr: 3 month
Triibung: turbidity
Results in Amsterdam
Geschmackszahl: taste number
Reinigungsfrequenz der Langsamfilter:
purification frequency of slow filters
nach Langsamfiltr: after slow filtration
0_: Ozonatlon
SF: rapid filtration
AK: activated carbon filtration
LF: slow filtration
-------
165
In Fig- 3 the results obtained at Amsterdam on the influence
of the final water quality after slow sand filtration on
the service time of the activated carbon are shown. The
service time is defined as the period during which the value
of a quality parameter (in this case the UV absorption) in
the final effluent does not exceed a pre-determined value.
The values of the service time have been calculated as
follows. The "breakthrough curves" are described by one of
the three following purely empirical equations:
Log (A%) = A log T + B1
Log (A%) = A_ T + B_
Log c = A., log T + B
where:
A% = percent reduction of the UV absorption over the
whole pilot plant at time T
c = value of the UV absorption after slew sand filtration
at time T
In each case that equation v/as used which gave the highest value
of the correlation coefficient, the values of which ranged from
0. 8 to 0. 9 .
It may be seen that the difference in service time between the
two systems without ozonation is insignificant, whereas the
service time for the system with ozonation is much longer.
Application of the same method to the values of the KMnO.
consumption leads basically to the same results. Unfortunately
the DOC values were not measured in Amsterdam. One should
realise that the effect of ozonation on the DOC value is
generally much lower than the influence on UV absorption
and KMnO. consumption.
-------
166
3501
300-
250-
200-
150-
100-
50-
Service Time (days)
Place '• Amsterdam
Fbram. : UV-Absorption
0 ;03*SF + AK+LF
A :SF + AK+LF
0 : AK^ LF
0.050 0.100
0.150 0200 0.250 0300 Q350
UV-requirement (-X=240nm,-l=4cm)
figure 3: Service time as a. function of the filtrate quality
-------
167
Results obtained at Andijk and Rotterdam
In the main, discussion is restricted to the results obtained
with the DOC as quality parameter. A rather unconventional
method to process the measured DOC values was chosen in order
to evaluate the water quality after the activated carbon fil-
tration. From the DOC values, measured once or twice a week
in influent and effluent of a filter, the total quantity of
2
DOC applied to the filter (expressed e.g. as kg DOC per m
of filter area) was calculated together with the total quanti-
ties of DOC removed by the carbon (e.g. kg DOC per m of
carbon ), and the DOC in the effluent of the filter as a function
of time. From these quantities over any period of time it was
possible to calculate the average DOC value before or after
the carbon over the same period. All requirements regarding
the quality of the effluent are either expressed as cumulative
quantities (e.g. kg DOC applied per m of filter area) or as
an average value in the total quantity of water before and
after filtration (e.g. gram DOC per m of water).
We shall deal with the following three aspects of activated
carbon filtration as a treatment process;
(a) Influence of the (apparent) linear velocity at
constant contact time
(b) Influence of the season (i.e. the water temperature)
(c) Influence of the (apparent) contact time and water
quality requirements at constant linear velocity
Table III shows the effect of the linear velocity at constant
contact time. This Table gives the value of the service time
as a function of the quality target and linear velocity for
a number of contact times. For a given value of the contact
time (e.g. 4 minutes) we have calculated from the experimental
DOC values how long the service time is for three values of
the linear velocity in the treatment of a constant volume of
water per hour (identical in all three cases) and using the
same quantity of carbon.
-------
168
Target
T
(min)
4
4
4
D
6
8
8
12
12
c (gr.nT3) 3.80 3,38 2.96
5 % Reduction 10 20 30
1 I
h j v
(rn) l(ra . m ^".hr )
1
0.5 7.5 152 28
1.0 15 150 37
2.0 30 141 28
1.5 15 197 52
3.0 30 172 73
1.0 7.5 270 90
2.0 15 240 61
1.5 7.5 j 144 49
3.0 15 137 52
Table III : Effect bf linear velocity (v) at constant cor/tact time (T)
Value of the service tine (days) in relation to target
and velocity.
-------
169
The faults, inherent in the method, may be a possible explana-
tion for the discrepancies between the various results because,
with the possible exception of the results for t = 8 minutes,
no systematic influence of the linear velocity on the value
of the service time was obtained. In any case, it can be seen
that the effect of contact time and quality requirement on
the service time is much greater.
Application of the same method to the UV absorption and the
KMnO. consumption confirmed the results described above.
In conclusion it may be said that at constant contact time
the effect of the linear velocity on the service time is
comparatively small, at least when dealing with quality
parameters such as UV absorption, DOC and KMnO. consumption.
The effect of the seasonal variation in the water is shown
in Fj-$ • J_, where the amount of DOC, taken up by the carbon
_
(expressed as kg DOC per m of carbon) is related to the
2
amount of DOC applied to the carbon (kg DOC per m of filter
area) . With the same amount of DOC applied the amount taken
up by the carbon during the summer is considerably higher
than the amount taken up during the winter run. This difference
can be explained by the action of biological processes in the
carbon filters. These biological processes manifest themselves
in the oxygen consumption by the carbon filters. In winter
this consumption amounts to approx. 6 x 1O g 0^ per kg of
carbon per hour, while in the summer it ranges from
— 3 — 3
24 x 10 to 3O x 10 gr 0 per kg of carbon per hour
(measurements at PVJ1I, Andijk, t = 3O min.).
The influence of the contact time at constant linear velocity
is shown in Fig. 5 and Table IV. Two marked effects are
noticeable :
-------
170
_2
Total loading (kg • m )
Place . Andijk
F&rameter DOC
O
A
Winter test
Summer test
Retention time: 30 min
(kg nf3)
3
Figure 4: The effect of the seasonal loading (kg DOC/m ) activated carbon)
in dependence of the total loading
-------
Service time fdavs)
250-
200-
150-
100-
50-
Rotterdam
DOC
~ 2 ,OM Q nn
= 3,10
3
Ffitention time Cmin.)
Figure 5: Service time as a function of the retention time.
-------
jocation
Target
— —3
c (gr.rn )
Contact time [
(min.) |
12
16
20
24
2.84
3
17
35
52
74
146
ROTTERDAM
2.90
4
21
42
63
87
156
2.96
5
26
49
73
100
172
3.01
6
30
58
84
114
183
3.06
8
35
65
96
127
203
3.11
9
40
73
107
141
218
Contact time
(min.)
7.5
15
22.5
30
A N D I J K
2.05
6
36
85
145
2. 11
39
92
IG:
t\>
Table IV
Effect of target
and contact time on service time (days).
-------
173
1) a strong effect of contact time on service time;
2) a strong effect of the target on service time (an
effect which is more marked for shorter contact times).
The UV measurements have been processed in an analogous way
and give similar results, as is illustrated in Fig. 6. The
service time is plotted as a function of the UV absorption
target in the effluent averaged over the service time
for Amsterdam, Andijk and Rotterdam. All curves relate to a
contact time of 15 minutes. In Amsterdam we have chosen the
results of the system: rapid sand filtration, activated carbon
and slow sand filtration. While the average values for the
UV absorption in the influent of the carbon filters in Andijk
and Rotterdam do not differ greatly from each other, the UV
absorption in the installation in Rotterdam is much lower.
As we see,the quality of the raw water exerts a strong in-
fluence on the performance of the carbon.
When a waterworks starts using activated carbon and, for
example, uses several filters in parallel, it may be advan-
tageous to bring these filters into operation at regular
intervals of time instead of putting them all into operation
at the same day. This "time-spaced" operation has two advan-
tages, the first of which is rather obvious. Where the
exhausted activated carbon is (thermally) reactivated by the
waterworks itself, much smaller reactivation facilities are
required.
The second advantage can be a much longer service time of
the individual filter contents as long as the requirements
to the water quality permit a partial "breakthrough of a
quality parameter". We shall prove this latter point on the
basis of the results obtained for the DOC in the Rotterdam
pilot plant.
-------
250-,
200-
150-
100-
50-
Service time (days)
Parameter UV Absorption
Retention 15-16 Miry
time:
Place Co
O - Andijk 0.500
A - Amsterdam 0.5/.0
0 - Rotterdam 0,240
0.100 0200
TTV requirement U =
0.300
Figure 6: Service time as a function of the water quality
requirement
-------
175
Table V shows the values of the service time for two extreme
cases:
(a) all filters are started simultaneously;
(b) the filters are put into operation at exact time
intervals (e.g. 12 filters in parallel, service time
for each filter one year, reactivation of the contents
of one filter each month).
Let us assume that n be the number of filters, c the average
DOC value in the effluent of one filter, 5 the average
(percent) DOC reduction over a filter, where c is the
average value over the service time. The average DOC value
in the total effluent of all filters is C, the average DOC
reduction over all filters together is A. When the average
DOC value in the final effluent must not exceed the value
o
of 2.54 gr.m (i.e. an overall average DOC reduction of
4O %), the service time for the first basic case (simultaneous
start) equals 37 days. When the filters are not simultaneously
put into operation and the contents of a filter are reacti-
— — ^
vated (or replaced) as soon as c > 2,54 gr m (effluent of
this filter), the service time T will become 82 days because
- -3
the average overall value c = 2,15 gr m (for n = 18). When
C must not exceed a value of 2. 5O gr. in (n = 18) , T even
±j
becomes 182 days if we use example 2. As one can see, the
service time in the two above mentioned basic cases is com-
pletely different. A stepped start of the filters is for that
reason essentially cheaper than a simultaneous start. The
calculations above apply only for cases where a breakthrough
> 0 in the overall effluent is permitted. If the water con-
tains substances which must be completely removed, these
calculations do not apply- In that case, however, a stepped
starting is desired because of the size of the reactivation
installation. This effect is presumably quite general because
it is connected with the limited speed of the mass transfer
processes and with the fact that only part of the organic
matter contributing to parameters such as DOC, UV absorption
etc. is adsorbed by the activated carbon. When carbon is used
-------
176
6
TL
fcL
(gr. nT3) 2.96
% Reduction 30
n Ac
12 40.2 2.53
18 40.8 2.50
24 41.0 2.49
(days) 172
(days) 82
l
2.54
40
A c
43.8 2.16
49.2 2.15
49.4 2.14
82
3V
Table V
Effect of different starting times for the various
filters en the average values of tha water q;:::.iity
of the overall effluent and on the service tiro a.
Parameter . DOC
Location : Rotterdam
-------
177
for the decolourisation of sugar or glucose this effect is
generally made use of.
Costs of carbon application
The results obtained in Rotterdam and Andijk have been used
for an estimation of the costs of the carbon treatment. The
basis of this calculation is shown in Table VI. It has been
assumed that at constant contact time the effect of linear
velocity on service time is smaller than 10 %, an assumption
which, as one has already seen, is presumably correct.
Fig. 7 shows the results for Andijk, where the costs (expressed
in cents (Dutch) per IT. of treated water) are plotted as a
function of contact time. We may draw the following conclusions:
(a) the contact time exerts a strong influence;
(b) with the exception of short contact times the costs
with concrete filters are lower than those for steel
filters;
(c) the optimum value of the contact time for concrete is
lower than for steel filters.
These results were obtained on the basis of stringent require-
ments on the water quality (55 % reduction of DOC).
Fig. 8 gives some idea of the effect of the water quality
requirements on the treatment costs. As one would expect,
the requirements exert a strong influence on the treatment
costs. The optimal value of the contact time depends on water
quality requirements.
-------
178
Two basic cases
Water tnroughput
Rsactivi.tioii of tKe carbon
Reactivation losses
Depreci ation
Interest
Concrete Filters
Steel Filters
6000 m3 per hour
thermal, in the water works
8% by volume
asinuity
Number of filters
Diarcetor (m)
Concrete
12
12-21
3.5-6.0
layer (m) 1.7-5.0 3.5-5.0
Linear velocity
(apparent, m3.m"2.hr~1) 10-20 10-52
Filter area (m2) 20-50
Concrete
Steel
Control equipment etc.
Depreciation Maintenance
(years) (%)
30
15
10
Table VI
Basis of cost estimation.
-------
179
12
10
Costs (Dutch ct.
Place: ; Andijk
Parameter : DOC
Concrete
qteel
—— Reactivation and
compensation
Total Cost
Interest
+
Amortization
10
20
Retention time:
30
(min.)
Figure 7: Costs of activated carbon filtration as a function of
retention time.
-------
180
16-
12-
10-
8-
Costs (Dutch ct..m )
Place: ; Rotterdam
Parameter DOC
C-
requirement
Concrete
Steel
O £3.11 gr.m-3
A «2.84grm"3
10 20
Retention time
Figure 8: Total costs of activated carbon filtration as a function
of the retention time.
-------
181
Finally, one should realize that these two cost exercises
must be regarded as illustrative to a possible method of
operation. The starting point? for this calculation
(depreciation rate, reactivation costs etc.) play an important
part, and it is possible to choose a completely different set
of conditions. One may, however, state that when imposing
rather strict targets regarding the water quality, a
comparatively long contact time may be quite attractive from
an economical point of view.
-------
182
THE USE OF ACTIVATED CARBON TO ANALYSE NATURAL WATERS
WITH REGARD TO THEIR BEHAVIOUR IN WATERWORKS FILTERS
by F. Fuchs and W. Kiihn, Karlsruhe
The use of activated carbon as an analytical technique for
the concentration of water-soluble organic substances was
first described by BRAUS, MIDDLETON and WALTON (1951) and
by MIDDLETON et al (1952). The extraction of the loaded
carbon was carried out with ether and the extract was then
broken up into S different fractions, in acid and alkaline
media. Identification of the organic material was made using
paper chromatographic techniques.
HOLLUTA took into consideration these studies when he in-
vestigated the river Rhine in 1953, at the Department of
Water Chemistry of the University of Karlsruhe. In this case
extraction of the carbon was carried out in several stages,
using ether, pentane, benzene, and later on with chloroform
(HOLLUTA, 196O). The carbon was loaded by shaking 4O 1 of
water for 30 minutes with 2O g of powdered carbon. In 1962,
it was possible to obtain about 2 mg of extract per litre,
extracting the carbon with ether (HOLLUTA, 1959,1960). In
comparison, today the control filter technique described in
this paper produces about 8 mg/1, using di-methyl formamide
as the extraction solvent. This quality, four times as great
as in 1962, measured at the same river flow-rate, is not
only due to the increased pollution of the Rhine, but
especially to the higher loading obtainable on modern acti-
vated carbons, and a nearly quantitative desorption by DMF.
Analysis of the extract reveals a polar, biodegradable fraction
and a non-polar fraction, which constitutes about 2O percent
of the total (HOLLUTA, 1964) . Similar fractions of polar and
non-polar material are found today. However, whereas formerly
the most important of the non-polar compounds were mineral oil
-------
183
hydrocarbons, today analysis shows that the extensive group
of lipophilic, frequently toxic, organo-chloro compounds are
much more important.
HOLLUTA et al (1964) separated the non-polar compounds from the
total extract chromatographically using Al-O., followed by a sub-
sequent elution with pentane. This method is still employed
today in an improved form for this purpose. An elemental analysis
of an activated carbon extract from the Lower Rhine gave values
of sulphur between 3 and 5 per cent (HOLLUTA, 1964); these
values also correspond to those obtained today.
In the USA extraction of the organic material adsorbed onto
the activated carbon is carried out using chloroform and ethyl
alcohol as solvents. This is the so-called CCE- and CAE-method
(BUELOW, CARSWELL and SYMONS, 1973; STEVENS, 1974). The organic
compounds, which are adsorbed onto the activated carbon, grain
diameter 0.4 - 1.4 mm, are extracted in 2 stages with the above
solvents. The conditions of adsorption as well as the extraction
and evaporation procedure are exactly defined. The amount of
extract found is determined gravimetrically. The limits proposed
for drinking water are O.7 mg/1 and 3.O mg/1 for the chloroform
and ethanol extracts, respectively. However, we have found the
above procedure has some disadvantages. As a result of the low
contact time only a relatively small part of the organic sub-
stances are adsorbed (see Table 1).
Table 1: Comparison of the CCE/CAE method with the
DIOX/DMF method
CCE/CAE
DIOX/DMF
Filter Data
activ.
carbon
g
70
100
Ds
m /kg
0.86
3.10
FG
m/h
O.6
0.8
VZ
min
4.5
17
Extract obtained
using same tpye of
activated carbon
amount of extract
g/kg activ. carb.
CCE/CAE: 14.2/16.3
DIOX/DMF: 24.9/5O.4
Ds = water throughput of filter
FG = filter velocity
VZ = retention time referring to void volume
-------
In addition, chloroform is not mjscible with water, so that the
carbon must be pre-dried. It has the additional disadvantage
that determination of chlorine in the extracted organic sub-
stances is no longer possible. Furthermore, the ethanol extraction
is incomplete when compared with DMF. These problems led us to
develop the analytical technique outlined in this paper.
In 1971, in this Institute,MAIER undertook research on the
desorption of loaded activated carbon, examining the possibility
of chemical regeneration of activated carbon. His results suggested
a possible technique for the analytical separation of compounds
adsorbed onto the carbon. On the activated carbon employed in
practice, a great variety of organic compounds are always ad-
sorbed. In an analytical technique it is important to distinguish
between non-polar and polar substances and to employ corresponding-
ly selective solvents.
Most of the organic substances soluble in water coming from a
natural origin have polar properties. For that reason, the first
step in an extraction cannot be carried out using a polar solvent
like DMF or DMSO. In this case the small quantity of non-polar
compounds, such as the chlorinated hydrocarbons would be included
in the extract of the polar substances, since the non-polar
compounds are generally less than 1O percent of the total loading.
For this reason, in the first stage the non-polar or substances
of low polarity are separated with a non-polar solvent, and then
subsequently the polar substances are extracted with a polar
solvent. Some results obtained with different solvents are shown
in Table. 2
There are few non-polar solvents which are water-soluble, of
these dioxane proved to be satisfactory. This compound, on the
one hand, is able to dissolve non-polar substances, while at
the same time it is miscible in water at any ratio, because
it is a symmetrical ether and therefore able to form hydrogen
bonds.
-------
185
Table 2: Extract yields from activated carbon, dipole moments
and solubility in water of various solvents
Solvent
Carbon
Disulphide
n-hexane
Cyclohexane
Carbon tetra
chloride
Benzene
Chloroform
Dioxane
Ethanol
Acetone
Dimethyl-
formamide
Extract
yield
g/kg
act. carb.
0.4
0.5
1 .0
1 .5
2. 1
2.5
4.4
9.6
10.9
29.7
Dipole
moment
Debeye
O
O
0
0
O
1.05
0
1 .70
2.84
3.80
Solubility
in water
-
-
-
-
+
+++
+++
+++
+++
The hydrogen-bonding property of dioxane is responsible for the
removal of only small quantities of polar compounds. The great
proportion of the polar material is then desorbed using DMF.
In spite of the fact that the extraction of the compounds on
the activated carbon is almost complete, it cannot be avoided
that a great deal of the low boiling point, volatile, organic
compounds are lost because the relatively high boiling point
of dioxane (102 °C) and DMF (154 °C), necessitate the use of
vacuum distillation for their complete removal. A great deal
of effort has been expended to improve the analytical technique.
-------
186
PARK (1974) found an improved method of eluting the carbon at
normal temperature. Also, the low boiling substances may be
measured by the Headspace-method or the stripping technique
devised by GROB (1973,1974), which is an accumulation method
on activated carbon. STIEGLITZ (1975) has successfully employed
this method in his research of the river Rhine. The results,
including only the main compounds, are shown in Table 3.
Table 3: The main components of easily volatile compounds
in the river Rhine at Karlsruhe
Definition
Cyclohexane
Trichloro
ethylene
Toluol
Tetrachloro
ethylene
Monochloro
benzene
Xylol
Tetrachloro
ethane
Bromo benzene
Cumene
Mesitylene
Isocumene
Boiling
point
80
87
110
121
132
142
147
156
163
159
159
Definition
Dichloro benzene
Isobutyl benzene
Hexachloro ethane
(subl.)
Tetrachloro
butadiene
Pentachloro
butadiene
Trichloro benzene
Hexachloro
butadiene
Dodecane
Tetradecane
Pentadecane
(
Boiling
point
179
170
185
188
_
213
215
215
252
270
-------
187
In this Table, the compounds are listed according to their
retention time in a gas-chromatograph, which roughly corresponds
to the increasing boiling point. At the same time about 1OO
compounds, which were all identifiable, where determined using
the stripping method with the same surface water.
The analysis of organic substances in water, as practised
in the Institute for the last two years, makes use of accumulation
on activated carbon control filters. During this period about
50 control filters have been in operation, and a large quantity
of data has been obtained.
The aDDarat,i.9 (Fig. 1) is simply constructed,so it can be
operated in a waterworks without any trouble. The filtration
velocity of O.7 m/h is very low, therefore even in very polluted
water anbreakthru DOC value can be measured after a filtration
quantity of 3OO-4OO litres. If the water contains little organic
material the filtration quantity for 1OO g activated carbon may
be 1OOO litres or more before a break-through of the filter
occurs. The loading of the carbon should be at least 1 - 2 per
cent of the carbon weight, to ensure that the zero value is not
more than 5 per cent of the loading.
Fig. 1
To guarantee good adsorption kinetics, a finely granulated
activated carbon, for instance F 40O or finely granulated LSS,
is used in the control filters. The sand filter, arranged
above the activated carbon filter, removes colloid or suspended
particles and gases if the water is supersaturated. In contrast
to the analysis of individual samples, an average value measured
over a longer time is obtained. Nevertheless, this method has also
disadvantages as only about 6O per cent of the dissolved organic
substances are found again in the concentrated extract, as can
be seen in Table 4.
-------
188
Uberlouf 2
stat. Hbhe . 1320mm
Durchsatz . 1 l/h
Gesamtdurchsatz: 700-10001
spez.Durchsatz 7-10m3/kgAK
FiltergBschw
Verweilzeit
AK-Menge
Sand
ca 71 cm/h
. ca 17 min
: 100 g
1,0-2,0 mm
Kapillare 0,35 mm 0
Fig. 1: Layout of the control filter
' Zulauf: inlet 9 Beluftung: ventilation
zuberlauf: overflow
3 Sand: Sand
4 Spiilleitung fur Sandfilter: backwash for sandfilter
s Spiilleitung. backwash discharge
« A-Kohle: activated carbon
7 Spulleitung fur Ak-Filter:
8 Kapillarei: capillary tube
stat. Hohe: static head
Durchsatz: throughput
Gesamtdurchsatz: total throughput
Spez. Durchsatz: specific throughput
Filtergeschwindigkeit: filtration rate
Verweilzeit: contact tine
AK-Menge: quantity of activated carbon
backwash for activated carbon filter
-------
189
Table 4: Efficiency of control filters for
measuring the dissolved organic substances
Sampling
Station
Lake of
Constance
Rhine at
Basel
Rhine at
Duisburg
Neckar at
Heilbronn
Fulda at
Kassel
Ruhr at
Miilheim
groundwate
Karlsruhe
bank filtr
Diisseldorf
Benrath
bank filtr
Hamborn
organic
subst.
(from DOC)
mg/1
2.8
5.6
12.0
9.2
7.6
10.6
0.6
5.0
6.0
adsorbed
org. sub-
stances
mg/1
1.3
2.9
6.5
4.6
4. 1
6.O
0.31
4.4
5.3
non-polar
org. sub-
stances
mg/1
0.30
O.36
1.19
0.41
0.73
0.96
O.O4
0.87
0.66
This is due to the fact that substances such as carbohydrates
are not readily adsorbed onto activated carbon. Furthermore,
during an operation time of 6 to 8 weeks biological decomposition
is also possible. Therefore the analysis of bankfiltrates leads
to higher control filter efficiencies. This indicates that after
ground filtration non-biodegradable compounds remain in the
water. These compounds, important for the purification of
water,are adsorbed by the control filter. In the mass balance,
however, the low-boiling volatile compounds are absent, because
they are lost at the distillation of the solvents.
-------
190
Fig. 2: Schematic layout of analytical procedure
In Fig. 2 a schematic layout of the analytical procedure is
shown. The activated carbon from the control filter is dried
at 4O °C. One gram of it is used to determine the total chlorine
of all organic compounds and the chlorides by pyrohydrolysis
(KUHN, SONTHEIMER, 1974). The inorganic chlorides are determined
separately. To obtain the quantity of chlorine in the organic
compounds, the amount of inorganic chloride must be subtracted
from the pyrohydrolysis value.
A further quantity of 20 g dried activated carbon is extracted
with dioxane and then with DMF. The liquid dioxane extract
is immediately used to determine the amount of chlorine due to
the non-polar chlorinated hydrocarbons,using a microcoulometer.
Since it is possible to inject the dioxane extract directly
into a gas-chromatograph, individual compounds may also be
analysed. In this way the group analysis of non-polar chlorine
compounds can be complemented by the identification of single
chemical compounds. To find out the amount of organic substances
extracted by this solvent, the dioxane had to be distilled off.
The residue after distillation corresponds to the quantity of
non-polar organic substances. Similarly, with the DMF extract
the solid residue part is determined gravimetrically. This
contains mainly non-volatile polar compounds such as humic
acids and ligninsulphonic acids.
The amount of volatile substances not recorded in both extracts
is about 1O per cent, according to our experience. The group of
polar compounds mostly comprises organic acids. To record this
acid group of chemical substances, MAIER (1975) proposed a
simple method of determination.
-------
an erg
191
7 unpolares Chlor .
(Microcoulometer) |Dioxan-Ruckstand|
8 ' Einz»lsubst. QCl '• 11
DMF-Ruckstand
_£
lOC.H.N.S-Best
vereinigte Ruckstande
10C,H,N.S-Best
I I
lOC.H.N.S-Best. Chromatographie
Analysenschema
Schematic layout of analytical procedure
iKF: control filter
zanorg. Chlor: inorganic chloride
2 organ. Chlor: organic chlorine
' Kohle F 4OO: activated carbon (Filtrasorb 4OO)
4Gesamtchlor (pyrohydrolyse): total chlorine (pyrohydrolysis)
sExtraktion. extraction
« extrahiert: extracted
7 Unpolares Chlor: non-polar crgano chlorine
s Einzelsubstanz GC: single compounds, gas chromatograph
9 Riickstand: residue
10 C,H,N,S.-Best.: C,H,N,S, determination
11 vereinigte Ruckstande: combined residue
-------
192
Because the titration of extremely weak acids in a water solution
is not possible, a water-free solvent with a pKg-value > 16 must
be taken. DMF is employed as a solvent, and in this case becomes
both extraction agent and solvent. For titration of the acids
potassium hydroxide in a propane-benzene solution is taken,
using thymol-blue as an indicator.
Some results of these measurements are shown in Table 5 where
the acid equivalents are listed in mmol/m water. The increasing
values fromthe Lake of Constance to the Lower Rhine can be seen
as well as the decreasing acid equivalents in bank- and ground-
filtration.
In addition, with this method it can be shown that different
types of activated carbon show different properties in the
adsorption of polar acid compounds.
Table 5: Acid equivalents at different sampling stations;
mmol KOH/m water
Sampling station
acid equivalent
Lake of Constance
Rhine at Basel
Basel, after ground water filtr.
Rhine at Cologne
Cologne, bank filtrate
Rhine at Duisburg
Duisburg, bank filtrate
Esch, after ground water filtr.
Weiler, after ground water filtr.
Donau at Leipheim
Neckar at Ludwigsburg
Fulda at Kassel
Weser at Bremen
Ground water, Grenzach
3.4
5.9
1.9
18.9
6.8
19.0
12.7
12.2
4.3
6. 1
1O.4
9. 1
11.4
1 .8
-------
193
Table 6: Molar acid numbers in water works filters.
activ.
carb.
F 3OO
F 3OO
F 3OO
F 300
LSS
LSS
LSS
LSS
Ds
64
61
79
37
34
34
35
60
SZm above
3.14
2.O8
2.36
2.48
3.73
3.12
3.10
2.02
SZm below
3.33
3.16
2.17
2.46
4.46
4.28
4.44
4.01
percent of increase
or decrease
+ 6
-6
-8
-0.8
-20
+ 37
+43
+49
_ _ 3 ., SZm above = molar acid number, upper layer
' "' SZra below = molar acid number, lower layer
This fact is shown in Table 6 where the distribution of acids
in water works activated carbon filters is shown. It was possible
to prove that activated carbon with less affinity to organic
acids, such as LSS, show in the lower part of the filter much
more accumulation of acid substances because of displacement
by non-polar compounds from the upper to the lower part of the
filter. F 3OO, however, givesa relative equal (symmetric)
distribution through the whole height of the filter. This
behaviour, characteristic for polar compounds, is reversed
in the use of non-polar chlorinated hydrocarbons, as can be
seen in the results to be discussed later.
Table 7 shows some analogous measurements at two otherwater works
filters, filled with the same types of activated carbon.
-------
Table 7: Molar acid numbers of control filters
before and after water works filters
F 4OO KF before GF
F 3OO GF above
GF below
F 4OO KF after GF
F 4OO KF before GF
LSS GF above
GF below
F 4OO KF after GF
KF = control filter
GF = water works filter
SZm =
SZm =
SZm =
SZm =
SZm =
SZm =
SZm =
SZm =
3
2
3
2
2
3
4
3
.44
.98
.16 + 6 %
.71 -21 %
.67
.73
.46 +2O %
.34 +25 %
SZm = mmol KOH/g extract
(molar acid number)
At this plant, however, measurements are carried out with
control filters too, one being installed before and one after
the water works filter. The resulting data showed that the
activated carbon type F 3OO adsorbs organic acids, whereas the
filtrate of the water works filter,containing type LSS, shows
much higher acid concentration than in the water supply. In
this case primary adsorbed acids are displaced from the acti-
vated carbon by less polar substances such as organic chlorine
compounds.
Among other things, the group of polar substances includes the
organic sulphur compounds (SCHWEER et al, 1975). Of these,
those with an aromatic group are preferably adsorbed onto
activated carbon. Because the organic sulphur compounds
commonly are of low volatility, the DMF extract is used for
their determination.
-------
195
Table 8: Proportional comparison of organic bound sulphur
and organic bound chlorine in activated carbon
control filters at different sampling stations
Sampling |
Station \
! ]
iLake of
Constance :
Rhine at
j: Basel i
! :
Rhine at
; Duisburg
| Donau at
| Leipheim
| Neckar at
| Heilbronn
i Fuda at
Kassel
Ruhr at
Mulheim
adsorb.org. |
substances \
mg/m ;
1300 j
]
2900 I
65OO
2OOO
46OO
4100
3OOO
...... _.
sulphur |(
\
O.4 1
\
1.5 j
]
j
5.1 i
!
1 .0 :
!
1.4 i
0.6
2.5
chlorine | org.
I bound
% i sulphur
I mg/m
0.5 5
2.3 44
2.3 332
1.2 20
1.2 64
0.3 25
0.9 78
org.
bound
chlorine
mg/m
6
67
150
24
55
12
26
In this table the organic substances adsorbed by activated
carbon from water and recovered by extraction are shown, the
organic bound sulphur and the organic bound chlorine in one
m water, respectively- Along the length of the Rhine, the total
amount of adsorbable organic substances is clearly increasing;
at the same time the contents of sulphur and chlorine in the
extraction are increasing too. The values of the river Ruhr
are remarkably lower than those of the Rhine near Duisburg.
In Table 8 it can be seen that the lowest values are obtained
of the lake of Constance and the river Fulda. These measurements
give a good indication of the pollution of surface waters,
because natural waters do not contain organic chlorine or
organic sulphur.
-------
196
In Fig. 3 results obtained with control filters in water
treatment plants at the Lower Rhine are shown.
Fig. 3: Change of the composition of organic substances
during the treatment process of water from
the Lower Rhine (mean values 1974)
The values are given for the Rhine, the bank filtrate and
for purified water. The first column in the diagram contains
the total organic substances calculated from DOC measurements,
while in the second column the organic material adsorbed onto
the activated carbon filter, measured as dried extract, is shown.
The third column refers to the organic sulphur compounds and the
fourth shows the organic chlorine compounds determined by pyro-
hydrolysis. The efficiency of bank filtration can be seen from
the DOC and control filter measurements. Similarly, the organic
sulphur compounds are considerably reduced during bank filtration.
However, the organic chlorine compounds remain unaffected by
bank filtration. The latter can be removed only in the activated
carbon filters in the waterworks.
The widespread practical importance of chlorine- and sulphur
compounds can be seen from the investigations of the filters
in various waterworks. The difference in performance, as mentioned
before, results from the different sorts of activated carbon.
The schematic drawing in Fig. 4 shows the loadings in the upper
and lower layer of two different activated carbons at the same
specific throughput.
Fig. 4: Average loading of activated carbon in water works
filters at the waterworks along the Lower Rhine
-------
197
77"
mg/[
p| Rhein
P Uferfiltrat
g| aufbereitetes Wasser
6,5
5,2
3,5
jl
~
1
T',
'/
' j,
4,8
3,4 3,4
• i
= (/. 1.3
gesamte gdoste an AK adsorber- org. Schwefel- org. Chlorver-
org. Substanz te org Substanz verbindungen bmdungen
(DOC) aus Festextrakt aus Festextrakt (Pyrohydrolyse)
Fig. 3: Change in composition of organic substances during treatment
of water from the Rhine, in the Lower Rhine (average values 1974)
Gesamte geloste org. Substanz (DOC): total dissolved organic
carbon (DOC)
an AK adsorbierte org. Substanz aus Festextrakt:
activated carbon adsoiiable substances as solid extract
org. Schwefelverbindungen: organic sulphur compounds as
solid extract
org. Chlorverbindungen : organo-chloro compounds
Rhein: Rhine
Uferfiltrat: bank filtrate
aufbereitetes Wasser: treated water
-------
198
Aktivkohle A Aktivkohle B
D=53m3/kg D = 50m3/kg
Aktivkohlebeladung
bei Vorchlorung des
Rohwassers
D=73 m3/kq
restliche
org Verbindungen
org S-Verbindungen
org Cl-Verbindungen
Average loadings of activated carbon in waterworks
on the Lower Rhine
restliche org. Verbindungen: remaining organic compounds
org. S-Verbindungen: organic sulphur compounds
org. Cl-Verbindungen: organo-chloro compounds
Aktivkohlebeladung bei Vorchlorung des Rohwassers:
Loading on activated carbon after pre-chlorination
of raw water
-------
199
The results on the left are the loading of the upper layer,and
on the right those of the lower layer, resp. Activated carbon A
has a great affinity to organic hydrocarbons, which enrich
especially in the upper layer, while activated carbon B shows
better adsorption of the total organic substance and conse-
quently of more polar organic sulphur compounds. The third
schematic drawing shows an activated carbon which was used
in the purification of raw water, subjected to a pre-chlorination.
Since the content of humic substances was relatively high, the
loading of chlorinated hydrocarbons is considerably greater and
as a result exceeds the common quantity of 20 per cent of the
total loading.
For completeness' sake it ought to be mentioned that the
control-filter method enables one to show the effect of
chlorination on the formation of organic chlorine compounds.
Some typical examples of these investigations are shown in
Table 9.
Table 9: Increase of organo-chloro compounds as a result of
chlorination of raw waters, total organic bound
chlorine and non-polar bound chlorine in yg/1
Surface
water
19/5
-
11/10
173/29
bank
filtrate
-
90/19
-
79/29
after
chlorination
128/22
212/22
237/49
343/24
after
activated carbon
71/2
65/10
171/33
194/22
135/18 83/9 ozonization 32/4
53/12 - ground 3O/8
filtration
, 1 mg Cl
IJ/ ' per litre J4/
,0 ground c ,^ 0
.5 mg Cl ,,_,,
3 filtr. ^'° per litre '"' '
-------
200
Without regarding details, it can be seen that especially
breakpoint chlorination results in the formation of a large
amount of organic chlorine compounds. The last example in
Table 9 shows that a considerable number of chlorine compounds
were not resistant to the purifying process. In this case,
chlorination was carried out in a multimedia filter before
the removal of solids. This was followed by ground filtration,
which decreased the concentration of organic bound chlorine;
but the final safety chlorination caused a small increase of
these compounds.
The numbers before the diagonal line in Table 9 refer to the
total organic bound chlorine, those following it to the non-
polar organic chlorine. For comparison, the results from
waterworks which do not use chlorination but ozonization and
ground filtration are shown in the middle section of the
Table. In this case, there is an effective decrease of the
organic chlorine content of raw water.
Information on the mechanism of the formation of chlorinated
hydrocarbons as a consequence of superchlorination of water
is given by ROOK (1974 and 1975), BELLAR et al (1974) and
ROBECK (1975).
The methods used in the control filter investigations may
al'so be employed in the examination of the efficiency of
waterworks filters. For this purpose, samples of activated
carbon were taken from the upper and lower layers of the
waterworks filters (KUHN, FUCHS, 1975).
-------
201
In the following section the statistical evaluation of a large
amount of data from a waterworks filter is given. The data
refer to one waterworks at the Lower Rhine, since the evaluation
of different types of activated carbon is only possible on the
same raw water. To characterize two types of activated carbon
the total loading has been measured and broken-down into its
dioxane and DMF extract fractions. In addition, the loading of
polar and non-polar organo-chloro compounds was measured. The
data shown are average values of the loading of the upper and
lower section of the filter. These values are related to the
specific water throughput. Because of the scatter in the data,
to be expected in an industrial plant, mean values have been
calculated. The resulting data are shown in Fig. 5.
Fig. 5.
The following conclusion can be drawn: Both types of activated
carbon show a decrease in their total loading after a specific
flow rate of 7O m /h is reached, although the maximum is reached
somewhat earlier with LSS than with F 3OO. At maximum loading,
F 3OO contains about 6.5 per cent by weight of organic material
and LSS about 5.5 per cent. The subsequent decrease in loading
after reaching the maximum value may be partially due to biolo-
gical processes taking place on the carbon.
However, the amount of dioxane extract shows a reverse tendency,
here LSS has a larger capacity than F 3OO. In addition, it may
be seen that the decrease in dioxane-extractable material occurs
earlier than with the humic compounds, which are present at a
much higher concentration, and which hinder the adsorption of
non-polar substances.
The general conclusion to be drawn is that these activated
carbons have an optimum specific throughput of about 5O m /kg
of carbon.
-------
202
Ol
16
8|
OJ
56
48
40
c
£ 32
£ »
Q
r, 16
Gesamt Extrakt
16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
DMF-Extrakt
16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
Dioxan-Extrakt
. 5:
16 32 48 64 80 96 112 128 144 160 176 192 208 224 240
o
Spezifischer Durchsatz m / kg AK
Waterworks filter with LS Supra and F 3OO activated
carbons. Dependence of loading on specific throughput
Gesamtextrakt: total extract
DMF: DMF
Beladung: loading
Spezifischer Durchsatz: specific throughput
-------
203
The corresponding curves for organo-chloro compounds are shown
in Fig. 6.
Fig. 6
The maximum loading of LSS was about 3.8 g/kg of activated
carbon while F 30O had a value of about 2.8 g/kg. These
figures correspond to about 7 per cent of the total organic
loading for LSS and about 5 per cent for F 3OO. However, the
differences in the affinities of the two carbons for non-polar
organo-chloro compounds are much more striking. The average
value obtained for LSS was approximately O.88 g/kg (1.5 per cent
of the total organic loading) and 0.65 g/kg for F 30O (1 per cent
of the total organic loading). Thus it may be seen that LSS is
able to adsorb more non-polar organo-chloro compounds than
F 3OO; on the contrary, the latter activated carbon has a
greater affinity for high molecular weight aromatic compounds.
This may be seen in its ability to give a higher UV removal
(KOLLE, SONTHEIMER, 1973; KOLLE, SONTHEIMER, STIEGLITZ, 1975).
The inorganic chloride loading is shown in the bottom section
of Fig. 6. This data was determined by nitrate exchange on the
activated carbon (KiiHN, SONTHEIMER, 1974) . Since raw water con-
tains a far greater quantity of chloride than organo-chloro
compounds, it is to be expected that the inorganic chloride
is also adsorbed. Comparing the data, it may be seen that the
chloride adsorption is the same order of magnitude as the
adsorption of non-polar organo-chloro compounds, lying between
0.5 and O.9 g/kg of activated carbon.
