Environmental Protection Technology Series
INDEPENDENT PHYSICAL-CHEMICAL
TREATMENT OF RAW SEWAGE
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-600/2-77-137
August 1977
INDEPENDENT PHYSICAL-CHEMICAL
TREATMENT OF RAW SEWAGE
by
Leon S. Directo
Ching-Lin Chen
Robert P. Miele
Los Angeles County Sanitation Districts
Whittier, California 90607
Contract No. 14-12-150
Project Officer
Irwin J. Kugelman
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U. S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U. S. Environmental Protection Agency,
nor does mention of trade names or commercial products constitute endorse-
ment or recommendation for use.
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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 problems, measuring its impact, and searching
for solutions. The Municipal Environmental Research 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.
Independent physical-chemical treatment of municipal wastewater is an alter-
native technology to biological treatment for achieving secondary effluent
standards. This report summarizes a successful long-term pilot plant
investigation of one mode of this new concept in wastewater treatment.
Francis T. Mayo
Director, Municipal Environmental
Research Laboratory
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ABSTRACT
A 3.17 I/sec (50 gpm) pilot plant evaluation of the independent
physical-chemical treatment (IPC) process was conducted for 27 months at
Pomona, California under the auspices of the U.S. Environmental Protection
Agency and the Los Angeles County Sanitation Districts. The pilot plant
consisted of chemical clarification with alum at 25 mg/1 as Al and an
anionic polymer at 0.3 mg/1 followed by a single-stage, pressurized down-
flow carbon column operated at a hydraulic loading of 2.71 1/sec/m2
(4 gpm/ft2) and an empty-bed contact time of 30 minutes. The main objectives
of the study were to evaluate various methods of controlling sulfide
generation in the carbon column and to determine the effects of repeated
thermal regeneration cycles on the adsorption capacity, carbon loss,
pressure buildup of IPC carbon.
Performance data obtained have demonstrated the stability of the IPC
system in producing effluent of excellent overall quality. The suspended
solids, total COD and total phosphate removals in the IPC system were
96.6%, 94%, and 92%, respectively.
In the course of the study, several methods of controlling sulfide
generation in the carbon column, such as oxygenation, chlorination, and
sodium nitrate addition, were evaluated. Of the methods evaluated,
continuous sodium nitrate addition to the carbon column at an average
dosage of 5.4 mg/1 N was found most effective in preventing sulfide
generation.
The addition of nitrate had another favorable effect in that it permit-
ted, through enhancement of biological activity, a very high organic
loading on the carbon column. At the end of the first cycle, the carbon
capacity was 3.54 Kg total COD removed/Kg carbon and 1.54 Kg dissolved
COD removed/Kg carbon.
Although regeneration was not necessary, it was conducted in an effort
to obtain data on the effects of repeated regenerations on the carbon
characteristics. These were the first large-scale regenerations of granular
activated carbon used in the IPC mode. In all respects, the regenerations
were as successful as those conducted on granular activated carbon used in
the tertiary treatment mode. The performance of the regenerated carbon was
found equal to or slightly better than that of the virgin carbon.
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This report was submitted in fulfillment of Contract No. 14-12-150 by
the Los Angeles County Sanitation Districts, Whittier, California under spon-
sorship of the U.S. Environmental Protection Agency. This report covers the
period from January 1973 to August 1975.
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CONTENTS
Di s cl a i mer i i
Foreword i i i
Abstract i v
Figures viii
Tables x
Acknowledgements xii
1. Introduction 1
Background of the study 2
2. Conclusions 3
3. Recommendations 6
4. Experimental Program 7
Pilot plant description and operation 7
Sampling and testing program 16
5. Experimental Results 18
Chemi cal treatment phase 18
Carbon treatment phase 39
Carbon regeneration results 71
Discussion of system performance 83
6. Economic Analysis 97
Chemical treatment costs 97
Carbon treatment costs 102
IPC system costs 102
References 105
vi
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FIGURES
Number Page
1 Schematic diagram of the IPC pilot plant 8
2 Carbon contactor detai1 10
3 Detail of the carbon column underdrain system... 12
4 Cross sectional view of the multiple hearth furnace 13
5 Schematic diagram of the air pollution control system 15
6 Hourly variation in suspended solids concentration 20
7 Variation in suspended solids concentration and alum dose .... 22
8 Suspended solids removal patterns in the IPC system -
first cycle 24
9 Suspended solids removal patterns in the IPC system -
second cycle 27
10 Suspended solids removal patterns in the IPC system -
third cycle 28
11 Zone settling velocity as a function of suspended solids
concentration 30
12 Batch flux curves of IPC sludge with and without polymer 31
13 Batch flux curve with polymer 32
•
14 Effect of cycle time on filter yield and cake solids 34
15 Performance of various chemical conditioning agents
at 2 minutes cycle time 35
16 Performance of various chemical conditioning agents
at 4 minutes cycle time 36
vm
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FIGURES(CONTINUED)
Number Page
17 Effect of chemical dosage on filtrate quality 37
18 Variation in the carbon effluent total sulfide concentration.. 42
19 Effect of nitrate feed disruption on sulfide production 47
20 Surface wash-water backwash schedule 50
21 Air-water backwash schedule 51
22 Carbon column suspended solids loading and pressure drop -
first cycle 53
23 Carbon column suspended solids loading and pressure drop -
second cycle 56
24 Carbon column suspended solids loading and pressure drop -
third cycle 57
25 COD removal through the carbon column - first cycle 59
26 COD removal through the carbon column second cycle 63
27 COD removal through the carbon column - third cycle 65
28 Effect of regeneration on DCOD removal capacity 67
29 Effect of regeneration on per cent DCOD removal 68
30 DCOD profile through the carbon column 70
31 Turbidity and color removal through the carbon column -
first cycle 72
32 Turbidity and color removal through the carbon column -
second cycle 75
33 Turbidity and color removal through the carbon column -
thi rd cycl e 76
34 Effect of copper waste on COD removal 88
35 Effect of copper waste on suspended solids removal 89
36 Effect of copper waste on turbidity removal 90
37 Proposed IPC system flow sheet 100
ix
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TABLES
Number
1 Virgin Carbon Characteristics
2 Summary of Chemical Clarification System Performance
wi th Ferri c Chi ori de ......................... .
3 Summary of Chemical Treatment System Performance
wi th Al urn and Polymer ............... ,
4 Leaf Filter Test Results ..... .... ...... . ......... . ..... . ..... 38
5 H2S Control Measures i n the Carbon Col umn ................ .... 40
6 Performance of the Various H S Control Measures .......... .... 48
7 Carbon Capacity in IPC Plants ........................... . ____ 69
8 Carbon Col umn Performance ...... ................... .......... . 77
9 Effect of Regeneration on the IPC Carbon Characteristics ..... 79
10 Furnace Operating Conditions during IPC Carbon
Regenerati on .............. . ....... ....... ...... ..... ..... . . 81
11 Summary of Air Pollution Control System Performance ...... .... 84
12 Summary of IPC System Performance ... ................. . ...... 86
13 Heavy Metal Analyses .................. . ................. . ____ 91
*
14 Mineral and Miscellaneous Analyses ... .................... .... 92
15 Heavy Metal Constituents of Quench Water and Carbon Samples .. 94
16 Nitrogen Removal in the IPC System .. ____ .... ____ . ....... ..... 95
17 IPC System Design Data ........ .... .......................... 98
18 Unit Costs for Operation and Maintenance Estimate ---- ........ 99
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TABLES(CONTINUED)
Number Page
19 Estimated Chemical Treatment Costs "101
20 Estimated Granular Activated Carbon Treatment Costs 103
21 Estimated IPC System Costs 104
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ACKNOWLEDGEMENTS
This project was undertaken through a cooperative effort of the
Environmental Protection Agency and the Los Angeles County Sanitation
Districts. The pilot plant evaluation was conducted at the Sanitation
Districts Advanced Waste Treatment Research Facility in Pomona, California.
Acknowledgement is made to Mr. Arthur N. Masse, Former Chief, Municipal
Treatment Research Program of the Advanced Waste Treatment Research
Laboratory in Cincinnati, Ohio, for his invaluable advice in the planning
stage of the project. Thanks are also extended to Mr. William Lee, Former
Project Engineer of the Sanitation Districts, for his participation in the
initial stages of the pilot plant study.
The untiring efforts and assistance of both the laboratory and the pilot
plant operating personnel of the Pomona Advanced Waste Treatment Research
Facility are gratefully acknowledged.
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SECTION 1
INTRODUCTION
The application of granular activated carbon in wastewater treatment
technology has been greatly explored during the past ten years. This wide-
spread use of the carbon has been attributed to the successful development
of economical methods of regenerating the exhausted carbon. The large-scale
use of granular activated carbon in wastewater treatment, however, has been
primarily confined to the so-called tertiary treatment approach, in which
the carbon treatment phase follows the conventional biological secondary
treatment. In this treatment approach, there are inherent benefits achieved:
lower organic load to the carbon bed thus allowing either higher effluent
quality or shorter contact time; lower influent suspended solids, thus
reducing the headless through the carbon bed and obviating problems related
to physical plugging, ash buildup and eventual accelerated loss of the adsorp-
tive capacity of the carbon after repeated thermal regeneration cycles; and
finally, lower supply of bacterial nutrients in the feed to the carbon column,
thus reducing problems associated with abundant biological growth, septicity
and possible hydrogen sulfide generation.
The other carbon treatment approach which has gained widespread interest
in recent years is the independent physical-chemical treatment (IPC) of
municipal and industrial wastewaters, in which chemically clarified raw
sewage or primary effluent, with or without prior inert media filtration,is
applied to the carbon column. This carbon treatment approach attempts to
maximize the use of the granular activated carbon by including in its
function not only the removal of refractory dissolved and biodegradable
organic materials but also the use of the column as a deep bed filter for
the removal of suspended and colloidal solids. Consequently, the carbon bed
is loaded as heavily as possible within the limits of desired effluent
quality. The IPC approach thus seeks to supplant conventional biological
treatment processes. In this respect, the IPC process inherently offers
several major advantages over conventional biological treatment systems,
namely, IPC is practically immune to upsets due to materials toxic to
biological systems, such as heavy metals from industrial waste discharges;
it is more readily adaptable to rapid changes in influent flow and waste-
water composition;it has lower space requirements; and finally, the IPC
process can remove a significant amount of heavy metals.
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BACKGROUND OF THE STUDY
In recent years, there have been several IPC pilot plant studies con-
ducted by various investigators (1,2,3). Although these studies have
indicated that IPC system can achieve excellent wastewater treatment, none
was conducted for an extended period of time. Thus, operational problems
such as sulfide generation, excessive column headless and deterioration of
carbon properties which can only become manifest with time, were not
thoroughly investigated. In addition, at none of these installations was
carbon regeneration practiced. While the technology for carbon regeneration
in a multiple hearth furnace has been well developed and demonstrated for
granular activated carbon used after biological treatment (tertiary treat-
ment mode), it has not yet been applied for granular activated carbon used
in the IPC mode. Therefore, this study was conducted to evaluate the per-
formance over an extended period of time of an IPC system which includes
regeneration of the granular activated carbon.
The specific objectives of the study were: To evaluate the performance
of the chemical clarification system using alum and polymer; to demonstrate
on a long-term basis, the effectiveness of granular activated carbon in the
removal of soluble organic matter from chemically clarified raw sewage; to
evaluate methods of controlling hydrogen sulfide generation in the carbon
column; to determine the effects of repeated thermal regenerations on the
carbon characteristics and performance, and finally to develop the cost
estimates for the IPC system.
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SECTION 2
CONCLUSIONS
1. The IPC pilot plant, consisting of a 3.78 I/sec (60 gpm) chemical
clarification system followed by a 3.16 I/sec (50 gpm) single-stage, packed-
bed, down flow granular activated carbon column, was operated successfully
for 27 months. Extensive operating data collected during the field eval-
uation had demonstrated the capability of the IPC system in consistently
producing effluents of excellent overall quality. The average carbon
effluent TCOD, DCOD, suspended solids, turbidity and color were 19.3 mg/1 ,
13.5 mg/1, 6.7 mg/1, 6.3 JTU and 7.8, respectively.
2. During the virgin adsorption cycle, the carbon capacity was 3.54
Kg TCOD removed/Kg carbon and 1.54 Kg DCOD removed/Kg carbon. The corres-
ponding carbon dosage was 0.021 Kg carbon/m3 (173 Ibs carbon/mil, gal).