In the case of the more lightly loaded activated carbon in the
control filter, the chloride loading often may be more than
5O per cent of the total chlorine loading.
-------
204
Gesnml Chtor
64 8D 96 112 126 VA 160 116 192 2DB 224 24D
155
F30D
L55
96 112 128 144 *D 176 192 208 224 24D
CMErrid
Fig . 6 1
0 16 32 X.B 64 8D 96 112 128 144
SpEzi-fscher Durchsotz «
Waterworks filter with IS Sajpra
carbons. Dependence of -loading
192 3DB 224 24D
AK
F 3OO
specific tinrougiipnt
GesamtciilDXj total cfelorine
nnp. Chlor: non-polar organic chlorine
Chlorid: chloride
Beladnngj loading
Speziiischer Burchsatzs specific
-------
205
The chlorine loading drops if other readily adsorbable substances
are present. This presents the possibility of obtaining a rapid
indication of the appropriate loading. Analogous effects can be
seen when the chloride loading in the upper and lower sections
of the filter are examined. It is always found that the lower
section is more highly loaded than the upper section. However,
this will not be examined in further detail as it is of more
academic interest than practical importance. However, it is
important that by means of a simple chloride determination it is
possible to obtain a rough indication of the degree of loading
of the carbon. This method is practicable, provided the chloride
concentration in the water remains in the same concentration
range.
Similar investigations on other waterworks filters are shown
in the upper section of Fig. 7. From these results the following
conclusions can be drawn:
1) The percentage of dioxane-extractable material decreases
with increasing throughput.
2) With throughputs of more than 5O m /kg the loadings on
LSS and F 3OO remain constant under the existing water
composition.
3) Norit activated carbon shows the highest increasing in
loading even at high throughputs, with organic material
of a polar nature.
From the data in the lower section of Fig. 7 the following
conclusions can be drawn:
1) In the case of activated carbons with strongaffinities for
polar substances such as F 3OO or Norit, the loading of
organo-chloro compounds increases only in the lower section
of the filters at higher throughputs.
-------
80-
70-
60-
50-
40-
30-
20-
10-
o-
12-
11-
10-
8-
7-
6-
5-
4-
3-
2-
1-
n
H^es - Ex rakt ggn
^ DMF - Ex rakl
[^jDioxon-Ex rakt
60
L5S
1
50-
40-
30-
20-
10-
80
70
60-
F300
50-
[
40-
30-
20-
10-
: n
Nont 5
102030405060708090 100110 120130140150 10 20 30 40 50 60 70 80 90 100110 120 130140150 "6 10 20 30 40 50 60 70 80 90 100110 120130140150
| obere Schicht
Q untereSchicht
LSS
11-
10-
9-
8-
7-
6-
5-
4-
3-
2-
1-
, , . , n
12-
li-
ra-
F300 9
7
6-
5-
4-
3-
2-
1-
, — , — , — i — i — i n
Norit S pvj
O
a>
Durchsatz m3/kgAK
Fi_g_. 7: Dependence of loading on specific throughput for
"different activated carbons
Obere Schicht: upper section
untere Schicht: lower section
Ges.-Extrakt; total extract
Beladung: loading
Durchsatz: throughput
-------
207
2) LSS has the highest capacity for organo-chloro compounds
in the upper section also at the higher throughputs while
still retaining available capacity in the lower section.
3) Activated carbon with a high affinity for organo-chloro
compounds, such as LSS, generally has a small adsorption
capacity for higher molecular weight organic substances.
It should be pointed out that these conclusions may be valid
only in this particular instance and should not be taken as
the general case, since different waters show different behaviour
with the same carbons.
It may be concluded by saying that the above outlined methods
provide a good means of investigating the properties of activated
carbons,and their application may contribute to improve the use
of activated carbons in waterworks.
-------
208
CONSIDERATIONS ON THE OPTIMIZATION OF ACTIVATED CARBON USE
IN WATERWORKS
by H. Sontheimer
The reports on practical experience with activated carbon
filters in waterworks show how different the results and
optimum solutions may be in practice. Most important in
this respect is the pretreatment prior to the activated
carbon filters. As a supplement to the reports by
POGGENBURG, HEYMANN, SCHEIDTMANN, JANATA and VAN LIER,
some additional considerations are presented below.
Firstly, it must be stressed once more that specifying the
degree of purification to be achieved is of utmost importance
for determining the choice of carbon and the optimization of
the whole treatment process. It is therefore most important
that a suitable analytical method is proposed for the control
of the activated carbon filter.
About 2O years ago, when activated carbon filters were used
for the first time in Western Germany for dechlorination and
further improvement of water quality, the analytical methods
were relatively simple and only the odour threshold number
was measured regularly (HOLLUTA 196O). The method of measure-
ment may have been subjective but, since it was always carried
out in the waterworks by the same person, provided satisfactory
and comparable data. By measuring the threshold number at
different heights in the filter it was also possible to obtain
some indication of the expected running time of the filter.
Today it is still necessary to remove taste and odour with
activated carbon filters, but this task is not of primary
importance now because it has been shown many times that taste
and odour are fully removed when the filter process is orien-
tated towards lowering the total concentration of dissolved
-------
209
organic carbon or towards an extensive removal of organo-
chloro compounds. However, there are considerable differences
in the effectiveness of different activated carbons, depending
on the analytical method used, as illustrated in the following
Table.
Table 1: Comparison of different activated carbon types
according to different parameters
DMF-extract solution (Langenau waterworks) spiked with
organo-chloro compounds (raw water used for testing)
n n c. 119.9 mg/1
COD 254.5 mg/1
U V (25O rim) 1 .32
Org. Cl 14.8 mg/1
Lindane O.6 mg/1
Residual concentrations after 4O hours at 5 g/1 activated
carbon dosage
Carbon
type
L S
LSS n
LSS a
C 2
F 40O
B 1O
DOC
34.7
25.6
28.4
29.2
24.8
21.0
COD
42.9
19.2
25.3
30.3
23.2
14.6
UV
0.050
0.015
O.O10
O.O95
<0.010
O.04O
Org.Cl
11.2
11.9
22.0
10.9
11.9
14.3
Lindane
O.OO9
O.OO2
0.002
0.002
O.OO1
0.001
-------
210
In this Table the results of several experiments are presented
in which a number of different types of activated carbon were
used in a solution of a carbon extract from the Langenau
waterworks, spiked with different organo-chloro compounds.
After adsorption a variety of parameters have been measured.
These included sum parameters, such as the DOC and the COD,
and group parameters such as UV extinction and the organic
chlorine concentration. Additionally, in this instance a
single compound, Lindane, was also analysed.
It may be clearly seen from the results that, depending on
the analytical method, no particular carbon is shown to be
the most effective. This means that the judgement on acti-
vated carbons is largely dependent on the analytical method
and the evaluation criteria. More detailed discussions on
the problems connected with testing procedures for acti-
vated carbon are presented in subsequent papers.
However, it should be noted that the choice of testing para-
meters has a marked influence on the treatment conditions.
It has been shown many times that the adsorption of odour is
considerably faster than the adsorption of many other organic
substances. As long as the removal of taste and odour were the
only considerations, it was possible to use filter velocities
of 3O m/h without deleterious effects. However, a high degree
of removal of all organo-chloro compounds requires longer
contact times, and under these circumstances the effect of
competitive adsorption must also be considered (WEBER and
MORRIES 1964, KOPPE 1967).
Where high degrees of removal are required, the optimization
of the pretreatment processes is of increasing importance,
since it not only has an effect on the removal of odour
compounds but also on the removal of all contaminants. Thus
-------
211
the different pretreatments used at each waterworks require
individual carbon evaluation procedures. In addition to the
papers of HEYMANN and SCHEIDTMANN some recent results obtained
from the testing of water from the river Ruhr, which clearly
illustrate the variety of different pretreatment processes,
are described in the following chapters (NOLTE, VOLLMER 1975).
There the question arose whether it might be possible to
obtain very low residual amounts of organics in the processed
water, using a suitable pretreatment prior to adsorption.
Therefore, the adsorption capacity after various pretreatments
of Ruhr water was examined, the results of which are presented
in Fig. 1.
Fig. 1: Carbon consumption required to achieve a
set DOC in pretreated water from the river Ruhr
In this Figure the carbon consumption required to obtain a
certain DOC level is presented, which was calculated from
equilibrium measurements obtained for two activated carbons.
It can be seen that the carbon dosage, which is necessary to
obtain a certain residual organic level, is lowered by additio-
nal ozone treatment. It is interesting that an identical effect
can be obtained if chlorine is used in place of ozone. This
procedure, however, has the disadvantage of causing a very
rapid loading of the filter with organo-chloro compounds,
resulting in a more frequent filter regeneration. Also, it
was found that a total removal of organic material of more
than 8O to 9O per cent was necessary to remove all organo-
chloro compounds formed through chlorination. Furthermore,
it may be seen from Fig. 1 that 1O g/m chlorine produce
about the same result as 3 g/m ozone. An additional result
was that greater effectiveness of the activated carbon can
be obtained after ozone application followed by flocculation.
This results in the partial removal of the polar substances
formed during ozonization.
-------
212
1-Flockung
2-Flockung + 2,26 mg03/l
3-Flockung +2,91 mg 03/1
3 ~ 2 1 0
Restkonzentration in mgC/l
4-Flockung + 10mgCl2/l
5-Flockung + 2J51mg03/l
Nachflockung
3210
Restkonzentration inmgC/l
Fig. 1;
Kohleverbrauch in g/m Wasser: carbon consumption in g/m water
Flockung: flocculation
Restkonzentration in mg C/l: residual concentration in mg C/l
Nachflockung: after-flocculation
-------
213
From the results presented it may be seen that the type of
pretreatment determines also which of the two carbons shows
a better effectiveiess, that is to say, a lower consumption
of carbon to reach the same residual concentration of organic
material.
In the presented figures the carbon consumption has been
calculated from equilibrium measurements. If one also con-
siders the adsorption kinetics and the different effects
of various pretreatments on biodegradation in the carbon
filter, together with plant-to-plant and season-to-season
variations of different contaminants, it becomes obvious
that it is not possible to set generally valid rules for
the optimization of the activated carbon treatment and the
preceding pretreatment process.
Judging by the experience gained so far, there seems to be
no other way than to carry out in each individual case suitable
parameter studies on existing plants or test plants, and to
ascertain the specific dependencies. Thus different results
are obtained in each individual case, which is to be ex-
pected, considering the different combinations of organic
compounds. Nevertheless, one may draw the following general
conclusions regarding the optimization of an activated carbon
treatment:
1) Optimum activated carbon use requires regular process
controls, whilst at the same time various parameters
have to be checked.
2) In general, each change within the treatment process
before the carbon filter has both advantages and dis-
advantages. Thus, the use of ozone may improve the
adsorption equilibria as well as the biological effective-
ness of the activated carbon, but may impair the adsorption
kinetics. Similar problems arise with most treatment
processes.
-------
211*
3) Only in rare cases experience gained at one waterworks
may be transferred without modification to another works.
In each case it is essential to check the consequences
of certain measures, and only then may conclusions be
drawn from the results.
4) It appears that the best optimization is achieved by
an exact control of the plant performance in such a
way that one can draw final conclusions from the results,
taking into account the experience gained at other works.
This type of procedure has proved successful during the
past five years.
-------
215
COMPARATIVE ASSESSMENT OF ADSORBENTS
by
J. Klein, Essen
Introduction
For decades, adsorbents have brought the solution to problems
of various kind, as e.g. in the .field of air and water
purification, gas drying, solvent recovery etc.: activated
carbon e.g. is used for gas and vapour adsorption, as de-
coloration agent, in respiratory apparatus, for water treat-
ment, medical purposes, batteries,and as catalyst or catalyst
carrier. Aluminium oxide is used mostly for drying purposes,
as catalyst or catalyst carrier, but may also be used for
adsorption and precipitation of liquid-phase polar matter.
Silica gel is mainly used for drying purposes or as catalyst
or catalyst carrier. Molecular sieves are used for drying
and purification of gases and for hydrocarbon recovery.
This variety of applications requires a characterization of
the individual adsorbents and necessitates specification of
the individual product with respect to the process applied.
For this reason, research and development work was carried
out over many years in order to establish suitable testing
methods, but due to the very specific characteristics of the
individual adsorbents, the respective testing methods exhibit
correspondingly very specific features. However, some of the
testing methods could be standardized. Thus, e.g., BIN 19 6o3
"Technische Lieferbedingungen fur Aktivkohlen zur Wasserauf-
bereitung" (Technical supply conditions for activated carbon
for water treatment) contains determination procedures for
bulk density, water content, phenol adsorption capacity,and
-------
216
dechlorination capacity. So, parameters are quoted which
possibly are useful for assessment of the adsorbent and which
may be complemented by any further parameters required.
For determination of the adsorption capacity or the adsorption
performance, however, only very few standard methods are
available, but a variety of specific bases of evaluation
developed by the manufacturers or users of adsorbents is partly
used outside their specific field of application. In the
present paper, some assessment methods for adsorbents will be
explained,and proposals will be submitted for comparative
evaluation of the methods in order to assess their value for
operation practice.
Description of test methods
The most important characteristics for adsorption are size
and state of surface and the pore structure. The term "pores"
stands for the hollow spaces in solid-state particles
(qdsorbatej
accessible to the adsorptive,/subdivided according to IUPAC
standard into macropores (d > 25o AE), mesopores (25o AE
> d?2o AE), micropores (2o AE> d > 4 AE) and submicropores
(d < 4 AE). The walls of these hollow spaces constitute the
inner surface, generally determined according to Brunauer,
Emmett and Teller (BET) bj gas adsorption (see DIN 66 131) .
Apart from the sodetermined size of surface, its chemical constit-
ution is of specific importance, characterized in a simple
way by differences in the affinity between adsorbent and
different classes of adsorptives. Data on the pore structure
may be obtained from the distribution of pore radii to be
calculated, e.g., for radii > loo AE by Hg-porosimetry and
for smaller radii (micropores), e.g., on the basis of benzene
or steam adsorption.
These three properties of adsorbents always have a combined
influence on the adsorption process as may be seen from
the adsorption isotherms of four different adsorbents ,with
water and benzene used as adsorptive (see Figure 1). The
-------
217
Wasser
Benzol
0 0,1 0,2 0,3 OA 0,5 0,6 0,7
a = Aktivkohle c=Molekulorsieb
b = AI203 d=Kieselgei
03 1,0
P
0,1 0,2 0,3 0,4 0,5 0,6 0,7
0,9 1,0
P
Figure 1: Adsorption isotherms of different adsorbenl
V/ater Benzene
a) activated carbon c) molecular sieve
b) A1203 d) silica gel
-------
218
relative adsorbate volume V/V is plotted as a function of the
relative partial pressure of the adsorptive P/PS-
Water as adsorptive may be considered first: In case of the
zeolitic molecular sieve (curve c) the load increases sharply,
already at very low partial pressure, reaches saturation,
followed at p/p ^ 0.8 by further increase. This isotherme
o
corresponds to type II of the Brunauer classification.
The behaviour of A120, (curve b) towards water is similar.
However, in this case a considerably slower increase of load
at low partial pressure is stated. This type of isotherm
(type II) indicates the existence of two different adsorption
mechanisms, i.e. two different pore systems. In case of silica
gel (curve d) a nearly linear course is obtained fulfilling
Henry's law over a large range of partial pressures.This
curve, however, may be understood as a limit case of isotherm
type I. In case of activated carbon (curve a) it is isotherm
type V we are dealing with, i.e. at low partial pressures only
very few active centres for adsorption are available and,
above p/p
-------
219
shows the highest interaction between adsorptive and adsorbent,
followed by silica gel, Al-CU and activated carbon. In case of
benzene(. adsorption interaction is highest with activated
carbon and lowest with silica gel. Substances exhibiting high
interaction with water are called hydrophillic and those with
high interaction with non-polar aromatic matter are called
hydrophobia.
Quantitatively, a hydrophobia quotient may be defined as the
ratio of interaction energy of water and benzene to the
adsorbent; determination may be carried out experimentally
by measuring the heat of immersion.
Since all adsorbents may be characterized comparably by means
of adsorption isotherms, the present article will be confined
to activated carbon as adsorbent. Described are the
test methods for the five adsorptlves normally used, i.e.
phenol ,. iodine, methylene blue, TBS (tetra propylene benzene
sulphonate) and molasses.
Phenol adsorption
Phenol adsorption was initially used for determining the
capacity of activated carbon to remove aromatical matter-
Two standardized methods exist: DIN 19 6o3 dealing with
determination of the isotherm'of ground activator!
carbon using an initial concentration of lo rag/1 of phenol
(c/Ce-^ o.oool) , whereas according to AVrVJA instructions the
O
phenol desorption by a layer of granulated activated carbon,
saturated by a phenol solution (pooo rag/1 = c/c,-, = o.o5)
is determined. Figure 2 shows for comparison the results
obtained by both methods for activated carbon qualities of
different degrees of activation. From the mere phenonenologics:
point of view,we may state that the phenol load increases
initially with the degree of activation, reaches a peak and
then decreases. This may be explained by the change in the
pore structure of activated carbon during the activation
process, as has been explained previously by Juntgen.
-------
220
o
p
03
>
•H
-P
O
CO
ai
o
H
r-t
O
a
200
150
100
50
^— Granutat. t=24h
--— Granulat t= 1 h (AWWA)
..... puiver t= 3 h (DIN 19603)
Q0001
Q0001
degree of activation
Figure 2: Characterization of the adsorption capacity in
aqueous solution
granualated material (matter) t = 24 h
" " t = 1 h (AWA)
..." " t = 3 h (DIN 19 6o3)
-------
221
Using the AV,n/,rA regulations, we obtain the upper dark-line
curve for a pre-determined contact period of one hour and
an initial concentration of c/cg = o.o5 for a cylindrically
formed1, carbon. With a contact period of 24 hours,
sufficient for obtaining the equilibrium load, the upper curve
is obtained for the same series of activated carbon quality
at c/cs = o.o5. The middle full-line curve indicates the
equilibrium load at c/c = o.oo5- It may be seen that the load.
o
obtained according to AVAVA instruction is by 5o % smaller than
the equilibrium load and corresponds to the one obtained at
equilibrium for an initial concentration which is by lo times
smaller. The fact that the dash-line curve shifts
to higher degrees of activation is due to the diffusion
effects in the small-diameter pores.
The result of DIN instruction using pov/der-fine activated
carbon corresponds approximately, at identical initial con-
centration, to the equilibrium load. The smaller grain size
creates new active centers entailing higher load at lower
degrees of activation, but favourizes also the adsorption
kinetics so that equilibrium is obtained already after
three hours.
Determination of iodine number
The iodine number is defined as the quantity of iodine in mg
adsorbed by 1 g of activated carbon, the residual concentration
of the iodine solution being o.o2 normal. There are several
instructions, e.g. by AWA and PPC/ according to which the
ground activated carbon is vibrated over 3o seconds with a
0.1 n iodine solution (C/CQ = 0.8) and a load, value for a
O
residual concentration of o.o2 n (c/Cp = o.l6) is taken as
the iodine number.
Iodine is found in aqueous solution as i^ molecule which is
of similar size as the benzene molecule. Therefore, in
Figure 3 the iodine adsorption from a liquid phase is compared
to benzene adsorption from the gaseous phase at equal external
-------
222
CO
O
0)
-p
Cli
•H
-P
O
cd
H
rH
O
e
T3
e
ro
.a
JH
O
W
"O
rd
-P
•H
-P
a
CD
Benzol (Gasphase ;£ =0,16)
Benzol (Gasphase. Monoschcht I
Jod IKJ.H20;-§-s=O.I6l
degree of activation
Figure 3: Characterization of the inner surface
benzene (gaseous phase c
= o
.16)
tenzene (gaseous phase, mono-layer)
iodine (KJ + H90 - = o.ol6)
-------
223
concentration c/c0 -- o.l6 . The upper curve applies to benzene,
O j. j-
the lower one to iodine. When evaluating the benzene isotherm
according to BET we obtain the mono-layer load (see the middle
curve on Figure 3)- Supposing the same space requirement for
the iodine molecule and the benzene molecule, the decrease of
the idone values, above all in case of large-pore products,
rna'y be explained by the simultaneous adsorption of water
molecules or of separated ions. It may be seen that the iodine
figure moves in parallel to the benzene-determined surface so
that probably it can be regarded as effective surface for
non-polar matters in aqueous phase.
Methylene-blue adsorption
The volume of a o.!5c/o solution in ml, decoloured by loo mg of
activated carbon within 5 minutes,is the titration standard
for methylene-blue according to DAB instruction . For this
method, a residual concentration cannot be determined exactly
so that the isotherm value cannot be defined exactly either.
Figure 4 shows the methylene-blue load for activated carbon
qualities of different degrees of activation characterized here
by the iodine number according to the method described before
Adsorption of the compact methylene-blue molecule starts at
an iodine number > 5oo. The stepwise course of the adsorption
curve is due to the necessary pore size of 15 AE being reached
from a certain degree of activation onwards,and to the form-
ation of smaller pores (with increasing activation) which do
not retain the methylene-blue further.
TBS adsorption
As for phenol adsorption according to DIN 196o3 an isotherm
is used for characterization. The load equilibrium of finely
ground activated carbon in a solution of 2o mg of TBS/1 is
reached within a contact period of three hours. The residual
load in per cent by weight, at a residual concentration of
1 and o.l mg/1, is stated as TBS load (LAT-procedure I\io. 311).
Figure 4 shows the respective load curve in comparison with
rnethylene-blue adsorption. Obviously, the shift of the step
-------
[tCH3)2N^SY>N(CH3)2|cf « • •
(M=276)
(0)3-0^3)4-0-503] No* o o o
(M=322)
30
-p
.c;
to 20
•r-(
(I)
>s 10
>* Methylenblou
(d>15AE)
TBS
!d>20AE)
J
500 1000
iodine number
1500
Figure 4: Adsorption on activated carbon from aqueous solution
various molecule sizes
methylene-blue (d >15 AE)
-------
225
towards higher iodine numbers which means greater pore diameters
may be seen. The determination of TBS load is a testing method
which is of specific importance for detergent production. In
unspecific use this method provides a possibility of comparison
between adsorptive molecules of different size which allows
conclusions with respect to pore diameters.
Molasses adsorption
For determining the decoloration capacity of activated carbon
with respect to decoloration of sugar-clearing liquors,the raw
material for sugar production, molasses, is used. Since
many yellow colouring substances are similar to molasses colour
with respect to adsorption behaviour, the molasses adsorption
is considered an important test for activated carbon used in
decoloration. Since the composition of the molasses solution
cannot be precisely defined, the load is not stated in th-i.s
test but the change in extinction, compared with the change
of extinction obtained by a standard activated carbon
(Carboraffin). The extinction is measured mostly by means of
a Lange colorimeter. The term "molasses factor" stands for
the quantitative relation of activated carbon to be tested
to the activated carbon quality used as a standard at the
same extinction (LAT procedure•No. 228). It is known that
molasses colours do not penetrate pores smaller than 28 AE.
Use of testing -procedures for commercial activated carbon
In the previous chapter the adsorption of five widely used
testing substances for activated carbon of different degree of
activation, i.e. different pore structure but of identical
chemical surface conditions, was discussed. Y/hen testing some
commercial-grade activated carbons, differences in adsorption
properties are found which result from different manufacturing
processes and different raw material for the products.
-------
226
As previously explained by Juntgen the raw material has a
decisive influence on the pore structure. Thus, e.g., the maximum
of differential pore radii distribution at the same degree of
activation may be shifted by the factor 2 only by using another
raw material. Figure 5 shows the methylene-blue adsorption for
two degrees of activation of different raw materials;from this
graph a shift of the load curve towards smaller iodine numbers
may be seen. Furthermore, corresponding values for some commercial
products are plotted as well. It becomes obvious that apart from
some deviations the iodine numbers are in the same order of
magnitude for all products. On the other hand, however,considerebl
differences in methylene-blue adsorption are stated. If now, for
commercial products showing a comparable iodine number a relation
between methylene-blue and TBS adsorption to the molasses factor
is established, it is surprisingly found that, as shown in
Figure 6, with increasing molasses factor, i.e. with decreasing
decoloration performance,adsorption of the smaller molecules
of methylene-blue and TBS increases.
This behaviour may be explained by adsorption of the relatively
large molecules of the colouring substances requiring large pores
which, during manufacture, are formed to the detriment of the
smaller pores which, in turn, constitute the adsorption potential
for the smaller molecules.
Another correlation is found by plotting the methylene-blue
adsorption against TBS adsorption (Figure 7). We first see
general increase of methylene adsorption with increasing
TBS adsorption for the experimental qualities of different
degrees of activation (circles) and also for the selected
commercial products (dots). When looking particularly at the
experimental qualities, we find a kind of saturation of the
methylene-blue adsorption with increasing TBS load. This confirms
the hypothesis according to which the size of
the molecules determines the adsorption.
-------
227
o
•H
-P
O
W
TJ
CO
0) -P
? ,c
H to
,0 -H
I 01
0) >
0)
B
30
20
10
500 1000
iodine number
1500
Figure 5: Methylene-blue adsorption on different activated
carbon Qualities
30 •
-x 20
-p
,c
(JO
•H
10
Orboraftin LS-Supra
PWlkoksLP F300
o
MethylenWau
TBS
0 5 10
molasses factoi
15
Figure 6: Correlation betv/een molasses factor and adsorption
of methylene-blue and TBS at comparable iodine nur,ber
(v 9oo)
-------
228
fl
o
•H
-P
O
M'
fad
CD -H
3 0)
I >,
30
2°
10
/
AK
.BKC
X LS-Supra X
.
Corboroffin
02
10 15 % (by weight)
TBS-Adsorption
Figure 7: Correlation between methylene-blue adsorption and
TBS adsorntion for various activated carbon qualities
-------
229
Evaluation with respect to operation practice
The testing methods discussed here are fairly different with
respect to the value of their results. In all cases an isotherm
value is indicated as characteristic figure, and this isotherm
value is badly defined for methylene-blue and molasses adsorption
Vhen using granulated matter, the test methods indicate load
values which almost surely do not correspond to any equilibrium
load. Despite of these deficiencies, however, it was shown that
they supply certain general information on the pore structure
given in the activated carbon quality under test.
Of course, the values for equilibrium load and adsorption kine-
tics which are of decisive influence for the break-through
behaviour of an adsorption bed and which are required for the
design of adsorptive purification plants are not determined by
these testing methods. In addition to that, only in very few
cases of industrial practice an individual substance or type
of substance is contained in the water to be treated. Moreover,
these waters contain complex blends of pollutants the adsorption
behaviour of which cannot be simulated in reduced-scale tests.
For the solution of water treatment problems, especially for the
design of adsorption plants > tests with the actual water to be
treated must be carried out for determination of the adsorption
isotherms and adsorption kinetics, a practice which, to some
extent^ has been adopted for waste-water treatment technology.
For the future, however, it will certainly be useful to find
useful parameters by well- defined basic research which allows
a general prediction of the adsorption behaviour for any blend
of substances.
-------
230
INVESTIGATIONS INTO THE CONTROL OF ACTIVATED CARBON FILTERS
AT WATERWORKS
by W. Janata, Cologne
The Gas-, Electricity- and Waterworks of Cologne (GEW) have
been using an activated carbon treatment plant since 1972;
and a second plant is under construction.
AS at other waterworks, the problems of reactivation and
exchange of carbon arise also here, so that the foremost aim
was to find the best parameters for determining the best time
for exchange of the carbon.
In cooperation with the Engler-Bunte-Institut the following
evaluation procedures were used.-The total loading on the
carbon was determined using the Dioxan/DMF extraction technique
developed by FUCHS (1973) while the total organic chlorine com-
pounds were determined by pyrohydrolysis (KliHN 1973).
Both methods provide a good indication of the extent of the
total loading of the carbon when taken in conjunction with the
continuous measurement of the UV extinction of the water before
and after activated carbon treatment.
In order to obtain further analytical information on the method
of loading of the activated carbon and especially on the extent
of the important organo-chloro compounds, the gaschromatrography
technique developed by PARK at the Engler-Bunte-Institut
(Jahrbuch vom Wasser 1974) was also used. Slight modification
of the programme procedure was found to be necessary. The
procedure is shown schematically in Fig. 1.
-------
231
2 g moist activated carbon
+ 15O ml DMF
elution
column 1
d
20 cm
1 cm
Eluted product
+ 6OO ml H20
+ 30 ml n-hexane
extraction
extraction flask
V = 1 litre t = 5 min
n-hexane phase
+ sodium sulphate
V
u
beaker
= 50 ml
drying
n-hexane phase
+ n-hexane
filtration
volumetric flask
25 ml
1 - 3 yl in GLC
gas chromatro-
graphy
column: 1.8m packed with 3 % SF 96
on Chromosorb W-
carrier gas:
Ar/CH (95/5) 20 ml/min
temperature programme:
30° i^°» 30° 1
8 min 10min
detector: -BCD puls rate 5O Jmp./sec
output: over integrator
Fig. 1; Analytical process for the determination of organo-
chloro compounds on activated carbon
-------
232
Procedure:
Separate, well-mixed samples (= 1 kg) of moist activated carbon
were obtained from the upper and lower sections of the filter.
A 2 g sample was then placed in the elution column and the
adsorbed material was then slowly eluted in portions with
150 ml of DMF. The eluted material was then mixed with 600 ml
water and 3O ml n-hexane in a laboratory shaker for five
minutes. The organo-chloro compounds were extracted into the
n-hexane phase and, after being dried with Na2SO4 and filtered
to remove any residual material, were analysed by GLC. (The
quantitative desorption and transfer of organo-chloro compounds
into the n-hexane phase was investigated by PARK, who found the
recovery to be better than 95 percent.)
A 1.8 m glass column packed with 3 percent methyl-silicone
SF 96 on Chromosorb W was used in the GLC. However, other
silicone packings produce similar chromatograms. An BCD detector
was found to be most suitable for the organo-chloro compounds.
The following temperature programme was used:
30° ISO » 30° 6-!/mi^ 240° £1° -*240°—»30°
8 min 10 min
This adjustment has the advantage of separating the readily
volatile, medium and difficult-to-volatilize components.
The peak area units obtained by the integrator were used
for the actual evaluation.
The following illustrations show some typical results for loaded
activated carbon obtained from industrial filters. The chromato-
grams clearly illustrate the difference in loading at the top
and bottom of the column, and the adequacy of the carbon in
removing the total spectrum of chloro-compounds.
Fig. 2;
-------
233
/Tetrachlordthylcn
leichtfllichtige
organische Cl-
Verbindungen
z.B.Lbsungsmit-
tel
Filterkessel 1 oben
/Hexachlor butodien
mittelfllichtige
organische Cl-
Verbindungen
z.B.industrielle
Zwischenprodukte
schwerfllichtige
organische Cl-
Verbindungen
z.B.Cl-Pestizide
und PCB's
176 %
* 95 %
* 100% Abnahme
Filterkessel 1 unten
Fig. 2:
j'i.!. ter?;essel 1 ooen:
iej.chti luciitige. . . :
rnittelfluchtige . . . :
" lucn tiye. . . :
filter vessel No. 1, top
readily volatile organo-chloro
compounds such as solvents
medium volatile organo—chloro compounds
such as industrial intermediate products
: uir f; cul t-to-volatilize organo-chloro
compounds such as Ci-pesticides and PCB's
'11terkessei 1 unten: filter vessel No. 1, bottom
Durchsatz: througnput
Abnahme: reduction
-------
231*
The tendency of the carbon at the bottom of the column to
first load with the readily volatile chloro compounds can be
easily seen, while the difficult to volatilize lipid-soluble
and toxic chloro compounds are mostly retained in the upper
layer of the filter. These substances break through relatively
late, fortunately.
For evaluation, the determination of single substances was
deliberately disregarded after the first tests, and instead
an arbitrary classification of compounds into readily volatile,
medium and difficult to volatilize was used. In this way results
can be obtained more rapidly and one can see from the chromatograms
that such a division is relatively easy to carry out.
Tetrachloroethylene, hexachlorobutadiene and lindane were chosen
as guide compounds for each group as they have been always found
in the upper layers of the filter. Then the total loading of
chloro compounds from these three groups was compared in the
upper and lower sections of the filter.
The practicability of this method, which requires five hours
for testing one filter, was proved in that a sufficient linearity
was found in the concentration range under investigation.
However, Fig. 3 shows that there can be large differences
amongst different filters.
From the differences in the chromatograms it can be seen that
the very volatile compounds have already accummulated at the
bottom of the filter bed and that therefore a breakthrough
of the solvent front can be soon expected,or that this may have
already occurred.
Fig. 3
-------
235
'Tetrachlortithyten
leichtfliichtige
Cl-Verbindungen
Fiiterkesset 6 oben HZ.S.TSI
xHexachtorbutadien
rnittelfllichtige
Cl-Verbindungen
schwerfllichtige
Cl-Verbindungen
Filterkessel 6 unten 112 a 751
Durchsatz. 3.2 X 1Q6 if?
t 91"/. Abnahme
:rxl ter'^essel 6, ooen: illter vessel ,;ju. 5, top
1eicntilucntiyf „..: readily volatile organo—cnloru compounds
mittelflucntige... : medium volatile ...
schwerfluchtige... : difficult-to-volatilize...
Abnahme: reduction
-------
236
However, it is consoling to know that the medium and not-easily
volatilized compounds are retained, which can be explained by
their different adsorption properties.
The strong increase in loading of the readily volatile chloro
compounds in the lower section of the filter bed provided
sufficient reason to exchange the carbon immediately, although
the total loading determined by DMF extraction was 62 percent
lower in the bottom than in the upper layer.
Subsequently, a number of similar tests were carried out.
Fig. 4 gives a general view of a test series carried out in
July and August.
Fig. 4
The figures shown at the top of the diagram indicate the
specific water throughput capacity (m /kg) in each case whilst
the height of each graph represents the percentage reduction
in chloro compounds through the filter.
One can see that with increasing throughput the loading of
readily volatile substances increases markedly at the bottom
of all filters. From this behaviour a criterion for the time
for reactivation may be set.
Further investigations are planned, whereby comparative tests
are to be made concurrently. However, it may be said that the
above GLC method provides a rapid practical means of evaluating
the effectiveness of activated carbon filters.
-------
237
ioo*;.
l-i O
0) O
CO flO
rH X
t-l -~*
01 TS
O. CO
a o
3 rH
pared to
o-chloro
6 C
O rt
O 00
S-i
M O
0)
!*i tJ
CO Ol
re
Ol
S )i
O 0)
rH 3
o
C rH
•rl
1
T3
tO TJ
O to
rH C
o
M O
O M
rH C
O ,C
1 0
O 1
C O
to C
60 tO
l-i 6C
O M
O
a
•H SH
0)
01 >-
en co
tfl rH
0)
1H I-J
O 0)
01 P.
a c
&-5 ^
GO
^
.20
0
-10
100
cd
o ao
0 wi
M *J
O
i-H
^ n
Cj ^
1
O
rt M
60
^J
0 .0
Eacaiiiiuuuiiy uvi ujyui iiafciiBu . *-n«i ««—.«— — ^ —
17
' -Flterkessel a.4.6 WW Hochkirchen-
"^w. .....-- •
^^ 2.15
"*"^i
2.03
\ S"
• • - » - •
| B 29* 32 [water throughput, m /kg)
leichtflucMia* . . . 7".^^ f
,
"--^.^
xx
VV
^^^.^
^"
^J miltelfluchtiu* 1 .
rt" 1QQ
rH
^ BC
QJ
PU
p^
J3 6Q
40
20
0
/'"
______
r~-- '
~~-
achwcriluchllge
Filt.r 3 A 6
SesTiininiung der organischen Cnlorveroindungcn: aefinicion of
or gano—en ±uj. o coinpounus
Filterkessel 3.4.6 WW Hochkirchen: Filters 3,4,6 at Hochkirchen
Waterworks
leichtfliichtige - very volatile organo-chloro compounds
mittelfluchtige - medium volatile organo-chloro compounds
schwerfluchfige - slightly volatile organo-chloro compounds
-------
238
TESTING OF ACTIVATED CARBON FILTERS IN WATERWORKS
by F.J. WeiBenhorn, Diisseldorf
The increasing pollution of surface waters with non-biodegradable
and sometimes dangerous organic substances requires an increased
use of activated carbon in water treatment. On account of the
large spectrum of dissolved organics which, from an analytical
point of view, are present in comparatively small concentrations,
and on account of the necessity to eliminate these compounds
as far as possible, the activated carbon used in waterworks
has to meet especially high standards. This requires efficient
tests in order to obtain information on the adsorption behaviour
of the tested carbons for practical use.
As measurements of defined organics are not conclusive for
our raw water in practice, summary parameters must be used
for analytical checking. For many years the method of extinction
measurements in the UV range has proved a good parameter for
this because this method
can be carried out easily and quickly
provides exact results, and
requires no specially trained laboratory personnel.
At the Diisseldorf waterworks (Stadtwerke Diisseldorf AG) such
measurements are carried out in order to control the activated
carbon filters.
The following numerical values are the result of these
measurements:
- UV extinction of the filter inlet, E
o'
UV extinction of the filter outlet, E, and
throughput of water, V.
According to the formula
(1 - E/E ) • 1OO = A
the values for E and E result in the actual adsorption
efficiency, A, of the activated carbon filling in percentage
for each time of sampling.
-------
239
* 3
The specific throughput, V , in m water/1 activated carbon
is calculated from the throughput of water, V, and the volume
of the c
formula
of the activated carbon, V in the filter according to the
K
V/VK = v*
The evaluation of many measurements showed that if the
obtained values for the percent adsorption efficiency A
are plotted against the specific throughput on a semi-logarithmic
graph , the following empirical relation is found
A = AO exp (-kV*)
in which the constants A represent the percent adsorption
efficiency for a zero specific throughput , while k is the
adsorption constant in 1/m (Table 1).
A and k can be taken from the diagram or, more precisely,
can be determined by using a calculating programme using the
corresponding pairs of values for A and V .
TABLE 1
a) Measurements
E - extinction of the filter inlet
E - extinction of the filter outlet
•z
V ra throughput of water
VK 1 volume of the activated carbon
b) Evaluation
(1 - E/Eo) , "loo = A
v/vK = v*
A = AQ exp (-kV'')
-------
21*0
A % adsorptive power for V = 0
A % actual adsorptive power
V* in^/I specific throughput of water (water/activated carbpn)
k l/m^ adsorption constant
r - correlation coefficient
n - number of evaluated measurements
Using this relation, which was first found to apply to our
large carbon filters, it is possible by the constants A and k
- to characterize the activated carbons
- to estimate filter running times, and
- to judge the reactivation effects
Of course, it was of interest in this connection to find out
whether this relation is also valid for test filters of
considerably smaller dimensions, and whether such results
can be transferred to waterworks filters. If so, this would
enable us to do test runs for our new or regenerated activated
carbons in a comparatively short time.
i
In order to obtain conditions as constant as possible during
this test, the test filters were fed with the untreated water
of one pump works only, whereas the large filters got ozone-
treated water from several pump works.
The conditions for the test concerning the large and the test
filters are compiled in Table 2.
-------
TABLE 2
formula sign
filter surface A-,-,
jj
filter diameter d™
filter length 1
ivolume of the
activated carbon V.,
A.
mass of the
activated carbon ST.
A.
discharge volume. V
filtration rate v-,
time of direct
contact t
dissolved organic pQC
carbon
extinction (d=1m) E
O=24o/254 nm)
m2
m
m
m5
kg
m5/h
m/h
min
g/m5
_
filters factor
large test f
19,63 i o,o154 128o
5 o,14 36
2,3 1,o 2,3
45 o,o154 29oo
18ooo 6,2 29oo
4oo-6oo o,3 165o
2o-3o 2o 1,3
4,6-6,9 3,o 1,9
I
2,2 2,4 o,9
6/2,5 10/5 ] 0,5
Note: Commas are decimal points.
Figure 1 shows the experimental data and the calculated straight
lines for a* activated carbon "T" in a large filter (TG) and
in a test filter (TV). This diagram clearly shows, for the
large filter,
- a higher A value
- a more level course of the function, but also
- the larger dispersion of the measuring points due to
the unsteady conditions of operation
-------
2«t2
100
A
50-
20-
eTV oTG
r -0-9937 -0-9736
n 9 19 ,
k -0-152 -0-083 l/m3 0-55
AD 4 7-7 56-2 % M8
10
0 2 4 6 8 10 12V* m3/!
Fig. (1): Activated Carbon "T"
r;.'V = test filter
TG = l,-r;;e filter
-------
If one compares the constants for the large filters and the
test filters, one finds that for the large filters
- the A values are higher by the factor 1.1 to 1.2 and
- the k values are lower by the factor O.5 to O.6
This means that, according to our experience, there are,
by about the factor 2, higher loadings and longer filter
running times, respectively, in large filters than there
are in test filters.
It has not been possible so far to explain the reason for
this different behaviour. It might be that the different
geometrical conditions are responsible for this. Here,
further studies will be made.
In order to show the influence of the wave length on which
the UV measurements are carried out, the results for the
activated carbon "T" are represented at X = 24O nm and
X = 254 nm in Fig. 2. As a rule,a parallel shift with higher
values for X = 254 can be found, whereas k practically does
not change. Presumably this effect can be attributed to the
influence of the nitrate ion which adsorbs at 24O nm.
However, as
- the measurements provide more precise results on the
average at 24O
- the contents of nitrate are nearly constant and their
changes do not affect the accuracy of the measurements,
and as
- most of the experience has been gained on this wave length
this wave length is maintained for internal tests.
-------
10CH
A
50-
20-
10
* 240 254 nm
r-0.9937 -0-9899
n 9 9
k-0152 -0-U3 1/m3
A0 A7-7 63.6 %
02468 ~~JO 12 V* m3/l
(f): Activated Carbon "T"
:iCDG';.rci.-,ont,^ Co ?.>;!- n U':d 2'4-o
(te,:;t fil/cer)
-------
Apart from a careful choice of new activated carbon, whereby
many difficulties have been avoided by this test, the reacti-
vation of loaded activated carbon is of eminent interest.
This year a plant will be put into operation on site to
reactivate the activated carbon used in 3O large filters with
a total weight of about BOO t.
As shown by the reactivation tests carried out so far, this
method permits to prove the influence of the parameters,
temperature and time of direct contact, on the adsorption
behaviour of the reactivated carbon during thermic reactivation.
Thus we were in a position to adjust these conditions so that
the quality of fresh coal was regained, or even surpassed
occasionally, as can be seen in Figs. 3 and 4 showing fresh
and reactivated carbons "F" (FF and FR) and "L" (LF and LR).
These results of measurement were achieved in large filters.
On account of general experience we could assume that a
reduction of the average grain diameter would lead to a higher
adsorption efficiency. Two different activated carbons were
examined in the test filter with two different medium-size
grains in order to check this assumption.
Fig. 5 shows the results of a test with an activated carbon "S"
with an average grain diameter of 1.2 mm (S12) and 2.O mm, resp.
(S2O). Here the difference in capacity amounts to nearly 30 %
within the scope of the measurements. This difference becomes
even more evident in Fig. 6 where data for an activated carbon
"C" with an average grain diameter of 1.O (C 1L) and 1.8 mm
(C 18) resp.are shown. Here the considerably increased values
of adsorption at the beginning of the test are most striking,
which are probably caused by a certain portion of fine carbon.
-------
50
20
10
k -OU9 -0-U8 l/m3
A0 80-9 88-3 %
0 ~2 I 6 ~8 10 iTv* m3/l
(3): Act.Carbon t-'O-nr^e filter)
FF = fresh cor.l
FR = rco.ctivate
100
A
50+
20+
10
r -0-9917 -0.9848
n 12 15
k -0111 -0-1U l/m3 °N
An 769 849 %
0 ~2 I 6 8 10 12 V* rr^l
: Act.Carbon"L"(l.-..r^e filter)
LF = fresh cool
LR = reactivate
-------
2V7
100-,
50-
20-
10
oS20 oS12
r -0-9913 -0-9933
n 6 11
k -0-159 -0-151
A,, 6L6
771
0 ~5 Z 6 8 10 12 V" m3/!
i'nig. (5) : Act.Carbon*S"(ter:t filter)
S 12 = average [jro.in diameter 1,2 rnra
S 2o = " " » 2,o nm
100
50
20-
10
r -0-9865-0-9761
n 7 9
k -0-1U -0107 l/m3
A0 ^3-7 281 7=
12V*
"0 2 /, 6 8 10
1?iC- (6):-Act.-Carbon"c*'(te:;t filter)
C 1o = average grain diarneter 1,o nm
C 18 =
-------
The observed increase in adsorption efficiency with a decreasing
average grain diameter,which was found in a test under conditions
similar to practice encourages the use of activated carbon with
i
as low a grain size, as possible. However, there are certain
limitations to the practical operation of fine granules because,
on the one hand, there is the danger to lose them during back-
washing, while, on the other hand, the increase of pressure will
become to high during filtration. In this context, the question
must be examined of how the grain distribution effects the
reactivation.
Finally, two additional examples in Fig. 7 are to show how a
comparatively small inner surface or an insufficiently developed
supply pore volume take effect. The inner surface of the A coal
2
"W" is at approx. 850 m /g at the lower limit of currently used
activated carbons for water purification and shows, according
to our standards, a totally insufficient adsorption efficiency.
Although the inner surface of the A coal "H" amounts to 1,2OO
m /g, the adsorption capacity is also unsatisfactory here,
which probably has to be attributed to the insufficient supply
pore volume, particularly as the average grain diameter of O.74 mm
is at a very low level.
To summarize the results of this activated carbon test, the
following conclusions may be made: The adsorptive power of
activated carbons can be characterized under conditions similar
to practice by the values A , the adsorption for the specific
water throughput by zero, and k, the adsorption constant.
These two constants allow a comparison of different activated
carbons as well as predictions about the prospective running
time of a filter. The insults of the test filters, which are
completed after a minimum of three and a maximum of eight days,
can also be taken to predict the performance of large filters.
At present, an attempt is being made to find correlations between
UV measurements and DOC or DOC1 measurements by means of parallel
investigations in order to obtain additional criteria of
evaluation.
-------
100
A
50-
20-
10
o H
>W
r -0-9812 -0-9969
n 7 3
k -0165 -0-182 l/m3
An 43.3 26.2 %
0 ~2 I 6 8 10 12 V* m3/l
(7):Activated Carbons "H" -and
(test filter)
"W
-------
250
REALISTIC LABORATORY TEST METHODS FOR THE EVALUATION OF
ACTIVATED CARBON
by H. Sontheimer
Experience to date indicates that the present test methods such
as phenol value and iodine number for evaluating the characteri-
stics of activated carbon give no useful information for
drinking water treatment, because they make no valid statement
on the effectiveness of different types of carbon in water-
works filters. This is the case not only when using activated
carbon in water treatment. Thus, the use of molasses for
testing activated carbon for decolourization of sugar solutions
shows that test methods directly related to practical require-
ments are also of advantage in other industries (BRATZLER
1944, BAILLEUL 1962, HASSLER 1967).
As the common test methods cannot be transferred, better
techniques had to be found, and some studies of more relevant
methods have been published. In this connection the studies
made by WEISSENHORN in Dusseldorf have produced an interesting
method, requiring a pilot plant. However, the measurements
need 8 to 14 days and do not allow a rapid evaluation.
Studies made at the Engler-Bunte-Institut, carried out in
conjunction with different waterworks, were undertaken to
develop a process for laboratory tests, taking as a guide
for the results the data obtained from large filters, as they
have been reported by FUCHS. The requirements for a laboratory
test method to test activated carbons used in waterworks
have been summarized in the following summary.
-------
251
1) Realistic test conditions
a) low concentrations
b) similar organic substances as in the
treated water
2) Orientation towards the practical problem
a) adsorption from a mixture
b) investigation of the specific effect
for the adsorption of organo-chloro compounds
and of the total amount of dissolved organics
3) Rapid and simple procedure
a) simple method of analysis (UV extinction)
b) orientating results with few measurements
4) Orientation towards the technical process
a) measurement of the adsorption equilibrium
b) measurement of the adsorption kinetics
The test conditions should be realistic, which makes it
essential that the work is carried out in the same concen-
tration range as is found in waterworks and also with
similar organic compounds, as results can only then be ex-
pected which can be transferred to the behaviour of large
filters.
The activated carbon filters have to meet different require-
ments simultaneously in the different works - in most cases
the two problems of special importance are the removal of
hazardous organo-chloro compounds and a certain reduction
in the overall concentration of dissolved organics. Because
different behaviours were observed with different types of
carbon, particularly in respect of the above aims (FUCHS 1975),
-------
252
specific results ought to be obtained concerning the
effectiveness in connection with these two tasks, while
using a mixture of adsorptives. At the moment no statement
can be made on the behaviour of a mixture from investigations
with single substances only (FRITZ 1974, BALDAUF 1975).
Moreover, the test ought to be rapid and simple. This aspect
is of particular importance for the control of regeneration
plants such as are being installed in some works at the moment.
This requirement excludes all complicated methods of analysis.
However, certain mixtures of organics can be examined by UV
measurements (JAFFEE 1962, FRITZ 1974) with two wave lengths
in a very short time.
Upon thorough reflection, it became apparent that relevant
results on the technical processing can only be rapidly ob-
tained when equilibria and kinetics measurements are made
simultaneously. However, combined measurements in a filter
test have the disadvantage that they require too long a
time.
From the onset, one of the main problems was to find a suitable
mixture of substances. An exceptional number of tests were made
in this connection, just one example of which is presented in
this report (Fig. 1); further examples can be seen in the ARW
reports (1972-1974).
Fig. 1: Simultaneous adsorption of tetrapropylene
benzolsulfonate
Here a mixture of tetrapropylene benzolsulfonate (TBS) and
chloro-phenol was used; both in a relatively high concentration.
The residual concentrations and loadings are listed in the
Figure. One can see that the order of the carbon adsorption
capacity for TBS corresponds with that which is obtained in
-------
253
Aktivkohle-
sorte
F 300
Norit supra
Nuchar
BS
LSS
TBS
Restkonz Beldng
inmg/l
28,7
28.5
29,6
33.6
37,7
mg/gA<
U2
H3
136
109
82
p-Chlor phenol
Restkonz. Beldng
in mg/l
29.3
27,5
27,5
23.3
20,8
mg/gAK
138
150
157
178
195
Gesamt
Beldng
mg/gAK
280
293
293
287
111
Fig. 1
Aktivkohlesortt: type of activated carbon
Restkonzentration: residual concentration
Beladung: loading
Gesarntbeladung: total loading
-------
practice concerning the removal of the overall concentration
of organics. One can also see that the order is the reverse
concerning the removal of chlorophenol, which also corres-
ponds to that which is observed in practice.
The use of the above, or a similar mixture of two defined
organics,seems to be quite successful and should be investi-
gated in greater detail. However, there are still a number
of problems concerning the analytical methods and the choice
of organic pairs.
The use of such a mixture has the major advantage that such
a test can also be carried out by the manufacturer. Never-
theless, there is the disadvantage that this test will not
take into account the different conditions existing at each
waterworks, which have an effect on the optimum choice of
carbon, as can also be seen from the results obtained from
large filters.
We have therefore decided, especially with regard to con-
trolling reactivation plants, first of all to develop a test
using raw water which is to be treated with activated carbon.
To this water p-nitrophenol (pNP) is added as a substitute
for chloro compounds, because the latter cannot be easily
measured by UV analysis. The behaviour of this substance
towards adsorption is similar to that of the chloro compounds,
and because it belongs to the important toxicological group
of nitro compounds it is of some significance in practice too.
The advantage of pNP is that it can be easily measured by UV
analysis since it has a distinct peak at 317 nm. The exact
method of procedure during this test is described below.
-------
255
As a first step, the UV extinction of the raw water is measured
at 254 nm and at 317 nm. When the specific UV extinction, i.e.
the relation of UV extinction to the concentration of dissolved
organic carbon (DOC), is known, the DOC can be calculated from
these data. Instead of the raw water, a solution of a carbon
extract can be used which should have about the same DOC. If
the specific UV extinction is unknown, the DOC value should
also be measured. Although this value does not vary greatly
with time, it must be checked occasionally. It is possible too
. ., .„._ . . . . . -1 . (equivalent pathlength 1. meter)
to use the UV extinction in m /as a concentration figure.
Nitrophenol is added to the test water in two different amounts
(e.g. 0.8 mg/1 and 4 mg/1). It is also possible to use one
concentration only (2 mg/1) and run a parallel test using raw
water alone. Then the activated carbon is added (2O mg/1 and
4O mg/1) which has been finely ground in order to reduce the
time required to achieve equilibrium. The degree of grinding
influences the adsorption time (3-24 hours). The carbon is
then filtered off and the UV extinction determined at 254 nm and
at 317 nm. Prior to the measurement the sample must be acidi-
fied, otherwise errors may result in the UV measurements. From
the UV data the DOC values can then be calculated.
Fig. 2; Summation of spectra of processed river bank
filtrate from the Rhine and p-nitrophenol
at equal DOC rates
Fig. 2 shows the superimposed curves of the two test sub-
stances. For a statement on the two concentrations two measure-
ments are required which are in the region of the peak at
317 nm and of the minimum at 254 nm. For a calculation of the
two unknown concentrations it is assumed that the UV extinction
increases proportionally to the DOC, so that the specific UV
extinction is necessary as an additional value for the calcu-
lation. In Fig. 2 the two formulas are shown which are required
-------
256
2mg/l DOC als Extrakt
2 mg/l DOC als pNP
254 317
Wellenlange X in nm
400
Fig. 2
Nullinie: zero line
Wellenlange: wave length
2 mg/l DOC als Extrakt: 2 mg/l DOC as extract
-------
257
for the calculation of the concentration of the original
organic substances or the carbon extract (Ex), respectively,
and those of p-nitrophenol (pNP). The symbols in Fig. 2 are
set out below. -
c1 = concentration Ex (mg DOC/1)
c? = concentration pNP(mg DOC/1)
E = UV extinction at 254 nm (nT1)
E1 = UV extinction at 317 nm (m~ )
m.. = spec. UV extinction of Ex at 254 nm
m.! = spec. UV extinction of Ex at 317 nm
m_ = spec. UV extinction of pNP at 254 nm
m' = spec. UV extinction of pNP at 317 nm
spec. UV extinction = =rr— . m .
g
The simple relationship expressed in the two formulas is
also valid for other substances.
As can be seen in Fig. 3, when there is a mixture of organics
in the raw water or in an extract, their composition may
change through adsorption.
Fig. 3: Change of UV-DOC dependence by adsprption
onto activated carbon
Normally, any decrease of extinction should lead to a correspon-
ding DOC decrease. However, this is usually smaller so that a
correction may become necessary; one example is shown in Fig.3.
One can easily determine experimentally the correction function,
for example, from the knowledge of the outflow values of the
-------
258
40
35
30-
7 25
'E
E 20-
Adsorptiv Extrakt ( Flehe) c0= 12.9mg C/l
Die versch Restkonz warden durch Adsorption an
versch Pulverkohlemengenl LSS 0,5 -y>)
erreicht
456789
Restkonzentration c in mg C/l
10 11
Fig. 3
Die versch. Restkonzentrationen... : The various residual
concentrations were obtained by adsorption onto different
amounts of powdered carbon.
Restkonzentration: residual concentration
-------
259
carbon filter and from the change in specific UV extinction
occurring through filtration. In cases where the following
relationship, which can be seen in the figure, is valid for
extract (Ex)
2.5 n
E = m
1
1
the calculation formula for c.. shown in Fig. 2 must be
modified as follows:
K -*-*, • *V'
C1 =1 ' ' j
Vm1 ' m2 - m1 ' m2 /
The formula for c~ remains unchanged since with pNP there is
always a linear relationship between UV and DOC.
Through the described measurements and calculations all the
data are obtained which are necessary for the test evaluation,
typical results of which are shown in the following Table.
Table 1: Results of comparative tests of activated
carbon with bank filtrate Flehe
AK
Lsg 0
Lsg A
Lsg B
AK M
AK L
Zugabe an
pNP AK
g/m3 g/m3
0 0
0,8 0
4,0 0
0,8 20
0,8 40
4,0 20
4,0 40
0,8 20
0,8 40
4,0 20
4,0 40
UV-Extinktion bei
254 nm 317 ran
m"1 m"1
5,08 1,95
5,60 7,46
8,02 29,58
1,16 0,52
0,66 0,22
2,90 10,92
1,24 2,0
2,44 0,98
1,20 0,42
3,84 11,62
1,8 2,62
DOC flir
org.Sub. pNP
g/m3 g/m3
2,0 0
2,0 0,414
2,0 2,07
1,10 0,006
0,89 0,001
1,32 0,77
1,07 0,12
1,49 0,003
1,12 0,001
1,56 0,79
1,26 0,15
% Entfernung
org.Sub. pNP
% %
45 98,6
55 99,8
34 63
46 94
25 99,3
44 99,8
22 62
37 93
AK-Verbr.fiir eine Entf.
org.Sub. pNP
50 % 90 %
27,6 8,8
27,6 8,8
49 35
49 35
48,2 3,5
48,2 3,5
63 36,8
63 36,8
0,898
1,420
"1
0,345
=13,35
Note: Commas are decmil points
Table 1
Zugabe an: addition of
UV Extinktion bei: UV extinction at
%Entfernung: removal jn percentage
AK-Verbrauch...: consumption of activated carbon for the
removal of
organics
AK: activated carbon
-------
260
In the uppermost line the data of the raw waters are listed,
and below the data of the waters to which p-nitrophenol has
been added. The increase of the extinction at 317 nm after
the addition of p-nitrophenol is particularly noticeable.
The two solutions were then mixed with 20 mg/1 and 4O mg/1
of activated carbon. Two different types of carbon were used
in this test. After the equilibrium was achieved the UV values
were measured again. They indicate that both carbon types
have slightly different properties. Lower values were obtained
with carbon type M for both wave lengths, so this carbon has
better qualities in this case.
This can be seen even more clearly from the DOC values which
were calculated from the extinctions, according to the formu-
las given previously. They also show that a conversion was
necessary because the differences between the two types of
carbon are only evident when the total amount of organics is
compared, whilst the effectiveness with p-nitrophenol is
similar, within the range of error. The smaller dosage of
pNP was nearly completely adsorbed in both cases, so that
in fact smaller amounts of carbon would have been sufficient
in these experiments.
The simplest way of evaluating these data seems to be the
calculation of the percentage of removal. More informative,
because it can be converted directly into operation costs,
is to determine the consumption of activated carbon required
for a definite degree of removal of the two groups of sub-
stances. For this purpose it has to be assumed that the ad-
sorption kinetics can be described according to FREUNDLICH.
If we define: CQ = initial concentration (g/m3)
c. = concentration after addition of A1
of activated carbon (g/m )
c~ = concentration after addition of A_
of activated carbon (g/m )
-------
261
o
- C
0
- C
Using these figures, we can find the amount of activated carbon
(g/m ) which reduces the concentration by x per cent:
F =
X
log c
1 *\ / TT\
V C— C ) * GXp,. _ I r J
w 1 0
100 - x
C0 { 100 '
(log Q2 - log Q.. ) + log Q..=log
c_ + log Q_ - log c1
•^- ^ I
log c - log
Making use of a simple calculation procedure, A can then be
calculated for different values of x. In Table 2 the values
are given for 5O per cent removal of extract and 90 per cent
removal of pNP.
These results show that, in the presence of large amounts of
p-nitrophenol, which has a suppressing effect, the adsorption
performance for the total amount of organics declines con-
siderably. This results in an increased carbon demand of
about 30 to 7O per cent. The difference in efficiency of the
two types of carbon is also visible from the data in Table 1.
The extent to which different types of organics can influence
their possible removal by adsorption is shown in Table 2.
Table 2; Comparative tests using different extracts
with the same carbon quality
Extraktherkunft
Kbln
Koln
Holthausen
Holthausen
Langenau
Langenau
p-Nitrop
in .
g/m3
0,8
4,0
0.8
4,0
0,8
4,0
lenolzug
DO Co
Exlrakt
in ,
g/m3
2,04
2,04
2,60
2,60
1,58
1.58
Kohleverbrauch bei d
50%Entf. 90%Entf.
org.Subst. pNP
26 19
51 46
42 18
62 47
21 21
36 50
;n Sorten N und L
50% 90%
org.Subst pNP
33 10
50 40
44 1
74 38
31 4
41 41
Table 2
Extraktherkunft: origin of extract
p-Nitrophenolzugabe: addition of p-nitrophenol
Kohleverbrauch... : consumpt.of carbon type N and L
50% Entf-: 50 per cent removal
-------
262
The Table gives values for three extracts on two carbon types.
From the data it can be seen that the DOC decrease and the
carbon consumption, designed to achieve a defined effect, is
different with each type of water, and that the carbon types
react differently too. This justifies the use of raw water
for the test because the given results conform with the practi-
cal experience gained with large filters.
The most expressive and perhaps the most useful way of evalua-
tion of the analytical data is shown in Fig. 4.
Fig. 4: Dependence of the purification effectiveness
of an activated carbon filter on the water
throughput for each m of activated carbon
(or on the running time of the filter)
Plotted here is the percentage elimination as a function of
the water throughput, which is proportional to the filter
running time, at complete utilization of the carbon. The
values can be calculated from the carbon consumptions required
for a defined degree of removal. For this it is merely necessary
to know the bulk weight and to estimate the height of the
layers and the filter velocity in a filter. In this example,
a height of 2.5 m was assumed for the carbon layer and a
filter velocity of 15 m/h. Plotted are the values for the
residual concentration of the overall DOC and the p-nitrophenol
after certain filter running times, in each case in relation
to the initial concentration. Here again, the analytical data
of the tests with two different carbon types, shown in Table 1,
are used to illustrate the significance of the results. From
the position of the curves the advantages of the carbon type L
for both parameters can be seen; however, after a certain
running time the curves for the extract overlap. In general,
there are no great differences, they amount to 1O per cent in
-------
Fid. 4
263
Filterdaten : VF = 15 m/h , lp = 2,5 m
Zulauf : 4,18 mg DOC, dcwon 50V.p-Nitrophenol
und 50%Extrakt(Flehe)
Berechnung erfolgte unter Vernachltissigung der
Kinetik
10000
20000
30000
m3Wasser/ m3AK
40000
50000
45676
Laufzeit in Monaten
10 11
Filterdaten: filter data
Zulauf: feed
Berechnung...: calculation was made without kinetics
Laufzeit in Monaten: running time in months
4.18 mg DOC, davon...: 4.18 mg DOC, of which...
3 233
m Wasser/m AK: m water/m AC
Extrakt als DOC: Extract as DOC
-------
this particular case, at an average running time of three
months. If the difference in price for both carbon types
were to be of this order, related to the costs for one filter
filling, then both types of carbon would be equal.
However, the above is only valid when there are no additional
rating criteria, i.e. if it were possible to describe the
behaviour of activated carbon filters solely by equilibrium
measurements. This is not so, in fact kinetic measurements
are required as well. That this is of importance as regards
the two carbon types in question has been made clear by a
parallel filter test made in Diisseldorf, which showed a
greater difference between the two carbon types than had been
calculated from the equilibria measurements. Therefore, kinetic
measurements were also made, using first phenyl acetic acid
(PAA) at high concentrations, the results of which are shown
in Fig. 5.
Fig. 5: Adsorption kinetics with different types
of activated carbon with phenyl acetic acid
The illustration shows the progress with time for the ad-
sorption process using three different types of carbon. The
a'mounts used were measured by weight, not by volume, which
is of importance in this case because of the very much lower
bulk weight of carbon type M. It may be seen that the equi-
librium concentration using carbon type M is slightly better
under the test conditions, and that this type shows a more
favourable kinetic behaviour under the high concentrations
used in this test.
This relation between the different types of carbon did not
change when, instead of PAA, an extract was used which had
about the same concentration.
Fig. 6: Adsorption kinetics on different types of
carbon with extract (Flehe)
-------
285
o
£ 2
Versuchsbedingungen :
Adsorptiv PES c0=5rriMol/l
L =0.41
S = 0.5g
Upm = 400
LSSO,5-1,5
• LSS 0,5-2,5
M
Abb.5
9 10 11 12 13 14 15 16 17 18
Zeit I in h
Versuchsbedingungen :
Adsorptiv : ExtrakH Flehe) c0= 200mg C /I
L 0,4 I
S 0,5 g
Upm =400
30
Zeit t in h
Figs.5,6
Versuchsbedingungen: test conditions
UpM: rpm
Zeit t in h: time t in h
PES:. Phenyl acetic acid
Konzentration: Concentration
-------
266
However, under the chosen test conditions, i.e. equal carbon
dosage in mg/g, the residual concentrations differ considerably
so that it is difficult to draw any definite conclusions.
Special calculation proves too that at the high concentrations
of dissolved organics there is no obvious difference between
the three carbon types concerning the adsorption kinetics, but
they differ regarding equilibria data.
However, this situation changes when the adsorption kinetics
are investigated in the region of low concentrations (see
Fig. 7).
Fig. 7: Adsorption kinetics using equal amounts of
different types of carbon
Here not only the adsorption equilibria are very similar -
contrary to the behaviour at high concentrations - but it
is also obvious that the carbon type M, which had the better
adsorption kinetics at high concentrations, initially adsorbs
less rapidly at the low concentrations than the carbon LSS.
This example shows once more the importance of carrying out
all test procedures in a realistic investigation of carbon
properties in a range of concentration comparable with the
actual conditions.
In this particular case, the differences illustrated in the
figure explain the observations made in practice when taking
into consideration the different bulk weight of the carbons.
If a test is made with carbon amounts of equal volume, the
difference between the carbon types is still more evident,
as can be seen from Fig. 8.
Fig. 8: Adsorption kinetics using equal-volume
amounts of different types of carbon
-------
267
Versuchsbedingungen
Adsorptiv Extrakt (Flehe) c0 = 12,42 mgC/l
L 41
S = 0,4 g
Upm= 350
Abb. 7
Zeil t mh
Versuchsbedingungen .
Adsorptiv Extrakt (Flehe) c0= 12,42 mgC/1
L 4 I
Upm=350
0,4 g LSS 0,5-1.5 = 0,896 cm3
0,,2885g (^6,2 =0.869 cm3
30 40
Zeit t in h
70
Abb.8
Figs. 7, 8
Versuchsbedingungen: test conditions
UpM: rpm
Zeit t in h: time t in h
Konzentration: Concentration
-------
268
When the kinetic measurements, as shown in this figure, are
taken together with the measured equilibria data, the con-
clusions obtained conform well with experience gained in
practice and with effects observed in waterworks filters.
Nevertheless, extensive research and investigations are still
necessary to be able to optimize the described test. For this
purpose, appropriate samples should be examined at the water-
works which use activated carbon filters in the way as des-
cribed above. If, parallel with such tests, the usual analytical
measurements are made with the large filters, it should become
obvious in the course of time how to evaluate the results from
such tests in order to achieve concrete statements for practical
use and thus obtain a clear criterium for activated carbon
quality.
It will, furthermore, be necessary to extend the test procedure
by using defined organic substances. This is essential to
enable manufacturers of activated carbon to make a regular
quality check and also to have a test method which is inde-
pendent of fluctuations in the quality of the raw water. The
choice of the defined individual substances should be determined
by a comparison with the results obtained from tests with raw
waters.
In conclusion it must be mentioned that the test methods for
the evaluation of the quality of activated carbon discussed
in this paper still have various shortcomings and are by no
means ideal in every sense. There is still much work to be
done in this field. The results obtained so far indicate,
however, that the proposed procedure was a step in the right
direction and that it is worth-while to continue the work
in the manner suggested.
-------
263
PHENOMENA OF ACTIVATED-CARBON REGENERATION
by
H. Juntgen, Essen
Introfluction
The adsorption of organic matter by means of activated carbon
in a filter is a known nonsteady process, i.e. after
a period of time determined by stream rate, concentration of the
matter to be adsorbed and by the adsorption capacity of the
activated carbon,the filter has reached the limit of its capacity
so that no further adsorption can take place. The spent
activated carbon has to be regenerated then. The terra "regener-
ation" stands for the removal of the adsorbste anisimultaneous
re-establishment of the previous adsorption capacity of the virgih
activated carbon. The regeneration of spent carbon used
in water works may be carried out basically by
means of extraction or by thermal treatmerrtThe present paper
shall be confined to the last-mentioned treatment.
The thermal regeneration is carried out in two steps: at
temperatures above approx. loo °C desorption of the water
and of most of the organic matter adsorbed is started. As will
be explained later on, it is impossible, hov/ever, to obtain
complete desorption of all adsorbate so that in a second step
a reactivation of the activated carbon must be carried out in
order to destroy the residual load remaining after desorption,
and to re-establish the former adsorption capacity of the
activated carbon. Generally, for this purpose a reaction by
means of oxidation agents under well defined conditions is used.
2. Desorption mechanism
The desorption of adsorbatesfrom activated carbon has been studied
in detail. It is known that desorption is a first-order reaction.
Its rate is proportional to the residual load at a tine t.
(HAYWARD, 1964). The
-------
270
activation energy of desorp tion in that case must be greater or equa?
to the adsorption energy. In order to avoid, back-reaction (in our case
this means adsorption), the adsorbate must be removed from the
surface as soon as possible. This can be carried out e.g. by use
of a flushing gas.
Bergbau-Forschung developed a non-ir.othermal measuring method to
study the desorption of adsorbates from activated carbon. A set up
using that method is shown in Figure 1. The sample is placed
on a wire mesh through which a pre-determined quantity of flushing
gas is led. By means of an electric heater, the wire mesh and the
sample are heated up at constantly increasing temperature.
Simultaneously, the alsorbate is measured(by a downstream gas
chromatograph or a mass spectrometer)versus time or versus
sample temperature. Figure 2 shows a typical result obtained by
this technique. The quantity per time unit of phenol desorbed
by activated carbon is plotted as a function of sample temperature
During these tests a constant heating rate of 2 °C/min. was
maintained. It may be seen that desorption at low stream rate
of the flushing gas is slow and does not reach its end but at
temperatures of approx. Aoo C, i.e. after 2oo minutes. If the
stream rate is boosted to approx. 18 1/h, the end of desorption
is reached at approx. 26o °C, i.e. after 13o minutes.By further
increase of the flushing gas rate no reduction of the desorption
time is obtained. In this way, the conditions under which a
back-reaction is avoided have been found out. It is remarkable
that desorption rate first increases rapidly, reaches a maximum
and then decreases slowly. This phenomenon may be explained
theoretically; however, when using the simple theory,another
desorption curve, as shown in Figure 3, should be obtained.
The curve calculated theoretically according to simple con-
ditions presumed shows a less steep initial gradient and falls
rapidly after having reached the peak. Detailed investig-
ations have shown that the reason for this deviation from the
simple theory is to be found in the desorption rate depending on
the initial load, as shown in Figure 4. It may be seen that vith
low load, e.g. approx. 1 mmol/g, the maximum of desorption rate
J, VAN HEEK, 1970)
-------
271
i Thermoelement
2 Beladungsgefdfle
5 Dosier-
vorrichtung
Gaschromato -
graph
11
Heliumtrenner
^^Heizwindungen
7 Probe
Thermo-
Stat
3 Dosierventil
WSo
o
o
o
4
i 1
— -— _
I
9
_T
! 10
Platinnetz
Ofen-
Regelung
Temperatur-
Messung
4 Durch-
fluO-
messer
I Gewichtswert I
M~
. zur
Pumpe
13
Massenspektrometer
14
Thermo- Chromato- Massen-
gramm gramm spektrum
Fig. 1 Flow gas apparatus for the investigation of vapour
desorption from, activated carbon
i Thermoelement: thermo-element
2 BeladungsgefaBe: loading vessels
sDosierventil: dosage vent
4Durchfluflmesser: flow-through meter
sDosiervorrichtung: dosing unit
6 Heizwindungen: heating thermocouple
^ Probe: sample
8Platinnetz: platinium net
9 Ofen-Regelung: furnace adjustment
10Temperaturmessung: temperature survey
"Gewichtswert: weight
12Heliumtrenner: helium separator
13zur Pumpe: to the pump
i4Massenspektrometer: mass spectrometer
-------
272
x10"2
o n
n fl
n L
n n -
dn
dT
f mmol 1
1 g-grd 1
/
_r\
~T_
f /
/
Vs = 0.23 —
— v -18 —
1 ~ h
V-X »V3*
S. X
0 100 200 300 400T[°C]
Fig. 2 Effect of flow rate on the desorption curve of phenol
$[V*
i
7 •
Q _ .
0
Fig. 3 Desor
dn rmmol]
dT [g.grdj
8
/ (
I/-
oJ ^
0 5
Fig. 4 Non-isc
mi
gr
=±
^
i
V
/ \ E =15 kcal/mol
1 \ k
I \ n(oj c 10~3mol
V
50 100 150 200 T ft;
ption curve calculated under simplified conditions
/""\ Vs 0.63 ^
/ '• ^ ard
//i
min
nne mmol
n01 - u4Jb g
: • i; "02-i.iJ
/ / S^ n03 = 3.09 "
'/ / \ not = 4,26 -
///N
'// ,-
***
L — — —^ nQ5 = 5,32 "
\ n _ 7 jc
T7 ^
,/^^^~^^_
0 ' 100 ' 150 200 250T[°C]
^thermal desorption of phenol from activated carbor
at different initial loads
grd: ° Celsius
-------
273
is reached at 15o °C. In this case, nearly a symmetrical curve
is obtained. At high loads (1 mmol/g), however, the maximum is
reached at 80 °C, but the curve then shows a tailing up to
22o °C. This behaviour may be explained by the binding energy
between the adsorbate and the surface being dependent on the
state' of load. In case of an energetically heterogeneous
activated-carbon surface centers with high adsorption heat are
occupied first by initial small loads and then during further
adsorption, centers of lower adsorption heat are occupied. The
course of desorption is analogous: With decreasing residual load,
activation energy of desorption increases.
Meanv/hile, a theory has been developed which allows for the
heterogeneity of the surface,so that actual curves of desorption
can be established with sufficient precision. In many cases it
is even possible to draw conclusions with respect to activation
energy of desorption from the adsorption heat values calculated
from one of the measured isotherms, both values being functions
of the load. Thus, in case of a known isotherm, the course of
desorption may be generally calculated in advance. ' Figure 5
shows,for activated carbon of different micropore volumes,a
comparison between the activation heat values (dotted line)
measured during desorption of phenol,and the corresponding
adsorption heat values measured during adsorption as a function
of the load. It may be seen that in case of large-pore activated
carbon (V0 = o.Sl g/cm ) the respective data are fairly con-
3
gruous, whereas with narrow-pore activated carbon (V = o,3^ g/ccr,
s
the activation energies found for desorption are lower than
the adsorption heat values found by adsorption measurements. The
last-mentioned deviation may be explained as follows: Due to
the high residual load at desorption in this particular case,
the surface does not participate in its totality in the de-
sorption, and especially the adsorption centers of higher
activity do not desorb the bound adsorbate.
3) (SEEWALD, 1974)
-------
ne
Fig. 5 Calculated and measured activation energies of phenol
desorption as a function of amount adsorbed.
-------
275
Thus, by supposing a first-order reaction for the desorption,
and furthermore by means of the interdependence found betv/een
adsorption heat and the desorption's activation energy we obtain a
satisfactory explanation and description of the desorption.
This implies higher activation energy at desorption of substances
which' have been adsorbed more strongly, i.e. these substances
are desorbed under analogous conditions in higher temperature
ranges. An example is given in Figure 6 showing in the lower
section a comparative desorption of phenol, cresol and naphthalene.
This comparison leads to the conclusion that in any case the
molecule with a higher molecular weight and, thus, with a higher
adsorption heat is desorbed at higher temperatures. From this,
we further may deduce that the residual load increases with in-
creasing adsorption heat and that substances with high molecular
weight exist which are desorbed at such a high temperature that
their decomposition takes place before the theoretical de-
sorption temperature is reached. Normally, this phenomenon takes
place simultaneously with the formation of carbon deposits on
the surface. Furthermore, catalytic reactions of the adsorbate
during thermal treatment, enabling dimerisation, polymerisation
or condensation of the adsorbate, seem possible. Observations
of that kind are observed e.g. in the case of phenol. The re-
sulting residual load prevents the active centers of the activ-
ated carbon from being free after desorption,so that theoretic-
ally the initial activity of the activated carbon cannot be re-
established. An example is shown in Figure 7, illustrating the
adsorption capacity of different types of activated carbon
after a series of desorptions (3oo ninu't'B.s at 800 °C). The
activated carbon was charged with phenol.
All thus treated carbons exhibit
considerable decrease in activity, possibly continuing until
complete loss of the intial properties. For re-use of
activated carbon loaded in this way, a re-activation seems
appropriate.
Re-activation mechanism
Numerous investigations during production of activated carbon
have shown that at increased temperature steair and other fluids
react selectively with activated carbon in a way that the
-------
276
d V
dT
Fig. 6
adsorber outlet
adsorber middle
I I
adsorber inlet
ene
200
300
400
500 T [°C]
Desorption of various compounds from activated carbon
treated with waste water from a coke oven plant
100
Aktivitats-
anderg.
10 12 14
Regenerationszyklen
Fig. 7 Change of Adsorption capacity of different activated
carbons as a function of phenol adsorption and de-
sorption runs
Aktivitatsanderung : change in activity
Regenerationszyklen: regeneration cycle
-------
277
reaction takes place immediately on the inner surface of the
activated carbon. For this it is necessary that a temperature
range is chosen in which the chemical reaction exclusively
controls the rate for the whole course of reaction. Furthermore,
it was found that the reactivity of the carbon surface is locally
different. Faults in the grid structure or small crystallites
%
with many edges react better than crystallites with larger
surfaces. This might lead to the assumption that those
carbonaceous compounds formed in the course of the thermal de-
sorption treatment show a higher reactivity, due to their faulty
structure, than the surface of the activated carbon. As a
prerequisite, however, the activated carbon itself must have a
relatively homogeneous carbon surface so that its reactivity
is low from the beginning. Under these conditions it should be
possible to treat the loaded activated carbon e.g. by a careful
control of the water-gas reaction selectively, in a way that the re-
maining adsorbed rna.tter is purposely destroyed in order to re-
establish the previous surface structure of the activated carbon.
In this field, detailed investigations have been carried out
by Bergbau-Forschung. In the first place, these investigations
dealt with the reactivity of virgin carbon. A typical
result of these initial investigations is shown in Figure 3
illustrating the reactivity of different activated carbon
qualities as a function of temperature. ^ The term "reactivity"
stands for carbon matter gasified per unit of time by the
water-gas reaction. These tests were carried out under constant
partial pressure of steam. As expectei.f or all activated carbon
qualities tested the reaction rate of steam decomposition rose
exponentially with increasing temperature. It was surprising
that the individual activated carbon qualities exhibit sub-
stantially different reactivity, and that obviously the raw
material is a certain determining factor for these properties.
The reactivity of activated carbon made from wood is
particularly high compared with the low reactivity of activated
carbon made from hard coal.
9 shows the curve of the reaction rate of a loaded activ-
ated carbon at different constant temperatures as a function of
4) (REICHENBERGER, 1974)
-------
278
W
E-i
a
PC;
PH
CO
en
O
E-i
a
Fig. 8
2
700
800
900
Tf>mperatur[°C]
Reactivity of activated carbon produced from different
materials as a function of temperature
-------
279
min
06
04
02
0
—
— s
V r,«
.
\
x
— -«.^
_ _ _
so r
^~T=800°C
_ 1 ~ I
j
= beladen
= unbetaden
-
i
7SV'C
5 15 3C 45 ' 60 75 90
ZeitfminJ
•f*
Lrr,
0,7]
0.5
beladen
"~^x = unbeladen
N !