The DCOD removal efficiency did not change appreciably in the course of the
virgin run, during which time 113,550 m3 (30 million gallons) of chemically
clarified raw sewage was processed through the column.
3. The organic removal through the carbon column during the entire
study averaged 79.9 percent for TCOD, 72.2 percent for the DCOD and 78.5 for
BOD5. The DCOD removal efficiency through the carbon column increased
following sodium nitrate addition to the carbon column as a result of
enhancement of biological activity. The DCOD removal efficiency of the
regenerated carbon was higher than that of the virgin carbon. The carbon
capacity of the twice-regenerated carbon was slightly less than that of the
once-regenerated carbon.
4. Analyses of metals on carbon prior to and after the first regen-
eration indicated that some of the metals which were removed from the sewage
were not removed during regeneration. However, most of the metals removed
by the carbon did not remain on the carbon but were carried out of the
furnace with the flue gases. Dust collected from the baghouse contained high
levels of Ca, Cd, Cu, Cr, Al , Fe, Sn, Pb, Ni and Zn. Some of these came
from corrosion in the carbon column rather than from the sewage.
5. An evaluation of the carbon characteristics following repeated
thermal regenerations showed that after three regenerations, the iodine
number and methylene blue number decreased about 26 and 5 percent, respec-
tively. During the same period, the molasses number increased about 3.6
percent. The ash content of the carbon increased about 67 percent from
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a virgin level of 6.4 to 10.7 percent after the first regeneration. On the
second regeneration, only a slight increase in ash content was observed
while a decrease was noted in the third regeneration.
6. The carbon regeneration loss ranged from 2.5 to 6 percent with an
overall average of 4.3 percent for the three regenerations.
7. Of the various methods of sulfide control evaluated-namely, oxygen
addition, chlorination, air-water backwash and sodium nitrate addition,
continuous sodium nitrate addition to the carbon column at an average
dosage of 5.4 mg/1 N was found most effective in inhibiting sulfide
generation in the carbon column.
8. The level of sodium nitrate required is a function of the
organic concentration in the feed to the carbon column. The level
required at Pomona to prevent sulfides is specific for the wastewater, and
should not be directly transferred to any other situation. A rough rule
of thumb is that the nitrate should be about 15 percent of the DCOD in
the feed to the carbon column.
9. The carbon column, which served both as deep bed filter and an
adsorber, was routinely backwashed on a daily basis with a volume of
secondary effluent equivalent to 7 percent of the product water. The net
headloss through the column during the daily backwash cycle varied
considerably during the study. The weekly average net headloss varied
from 0.11 Kg/cm2 (1.6 psi) to 3.1 Kg/cm2 (44 psi). The net headloss was
equal to or less than 1.76 Kg/cm2 (25 psi) 50 percent of the time.
10. The bulk of the pollutant removal in the IPC system was accomplish-
ed during the chemical clarification phase. Chemical clarification using
alum at an average dosage of 25 mg/1 Al (275 mg/1 alum) with 0.3 mg/1 of
anionic polymer (Calgon WT-3000) was very effective throughout the study
in producing good quality clarified effluent from raw sewage. The clar-
ified effluent had an average turbidity, suspended solids and TCOD
concentrations of 22.2 JTU, 28.3 mg/1 and 95.8 mg/1, respectively. The
total phosphate in the raw sewage, which had averaged 11.1 mg/1 P, was
reduced by 88 percent, resulting in a clarified effluent with total
phosphate concentration of 1.3 mg/1 P.
11. Results of bench-scale sludge studies performed in the course of
the study showed that the alum-sewage produced was difficult to dewater.
Chemical conditioning at a cost of $15-$17 per ton dry solids was
required to achieve a yield of 4.9-9.8 Kg/m2-hr (1-2 Ib/ft2-hr) with
cake solids of 18 percent.
12. The total treatment cost for a 37,850 cu m/day (10 mgd) IPC
system designed to produce a product water with an average TCOD of 25 mg/1,
DCOD of 16 mg/1 and suspended solids of 8 mg/1 using alum and polymer, is
estimated at 8.69<£/m2 (32.57(^/1000 gallons). The estimated cost is based
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on using an 8 x 30 mesh granular activated carbon with carbon dosage of
0.03 Kg/m3 (250 Ib/mil. gal) and a carbon regeneration loss of 5 percent
per cycle. If regeneration were not required the cost is reduced to
7.92<£/m3 (29.68(^/1000 gallons). These cost estimates are representative
of price levels as of March 1975, with an EPA sewage treatment plant
construction cost index of 232.1.
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SECTION 3
RECOMMENDATIONS
1. The results of the pilot plant study presented in this report
indicate that the granular activated carbon column performance in the
first adsorption cycle remained virtually unchanged throughout the 18.5
months of operation. Although not necessary, the column was regenerated
to obtain data on the effects of repeated thermal regenerations on the IPC
carbon column performance. It is recommended to conduct a long-term eval-
uation of the IPC carbon column without regeneration to determine the ulti-
mate COD removal capacity.
2. Further studies should be carried out to determine the mechanism
by which the biological acitvity on the carbon column allowed significantly
higher carbon capacity. In this connection, attempts should be made to
determine the cause of the apparently higher COD removal capacity of the
regenerated carbon compared to virgin carbon.
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SECTION 4
EXPERIMENTAL PROGRAM
PILOT PLANT DESCRIPTION AND OPERATION
Figure 1 shows the process flow sheet of the IPC pilot plant. The
pilot plant consisted of a 3.78 I/sec (60 gpm) chemical clarification system
followed by a 3.15 I/sec (50 gpm) single-stage, packed-bed, granular
activated carbon column operated in downflow mode. A carbon regeneration
facility complete with an air pollution control system was available in the
pilot plant site. The details of the design and operation of the various
components of the pilot plant are discussed in subsequent sections.
Chemical Treatment System
The chemical treatment system consisted of a rapid mixing unit 0.76m
square (2.5 ft. square) with 1.07m (3.5 ft.) liquid depth followed by a
three-compartment flocculation unit 1.37m (4.5 ft.) wide and 4.11m (13.5 ft.)
long with 1.67m (5.5 ft.) liquid depth equipped with three variable speed
paddle-type flocculators. The raw sewage was pumped at a constant rate of
3.78 I/sec (60 gpm) into a rectangular stilling tank provided with a V-notch
weir for flow measurement. The chemical coagulant, either alum or ferric
chloride, was fed directly to the rapid mixing unit by means of three timer-
controlled positive displacement chemical pumps paced in such a way as to
approximately match the incoming suspended solids concentration. The
diurnal variations of the raw sewage suspended solids concentration was
previously established by the analysis of hourly samples collected over
several 24 hour periods. This feeding pattern was periodically checked
during the course of the study by routinely analyzing for suspended solids,
six four-hour composite samples of raw sewage and clarified effluent. An
anionic polymer (Calgon WT-3000) was added as a coagulant aid at an average
dosage of 0.3 mg/1. The polymer addition was confined to only 12 hours per
day, from 11 a.m. to 11 p.m. to coincide with the period of high coagulant
dosage. After 2.8 minutes of rapid mixing at 140 rpm, the sewage flowed
into the flocculation unit where slow stirring for 42.5 minutes theoretical
detention time was provided. The flocculation was operated at a velocity
gradient, G of about 54 seconds"1. The G value was obtained by calculation
assuming a drag coefficient of 1.5 and a water velocity equal to 3/4 of the
radial velocity at the center of the wooden paddles. The G value for rapid
mixing was not estimated since an auxiliary air mixing was also used.
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RAPID FLQCCULATION
MIX
POLYMER
SEDIMENTATION
ALUM.
OR
FeCk
SEWAGE
co
ADSORPTION
NdN03
1
I 1 ! I I
J C
n r
i i i » i
-
^*-SLUDGE
CARBON
RETURN
TO REGENERATION
*~ FACILITIES
PRODUCT
Figure !. Schematic diagram of the IPC pilot plant.
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The chemically coagulated raw sewage flowed into a rectangular clar-
ifier where it was settled for a theoretical detention time of 84 minutes.
At the flow rate of 3.78 I/sec (60 gpm)5 the clarifier overflow rate and
weir rate, were respectively, 48 cu m/day/m2 (1180 gpd/ft2) and 2.06
1/sec/m (10 gpm/ft). The clarified effluent flowed by gravity to a 1.89-
cu m (500-gallon) surge tank from which 3.15 I/sec (50 gpm) was pumped
continuously to the carbon column. The clarified effluent tank was
provided with an overflow and a low level cut-off switch for pump protection
The chemical sludge was pumped continuously from the clarifier sludge
hopper at a constant rate of 0.17 I/sec (2.8 gpm) during the first 14
months of the study. Thereafter, the chemical sludge pump operation was
placed on a timer control to withdraw sludge at 0.17 I/sec (2.8 gpm) for
15 minutes every hour. The intermittent sludge withdrawal was initiated
in an effort to obtain more concentrated sludge.
Carbon Treatment System
The carbon column, shown in detail in Figure 2, was 1.22m (4 ft) dia-
meter by 9.45m (31 ft) high and was designed for a working pressure of
3.52 Kg/cm2 (50 psi). The interior of the column was coated with three
coats of 8 mills each of Koppers Bitumastic 300 M coal tar epoxy to inhibit
corrosion. The column contained 2360 Kg (5200 Ibs.) of Calgon Filtrasorb
300 (8 x 30 mesh granular activated carbon) having virgin characteristics
shown in Table 1. The 4.87m (16 ft) deep carbon bed was supported by
20.32 cm (8 in) layer of graded gravel placed over Leopold filter blocks.
Figure 3 shows the detail of the column underdrain system.
The chemically clarified raw sewage entered the top of the column
through a 10.16 cm (4 in) pvc pipe. Throughout the study, the column was
operated in a downflow mode at a constant flow rate of 3.15 I/sec (50 gpm)
thereby providing a hydraulic loading of 2.71 1/sec/m2 (4 gpm/ft2) and an
empty-bed contact time of 30 minutes. The column influent discharge outlet
was located about 3.66m (12 ft) above the top of the carbon bed, thereby
providing a capability of as much as 75 percent bed expansion during back-
washing. The column was provided with rotary surface wash mechanism
mounted about 7.62 cm (3 in) above the unexpended carbon bed to aid in the
routine column backwashing.
Carbon Regeneration System
The carbon regeneration facility at the pilot plant site consisted of
a 7 6 cm (30 in) internal diameter vertical refractory-lined Bartlett-
Snow-Pacific, Inc. multiple hearth furnace. As illustrated in Figure 4,
the furnace contained six hearths with two gas burners and steam inlets
in each of the lower three hearths. The furnace was natural gas-fired with
steam added to enhance the regeneration.
The partially dewatered spent carbon from the drain bin was fed by
a screw conveyor provided with a variable speed drive so that the desired
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II" X 12"
PORTHOLE
INFLUENT
BACKWASH
WASH
WATER*
oo
evi
<£>
ro
EFFLUENT-*-,
BACKWASH-
CARBON BED SURFACE
4ft.
REGENERATED CARBON
CHARGE
ROTARY SURFACE SPRAY
2ft. MANHOLE
CARBON DISCHARGE
-UNDERDRAIN SYSTEM
I =2.54 cm.
Figure 2. Carbon contactor detail.
10
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TABLE 1. VIRGIN CARBON CHARACTERISTICS
Carbon Characteristics
Iodine Number ,
Apparent Density ,
Molasses Number
Methyl ene Blue Number,
Ash , %
Mean Particle Diameter
Sieve Analysis :
% retained on #
mg/g
3
g/cm
mg/g
, mm
8
10
12
14
16
18
20
30
pan
Calgon Filtrasorb 300
(8 x 30 mesh)
1040
0.484
222
256
6.4
1.44
3.5
12.6
19.2
16.3
15.1
9.0
6.8
11.7
5.8
11
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LEOPOLD —
FILTER BLOCK
'••'."2" LAYER '/Q- 10 MESH '.'.
LAYER '4" -'/8"
cm
CARBON EFFLUENT
LINE
Figure 3. Detail of the carbon column underdrain system.
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CARBON IN
GAS OUT
6'-0
DRY CARBON
SAMPLING
SHAFT
DRIVE
UNIT
RABBLE
ARM
RABBLE
TEETH
3-0 DIAMETER
1"= 2.54 cm
REGENERATED
CARBON OUT
TO QUENCH
TANK
Figure 4. Cross sectional view of the multiple hearth furnace.