_. _ \^ _. i T=850'C J ,..
^" >.
x
^x
xv. r» eoo *c
i
"~~--_ T=750'C
, i — , — , — ,
°>~ — _ —-. _
^ I—,—,—, 1—,—,—,—I
5 15 30 45 60 75 90
Zeit [rnin]
Fig. 9 Reactivity of untreated activated carbon in comparison
to reactivity of carbon loaded with phenol (upper part)
and components of waste water from a coke oven plant
(lower part)
beladen: loaded
unbeladen: unloaded
Zeit: time
-------
280
time. The upper part pertains to activated carbon loaded with
phenol,and te lower part pertains to activated carbon used for
treatment of coke oven plant waste water- A common feature of
all curves is the fact that the loaded activated carbon initially
shows a higher activity than the fresh activated carbon. After
a characteristic period of time the initial reactivity decreases
and reaches the values of non-loaded activated carbon. It is
to be seen that the decrease to the reactivity values of un-
treated activated carbon is accelerated with higher reacti\etion
temperature. According to the previous considerations, this
phenomenon may be explained in that the water-gas reaction
actually destroys first the carbon contained in the load.
Further investigations have shown that the activity of regener-
ated carbon actually reaches its original value if reactivation
is stopped at the specific point of time at which the reactivity
has reached the value of fresh activated carbon. From figure lo
it may be seen that by reactivation of phenol-loaded activated
carbon at a period of stay of 2o minutes at 800 °C actually,
even after many subsequent reactivations,a state of unchanged
activity (upper section) and weight (lower section) is maintained
These reactivation conditions result from reactivity investig-
ations. It is left up to the engineer to determine the reaction
conditions for each specific case by appropriate choice of
temperature and period of stay for the solid matter. Of
course, these reaction conditions depend to a very large extent
on the kind and quantity of the adsorbate,as well as on the
quality of the activated carbon used. By appropriate preliminary
tests, however, it is generally possible to determine the
conditions of desorption and reactivation enabling best-possible
re-establishment of activity and very low losses of activated
carbon during treatment. Losses of activated carbon occur always
if reactivation is not carried out as selectively as described
here. In such cases, the achievement of activity implies over-
activation, i.e. a part of the activated carbon adsorbent
is destroyed during reactivation.
5) (JUNTGEN, KLEIN, 1974)
-------
281
Aktiyitatsdnderung (
JO 12 U
Regenerationszyklen
RestbeladungfGew. %]
12
-20-
-40
Aktivierungsgrad 38
T = 800 °C
\,t=1
024 6 8 » 12 74
Regenerationszyklen
Fig. 10 Effect of residence time on activity and change of
weight of activated carbon
Aktivitatsanderung: change in activity
Regenerationszyklen: regeneration cycle
Aktivierungsgrad: degree of activation
Restbeladung: residual loading
OKW %: % by weight
Aktivierungsgrad 38: Activation grade 38
-------
282
Regeneration process
In practice, usually desorptiori and subsequent reactivation
can be carried out in one process unit which, however, should
be designed in a way to allow for appropriate sequence of oper-
ation steps.In special cases, two-stage operation is re-
commendable, i.e. if the adsorbates are to be recovered
during desorption. In the past, generally rotary kilns were
used for regeneration. In recent years, fluidized-bed rege-
neration has been practised to an ever-increasing extent.
Fluidized-bed regeneration offers the following advantages:
1. Due to favourable heat and material transfer, the reaction
is faster,so that'smaller reaction volumes are required
and the process takes less time. Thus, the reaction space
of the fluidized bed can be kept considerably smaller than
the one of rotary kilns.
2. The particles are in suspension during reaction. Thus,
abrasion losses are smaller than with rotary kilns.
3. On the basis of sufficient knowledge and by means of
appropriate techniques, the retention time distribution for
the solid matter in a continuously operated fluidized bed
may be controlled, i.e. the required average period of
stay can be reliably adjusted and rapidly re-adjusted
or adapted, if necessary, according to the operational
requirements.
4. By a reactor design it is possible to impose strict limits
to the retention time distribution so that a homogeneously
reactivated product is obtained and, at the same time,
the losses during reactivation are minimized.
However, design and construction of a fluidized-bed reactor
require considerably more information than the construction of
a rotary kiln.
-------
283
Conclusions
It has been shown that regeneration comprises two steps,
i.e. desorption and reactivation; both have been investigated
as to the phenomena involved, and can now be controlled
operationally. In normal practice, one single process unit
t
comprising different zones is used. At present, the use
of a fluidized bed for reactivation is to be regarded as
the best techniaue.
-------
28^
OPERATION, PROBLEMS, AND ECONOMY OF ACTIVATED CARBON
REGENERATION
by B. Strack, Wuppertal
Introduction
The use of activated carbon in industrial processes for the
adsorption of organics from liquids and gases has been known
for centuries. In the waterworks of the Lower Rhine activated
carbon has been used for water treatment since the 1960s and
is becoming of increasing importance.
The constantly increasing problems of water treatment and thus
the increasing use of treatment material and chemicals forced
the waterworks to give further considerations to the use and
to the economical regeneration of suitable activated carbon.
As the problems in the different waterworks of the ARW
(Arbeitsgemeinschaft Rheinwasserwerke) were of a similar
nature, an intensive exchange of experience has been taking
place in recent years.
Outstanding support was given in this connection by the
Water Chemistry Section of the Engler-Bunte-Institute at
Karlsruhe, the Mining Research Institute at Essen, together
with the manufacturers and suppliers of activated carbon
and constructors of the relevant processing plants.
Present processing techniques
At present, activated carbon is bought from and regenerated
by the manufacturers situated in Germany and abroad. The
regeneration requires an exact schedule planning and agreement
between the waterworks, the transport firms and the activated
carbon manufacturers.
-------
285
7-i.ny interruptions which may be caused by one of the firms
taking part may lead to a disruption in the processing sequence.
This makes it essential to maintain appropriate capacity for
storing exhausted, regenerated, and virgin carbon. Also, there
must be facilities for the removal of carbon and the filling
of the filters. The same applies to the loading and unloading
of the carbon transporters.
Apart from considerations of economics, the technical require-
ments led to the conclusion to include the regeneration furnace
in the waterworks in the carbon cycle between the filter,
storage containers and the transportation facilities.
As the additional facilities would require further space and
would also incur higher costs than the actual reactor, and
as these facilities would have to be adjusted to meet the
requirements of each waterworks, the planning and tests descri-
bed here for the Benrath waterworks of the city of Wuppertal
are to be regarded as an example. Therefore, a description of
this waterworks is given below.
Layout and operation of the Benrath waterworks
The waterworks is divided into 6 main sections:
raw water tank, 6OOO m capacity
plant house
filter plant, consisting of 16 filters
pure water tank, 10OOO m capacity
sedimentation tanks and sludge treatment facilities
auxilliary buildings
The positioning of the individual sections of the waterworks
is dependent on the process requirements. A layout of the
works is shown in Fig. 1
-------
286
Fig. 1: Ground plan of Benrath waterworks
The Rhine bank filtrate is lacking in oxygen and contains
small quantities of iron, manganese and ammonium ions. It
contains excessive aggressive carbon dioxide and is heavily
loaded with organic odour and taste substances. Based on
pilot plant tests, a treatment process was chosen with the
following process steps:
Open Spraying Tower - Ozone Contact Filtration
Activated Carbon Filtration
Fig. 2: Schematic layout of the Benrath water
treatment plant
During spraying the raw water is saturated with oxygen,
whereby iron and manganese are converted to their tri- and
quadravalent states, resp., in which form they may be re-
moved by filtration. At the same time dissolved free CO9
and volatile odour and taste substances are expelled.
In the second step the water passes through an ozone-contact
filter. Here the organic components which have not been ex-
pelled in the first step react with the ozone whilst the
iron and manganese are removed at the same time by filtration,
and the remaining excessive dissolved CO_ is converted to
carbonate. This filter is a combination of a closed "dry filter'
and an ozone washer, where the usual ceramic packing is re-
placed by quartz gravel. The water passes through the large
contact surface of the filter material in the presence of an
ozone-containing air mixture, maintained slightly above
atmospheric pressure. The ozone is almost completely stripped
out and is used to oxidize the dissolved organic material.
The exhaust air from the ozone contact filter is passed to
the spraying tower where any remaining residual ozone is
removed.
-------
287
Fig. 1
- a -
c . , .,.,,.
5 auxiliary buildings
6 sedimentation tanks
1 raw water tank
2 plant house with spraying tower 7 sludge dewatering plant
3 filter plant 8 reactivation plant
4 pure water tank 9 .natural gas regulating station
Offene Steilverdlisung - Ozon-Kontaktfi"ltration - Aktivkohlefiltration.
5 Verdusung
2 Rohwasser- „ '
Mischkommer Rohwasser
lOTrockner
—D—
90zoneur 11 Verdchter
6000m3 Pumpe 4
emufer
filtrat 3
Fig. 2
'Rohwasser: raw water
'Rohwasser-Mischkammer: raw water mixing chamber
3Rheinuferfiltrat: Rhine sandbank filtrate
*Pumpe: pump
sVerdusung: sprinkler unit
*Ozonung und Filterung: ozonization
and filtration
7 Kies: gravel
»Aktivkohle: activated carbon
9Ozoneur: ozone generator
lOTrockner: drier
nVerdichter: compressor
uWasser: water
"Reinwasser: treated water
uChlorit-Lb'sung: chlorite
solution
-------
288
In the third step the water is passed through an activated
carbon filter. This treatment step gives the water its final
polishing by adsorption of organics, removal of residual
ozone and odour and taste substances, and by biological
degradation of ammonium ions.
The filters consist of 16 two-story units, the upper con-
taining the ozone contact filter (dry filter) and the lower
the activated carbon filter. The filters are constructed of
prefabricated reinforced concrete and are pre-stressed in
3 axes. They have an inside width of 2.7 m and an internal
length of 14.O m, and each has a filter surface area of
2
37.8 m . The filter veloci'
filter is shown in Fig. 3.
2
37.8 m . The filter velocity is 12 m/h. A diagram of a
The water distributors in the ozone contact filters consist
of ring pipes equipped with so-called full jet spray nozzles
which have a square spraying area. The spraying areas, arranged
in a row, provide a uniform distribution of water in the filter.
Fig. 3: Cross-section of a filter, pipe-layout
From a distribution ring main the ozone-containing air is
passed through flow meters to the filters, co-current with the
water. The water level in the filters is kept constant below
the filter support tray with the aid of an externally installed
automatic float valve.
Activated carbon filtration is carried out in wet-filters.
Six tube generators are used for the production of ozone,
each with a capacity of 2.5 kg/h, which give a total capacity
of 15 kg/h. The plant allows an ozone dosage of up to 2 g/m
water. The exit air is then compressed with water-ring pumps.
It is then passed through a water separator and two parallel,
automatically operated cooling and drying columns, before
reaching the ozone generators.
-------
289
Filter 8-16
Entluftunq
Fig. 3
Entliiftung: ventilation
Rohwasser: raw water
Spiilluft: backwash air
Kies: gravel
Kohle: carbon
Waschwasser: backwashing water
-------
290
The backwash water from the filter is pumped to three sedi-
mentation tanks. The thickened sludge is de-watered in
chamber filter presses and is then disposed of.
Activated carbon regeneration
Method of regeneration
Under certain conditions, biological regeneration of the
activated carbon in the filter can be of advantage, because
a regeneration outside the filter is then only rarely necessary.
However, this procedure has not been tested sufficiently to
give generally valid information, and it may be that it can
only be used in special cases.
It is also possible to use chemical regeneration where the
adsorbed substances are removed from the carbon by extraction,
using an organic solvent. However, in waterworks chemical
regeneration creates problems because of the toxicity of the
solvents and the difficulties inherent in their removal from
the carbon.
It appears that thermal regeneration of activated carbon
produces the least problems. Although the mechanism of re-
generation has not been completely explored and there are
still many tests necessary for the optimization of a
regeneration plant, it can be said with certainty that such
plants can be operated in waterworks.
Types of regeneration furnaces
For regeneration three main types of furnaces are used.
These are the rotary kiln, the multiple-hearth furnace and
the fluidized-bed furnace. On account of the experience
-------
291
already available, a fluidized-bed furnace was chosen for
regeneration, in a waterworks, whose main task is not the
regeneration of activated carbon, the operation of such a
plant must be easy to perform by the existing staff. The
fluidized-bed furnace meets these requirements to a large
extent by the following characteristics:
- simple construction, no movable parts
short start-up and turn-off periods due to low
sensitivity against temperature changes
simple supervision and control
- low losses in regeneration
- satisfactory efficiency
Regeneration at the Benrath waterworks - planning, tests,
operation
The regeneration furnace
The projected furnace, a single-step fluidized-bed furnace,
is designed to meet the following requirements:
throughput: 2OO kg/h dry carbon, initial moisture
5O % water, final moisture O % water
bulk weight of the loaded wet carbon: 55O kg/m
granulation size of carbon: O.5 to 2.5 mm
specific heat requirement of carbon: approx. O.2 kcal/kg
and 1 C
temperatures: feed approx. 10 °C, finished product approx.
6OO °C, combustion gases before the fluidized bed approx.
1OOO °C, afterburning at approx. 9OO °C, exhaust gases
after afterburning approx. 5OO °C
energy requirements: 115 m /h natural gas for the reactor
including afterburning
current: approx. 3O kW; water: approx. 4OO kg/h (liters/hr)
-------
292
Figure 4 shows a schematic layout of the furnace.
The natural gas is stoichiometrically burnt in a superimposed
combustion chamber, and the combustion gas is cooled down to
the desired temperature by injection of water. The gas mixture
enters the fluidized layer of carbon through a distributor
ensuring even distribution.
Fig. 4; Regeneration furnace
The distributor tray is made of a refractory, compressed
material with heat-resistant nozzles. No additional sections
are provided for the fluidized layer because the tests, made
with different types of activated carbon, produced in each
case a satisfactory homogeneous regenerated material.
The furnace chamber widens above the fluidized layer. Due to
the reduced gas flow velocity, this results in a stabilization
of the fluidized layer on the one hand, and a limitation of
the dust discharge on the other.
The dust granules discharged from the fluidized bed have a
diameter of less than O.2 mm. This dust would also be elimi-
nated with the backwashing of the filters.
The retention time of the carbon in the furnace is dependent
on the height of the fluidized layer at a constant rate of
addition of carbon. The adjustable outlet weir allows a
variation of +_ 50 % in the height of the fluidized layer
and thus also of the retention time. In addition, the retention
time can be regulated by the rate of throughput.
The outlet temperature of the regenerated carbon is used as
the normal set point for the process. At a constant throughput
of fuel gas this temperature is stabilized by altering the
speed of rotation of the feed screw.
-------
293
I
Ficj. 4 .
1) i'luidized bed plant
2) product inlet
3) discharge arid control for height of fluidized
•i) Hue yas inlet
5) rlue gas outlet
Beruhigungs raum - Chamber for quieting gas flow
Wirbelsch icht - Fluidized bed
Zuluftkasten - Incoming air chamber
-------
29^
Fig. 5: Schematic layout of the regeneration plant
The furnace is connected with an afterburning chamber. The
exhaust gas analyses obtained from the test reactivations
and the regulations from the "TA Luft" (technical regulations
for retaining air clean) make it necessary to provide for
waste gas purification. This is shown schematically in Fig. 5.
The waste gas passes through a double cyclone before reaching
the combustion chamber which is heated with an infinitely
variable reaction burner. The furnace air is pre-heated in a
heat exchanger by utilizing the heat content of the purified
waste gas. Dust separation and afterburning guarantee that
the quality of the waste gas meets the requirements of the
"TA Luft", i.e. that the dust discharge is less than 75 mg/m .
Auxiliary plant, transport facilities
The regeneration plant is installed in its own building. As
indicated in Fig. 6, the building consists of a reinforced
concrete supporting structure with a light metal facing.
Fig. 6: Activated carbon regeneration plant building
Three rectangular concrete silos form one end of the building.
The building is located in the waterworks in such a position
that the transport distance for the carbon between the filter,
the regeneration plant and the carbon discharge trays is as
short as possible.
A schematic layout of the complete activated carbon system
is shown in Fig. 7.
-------
295
Fig. 5
Ron-Abgas:
L u r i:: a i r
o C a u o: u w s
flue a a s
Fig. 6: Activated carbon regeneration plant building
-------
296
The exhausted activated carbon is hydraulically transported
from the filters to the activated carbon sedimentation tank.
The tank simply acts as a buffer so that the time for back-
washing and discharge processes can be kept as short as
possible.
Fig. 7: Activated carbon regeneration plant with
transport-, storage- and auxiliary facilities
The exhausted carbon is transported, using an injector, from
the sedimentation tank to the exhausted carbon storage silo,
a process normally taking one hour.
The exhausted carbon silo has, similar to the other two silos,
a capacity of approx. 88 m and can take the carbon from one
filter. From the silo the carbon is hydraulically transported
via a gravel-carbon-separator to an intermediate tank. In this
separator the supporting gravel, carried with the carbon from
the filter, is then separated from the exhausted carbon. This
is necessary as the gravel interfers with the operation of the
injectors and the regeneration furnace. The separator was
especially developed for this purpose and produces a carbon
product containing less than O.5 % gravel.
The intermediate tank, of 8 m capacity, acts as a storage
tank for the feed screw on the regeneration furnace. With a
regeneration capacity of 2OO kg/h dry carbon, a buffer period
of about 2O hours is obtained when there is no carbon feed.
The de-watered carbon is then fed to the fluidized bed. After
the regeneration process the reactivated carbon is cooled in
a quenching- and wetting tank. The hot gas contained in the
carbon contracts so that the cold water may easily fill the
pores. The remaining gases are dissolved in water and the
carbon is wetted. The available storage volume of the
quenching tank gives a two-hour buffer period.
-------
297
-'•d '
j , accivaueu car bur, j.j.ir.er
._ ; seairnen cation basin
j) storage tank i'or loaded carbon
••\] separation plant
:>) intermeaiate tan!-;
o) conveyinq screw
'/ ', rii'.:ii- uciinperature riuici^ed oeo
•
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298
From the quenching tank the reactivated carbon is conveyed
by an injector to the washing tank, where the fine carbon
particles are washed out. From the washing tank the carbon
is transported to the reactivated-carbon silo. This silo
provides the necessary buffer period of about 4 hours
required for the filling of a filter with carbon.
In the third silo the new carbon - to replace that lost in
regeneration - is stored. Before being used in a filter, the
new carbon is wetted in the rinsing- and wetting tank where
it is subjected alternatively to increased and to reduced
pressure, and it is then passed to the reactivated-carbon
silo where it is mixed with the other carbon.
The water used in the transport process is passed to a tank
which has an internal volume of 3O n . Into this tank the
water discharged from the containers carrying activated carbon
is also passed. Any carbon carried in the water settles to
the bottom of the tank, from where it is then passed to the
exhausted-carbon silo by an injector. Finally, the water
flows to the sludge sedimentation tanks.
The activated carbon is transported from the sedimentation
tank to the silo for exhausted carbon in a stainless steel
pipe, NW 125. The pipeline is coated with synthetic material
and layed in such a way that it can be cleaned or freed from
blockages without difficulty. The outer wall of the pipe bends,
which have a large radius of curvature, are double-skinned to
allow for abrasion wear. At the Diisseldorf waterworks they
are lined with basalt.
The carbon washed into the sedimentation tank contains about
2 - 3 % gravel of various sizes, ranging from O.7 to 1O mm.
Since the gravel may interfere with the operation of the
injector, a sludge pump is provided as an alternative. As
the level of the carbon in the tank alters, the position of
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299
the sludge pump is shifted, using an electric hoist. The
rate of discharge of carbon from the tank to the silo is
adjusted by a suitable control system.
The speed of ascent of the activated carbon/gravel mixture
entering the silo is kept below 1.6 m/h. Previous experiments
have shown that, at a velocity of 1O m/h, activated carbon is
washed out through the overflow pipe. During the filling
process a gauge intermittently measures the height of the
carbon in the silo. The measured value is transmitted to the
sludge processing- and activated-carbon regenerator control
panels. The filling process is switched off manually when
the desired height of carbon has been reached.
Conveyance of the carbon from the silo to the intermediate
tank, via the separation tank, is automatically controlled.
When the minimum carbon level in the silo or the maximum
carbon level in the intermediate tank are reached, the con-
veying process is halted. It re-starts automatically when
a minimum level is reached in the intermediate tank.
Contrary to this, when the level in the silo reaches a
minimum value, the process has to be re-started by hand
after the silo has been refilled.
With an intermediate tank filled with carbon and the wetting
tank filled with water and after the desired furnace tempera-
ture has been reached, the feeding screw is automatically
started and carbon is fed into the furnace. The intermediate
tank is filled automatically, controlled by an impulse con-
tactor. If the filling process is interrupted the feed to
the furnace is continued for another hour, then the furnace
is switched off, having received optical and acoustical
signals. Only when the intermediate container has been re-
filled can the furnace be restarted, either automatically
or by hand.
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300
An alternative example of the external storage and transport
of activated carbon is provided by the Diisseldorf waterworks.
Here silo trailers are used for the intermediate storage and
transport between three waterworks, in addition to the fixed
silos. The transportable silos can be connected to any fixed
silo. They are also used for the transport of exhausted and
regenerated carbon. A schematic layout of this plant is shown
in Fig. 8.
Fig. 8: Transport system, external storage
(Diisseldorf waterworks)
The processing tests for the separation of gravel and carbon
led to the installation of continuously operating separation
equipment. The separator is filled by hand before the gravel/
carbon mixture is introduced through two diametrically opposed
feed pipes, and is at the same time automatically vented. The
gravel separates from the carbon due to the different settling
velocities of the two materials. The activated carbon slowly
fills the separator and is removed through a pipe at the top
of the separator. When the gravel has reached a maximum level
in the separator, it is removed (see Fig. 9).
Fig. 9: Gravel/carbon separator
Here the E-armature exit pipe is automatically opened by a
radioactive sensor and is closed after gravel removal is
complete by a second sensor. If there is an interruption
during gravel removal there is the danger that gravel is
carried with the carbon to the furnace. Therefore a time
relay gives an optical and acoustical signal when the
maximum gravel level is maintained longer than a set time.
The separator has a diameter of 8OO mm and a height of
185O mm. The base is fitted with nozzles, 10O per m .
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301
i Auffang- sReaktiv- 3 Frischkohle
Silo Kohle
4 zum Reaktor
7 Kohlefliter
5 Siloanhdnger (externer Transport)
Fig. 8
lAuffang-Silo
jReaktivkohle
3Frischkohle
4 zum Reaktor
5Siloanhanger
'Frischwasser
receiving silo
reactivated carbon
fresh carbon
to the reactor
silo trailer (external transport)
fresh water
vom/zum Kohlefliter: from/to activated carbon filter
activated carbon - reactivation plant - transport system
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302
Kohleabzug
c
Gemischzugabe •• «_
0 - 2 m/h ' mf
1
\s \ v
v\
\
\
\ N
< X . \
^y
x$$
K'<."V
_Xy/V_V
<•////
\
' 1
X7
I
1
6
t U
2 8
:»-,
/ §
^
S
2
1
TTT
Spii/wosser Q-6f25rif/h , y-SOm/h
Fig. 9
Kohleabzug : carbon outlet
Gemischzugabe: mixture feed
Spulwasser : backwash water
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303
New carbon is supplied in a silo-transporter. The hose of
the silo-transporter is coupled to the fresh-carbon silo
injector. The silo volume has been designed so that it holds
the contents of several transporters, which at the same time
ensures that unwetted carbon is not carried av/ay with the
overflow v/ater.
During the filling process a sensor measures intermittently
the filling height of the carbon. This data is transmitted
to the control panel of the carbon regeneration plant. When
the silo-transporter is empty, the filling process is switched
off manually. After completion of the filling the water supply
valve is opened and the water rises up to just below the
overflow level, the level being controlled by a float valve.
After some days the carbon is superficially wetted. The final
wetting is carried out under pressure in the flushing and
wetting tank.
As already described, between 2OO 1/h (normal) and 400 1/h
(maximum) of water are required for the regeneration furnace
as spray water for the regulation of the temperature of the
combustion gases. On account of its composition, the v/ater
has to be processed with an automatically operated quality-
controlled water softener. The regeneration of this plant
is also carried out automatically.
Because they may cause trouble in practice, some ''groups"
of problems concerning the auxiliary plants are to be
mentioned separately. For feeding equipment there was the
choice of injectors, channel impeller pump, feed containers,
feed screws. The feeding of the water-activated carbon mixture,
at a rate of 3 : 1, was to be undertaken with as low a wear
and tear as possible and at a low energy expenditure. Of most
advantage seems to be the use of injectors because they show
the least wear. In addition, water with the required pressure
is available to operate the system.
-------
The channel impeller pump causes an increased abrasion of
the feeding material and is itself subjected to wear and
tear. When used in a container, the re-adjustment of the
pump requires an increased technical effort. In addition,
electrical energy is required.
Feeding containers operate intermittently. This method is
also low in wear but has not been sufficiently tested.
The feeding screw undertakes the important task of providing
the reactor with a constant supply of activated carbon while
at the same time separating the carbon from the water and
providing an air-tight seal. For this purpose, attention
must be paid to the setting angle, the clearance number of
turns, the pitch and the rotational speed. If it is in-
correctly constructed, the moisture content of the carbon
will be too high, or the feed rate of the carbon insufficient,
or the attrition of the carbon will be too high. All this
will affect the regeneration process. Figures 1O, 11 and 12
show some data on the feed screw performance, the effect of
rotational speed on water content (which also depends on
the type of carbon), and of the slight size reduction of the
granules caused by the feeding process.
Fig. 1O: Capacity of the feed screw
Fig. 11: Water content of conveyed activated carbon,
dried at 11O °C, 24 hours
Fig. 12: Attrition test of activated carbon after
repeated passage through the feed screw
-------
RPM
I
60
50
40
30
20
10
305
oooo ooooooooooooo
ooooooooooooooooo
~ Liters/hour
Fig. 10 Capacity of the feed screw
100 -
80 -
60 -
40 -
20 -
10
20
30
50
RPM
Fig. 11: Water content of conveyed activated carbon,
dried at 11O °C, 24 hours
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306
10,0 —
Jl
I-
5.0 —
Forderschnecke fur WW Benrath
Chemviron F300 nach
30-fachem Durchgang
durch die Forderschnecke /
T-Chemviron F300
I I I I I I I I I I
05 1.0 1.5 2.0 2J5
Particle Size - mm ^
Fig. 12
F'orderschnecke fur WW Benrath: conveying screw for Benrath
waterworks
Chernviron F300..-: Chemviron F300 aTter passing through the
conveying screw for 30 times
Gew.-%: weight per cent
-------
307
It has been found that stainless steel was the most suitable
material for containers and pipe bends which come into contact
with activated carbon. In addition, it is corrosion-resistant
and has a good coefficient of friction. For straight pipe
pieces synthetic material is sufficient.
The velocity of the water/carbon mixture in the pipelines can
only be varied within certain limits. If the velocity is too
high, there is a high abrasion of the carbon and wear of the
pipelines, while if the velocity is too low carbon is deposi-
ted, which leads to blockages. Experience shows that veloci-
ties between 1.5 m/s and 3 m/s are free from interference.
Continuous measurement of the quality of the regenerated
material is also a problem, which is being investigated at
many places including the Engler-Bunte-Institute at Karlsruhe.
Of particular interest is a simple and rapid control method
for the operator which, circumstances permitting, could be
used to control the operation of the regenerator. The present
regeneration tests consist of measuring the bulk weight, the
hardness, the ash content and the benzene load for volume
ratios of 9/10, 1/1O and 1/1OO. In addition, isotherms are
determined by UV extinction at 254 nm and compared with the
values of new carbon. Also the methylene-blue number and the
molasses factor are used for further evaluation. Some test
results are shown in Fig. 13 and Table 1. In addition, in
Table 1 screen analyses are shown of the distribution of
granule sizes with the number of regeneration cycles.
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308
0,020 -
0.015-
0.010
0,005
10 mg
30 mg
50mg
A-Kohle
Fig. 13: Adsorption isotherms after
repeated regeneration
1 - isotherm new activated carbon
2 - isotherm after first reactivation
3 - isotherm after third reactivation
4 - isotherm after fifth reactivation
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309
Table 1: Comparison of new and regenerated
activated carbon
Measuring procedure: 1 1 water +
1O/3O/50 mg powdered activated carbon
is stirred for 2 h at 7O rpm. It is then
centrifuged and the UV adsorption is
measured at 254 nm in a 1 cm cuvette.
Probe
Schuttgewicht kq /I
Siebonalyse Gew %
» 3,15mm
2,00 3,15mm
1,25 - 2.00mm
0,80 - 1,25mm
- 0,80mm
Harte in Gew %
Benzol beladunq Gew %
'/10
710
Ascheqeholt Gew %
UV-Adsorphon
254 n m / 1cm Kuvette
0 mg
10 mg
30 mg
50 mg
F300 Neu
0,485
0,5
26,0
40.0
29,1
4,4
98,9
28,5
33,0
4,2
0.039/ AUV
0,033/0.006
0.025/0.014
0.018/0.021
FSOOReakhvat
Ixreaktiviert
0,480
0
24,3
39,7
27,1
8,9
95,0
29,0
34,9
5.2
0.039/ AUV
0,033/0.006
0.024/0.015
0.017/0.022
3«reaktiviert
0,490
0
20,1
44,0
27,4
8,5
93,5
28,2
34,3
6,8
0.039/ AUV
0,033/0006
0,024/0,015
0.018/0.021
0,490
0
10,3
48,0
31.6
10.1
91.8
26,5
33,9
8,2
0.039/ AUV
0.032/0,007
0.023/0.016
0.016/0.023
Table 1
Schuttgewicht: bulk density
Siebanalyse: grain size
Hiirte in Gew';t>: hardness in weight per cent
Benzolbeladung: benzene loading in weight per cent
Aschegehalt: ash content in weight per cent
Probe: sample
F 3OO neu: F 30O new
reaktiviert: reactivated
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310
Economics
The planning was preceded by an investigation of the economics
of the regeneration process. Taking as a basis a regeneration
plant with a throughput of 5 t/d, it was found that the plant
was sufficiently utilized when the annual throughput is of
the order of 1000 tons per year.
On-site regeneration was estimated at about 40O DM/t, com-
pared with 10OO DM/t when regeneration is carried out at
another plant. This means that the investment of about
2 million DM for the regeneration plant will amortize quickly.
The calculations, which have to be compiled for each indi-
vidual works, take into account: regeneration costs at an
outside firm, transport costs, regeneration and transport
losses, energy costs, labour and maintenance costs, servicing
of investment.
With regard to the investment costs, it must be remembered
that particularly in the case of plants with a capacity of
up to 5 t/d there is a rapid reduction in the specific cost.
However, with larger plants the specific costs diminish only
slightly. The following values were used:
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311
Natural gas : O.16 DM/ni3
Electricity : 0.1O DM/kWh
Investment service: 11 per cent
Shift length : 9 h/d
Maintenance costs : 5 per cent of the investment on
machinery and transport system
The losses during regeneration were estimated at 5 per cent,
and the total losses (including transportation) at approx.
15 per cent.
Final considerations
A report on the experience and the actual operation of a
regeneration plant can only be made after the plant has been
in operation for several months. Although it means a new
departure for a v/aterworks, due to the experience gained
with pilot plants and existing plants, sufficient safety is
guaranteed for a fault-free operation of the plant and its
economics.
The special advantages of a waterworks having its own
regneration plant are as follows:
1. To be in a position to satisfy at any time an increased
demand for activated carbon.
2. To be able to adjust the regeneration of the activated
carbon to the particular requirements to an optimum
extent, and to obtain a satisfactory regenerated material.
Finally, all these efforts serve the endeavour to supply the
public with an acceptable quality of drinking water.
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312
INVESTIGATIONS CONCERNING THE MICROBIOLOGY OF ACTIVATED
CARBON FILTERS
by M. Klotz, P. Werner, R. Schweisfurth, of Homburg/Saar
Introduction
Activated carbon is used to an increasing extent for the
processing of drinking water from surface- and ground waters -
and perhaps even from wastewater in the future. Practical
experience has shown that there is a mass increase of micro
organisms (bacteria and fungi) in the carbon filters and also
in the filtrate.
Almost nothing is known of the basic factors controlling the
formation of a micro flora, its activity, numbers, species
and composition in the system under discussion, i.e. flowing water
of varied chemical composition and activated carbon. In addition,
little is known of the influence of the micro organisms on
adsorption and desorption.
Investigations on this problem reported in this paper were
carried out in close cooperation with several waterworks; the
keypoint was at the Rhine-water treatment plant at Wiesbaden-
Schierstein, whose equipment and facilities were used.
Methods
From a methodical point of view, the definition of the amount of
micro organisms in the water presents no difficulty if, after
an adequate pretreatment, nutrient media, breeding temperature
and breeding time are suitably chosen.
The definition of the colony numbers present in the water,
as recommended by "DEV" (Deutsche Einheitsverfahren = German
Standard Methods) proved to be inadequate for our investigations
because only a small part of the micro flora is covered by this
method. As expected, all nutrient media tested showed considerably
increased colony numbers after breeding for seven days, than
after breeding for two days. The best media for a quantitative
coverage of micro organisms was found to be P-Agar which
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313
contained few nutrients (WOLTERS,1956) and SPC-Agar which was
rich in nutrients (STANDARD METHODS 1966), both were incubated
at 27 °C for more than 7 days. The colony numbers shown in
Fig.1 refer to the medium rich in nutrients. The activated carbon
was crushed in a simple mixer and the homogenized material was then
processed for the determination of the colony numbers in the same
manner as water samples.
The cell number, i.e. the total number of all living and dead
bacteria, was determined by microscopical counting after accumu-
lation on the membrane filters and colouring.
Apart from a few modifications, the tests were carried out as
recommended by D E V whenever possible.
Fig.1: Annual mean values of colony numbers of bacteria
in dependence of the treatment steps at the Rhine-water
processing works at Wiesbaden-Schierstein (obtained
from SPC-Agar after an incubation of 7 days.
Results
1. Quantitative coverage of the population of micro organisms
1.1 Survey of the colony numbers in the different treatment steps
For a better understanding of the work presented below, it is
necessary to know the method of treatment used at the Wiesbaden
works, where Rhine-water is pretreated before infiltration
for an artificial augmentation of the ground water. The water is
taken from the river, aerated, plain settline , after which
it is chlorinated and flocculated. Then follows a rapid filtration
through sand and activated carbon before the water is infiltrated
into the underground. In Fig. 1 the mean values of the colony
numbers are given from March 1973 to March 1974. There is a decrease
of the colony numbers between the Rhine and the entrance to the
carbon filter (sand filtrate). The biggest effect is achieved
/-point
by the break/chlorination. Fresh populations of micro organisms
are formed in the activated carbon filters, so that very high
colony numbers can be traced at the filter exits using the
special method. Using the methods normally applied
for the definition of colony numbers, as recommended by the DEV
for the control of drinking water, the water quality is satis-
factory as a rule.
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311*
AKoloniezahl/ml Wasser(SPC)
10 T ^
Aufbereitunqsstufen-
Fig.
Aufbereitungsstufen: treatment steps
Koloniezahl/ml Wasser: colony numbers/ml water
Werkseinlauf: works inlet
Sammelablauf: collecting outlet
Aktivkohlefliter: activated carbon filter
Sandfiltrat: Sand filter effluent
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315
1.2 Composition of micro organism populations in an
activated carbon filter
The composition of these populations was examined in freshly
filled large filters and test plants. The test plant was
dimensioned as follows: 4 successive glass tubes with an
inside diameter of 4 cm. Layer height of the activated carbon
bed 3.2 m (4 x 0.8 m). The behaviour of the micro-organism popula-
tions was found to be the same in both the test- and in the large
filters. Passage of water through each individual filter is called a "filter
step."
Within the first 2O day the colony numbers reached a maximum -
after a linear increase - of 10 to 1O /ml of water, after which
they declined an<^ remained at a slightly lower level (see Fig. 2) .
In the beginning there were large differences at times between
the individual filter steps, which disappeared after about 3O days
after the level phase had been reached. Examination of the formation
of the micro organism populations on the carbon show
that the characteristics described above for the conditions
present in the water are not very marked (see Fig.3). Because
the inflowing water contains bacteria, the originally germ-free
carbon has high initial colony numbers. They reach values of
10 to 10 /g of wet activated carbon after some time.
Fig.2; Composition of micro organism populations in a test filter
(colony numbers in the water obtained on SPC-Agar after
7 days' incubation)
Fig.3; Composition of micro organism populations in a test filter
(colony numbers on the carbon obtain on SPC-Agar after
7 days' incubation)
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316
Koloniezahl/ml Wasser (SPC)
Stufe 1
— Stufe 3
Koloniezahl/gA-Kohie( naf))
' (SPC)
• Auslauf
Stufe 1
.Stufe 3
60
Zeit (Tage)
Stufe 2
Stufe U
Abb.2
Abb. 3
Fig. 2,3
Koloniezahl/ml Wasser: colony numbers/ml water
Zeit (Tage) : time (days)
Stufe: step
Auslauf: outlet
Koloniezahl/g A-Kohle (naB): colony number/g activated carbon (wet
-------
317
1.3 Influence of the filter velocity on the
construction of the population
Based on the filter velocities used at the Rhine-water processing
works, a range of 4 to 20 m/h was chosen for the test plants.
The slope of the curves during the initial phase (see Fig.2)
decreases with increasing velocity and with increasing filter
length. The maxima are more pronounced as the velocity decreases.
At the level stage there are only slight differences, the colony
numbers are lowest with the lowest velocity.
1.4 Microbiological and chemical conditions in an operating
large filter
With the aid of a characteristic individual test, the conditions
as they are typical for an °P^r
-------
318
10%
Kolonie-bzw Zellzahl/ml Wasser
freies ChlorbigA)/
-0,4
-0,3
-0,2
-0,1
o Koloniezahl / ml Wasser
o Zellzahl/ml Wasser
- -o freies Chlor (mg/l)
Fig. 4
Kolonie- bzw.Zellzahl/ml Wasser : colony- and cell number, resp.,/
ml water
freies Chlor: free chlorine
Sauerstoff: oxygen; Einlauf: inlet; Auslauf: outlet; Stufe: step
Koloniezahl /ml Wasser: Colonies/ml water
Zellzahl/ml Wasser: cell numbers/ml water
-------
319
In the uppermost carbon layers the chlorine content falls below
0.1 mg/1, where it no longer has any perceptible influence On the
increase of bacteria.
Anindicator for microbial activity is the change in the oxygen-
and carbon dioxide content of the water,- as shown in Fig. 5.
During the filter passage there is an oxygen consumption of approx,
1.5 mg/1 and at the same time there is a production of carbon
dioxide of approx. 4.5 mg/1 (to be compared with Table 2).
Fig. 5: Content of oxygen and free carbon dioxide in dependence
of the filter distance in a large filter
The change of the content of organics is illustrated in Fig. 6
by three parameters. In the case of the UV adsorption at 24O nm
and of the DOC the values decreased by about 55 % after the
filter passage, and by about 45 % in the case of KMnO..
Nevertheless, the change in degradability during filter passage
is slight, as the results of BOD,,-, BOD - and BOD- evaluations
show. The degradability of organics is also slight; this must
be taken into account when evaluating the activity of micro
organisms.
Fig. 6: Content of organics in dependence of the filter
length in a large filter
1.5 Behaviour of populations during a period of 3 years
The influence of the season and of the raw water on the micro
organism populations in the treatment steps at the Rhine-water
processing works was studied for several years. In Fig. 7
the relations for 3 characteristical steps are
presented: works inlet (Rhine-water after aeration and basin
passage), carbon filter inlet (sand filtrate) and carbon filter
collecting outlet (infiltration water).
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320
freies Kohlendioxid(mg/l)
° Sauerstoff (mg/l)
« frejes Kohlendioxid (mg/l)
0,13-
0,12-
0,11-
010-
009-
OJ38-
OP7-
006-
005-
0,(X-
0,03-
UV^bsorption(2/,Onm) Extinktion
g/D
KMnO^-Verbrauchlmg/l)^
3-
2-
-11
-10
9
- 8
- 7
- 6
- 5
- I,
- 3
o - o UV-Absorption(240 nmlExtinktion
- — «TOC(mg/l)
o- ....... -o KMnO^-Verbrauchlmg/l)
Fig. 5
Fig. 6
freies Kohlendioxid (mg/l): free carbon dioxide (mg/l)
KMnO.-Verbrauch (mg/l): KMnO. consumption (mg/l)
Sauerstoff: oxygen; Einlauf: inlet; Auslauf: outlet; Stufe: step
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321
Fig. 7
106-
105-
103-
102-
Koloniezahl/ml Wasser
MljIjlAJSlolNlO
1972
— Werkseinl.
jlFlMlAlMljIj UlslolNlD
1973
1974
1975
-Sandfiltrat • Kohlefiltersammelabl.
Werkseinlauf: raw water inlet
Kohlefiltersammelablauf: carbon filter collefcting outlet
Sandfiltrat: sand filtrate
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322
The special methods under discussion, developed for the
determination of the bacteria number - particularly after a long
incubation time of 7 days - are much better suited for a
quantitative determination of the micro organism populations
than the hygienic-bacteriological methods according to DEV.Using
this method,very high colony numbers were traced in the water
of the works inlet and of the carbon filter collecting outlet.
No conclusions can therefore be drawn from the colony numbers
given here on the hygienic-bacteriological quality of the waters
according to the present standard for drinking water. If these
waters are examined using the method prescribed by DEV
it appears that only the works inlet (i.e. the raw water)
contains equally high colony numbers, but that the carbon filter
collecting outlet meets the respective requirements. In this
connection it must be pointed out that tests carried out at
five German waterworks,using different treatment modes and
different raw water qualities,similar differences with the
results of the determination of colony numbers were found by
using the special method described above as compared with the
methods of the DEV. In all tested cases the outlets of the
activated carbon filters showed similarly high colony numbers. Simi-
lar observations have been reported by scientists in Switzerland
and the Netherlands.
Of some interest are also the efforts being made,aiming at
employing the micro organisms in the activated carbon filter
to improve the water - as against the previous intention to
destroy them. The conditions at Wiesbaden-Schierstein are as
follows: the influence of the seasons on the extent of colony
numbers is slight; however, there seems to be a tendency for a
decreased microbial activity in winter, as indicated by the
chemical data (oxygen consumption, carbon dioxide production.
Changes in the water quality (marked by 1 to 3 in Fig. 7)
resulted in a distinct change of the colony numbers.
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323
2. Activity of the micro organism populations in the
activated carbon filter
The problem of finding out to which extent the micro organisms
were responsible for the change of substances and/or their
decrease during filtration was solved by a comparison between
a sterile and an unsterile operated test filter plant.Parallel
with the large filters, two pilot plants consisting of 4
series-connected glass tubes with an inside diameter of 6 cm
were operated under similar conditions. The layer height of
the activated carbon bed was 2m (4mx0.5m). One of the plants
was kept free of germs by sterile filtration for more than two
months at a filtrate amount of 15m . All the other methods of
keeping the plant sterile have the disadvantage of the presence
of an additional bactericidal substance and of a large number
of dead micro organisms.
In order to increase the amount of degradable organic substances
the inlet was loaded with about 5O mg/1 phenol during the second
part of the test,by retaining the previously used activated
carbon.
Results of these tests are given in Tables 1 and 2. When the
filter inlet is unloaded (sand filtrate) the share of the micro
organisms in the decrease of organics is very small - as far
as it can be measured by UV adsorption, DOC and KMnO. consumption.
On the other hand, the share of the micro organisms in the
decrease of easily degradable organics is high. This is of special
importance because it means that the regrowth of bacteria that usually occurs
in the distribution system now occurs in the waterworks itself.
When the inlet is loaded with phenol the activity of the micro
organisms is slightly greater; it must be remembered, however,
that the adsorption capacity of the carbon was very high for
phenol.
Table 1: Percentage share of micro organisms in the removal
of organic substances during activated carbon filtration
Table 2: Percentage share of micro organisms in oxygen consumption
and carbon dioxide production during activated carbon
filtration
-------
32k
^^[tohwasser
Porameter^\
DOC
KMnO^
Verbrauch
UV-Absorption
2iO nm
UV-Absorption
254 nm
BSB2
BSB5
BSB20
Durchschnitt
der Mikroor
an der Entf
organischen
Sandfiltrat
<1,0 %
3,7 %
<:1,0 %
1,2 %
69 %
46 %
17 %
icher Anteil
ganismen
srnung von
Substanzen
phenol -
belastetes
Sandfiltrat
6,0 %
3,1 %
2.8%
6,2 %
-
Table 1
phenolbelastetes Sandfiltrat: phenol-loaded sand filtrate
Sandfiltrat: Sand Filter Effluent
Durchschnittlicher...Percentage share by microorganisms in the removal
of organic substances during activated carbon filtration.
Rohwasser: Raw water
KMnO, Verbrauch: KMNO. Consumption
BSB2: 2 Day BOD
BSB : 5 Day BOD
BSB •. 20 Day BOD
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325
^\^phwasser
Parameter\
Sauerstotf-
verbrauch
Kohlendioxid -
produktion
Durchschnittlicher Anteil
der Mikroorganismen
Sandfiltrat
58 %
61 %
phenol-
belastetes
Sandfiltrat
68 %
64 %
Table 2
Sauerstoffverbrauch: oxygen consumption
Kohlendioxidproduktion: carbon dioxide production
Durchschnittlicher...Percentage share by microorganisms
Phenolbelastestes Sandfiltrat: Phenol-loaded sand filtrate
Sand Filtrat: Sand filter effluent
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326
3. Distribution of micro organisms in the system water-carbon
3.1 Electron-scan microscopic examination of the filter granule
During the filter passage the micro organisms increase from
about 1O colonies/ml to about 10 colonies/ml. The doubling period
for bacteria is around 20 minutes, even at the optimum environment
conditions. This leads to the conclusion that, because the water
remains in the filter for a short time only, the increase of
micro organisms has to emanate from the bacteria on the
activated carbon.
Q
Tests have shown that there are colony numbers of up to 1O /g
of wet material on the carbon. The actual cell number, obtained
by cell counting, can exceed these numbers by almost 1OO %.
A variety of electron-scan microscopic tests of differently
treated activated carbons produced a general view of the
distribution of micro organisms on the filter granule: as a rule,
the micro organisms are sparsely scattered, they are always in
the form of a single bacterial layer; the area available (carbon
surface up to a pore diameter of 1 ,um) is only fractionally
utilized (about 1 %). This is even the case when the carbon had
been put into a nutrient solution for some time.
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327
3.2 Tests on the adsorption of micro organisms onto
activated carbon
It seems reasonable to explain the adhesion mechanisms of the
micro organisms onto activated carbon by the adsorption processes.
Investigations on the adsorption of micro organisms onto activated
carbon were made using starved and washed bacteria (mixed
populations) in a nitrogen-free environment.
Fig. 8 shows an adsorption isothermj carbon load of bacteria
in dependence of the adsorptive concentration. At high colony
numbers (larger than 10 ) the system tends towards saturation.
7 8
At numbers around 1O and 1O up to 90 % of the bacteria are
adsorbed.
The investigation of the influence of time on adsorption proved
to be difficult (see Fig.9). Despite extensive precautions, it
is impossible to avoid increase and extinction processes over a
longer period (dashed curve). After an incubation period of 20 to
30 hours adsorption and desorption are nearing a steady state.
With increasing ion concentration (phosphate buffer pH 7.2)
the bacteria loading of the carbon increases as shown in Fig.10.
No dependence of the adsorption on the temperature in the range
of 5 - 37 °C and of the pH value (pH 5-8) was noted. Dead bacteria
are slightly better adsorbed than living bacteria.
Fig.8: Loading of activated carbon with micro organisms in
dependence of the adsorptive concentration
Fig.9: Loading of activated carbon with micro organisms in
dependence of time
Fig. 1O: Loading of activated carbon with micro organisms in
dependence of the ion concentration
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328
10"
f Beladung
(Koloniezahlen/g A-Kbhle)
io° -i
10'
106
, 'i •' "i' • "i • • "i • "•! • • "i =*
106 107 108 109 1010 IQ11 1012
Adsorptivkonzentration
(Koloniezahlen / 200ml
Puffer)
Beladung
100 -
50-
106 107 108 109 1010 1011 1012
Adsorptiv konzentration
(Koloniezahlen / 200 ml
Puffer)
Fig. 8
Beladung: loading
Puffer: buffer
Koloniezahlen: colony numbers
A-Kohle: activated carbon
Adsorptivkonzentration: adsorptive concentration
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329
50-
40 -
30 -
20 -
10 -
Beladung
i ' I • i ' i n | ' i ' -"
10 20 30 40 50 60
Zeit
(Stunden)
'-~° Koloniezahlen
•--- Zellzahlen
^ Beladung
20—
10—
200 ml Puffer pH 7,2
KH2PO/i/Na2HP04
(mmol)
I\bb.l0
Fig. 9,10
Beladung: loading
Zeit (Stunden): time (hours)
Puffer: buffer
Koloniezahlen: colony numbers
Zellzahlen: cell numbers
-------
330
Discussion and Results
When activated carbon is used for the treatment of drinking water
there is always a growth of micro organisms on the filter
granules. Depending on the eco-system the micro organisms are
insufficiently counted when using the DEV method. This made it
necessary to develop a special method for the quantitative coverage
of micro organism populations. As a rule, the water can be
declared satisfactory, according to the present standards for
drinking water. This erowth was noted by several waterworks
in Germany, irrespective of the method of treatment; it cannot be
avoided by any of the treatment methods used for the processing
of drinking water.
After a short synthesis phase the micro organism populations
reach high colony numbers, which can only be measured by special
methods; after that, the numbers remain constant for a long time.
Changes in the composition of the water have an influence on
these numbers.
The micro organisms contribute to the purification of the water
by their activity, which is not only indicated by
colony numbers. This contribution depends not only on the
quantity of organic substances but also on their quality and
especially on their degradability. Inorganic as well as organic
substances are changed or degraded.
The activity of the bacteria is also influenced by their number,
their distribution and their retention time in the water-carbon
system. These parameters are mainly influenced by adsorptive
processes.
The research programme will be continued by carrying out
investigations on the qualitative definition of the flora of
micro organisms and on the influence of activated carbon on
their metabolism.
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331
EXPERIENCE WITH THE USE OF BIOLOGICALLY EFFECTIVE ACTIVATED
CARBON
by M.Eberhardt, Bremen
1. Introduction
This report covers the mineralization of organic substances
during the treatment of surface waters by using biologically
operating activated carbon filters. Almost no practical
experience is available at present on the use of such filters
in a large waterworks plant. Our experience is limited to
relatively small pilot plant filters which have been in
operation for several years. A simultaneously operated slow
filter plant makes it possible to compare the results and
conclusions drawn.
Water from the river Weser which had been pre-cleaned by
flocculation and rapid sand filtration - the so-called
rapid filtrate - was treated in four successive test filters,
each having a layer height of 1.5 m. The total layer height
of the filters amounted therefore to about 6 m. For comparison,
four other filters, provided by courtesy of the Lurgi company,
were operated in parallel with different types of activated
carbon. In addition, a second pilot plant with a layer height
of 3 m was used for the tests with ozone pretreatment.
Detailed reports on the test plants were made on previous
occasions (EBERHARDT 1971; EBERHARDT, MADSEN, SONTHEIHER 1974
and 1975). As a first step, some theoretical considerations
are to precede the discussion of practical test results.
-------
332
2. Mineralization of organic substances
2.1 Process and possibility of measuring
The complete mineralization of organic substances in water
can generally be described by the following summation
formula:
Ca Hb °c + (a + I - f > ' °2 = a ' C02 + ! ' H2°
From this it can be seen that the relation of
degraded organic carbon
resulting inorganic carbon
or that
TO ' if - •»»«« <»'
3 g DOC must therefore be converted to 11 g CO,, by minerali-
zation, independent of the type of organic substances.
(A DOC = degraded dissolved organic carbon in g/m ;
A CO2 = increase of carbon dioxide in g/m )
Unfortunately, the analytical determination of small concen-
trations of carbon dioxide in water is difficult. If this
analytical problem can be overcome, it will be possible to
get exact data for the mineralized organic substances in-
directly by CO2 determination. On the other hand, it will
also be necessary to determine the concentration of the
dissolved organic carbon (DOC), which can be done very
easily now by using the method of WOLFEL and SONTHEIMER (1974)
-------
333
Many kinds of analytical methods have been proposed for
the determination of organics in water. Originally, the
residue from burning at high temperatures was used to
measure the organic substances because the reaction products
carbon dioxide and water volatilize during complete combustion.
However, the result is sometimes doubtful because of the
other compounds in the water which may change during pyrolysis.
Later on, the oxidizability was measured with potassium
permanganate. Even today there are analyses sheets containing
the term "organic substance" instead of "oxidizability".
After several variations of oxidizability with potassium
permanganate remained unsatisfactory, another oxidation
agent is now being tried, namely potassium dichromate In
wastewater technique, on the other hand, the determination
of biological oxygen demand was used in order to be able to
draw conclusions on the effect of purification steps.
More or less,it was always the aim to be able to draw con-
clusions on the amount of organic substances by measuring
the oxygen required for their oxidation. That this is not
possible is shown by the quotient (Q) of oxidizability (COD)
and organic carbon (DOC) using the mineralization summation
formula. Even at complete oxidation, which is difficult to
achieve in most cases, the quotient can never be constant
but is always depending on the type of organic substances:
_ COD _ 2 4a + b - 2c _ 2 b - 2c. m
y DOC 3 a 3 ^ a ' v '
Therefore, the oxidizability should not be taken as a
criterion for the total amount of organic carbon present in
the water. Indeed, also in practice the relation is never
constant (SONTHEIMER 197O). All the same, a continuous control
-------
of the oxidizability, in addition to the content of organic
carbon, is of interest for the water quality, because con-
clusions can be drawn from the quotient on the nature of the
organic substances.
If one wants to investigate the process taking place in a
biologically operating activated carbon filter, the decrease
of the dissolved organic carbon (A DOC) and the increase of
inorganic carbon (A inorg. C) allows some important conclusions
to be drawn, provided there is only mineralization and ad-
sorption.
When A DOC - A inorganic C. = 0 (5)
then there is only mineralization. If the decrease of the
organic carbon content is higher than the increase of inorganic
carbon, i.e. if
A DOC - A inorganic C.> O (6)
then adsorption is more important, the increase being more
pronounced the bigger the positive deviation. In the opposite
case, i.e. when
A DOC - A inorg. C
-------
335
1. Adsorption
2. Biochemical degradation
Here mineralization is slowest and thus a velocity-determining
process.
When water which contains organic substances is treated in a
fresh activated carbon filter bed there is, in fact, at first
an adsorption. Only after some weeks (normally after two to
three months) the biochemical processes of mineralization
of organic substances are "in full swing1'. This breaking-in
period is apparently typical for all biochemical processes
because they are noticed on a similar scale also with the
biological removal of manganese or with the nitrification
of ammonia.
After the breaking-in period the adsorption and the biochemical
degradation of organic substances take place in parallel,
during which time either adsorption or mineralization may
exceed for a time. Here the velocity of mineralization is
constant and takes place in a steady manner, independent of
of the concentration of organics in water, when conditions
remain unchanged such as for instance temperature and filter
bed loading. In the fully loaded activated carbon bed only
that amount of organics can be newly adsorbed which has
previously been removed by mineralization (see Chapter 3.8).
Different situations arise when the concentrations in the
raw water vary (see Chapter 3.7).
Our tests have shown that the following differential equation
will be valid:
_ d DOC (8 »
dt
-------
336
This differential equation, which has been confirmed by the
results, leads to the following solution:
A DOC = DOCQ - DOC = k • t (9 )
If time t is replaced in this equation by
— (10)
VF
then the following formula results for the specific
biochemical filter degradation capacity:
NF = k • e = A DOC
Abbreviations:
DOC = concentration of dissolved organic carbon in g/m
after the carbon filter
DOC = dissolved organic carbon in g/m in raw water
A DOC = decrease of dissolved organic carbon during
filtration
1^ = filter length in m
r
v = filter velocity in m/h
e = relation of the water volume to the total
volume of the filter bed
N = specific biochemical filter degradation effective-
ness per m of filter bed volume in g DOC/m
per hour
Further parameters of the filter effectiveness are temperature,
activated carbon material, size of granules and type of organic
substance. The influence of these parameters on the filter
performance could not be defined in more detail, because they
did not remain constant during the practical tests. It can be
said, however, that the biochemical degradation effectiveness
N increases with increasing temperature, with the decrease
in size of the activated carbon granules and with an improved
-------
337
adsorption capacity as well as with larger conducting pores
of the activated carbon. It can be assumed that the degradation
efficiency is better when the substances in the water are more
easily biodegradable.
The degradation efficiency N achieved in the tests was in
3
the range of 1 to 4 g DOC per m activated carbon per hour.
3. Experience with the use of biologically effective
activated carbon
3.1 Experience gained with the common technology
The purpose of using activated carbon filters in water
treatment has always been the removal of undesired substances
from the water by adsorption. For a long time the main field
of using activated carbon filters was chiefly dechlorination.
At the beginning of the 1960s activated carbon was used with
success for the removal of taste and odour at the lower Rhine-
river. Here it was possible to overcome the problems of
steadily deteriorating quality of the surface waters (HOPF 1960)
The present state of process techniques is described in detail
in the other papers.
Already when using granular activated carbon as filter material
for dechlorination in the beverage industry,it was noticed that
even with high concentrations of chlorine of about 5 g/m in
the raw waterf it was not possible to avoid germ formation.
Only by subjecting the filter material to hot steam disinfection
every week, it was possible to solve this problem. However,
this method was not practicable in waterworks because of the
large filter sizes. Even the use of extremely high chlorine
concentrations brought about no improvement (ROGGENKAMP 1968).
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338
It is known that this observation of bacterial growth in the beverage
A^euwtidrerloweuse of activated carbon filters. On the other
hand, this effect did not occur with the filters along the
river Rhine. There is no explanation so far for this different
behaviour.
3.2 Microbiological degradation of persistent organic
substances using activated carbon
It was proved by laboratory tests that activated carbon can
improve biological degradation, because the biochemical
degradation of formic acid can be accelerated by the
presence of activated carbon. Furthermore, it was possible
to prove experimentally in the laboratory that normally per-
sistent pentaerythritol mineralizes completely in the presence
of granular activated carbon after a certain introductory
period of 6O days (KOPPE et al 1974). This is not surprising
when one remembers that activated carbon adsorbs organic sub-
stances by accumulating it at the surface and that there
seems to be no clearly defined boundary between biodegradability
and persistency.
It seems to be a question of time rather, and perhaps also of
biological adaption, to decide on the degradation and per-
sistency. So, if it becomes possible to fix, with the aid of
activated carbon, organics which are difficult to degrade
for a sufficiently long time in order to subject them to a
decomposition process long enough, then the limitations of
biological degradation in wastewater treatment will be eased
too. This could lead to a considerable success in wastewater
purification and to a better water quality of our surface
waters (RINKE et al 1975).
3.3 Pretreatment of the water before filtration
The presumption that the pretreatment of the water before
activated carbon filtration has a great influence was clearly
confirmed by the tests made in Bremen. Consequently, a
pre-chlorination proved to be adverse in every way.
-------
339
This was true regarding the high colony numbers of the filtrate
and the low removal efficiency of organic substances. According
to our observations, we feel that some unfortunate experience
in connection with activated carbon filters in the past was
due to the fact that prechlorination was used. If one avoids
this pretreatment, much better results will be obtained.
After an unused activated carbon filter has been put into
operation, a normal biological development occurs in the
filter bed, as we know it from slow sand filters (HUSMANN
1958), SCHMIDT 1963). This has been noticed with the test
filters in Bremen too, and could not be expected to be otherwise
because the supply of nutrients is high, and the activated
carbon adsorbs the organics contained in the water and stores
them in its pores. Therefore, the mineralizing bacteria have
an extremely large supply of nutrients at their disposal.
These bacteria may be compared with a herd of cows grazing in
a juicy and luscious meadow. It is also known that this
activated-carbon "meadow" is very spacious and rich in pores
because of its large specific surface, providing ample room
for many mineralizing bacteria, provided the pore structure
will be suitable.
This biochemical mineralization is obviously disturbed
decisively by pre-chlorination, the degree of the disturbance
depending on the chlorine concentration before the filtration.
The reason may be that chlorinated organic substances, formed
through chlorination,are lees biodegradable. According to our
measurements, a pre-chlorination impairs the effect of acti-
vated carbon filtration to such an extent that this type of
pretreatment ought not to be used in future. This is also
true regarding sewage treatment.
-------
On the other hand, one can be sure that the negative effect
of chlorine does not depend on its oxidation ability. Therefore,
preoxidation with potassium permanganate does not disturb the
biological activity of carbon filters, while a pre-ozonization,
using up to 5 g/m of ozone, improves the effectiveness of the
subsequent biological treatment step considerably (EBERHARDT
et al 1974) .
This improved biodegradability is due to the fact that some
organic substances are transformed by ozone to a lower molecular
weight. By this change they may become less adsorbable but more
easily biodegradable. The ozone attacks especially at the double
bonds of the organic substances and it may even remove organo
chlorine from a molecule (GILBERT 1974). This may be another
reason for the improved biodegradability. incidentally the
same effect can be obtained by Gamma radiation (GILBERT 1974).
The combination of ozone treatment with activated carbon filters
in sequence is now a common water treatment process at the
Lower Rhine (SIMON et al 1968). However, perhaps with the high
filtration velocities there will not be enough time to get the
full advantage of biological degradation within the activated
carbon filter.
3.4 Hygienic problems with activated carbon filters
It cannot be expected that the effluent of a biologically
operating activated carbon filter, with a filter velocity of
1O m/h, does not have any bacteria. . Similarly, this is not
possible with slow sand filters whose filter velocity is
10O times lower. Measurements have shown that there will be a
9O % reduction in bacteria and coliforms with a biological
activated carbon filter. In some cases there may be higher
values, especially after a change in temperature and an adaptation
of the micro-organisms to the new conditions. This is also true
for slow sand filtration. Ozonization can also lead to higher
numbers after a longer development period.
It will be worth-while therefore to consider an additional
-------
treatment step after a biofiltration to reduce the counts
Slow sand filters with higher velocities (SCHALEKAMP 1971) or a
low-dose chlor.ination may be advantageous. Only if there is an
extensive reduction of organic substances within the carbon
filter will there be a satisfactory disinfecting
efficiency. In that case, subsequent chlorination or slow
sand filtration will provide better safety and guarantee an
excellent drinking water. Any additional removal of organic
substances by the slow sand filter will not be possible,
normally.
3.5 Removal of ammonia
Whilst the ammonium-ion in the usual concentration in natural
waters has no toxic effects, difficulties may arise in the
distribution system in the presence of ammonia (MADSEN 1975).
It will be necessary therefore to remove ammonia when treating
surface water. This is possible by biochemical nitrification
in rapid sand filters, if the temperatures are higher than 5 °C.
It is only necessary to ensure that there is enough oxygen in
the water. Special means have to be taken if the NH .-concentration
3 4
exceeds 1.5 to 2 g/m .
Our tests have shown that nitrification in activated carbon
filters has at least the same rate as in rapid sand filters.
On the other hand, one cannot expect better results as ammonia
cannot be adsorbed onto activated carbon. There is some signifi-
cance in the test results in that carbon filters may have better
efficiencies at low temperatures compared with rapid sand
filters.
As usually it needs 3 months to start nitrification of ammonia,
difficulties may arise with a sudden increase of the concen-
tration in the surface water. In such a case it may be worth-
while to dose a small amount of ammonium salts to restore the
-------
biological activity. According to the results obtained from the
pilot plant, this produces better efficiencies also for a
temperature decrease below 5O C.
It can be expected that the larger surface and increased pore
volume of activated carbons will present some advantages of this
filter material compared with other filters. Nitrifying bacteria
may have more surface and space available. This may be the
reason for the better efficiency at low temperatures.
3.6 Recycling of filtered water
During pilot plant tests the question arose if it might be
possible to get a further reduction of the dissolved organic
substances by recycling the treated water through the same
filter. So a recycling test was made in which the removal of
C0~ and the enrichment in oxygen was achieved in a falling spray
tower (EBERHARDT 1973). However, the assumption that, after
several cycles, the water would be free from dissolved organics
was not confirmed in any way. It was observed that during the
recycling the DOC values even increased at first, after which
it took some time until they regained the original value of
the normal throughput. On the other hand, mineralization still
took place, as could be seen from the enrichment in CO,, and
the decrease in oxygen after each passage through the filter.
These values remained constant for several weeks. This leads
to the conclusion that the adsorbed organic substances will
be biodegraded and mineralized by recycling, as long as there
is sufficient oxygen for the reaction and as long as the
produced C0_ is removed. There was no large influence of the
concentrations of O_ and CO on the mineralization rate.
-------
31*3
These observations prove that adsorption precedes mineralization
in a biological activated carbon filter. They show further that
the rate of mineralization is of zero order and that it does
depend on the amount of loaded carbon and time only. This means
that there are steady-state conditions for this process and a
given filter.
3.7 Buffer effect of activated carbon filters.
Already during the initial stages of the pilot plant tests,
it was observed that the treated water from the carbon filter
had a more uniform quality than the filtrate from the slow
sand filters. The tests described above now explain why it was
possible to get a more constant water quality from the carbon
filters. Here we have a buffer effect through the combination of
adsorption and mineralization taking place at the same time.
Whilst there is almost no adsorption capacity in slow sand
filters, an increase in raw water quality will also lead to an
increase in the treated water. This is not the case with acti-
vated carbon filters where higher concentrations in the raw
water change the equilibrium data, so that higher loadings
will occur and a better removal efficiency. On the other hand,
with lower concentrations of raw water there may also be
desorption, and these two effects will lead to a more uniform
effluent of a biological carbon filter, which may have some
advantage.
3.8 Biological regeneration of activated carbon
As the mineralization of the organic substances adsorbed onto
the carbon is independent of the raw water concentration, a
stopping of the filter flow may lead to oxygen deficiency in
the filter and to changes in water quality through anaerobic
conditions. To avoid this, such carbon filters must have a
steady water flow. However, this is no disadvantage as one
might assume when regarding the costs for pumping. This is
due to the fact that it will be possible to do biological
-------
regeneration of the carbon also at times when low water
quantities are needed and makes it possible to use higher
velocities when maximum capacity is necessary. In this way,
biological regeneration is also possible during recycling
times.
Bearing this in mind, it may be said that biological carbon
filters differ from the usual adsorption plants by the fact
that apart from normal adsorption there is also a biological
regeneration of the activated carbon in use. From the pilot
plant data it cannot be said whether a total regeneration of a
carbon will be possible with this technique, because regeneration
would need several years. Such a long period is not very
attractive from a practical point of view.
But, in any case, biological regeneration will aid a longer
running time also in those cases where only normal adsorption
is needed; it will also mean better economics of activated
carbon filters. It will merely be necessary to have optimum
conditions for biological mineralization.
4. Design of biofilters using activated carbon
The design of a biological activated carbon filter can be made
by using the following formula:
A DOC • v
1F = ^—^ (13)
A DOC = reduction of DOC concentration by
the filter (g/mj)
v = filter velocity (m/h)
lp = length of filter (m)
N = specific filter efficiency (g/m per hour)
A value for Np of 1 g DOC/m /h may be generally
regarded as conservative.
-------
Assumed example:
DOC of raw water = 4 g/m3
DOC of treated water = 1 g/m3
A DOC = 3 g/m3
These data lead to different filter velocities:
vp = 10 m/h lp = 3 ' 10 = 30 m
VF = 3 m/h lp = 3 ' 3 = 9 m
If the 9 m are divided into two units, having a spray in between
(see Fig. 1), useful results and a satisfactory treatment can be
achieved. This plant also permits recycling without any parti-
cular problems, and this type of treatment is especially
advantageous during high temperatures in the summer, when it
provides the only means to avoid anaerobic conditions. Similar
results can be obtained by a so-called dry filtration. However,
care must be taken as mechanical deterioration of the carbon
granules may be of some influence.
Fig. 1
The calculated filter velocity of 3 m/h seems low if compared
with rapid sand filtration. However, it should be remembered
that a reduction from 4 to 1 g/m of DOC needs a high biological
activity. Slow sand filters normally need a filter area which
is 5O to 1OO times larger. In the tests the specific efficiency
of slow sand filters was calculated as
N = O.O2 g DOC/m sand • hour
From this figure it cannot be concluded that the same rules
apply to slow sand filters and to activated carbon filters;
however, a comparison may be made with the 1 to 4 g/m -h DOC.
-------
Abluft
Rohwasser
Zuluft
Reinwasser
Reinwasser=
ruckfuhrung
Fig. 1: Falling spray double filtration
Abluft: used air
Zuluft: fresh air
Reinwasser: treated water
Reinwasserruckfiihrung: recycling of treated water
Rohwasser: raw water
-------
5. Final remarks
Starting with some theoretical considerations, this report
presents a review of the results of the work at a pilot plant
over several years. The effectiveness of biological activated
carbon filters can be compared with that of slow sand filters
regarding the biological processes. The difference lies in the
reaction rate which is 10 to 1OO times higher per volume in
a carbon filter. This depends on the high concentration of
organics in the pores of the activated carbon, and on the fact
that the process starts with adsorption, after which biological
mineralization and regeneration takes place. This mechanism,
may be the reason that a degradation of normally persistent
substances can also be observed. For practical use, the buffer
capacity of such a system is of importance too.
Investigations of the mineralization rate have shown that
a zero reaction order can be used to describe the process
kinetics, which leads to a very simple design formula.
However, before adopting it, it should be checked whether
these results can be confirmed by other waterworks, because
the water used for these tests has undergone a very intensive
pretreatment.
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5oma investigations into tho presence and behaviour of.
bacteria in activated carbon filters
by D. van der Kooij, Netherlands
Introduction
The application of activated carbon filtration in tapwater preparation is
based on the adsorptive action of the carbon by which organic substances
like organochlorine compounds, taste and odour compounds and many organics
originating from industrial waste, can be removed from the raw water. Also
biological processes affect the quality of the water flowing through the
filter. These biological processes are mainly caused by the bacteria which oxi-
dized biodegradable organic substances and ammonia. However, this
bacteriological activity in the carbonfliters takes up oxygen from the water
and also results in the presence of large numbers of bacteria in the filtrate
(Bernard 1970, Ford 1973 Uallis et al 1974J.
It is generally assumed that the bacteriological activity in carbon filters is
intensified by the adsorption of organic substances (Sontheimer, 1974 and
Eberhardt et al., 1974) and that bacterial activity in carbon filters
results in a increase of the adsorption capacity (Eberhardt et al, 1974).
Much abtention is paid to the application of carbon filtration in drinking
water preparation processes in The Netherlands. As an increased amount of
t
drinking water must be prepared from surface water of a steadily decreasing
quality. Investigations were therefore carried out into biological and physico-
chemical processes in carbon filters at the Testing and
Research Institute of the Dutch Waterworks KIUA N.U.. Some experiments with
the bacteriological behaviour in carbon filters are described in this paper.
Experiments and results
The influence of the kind of filtermaterial on the development of bacteria
in the filterbed was investigated in three experimental filters. These
filters contained granulated activated carbon Norit ROW 0,8 Supra; non
activated (n.a.) carbon (Norit ROW 0,8); sand (0,85-1,00 mm) respectively.
The filters were fed with tapwater (13 °C-17 °C) (superficial contact time
and velocity: 3 minutes and 3,5 m/hr) during 10 months respectively.
Bacterial numbers on the filtermaterials were estimated at regular intervals
by the colony count technique on a diluted nutrient agar (0.35 gl beef-
1 *1
extract; 0,65 gl peptone and agar: 10 gl~ ) after incubation at 25 °C
during 10 days. The numbers of bacteria on the filtering materials were ex-
pressed in number per ml filter volume. The results of the experiments are
shown in Figure 1.
-------
01
E
3
t-l
0)
A activated carbon Norit ROW 0,8 Supra
A non activated carbon Norit ROW 0,8
O sand (0.85 - 1,00 mm)
Bacterial numbers on activated carbon ROW 0,8 Supra
ROW 0,8 (non activated) and sand (0.85 - 1,00 mm) when
fed with tapwater (Superficial velocity 3,5 m/hr).
107-J
106H
10-
I
10
12
14
Months
FIGURE 1
-------
350
Another experiment was carried out with samples of activated carbon
ROW 0,8 Supra and the non actiuated carbon ROW 0,8 (n.a.) taken from filters
which had been fed with prefiltered river water during one year. The wet
carbon samples of 150 ml were supplied with 50 ml of tapwater and seratrad
at 25 °C. The numbers of Coliforms, Pseudomonads and Actinomycetes on the
carbons were estimated weekly by selective media. The total number of
viable bacteria was estimated by the colony count on tha diluted nutrient
agar. All counts were expressed in numbor per cm filter volume. The oxygen
consumption of the carbons was estimated with a Y.S.I. Oxygen Monitor and
expressed in mg 09 liter filter volume per hour.
the results of the experiments are shown in Figs. 2 and 3.
Table 1 shows the 50 % reduction times of the bacteria on the activated
carbon and on the non activated carbon.
Discussion and conclusions
It is shown in Figure 1 that the numbers of bacteria on the activated carbon
were always about ten times higher than the numbers of bacteria on the non
activated carbon and the sand. The surface area at the disposal of one bacterial
cell can be calculated from the colony count and the hypothetical surface
area of the cylindrical carbon particles. The hypothetical cylindrical sur-
o r?
face area of the granulated activated carbon is about 40 cm /cm and when the
n n o
colony count is 10 /cm 40 /u of this surface will be at the disposal of one
bacterial cell. The real surface area of the activated carbon particles
2 3
however, is much larger than 40 cm /cm . This causes a very low-
density of bacteria on the surface of the activated carbon, even when it is
realized that the colony count is only a small minority of the bacteria
present on the particles. Observations with an electron-scan microscope
confirmed this conclusion and it is reasonable therefore to state that
adsorption processes are not hindered by the presenceof the bacteria on the
carbon.
It is shown in Figure 1 that the number of bacteria on the activated carbon
is decreasing after having reached its maximum. It can be concluded that
this decrease is not caused by exhaustion of the adsorptive capacity of the
activated carbon since this phenomenon was also observed, with the non
activated carbon and the sand. The decline in bacterial numbers might be
explained by the occurrence of a shift in the composition of tns bacterial
flora towards bacteria which do not participate in the colony counts.
The results of the aeration experiments are shown in Figs. 2 and 3 and in
Table 1. The numbers of both the Coliforms and Pseudomonads and total colony
forming bacteria decreased on the activated as well as on the non activated
carbon (Fig . 2).
-------
351
Q)
E
D
C
D
O
O
o
CJ
io4-|
Numbers, of Pseudomonads (•€>) and
C'o 1 i f o r m s (A A /
on activated carbon ROW 0,8 Supra (*A
and on non activated carbon ROW 0,8 (O A}
during aeration at 25 C
10-
10-
10-
\A
\
\
10
Figure 2
20 30
Days
40
50
60
70
80
-------
352
Numbers of bacteria (colony forming units) (A A;) aAd
numbers of Actinomy cetes (9f O )
on activated carbon ROW 0,8. Supra IA •/
and non activated ROW 0,8 (Ad ) during aeration at 25 C
oxygen consumption (mg 0,, 1 hr ) ROW 0,8 Supra
ROIUQ.,8 (n.a.)
o
Ho
1-100
0.01
o
_c
X
0)
-p
"H
CN
O
Q
•H
JJ
Q.
E
3
(0
C
O
(J
C
n)
en
>^
X
o
0.001
Figure 3
DAYS
-------
353
50 % REDUCTION TIF1ES (DAYS) OF DIFFERENT GROUPS OF BACTERIA ON
ROW 0,8 SUPRA AND ROW 0,8 l\l. A.
Table 1
Type of bacteria
Colony forming units(25 C, 10 days)
Colif orms
Pseudomonads
Actinomycetes
ROW 0,8
Supra
9
3
4,5
>50
ROW 03
n.a.
8,5
3,5
4,0
>50
-------
35*4
However, the numbers of Actinomycetes and the oxygen consumption did not
show a clear decrease within a 60 days period (Fig. 3). The 50 % reduction
times of the different groups of bacteria are shown in Table 1 . from this
table appears that Coliforms disappear quicker than all other bacteria.
There is hardly any difference between the 50 % reduction times of the
selected groups of bacteria on the activated carbon and the ones an the
non activated,carbon. It is therefore concluded that neither Coliforms nor
Pseudomonads nor the total colony forming bacteria had any advantage of the
organic substances which must be present on the activated carbon after
having been in contact with riverwater for one year. This conclusion is in
contrast with the general assumption that bacteria present in activated
carbonfliters are able to utilize adsorbed organic substances, (Sontheimer
1974, Eberhardt et al 1975).
The oxygen consumption of the activated and non activated carbons did not
decrease with the decreasing colony counts. Nor did the numbers of Actinomy-
cetes but these low numbers (Fig. 3) can not be held responsible for the
oxygen consumption. It is possible therefore that the oxygen consumption
o,f both types of carbon is caused by chjemical rather than by bacteriological
processes. The fact that the Actinomycetes showed decrease within 60 days
might be due to their ability of producing spores.
-------
355
The influence of dissolved organic compounds on flocculation
by G. Albert
Introduction
In water treatment flocculation is often brought about by the addition
of hydrolyzing metal salts. Generally, these salts give greater
reduction in turbidity, and in addition one obtains some degree of removal
of dissolved organic compounds. Thus these unwanted substances can be
partially removed simply and economically while at the same time reducing
loading on subsequent polishing steps, e,g. with activated carbon. It is
desirable therefore to make the flocculation conditions such that both
colloidal and dissolved organic compounds are removed together as far as
possible. In order to achieve this aim the fundamental mechanisms of
sorption of organic compounds to floes and of agglomeration or colloidal
material have to be understood.
Theoretical considerations
A considerable amount of work has been published concerning the effect
of various factors on flocculation processes in water treatment. PACKHAM
(1963) has completed an extensive review on the use of metal salts as
flocculants. Additional information can be obtained from later reviews
such as has been made by the COMMITTEE REPORT (1971) and also by O'MELIA
(1972). STUMM (1967) has discussed the different mechanisms responsible
for flocculation by adding hydrolyzing metal salts. Due to the hydrolytic
reaction of metal ion and the water, various hydrolysis products are formed
which are able to destabilize colloids in different ways. The metal ions
3+ 3+
are hydrated in water as aquo-complexes such as AlCi^O), and FeCl^O)^.
which are present at low pH values. The hydrolytic reactions of iron are
similar to those of aluminum so that only aluminum is considered in detail.
With increasing pH, the loss of hydrogen ions leads to the formation of
A1(H 0) OH2+, then to the formation of A1(H20)4 (OH)* and the uncharged
aluminum hydroxide A1(H20) (OH)3 which shows only a low solubility. With
-------
356
higher pH the highly soluble complex A1(H 0)2(OH), is present. Besides
these species also polymeric hydroxo metal complexes are formed. A number
of such complexes are known containing varying ratios of metal ion to
hydroxyl groups between 1:2,5 and 1:3. Distribution diagrams for the
different Al- and Fe(III)-species, calculated from the corresponding
thermodynamics equilibrium constants, are given by O'MELIA (1972) and
STUMM (1967), According to the equilibria, polymeric species are found
at pH-values between 4 and 6. They are very effective in destabilizing
negatively charged colloids becuase of their strong tendency to be adsorbed
at interfaces (STUMM and HAHN, 1967). At very low colloid concentration
this destabilizing ability is ineffective because of the low collision
efficiency. In such systems agglomeration of colloidal particles takes
place predominantly by coprecipitation; the particles are enmeshed in the
precipitating aluminum or ferric hydroxides. Consequently optimum floc-
culation conditions are found near neutral pH where hydroxide is formed.