13
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rate of carbon fed to the furnace could be accurately controlled. The
regenerated carbon was discharged from the furnace through a 7.62 cm (3 in.)
diameter stainless steel chute leading from the bottom hearth into a quench
tank, from which the regenerated, quenched carbon was continuously educted
back to the carbon contactor.
Air Pollution Control System
In order to control noxious odors and particulate emissions, which are
the two major air pollutants associated with thermal regeneration of
granular activated carbon, the regeneration furnace was equipped with an
air pollution control system shown schematically in Figure 5. The air
pollution control system consisted of a single cyclone dust separator, a
baghouse, and a natural gas-fired afterburner. During carbon regeneration,
the furnace flue gases first passed through the cyclone, which was designed
to trap all burning particulates 10p in diameter or larger before reaching
the fabric filters in the baghouse. From the cyclone, the gases flowed
through a series of ducts into a baghouse. The ductwork leading to the
baghouse was provided with a valved connection for dilution air addition.
The baghouse was a reversed-air jet cleaned unit (Model 9-6-100 Mikro-
Pulsaire Dust Collector manufactured by Mikropul Division of Slick Corpor-
ation) containing nine 11.43 cm (4.5 in.) diameter Nomex felt filter bags
with a combined filter area of 5.94 sq. m (64 sq.ft.). Each filter bag
was 1.83m (6 ft.) long and was designed for a maximum operating temperature
of 218.3°C (425°F). The filter bags had a rated porosity of 0.17 to 0.99
cu m/min. (25 to 35 scfm) at 1.27 cm '(0.5 in.) water column. The dust-laden
flue gases flowing at a rate ranging from 3.96 to 4.53 cu m/min (140 to 160
scfm) entered the lower section of the baghouse and travelled upward through
the fabric filter cylinder where the dust particles collected on the
exterior surface of the filter bags. A pull-through exhaust fan mounted
on top of the baghouse provided the driving force for the gas flow through
the system. As the dust mat built up on the fabric surface, the pressure
differential across the filters increased to a level at which the deposited
solids had to be removed by reverse air flow. In order to control the
pressure drop through the filter within the desired limits of 2.54 cm (1 in.)
to 15.24 cm (6 in.) of water column, a cyclic timer periodically (2 to 45
seconds interval) actuated solenoid valves which delivered momentary
surges of compressed air rated at 7.03 Kg/cm (100 psi). The dust dislodged
from the exterior surface of the filters during the reverse jet cleaning
operation were collected in a storage drum attached to the discharge "hopper
of the baghouse. The filtered gases from the baghouse then flowed through
the afterburner which was operated between 704.4°C (1300°F) and 760°C (1400°
F) for odor control before final discharge into the atmosphere.
14
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c_n
TO
ATMOSPHERE
FUEL
AIR
AFTERBURNER
BLOWER
SPENT CARBON IN-
MULTIPLE
HEARTH
FLUE GAS
FURNACE
STEAM-
FUEL-
COMBUSTION AIR-
CYCLONE
REGENERATED
CARBON OUT
DUST TO
STORAGE DRUM
QUENCH
TANK
TO
CARBON
COLUMN
MAKE-UP WATER
MOTIVE WATER
«—-COMPRESSED AIR FOR
PULSED AIR
CLEANING OF BAGS
BAGHOUSE
DUST TO
STORAGE DRUM
EDUCTOR
Figure 5. Schematic diagram of the air pollution control system.
-------
Carbon Transfer and Regeneration Procedures
Prior to each regeneration the spent carbon was backwashed with 56.8
m3 (15,000 gallons) of secondary effluent from the main Pomona plant and
hydraulically transferred to the dewatering bin. The dewatered spent
carbon, with about 50 percent moisture content, was conveyed through a
screw conveyor into a six-hearth furnace where it was regenerated at
temperatures ranging from 899°C (1650°F) to 977°C (1790°F). Steam in the
amount of 0.6'Kg steam/Kg carbon was added to the lower two hearths to
enhance regeneration. The regenerated carbon was discharged from the
furnace at the rate of 35-41 Kg/hr (77 to 90 Ibs/hr) into a quench tank
from which it was continuously educted back into the carbon contactor. The
regeneration of one batch of spent carbon normally required 53-66 hours to
complete. After regeneration, the regenerated, quenched carbon was back-
washed with 75.7 m3 (20,000 gallons) of secondary effluent to remove the
carbon fines and the appropriate amount of virgin make-up carbon was added
to replace the carbon lost during the regeneration. The weight of the
virgin carbon added to make up to the original volume was used as the
measure of the carbon loss. The column, with the added make-up carbon, was
then given a final backwash of 7.57 m (2000 gallons) of secondary effluent
before it was placed back in operation.
SAMPLING AND TESTING PROGRAM
In this study, samples of raw sewage, chemically clarified raw sewage
and carbon effluent were obtained 5 days a week using specially designed
automatic samplers programmed to collect six 4-hour composite samples a
day. Each 4-hour composite was made from samples collected automatically
for 3 to 5 seconds once every 15 minutes. For sewage sampling, a Sirco
automatic sampler was used in conjunction with the aforementioned sampling
devices. The 4-hour composite sampl.es were manually combined to obtain
a 24-hour composite sample. All samples taken were refrigerated at 4 °C
prior to analysis. The 24-hour composite samples were analyzed daily for
total chemical oxygen demand (TCOD), dissolved chemical oxygen demand (DCOD),
turbidity, suspended solids and color; two to three times a week for
alkalinity, ammonia, nitrite, nitrate, total aluminum and total phosphate;
once a week for total dissolved solids, sulfate, organic nitrogen, methylene
blue-active substances; and once to twice a month for phenols, minerals
and metal constituents. About three times a week, the six 4-hour composite
samples were individually analyzed for COD and suspended solids in order to
monitor more closely the diurnal variations of these parameters. Tests for
pH, temperature, dissolved oxygen (D.O.) and total sulfides were performed
three to five times a week on grab samples. Grab samples of chemical sludge
were analyzed daily for suspended and volatile solids., and one to two times
a week for total phosphate and total aluminum. Periodically during the study,
thickening and filtration tests were performed on sludge samples.
16
-------
Occasionally, 24-hour composite samples from various depths of the
carbon column were collected using timer-controlled solenoid valves.
These samples were analyzed for DCOD to determine the movement of the
soluble organics wavefront through the carbon column.
Analytical Methods
All physical and chemical analyses were performed in accordance with
the 13th Edition of Standard Methods (4) or the FWPCA Methods for Chemical
Analysis (5) unless otherwise specified.
The mineral and metal analyses were performed using atomic adsorption
methods. Dissolved oxygen was determined by the use of Weston and Stack
dissolved oxygen analyzer. Turbidity was determined by the use of a
Rossum turbidimeter. Tests for ammonia, nitrite, and nitrate were performed
using a Technicon Auto-Analyzer. The activated carbon analyses were
performed using standardized procedures (6).
The thickening tests were performed using 2-liter graduated cylinders
each fitted with a picket rake mechanism operated at a rotational speed
of 1 revolution per minute (rpm).
r\
2 The leaf filtration tests were conducted using a standard 93 cm (0.1
ft ) Eimco leaf filter under a vacuum of 38cm (15 in.) of mercury. Two-
liter samples of gravity-thickened and chemically-conditioned sludge were
used in the filtration tests.
Regeneration Schedule
When the carbon became exhausted based on a predetermined level of
either effluent quality or organic loading, the column was taken off stream
in preparation for regeneration. In this study, the original criterion
for regeneration was a carbon effluent total chemical oxygen demand (TCOD)
limit of 40 mg/1. During the virgin adsorption cycle, however, it was
found that the carbon effluent TCOD concentration remained practically
constant at a level of about 20-24 mg/1 through the first 18 months of
column operation. Because of this observation, it was decided to dis-
regard the effluent TCOD criterion and to regenerate the carbon. Thus,
in the second and third adsorption cycles, the carbon was regenerated
every 3 to 5 months without regard to the state of exhaustion of the
carbon in an effort to obtain data on the effect of repeated thermal re-
generations on the carbon characteristics and performance. The data
generated in this study was divided into three groups to correspond to the
carbon column operation in between the regenerations.
17
-------
SECTION 5
EXPERIMENTAL RESULTS
CHEMICAL TREATMENT PHASE
Performance
During the first one and one half months of the study when the carbon
column was being installed, ferric chloride, which was available from a
previous study was used for coagulation. After this shakedown operating
period, ferric chloride was replaced with alum as the primary coagulant.
Table 2 presents the performance of the chemical treatment system with
ferric chloride addition. The raw sewage TCOD and suspended solids con-
centration during the ferric chloride addition period was about 50 percent
higher than that observed during the major portion of the study when alum
was used as the coagulant. Because of the high influent TCOD and suspended
solids concentration, the corresponding clarified effluent concentrations
were also high. When expressed as percent removal, however, the TCOD and
suspended solids removal with ferric chloride were comparable to those
observed with alum addition.
Starting in March 1972, when the carbon column was placed in operation
until the termination of the study, alum, at an average dosage of 25 mg/1
Al (275 mg/1 alum) was used as the primary coagulant in the chemical treat-
ment of the raw sewage. During the first month of alum addition, solids-
liquid separation in the sedimentation tank was rather poor, resulting in
excessive amounts of floe being carried over with the clarified effluent.
In order to enhance settling of the alum floe, an anionic polymer (Calgon
WT-3000) was added at an average dosage of 0.3 mg/1 to the first compart-
ment of the flocculation unit. While alum was fed continuously, the
polymer was added for only 12 hours per day corresponding to the period of
high alum dose. As mentioned previously, the alum feeding was varied through-
out the 24-hour period to approximately match the influent suspended solids
concentration. In order to check the effectiveness of the pacing of the
alum feed, hourly samples of raw sewage and clarified effluent collected over
several 24-hour periods were analyzed for suspended solids. The results of
one of these tests are shown in Figure 6. These hourly suspended solids data
clearly demonstrate the effectiveness of the chemical clarification system
in producing consistent effluent quality. Periodically, during the course
of the study, the effectiveness of the dosing pattern was checked by
18
-------
TABLE 2. SUMMARY OF CHEMICAL CLARIFICATION SYSTEM PERFORMANCE WITH FERRIC CHLORIDE
Ferric Chloride
Dosage, mg/1
Fed 3
80
107
Raw Sewage, mg/1
TCOD
495
483
Susp.
Solids
280
303
Total
P
11.4
12.7
Clarified Effluent (mg/1)
TCOD
160
136
Susp.
Solids
52
52
Total
P
2.1
1.8
% Removal
TCOD
67.9
71.8
Susp.
Solids
81.4
82.8
Total
P
81.6
85.8
-------
320
280
240
•^200
e
05
o
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S 160
Q
ID
O
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120
C/5
80
40
AVG.
'W-RAW SEWAGE
A .
ALUM. DOSE =24 mg/l AI3+
POLYMER DOSE = 0.3 mg/l
\
\
/ V
/
^
/,
\ /
•CLARIFIED EFFLUENT
I
7A.M.
3PM.
7
TIME
3A.M.
Figure 6. Hourly variation in suspended solids concentration.
20
-------
routinely analyzing for suspended solids the six 4-hour composite samples
of raw sewage and clarified effluent. Typical results of the analysis of
the six 4-hour composite samples for suspended solids, which are presented
in Figure 7, indicate that the pacing of the chemical dosage was indeed
effective in producing chemically clarified effluent of essentially constant
quality. Figure 7 was prepared by plotting the average of 17 days data for
the month of July, 1972. Data for other months also show similar perform-
ances.
Table 3 presents a summary of the average performance of the chemical
treatment system during the course of alum addition. The system perform-
ance during each of the three periods corresponding to the three adsorption
cycles of the granular activated carbon column is shown separately in the
table. As indicated in the table, the overall suspended solids and TCOD
removal efficiencies in the chemical clarification phase were 85.8 percent
and 70.2 percent, respectively. Throughout the study, the chemical treat-
ment system was highly effective and consistent not only in the removal of
suspended solids and TCOD, but also in the removal of total phosphate. The
chemically clarified effluent had an average TCOD of 95.8 mg/1 and an average
suspended solids of 28.3 mg/1. The dissolved COD concentration, however,
remained virtually unchanged during the chemical treatment. This observa-
tion is contrary to what other investigators have found (3,12). The average
total phosphate concentration in the raw sewage was reduced from 11.1 to 1.3
mg/1 P during the alum treatment. Additional removal of suspended phosphate
was achieved through the carbon column thereby boosting the overall total
phosphate removal efficiency through the IPC system to 91.9 percent.
Figures 8 through 10 illustrate the weekly average suspended solids
removal patterns. The data in these figures along with those presented in
Table 3, demonstrate that with the exception of the DCOD removal, the major
portion of pollutant removal was accomplished in the chemical treatment
system. Moreover, it is apparent from the data that in spite of the consid-
erable variation in the raw sewage strength, the chemical clarification
system performance remained relatively stable.
Sludge Thickening and Dewatering Properties
During the first fourteen months of the study, the sludge produced in
the chemical clarification system was withdrawn continuously at the rate of
0.17 I/sec (2.8 gpm) without any attempt to thicken the sludge. Because of
this continuous sludge withdrawal the sludge produced was rather dilute
with an average suspended solids concentration of only 4100 mg/1 (ranged
from 1700 to 6500 mg/1). From the 15th month until the termination
of the study, the sludge pumping operation was placed in an intermittent
mode in an attempt to further thicken the sludge in the sedimentation tank.
The total daily sludge volume withdrawn amounted to about 1.2% of pilot
plant flow. The suspended solids concentration of the sludge varied from
about 1 to 2% during the period when intermittent sludge withdrawal was
practiced. The sludge contained 1.6 percent total phosphate and 8.3 percent
total aluminum on a dry solids weight basis.
21
-------
320
280
240
E200
O
CO
Q 160
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O
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a.
(/)
CO I2°
80
40
i— r T • 1 s i
1 " 1
1 AVG. ALUM. DOSE = 24 mg/l AI3 +
j POLYMER DOSE =0.3 mg/l
_ ,_J | RAW SEWAGE;
1
~~ j^-4-HR. COMPOSITE
1 ^ 24- HR. COMPOSITE -
1
1
_ —
1
I
_ —
j .__
ALUM. DOSE^
CLARIFIED EFFLUENT"-
^r4-HR. COMPOSITE
^24-HR. COMPOSITE
111 i
30
20
10
7A.M. II 3RM. 7 II 3A.M. 7
TIME
u
CO
o
o
Figure 7. Variation in suspended solids concentration and alum
dose.
22
-------
TABLE 3. SUMMARY OF CHEMICAL TREATMENT SYSTEM PERFORMANCE WITH ALUM AND POLYMER^
Parameters
Suspended Solids, mg/1
Turbidity, JTU
TCOD, mg/1
DCOD, mg/1
BOD5, mg/1
Color
Total Phosphate, mg/1 P
Nitrate, mg/1 N
pH
Raw Sewage
(a)
205
331
50.4
11.3
7.65
(b)
180
295
45.6
11.1
7.67
(c)
198
315
50.8
9.6
7.78
Overall
Avq.
199
3?1
49.4
11.1
7.68
Clarified Effluent
(a)
30.9
24.4
9R 4
48
38.8
19.2
1.5
0.92
6.85
(b)
22.8
19.9
86.2
48.4
30.4
20.4
0.86
.87
6.64
(c)
24.5
20.6
98.2
52.1
33.6
21.6
0.85
.78
6.40
Overall
AVQ.
28.3
22.9
95.8
48.6
36.2
20
1.3
.90
6.75
Percent Removal
(a)
84.9
70.3
4.8
86.7
(b)
87.3
70.8
92.3
(c)
87.6
68.8
...
91.1
Overall
Avg
85.8
70.2
1.6
88.3
IN3
CO
* Average alum dosage = 25 mg/1 Al (275 mg/1 alum); Average polymer dosage = 0.3 mg/1 Calgon WT-3000
(a) 1st cycle average concentration
(b) 2nd cycle average concentration
(c) 3rd cycle average concentration
-------
4="
350
VOLUME TREATED, million gallons
5.5 7.3 8.8 10.3
12 16 20
STUDY PERIOD, (WEEKS)
12.6
UNIT CONVERSIONS
mil gal x 3785 = cu m
RAW SEWAGE
CLARIFIED EFFLUENT
CARBON EFFLUENT
Figure 8- Suspended solids removal pattern in the IPC system- first cycle
-------
350
12.6
14.4
VOLUME TREATED, million gallons
15.9 16.6 18.0 19.6
21.5
23.1
24.8
32
UNIT CONVERSIONS:
mil gal x 3785 = cu m
CLARIFIED EFFLUENT
40
44 48 52
STUDY PERIOD, (WEEKS)
56
60
64
Figure 8. Continued
-------
350
VOLUME TREATED, million gallons
24.8 25.6 28.6 30.0
300
£ 250
*>
9
_j
o
200
Q
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Q
Z
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a.
150
UNIT CONVERSIONS:
mil gal x 3785= cu m
RAW SEWAGE
CLARIFIED EFFLUENT
CARBON EFFLUENT
64
68
72 76 80 84
STUDY PERIOD, (WEEKS)
88
92
96
Figure 8. Continued
-------
350
1.8
VOLUME TREATED, million gallons
3.7 5.5 7.3 9.1
10.3
CLARIFIED EFFLUENT
CARBON EFFLUENT
T
UNIT CONVERSIONS:
mil gal x 3785= cu m
/*>
12 16 20
STUDY PERIOD, (WEEKS)
Figure 9. Suspended solids removal patterns in the IPC system-second cycle.
-------
IX)
CO
350
300
o>
£250
CO
Q
o
CO
Q
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Q
Z
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Q-
CO
200
150
50
VOLUME TREATED, million gallons
1.8 3.4 5.1
RAW SEWAGE
UNIT CONVERSIONS:
mil gal x 3785 - cu m
CLARIFIED EFFLUENT
CARBON EFFLUENT
8 12 16 20
STUDY PERIOD, (WEEKS)
24
28
32
FigurelO. Suspended solids removal patterns in the IPC system-third cycle.
-------
In the course of the study, a limited number of batch settling tests
were performed on grab sludge samples using two-liter graduated cylinders,
each fitted with a picket rake mechanism. The picket rakes were operated
at^a constant rotational speed of one revolution per minute to reduce wall
effects on sludge compaction in the graduated cylinders and thus approximate
to a certain degree the settling phenomenon observed in a full-scale
thickener. The batch settling tests were performed using various levels of
initial suspended solids concentrations with and without the use of polymers
as thickening agents. From the sludge settling curves obtained, zone
settling velocities were calculated by taking the slope of the initial
straight line portion of the settling profile. Figure 11 shows a log-
arithmic plot, of the zone settling velocity as a function of the initial
suspended solids concentration. The beneficial effect of polymer on the
settling properties of the IPC sludge is shown by comparison of the curves
in Figure 11. Figures 12 and 13 present solid flux curves, which were
derived by calculation using the zone settling velocity-suspended solids
concentration data in Figure 11. These batch flux curves are useful in
evaluating a number of alternate thicker design by selecting various
possible underflow concentrations. Operating lines drawn tangent to the
batch flux plot provide the maximum solids flux through the thickener at the
desired underflow concentration. For instance, as indicated in Figure 12,
for an underflow concentration of 4 percent solids the maximum solids flux
was 61 Kg/nr/day (12.5 lbs/ft"/day) for a sludge without polymer and 156.2
Kg/nf/day (32 lbs/ft-/day) for sludge thickened with 4.22 Kg/t (9.3 Ibs/ton
dry solids) of Dow Chemical C-41 polymer. As indicated in Figure 13, the
corresponding solids flux for sludge thickened with 0.82 Kg/t (1.82 Ibs/ton
dry^solids) of American Cyanamid polymer 905 N was 597.8 Kg/nr/day (122 Ibs
/ft2/day). While the solids flux data obtained have indicated a significant
reduction in the thickener size with the use of polymer as a thickening
agent, an economic analysis should be performed in order to determine whether
the polymer use is justified.
Several leaf filtration tests were performed using various types of
polymers for chemical conditioning. The conditioning agents were evaluated
at various cycle times to derive optimum filter performance based on
filter yield, cake solids and filtrate quality. The sludge samples were
first concentrated to about 2 percent suspended solids concentration by
gravity-thickening for a period ranging from 16 to 18 hours. The filter
tests were performed using a standard 93 cnf (0.1 ft2) Eimco leaf filter
under a vacuum of 38 cm (15 in.) of mercury. For each test run, a 2-liter
sample of the chemically-conditioned sludge was used. A monofilament
nylon 415 was used as the filter medium in all the leaf filter tests.
The two most important variables -controlling directly the economics of
sludge dewatering by vacuum filtration are the chemical dosage and the
filter yield. Moreover, the ultimate sludge disposal cost is influenced
directly by the moisture content of the filter cake produced during the sludge
dewatering operation. In an attempt to evaluate the relationships of the
29
-------
10
8
O
O
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> 1.0
1 8
ui 6
CO
ui
I 4
IPC SLUDGE
UNIT CONVERSIONS^
ft/hr x 0.305 = m/hr.
Ibs/ton x 0.5= kg/metric ton
TEMPERATURE 22°-23
O O WITHOUT POLYMER
£* -A WITH DOW CHEMICAL
POLYMER C-41 (9.3 Ibs.
O O WITH AMERICAN CYANAMID
POLYMER 905N (1.82 Ibs
/TON)
34 6 8 1.0 2 34
SUSPENDED SOLIDS CONCENTRATION, %
Figure II. Zone settling velocity as a function of suspended solids
concentration.
30
-------
40
35
30
25
I 20
•»
X
c/> 15
O
o
en
10
IPC SLUDGE
TEMPERATURE 22°-23°C
0—0 WITHOUT POLYMER
WITH DOW CHEMICAL
POLYMER C-41 (9.3lbs/TON)
UNIT CONVERSIONS:
Ibs/ton x 0.5= kg/metric ton
Ibs/ft2/day x4.9= kg/mVday
O
I
OPERATING
LINES
I
2345
SUSPENDED SOLIDS CONCENTRATION, %
Figure 12. Batch flux curves of IPC sludge with and without
polymer.
31
-------
IPC SLUDGE
TEMPERATURE 23° C
POLYMER DOSAGE— 1.82 Ibs/Ton
TYPE OF POLYMER---AMERICAN
CYANAMID 905N
UNIT CONVERSIONS:
Ibs/ton x 0.5= kg/metric ton
Ibs/ftVday x 4.9= kg/mVday
OPERATING
LINE
2345
SUSPENDED SOLIDS CONCENTRATION, %
Figure 13. Batch flux curve of IPC sludge with polymer.
32
-------
aforementioned variables, leaf filter tests were performed using various
types of polymers at different dosage levels and under three different
cycle times. The test results showed that the filter yield increased
with increasing chemical dosage and that the greatest yield increase
occurred at the 2-minute cycle time. Moreover, in comparing the data for
different cycle times., it is shown that while the lower cycle time pro-
vided relatively higher filter yield, it also provided a wetter cake. Thus,
in plant scale dewatering operation, a judicious choice of cycle time and
chemical dosage should be made in such a way as to achieve an optimum
combination of filter yield and cake moisture. Figure 14 summarizes the
effect of cycle time on both filter yield and cake solids.
The results of a second series of leaf filtration tests, in which
ferric chloride along with six different types of polymers were evaluated
at various dosage levels and cycle times, are summarized in Figures 15, 16
and 17. The parameters used to evaluate the performance of the various
chemical conditioning agents were filter yield, percent cake solids and
filtrate suspended solids concentration. To facilitate the comparison of
the performance of the various conditioning chemicals, the results are
presented in terms of the chemical cost expressed in $/ton dry solids.
Figure 15 shows the effect of chemical dosage at 2-minute cycle time
on the filter yield and cake solids. The corresponding data for the 4-
minute cycle time is presented in Figure 16. As indicated by the trend of
the curves in Figures 15 and 16, the filter yield increased with increasing
chemical dosage up to an optimum dosage level, beyond which, the yield
decreased with further increase in the dosage. Moreover, it is evident
from the curves that although higher chemical dosage provided higher
filter yield, it also resulted in a wetter cake. The effect of chemical
dosage on filtrate quality is shown in Figure 17. In comparing the perform-
ance of the various chemical conditioning agents, as shown in Figures 15 and
16, it is apparent that under the laboratory test condition, the Dow
Chemical C-31 showed the best performance based on filter yield and percent
cake solids. However, as depicted in Figure 17, the filtrate contained a
high concentration of suspended solids. All the other polymers evaluated
produced a clear filtrate at the higher dosage levels. Ferric chloride at
a dosage level as high as 12.3 percent by weight of sludge solids was not
found effective for IPC sludge conditioning.