This mechanism has been confirmed by PACKHAM (1965) who studied the co-
agulation of various dilute colloidal systems.
The first studies on the removal of organic compounds by flocculation were
reported by BLACK, SINGLEY et al in 1963 where the importance of chemical
mechanisms was affirmed. HALL and PACKHAM (1963) examined the removal of
humic acids and proposed a purely chemical precipitation of basic iron or
aluminum huminates. According to STUMM and MORGAN (1962) complex formation
reactions between aluminum and iron coagulant metal ions and carboxylic,
phosphate, sulfate and aromatic hydroxy functional groups are important in
the elimination of dissolved compounds. Therefore, the pH should play a
predominant role in this process. SCHILLING (1975), however, found that
pH did not have a marked effect on the removal of humic acids.
The precipitation of dissolved organic compounds may cause additional
turbidity. On the other hand, a large number of natural organic compounds
are of high molecular weight. Therefore it can be expected that they act
also as flocculant used in water treatment. In this case the flocculation of
colloidal material may be improved by the presence of organic compounds.
-------
357
In this study several typical organic compounds are evaluated on their
influence on turbidity removal.
Experimental
All experiments were carried out using a standard jar test in 1 1-beaker
in a constant temperature bath at 25 C. After the flocculant was added,
the suspensions were stirred for one minute at 150 rpm, then for 30 minutes
at 50 rpm. After a sedimentation time of one hour a sample was taken from
the supernatant in order to measure turbidity, pH and residual amount of
flocculant and of organic matter.
The turbidity was determined in aHach 2100 A turbidity meter. The measured
values were related to the values which were obtained without flocculant
addition at the sampe pH and amount of mixing.
The residual amount of flocculant was analyzed by standard analytical
techniques. Organic compounds which may interfere with the analysis were
removed by oxidation using an ultraviolet radiation technique (WOLFEL,
SONTHEIMER, 1974).
The residual amount of organic substances was determined photometrically,
or if this method failed by DOC-measurements. Unless noted otherwise,
analytical grade chemicals were used. pH was varied by adding HC1 or NaOH
before the addition of flocculant. Both tap water (total hardness: 3,5 mg/Jl)
and deionized water was used.
Quartz powder was selected as a typical turbid component in surface water.
The powder used, from the Quarzwerke, Cologne, had a specific surface of
n
A m /g (BET) and a size distribution between 1 and 10 ym. A suspension of
100 ppm SiO corresponds to a turbidity of nearly 20 JTU at neutral pH in
deionized water.
-------
358
Results
As is seen in Fig. 1, the maximum removal of quartz particles occurs in a
pH range where Al(OH). or Fe(OH). are present. It appears therefore that
the quartz particles are flocculated by enmeshment in metal hydroxide.
There are similar conditions to those found by PACKHAM (1962). Both curves
for iron and aluminum are nearly identical. The flocculation region is
extended if additional ions are present as can be seen by the results which
were obtained with tap water.
When an organic component, which does not react with aluminum to form an
insoluble complex, is present, no influence on flocculation - as is seen
from turbidity removal - can be detected. Also no removal of organics
takes place as can be seen from Fig. 2. There Q.Ill nunol Al/1 was added to
0.06 Tnmol vanillic acid. There are selected similar conditions for flocculant
concentration and dissolved organic carbon values to those generally obtained
where treating drinking water,
As is known, many dyes form insoluble complexes with multivalent cations.
Congo red, which was selected for this study, can be precipitated completely
by the addition of aluminum sulfate as is shown in Fig, 3, A ratio of 5.5 of
aluminum to congo red equivalents was used, which corresponds to the conditions
in Fig. 2. Because the percentage of trivalent aluminum ions, which reacts
with the dye, decreases with increasing pH due to hydrolysis, precipitation
occurs only in the acid region. The reduction in turbidity takes place in
the same region as the precipitation of organic substances. This indicates
that the quartz particles are removed by coprecipitation with the dye complex,
since A1(OH)3 floes are not formed at this pH. It is possible that floccu-
lation takes place by a similar mechanism to polyacrylic acid flocculants
where, according to VOLLMERT and SONTHEIMER (1973) colloidal particles are
enmeshed in the network of crosslinked polymers.
-------
359
100r
>,
•*-*
'•5
50
TP
0)
"3,0
itap
! water
100
100mgquartz/t
3mg Al/L
50
TO Qfl !10
PH
i
i
I
4,0 5,0
6,0
pH
Fig. 1
Turbidity removal by iron (III) and aluminum salts
100 ppm S±02/t, 0.111 mmol Al and Fe/£
FeC I,
100 mg quartz/I
6i2mgFe/L
7,0 8,0 9,0
-------
360
100
3 50
c
a
lOmg van.ac./ !
100mg quartz/1
3mg Al/l
J3,0
5,0 6,0 7,0 8,0 9,0
pH
c
o
*-•
u
3
T3
100r
T3
15
Wi
3
50
V
- no organics
4,0 5,0
6,0 7,0
pH
8,0 9,0
Fig. 2 Elimination of vanillic acid
10 ppm vanillic acid
O.lllmmol Al/?
100 ppm SiO., tap water
-------
361
100
8 50
'E
a
B>
o
0.
10mg congored/l
100mg quartz/ I
3mg Al/ I
3.0 4.0
5.0
6,0 7,0
pH
8,0 9,0
c
o
100r
/—..no organics
4,0 5,0 6,0 7,0
PH
Fig. 3 Elimination of congo red
10 ppm congo red
0,05 iranol Al/1
100 ppm Si02/l, deionized water
8,0 9,0
-------
362
Lignin sulfonic acid, a typical waste product of paper mills, acts in a
similar way. A commercially available product from Roth, Germany, was used
for these experiments. The acid number, which was determined according to
a method developed by MAIER (1975) amounts to 2.5 acid equivalents per gram
organic matter. As shown in Fig. 4, a sixfold excess of metal ions pre-
cipitated only 75 percent of the organic matter, the other 25 percent
remaining dissolved. The relatively sharp optimum for the removal of organic
material and for the turbidity reduction is due to the fact that only the
dissociated acid can react with the trivalent metal ion to form the insoluble
complex. The percentage of trivalent aluminum decreases but the dissociation
of the acid increases with increasing pH. The combination of these two
equilibria produces such an optimum. The precipitation occurs at lower pH
values because less hydroxyl groups are needed to neutralize the aluminum
ions. The precipitation by ferric chloride occurs at a lower pH than aluminum
sulfate due to the different hydrolysis constants, as can be seen from the
distribution diagrams for the two metal ions. A more extended optimum is
obtained by using Polyaluminum chloride (PAC) as a flocculant. This
relatively new flocculant was obtained from SACHTLEBEN AG, Duisburg. Another
typical water pollutant but of natural origin is humic acid. The used humic
acid was extracted from the Lake of Constance. The water was filtered through
a macroporous anion exchanger. By regeneration of the resin with sodium
hydroxide the sodium huminate was obtained which was converted in the hydrogen
form by a cation exchanger. After evaporation the solid residue was washed
with ethanol for several times until the salt content fell below 3%. The
product obtained was found to be mainly humic acid. Nearly 85% of the
substance could be precipitated by iron- or aluminum salts. It had an acid
number of 8.1 acid equivalents per gram. The results shown in Fig. 5 were
obtained by adding a 5.5 fold excess of equivalent metal ions. There are
some characteristic differences between the three flocculants used. Contrary
to aluminum sulfate ferric chloride produces a precipitate with humic acid,
where the quartz particles could be enmeshed. Under the given concentration
one can distinguish two zones. At low pH quartz particles are enmeshed in
-------
c.
o
o
•3
•o
4}
I A12(SQ)3
20 mg lign.sul.ac. /1
• 100 mg quartz/I
o no quartz/I
3mgAl/L
1CO
50
J3,0 4,0 5,0 6,0 7,0 8,0 9,0
pH
0
lOOr
6,2 mg Fe/L
3.0 4,0 5,0 ii,0 7,0 8,0 9,0
100
1 50
5
n
;'
i
,
i
1GU
no organics
5C
!
r\
3,0 4,0 5,0 6,0 7,0 8,0 9,0
PH
6,0 7,0 8,0 9,0
PH
Fig. 4 Elimination of lignin sulfonic acid (LS)
20 ppm LS
0.111 mmol Al and Fe/£
100 ppm SiO /I, tap water
50
0.
3mg Al/l
I I
3,0 4,0 5,0 6,0 7,0 8,0 9,0
pH
OJ
CO
3,0 4,0 5,0 6,0 7,0 8,0 9,0
DH
-------
*• - " •
10mg hum.ac. / I
• 100 mg quart?/I
o no quartz
3mg Al/L
100
c
o
J3,0 4,0 5,0 6,0 7,0 8,0 9,0
pH
>s
•5
50
0.
100
50
Fed,
100r
6,2mgFe/L
i i i i
3.0 4,0 5,0 6,0 7,0 8,0 9,0
PH
res.
• HocculantCA
5,0 6,0 7,0 8,0 9,0 ^3,0 4,0 5,0 6,0
pH pH
Fig. 5 Elimination of humic acid (HS)
10 ppm HS
0.111 mmol Al and Fe/£
100 ppm SiO./l, tap water
50
0.
» ICQ mg quartz.
o no quartz
3mg A!/I
3,0 4,0
5,0 6,0 7,0 8,0 9,0
pH
100r
r\. 1 1 7~~-" r- l 1
"3,0 4,0 5,0 6,0 7,0 8,0 9,0
pH
-------
365
the precipitate of ferric huminate; aluminum huminate causing only additional
turbidity. Near the neutral pH one observes coprecipitation by Al(OH) or
Fe(OH)3- The optimum of reduction in humic acid occurs at lower pH for
ferric chloride than aluminum sulfate or PAC. However, PAC gave turbidity
removal over a large pH range.
No marked influence of anions could be observed. Aid, and Al (SO.)
produced the same results (Fig. 6).
Also, neither the method of addition of the flocculant nor the way of mixing
influenced the removal of organic substances. In Fig. 7 the results of
experiments are shown where the speed of adding the floculant was varied.
When the precipitate was always removed and a new portion of flocculant was
added to the supernatant, the same result was obtained when the whole portion
was added. It indicates too that only chemical reactions are responsible
for reduction in organics. The nonlinear curve for humic acid in Fig. 8
may be due to the range of acids present, or it may be caused by a distri-
bution in the molecular weight of the acid.
Differences could be detected if the organic matter was added after the
flocculant. The anions of the humic acid are replaced by the hydroxyl ions
so that the removal of humic acid decreases with increasing age of the
aluminum hydroxide floe (Fig. 9).
The optimum pH of removal depends on the ratio of humic acid present in
solution. Increasing concentration of humic acid causes a shift of the
optimum to lower pH values because more anions are present to neutralize
aluminum, and therefore less OH-ions are needed (Fig. 10). In this graph
mass ratios are plotted (mg humic acid (HS per mg Al) where the ratio of 1 g
humic acid to 1 g aluminum corresponds to 8.1 equivalents humic acid to
0.111 equivalents of aluminum.
The use of a flocculant aid such as polyacrylamide (PAM) or polyacrylic
acid (PAS) does not change markedly the range of flocculation. It gave an
-------
366
100n
o
o
S>
°50
c
/A12{SOJ3
50
6,0 7,0
pH
8,0 9,0
Fig. 6 Comparison of elimination of humic acid by
Aid and Al (SO,).
10 ppm HS
O.llliranol Al/1, tap water
Ai/sq)3
100
o
o
en
50
o lOOmg quartz/I
o no quartz
pH = 5,5 ± 0,1
3mg Al/L
I- -8- - 8-
time (rnin)
10
Fig. 7 Influence of the way of dosing the flocculant on
elimination (same conditions as in Fig. 6)
-------
367
100
10
o
c
a
en
i_
o
c
c
o
-«-»
o
CD
50
10
0
A12(SOJ.3
C0= 100 mg/l
pH= 5,5*0,1
3mg Al/l
lianin sulf.acid
humlcacid
1 2 3
number of precip.
j
Fig. 8 Elimination of organic material by dosing the flocculant
in single steps
100 ppm organic matter
-------
368
100
in
•§50
o
en
c
o
u
-
10 mg hum.ac. / I
3mg Al/l
Jresh
\agod by heating
7
PH
1C
Fig. 9 Influence of the age of floe on elimination of humic acid
10 ppm HS, tap water
-------
369
910
Fig. 10 Elimination of humic acid (HS) by varying the addition of
aluminum.
-------
370
improvement in settling velocity of floes but not in turbidity removal.
Best results could be obtained by the nonionic flocculant polyacrylamide
(PAA) with a molecular weight
primary flocculant (Fig. 11).
(PAA) with a molecular weight of 5.10 when it was added together with the
It was found that the pH range of successful flocculation could be altered
depending on whether pH adjustment was made prior to or after the addition
of flocculant. As shown in Fig. 12 it is possible to broaden the pH range
of successful removal by lowering the pH before the addition of the flocculant
to the value pH, and then, after the addition, to adjust the pH on the
desired value.
Pretreatment by ozone did not improve flocculation. The ozonation produced
even more soluble substances, as a result the removal of organic material
deteriorated (Fig. 13).
Under similar conditions addition of multivalent cations to natural systems
causes a very pronounced flocculation effect. This is dependent on both
the functional groups and the molecular weight of dissolved organic material.
One component of humic acid, the hymatomelanic acid, shows such a behaviour
as was observed also with congo red and lignin sulfonic acid.
The hymatomelanic acid was extracted from the commercially available product
"humic acid" from ROTH, Germany, which is an extract made from peat. This
product was dissolved in sodium hydroxide. After filtration which removed
undissolved matter hydrochloric acid was added. The precipitate consists
of humic acids and hymatomelanic acid. After extraction with ethanol the
hymatomelanic acid which dissolves in ethanol was obtained by evaporation.
The end product had an acid number of 5.1 equivalents per gram. In order to
obtain similar conditions as with humic acid the 1.5-fold amount in grams
was added for the experiments shown in Fig. 14. Even the presence of calcium
ions caused flocculation (Fig. 14). Similar curves were obtained with
polyacrylic acid (14). In order to eliminate the influence of bivalent ions,
deionized water was used for the experiments, the results of which are shown
in Fig. 14. One can observe corresponding curves for the reduction in
-------
371
100-
VI
.y so
a
0.
•0,1mg PAA/L
*0,1mgPAS/L
3,0 4.0
_J
50
c.
o
ID
ttJ
1
6,0
pH
7,0
1 ______ I
8,0 9,0
100r
•a
15
Fig. 11 Influence of flocculant aid on elimination of humic
acid (HS)
10 ppm HS, tap water, 100 ppm Si02 0.111 mmol Al/£
0,1 ppm polyacrylamide (PAA) resp. polyacrylic acid (PAS)
simultaneous dosage of flocculant and flocculant aid.
-------
372
100-
A12(SOJ3
to
o
en
L_
O
50
pHd
from fig. 6
g 3456
0
ZT
7
pH
8
9
10
100
50
&
u,
3
0
8
PH
10
Fig. 12 Influence of pH on elimination of humic acid (HS)
10 ppm HS, tap water, 100 ppm Si09, 0.111 mmol Al/1
-------
373
100-
8 50
c
o
D)
0
- no ozone
reduction by ozone
_i_
3,0 4,0 o,0 6,0 7,0 3,0 '30
c
o
100
0
/ no ozone
_J L
3,0 4,0 5,0 6,0 7,0 8,0
pH
9.0
Fig. 13 Influence of ozonization
10 ppm HS, tap water
0.111 mmol Al/1. 2.8 ppm 0
-------
37^
100
•£ 50
o
O)
o
o.
c
o
3,0 4,0 5,0 6,0 7,0 8,0 9,0
pH
100r
50
Q
_i i
3,0 /,,0 5,0 6,0 7,0 8,0 9,0
pH
50
Cad,
4,0 5,0 6,0 7,0 8,0 9,0
PH
100
50
°3,0 4,0 5,0 6,0 7,0 8,0 9,0
PH
Fig. 14 Elimination of hymatomelanic acid
15 ppm h3rm. acid, deionized water
100 ppm SiO.
-------
375
organics and turbidity when aluminum sulfate is added. The range of reduction
is extended if more aluminum is present. The decrease of the curves with
higher pH is caused by the hydrolysis of aluminum. When bivalent cations
are added removal of organics occurs at higher pH-values as well as it is
observed in Fig. 14 where calcium cloride was added. However, there the
enmeshment of quartz particles in the precipitate occurs only at higher
pH-values. This may be due to the fact that the dissociation of the acid
increases and the intermolecular bonding between the polymer molecules
predominates. As a result, voluminous networks are produced where the
particles are enmeshed and tied up by multivalent cation bridges to the
polymer.
Results which were more similar to those with fulvic acid were obtained with
samples of two rivers such as the river Rhine near Karlsruhe (Maxau) and the
river Ruhr near Milheim. They were selected because they show a very
different behaviour concerning the purification for drinking water. As is
seen in Fig. 15 for both water samples the optima of reduction in organics
and turbidity differ if A1_(SO,) or FeCl_ was added. This means that at
the pH value at which maximum turbidity removal is obtained not all removable
organic substances are precipitated. Only by adding PAC both turbidity and
organic material removal can be matched. The differences between A1_(SO,)„
and Fed. are similar to those which are found for the other systems: maximum
removal of organic matter occurs at a low pH when FeCl is added; the
precipitates formed by adding Fed- are better able to enmesh colloidal
material, as is seen by the two optima in Fig. 15. This was observed in a
more pronounced manner for humic acid removal. For both rivers removal of
organics is greater with Fed,.
For this system too ozoniation does not increase the reduction since ozoniza-
tion causes an increase in solubility of organic matter, and therefore a
deterioration of precipitation (Fig. 16).
Conclusions
Surface waters contain both dissolved organic and colloidal material. It is
possible to choose the trectment conditions in such a way that maximum removal
-------
lOO
50
o
01
0L;
3.0 40 5.0
c
o
o
D
T3
2.0
1.0
0
AiMM
Rhein (Maxau)
TR.-7.3JTU
pHo = 8J0'5
3rngAI/L
6,0 7,0 8,0 9,0
PH
100
50
100
50
o
S>
o
6,0 7,0 8,0 9,0 -
pH £
©3,7JTU g
0
3,0 4,0 5,0
TD
-------
100-
AI2(SQ)3,
Ruhr(Mulheim)
TR. = 1,8JTU
DOC. = 4,4 mg C/L
pH. = 7,5
3mgAI/L
c
o
-o
4)
j ,
2,0
•a
La
1.0
0
100r-
50
0
3,0 4,0 • 5,0
6,0 7,0 8,0 9,0
pH
2,0
1,5
1,0
0,5
0
3,0 4,0 5,0 6,0 7,0 8,0 9,0
pH
Fig. 15 Reduction of organic content in
b) river Ruhr
0.111 mrnol Al and Fe/1
3,0 4,0 5,0 6,0 7,0 8,0 9,0
100-
50
0
2,5
2,0
10
0,5
0
3,0 4,0 5,0 6,0 7,0 8,0 9,0
pH
OJ
I i
3,0 4,0 5,0 6,0 7,0 8,0 9,0
PH
-------
378
100
in
o
o
S>
o
0
no ozon«
(DOC =3^9/1-)
At2(sq)3|
Rhein (Maxau)
pH.= 805(7,95).
lOmg 63/1
3mgAl/L
c
o
o
•3
T>
3,0 4,0 5,0 6,0 7,0 8,0 9,0
pH
2,0
0
~7
no ozone
' K6JTU)
3,0 4,0 5,0 6,0 7,0 8,0 9,0
PH
Fig. 16 Influence of ozone on elimination of organic compounds
-------
379
of turbidity and dissolved organic material takes place at the same time.
For this procedure the type of flocculant and the pH are the main variables.
Because physical operation parameters such as stirring velocity and time do
not influence the precipitation of the dissolved organic compounds, optimal
chemical parameters can be found in the classical jar test.
-------
380
STUDY ON THE ADSORPTION PROPERTIES OF ALUMINIUM OXIDE
AND ITS APPLICATION FOR THE PURIFICATION OF GROUND WATER
CONTAINING HUMIC SUBSTANCES
by S.H. Eberle, H. Stb'ber and D. Donnert, Karlsruhe
Activated carbon, already long in use for the purification of
water, adsorbs hydrophobic, slightly polar organic substances
and only to a smaller extent the hydrophilic and strongly polar
organic acids. But the latter ones, according to recent investi-
gations, make up the main fraction of organic carbon in water
(EBERLE 1973,1974; KOPPS 1972; KEMPF 1975). This conforms with
the practical experience that water treatment with activated
carbon results in a partial elimination of the organic carbon.
Therefore, the application of an adsorbent retaining preferably
organic acids could be of help to solve a number of existing
problems in the purification of waters. Applying it together
with activated carbon should make possible a complete purifi-
cation of waters, mainly polluted with non-biodegradable organics.
In the search for an adsorbent of this kind suitable for tech-
nical application we investigated which organic compounds*
dissolved in water,are removed with aluminium oxide. Its
ability to adsorb organic substances has been known for a long
time. In 1906 it was used for the separation of different organic
compounds from each other and not for their separation from
water. Evidently, no attention was paid for its use for this
purpose. Finally, in 1974 PLOET2 reported on successful experi-
ments concerning the purification of the waste waters from a
wood pulp bleaching plant with aluminium oxide. A large-scale
plant employing this method is due to come into operation in
a pulp and paper factory in Baienfurt in 1976. Other aluminium
compounds have been in use for a long time for water purification,
Aluminium hydroxide, prepared in situ, is a standard flocculating
agent in water treatment. It has a broad application spectrum
-------
381
due to its interactive and sequential action of several effects,
such as removal of turbidity, destabilization of colloids,
chemical precipitation and co-precipitation and adsorption on
the floe (EBI, 1967). In 1914 FREUNDLICH found that,
in doing so, organic acids were also removed from water
(KRCZIL, 1938). Solid aluminium oxide, pretreated at higher
temperatures, on the other hand, is thought to be effective,
principally due to its adsorption properties. Therefore, one
cannot expect at once the same broad spectrum of action. During
flocculation with aluminium salts the "adsorbent" is used only
once. It results in the elimination of the organic compounds
from the water treated, but not in their destruction. Indeed,
the subsequent treatment of the resulting sludge is a serious
problem. On the other hand, the idea of using solid aluminium
oxide for the purpose is motivated by the fact that it can be
regenerated thermally, while at the same time achieving the
combustion of the organic compounds.
Studied aluminium oxides
The aluminium oxides, chromatographic and technical ones,
used for this research, are summarized in Table 1.
Table 1: Data on
" ~ '
M9OS
"for column-
chroma tog raphy"
CTG-8O H activ.
alumina
FL 3OO H activ.
alumina
COMPALOX ,
compressed
activ. alumina
the tested
BET
surface
area
m /g
95
130
3OO
200
aluminiur
bulk "]
weight
3
g/cm ^
l.O
1.0
0.85
! 0.87
!
n oxides
grain
size
mm
0.1
0.07 - 0.15
O.05 - 0.15
1-3
-------
382
The X-ray diagram shows the lines of -y^-AlpO., except in the
case of the FL 300, which has an X—ray amorphous structure.
From the chemical point of view they are not pure,but oxides
hydrated at least on the surface. The water content is between
2 and 1O per cent, depending on the applied activation tempera-
ture (30O - 7OO °C) .
The properties important from the point of view of its practical
application and adsorption capacity are: the BET surface area,
the size of pores, the grain size and the mechanical stability.
Concerning the BET areas, all the tested oxides were inferior
to activated carbon. On the other hand, the pore size is about
1OO A, much greater than that of activated carbon. For the
latter, the pore diameters required for adsorption lie between
5 and 20 8, as given in the literature.
In the course of our own investigations, it appeared that the
basicity of the oxides is another important property. The
oxides contain in their original state, due to the manufacturing
process, up to 1 per cent of sodium, and therefpre give in an
aqueous suspension a strongly alkaline reaction. But in almost
all instances a high pH value is unfavourable for the elimination
of organic substances. The sodium may be washed out with diluted
mineral acid, so that afterwards the aqueous suspension of the
oxide has a pH value between 4.5 and 7. The pH value of a 1O %-
aqueous suspension is used as a reference number for the
acidity of the oxide.
The granular COMPALOX is intended for application in fix-bed
columns. Using fine oxide (
-------
383
Adsorption of pure organic compounds from water
Experimental technique
It was expected that hydrophobic compounds such as benzene,
nitrobenzene etc. would not have a high affinity for aluminium
oxide, and therefore no experimental work was undertaken with
these substances. On the other hand, a great deal of aromatic
acids, bases and phenols were tested by adding 1 or 2 g of the
oxide to 5O ml of an aqueous solution of the compound or the
waste water and shaking slowly for 24 to 48 hours. The determi-
nation of the residual concentration was carried out after
membrane filtration, for pure compounds spectroscopically,
while for the not so well-defined compounds, or for waste
waters, by measuring the dissolved organic carbon (DOC). The
difference between initial and residual concentrations ex-
pressed in per cent of the initial concentration is referred
to as the elimination. The term "adsorption" should be used
for these data only with caution since other mechanisms such
as precipitation may be responsible for the removal of part
of the organic material.
During experiments with some compounds, e.g. ligninsulphonic
acid, precipitation was visually observed in the bulk solution.
The following formulas were used for the calculation of the
data for isotherms:
p
residual concentration C = — • C (mg/1)
from UV measurements: o
oxide load: Q = (CQ-C) ^ (mg/kg)
where C = initial concentration (mg/1)
E = initial extinction at the measuring wave length
o
E = extinction after equilibrium restoration at
measuring wave length
V = dissolving volume for the charge in litre
m = oxide amount for the charge in kg
-------
38**
Adsorbing capacity and functional groups
The dependence of the adsorption capacity on the type of
functional group is shown in Table 2 for some representative
compounds.
Table 2; Elimination of aromatic compounds with aluminium
oxide. Charge: 5O ml solution containing 5OO mg/1
of the compound (1 g A10.,)
compound
p-toluidine
p-cresol
p-chlorophenol
p-nitrophenol :
picric acid
p-toluene sulphonic acid
3-aminobenzene sulphonic ac.
naphtalene-1-sulphonic acid
4-aminonaphtalene-l-sulphonic
acid
pyren-sulphonic acid
naphtalene-1-sulphonic acid
naphtalene-2,6-disulphonic
acid
naphtalene-1,3,6-trisulph.
acid
naphtalene-1,3,5,7-tetra-
sulphonic acid
benzole acid
p-hydroxybenzoic acid
phtalic acid
pyridine-3-carbonic acid
pyridine-2-carbonic acid
thiophene-2-carbonic acid
8-hydroxyquinoline-5-sulph.a.
Congo red
ligninsulphonic acid
humic acid
waste water from a
cellulose bleaching plant
DOC = 290
oxide/pH/
method of
measurement
CTG8O/pH5/UV
CTG80/pH5/UV
CTG8O/pH5/UV
CTG80/pH5/UV
M90S/3
CTG80/pH5/UV
CTG80/pH5/UV
CTG80/pH5/UV
CTG8O/pH5/UV
M90S/pH3/DOC
M90S/pH3/DOC
M90S/pH3/DOC
M90S/pH3/DOC
M90S/pH3/DOC
i M90S/pH5/UV
CTG80/pH5/UV
M90S/pH5/UV
M90S/PH5/UV
M90S/pH5/UV
j M90S/pH5/UV
j M9O/pH3/UV
j M90/pH3/UV
ICOMPALOX/pH3/DOC
M9OSS/pH5/DOC
COMPALOX/pH3/DOC
elimination
6 %
9 %
23 %
14 %
53 %
41 %
67 %
26 %
43 %
99 %
51 %
85 %
95 %
9O %
64 %
80 %
86 %
63 %
60 %-
53 %
78 %
99 %
80 %
56 %
76 %
-------
385
The results may be summarized as follows:
- all aromatic compounds containing dissociable hydrogen
atoms are adsorbed by Al-O.,. This is valid as well for
carbocylic and for heterocyclic compounds;
- the adsorption capacity is increasing in the sequence
bases
-------
Table 3:
386
Elimination from water as a function of the
molecular weight (1 g M90S, 50 ml, initial
concentration 500 mg/1, pH 5)
1
benzene sulphonic acid
naphthalene -l-sulphonic acid
anthraquinone-2-sulphonic acid
ligninsulphonic acid
humic acid from Lake "Hohloh"
humic acid from turf
Mol. Wt.
158
208
288
50 OOO
2O OOO
4O OOO
elimination
26 %
74 %
96 %
48 %
69 %
56 %
This tendency is not continued up to the ligninsulphonic
acid but, in any case, this compound is also adsorbed fairly
well. The same tendency was detected in the case of carbonic
acids. Concerning humic acids, it was shown that the sample
with lower molecular weight is better adsorbed than that with
a higher molecular weight. In the case of the compounds studied
in this connection, the extent of elimination is passing a
maximum with increasing molecular weight. The initial increase
may be understood as the consequence of the increase in mass
of the bonding groups which increase with the molecular weight.
The decrease for very big molecules may be interpreted as a
consequence of the diminishing of the inner surface area. For
the application of water purification it is of importance that
A10 eliminates humic acid and ligninsulphonic acid as well.
Influence of the pH value on the aqueous phase
The pH value was shown to be a significant adjustable parameter,
capable of influencing the adsorption.
Fig. 1: Elimination as a function of the final pH
(charge: 5O ml - 50 mg substance/1 + 1 g M90S)
-------
387
100
§50
-i-'
o
c
E
UJ
Anthrachinon-2-sulf onsdure
Ligninsulfonsaure
-pH
p -Toluidin
10
nach
Fig. 1
Anthrachinon-2-Sulfonsaure: anthraquinone-2-sulphonic acid
Ligninsulfonsaure: ligninsulphonic acid
p-Toluidin: p-toluidine
PH
nach'
final pH
-------
388
As shown in Fig. 1 with several examples,the elimination is
passing a more or less broad maximum with increasing pH, its
location of course depending on the type of the compound used,
and especially on its acidity. In most cases, already from the
pH of 9 onwards, the main part of the organic compounds remains
in the aqueous phase. The best range of activity for the elimi-
nation of organic acids lies between pH 4 and 6. Therefore,
basic oxides giving an alkaline reaction of the aqueous phase
show a worse elimination than acidic oxides. If, for example,
loaded oxide is treated with a basic buffer solution or sodium
hydroxide, desorption occurs. Indeed, the desorption is slow
and incomplete, and therefore a chemical regeneration is not
very promising.
While adjusting the optimal pH value, the fact has to be
considered that by contact with the oxide the pH may change
about two units, whereby it increases in strongly acid
solution and decreases in strongly alkaline solution. The
effect should be measured - particularly if waste waters are
concerned - by means of a preliminary test. As aluminium oxide
dissolves slowly at a pH lower than 2 or higher than 12, it
should not be used under these pH conditions. Apart from the
pH value, the presence of inorganic salts has an influence
on the elimination attained. In fact, it decreased with in-
creasing salt concentrations in the aqueous phase in the few
cases investigated by us. The same behaviour is known for ion
exchange resins.
Influence of the size of the inner surface area of the oxide
In Fig. 2 the relative adsorption strength of the oxides is
demonstrated as a function of the inner surface area on three
organic acids as an example.
-------
389
The low-molecular compounds vanillic acid and anthraquinone-2-
sulphonic acid are better eliminated the greater their inner
surface area. A behaviour of this kind is to be expected if the
oxides are differing only in the size of the inner surface area
and not in their topochemical qualities. For dyestuff waste-
waters containing mainly compounds with a molecular weight
between 3OO and GOO too, we found that the oxide with the
highest BET surface area has always the highest elimination
capacity.
For ligninsulphonic acid, a completely different tendency is
observed: its elimination is less satisfactory with increasing
inner surface area of the oxide. We are interpreting it as an
effect of the pore size. For the macromolecular ligninsulphonic
acid with a diameter of 30-90 8 (KRCZIL, 1938), only part of
it can reach the inner surface, depending on the pore size.
Fig. 2: Elimination of organic acids as a function of
the inner surface area of A1~O~
(charge 5O ml - 1 g substance/I + 1 g oxide)
This is in accordance with the fact that ligninsulphonic
acid is best adsorbed by the oxide type M15O(T),having the
greatest pore diameter of ISO 8. For other oxides the pore
diameter is decreasing with increasing surface area, and
therefore the capacity for the adsorption of ligninsulphonic
acid is also decreasing.
Isotherms
Some representative examples of isotherms are shown in Fig.3
where in a double-logarithmic diagram the oxide load is plotted
against the residual concentration. Within a range of two
powers of ten of the concentration, or the oxide load resp.,
the measured points are in a straight line. Therefore, the
adsorption may be described by the equation of FREUNDLICH-
-------
390
100
o
60
20
0
100 200
-m vg
Anthrachinon -
2-sulfonsre.
Vqnillin-
saure
Ligninsulfon
sciure
tilt t
.M150T M90S CTG80 COMPALOX FL300
300
SURFACE AREA
Fig. 2
Anthrachinon-2-Sulfonsaure: anthraquinone-2-sulphonic acid
Ligninsulfonsaure: ligninsulphonic acid
Vanillinsaure: vanillic acid
-------
391
Fig. 3: Adsorption isotherms of organic compounds
(PHinit. = 5)
. n
q = kF • c
q in mg/kg
c in mg/1
This is also valid for most of the other tested compounds.
But in some cases it was found by means of more intensive
measurements that the isotherm is obeying the Langmuir-
equation. This is, for instance, the case for vanillic acid,
as ROHMANN detected during his research work on the kinetics
of adsorption on AlCu (ROHMANN, 1975).
Oxide loading and costs of water treatment
For the discussion of the attainable oxide t>ad in dependence
of the initial concentration the FREUNDLICH equation in
logarithmic form may be applied:
Ig q = Ig k + n . Ig c (1)
Rearangement of the equation results in:
Ig kp = Ig q - n ° Ig c (2)
If Ig q (the oxide load at equilibrium) and Ig c (the residual
concentration at equilibrium) are kept constant, the logarithm
of the adsorption constant is a linear function of the adsorption
exponent. Here Ig c is the slope of the straight line. Technical
realization of the purification by adsorption will be done
preferably by countercurrent flow and removing that portion of
the oxide on the starting point of the column which has reached
an equilibrium state with the substance. Therefore, for the
final state of the load, the residual concentration is equal
to the inflow concentration. Thus, equation 2 is describing
-------
392
CT
o
en
c
D
"O
~0>
CD
i
ID
X
O
Anthrachinon-2-sulfonsdure
(M90S)
Ligninsulfonsdure
M 150 S)
p-Toluolsulfonsdure
COMPALOX)
(M90N)
p-Toluidin
COMPALOX)
Phenol
COMPALOX
10 100 1000
Restkonzentration C [mg/l]
Fig. 3
Anthrachinon-2-Sulf onsaure: anthraquinone-2-sulphonic acid
Ligninsulf onsaure: ligninsulphonic acid
p-Toluidin: p-toluidine
Oxid-Beladung : oxide loading
p-Toluolsulf onsaure: p-toluene sulphonic acid
Restkonzentration: residual concentration
-------
393
the straight line of those combinations of Ig k and n-values
which, at a certain inlet concentration, result in a certain
loading, in a diagram "Ig k vs. n" each compound occupies one
point. Each combination of Ig c and Ig q forms a boundary line,
above which lie such compounds which by the used inflow concen-
tration reach a higher loading than given by "Ig q".
In Fig. 4 the FREUNDLICH constants, obtained for various com-
pounds and oxides, are plotted in such a diagram. 10 mg/kg,
equalling 1 per cent, was chosen as a fixed value of loading,
which normally is the economical limit. All acids examined
yielded loads greater than 1 per cent for an inflow concen-
tration of 1OOO mg/1. Far worse is the case with simple phenols
and aromatic amines, as water purification by means of AlpO,,
is not possible. For many acids a load of 1 per cent is still
obtained for concentrations of 1OO mg/1 or a higher load at
correspondingly higher concentrations. Only few compounds are
attaining q = 1 per cent for the inflow concentration of
10 mg/1. To this group the higher naphtalene-sulphonic acids
belong, which are causing many problems for waste waters of
pigment and pharmaceutical manufacturing plants. Humic acid,
which is creating problems during the processing of drinking
water, also belongs to this group.
Fig. 4: FREUNDLICH constants of the elimination of
organic compounds with aluminium oxide from water
A load of 1 per cent for an inflow concentration of 10O mg/1
3
means an oxide demand of 1O kg/m . To estimate the costs of
water treatment, it can be assumed that the price for the
regeneration of 1 kg loaded oxide is about 0.15 to O.2O DM,
including investment costs for the whole plant and running
charges for the adsorption and regeneration process (rotary
kiln). The oxide demand ;jiven above corresponds to operating
costs of 1.5 to 2 DM/rn . Only in rare cases it may exceed
-------
391*
Pyromelhths
Kongorot
Naphtholmtetrasulfon s
Huminsa ure
Anthrachinon-2- sulfons
-Hydroxy chmol m-5 - sulfons
Naphthalin - insulfons-
Azobenzolsul fons
fcjaphth -disultons
Bleichereiabwasser
Phthals
—Lignmsulf ons
p- Hydroxy benzoes
Nicotins
M 90S
COMPALOX
CTG
M150T
3-A mi nobenzol sulfons
Ri_krins
Naphthalin-1 -sulfons.
AB S" - . ^
0benzol -
sulfons.
.
C0=10mg/l
Geraden fur
1% Beladung
0
0,5
n
1,5
Fig.
Bleichereiabwasser: waste water from a bleaching plant
Geraden fiir 1 % Beladung: lines for 1 per cent loading
-------
395
this order of magnitude for water purification. This means
that A12O3 can be used with advantage for waste waters of
high concentration prior to biological treatment. However,
for some compounds the isotherm shows suitable oxide load
values for lower inflow concentrations too. For humic acid,
for instance, the oxide demand lies at 0.5 kg/mJ for an inflow
concentration of 1O mg/l,and therefore the purification costs
3
are about O.O7 DM/m . From the results on the studies of pure
compounds it may be concluded that the application of aluminium
oxide is promising for all kinds of aromatic compounds con-
taining acid groups, especially for acids with high molecular
weights.
Experiments with waste waters
The adsorption isotherms of several selected waste waters
were measured, and for comparison percolation experiments in
multicolumn set-ups were carried out (3 to 5 columns, each
containing 2OO - 4OO g oxide, contact time 1O - 2O minutes
per stage).
As shown in Table 4, the oxide consumption, taken from the
isotherm, lies between 6 and 30 kg/kg C for the relatively
concentrated waste waters from production. However, in the
percolation experiments it was much lower. Evidently, well-
adsorbable substances accumulate from mixtures onto the oxide,
whilst in some cases compounds with poor adsorption properties
are penetrating sooner. In this case it is a question of
optimization of the process which degree of elimination and
which oxide consumption value is to be chosen. For the effluent
of an activated sludge process studied, the oxide demand for a
total elimination of the DOC is extremely high and therefore
an application of Al-0., in this case hardly seems acceptable
from an economical point of view.
-------
396
Table 4: Specific oxide consumption value for
waste water purification with Al-O,
Specific oxide
isotherm
1) Porteous filtrate
DOC-45OO mg/1, pH 3
FL3OOS
2) waste water of a
sulphite pulp plant
DOC 28O mg/1, pH 4
3) waste water of an
anthraquinone pigment
production FAM
DOC 9OO mg/1, pH 3
M9OS
4) Dye liquor from a
substantive dyestuff
DOC 380 mg/1, pH 7
FL300S
5) Outflow of an industrial
activated sludge step
DOC 87 mg/1, pH 5
COMPALOX
15 kg/kg C
30 kg/kg C
29 kg/kg C
6 kg/kg C
360 kg/kg C
consumption
percolation
experiment
15 kg/kg C
13 kg/kg C
14 kg/kg C
6 kg/kg C
Tests with ground-water containing humic substances
Isotherms
To confirm the applicability of the oxide consumption value,
obtained with a standardized humic acid, to other types of
oxides and natural substances present in water, the isotherms
of two "organic acids" separated from water by means of the
ALAMIN process (EBERLE, 1973) were measured. The first sub-
stance in question was an extract from water taken from the
river Rhine at Wiesbaden, containing ligninsulphonic acid
as the main pollutant. The second one was an extract from
gravel-filtered water from the waterworks at Fuhrberg near
Hanover which contained humic acid. The oxide used for the
measurement of isotherms and water treatment tests was
-------
397
acid-treated COMPALOX (1 to 3 mm). The concentration para-
meter measured in all cases was the DOC.
For both extracts the isotherm is higher than that of
ligninsulphonic acid, and lower than that of humic acid.
Fig. 5: Adsorption isotherms of high molecular organic
acids and ALAMIN extracts from waters
(pHinifc = 5, oxide acid-treated COMPALOX)
The isotherm plotted for the genuine COMPALOX is also a
good illustration of the poor adsorption effect of a basic
oxide. The very low elimination can be attributed to the
alkaline reaction of the aqueous phase, caused by this oxide.
After treatment with acid, the same oxide has an adsorption
effect, increased by some orders of magnitude , as shown by
the isotherms.
From the isotherm it can be concluded that the oxide demand for
the elimination of DOC from a gravel-filtered water, with
DOC = 10 mg/1, should amount to approximately 0.7 kg/m .
Laboratory tests using columns
The percolating experiments were carried out using three
glass columns, 20 x 3OO mm, with a retention time of about
3O minutes for each column. Each column was filled with
2OO g of acid-treated COMPALOX. The average measured values
of the inflowing water were as follows:
pH =4
DOC = 7 mg/1
KMnO4 =16 mg/1
Extractable by ALAMIN: approx. 6O percent of DOC
-------
398
10-
Huminstiure
Fuhrbergextrakt
Rheiwasserextrakt
Fuhrbergextrakt 1
Compalox originalj
10
c [mg C/l]
100
Fig. 5
Huminsaure: humic acid
Fuhrbergextrakt: extract from Fuhrberg plant
Rheinwasserextrakt: extract from water from river Rhine
Ligninsulfon sre: Lignin sulphonic acid
-------
399
The result of the longest test carried out in this connection
(2 months) is presented in Fig. 6.
Fig. 6: Data of a laboratory percolating test with
ground-water gravel filtrate from Fuhrberg
(3 x 2OO g, acid-treated COMPALOX)
After percolating 50 Ded volume the elimination efficiency
of the first column decreased to 60 %, and after about 50O
bed volume a constant level was reached: first column
55 %, second column 6O %, third column 65% elimination.
Up to the end of the experiment, after the percolation of
1500 bed volume no further decrease was observed.
Apparently, the water contains two groups of material, of
which only one, with a fraction of 6O %, adsorbs well on
AlpOo- The similarity of this percentage with the DOC fraction
extractable by ALAMIN suggests that ALAMIN and Al^O- belong
to the same group of substances.
At the end of the test the load of the oxide of the first
column was about O.6 %, that is almost the saturation load
calculated from the isotherm. However, since the column
still showed 50 % elimination efficiency, it may be assumed
that the capacity of the oxide is considerably higher than
the value calculated from the isotherm. Contrary to this
"better" experimental result , there is the negative obser-
vation that, on the whole, only 60 % to 70 % of DOC can be
removed from the water by A^C^. It should therefore be
checked whether the thus purified water meets the requirements.
Presumably it is not the aim of a waterworks to reach a zero
value of DOC.
-------
100
1+00
S^HIlUy-Messung)
200 400 600 800 100012001400
Kolonnenvolumina
Fig. 6;
UV-Messung: UV measurement
Saule: column
Kolonnenvolumina: Bed volume
-------
1*01
Pilot tests at Fuhrberg
To confirm the laboratory test results, the experiment was
repeated,-on a somewhat larger scale, at Fuhrberg (near Hanover),
but it is still by some orders of magnitude smaller than the
throughput of a waterworks.
Fig. 7: Pilot plant for adsorptive treatment of water
with A1-0-, (3 columns, 52 x 10OO mm)
The transportable apparatus (see Fig. 7) consists of a
sand-filled prefilter, two series-connected columns, 52 x
10OO mm, each filled with 1.8 kg of genuine COMPALOX, and
a third column of the same dimensions, filled with 0.7 kg of
activated carbon, type LS SUPRA. This charge was selected
expecting that the carbon would adsorb the substances not
adsorbed onto Al-0.,. The gravel-filtered water is pumped
through the apparatus with a rate of 4 m/h = 8 1/h. The
calculated retention time within the whole apparatus is
0.7 h.
Fig. 8; Data of a percolation test with the A^O.,-
activated-carbon pilot plant at the
Fuhrberg waterworks (2 x 1.8 kg COMPALOX-
Original, 1 x O.7 kg LS Supra)
Fig. 8 shows the results after four weeks of operation with
the first charge of adsorbents. The efficiency of AlpO, is
lower than that in the laboratory test. However, it must be
considered that COMPALOX-Original was used there and not the
much better acid-treated COMPALOX. Furthermore, the feed water
had an acidity of pH 8 and not of pH 4 as in the laboratory
test. The most important result is the fact that the combination
of AlpO,. with adsorbent carbon permits the total purification
of the Fuhrberg water. This result could not be obtained by
any of the other methods used at Fuhrberg so far. The exact
-------
2Sdulen: innen P 50mm
4 Longe 1000 m m
14 * 15
E- Anschluss Wassercnsc|iluss
fur Krpi selpurnpe
- 7= Pilot plant for absorptive treatment of water
with A12O3 (3 columns, 52 x lOOO mm)
iSaulenruckspulung Ausgang: Columns backwash outlet
iSaulen: Columns
3Innen : Diameter
*Lange: Length
sWasserzahler: Watermeter
« Saulenruck spulung Eingang: Columns backwash inlet
^Vorfilter: Prefilter
8Dosierpumpe: Dosage pump
»Uberlaufbecken: Overflow vessel
10 Auslaufventil: Outlet valve
n Schwimmschalter: Floating level control
12 E-Verteilung: Electronics
13 Ruckspulleitung f. Sandfilter: Backwash pipe for sandfilter
l 4E-Anschluss: Electricity inlet
is Wasseranschluss: Water inlet
i6Schmitt A-B: Cross section A-B
-------
1*03
g100
O
1
4^50
o
o
Saule HI
(A-Kohle)
Saule I
aulel (AI203)
1000 2000 3000
Durchsatz [ I ]
AOOO
Fig. 8
Saule: column
Durchsatz: throughput
A-Kohle: activated carbon
-------
amount of adsorbents required cannot be specified as yet.
First of all, it will have to be established in which way
and how often oxide can be regenerated. However, it can be
said that the oxide demand should be substantially lower than
3
O.5 kg/m , and the demand of adsorbent carbon lower than
O.I kg/m . The actual demand also depends on the desired
degree of water purification. If, for instance, an elimi-
nation of 5O % is considered sufficient, then only half the
quantity of the respective adsorbent has to be regenerated.
The experiments have shown that there are good prospects
for obtaining drinking water,with an adjustable residual
DOC content, from ground-waters of the Fuhrberg type, containing
humic substances, by using a combination of Al^O., with
activated carbon.
-------
^05
USE OF MACROPOROUS ION EXCHANGERS FOR DRINKING WATER PURIFICATION
by
W. Kb'lle, Hanover
During the early sixties ion exchange resins with macroporous structure
became commercially available. The initial reactants for the production
of this type of resin are styrene and divinyl benzene, the same as for
the production of conventional ion exchange resins. The macroporous struc-
ture of the resin is achieved by a special technique of co-polymerisation
of the initial reactants. The system of macropores remaines unaffected,
also during desiccation. In the soaked state, raacroporous resins show
therefore two fundamentally different types of porosity: the macropores
on the one hand and the gel porosity, caused by the soaking process and
corresponding to the porosity of conventional resins, on the other hand.
(HeftS, Engler-Bunte-Institute).
The pore system of macroporous resins is of special importance because
it makes the functional groups in the interior of the grains accessible
for macromolecular components of natural or polluted water. Among the
macromolecular organics, the organic acids play by far the most impor-
tant role (humic acids, sulphonated lignine). Therefore, macroporous
resins are produced as anion exchanger as a rule; there are weak basic
as well as strong basic resins available, both allowing a fast and rever-
sible exchange of organic acids, whereas conventional anion exchange resins
adsorb organic acids .incompletely and release them even more incompletely.
As a consequence, the capacity of conventional anion exchangers loaded
with water containing organic acids is decreasing continuously, an effect,
which is called "fouling".
Macroporous anion exchangers in the OH-form play an important role as
fouling resistent exchangers for production of boiler feedwater. It was
considered earlier,however, to use macroporous anion exchangers in the
Cl-status for additional purification of waters containing humic acids
(Martinola 19?0, Riiffer 1973). Investigations on the exchange kinetics
of macroporous resins, performed at Karlsruhe, showed that the exchange
of organic acids is very fast. This is of great importance for the use of
these resins'in practice (Reicherter 19?0, Ladendorf 19?1).
-------
Effects of water containing humic acids
The water-works of Hanover performed extensive experimental work with ad-
vanced purification of a coloured groundwater with the strong basic anion
exchanger Lewatit MP 500 A (Bayer, Leverkusen). It was used at the plant
of Fuhrberg, .where a water is treated that contains iron,
manganese, humic acids, and about 130 ppra of sulphate. With the aid of
aeration, chlorination, lime treatment,addition of potassium permanganate,
filtration, and break-point chlorination, an iron- and manganese-free
drinking water is obtained. However, the dissolved organic carbon of 9
ppm in the raw water decreases only to 6 ppm in the finished water.
Former attempts to reduce the content of humic acids by economically
acceptable processes (e.g. additional flocculation) were unsuccessful.
The first real chance of success originated from the possible use of
macroporous exchangers and, recently, by the use of activated alumina
(Eberle 1975).
The need for an additional purification of this water results directly
from its properties: the simultaneous presence of 6 ppm of organic car-
bon and of 10 ppm of oxygen results in aerobic bacterial growth. The
consequence is a marked tendency to nacterial development in this water..
Fig. 1 shows an example for the behavior of the Fuhrberg drinking water.
The bacteriarcontaining sample was taken on the occasion of a rou-
tine control of the water distribution system of Hanover and stored in
the laboratory at about 10 degrees centigrade during several days. The
bacterial count of this sample was ascertained daily by the use of
normal gelatin culture dishes. Obviously, after an adaptation period of
a few days the bacterial counts increase logarithmically until the;,' coras
up to about 10 per ml. This level remains approximately constant.
Fig. 1
A second disagreeable property of waters containing high concentrations
of organics is their high chlorine consumption. The water distribution
within the pipe system is therefore a permanent "running match" between the
chlorine consumption and the bacterial development.
It has to be .emphasized that chlorination of organically polluted water
is connected with undesired chlorination reactions which produce chloro-
-------
WOO 000
WO 000
WOOD
E
o
L^
a
<
D
N
1 000
700
10
Rohrnetzprobe WatdstraOe, 25.6.75
Tags
Fig. 1; Germ development in a sample taken from the
pipe system
Koloniezahl: bacterical counts per cm
Rohrnetzprobe: sample of "WaldstraBe", June 25, 1975
Tage: days
-------
form and other chlorinated hydrocarbons (Rook 197*0. Although an actual
danger to man is not yet proved, this fact is an important additio-
nal motive for lowering the content of humic acids in drinking waters.
Experimental results
The experiments at the plant of Fuhrberg may be explained with an example,
shown in fig. 2. They were carried out on an experimental filter filled
with Lewatit HP 500 A.
Fig. 2
Immediately after regeneration of the resin, about 58 % of the organic
carbon (6? % of the permanganate consumption) are removed from the wa-
ter. With increasing throughput, i.e. with increasing load of the resin,
the removal of organic carbon decreases to about 40 % after a throughput
of 5000 bed volumes. That means that 5000 m water can be filtered through
one ra of exchanger material with an average treatment effect of about
50 %, before the next regeneration becomes necessary. A decrease of the
organic carbon from 6 to 3 ppm in the Fuhrberg water results in a load
of 15 g of organic carbon per litre of resin.
The run, shown in fig. 2 was carried out with the maximum specific through-
put, tested during the series of experiments, of 5^ bed volumes per hour.
These conditions correspond to a contact time of 1.1 minutes and to a
filter velocity of 67.5 meters per hour (related to free cross-section,
each. Filter length = 1.25 meters).
The treatment effect does not significantly increase with decreasing fil-
ter velocity; thus, the planning of an additional treatment stage can be
based on high specific throughputs, which correspond to low investment
costs. Anyhow, in practice we can expect two effects which are somehow
ii-Cil-
balancing each other: low water consump corresponds to a high risk of
bacterial growth within the untreated water as well as to a better
treatment effect during filtration..
Laboratory tests for evaluating the tendency of a water for bacterial
growth are fraught with numerous experimental difficulties. However, ac-
cording to the tests carried out at the Hanover water works, a signifi-
cant effect of the MP 500 A treatment on the bacterial growth seems
to exist.
-------
1+09
700
80-
^ 40
en
c
20
spez. Belastung -54 BV/h
KMnO, -V.
org.C
0 1000 2000 3000
Durchsatz (Bettvolumina)
4000 5000 6000
Fig. 2: Percentage removal of organics by MP 500 A filtration
as a function of the throughput; data from several
regeneration cycles
Entfernung: removal (%)
spez.Belastung: specific throughput
Durchsatz: throughput (bed volumes)
= 54 bed vol. per hour
KMn04-V:
KMnO. consumption
-------
Fig. 3
In fig. 3 the observed number of doublings of the bacterial counts during
2k hours is plotted versus the organic carbon content of the samples. The
data are related to the logarithmic growth period of a pure culture of
bacteria. The decrease of the tendency of tacterial growth seems to be
correlated to the organic carbon concentration of the samples.
Fig. k
Fig. k shows results concerning the problem of chlorine consumption.
There is an excellent correlation between chlorine consumption and chemi-
cal oxygen demand. This correlation is evident in so far, as both of
these phenomena are based on oxidation reactions. In this context it has
to be considered, however, that kinetic data (chlorine consumption) are
compared with concentrations (chemical oxygen demand). During the experi-
ments the samples contained exceeding free active chlorine. The chlorine
consumption during the first hour was not taken into account.
It is obvious that the water from the Fuhrberg plant is an exception com-
pared with the chlorine consumption of the other drinking waters which
are distributed by the water works of Hanover. The MP 500 A treatment of
the Fuhrberg water has a significant effect which follows the correlation
mentioned above.
Despite these positive results the effects of a full-scale plant based
on MP 500 A treatment cannot be exactly evaluated with regard to practice.
The reason is that under real conditions the transition range between
low chlorine concentrations and beginning bacterial growth is of impor-
tance. According to experience, this situation is influenced by the con-
dition of the pipe walls to such an extent that its simulation within the
laboratory is quite impossible. These questions as well as the optimum
disinfection of the optimum disinfection °f the water have to be studied
in the full-scale range. In addition, we have to expect that also the
corrosive properties of the water are changed by MP 500 A treatment,
because organic acids are retarding the calcium carbonate precipitation
(Rudek 1975).. This problem has to be studied intensely, too.
-------
1*11
5-
s
Q.
O
I;
Reinwasser Fuhrberg
MP 500 A-Filtrat
Fig
01234567
TOO (mg/l)
3: Effect of MP 500 A - treatment on the rate of germ
development during the log. growth period
Keimverdoppelungen: doublings per day
Reinwasser Fuhrberg: drinking water Fuhrberg
MP 5OO A-Filtrat: MP 50O A filtrate Fuhrberg
O)
8 7h
O)
c
3
-C
N
_O
O
Reinwasser Fuhrberc
W
O Fuhrberg, MP 500A-Filtrat
WW G.
WB.
0
CSB (mg/l
10
20
Fig. 4: Consumption of free chlorine as a function of
chemical oxygen demand
Chlorzehrung: chlorine consumption (ppm) during 46 hours
Reinwasser Fuhrberg: drinking water Fuhrberg
Fuhrberg MP 5OO A-Filtrat: MP 500 A filtrate Fuhrberg
WW G.: plant at Grasdorf
WW B.: plant at Berkhof
CSB (mg/l O : COD (ppm O)
-------
1*12
Regeneration
The regeneration of the exhausted macroporous resin is carried out with
a solution containing 100 grams per liter sodium chloride and 20 grains
per liter sodiura hydroxide. Normally two bed volumes (2 Liters solution
per liter of resin) are used. However, according to fig. 5 tho regenera-
tion solution can be re-used several times.
Fig. 5
The increase of the organic carbon content of the regeneration solution
(in this case up to about JO grams per liter) does not significantly
affect the efficiency of the resin. The ratio between the volumes of
treated water and of regeneration waste can be raised under ideal con-
ditions up to 25000 : 1 (tenfold re-xise of two bed volumes). In practice,
the conditions may be less ideal. It has also be considered that sulphate
is enriched in the regeneration solution in a similar way as humic acids»
Nevertheless, the volume cf regeneration waste is sufficiently small to
discuss and study different alternatives for its disposal. The waste needs
not necessarily to be discharged into a river. Thermal regeneration a.nd
total recycling of the regeneration chemicals were the optimum method
with regard to the environment.
Conclusi on
The wide-spread opinion "reduced groundwaters" cere of minor quality because
of their sometimes very high content of iron, manganese, and hutnic acids,
proves to be untrue, because, as a rule, they are well-protected genui-
ne groundwaters. When it will be possible to solve the problems of
treatment of those waters in a satisfactory and economic way, unused
ground-water resources can be opened up which are to some extent already
known. In addition, ouch a treatment technique may get an increasing
importance as supplement for already existing techniques to treat surface
waters, because a combination of different adsorbents makes excellent
treatment effects possible.
-------
1*13
30
Regenerat-Wiederverwendung
20
Q:
5
10
0
0 20000
Bettvolumina
40000
Fig. 5; increase of organic carbon of the regeneration
solution during re-use
TOG im Regenerat: TOG (g/1)
Bettvolumina: bed volumes of the total throughput
Regenerat-Wiederverwendung: Regenerant recycling
-------
THEORY AND PRACTICE IN THE USE OF ADSORPTION PROCESSES
by H. Sontheimer
There are many outstanding experimental studies and theories
on the principles of adsorption processes. Des-pite this fact,
an empirical approach is at present preferred in practice,
and it is unlikely that this situation will change for some
time.
One of the reasons for this discrepancy lies in the fact
that all basic work so far has been carried out on simple
systems. In practice, rather than a single substance,
complex mixtures of dissimilar materials are encountered.
At the moment, however, there are still no suitable methods
available for their characterization and division into indi-
vidual groups. This complicates the numerical techniques
used in the calculation of adsorption columns.
This is one of the future problems of research work. One
possibility for progress lies in the introduction of process-
orientated analytical methods, which should be combined in a
suitable manner with chemical methods, in particular with
group analysis.
During a process-orientated analysis a characterization of
the organic substances in the water is carried out, according
to the relevant process parameters. The total amount of or-
ganics is divided into fractions, for instance depending on
the adsorption properties of different adsorbents, or by the
kinetics of adsorption on well-characterized adsorbents,
or by other appropriate criteria. So far, only suggestions
and investigations of suitable analytical methods of this
kind have been made. One, for example,is to measure the rate
of oxidation under different conditions in order to characterize
the organic material in the water (MAIER 1973). The same
-------
1*15
procedure is more difficult for the adsorption due to the
lack of knowledge of the individual processes taking place
during adsorption and the frequent occurrence of competitive
adsorption. It can be expected, however, that it will be
possible in the future to develop suitable methods, the results
of which will permit the prediction of the applicability and
optimization of the adsorption processes to achieve a satis-
factory removal of the substances under investigation.
A further difficulty in the application of adsorption processes
lies in the exact definition of the degree of purification
desired. Despite the undoubted progress which will be achieved
here, it cannot be counted on that one single measuring value
will suffice to characterize the process efficiency. Therefore,
it will still be necessary in the future to simultaneously
control and optimize activated carbon plants with different
parameters and methods of investigation.
The criteria which at the moment are especially important for
the evaluation of activated carbon filters are set out below:
1) Activated carbon filters should be operated in such a
way that the concentration of any organic substance
in the effJuent water, due to competitive adsorption,
must not be greater than in the influent.
2) Activated carbon filters must always have adequate
reserve capacities to ensure sufficient effectiveness
following a sudden increase in water pollution. It is
possible to meet this requirement by measuring the
carbon loading at the inlet and outlet of the filter.
3Ji The concentration of non-polar organo-chloro compounds,
if present in the raw water, should be reduced as far
as possible, and should not exceed 10 ug/1.
-------
4) The following additional requirements should be met
by the filter:
a) removal of taste and odour
b ) removal of heavy metals
c) adequate biological performance, if desired
d) lowering of the total concentration of dissolved
organics
The last-mentioned requirement has the advantage that it is
easy to control and measure, e.g. by UV extinction. Provided
sufficient experience is available, it has the additional
advantage that it may be correlated with the other criteria
when using the same raw water.
The above specifications clearly illustrate that it is essential
to deal more thoroughly with the criteria to be used for evalua-
ting the effectiveness of activated carbon filters. The methods
suitable for this purpose, which will not be gone into detail
here, should not only be rapid and automatic if possible, they
should also be orientated towards the aim of the treatment and
supply sufficient process information so that an optimum
operation can be guaranteed.
Important for the future is also the optimization of the pre-
and posttreatment combined with the adsorption process.
Practical experience shows that a considerable improvement
in the effectiveness of treatment plants can be achieved
when the various treatment processes are coordinated.
Considering the increase in the variety of applications of
adsorption processes, the use of activated carbon filters for
biological purification is of special importance. The degree
of purification achieved with this process technique allows
a partial replacement of the commonly used ground- and
slow sand filtration. Furthermore, it is important for the
future that more specific adsorbents are developed which are
-------
able to remove - either on their own or in mixtures with
other adsorbents - as much as possible of the particularly
undesirable components. Such a development is dependent on
a more thorough study of the fundamental processes of ad-
sorption. In particular, more detailed information on the
influence of chemical parameters on adsorption, especially during
the adsorption of mixtures of substances, is required. In
addition, we still lack sufficient knowledge of the accessi-
bility of the different pore systems in an activated carbon
filter, for a useful description of the adsorption kinetics.
The specific, or rather the general adsorbent characteristics
of activated carbon are of importance also for the most
advantageous placement of the adsorption process into the
total scheme of water treatment, whereby special attention
is paid to an optimum utilization of the specific adsorption
characteristics.
The mention of some research work which is of particular
importance in the near future is meant to show that the
development in this sector of adsorption has by no means
been concluded yet.
It was the aim of this course of lectures to summarize the
information and practical experience available so far in the
field of adsorption during drinking water treatment, paying
special attention to practical aspects. By this it was hoped
to pass on to others useful knowledge when applying this
method of treatment. When practical experience is combined with
a thorough knowledge of the basic process data, it will be
possible to achieve still better results in drinking water
treatment. It will then be possible to guarantee the supply
of drinking water of excellent quality at any time, even
under difficult conditions.
-------
1+18
REFERENCES
ABDERHALDEN, E., FODOP., A.
Studien Liber die Adsorption von Aminosauren, Polypeptiden und EiweiB-
kbrpern durch Tierkohle - Beziehungen zwischen Adsorbierbarkeit und
gelbstem Zustand
Koll. Zschr. 27 (192o), Nr. 2, S. 49-58
ABRAM, J.C.
The characteristics of activated carbon
Activated Carbon in Water Treatment, a Water Research Association Con-
ference at the University of Reading, 3-5 April 1973, Paper 1
ADAMSON, A.W.
Physical Chemistry of Surfaces
Interscience Publishers Inc., New York, 196o
AEHNELT, W.
in Ullmann's Enzyklopadie der techn. Chemie, 3. Auf1., 9 (1957), S. 800
ALDRIDGE, J.L.
Design of systems for applying powdered activated carbon
Activated Carbon in Water Treatm., a Wat. Res. Ass. Conf. at the
Univ. of Reading, 3-5 April 1973, Paper 7
###
Standard Methods for the Exam, of Wat. and Wastewat.
Am. Publ. Health Ass., Inc., New York, 12. Ed. (1966)
ARW
Berichte der Arbeitsgem. Rheinwasserwerke e.V. (ARW), Bde. 23-3o
(1966-74)
_ ATKINSON, J.W., PALIN, A.T.
Chemical Oxidation in Water Treatment
9th IWSA Congress, New York (1972), E 1 - E 9
-------
t+19
AWBR
Berichte der Arbeitsgem. Wasserwerke Bodensee-Rhein (AWBR)
Bde. 1-6 (1969-74)
Carbon Chloroform Extract (CCE) in Water
Journ. AWWA 54 (1962), S. 223-227
AWWA - Standard for granular activated carbon
Journ. AWWA 66 (1974), S. 672-681
BAILEY, D.A., BAYLEY, R.W., WAGGOTT, A.
Treatment of Waste waters with the aid of activated carbon
Activ. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ.
of Reading, 3-5 April 1973, Paper 6
BAILLEUIL, G., BRATZLER, K., VOLLMER, W.
Aktive Kohle
Ferdinand Enke Verlag, Stuttgart, 1962, S, 15
BALDAUF, G.
Untersuchungen liber die Adsorption organischer Stoffe aus wa'Brigen
Lbsungen an Einzel- und Mischkohlen
Diplomarbeit, Engler-Bunte^Institut, Lehrst. f. Wasserch., Uni
Karlsruhe, 1974
BALDAUF, G., FRITZ, W., SONTHEIMER, H.
Untersuchungen zur Adsorption von Adsorptivmischungen an Adsorbens-
gemischen
Vom Wasser 45 (1975), S. 91-lo2
BALDAUF, G.,
unverbffentlichte Messungen (1975)
BAUER, R.C., SNOEYINK, V.L.
Reaction of chloramines with active carbon
Journ. WPCF 45 (1973), Mr. 11, S. 229o-23ol
-------
1*20
BELLAR, T.A., LICHTENBERG, J.J., KRONER, R.C.
The occurence of organohalides in chlorinated drinking waters
Journ. AWWA 66 (1974), S. 7o3-7o6
BERNHARDT, H.
Entkeimung von Aktivkohlefiltern durch Erwarmung
Schriftenreihe d. Ver. Wasser-, Boden-und Lufthygiene, Berlin 33,
H. 31 (197o)
BRATZLER, K.
Adsorption von Gasen und Dampfen in Laboratorien und Technik
Techn. Fortschrittsber. 49 (1944), S. 72-76
BRAUCH, V., ZEMLIN, H.
Morphologische Untersuchungen von Aktivkohle mit einem Raster-
El ektronenmi kroskop
Verf.techn. 6 (1972), S. 39o-392
BRAUCH, V.
Theoretische und experimentalle Bestimmung der Beladungsfelder
bei-der Adsorption einzelner Wasserinhaltsstoffe an Aktivkohle
im Festbett
Dissertation, Fak. f. Chem.-Ing.-Wesen, Uni Karlsruhe, 1974
BRAUCH, V., SPAHN, H., SCHLONDER, E.U., SONTHEIMER, H.
Auslegung von Aktivkohlefiltern zur Adsorption organischer Sub-
stanzen aus wa'Brigen Lbsungen
Chem. Ing. Techn. 46 (1974), S. 332
BRAUCH, V.
Ober den Nachweis der Konzentrationsverteilung adsorbierter Sub-
stanzen im Aktivkohle-Korn
Vom Wasser 42 (1974), S. 371-376
BRAUCH, V., SCHLONDER, E.U.
The scale-up of activated carbon columns for water purification
based on results from batch tests. II Theoretical and experimen-
tal determination of breakthrough curves in activated carbon columns
Chem. Eng. Sci. 3o (1975), S. 539-548
-------
BRAUS, H. , MIDDLETON, F., WALTON, G.
Organic compounds in raw and filtered surface waters
Anal. Chem. 23 (1951), S. 116o-1164
BRDICKA, R.
Grundlagen der physikalischen Chemie, Deutscher Verlag der Wissen-
schaften Berlin (1962), S. 476
BRUNAUER, S., EMMETT, P.M., TELLER, E.
Adsorption of gases in multi-molecular layers
Journ. Am. Chem. Soc. 60 (1938), S. 309 - 319
BRUNAUER, S., DEMING, L.S., DEWING, W.E., TELLER, E.
On a theory of the van der Waals adsorption of gases
Journ. Am. Chem. Soc. 62 (194o), S. 1723 - 1732
BUELOW, R.W., CARSWELL, J.K., SYMONS, J.M.
An improved method of determining organics by activated carbon ad-
sorption and solvent extraction. Pt II (Test method)
Journ. AWWA 65 (1973), S. 195-199
BURLEY, M.J., SHORT, C.S.
Economics of acticated carbon treatment
Act. carb. in Wat. Treatm., a Wat. Res. Ass,. Conf. at the Univ.
of Reading, 3-5 April 1973, Paper lo
BUTLER, J.A.V., OCKRENT, C.
Studies in electrocapillarity. Part III. The surface tensions of
solutions containing two surface active solutes
Journ. phys. Chem. 34 (193o)5 S. 2841-2859
CARTER, J.W.
Isothermal and adiabatic adsorption in fixed beds
Trans. Inst. Chem. Eng. 46 (1968), S. 213-221
-------
1+22
CARTER, J.W., HUSAIN, H.
Adsorption of carbon dioxide in fixed beds of molecular sieves
Trans. Inst. Chem. Eng. 5o (1972), S. 69-75
COLLINS, J.J.
The LUB-equilibrium section concept for fixed bed adsorption
Chem. Eng. Progr. Symp. Ser. 63 (1967) Nr. 74, S. 31-35
COOKSEN, J.T. jr.
Adsorption of viruses on activated carbon
Env. Sci. and Techn. 1 (1967), S. 157-16o
COOKSEN, J.T. jr.
Mechanism of viruses adsorption on activated carbon
Journ. AWWA 61 (1969), S. 52-56
COOKSEN, J.T., ISHIZAKI, C. JONES, C.R.
Functional surface groups on activated carbon responsible for
adsorption of organics from water
AIChE Symp. Ser. 68 (1972) Nr. 124, S. 157-168
COONEY, D.O., STRUSI, P.P.
Analytical description of fixed bed sorption of two Langmuir
solutes under nonequilibrium conditions
Ind. Eng. Chem., Fund. 11 (1972), Nr. 1, S. 123-126
COUGHLIN, R.W., EZRA, F.S.
Role of surface acidity in the adsorption of organic pollutants
Environ. Sci. and Techn. 2 (1968), Nr. 4, S. 291-297
COUGHLIN, R.W.
Carbon as adsorbent and catalyst
Ind. Eng. Chem., Prod. Res. Dev. 8 (1969), Nr. 1, S. 12-23
###
DAB VI, Deutscher Apotheker Verlag, Stuttgart (1926)
-------
DEMMERING, W.
Anwendung der Adsorptionsspektralanalyse flir die Untersuchung und
Oberwachung von verunreinigtem Oberflachenwasser
Vom W'asser 11 (1936), S. 22o-237
De VAULT, D.
The theory of chromatography
Journ. Am. Chem. Soc. 65 (1943), S. 532 - 540
Di GIANO, F.A., WEBER, W.J.
Sorption kinetics in infinite bath experiments
Journ. WPCF 45 (1973), S. 713-725
DIN 196o3 - Aktivkohlen zur Wasseraufbereitung - Technische Liefer-
bedingungen (1969)
DIN 66131 Entwurf zur Bestimmung der spezifischen Oberflache von
Feststoffen durch Gasadsorption nach BRUNAUER, EMMETT
und TELLER (BET); Grundlagen (1971)
DRATWA, H., JONTGEN, H.
Rauchgasentschwefelung mit Adsorptionskoksen unterschiedl icher
Eigenschaften
Staub -Reinhaltung der Luft 27 (1967), S. 3ol-3o7
DRYDEN, C.E., KAY, W.E.
Kinetics of batch adsorption and desorption
Ind. Eng. Chem. 46 (1954), Nr. 11, S. 2294-23oo
EBERHARDT, M.
Untersuchungen zur optimal en Kombination von Adsorption, Filtration
und biologischer Reinigung
Verb'ff. Wasserchemie, Engler-Bunte-Institut, Uni Karlsruhe, Heft 5
(1971), S. 358-379
-------
EBERHARDT, M.
Ober die Aufbereitung reduzierter ungepufferter Grundwasser
Vom Wasser 41 (1973), S. 225-242
EBERHARDT, M., MADSEN, S., SONTHEIMER, H.
Untersuchungen zur Verwendung biologisch arbeitender Aktivkohlefilter
bei der Trinkwasseraufbereitung
Veroff. Wasserchemie, Engler-Bunte-Institut, Uni Karlsruhe, Heft 7 (1974)
und gwf Wasser/Abwasser 116 (1975), Nr. 6, S. 245-247
EBERLE, S.H., SCHWEER, K.H.
Bestimmung von Huminsaure und Ligninsulfonsaure im Wasser durch
FIL'ssig-Fllissig-Extraktion
Vom Wasser 41 (1973), S. 27-44
EBERLE, S.H., STDBER, H.
Untersuchungen liber organische Sa'uren im Rhein und seinen Zufllissen
Bericht KFK -1969 UF (1974)
EBERLE, S.H.
Eigenschaften und Anwendung von Aluminiumoxid
- dieses Heft -
EBI
Veroffentlichungen des Bereichs und des Lehrstuhls flir Wasserchemie
am Engler-Bunte-Institut der Uni Karlsruhe
Heft 1 - Entsauerung, Enteisenung und Entmanganung, 1966
Heft 2 - Rohol und Trinkwasser, Untersuchungen zum Pipelineproblem
am Bodensee (1967)
Heft 3-2. Vortragsreihe mit Erfahrungsaustausch Liber spezielle Fra-
gen der Trinkwassertechnologie - Flockung - (1967)
Heft 4 - Moderne Probleme der Wassergute und Wasserverteilung
- 1. Vertiefungskurs - (1969)
Heft 5-4. Vortragsreihe mit Erfahrungsaustausch Liber spezielle
Fragen der Wassertechnologie - Filtration - (1971)
Heft 6 - Untersuchungen zur Filtration (1973)
-------
1+25
Heft 7 - Untersuchungen zur Verwendung biologisch arbeitender
Aktivkohlefilter bei der Trinkwasseraufbereitung (1974)
Heft 8 - Verfahrenstechnische Grundlagen von Adsorption und lonen-
austausch (1975)
EDESKUTY, P.O., AMUNDSON, H.R.
Effect of intraparticle diffusion, agitated nonflow adsorption systems
Ind. Eng. Chem. 44 (1952), S. 1698 - 1703
ENGLISH, J.N., CARRY, C.W., MASSE, A.M., PITKIN, J.B., DRYDEN, F.D.
Denitrification in granular carbon and sand columns
Journ. WPCF 46 (1974), Nr- 1, S. 28-42
ERDOS, E., JftGER, L.
Simultane Adsorption von Phenol und 3.4.Dimethyl phenol aus ver-
dlinnten wa|3rigen Lbsungen
Coll. Czech. Chem. Comm. 24 (1959), S. 2851-286o
ERSKINE, D.B., SCHULIGER, W.G.
Activated carbon processes for liquids
Chem. Eng. Progr. 67(1971), Nr. 11, S. 41-44
FIESSINGER, F., RICHARD, Y.
La technologie du traitement des eaux potables par le charbon
actif granule, I Le choix du charbon
Techn. et Sci. mun. - L'eau (1975), No. 7, S. 271-283
FLENTJE, M., HAGER, D.G.
Re-evaluation of granular carbon filters for taste and odour control
Journ. AWWA 56 (1964), Nr. 2, S. 191-197
FORD, D.B.
The use of granular carbon filtration for taste and odour control
Act. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ.
of Reading, 3-5 April 1973, Paper 12
FREUNDLICH, H.
Ober die Adsorption in Lbsungen
Z.phys.Chem. 57 (19o6), S. 385-469
-------
i+26
FRITZ, W., SCHLONDER, E.U.
Simultaneous adsorption equilibria of organic solutes in dilute
aqueous solutions on activated carbon
Chem. Ing. Sci. 29 (1974), S. 1279-1282
FRITZ, W.
Unveroffentlichte Messungen (i 74-1975)
FRITZ, W.
Adsorption organischer Wasserinhaltsstoffe an Aktivkohle
Vortrag beim Nancy-Treffen, 28./29.6.1975
FUCHS, F., KOHN, W.
Anwendung von Aktivkohlen zur Untersuchung von Wassern;
Beurteilung von Aktivkohlen aufgrund ihres Verhaltens in
Wasserwerks-GroBfi1 tern
- dieses Heft -
FUCHS, F,
Institutsinterne Mitteilung (1973)
FURUSAWA, T. , SMITH, J.M.
Fluid-particle and intraparticle mass transport rates in slurries
Ind. Eng. Chem., Fundam. 12 (1973), Mr. 2, S. 197-2o3
FURUSAWA, T. , SMITH, J.M.
Intraparticle mass transport in slurries by dynamic adsorption studies
AIChE Journal 2o (1974), Nr. 1, S. 88-93
GARDINER, E.R.
Experience with powdered activated carbon for taste and odour control
Act. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ. of
Reading, 3-5 April 1973, Paper 11
GAUNTLETT, R.B., PACKHAM, R.F.
The use of activated carbon in water treatment
Act. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ. of
Reading, 3-5 April 1973, Paper 2
-------
1*27
GETZEN, F.W., WARD, T.M.
A model for the adsorption of weak electrolytes on solids as a
function of pH
Journ. of Coll. and Interf. Sci.31 (1969), Nr. 4, S. 441-453
GETZEN, F.W., WARD, T.M.
Influence of pH on the adsorption of aromatic acids on activated carbon
Environm. Sci. and Techn. 4 (197o), Nr- 1, S. 64-67
GILBERT, E., GOSTEN, M.
Der strahlenchemische Abbau biologisch resistenter organischer
Schadstoffe in wa'Briger Lb'sung
Vom Wasser 41 (1973), S. 359-368
GILBERT, E.
Ober den Abbau von organischen Schadstoffen im Wasser durch Ozon
Vom Wasser 43 (1974), S. 275-29o
GIRARDOT, P.L.
Utilisation du charbon actif en traitement des Eaux
Techn. et Sci.Municip. - L'Eau 65 (197o) No. 2
GOMELLA, C.
Criteres de choix d'un charbon actif pour le traitement des eaux
Techn. et Sci. Municip. L'Fau (Okt. 197o), S. 383-389
GOMELLA, C., BELLE, J.P.
Extraction de micropolluants par le charbon actif
Techn. et Sci. Mun. - L'Eau Mai 1975, S. 195-2o3
GRANDJAQUES, B.L., WALLER, G.
Design of carbon beds
Act. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ.
of Reading, 3-5 April 1973, Paper 8
-------
GROB, K.
Organic substances in potable water and in its precursor. Part. I
Methods for their determination by gas-liquid chromatography
Journ. of Chromatography 84 (1973), S. 255-273
GROB, K., GROB,G.
Technische Beilage, Neue Zlircher Zeitung vom lo.9.1973
GROB, K., GROB, G.
Organic substances in potable water and in its precursor. Part. II
Application in the area of Zurich
Journal of Chromatography 9o (1974), S. 3o3-313
HANSEN, R.E.
The costs of meeting the new water quality standards for total
organics and pesticides
95th Annual conf. of the AWWA at Minneapolis, June, 11 (1975)
HASSLER, J.W.
Activated Carbon
Leonard Hill, London (1967), S. 345 ff
HAYWARD, D.O,, TRAPNELL, B.M.-W.
Chemisorpti.pn
Butterworths Pub!,, London (1964)
HEDDEN, K.