Table 4 summarizes the leaf filter test results in which ferric chlo-
ride and various types of polymers were used as chemical conditioning agents.
The data in the table were obtained from the plot presented in Figure 16.
The last two columns of Table 4 show the filter yield and the corresponding
conditioning chemical cost to obtain 18 percent cake solids. The test
results indicated that alum-sewage sludge with initial solids concentration
of 1.61 to 2.26 percent were dewatered to 18 percent cake solids with yields
ranging from 2.4 to 5.4 Kg dry solids/hr/m2(0.5 to 1.1 Ibs.dry solids/hr/sq
ft of filter area). Of the chemicals evaluated, the Dow chemical anionic
polymer A-23 appeared to be the most effective in terms of chemical cost,
yield, cake solids, and filtrate quality. Moreover, it is of interest to
33
-------
25
20
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9
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X.
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o
15
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tri
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cr
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O—O CALGON WT. 2640 (73.4 Ibs./TON DRY SOLIDS)
DOW CHEMICAL C-41 (93 Ibs./TON DRY SOLIDS)
AM. CYANAMID 905N (0.54 Ibs./TON DRY SOLIDS)
UNIT CONVERSIONS:
Ibs/ton x 0.5= kg/metric ton
lbs/ft*/hr x 4.9= kg/mVhr
0
234
CYCLE TIME,min.
Figure 14. Effect of cycle time on filter yield and cake solids.
34
-------
25
CO
en
SUSP SOLIDS CONC.-»-l.85% TO 2.26% (IPC SLUDGE)
FILTER MEDIA -»> NYLON 415
CYCLE TIME-*2 MIN.ftO SECS.FORM TIME 8 80 SECS.
DRY TIME)
VACUUM-*38.1 cm Hg
n-OCALGON E207
-0 FERRIC CHLORIDE
CALGON WT. 2640
AM. CYANAMID 905 N
O-O DOW CHEMICAL C-31
O—o DOW CHEMICAL C-41
I I i
UNIT CONVERSIONS:
Ibs/ftVhr x4.9=kg/ma/hr
10
40
50
15 20 25 30 35
CHEMICAL COST, $ /TON DRY SOLIDS
Figure 15. Performance of various chemical conditioning agents at 2 min. cycle time.
-------
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en
25
20
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5 !0
£ 0
£ 2
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CALGON WT. 2640
FERRIC CHLORIDE
a-QCALGON E207
A-AAM. CYANAMID 905 N
0—0 DOW CHEMICAL C-41
-O-ODOW CHEMICAL C-31
•--•DOW CHEMICAL A-23
UNIT CONVERSIONS:
lbs/ft«/hr x4.9=kg/m*/hr
SUSP. SOLIDS CONC.-»-l.85% TO 2.26%(IPC SLUDGQ
FILTER MEDIA-* NYLON 415
CYCLE TIME-*4MIN.(IMIN. FORM TIME 8 3 MIN. DRY
TIME) , 1A
10
40
50
15 20 25 30 35
CHEMICAL COST, I/TON DRY SOLIDS
Figure 16. Performance of various chemical conditioning agents at 4 min. cycle time.
-------
12,000 f
CO
SUSPENDED SOLIDS CONC.-* 1.85% to 2.26% (IPC SLUDGE)
FILTER MEDIA— NYLON 415
CYCLE TIME-* 2 MINUTES (40 SECS.FORM TIME AND
80 SECS. DRY TIME)
VACUUM-^38.1 cm Hg
O— O
A--A
CALGON WT 2640
DOW CHEMICAL C-41
AM. CYANAMID 905 N
FERRIC CHLORIDE
CALGON E-207
O— O DOW CHEMICAL C-31
«--• DOW CHEMICAL A-23
D--D
0 5 10 15 20 25 30
CHEMICAL COST, VTON DRY SOLIDS
Figure 17. The effect of chemical dosage on filtrate quality.
r CLEAR FILTRATE
(SUSP. SOLIDS 4-
I00mg/l)
. --- , - .
35
40
-------
TABLE 4. LEAF FILTER TEST RESULTS
Feed Solids,
Percent
by weight
1.91
2.26
2.15
2.05
1.80
1.61
2.04
1.86
Conditioning
Chemicals
Used
Calgon WT-2640
Calgon E-207
Dow Chemical
C-41
Dow Chemical
C-31
Dow Chemical
A-23
Am- Cyan amid
905 N
Ferric Chloride
None
Chemical
Cost
$/Kg
0.59
0.46
0.17
0.68
3.85
3.74
0.13
0
Based on Optimum Yield
Yield, 2
Kg/hr-m
4.9
5.4
6.4
6.4
10.8
5.4
3.9
2.3
Cake Solids
%
18.5
17.5
12.5
20.0
11.5
13.0
22.5
21.0
Cost,
$/ton
15
20
14
21.5
15
20
8
0
Based on 18% Cake Solids
Yield, 2
Kg/hr-m
4.9
4.4
3.9
-
5.4
2.4
-
-
Cost,
$/ton
15
15
5.5
-
2
6
-
-
CO
co
* Filter media used was Nylon 415 (Eimco). Cycle time was 4 minutes,
-------
note that at 18 percent cake solids, the filter yield with the use of
American Cyanamid 905 N was about the same as that with unconditioned
sludge. As previously discussed .although the filter yield increased with
increasing chemical dosage, the resulting filter cakes were found to
contain higher moisture content except in those runs where ferric chloride,
Dow C-31 and Calgon WT-2640 were used.
CARBON TREATMENT PHASE
Sulfide Control Measures
The high concentration of soluble organics applied to the carbon
column are known to stimulate prolific biological growths within the column.
Although this biological activity enhances the overall carbon capacity
for dissolved organics removal (7), severe operational problems frequently
occur, such as clogging of the carbon bed and the development of ana-
erobic conditions with the attendant sulfide generation problem. Pressure
buildup and sulfide generation were two major operational problems encounter-
ed in the IPC carbon column operation.
In the biological oxidation of organic matter various hydrogen acceptors,
either organic or inorganic, are reduced. As indicated in the literature
(8,9), microorganisms tend to utilize various hydrogen acceptors
preferentially in the order: molecular oxygen, nitrate, sulfate and oxidized
organics. In the absence of dissolved oxygen and/or nitrate, sulfate-re-
ducing bacteria depend on sulfate reduction as a mode of anaerobic energy-
yielding metabolism with hydrogen sulfide as one of the reduced by-products.
For sulfate reduction to take place, the following conditions have to be
satisfied: presence of organic matter and sulfates; absence of dissolved
oxygen and/or nitrate and an environment with favorable temperature. The
biological slimes and deposits provide favorable sites where the microbial
environment becomes suitable for hydrogen sulfide generation. Thus, in
the use of columnar granular activated carbon beds for filtration-adsorption
of chemically clarified raw sewage, the potential for production of
hydrogen sulfide is high due to the accumulation of suspended solids and
other materials providing a large biomass with a correspondingly high oxygen
demand. For this reason, efficient surface washing and backwashing
techniques must be employed not only to prevent excessive pressure buildup
but also to minimize solids accumulation on the surface of the bed that
could trigger sulfide generation.
During the first adsorption cycle, the carbon column was operated con-
tinuously for two weeks before hydrogen sulfide was first detected in the
column effluent. In an effort to inhibit sulfide production, various
control measures were evaluated with varying degrees of effectiveness as
indicated by the summary data in Table 5 and in Figure 18. In the first
two months of the column operation, the bed was routinely cleaned by sur-
face wash-backwash procedure, as discussed in detail in the following
section. During that period, the total sulfide concentration of the column
ranged from 1.0 to 5.7 rng/1 S, and averaged 2.9 mg/1 S. Because of this
39
-------
TABLE 5. H S CONTROL MEASURES IN THE CARBON COLUMN
Control Measures
Remarks
(a) Surface wash - water backwash
(b) (a) + 02 addition to carbon
column to D.O. level 4 mg/1
intermittently (4 hrs/day).
(a) + Continuous 02 addition
to the carbon column to D.O.
level of 4 mg/1.
(c) Surface wash and air/water
backwash techniques.
(d) (c) + aeration of the
chemically clarified
effluent to D.O. level
2-6 mg/1.
of
(e) (d) + 20 mg/1 Cl2 added to
carbon influent.
(f) (d) + 40 mg/1 Cl2 added to
carbon influent.
(g) (d) + NaNO? addition to
carbon influent at 2.9
mg/1.
Sulfides formed.
A reduction in sulfide formation was
observed.
A reduction in sulfide formation was
observed. Excessive pressure drop
occurred in the carbon column.
During the first few days of air/water
backwash operation, about 17.8 cm of
carbon was lost to the underdrain pre-
sumably due to the disturbance of the
gravel layer. The bed cleansing
efficiency of this technique was not
significantly better than that of (a).
A slight reduction in sulfide
formation was observed.
Observed results were essentially the
same as (b).
Observed sulfide level in the carbon
effluent slightly lower.
Significant reduction in the^sulfide
concentration was observed. In
addition, column headloss was signifi-
cantly lower than previously observed.
The continuous addition of sodium
nitrate, which is preferentially
reduced during the anaerobic process
had been the most effective in
eliminating sulfides.
40
-------
TABLE 5 (continued)
Control Measures
Remarks
(h,i) (d) + NaNO, addition to
carbon influent at 4.5-
5.1 mg/1.
(j) (a) + NaN03 addition to
carbon influent at 5.4
mg/1.
Complete elimination of sulfide.
Complete elimination of sulfide.
41
-------
ro
STUDY PERIOD, wt^ks
81 **3
*<^
16
20
a &
M M
H o
' 0
,1
1 g
CCj
-------
20
6r
25
STUDY PERIOD, weeks
29 34
38
43
O>
E
co"
UJ
Q ,
u. 3
_i
ZD
CO
O
s
o
j 1 pQ
o <;
o o
- H U~|
P P H
O W "^
oo Q
'O H O
H 3
-H O
2! N 23
AUGUST
SEPTEMBE
OCTOBER
1972
Figure 18. Continued
-------
STUDY PERIOD, weeks
4
6
5
__
>^
a>
£4
co"
UJ
Q
^ •*
CO 3
_J
O
H
2
O
*3 45 47 5! 55
1 M H II
C/3
1— 1
H PH
§
O
"* O Pi
0
O
2 £5
< O
0 Q
S 0 H
t> H <5
g g s
CO Q 3
/^ | ^ 2^
+ <1^f^fCai^-a!nJf
I 18 * 31/1
JAN.
28/1
31/1
FEB.
1973
MARCH
Figure 18. Continued
-------
high carbon effluent sulfide level, oxygen was added to the carbon column
in order to prevent sulfate reduction. Although the carbon effluent sulfide
level decreased slightly, this procedure was abandoned because of excess-
ively high headloss which occurred in the carbon column as a result of
increased biological activity.
Since sulfate-reducing microorganisms tend to concentrate on biological
slimes and deposits, it follows that an effective bed backwashing would
help in controlling sulfide formation. Consequently, an auxiliary air
scour was used in conjunction with the surface wash-water backwash procedure.
The expected benefit of the air-water backwash technique, however, was not
achieved. To some extent this may be because the underdrain of this column
was not basically designed to function with air scour. Even the oxygenation
of the chemically clarified effluent to dissolved oxygen level of 2-6 mg/1
in conjunction with the air-water backwash technique did not produce a
significant decrease in the carbon effluent sulfide level.
In view of this, another control measure, that of continuous chlorine
addition to the carbon influent at dosages ranging from 20 to 50 mg/1 Cl,
was evaluated. While chlorination of the carbon influent effected some
reduction in the total sulfide formed, the results obtained were not at all
encouraging because of the high dosage required. Even at a chlorine dosage
as high as 50 mg/1 Cl, sulfide was still present in the carbon effluent.
In addition, although the average total sulfide concentration in the carbon
effluent during the high chlorine dosage was only 1,13 mg/1 S, at no time
during the 21 days of continuous chlorine addition, was the sulfide main-
tained at a consistently low level. The sulfide concentration in fact
fluctuated throughout the period from .09 to 2.6 mg/1 S as indicated in
Figure 18. It is of interest to note that during periods of chlorine
addition, especially at the higher dosage of 40-50 mg/1 C], headlosses
through the carbon column were consistently low in spite of the relatively
high influent suspended solids. This observation demonstrates that the
high pressure drop observed prior to chlorination and after chlorine
addition ceased, were indeed caused by abundant biological growths in the
carbon column. Subsequent experience further confirmed the above obser-
vation in that drastic increase in headloss occurred when chlorination
was interrupted for only a few hours.
In using chlorine for sulfide control in carbon columns, it must be
recognized that activated carbon is an effective dechlorination medium.
Results of chlorine residual determination of samples obtained at various
depths in the carbon column have indicated the complete removal of chlorine
at the top 38.1 cm (15 in.) of the carbon bed. The average total chlorine
residual in the liquid just above the carbon surface was about 20 mg/1.
Since the chlorine was completely removed at the top layers of the carbon col
umn, the viable sulfate-reducing organisms remained virtually unchecked in
the lower carbon layers. Unless the sulfate-reducing organisms are complete-
ly inhibited throughout the column depth, erratic sulfide inhibition would
result as experienced in this study.
45
-------
Because chlorination at a dosage up to 50 mg/1 was neither completely
effective in eliminating sulfide formation, sodium nitrate addition to the
carbon column was initiated. During the first month of nitrate addition,
the nitrate dosage was varied from 1.8 to 3.8 mg/l N. As anticipated, the
nitrate was almost completely removed in the carbon column by biological
denitrification. The reduction of nitrate in the carbon column was accom-
panied by high headless through the bed. The total sulfide concentration
of the carbon effluent averaged only 0.36 mg/l S, which was appreciably
less than that obtained with chlorination and other methods previously
evaluated. From the second to the 7th month of sodium nitrate addition,
the nitrate dosage was maintained in the range of 4.5 - 5.4 mg/l N.
Thereafter, the nitrate dosage was maintained at an average level of 5.4
mg/l N. The continuous addition of nitrate to the carbon column influent
at the dosage of 5.4 mg/l N was found very effective in inhibiting the
hydrogen sulfide generation in the carbon column. Figure 18 shows the
weekly average total sulfide concentration in the carbon effluent. As
shown in the figure, the total sulfide concentration remained consistently
at zero level. On a number of occasions, however, nitrate feeding to the
carbon column was disrupted due to a malfunction of the chemical feed pump.
As a result of the cessation of the sodium nitrate feed, sulfide generation
in the carbon column started immediately as indicated in Figure 18 by the
increase in the carbon effluent sulfide concentration during the middle of
October and in the last week of November 1972. Once the sulfate-reducing
organisms were established in the column, it took several days of contin-
uous nitrate feeding before sulfide generation was fully controlled.
Figure 19 shows detail on the periods when nitrate feed failed. Thus, the
data obtained during the periods of unintentional interruption of sodium
nitrate feeding proved valuable in demonstrating the need for continuous
nitrate feeding to achieve sustained control of hydrogen sulfide generation.
A comparative performance of the various hydrogen sulfide control measures
is shown in Table 6.
In the second and third adsorption cycles, nitrate addition was not
started until after the first two weeks of operation when sulfides appear-
ed in the column effluent. The sulfide level was virtually zero in the
column effluent throughout the second and third cycles, except for occasion-
al periods when malfunction of sodium nitrate feed pump occurred.
Column Headloss Data
Since the granular activated carbon column was operated in a packed-
bed, down flow mode, the column served as a deep bed filter and as an
adsorber. Thus, the direct application to the column of chemically clar-
ified effluent which contained suspended solids ranging from 25^40 mg/l led
to progressive clogging of the bed with an attendant increase in headloss.
In addition, bacterial growth in the bed played a significant role in the
development of bed pressure drop. To maintain proper column operation, the
column was backwashed on a daily basis with a volume of secondary effluent
46
-------
SODIUM NITRATE FEED
PUMP MALFUNCTION
0
10 15
TIME, DAYS
Figure 19. Effect of nitrate feed disruption on sulfide production.
-------
TABLE 6. PERFORMANCE OF THE VARIOUS H S CONTROL MEASURES
MS Control Measures
(1) Surface wash-backwashing technique
(2) (1) + intermittent 02 addition to
carbon column at D.O. level =
4 mg/1
(3) Surface wash + air/water backwash
plus oxygenation of the chemically
clarified effluent to D.O. 2-6 mg/1
(4) No. (3)+ 20 mg/1 C12* added to
carbon influent
(5) No. (3)+ 40 mg/1 C12 added to
carbon influent
(6) No. (3)+ 2.9 mg/1 N+ added to
carbon influent
(7) No. (3)+ 4.5 mg/1 N
(8) No. (3)+ 5.1 mg/1 N
(9) No.(l)+ 5.3 mg/1 N
(10) No.(l)+ 5.4 mg/1 N
Carbon Effluent Total Sulfide
Cone. , mg/1 S
Average
2.86
1.85
1.87
1.74
1.13
0.3
0.13
0.05
0.019
0
Range
1.0 - 5.7
1.4 - 2.5
0.8 - 3.0
0 - 4.3
0.09- 2,6
0 - 0.95
0 - 0.60
0 - 0.26
0 -*0.10
0 - 0.05
* Added as sodium hypochloride solution.
+ Added as sodium nitrate solution.
48
-------
equivalent to 6 to 8 percent of the product water. During the course of
the study a number of carbon bed cleaning procedures were evaluated. The
actual backwash duration varied from 30 to 60 minutes depending on the
procedure used. Initially, a surface wash-water backwash procedure was
used. After the column was on stream for several days, with the routine
daily surface wash-water backwash bed cleaning procedure, it was found that
at the end of 24 hours of column operation, the water drained very slowly
from the carbon column. Thus, during the first adsorption cycle, which
covered the first 18 months of the study, the rotary surface spray was used
without draining the carbon bed. At the end of the first adsorption cycle
an auxiliary drain line was installed in the carbon column which made it
possible to drain the water in the column to about 38 cm (15 in.) above
the carbon bed before initiating the surface wash cycle. This auxiliary
drain line was used starting with the second adsorption cycle until the
completion of the study.
Figure 20 shows the surface wash-water backwash schedule. During back-
washing the backwash water was discharged into a holding tank designed to
capture any accidental carbon spills and to allow visual observation of the
clarity of the backwash water. The backwash water containing chemical-bio-
logical floe and some carbon fines overflowed a weir in a holding tank and
was pumped into the head end of the primary clarifiers of the Pomona acti-
vated sludge plant.
For a period of about six months during the first adsorption cycle, an
auxiliary air scour was used in conjunction with the regular surface wash-
water backwash method in an attempt to achieve better bed cleaning and to
provide a means of controlling sulfide generation. Figure 21 shows the
air-water backwash schedule. The air was injected directly into the back-
wash line. The air-water backwash procedure was found to be only slightly
more effective than the regular surface wash-water backwash procedure. It
should be pointed out, however, that the column, which was provided with
the Leopold filter blocks underdrain system, was not designed for air injec-
tion and this could have accounted for the performance observed with the
air scour method. The loss of about 87 Kg (191 Ibs) of carbon through the
underdrain system during the first few days of the air-water backwash
operation demonstrated that the column underdrain system was not suited for
air injection. This carbon loss probably occurred when the sudden surge
of air disturbed the graded gravel layers.
The effectiveness of the various backwash procedures is shown by the
observed column headloss just after backwash and also by the rate of
subsequent headloss buildup. The headloss just after cleaning was found to
be essentially the same irrespective of the bed cleaning procedure used.
The daily headloss buildup, however, fluctuated considerably during the
course of the study. A regression analysis of the net headloss (headloss
before the daily backwash minus headloss after backwash) and the column
influent suspended solids showed no correlation between the two variables.
This lack of correlation suggests that the major portion of the headloss
49 u.s. bPA
-------
30
CM
U_
°- 20
C9
BACKWASH RATE,
D 0
-
-
-
2
II
1
4
i n
4
4
VSURFACE WASH
III!
-
10
(WASH
1 1
TOTAL BACKWASH
WATER=l6.7cu m
UNIT CONVERSIONS:
gpm/ft*x0.68=l/sec/m* -
1 1
15
TIME, MINUTES
20
25
30
35
Figure 20, Surface wash-water backwash schedule.
-------
4O
30
O
o
CO
2 «
r\
20 U 30
TIME, MINUTES
Figure 21. Air-water backwash schedule.
-------
was due to biological growths within the carbon-bed which were not complete-
ly removed during the routine backwash. The variations in the weekly average
net headloss and influent suspended solids concentration are presented in
Figure 22 for the first cycle, Figure 23 for the second cycle and Figure 24
for the third cycle. As indicated in Figure 22, the pressure losses through
the carbon column were very low, ranging from 0.11 to 0.25 Kg/cm2 (1.6 to
3.6 psi), during the first four weeks (week No. 1 to 4 of column operation).
On two other occasions, weeks 11 and 45, the pressure losses were also low
following a period when the column was out of service for extended periods
for repairs. Moreover, relatively low headlosses, ranging from 0.56 to
1.38 Kg/cm2 (7.0 to 19.6 psi), were observed during the period (weeks 13 to
23) when chlorine was added to the carbon column influent for sulfide control.
However, with the termination of chlorine addition and the subsequent use
of sodium nitrate for sulfide control, generally higher headlosses were
observed. On several occasions, pressure losses exceeding 3.5 Kg/cm2 (50
psi) before the daily backwash cycle were recorded. As indicated previously,
these high pressure losses were probably due to biological solids which
accumulated on and near the top layers of the carbon bed. These excessive
pressure losses were similar to those observed in previous studies at
Pomona(lO) when granular activated carbon columns were used for denitrifi-
cation purposes.
As shown in Figure 24, the headlosses during the first three weeks of
the third adsorption cycle were also low and exhibited about the same as
that in the first adsorption cycle. In the second cycle, however, the
headloss which is shown in Figure 23 were high during the first two weeks
following carbon regeneration. These observed high headlosses were
probably due to carbon fines which were not completely removed in the
initial extended backwash following the carbon regeneration. In subsequent
periods, weeks No. 3 to 7, the headloss ranged from 0.2 to 0.62 Kg/cnr
(2.8 to 8.8 psi) and showed about the same headloss pattern as in the first
and third adsorption cycles.
In a two-day period in December, 1972, about 27.94 cm (11 in.) of
carbon depth equivalent to 136 Kg (300 Ibs) carbon was lost from the carbon
column. This appreciable amount of carbon loss, coupled with the observed
high headloss at the top 38.1 cm (15 in.) of the carbon bed prompted an
examination of the routine backwash procedure. It was found that the flow
through surface spray line, which normally was about 0.82 I/sec (13 gpm) with
the valve fully opened, increased to about 3.16 I/sec (50 gpm). Th*s ob-
servation led to the examination of the column interior. It was then
discovered that the entire rotary surface spray assembly including its
supply pipe was dislodged from its support and buried in the carbon bed.
Accordingly, the column was taken out of service and the carbon, after a
thorough backwash, was hydraulically transferred to an empty carbon column
in order to retrieve the surface spray assembly. The rotary spray assembly
was found intact whereas the 3.81 cm (1 1/2 in.) diameter supply line
(schedule 40,304 stainless steel pipe) was sheared at two locations. The
shear failures occurred at the threaded connections where the pipe thickness
52
-------
80
05
§60
O
CD
2.7
VOLUME TREATED, million gallons
4.7 6.4 8.8
10.6
12.2
a
LU
a
z
UJ
Q_
0)
40
60
en
o
a
<
LU
40
LU 20
I
I
I
UNIT CONVERSIONS:
mil gal x 3785= cu m
psi x 0.0703 = kg/cm2
10 15 20
STUDY PERIOD, (WEEKS)
25
30
Figure 22. Carbon column suspended solids loading and
pressure drop- first cycle.
53
-------
_ 80
14.0
VOLUME TREATED, million gallons
153 16.6 18.3
__ -j— p-
21
23.2
mil gal x 3785= cu m
psi x 0.0703 = kg/cm*
to
in
(/)
z
Z>
o
o
z
o
CD
z E o
FLOCCULATOR DOWN
«*-
FOR REPAIRS
30
35 40 45 50
STUDY PERIOD, (WEEKS)
55
60
Figure 22. Continued
54
-------
\ 80
CO
VOLUME TREATED, million gallons
25.2 274 29.7
Q
LJ
Q
60
CO
OL
UNIT CONVERSIONS:
mil gal x 3785= cu m
psi x 0.0703 = kg/cm*
I
I
60
65 70 75 80
STUDY PERIOD (WEEKS)
85
90
Figure 22. Continued.