Kohleveredelung
in Ullmann's Enzyklopadie der techn. Chemie (1958), Bd. lo, S. 362
HEIL, G.
Untersuchungen zum Transportmechanismus bei der Adsorption organi-
scher Stoffe aus wa'Brigen Lb'sungen an Aktivkohle
Dissertation, Fakultat fur Chemie, Uni Karlsruhe, 1971
-------
HEIL, G., SONTHEIMER, H.
Bestimmung der Beladung von Aktivkohle mit organischen Stoffen liber
die Geschwindigkeit der Wasserstoffperoxidzersetzung
Fres. Z. f. Anal. Chem. 261 (1972), Nr. 2, S. 117-123
HERMANS, P.M.
Beobachtungen liber die Adsorption der beiden stereoisomeren Hydro-
benzoine an Kohle
Z. f. phys. Chem. 113 (1924), S. 385-388
HEYMANN, E.
Wege zur Aufbereitung eines belasteten Uferfiltrats
Wasserfachliche Aussprachetagung (WAT), Duisburg 1974
HEYMANN, E.
Erfahrungen bei.der Anwendung einer Flockungsfnitration vor den
Aktivkohlefiltern
- dieses Heft -
HIDDINK, G.J.
Erfahrungen mit der klinstlichen Grundwasseranreicherung im Hardhof,
Grundwasserwerk der Wasserversorgung Zlirich
GWA 54 (1974), Nr. 9, S. 393-412 und Nr.ll, S. 5o7-518
HOBDEN, J.F., JELLINEK, H.H.G.
Adsorption of high polymers from solution on to solids
I. Adsorption of polystyrene on charcoal
J. Polymer. Sci. 11 (1953), S. 365 - 378
HDLZEL, G.
Experimentelle Bestimmung der effektiven Diffusionskoeffizienten
fur die Adsorption einzelner organischer Wasserinhaltsstoffe
an technischen Aktivkohlen aus Becherglasversuchen
Diplomarbeit, Engler-Bunte-Institut, Lehrstuhl flir Wasserchemie,
Uni Karlsruhe, 1975
HOLZEL, G.
Unveroffentlichte Messungen, 1975
-------
HOLLUTA, J.
Geruchs- und Geschmacksbeeintrachtigungen uferfiltrierter Trink-
wasser am Niederrhein und ihre Beseitigung
Vortrag, Haupttagung des Sudw.-deutsch.Mass.wirtsch.verb.e.V.
Konstanz 1954, Tagungsniederschn'ft
HOLLUTA, J.
Untersuchungen Liber die Ursachen der Geruchs- und Geschmacks-
beeintrachtigung uferfiltrierter Trinkwasser am Niederrhein,
Methodik und Ergebnisse
gwf, Wasser/Abwasser 96 (1955), Nr. 14, S. 449-461
HOLLUTA, J.
Zwei Jahre Geruchsmessungen am Niederrhein
Kommunalwirtschaft (1959), Heft 6, S. 223-229
HOLLUTA, J.
Geruchs- und Geschmacksbeeintrachtigung des Trinkwassers.
Ursache und Bekampfung
gwf Wasser/Abwasser lol (196o), S. Iol8-lo23 und S. Io7o-lo78
HOLLUTA, J. et al.
Untersuchungen Liber geruchsbildende organische Stoffe im Wasser
und deren Isolierung und Identifizierung
Monatsbull. SVGW 4o (196o), S. Io5-112
HOLLUTA, J.
Organische Extraktstoffe in Oberflachenwassern und deren Bedeutung
fur die Trinkwasserversorgung
Forschung und Fortschritte 38 (1964), Nr. 6, S. -164-166
HOPF, W.
Versuche mit Aktivkohlenzur Aufbereitung des Dusseldorfer Trinkwassers
gwf Wasser/Abwasser lol (196o), Nr. 14, S. 33o-336
HOPF, W.
Zur Wasseraufbereitung mit Ozon und Aktivkohle (Dlisseldorfer Verfahren)
gwf Wasser/Abwasser 111 (197o), Nr. 3, S. 156-164
-------
HUSMANN, S.
Untersuchungen Liber die Sandluckenfauna der bremischen Langsamfliter
Abhandl. der braunschw. Ges. lo (1958), S. 93
HUTCHINS, R.A.
New method simplifies design of activated carbon systems
Chem. Eng. Sci. 2o (1973), Nr. 8, S. 133-138
HYNDSHAW, A.Y.
Activated carbon to remove organic contaminants from water
Journ. AWWA 64 (1972), Nr. 5, S. 3o9-31o
Berichte der International Arbeitsgemeinschaft der Wasserwerke
im Rheineinzugsgebiet (IAWR), Bde. 1-4, 1971 - 1974
*#*
lUPAC-Klassifikation (1972)
JAGER, L., ERDOS, E.
Simultane Adsorption von Phenol und p-Kresol aus verdlinnten
wa'Brigen Lbsungen
Coll. Czech. Chem. Comm. 24 (1959), S. 3ol9-3o23
JAFFE, H.H., ORCHIN, M.
Theory and applications of UV-spectroscopy
John Wiley sons, London, New York, Kap. 2o (1962), S. 557 f
JONTGEN, H.
Habilitationsschrift, Uni Heidelberg (1966)
JONTGEN, H.
Entstehung des Porensystems bei der Teilvergasung von Koksen mit
Wasserdampf
Carbon 6 (1968), S. 297-3o8
-------
JONTGEN, H., van HEEK, K.H.
Reaktionsablaufe unter nicht-isothermen Bedingungen
Fortschr. d. chem. Forschg. 13 (197o), 3/4, S. 6ol-699
JONTGEN, H., KLEIN, J.
Golden Anniversary of the Division of Fuel Chemistry of
the American Chemical Society
Atlantic City, 8.9.1974
JONTGEN, H., KLEIN, J., REICHENBLRGER, J.
Treatment of waste water by activated carbon - design and opti-
mization of the adsorption and reactivation process
Vortrag Mlinchen, GVC/AIChE-Joint Meeting 1974
JONTGEN, H., SEEWALD, H.
Charakterisierung der Porenstruktur mikropordser Adsorbentien
aus Kohlenstoff
Ber. Bunsenges. f. Phys. Chem. 79 (1975), S. 734-738
JONTGEN, H.
Gezielte Herstellung von Porensystemen aus kohlenstoffhaltigem
Material
Ber. Bunsenges. f. Phys. Chem. 79 (1975), S. 747-748
JONTGEN, H.
Herstellung und Eigenschaften von Aktivkohle
-dieses Heft-
JUHOLA, A.J.
Regeneration of activated carbon
Activ. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ,
of Reading, 3-5 April 1973, Paper 9
KAWAZOE, K., SUZUKI, M., CHIKARA, K.
Chromatography study of diffusion in molecular sieving carbon
Journ. of Chem. Eng. of Japan 7 (1974), Nr. 3, S. 151-157
-------
1*33
KAWAZOE, K., KAWAI, T., EGUCHI, Y., ITOGA, K.
Correlation of adsorption equilibrium data of various gases and
vapours on molecular-sieving carbon
J. of Chem. Eng. of Japan 7 (1974), Nr. 3, S. 158-162
KAWAZOE, K., TAKAUCHI, Y.
Mass transfer in adsorption on bidisperse porous materials,
macro-and micropore series diffusion model
Journal of Chem. Eng. of Japan 7 (1974), Nr. 6, S. 431-437
KEMPF, T., PRIBYL, J.
Untersuchungen Liber organische Sa'uren in Gewassern
gwf Wasser/Abwasser 116 (1975), S. 278-281
KIPLING, J.J., TESTER, D.A.
Adsorption from binary mixtures of nonelectrolytes
Nature 167 (1951), S. 612
KIRK, 0.
Encyclopedia of Chem. Techno!., 6. Ed. (1964), Vol. 4, S. 149
KNOBLAUCH, K.
Zur Adsorption organischer Moleklile aus verdlinnten wa'Brigen
Lbsungen an Adsorptionskoksen
Dissertation, TH Aachen 1968
KNOPPERT, P.L., ROOK, J.J.
Treatment of River Rhine water with activated carbon
Activ. Carb. in Wat. Treatm., a. Wat. Res. Ass. Conf. at the
Univ. of Reading, 3-5 April 1973, Paper 5
KOLLE, W., KOPPE, P., SONTHEIMER, H.
Taste and odourproblems with the River Rhine
Proc. Soc. Wat. Treatm. and Exam. 19 (197o), Nr. 2, S. 12o-135
-------
KULLE, W., SONTHEIMER, H.
Experience with activated carbon in West-Germany
Activ. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the
Univ. of Reading, 3-5 April 1973, Paper 15
KOLLE, W., SONTHEIMER, H., STIEGLITZ, L.
Eignungsprlifung von Wasserwerks-Aktivkohlen anhand ihrer Adsorptions-
eigenschaften fur organische Chlorverbindungen
Vom Wasser 44 (1975), S. 2o3-217
KOMIYAMA, H., FURUSAWA, T., SMITH, J.M.
Effectiveness factors for adsorption in slurries
Ind. Eng. Chem., Fund. 13 (1974), Nr. 3, S. 293-296
KOMIYAMA, H., SMITH, J.M.
Intraparticle mass transport in liquid-filled pores
AIChE-Journal 2o (1974), Nr. 4, S. 728-734
KOMIYAMA, H., SMITH, J.M.
Surface diffusion in liquid-filled pores
AIChE-Journal 2o (1974), Nr. 6, S. lllo-1117
KOPPE, P.
Untersuchungen Liber die konkurrierende Adsorption an Aktivkohle
bei der Wasseraufbereitung
Ges.-Ing. 88 (1967), S. 312-317
KOPPE, P.
Untersuchungen Liber schwer abbaubare Sa'uren im Abwasser,
FluBwasser und Uferfiltrat
Informationsblatt der Federation Europaischer Gewasserschutz
No 19 (1972), S. 22-26
KOPPE, P., SEBESTA, G., HERKELMANN, H.
Vorlaufige Mitteilung Liber die biologisch chemische Oxidation
einer schwerabbaubaren Substanz in Gegenwart von Aktivkohle
Ges.-Ing. 95 (1974), Nr. 2, S. 33
-------
1*35
KRCZIL, F.
Aktive Tonerde, ihre Herstellung und Anwendung
F. Enk.e Verlag 1938, S. 112 ff
KOHN, W.
Untersuchungen zur Veranderung der Lage von Adsorptionsisothermen
durch oxidative Behandlung von Aktivkohlen
Dipl.-Arb., Engler-Bunte-Institut, Lehrstuhl flir Wasserchemie,
Uni Karlsruhe (1972)
KOHN, W., SONTHEIMER, H.
EinfluB chemischer Umsetzungen auf die Lage der Adsorptionsgleich-
gewichte an Aktivkohlen
Vom Wasser 4o (1973), S. 115-123
KOHN, W., SONTHEIMER, H.
Einige Untersuchungen zur Bestimmung von organischen Chlorver-
bindungen auf Aktivkohle
Vom Wasser 41 (1973), S. 65-79
KOHN, W.
Untersuchungen zur Bestimmung von organischen Chlorverbindungen
auf Aktivkohle
Dissertation, Fak. f. Ghemie-Ing.wesen, Uni Karlsruhe (1974)
KOHN, W., SONTHEIMER, H.
Zur analytischen Erfassung organischer Chlorverbindungen mit
der temperaturprogrammierten Pyrohydrolyse
Vom Wasser 43 (1974), S. 327-341
KOHN, W., FUCHS, F-
Untersuchungen zur Bedeutung der organischen Chlorverbindungen
und ihrer Adsorbierbarkeit
Vom Wasser 45 (1975), S. 217-232
KURAPKAT, H., WALTHER, E.
Theorie und Praxis der Anschwemmfiltration von Oberflachenwasser
Mitt. VGB 82 (1963), S. 49-55
-------
1+36
LADENDORF, K.F.
Untersuchungen Liber die Austauschkinetik organischer Anionen
an makroporbsen Anionenaustauscherharzen
Dissertation, Uni Karlsruhe (1971)
LANDERS, H.
Aktivkohle als Katalysator bei der Autoxidation in Wasser
geloster Substanzen
Dissertation, TH Aachen (1974)
LANGMUIR, J.
Constitution of solids and liquids
Journ. Am. Chem. Soc. 38 (1916), S. 2221
LINNER, E.R., GORTNER, R.A.
The effect of organic structure on adsorbability
Journ. Phys, Chem. 39 (1935), S. 35-67
LOVE, O.T. jr., ROBEK, G.G. SYMONS, J.M., BUELOW, R.W.
Experience with activated carbon in the USA
Act. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ.
of Reading, 3-5 April 1973, Paper 13
LURGI
Aktivkohle-Reaktivierung. Thermische Reaktivierung kbrniger
Aktivkohlen im zweistufigen FlieBbett
Lurgi-Schnellinformation T lo89/8.75
MADSEN, S.
EinfluB der Oberfla'chenwasserbeschaffenheit auf die Trinkwasser-
qualitat am Beispiel der Ammoniumverbindungen
Vom Wasser 45 (1975), S. Io3-128
MAIER, D.
Untersuchungen zur chemischen Regeneration von erschbpften
Wasserreinigungskohlen
Dissertation, Fak. f. Chemie-Ing.wesen, Uni Karlsruhe (1971)
-------
MAIER, D.
Eine verbesserte Methode zur Bestimmung des chemischen Sauer-
stoffbedarfs mit Kaliumdichromat (COD-Methode)
gwf Wasser/Abwasser 114 (1973), S. 366-37o
MAIER, D.
Wirkung von Ozon auf die gelosten organischen Substanzen
im Bodenseewasser
Vom Wasser 43 (1974), S. 127-16o
MAIER, D., FUCHS, F., SONTHEIMER, H.
Bestimmung von organischen Sa'uren in Wassern und auf Aktivkohlen
gwf Wasser/Abwasser 117 (1976), Nr. 2, S. 7o-74
MANTELL, C.L.
Adsorption
Verlag McGraw Hill, New York, London (1951)
MAQSOOD, R., BENEDEK, A.
The effect of low temperature on organic removal and
denitrification in activated carbon columns
pres. at the 47th Annual Meeting, WPCF, Denver, Col., 1974
MARTINOLA, F., RICHTER, A.
Makropordse lonenaustauscher und Adsorbentien zur Aufbereitung
organisch belasteter Wasser
Vom Wasser 37 (197o), S. 25o-264
MASAMUNE, S., SMITH, J.M.
Adsorption rate studies, interactions of diffusion and surface
processes
AIChE-Journal 11 (1965), S. 34-4o
MATTSON, J.S., MARK, H.B. jr., MALVIN, M.D., WEBER, W.J. jr., CRITTENDEN, J.C.
Surface chemistry of active carbon,Specific adsorption of phenols
Journ. of Coll. and Interf. Sci. 31 (1969), S. 116-13o
-------
MATTSON, J.S., KENNEDY, F.W.
Evaluation criteria for granular activated carbons
Journ. WPCF 43 (1971), S. 221o-2217
MELBOURNE, J.D., MILLER, D.G.
The treatment of River Trent water using granular activated
carbon beds
Act. Garb, in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ.
of Reading, 3-5 April 1973, Paper 4
##•»
Rheinwasserverschmutzung und Trinkwassergewinnung
Memorandum der IAWR (Miinchen, Zurich, Amsterdam), Mai 1973
MERK, W.
Berechnung von Sorptionskolonnen bei unglinstigem Gleichgewicht
(proportionales Muster)
Seminararbeit, EBI, Lehrstuhl f. Wasserchemie, Uni Karlsruhe (1974)
MERK, W.
Experimentelle Bestimmung der zeitlich und drtlich veranderlichen
Beladungen bei der simultanen Adsorption von p-Nitrophenol und
Phenol aus wa'Briger Lb'sung an Aktivkohle im Festbett
Diplomarbeit, EBI, Lehrstuhl f. Wasserchemie, Uni Karlsruhe (1975)
MIDDLETON, F., BRAUS, H., RUCHHOFT, C.
Fundamental studies of taste and odor in water supplies
Journ. AWWA 44 (1952), S. 538-546
MILLER, C.O.M. et al.
A Liquid-phase adsorption study of the rate of diffusion of
phenol from aqueous solution into activated carbon
AIChE-Journal 16 (197o), S. 169-172
MYERS, A.L.,PRAUSNITZ, J.M.
Thermodynamics of mixed gas adsorption
AIChE-Journal 11 (1965), S. 121-127
-------
NAEGELI, F.
Auswirkungen des Phenolunfalles vom 2o.9.1967 im Wasserwerk
der Stadt Zurich
GWA 49 (1969), Mr. 11, S. 372-377
NERETNIEKS, I.
Adsorption of components having a saturation isotherm
Chem. Ing. Techn. 46 (1974), S. 781
NOLTE, VOLLMER
mlindliche Mitteilung, 1974
OCKRENT, C.
Selective adsorption by activated charcoal from solutions
containing two organic acids
J. Chem. Soc. Part I (1932), S. 613
PACKHAM, R.F-
Coagulation of dispersed clays
J. of Coll. Sci. 2o (1965), S. 81
PARK, Y.K.
Beitrag zur Untersuchung von unpolaren organischen Chlorver-
bindungen in Wassern und auf Aktivkohlen
Dissertation, Fak. f. Chem. Ing.wesen, Uni Karlsruhe (1974)
PARK, Y.K., SONTHEIMER, H.
Beitrag zur Untersuchung von unpolaren organischen Chlorver-
bindungen in Wassern und auf Aktivkohle
Vom Wasser 43 (1974), S. 291-313
PEINZE, T., BOLOW, M., SCHIRMER, W.
Eine Methode zur Berechnung par
aus den Daten der Einzelkompone
Z. phys. Chem. 255 (1974), S. 765-772
Eine Methode zur Berechnung partieller Gemischadsorptionswerte
aus den Daten der Einzelkomponentenadsorption
-------
PERRY
Chemical Engineerings Handbook
5thEd. Mc.Graw Hill (1974), S. 16-22
PHELPS, H.J., PETERS, R.A.
The influence of hydrogen ion concentration on the adsorption
of weak electrolytes by pure charcoal
Proc. Roy. Soc. 124 (1929), S. 554-568
PICK, M.
Entchlorung von Trinkwasser durch aktive Kohle
Vom Wasser 3 (1929), S. 71-91
PLOETZ, Th.
Reinigung von Bleichereiabwasser der ZellstoffIndustrie mit
Aluminiumoxid
Das Papier 28 (1974), V 39-V 43
POGGENBURG, W., ENGELS, C., WEISSENHORN, F.J., FUCHS, F., SONTHEIMER, H.
Untersuchungen zur Aktivkohleanwendung bei der Aufbereitung von Rhein-
uferfiltrat
WAT, 27.-29.3.1974, Duisburg
PRUSS, W.
Die Bestimmung der Porengrb'Ben und Porenverteilung in Kohle und Koks
Brennstoff-Chemie 42 (1961), S. 157-16o
RADKE, C.J., PRAUSNITZ, J.M.
Thermodynamics of multi-solute adsorption from dilute liquid solution
AIChE-Journal 18 (1972), S. 761-767
RADKE, C.J., PRAUSNITZ, J.M.
Adsorption of organic solute from dilute aqueous solution
on activated carbon
Ind. Eng. Chem., Fund. 11 (1972), S. 445-451
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REICHENBERGER, J.
Zum Mechanismus der thermischen Regeneration von beladenen Aktiv-
kohlen im Wirbelbett in Gegenwart von Wasserdampf
Dissertation, TH Aachen (1974)
REICHERTER, U.
Untersuchungen Liber das Gleichgewicht bei der Sorption von
Phenylessigsaure an Anionenaustauscher LEWATIT MP 500
Diplomarbeit, EBI, Lehrstuhl f. Wasserchemie, Uni Karlsruhe (197o)
REIF, G., van der HEIDE, R.
Untersuchungen Liber Adsorptionserscheinungen bei organischen
Sa'uren in Alkohol-Wasser-Gemischen an aktiver Kohle mit besonde-
rer Berucksichtigung der in Lebensmitteln vorhandenen Sa'uren
Zschr. f. Untersuchung d. Lebensmittel 64 (1932), S. 513-532
RENN, C.E., BARADA, M.F-
Removal of ABS from heavily polluted waters
Journ. AWWA 52 (1961), S. 129-134
REZANOVICH, A., JEAN, W.Q., GORING, D.A.I.
High resulution electron microscopy of sodium lignin sulfonate
J. appl. polym. Sci.8 (1961), S. 18ol-1812
RICHARD, Y.
Experience with activated carbon in France
Act. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ.
of Reading, 3-5 April 1973, Paper 14
RINKE, G., IRMER, M., GOTTSCHINK, L., DALPKE, H.L.
Gutachten Liber Einzel- und volkswirtschaftliche Auswirkungen
des geplanten Abwasserabgabengesetzes auf die Papier - und
ZellstoffIndustrie
TH Darmstadt, Mai 1975
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ROBEK, G.
Evaluation of activated carbon
US Environm. Prot. Agency, Res. Center, Cincinnati, Ohio 45268,
March 1975
ROGGENKAMP, K.H.
Auswirkungen der Vorchlorung -on Oberflachenwasser bei der Trinkwasser-
aufbereitung
gwf 'Jasser/Abwasser llo (1969), rlr. 16, S. 435
ROHMANN, U.
priv. Mitteilung (1975)
ROOK, J.
Formation of haloforms during chlorination of natural water
Wat. Treatm. and Exam. 23, Part 2 (1974), S. 234-243
ROOK, J.
Bromierung organischer Wasserinhaltsstoffe als Nebenreaktion
der Chlorung
Vom Wasser 44 (1975), S. 57-67
RUBIN, A.J.
Chemistry of water supply treatment and distribution; influence
of surface oxides on adsorption and catalysis with activated carbon
Ann Arbor Science Publishers Inc., Ann Arbor, Mich. (1974), S. 2ol-231
RUDEK, R.
EinfluB von Huminsauren auf die Ausfallgeschwindigkeit von CaC03
aus ubersattigtem Leitungswasser
Diplomarbeit, EBI, Lehrstuhl f. Wasserchemie, Uni Karlsruhe (1975)
RUFFER, H., MDHLE, K.A., SCHILLING, J.
Versuche zur Aufbereitung huminsaurehaltigen Oberflachenwassers
Vom Wasser 41 (1973), S. 243-276
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SCHALEKAMP, M.
Untersuchungen zur AbkVarung des Phanomens der Wiederverkeimung
in Rohrnetzen im Zusammenhang mit Ozonung
GWA 49 (1969), Nr. 8, S. 253-257
SCHALEKAMP, M.
Neueste Erkenntnisse Liber die Wandermuschel Dreissena
Polymorpha Pallas (DPP) und ihre Bekampfung
GWA 51 (1971), Nr. 11, S. 329-336
SCHALEKAMP, M.
Warnung vor der Wandermuschel Dreissena Polymorpha Pallas (DPP)
und Bekampfung derselben
GWA 51 (1971), Nr. 3, S. 49-66
SCHALEKAMP, M.
Die Wirksamkeit von schnellbetriebenen Langsamfiltern
Verbff. Wasserchemie, Engler-Bunte-Institut, Uni Karlsruhe,
Heft 5 (1971), S. 326-357
SCHALEKAMP, M.
Untersuchungsergebnisse von zwei Seewasseraufbereitungsverfahren
mit verschiedenen Aktivkohlen, von Splilversuchen und Mehrschicht-
Aktivkohlefiltern und von Chlorzehrungsversuchen, im Zusammenhang
mit der Bekampfung von DPP-Larven
GWA 53 (1973), Nr. 11, S. 369-384
SCHALEKAMP, M.
Les eaux de lac comme source d'eau de boisson- situation suisse
GEEU 1975, Societe Suisse de VIndustrie du Gaz et des Eaux, Zurich
SCHALEKAMP, M.
Mehrschicht-Schnellfiltration - Vergleichsuntersuchungen
GWA 55 (1975), Nr. 9. S. 495-5ol
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SCHEIDTMANN, H., THRONE, H., SONTHEIMER, H.
Untersuchungen zur Verbesserung der Trinkwasseraufbereitungstech-
nologie am Niederrhein (2. Bericht) Flockungsfiltration in
Mehrschichtfi1 tern
gwf Wasser/Abwasser 114 (1973), S. 467-471
SCHEIDTMANN, W.
Untersuchungen zur Optimierung der Vorbehandlung bei der Anwendung
von Ozon
- dieses Heft
SCHENK, P.
Die Wasseraufbereitungsanlage des Wasserwerks Dlisseldorf "Am Staad"
gwf Wasser/Abwasser Io3 (1962), S. 791-798
SCHMIDT, K.
Die Abbauleistungen der Bakterienflora bei der Langsamfnitration
und ihre Beeinflussung durch die Rohwasserqualitat und deren Um-
welteinflusse
Verbff. d.hydrologischen Forschungsabteilung der Dortmunder
Stadtwerke AG
Diss.Nr. 5 (1963)
SCHWANDER, D.
Stationare Diffusion von Pyridin in wa'Briger Lbsung durch die Wand
eines Aktivkohlezylinders
Bericht Nr. 46-72/K 8 (21.2.1972), Bergbau-Forschung, Essen
SCHWARTZ, H.G. jr.
Adsorption of selected pesticides on activated carbon and mineral
surfaces
Environ. Sci. and Techn. 1 (1967), S. 332-337
SCHWEER, K.H., FUCHS, F., SONTHEIMER, H.
Untersuchungen zur summarischen Bestimmung von organisch gebundenem
Schwefel in Wassern und auf Aktivkohlen
Vom Wasser 45 (1975), S. 29-43
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SCHWUGER, M.J.
Adsorptionskinetik organischer Moleklile an Aktivkohle definierter
Porenstruktur unter den Bedingungen der Trinkwasseraufbereitung
Dissertation, TH Aachen (1966)
SCHWUGER, M.J., JONTGEN, H., PETERS, W.
Adsorption in Wasser gelbster Substanzen an Aktivkoksen
Teil I Kinetische Messungen im Schlittelreaktor bei abnehmender
Konzentration
Chem. Ing. Techn. 4o (1968), S. 9o3-91o
SCHWUGER, M.J.
Adsorptionskinetik von Tensiden und organischen Sa'uren an Aktivkohle
Chem.-Ing. Techn. 42 (197o), S. 443-438
SEEWALD, H.
Untersuchungen zur Sorption organischer Stoffe an Aktivkohlen
Dissertation, TH Aachen (1974)
SEILER, H.
Zur Adsorptionskinetik organischer Moleklile in mit wa'Brigen
Lbsungen durchstrbmten Aktivkohleschlittungen unter den Bedingungen
der Wasseraufbereitung
Dissertation, Uni Aachen (1971)
SEILER, H., JONTGEN, H., PETERS, W.
Adsorption in Wasser gelbster Substanzen an Adsorptionskoksen
Teil III Kinetische Messungen am Integralreaktor bei konstan-
ter Eingangskonzentration
Chem. Ing. Techn. 44 (1972), S. 663-67o
SHILOW, N., NEKRASSOW, B.
Adsorption und chemische Natur einiger organischer Verbindungen
Zschr. f. phys. Chem., Cohen Festband, 13o (1927), S. 65-72
SIGWORTH, E.A., SMITH, S.B.
Adsorption of inorganic compounds by activated carbon
Journ. AWWA 64 (1972), S. 381-391
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SIMON, M., BURGEREIS, W.
Die Beseitigung der Geruchs- und Geschmacksstoffe im Trinkwasser
durch Aktivkohlen (Duisburg)
gwf Wasser/Abwasser lol (196o), Mr. 14, S. 337-339
SIMON, M., SCHEIDTMANN, H.
Die neue Ozonanlage der Stadtwerke Duisburg
gwf Wasser/Abwasser Io9 (1968), S. 877-882
SMISEK, M., CERNY, S.
Active Carbon
Elsevier Publishing Comp., Amsterdam, London, New York (197o)
SNOEYINK, V.L., WEBER, W.J. jr., MARK, M.B. jr.
Sorption of phenol and nitrophenol by active carbon
Environm. Sci. and Techn. 3 (1969), S. 918-926
SNOEYINK, V.L., JAIN, J.S.
Adsorption from bisolute systems on active carbon
Journ. WPCF 45 (1973), S. 2463-2479
SONTHEIMER, H.
Gemeinsame Entwicklungstendenzen und Probleme bei der Wasserauf-
bereitung und Abwasserreinigung
gwf Wasser/Abwasser Io7 (1966), S. 1138-1145
SONTHEIMER, H.
Einige Oberlegungen zum Korrosionsproblem bei der Trinkwasser-
verteilung
Verb'ff. des Engler-Bunte-Instituts der Uni Karlsruhe, Heft 4
(1969), S. 341-350
SONTHEIMER, H.
Untersuchungen zur Belastung des Rheins mit organischen Stoffen
gwf Wasser/Abwasser 111 (197o), Nr. 8, S. 42o-426
-------
SONTHEIMER, H.
Einsatz und Regenerierung von Aktivkohle
WAT lo.-12.3.1971, Wiesbaden
SONTHEIMER, H.
Chemische Parameter der Gewasserverschmutzung
Chetnie in unserer Zeit 6 (1972), S. 175-183
SONTHEIMER, H., MAIER, D.
Untersuchungen zur Verbesserung der Trinkwasseraufbereitungs-
technologie am Niederrhein (1. Bericht)
gwf Wasser/Abwasser 113 (1972), S. 187-193
SONTHEIMER, H.
Aufgaben und Mbglichkeiten des Gewasserschutzes am Beispiel des Rheins
Chem. Ing. Techn. 45 (1973), S. 1185-1191
SONTHEIMER, H.
Untersuchungen zur Aktivkohleanwendung bei der Aufbereitung von Rhein-
uferfiltrat
WAT, 27.-28.3.1974, Duisburg
SONTHEIMER, H.
Use of activated carbon in water treatment practice and its regeneration
Spec. Subj. 3, IWSA Congress Brighton (1974)
SONTHEIMER, H., WEINDEL, W.
Anwendung summarischer Parameter bei der Bestimmung organischer
Wasserinhaltsstoffe unter besonderer Berlicksichtigung der
UV-Extinktion
Hydrochem., hydrogeol. Mitt. 1 (1974), S. 55-7o
SONTHEIMER, H.
Chemische Gewasserverunreinigung und Wassernutzung
Schweiz. Zschr. f. Hydrobiol. 37 (1975), S. 118-134
-------
SONTHEIMER, H.
Neue Erkenntnisse zur Frage der Rheinverschmutzung
Vortrag, IAWR-Jahrestagung, 1-3 Oktober 1975, Amsterdam
SONTHEIMER, H.
Kriterien fur die Oberwachung von Adsorptionsprozessen bei
der Trinkwasseraufbereitung
Vortrag WaBoLu-Kurs, Berlin 3-7, November 1975
SPAHN, H.
Bestimmung der Adsorptionsgeschwindigkeit von organischen Wasser-
inhaltsstoffen an Aktivkohlekbrnern
Dissertation, Fak. f. Chem.-Ing.wesen, Uni Karlsruhe (1974)
SPAHN, H., BRAUCH, V., SCHLONDER, E.U., SONTHEIMER, H.
Auslegung von Aktivkohlefiltern zur Wasserreinigung, Teil I Unter-
suchung der Adsorption am Einzelkorn
Verfahrenstechn. 8 (1974), S. 224-231
SPAHN, H., BRAUCH, V., SCHLONDER, E.U., SONTHEIMER, H.
Auslegung von Aktivkohlefiltern zur Wasserreinigung, Teil II Theore-
tische und experimentelle Bestimmung der Beladungsfelder in Aktiv-
kohlefestbetten
Verfahrenstechn.9 (1975), S. 27-31
SPAHN, H., SCHLONDER, E.U.
The scale up of activated carbon columns for water purification
based on results from batch tests - I Theoretical and experimental
determination of adsorption rates of single organic solutes in
batch tests
Chem. Eng. Sci. 3o (1975), S. 529-537
SPINDLER, P.
Beitrag zur Beschreibung des Konzentrationsverlaufes in Schnell-
filtern der Wasseraufbereitung
Verbff. d. Engler-Bunte-Instituts der Uni Karlsruhe, Heft 6 (1973)
-------
STEENBERG, B.
Ein neues Desorptionsverfahren
Naturwissenschaften 29 (1941), S. 79
STEENBERG, B.
Adsorption and exchange of ions on activated charcoal
Almquist u. Wikseels, Uppsala, Schweden (1944)
STEVENS, A.
Statement on current status of organic carbon adsorbable test
US Environm. Protect. Agency, Res. Center, Cincinnati Ohio 45268,
Feb. 1974
STIEGLITZ, L.
unverbffentlichte Messungen (1973-75)
STUMM, W.
Kinetik der Flockung
Verbff. d. Bereichs Wasserchemie, Engler-Bunte-Institut, Uni
Karlsruhe, Heft 3 (1967), S. 98
SUIDAN, M.F., SNOEYINK, V.L.
Reduction of aqueous free chlorine with granular activated carbon
UILU-WRC-75-olo3,Res. Report No.loS
Univ.of Illinois at Urbana Champaign 1975
SUZUKI, M., KAWAZOE, K.
Batch measurement of adsorption rate in an agitated tank. - Pore
diffusion kinetics with irreversible isotherm
Journ. of Chem. Eng. of Japan 7 (1974), S. 346-35o
SYMONS, J.M.
Taste and odour control
Seminar 95th AWWA Annual Conf. Minneapolis, June 8-13 (1975)
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1+50
SYMOriS, J.M.
National organics reconnaissance survey for halogenated
organics in drinking water
US Environm. Prot. Agency, pre-publication copy,
Cincinnati, Ohio (1975)
THOMAS, W.J., LOMBARDI, J.L.
Binary adsorption of benzene toluene mixtures
Trans. Inst. Chem. Eng. 49 (1971), S. 24o-25o
TIMOFEJEW, D.P.
Adsorptionskinetik
VEB-Verlag fur Grundstoffindustrie Leipzig (1967)
VERMEULEN, Th.
Separation by adsorption methods
Advances in Chem. Eng. Vol. II, New York, Academic Press. Inc. (1958)
VERMEULEN, Th., KLEIN, G.
Recent background developments for adsorption column design
Am. Inst. Chem. Eng. Symp. Ser. 67 (1971), 117, S. 65-74
VERMEULEN, Th., KLEIN, G., HIESTER, N.K.
Adsorption and ion exchange
Sect. 16 Chem. Eng. Handbook, R.H.Perry u. C.H. Chilton
5. Aufl.,New York, McGraw Hill (1973)
VOSTRCIL, J.
Die Entwicklung, Theorie und Anwendung der Anschwemmfiltration
bei der Wasseraufbereitung
Vom Wasser 38 (1971), S. 269-317
WALKER, P.L. jr.
Chemistry and physics of carbon
Marcel Dekker Inc., New York (1966)
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WALLIS, C. et al.
The hazards of incorporating charcoal filters into domestic
water systems
Water Research 8 (1974), S. 111-113
WEBER, H.H.
Entfernung biologisch schwer abbaubarer Substanzen aus dem Abwasser
Chetn. Ing. Techn. 44 (1972), S. 659-662
WEBER, W.J. jr., MORRIS, J.C.
Kinetics of adsorption on carbon from solution
J. San. Eng. Div., Proc. ASCE (1963), SA 2, S. 31-59
WEBER, W.J. jr.
Competitive interactions in adsorption from dilute aqueous bisolute
systems
J. appl. Chem. 14 (1964), S. 565
WEBER, W.J. jr., MORRIS, J.C.
Equilibria and capacities for adsorption on carbon
J. San. Eng. Div., Proc. ASCE (1964), SA 3, S. 79-lo4
WEBER, W.J. jr., MORRIS, J.C.
Adsorption in heterogeneous aqueous systems
Journ. AWWA 56 (1964), S. 447-456
WEBER, W.J. jr., .XEINATH, Th. M.
Mass transfer of perdurable pollutants from dilute aqueous solu-
tion in fluidized adsorbers
Chem. Eng. Progr. Symp., Ser. 63 (1967), Nr. 74, S. 79-89
WEBER, W.J. jr.
Physico-chemical processes for water quality control
Wiley Interscience, New York (1972)
-------
WEBER, W.J. jr.
Powdered Activated Carbon - Application, regeneration and reuse
in wastewater treatment systems a discussion; Proceedings
Sixth Conf. of the International Ass. on Wat. Poll. Res.
Jerusalem, Pergamon Press Ltd., Oxford (1973)
WEBER, W.J. jr.
The prediction of the performance of activated carbon for
water treatment
Act. Carb. in Wat. Treatm., a Wat. Res. Ass. Conf. at the Univ.
of Reading, 3-5 April 1973, Paper 3
WEBER, W.J. jr., et al.
A numeric method for design of adsorption systems
Journ. WPCF 47 (1975), Nr. 5, S. 924-94o
WERNER, R., WURSTER, E., SONTHEIMER, H.
Korrosionsversuche des Zweckverbandes Landeswasserversorgung
mit feuerverzinkten Stahlrohren
gwf Wasser/Abwasser 114 (1973), S. Io5-117
WESTERMARK, M.
Kinetics of activated carbon adsorption
Journ. WPCF 47 (1975), S. 7o4-719
WHEELER, J.M., MIDDLEMAN, S.
Machine computation of transients in fixed beds with interparticle
diffusion and nonlinear kinetics
Ind. Eng. Chem., Fund. ? (197o), S. 624-627
WILLE, H.
Untersuchungen zur Beschreibung der Vorgange in Aktivkohlefiltern
Dissertation, Fak. f. Chem.Ing.wesen, Uni Karlsruhe (1971)
WDLFEL, P., SONTHEIMER, H.
Ein neues Verfahren zur Bestimmung von organisch gebundenem
Kohlenstoff im Wasser durch photochemische Oxidation
Vom Wasser 43 (1974), S. 315-325
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WOLTERS, N., SCHWARTZ, W.
Untersuchungen liber Vorkommen und Verhalten von Mikroorganismen
in reinen Grundwassern
Arch. f. Hydrobiol. 51 (1956), S. 5oo-541
WOODWARD, R.L., DOSTAL, K.A., ROBEK, G.G.
Granular-activated-carbon beds for odour removal
Journ. AWWA 56 (1964), S. 287-295
ZETTLEMOYER, A.C., NARAYAN, K.S.
Adsorption from solution by graphit surfaces
Chemistry and physics of carbon, P.L. Walker jr., Ed.,Vol. 2
(1966), S. 197-224
ZOGORSKI, J.S., FAUST, S.D., HAAS, J.H. jr.
The kinetics of adsorption of phenols by granular activated carbon
pres. at 49thNational Coll. Symp., Potsdam College 16(1975)
ZUCKERMANN, M.M., MOLOF, A.H.
High quality reuse water by chemical-physical waste-water treatment
Journ. WPCF 42 (197o), S. 437-456
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454
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/9-76-030
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
TRANSLATION OF REPORTS ON SPECIAL
PROBLEMS OF WATER TECHNOLOGY
Volume 9 - Adsorption
5. REPORT DATE
December 1976 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
H. Sontheimer (Editor)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Engler-Bunte-Institute
University of Karlsruhe
Karlsruhe, Federal Republic of Germany
10. PROGRAM ELEMENT NO.
1CC614
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
In the summer of 1975 a Conference was held at the Engler-Bunte-Institute
in Karlsruhe, Federal Republic of Germany on the subject of adsorption and
reactivation as a water treatment unit process. Twenty-four papers were presented
by the leading scientists and engineers in Western Europe. The Proceedings of
this Conference have been translated and are presented herein. The information
on the adsorption process formerly available only in German is now available in
English. Copies of the previous 8 volumes are available in German from the
Engler-Bunte-Institute.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Adsorption
Activated Carbon
Treatment
Adsorbents
Activated Carbon
Water Treatment
Chemical Removal
(Water Treatment)
Water Analysis
Potable Water
Activation
b.IDENTIFIERS/OPEN ENDED TERMS
Reactivation Furnaces
Western Europe
Federal Republic of
Germany
The Netherlands
Zurich
c. COSATI Field/Group
13B
3. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
464
20. SECURITY CLASS (This page}
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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