55
-------
80
CO
Ii 60
O
CO
2.1
Q
UJ
Q
2
UJ
Q_
CO
Z>
CO
40
UJ
ID
20
60
CO
Q_
CO
CO
O
40
UJ
X
20
VOLUME TREATED, million gallons
4.5 6.9 9.1 S0.3
—T I I 1
UNIT CONVERSIONS:
mil gal x 3785 = cu m
psi x 0.0703 = kg/cm*
10 15 20
STUDY PERIOD (WEEKS)
25
30
column suspended solids loading and
pressure drop— second cycle.
56
-------
_ 80
\
CP
E
co"
9
d60
CO
Q
UJ
Q
40
CO
Z>
CO
UJ 20
Z)
_J
Li.
60
CO
Q_
CO
CO
O
40
UJ
X
VOLUME TREATED, million gallons
2.2 4.3 5.5
I
T
T I
UNIT CONVERSIONS:
mil galx 3785scu m
psi x 0.0703= kg/cm*
JL
10 15 20
STUDY PERIOD, (WEEKS)
25
30
Figure 24. Carbon column suspended solids loading and
pressure drop— third cycle.
57
-------
was considerably less than the nominal wall thickness of 3.18 mm (1/8 in.).
The supply line was replaced with thicker walled 3 04 stainless steel
schedule 80 pipe and welded socket fittings were used to connect the rotary
spray assembly to the supply line. In addition, a 5.08 cm x 5.08 cm x 0.64
cm (2 in. x 2 in. x 1/4 in.) angle iron coated with bitumastic coal tar
epoxy was welded to the supply line for support.
During the three-week period (Dec. 27, 1972 to Jan. 17, 1973) when the
column was off stream, the graded gravel layers over the Leopold blocks were
removed to examine the underdrain system. The gravel layers were completely
intermixed with carbon, probably due to the use of the auxiliary air scour
during routine backwash. In examining the Leopold blocks, it was found that
at two locations in the underdrain system the grout was dislodged leaving a
gap of 3.18 to 6.35 mm (1/8 to 1/4 in.) wide by about 15.24 cm (6 in.) long
between the filter blocks and the tank interior. The sudden surge of air
during the air-water backwash procedure could have caused the dislodgement
of the grout. Possibly, some carbon losses occurred through these openings
and some losses also occurred during the backwash since carbon was found in
the backwash water scavenger tank. The openings between the filter block
anH the tank interior were refilled with grout and a new 20.32 cm (8 in.)
uy'ei of graded gravel was placed over the filter blocks. When the column
operation resumed on Jan. 17, 1973, the use of the air scour was terminated
and the surface wash-water backwash procedure was adopted until the comple-
tion of the study. In all subsequent periods, no sizeable carbon loss was
observed.
Organic Removal and Effluent Quality
The major function of the carbon treatment step is the removal of
soluble organic material from the chemically clarified raw sewage. In
addition, substantial removal of organic suspended solids was expected as
the packed bed of carbon served as a filter. In evaluating the column per-
formance, the COD test was used as the primary parameter. The COD removal
patterns for the three adsorption cycles are presented in Figures 25 through
Figure 27. It is evident from the figures that the column removed a major
portion of the influent COD both suspended and soluble.
The COD removal through the carbon column during the virgin adsorption
cycle is presented in Figure 25. As the COD breakthrough curves show, the
organic removal through the carbon column was excellent and remaine*d practi-
cally constant throughout the entire cycle. The column treated 113,550 m3
(30 million gallons) of chemically clarified raw sewage before it was taken
out of service for regeneration. It should be pointed out, however, that at
the time the column was taken off-stream for regeneration, the carbon was
still far from exhausted3 based on the original regeneration criterion of
an effluent TCOD of 40 mg/1. The decision to regenerate the carbon was
based entirely on the need to obtain data on the effect of repeated thermal
regenerations on the carbon performance and characteristics. In subsequent
adsorption cycles, the column was regenerated after 3 to 5 months run with-
58
-------
en
i-D
150
125
100
0
8
50
25
UNIT CONVERSIONS'
mil gal x 3785 = cu m
_L
STUDY PERIOD, weeks
8
13
CARBON INFLUENT TCOD
ARSON INFLUENT DCOD
I
CARBON EFFLUENT DCOD
I
246
VOLUME TREATED, MILLION GALLONS
18
ARBON EFFLUENT TCOD
Figure 25. COD removal through the carbon column- first cycle.
-------
cr>
O
150
125 -
100 -
o>
£
Q"
O
O
STUDY PERIOD, weeks
30
CARBON INFLUENT TCOD
UNIT CONVERSIONS:
mil gal x 3785= cu m
CARBON INFLUENT DCOD
/CARBON EFFLUENT TCOD
-JH
CARBON EFFLUENT DCOD
I
10 12 14
VOLUME TREATED, MILLION GALLONS
Figure 25. Continued
-------
en
150
40
125
100
o>
E 75
e»
O
O
O
50
25
,-o
16
48
STUDY PERIOD, weeks
53
57
62
Figure 25. Continued
II
CARBON INFLUENT TCOD
UNIT CONVERSIONS:
mil gal x 3785= cu m
CARBON INFLUENT DCOD
CAR80N EFFLUENT TCOD
\CARBON EFFLUENT DCOD
\
18 20 22
VOLUME TREATED, million gallons
24
-------
CTl
IX)
62
125
100
E 75
o~
O
O
50
25
24
STUDY PERIOD, weeks
67 71
76
1
UNIT CONVERSIONS:
mil gal x 3785 =cu m
CARBON INFLUENT TCOD
CARBON ^FLUENT DCOD
CARBON EFFLUENT TCOD
'CARBON EFFLUENT DCOD
I
I
26 28 30
VOLUME TREATED, million gallons
32
Figure 25. Continued
-------
CO
150
125
100
75
Q
O
O
50
25
0
STUDY PERIOD, weeks
9
UNIT CONVERSIONS:
13
CARBON INFLUENT TCOD
EFFLUENT DCOD
.CARBON EFFLUENT TCOD
* «v
•*.-*•.--o>»<
246
VOLUME TREATED, million gallons
17
CARBON INFLUENT DCOD
8
Figure 26. COD removal through the carbon column - second cycle.
-------
150
STUDY PERIOD, weeks
18 22
125
100
Q
O
O
75
50
25
T
UNIT CONVERSIONS:
mil gal x 3785 = cu m
CARBON INFLUENT TCOD
CARBON INFLUENT DCOD
I
CARBON EFFLUENT TCOD
CARBON EFFLUENT DCOD
I
10 12 14
VOLUME TREATED, million gallons
16
Figure 26.Continued
-------
CTv
cn
150
125
100
o»
E
Q
O
O
r 75
50
25
STUDY PERIOD, weeks
5 9
13
TT
CARBON INFLUENT TCOD
T V
UNIT CONVERSIONS:
mil gal x 3785 = cu m
,CARBON EFFLUENT DCOD
CARBON INFLUENT DCOD
rCARBON EFFLUENT TCOD
J I
0246
VOLUME TREATED, million gallons
Figure 27 COD removal through the carbon column—third cycle.
8
-------
out any regard to the state of exhaustion of the carbon. Based on the total
throughput volume of 113,550 m3 (30 million gallons) the carbon capacity
during the virgin cycle was 3.5 kg TCOD removed/kg carbon and 1.54 kg DCOD
removed/kg carbon. The corresponding carbon dosage was 0.021 kg carbon/m3
(173 Ibs carbon/mg).
The effect of repeated thermal regenerations on the DCOD removal
capacity at various levels of DCOD applied is presented in Figure 28. As
shown by the curves, the DCOD removal capacity of the twice-regenerated
carbon is predictably slightly less than that of the once-regenerated carbon.
Moreover, it is also apparent from the curves that the regenerated carbon
performance was unexpectedly much better than that of the virgin carbon.
The observed higher DCOD removal capacity of the regenerated carbon during
the second and third adsorption cycles could be ascribed to enhanced bio-
logical activity resulting from continuous sodium nitrate addition to the
carbon column. It should be pointed out that during the virgin adsorption
cycle, sodium nitrate was not added to the carbon column until after 0.8 kg
DCOD/kg carbon was applied to the column. As Figure 28 shows, in subsequent
periods following the nitrate addition, the DCOD removal capacity of the
virgin carbon improved significantly to such a degree as to parallel the
DCOD removal curves for the regenerated carbon. Figure 29 shows a plot of
DCOD removal in each cycle as a function of DCOD applied. The data clearly
show the improved organic removal performance during the second and third
adsorption cycles and the favorable effect of nitrate addition on virgin
carbon. These observations have significant economic impact in that con-
tinuous sodium nitrate addition to the column for sulfide control also
enhanced the biological activity within the column, thereby increasing the
apparent COD removal capacity of the carbon. With increased carbon
capacity for organic removal, the carbon column could be operated for extend-
ed periods of times without regeneration and still maintain practically con-
stant effluent quality. This was successfully demonstrated during the virgin
adsorption cycle when the column effluent COD remained virtually unchanged
through 113,550 m3 (30 million gallons) of throughput volume. Thus, with
higher carbon capacity or lower carbon dosage, the regeneration cost, both
for initial capital investment and operation cost, would be proportionately
lower.
For purposes of comparison, carbon capacity and TCOD removal data from
other IPC pilot plants are presented in Table 7 along with the first adsorp-
tion cycle data from the Pomona study. The data clearly show the unusually
high carbon capacity obtained at Pomona. As previously discussed, this high
carbon capacity has been attributed to the enhanced biological activity with-
in the column resulting from continuous sodium nitrate addition.
Figure 30 presents the DCOD removal profile through the carbon column
at eight different cumulative throughput volumes during the virgin cycle.
These wavefront data show that about 50 percent of the soluble organic
material in the chemically clarified raw sewage was removed during the first
66
-------
1.5
CP,
o
OQ
o:
<
o
1-0
Q
bJ
O
CL
Q
8
Q
ONCE-REGENERATED CARBON
START NITRATE ADDITION
•TWICE REGENERATED CARBON
VIRGIN CARBON
0
1.0 1.5
DCOD APPLIED, kg/kg CARBON
2.0
2.5
Figure 28.Effect of regeneration on DCOD removal capacity.
-------
01
oo
100
90
80
UJ
sr
o
O 70
o
Q
UJ
o
S60
a.
50
•IV-
ONCE-REGENERATED CARBON
TWICE-REGENERATED CARBON
START N09 ADDITION
JL
I
0.2 0.4 0.6 0.8 1.0 1.2
DCOD APPLIED, kg/kg CARBON
1.4
T
2.2 2.4
Figure 29. Effect of regeneration on percent DCOD removal.
-------
TABLE 7. CARBON CAPACITY IN IPC PLANTS
Plants
Lebanon, Ohio
Blue Plains, Washington, D.C.
Ewing - Lawrence, N.J.
Pomona, California
TCOD, mg/1
Influent
67
55
75
98.4
Effluent
27
15
20
23.6
TCOD
Removed,
%
59.7
72.7
73.3
76
Carbon Capacity,
Kg TCOD removed/Kg carbon
0.5
0.7
0.8
3.5
CT)
-------
1.0
LU
EC
O
O
o
Q .6
o
o
\
o
-4
.2
8.3 MG.
I3.9TMG.
UNIT CONVERSIONS:
mil gal x 3785= cu m
10
15 20 25
CONTACT TIME, MINUTES
30
35
Figure 30. DCOD profile through the carbon column.
-------
seven minutes of contact time. Although the DCOD removal increased with
increasing contact time, it is evident from the curves that the soluble
organics removal did not improve significantly beyond the 19.5 minutes con-
tact time. Furthermore, the data show that over the 18.5 month period
during which time the carbon processed about 113,550 m3 (30 million gallons)
of chemically clarified raw sewage, the carbon suffered only a slight
decline in performance.
The turbidity and color removal patterns through the carbon column are
shown in Figures 31 through 33. As indicated in the figures, both the
carbon effluent turbidity and color remained at low levels throughout the
study. During the three adsorption cycles, the carbon column removed 72.5
percent of the turbidity and 61 percent of the color, thereby producing an
effluent with an average turbidity of 6.3 JTU and an average color of 7.8.
Table 8 presents a summary of the column performance for each of the three
adsorption cycles.
These data all indicate a model for the performance of the granular
carbon column in this study. It is theorized that the granular carbon
column removes all the suspended organics applied through the mechanism of
filtration. Removal of dissolved organics takes place by a combination of
carbon adsorption and bacterial uptake. The bacterial metabolism of these
organics both those adsorbed on carbon and those taken up by the bacteria
leads to a demand for a hydrogen acceptor and production of new cells.
These cells and the suspended organics are in effect wasted from the system
during the backwash. The following calculation indicates that this theory
has some validity. The average DCOD removal across the carbon column was
35.1 mg/1. The nitrate used was 5.4 mg/1 as N or 18.5 mg/1 as 0. Since the
DCOD which is not oxidized is synthesized, the cell production must be 35.1-
18.5 = 16.6 mg/1 as 0 or 16.6/1.42 = 11.7 mg/1 VSS. Here 1.42 is the COD
equivalent of the bacterial cell mass. This produces a sludge yield of
11.7/35.1 or 0.335 mg VSS per mg COD removed. This value is close to that
reported for the synthesis yield in activated sludge denitrification systems
(15). It is impossible to expect exact correlation because the SRT in a
carbon column system is unknown.
CARBON REGENERATION RESULTS
Carbon Regeneration Process Control
The primary goal of carbon regeneration is to restore as much as possible
the exhausted carbon it its virgin properties by effecting maximum removal of
the adsorbed impurities from the pores of the spent carbon with a minimum
damage to the basic pore structure. Thus, during regeneration the furnace
operating variables such as temperature, carbon feed rate and steam feed
rate are closely controlled. Moreover, several laboratory control tests,
such as the tests for apparent density, iodine number and molasses number
are performed in the course of regeneration to monitor the quality of the
regenerated carbon.
71
-------
2.
VOLUME TREATED, million gallons
4.0 ft 5.5 7.3 8.8 10.3
12.6
i I
CLARIFIED EFFLUENT
CARBON EFFLUENT
UNIT CONVERSIONS
mil aal x 3785= cu
CLARIFIED EFFLUENT
CARBON EFFLUENT
12 16 20
STUDY PERIOD (WEEKS)
Figure 31. Turbidity and color removal through the carbon column-first cycle.
-------
CO
30
12.6 14.4
32
36
VOLUME TREATED, million gallons
15.9 16.5 18 19.6 21.5
23.1 24.8
I
.CLARIFIED EFFLUENT
1
I
'CARBON EFFLUENT
•1 1 1 1 1 1 h
UNIT CONVERSIONS:
mil gal x 3785= cu m
CLARIFIED EFFLUENT
CARBON EFFLUENT
40 44 48 52
STUDY PERIOD (WEEKS)
56
60
64
Figure 31. Continued
-------
-pi
24.8
10,
o
-3 40
t
9
03
§20
h-
TREATED, million gallons
25.6 28.6 30.0
68
T
T
CLARIFIED EFFLUENT
CARBON EFFLUENT
CONVERSIONS:
mil gal x 3785 =cu m
CLARIFIED EFFLUENT
CARBON EFFLUENT
JL
72 76 80 84
STUDY PERIOD (WEEKS)
92
96
Figure 31. Continued
-------
30
to 20
Z
ID
-------
en
30
05 20
(T
o
O
O
10
40
O
CD
20
1.8
4»
i
3.4
5.1
VOLUME TREATED, million gallons
CLARIFIED EFFLUENT
CARBON EFFLUENT
UNIT CONVERSIONS:
mil gal x 3785= cu m
CLARIFIED EFFLUENT
CARBON EFFLUENT
_L
8
12 16 20
STUDY PERIOD (WEEKS)
24
28
32
Figure 33.Turbidity and color removal through the carbon column- third cycle.
-------
TABLE 8. CARBON COLUMN PERFORMANCE
Parameters
Total COD:
Influent,
Effluent,
Removal , %
Dissolved
Influent,
Effluent,
Removal , %
Color:
Influent,
Effluent,
Removal , %
Suspended
Influent,
Effluent,
Removal , %
Turbidity:
Influent,
Effluent,
Removal , %
mg/1
mg/1
COD:
mg/1
mg/1
color units
color units
Solids:
mg/1
mg/1
JTU
JTU
Adsorption
1
98.4
23.6
76.0
48.0
16.1
66.5
19.2
9.8
49.0
30.9
8.3
73.1
24.4
7.7
68.4
2
86.2
10.0
88.4
48.4
7.2
85.1
20.4
6.0
70.6
22.8
4.0
82.5
19.9
3.8
80.9
Cycles
3
98.2
11.5
88.3
52.1
9.4
81.9
21.6
4.7
78.2
24.5
3.8
84.5
20.6
3.6
82.5
Overall
Averages
95.8
19.3
79.9
48.6
13.5
72.2
20.0
7.8
61.0
28.3
6.7
76.3
22.9
6.3
72.5
77
-------
The apparent density test was used as the primary control test during
regeneration with the decolorizing tests for iodine and molasses numbers
used as supplemental control tests. The apparent density, which usually
ranged from 0.48 to 0.49 g/cm3 for virgin carbon, increased to about 0.59
to 0.63 g/cm3 when the carbon becomes exhausted. When the spent carbon is
properly regenerated, most of the adsorbed impurities are removed thus
restoring the apparent density to the virgin level.
During regeneration, the apparent density test was determined routinely
every hour whereas the tests for iodine and molasses numbers were performed
every 4 and 2 hours, respectively. The hourly samples of regenerated and
quenched carbon were composited over the regeneration period and analyzed
along with the spent carbon composite sample for apparent density, iodine
number, molasses number, methylene blue number, ash content, and particle
size distribution.
Effect of Regeneration on Carbon Properties
As a result of thermal regeneration, some losses inevitably occur both
in the carbon adsorptive capacity and the carbon quantity. These losses
are of economic importance since they constitute a significant portion of
the carbon regeneration cost. The carbon loss during the three regeneration
cycles varied from 2.5 to 6 percent. In this report, the carbon loss is
defined as the difference in the carbon volume in the contactor just before
transfer to the drain bin and just after backwash of the regenerated carbon.
The carbon loss can be ascribed either to the direct oxidation of the ex-
terior surfaces of the carbon granules by the activating gases and/or to
the normal handling attrition if the basic carbon structure had been prev-
iously weakened by internal over-activation (11).
The complete removal of adsorbed organics from the carbon pores is
actually never attained during regeneration. In addition to ash buildup
in the carbon pores, some of the carbon granules are unavoidably burned
with the adsorbate thereby reducing further the total surface area available
for adsorption. Consequently, with the physical loss of carbon during
regeneration is the attendant decrease in the adsorptive capacity as
measured by DCOD removal, iodine number and molasses number.
The changes in some of the physical properties of the carbon before
and after regeneration are shown in Table 9. It is apparent from fhe data
that repeated thermal regeneration had the effect of decreasing the iodine
number and increasing the ash content. The iodine number, which relates
to the surface area of pores larger than 10 A° diameter, was used in this
study as an index to measure the extent to which the carbon micropores were
cleared of adsorbate during regeneration. As indicated by the data in
Table 9, the iodine number decreased about 26 percent from a virgin level
of 1040 to 773 mg/g after three adsorptive cycles. The ash content of the
carbon, which measures the amount of calcium and other inorganic residues
picked up by the carbon during service increased about 67 percent from a
virgin level of 6.4 to 10.7 percent after the first regeneration. On the
78
-------
TABLE 9. EFFECT OF REGENERATION ON THE IPC CARBON CHARACTERISTICS
Carbon
Characteristics
Iodine No. , mg/g
Apparent Density,
g/cm3
Molasses No.
Methylene Blue No. ,
mg/g
Ash, %
Mean Particle Dia. ,
mm
Virgin
Carbon
1040
0.484
222
259
6.4
1.44
Spent Carbon
(Composite Sample)
1st
Req.
402
0.629
120
147
10.3
1.46
2nd
Req.
572
0.585
168
153
8.22
1.58
3rd
Req.
570
0.594
154
153
8.67
1.48
Regenerated Carbon (Composite Sample)
Before Quench
1st
Req.
805
0.528
213
223
10.7
1.57
2nd
Req.
722
0.537
233
243
11.6
1.50
nq
3rd
Req.
773
0.526
230
246
7.81
1.54
After Quenching
1st
Req.
751
0.565
189
227
12.0
1.55
2nd
Req.
727
0.548
221
239
12.2
1.50
3rd
Req.
721
0.535
204
245
9.0
1.43
-------
second regeneration, only a slight increase in ash content was observed with
a decrease noted in the third regeneration. With the ash buildup following
repeated regenerations, was a corresponding increase in the apparent density
from 0.484 to 0.528 g/cm3.
In the course of repeated thermal regenerations some degree of internal
overactivation may occur which eventually results in an increase in macro-
pore volume. The molasses number, which relates to surface area of pores
larger than 28 A° diameter, is taken as a measure of pore enlargement.
Another parameter used to measure pore enlargement during thermal regener-
ation was the methylene blue number, which relates to surface area of
carbon pores larger than 15 A° diameter.
While the iodine number decreased after repeated regeneration cycles,
both the molasses and methylene blue numbers of the regenerated carbon
remained at about the same levels as those of the virgin carbon. This
observation suggests that a portion of the microspores had not been cleared
of adsorbate and that a shift of pores to larger size due to internal
damage of the carbon pore structure, was obviated during the regeneration.
Table 10 summarizes the furnace operating data for the three regenera-
tion cycles. The data show some variations in the duration of the regen-
eration run, furnace loading rate and fuel used. The variations in the
furnace operation have been attributed to the varying degrees of operating
problems encountered during the regeneration. The first and third
regenerations preceded without any major operational difficulties.
During the second regeneration cycle, the regeneration run was stopped
after 36 hours of continuous furnace operation because problems which
developed in maintaining proper carbon feed rate to the furnace caused a
rapid rise in the temperature within the baghouse; eventually resulting in
the burning of all the nomex felt filter bags. In the second half of the
regeneration, the furnace was operated only between 6 and 8 hours/day,
instead of the usual continuous furnace operation. The carbon loss was
estimated at 6 percent, which was much higher than 2.5 percent carbon loss
observed during the first carbon regeneration. The high carbon loss could
be attributed primarily to the intermittent mode of regeneration. Moreover,
in the second regeneration, difficulties were encountered not only in the
carbon feeding to the furnace but also in the frequent plugging of the
quench tank screen with gravel. Apparently, some of the gravel frt5m the
column underdrain system was carried over with the spent carbon during the
hydraulic transfer to the drain bin.
Despite these permanent changes in carbon characteristics as a result
of regeneration, based on organics removal, the regenerated carbon was as
good as or better than the control
80
-------
TABLE 10. FURNACE OPERATING CONDITIONS DURING IPC CARBON REGENERATION
co
Parameters
Duration of Regeneration, hours
Furnace Loading, Kg carbon/hr (Ib/hr)
Steam Used, Kg/Kg carbon
Fuel Used Kj/Kg Carbon
(BTU/lb Carbon)
Average
Temp. ° C
(° F)
Furnace
Afterburner
Total
Hearth
Number
1
2
3
4
5
6
Afterburner
Carbon Loss, %
Regeneration Number
1 2 3
53 66 60
41.4 (91.1) 34.8 (76.6) 38.3 (84.3)
0.58 0.68 0.62
8427 (3620) 10,086 (4332) 7184 (3086)
7378 (3148) 12,573 (5400) 9764 (4194)
15,756 (6768) 22,660 (9730) 16,948 (7280)
367 (693) 338 (641) 337 (639)
485 (905) 470 (878) 449 (840)
596 (1108) 590 (1095) 558 (1037)
925 (1699) 900 (1652) 896 (1646)
975 (1788) 936 (1717) 942 (1728)
958 (1760) 954 (1750) 946 (1736)
741 (1368) 726 (1339) 719 (1326)
2.5 6 4.4
-------
Air Pollution Control System Performance
The flue gases discharged from the top hearth of the multi-hearth fur-
nace contained both particulate and obnoxious-smelling substances. These
air pollutants were controlled through an air pollution control system con-
sisting of a baghouse for particulate removal and an afterburner, operated
in series with the baghouse for odor control. The afterburner was operated
at a temperature range of 719°C (1326°F) to 741°C (1368°F). The baghouse
was operated at a temperature ranging from 149°C (300°F) to 163°C (325°F).
While it is advantageous to maintain a high temperature in the baghouse to
prevent condensation problems, due precaution had to be exercised to prevent
the temperature from rising to within 10°C (50°F) to 38°C (100°C) of the
critical temperature of the fabric filter. Thus, to minimize the danger of
burning the filter bags, the baghouse inlet was equipped with a valved side
connection for dilution air addition. Under normal furnace operating condi-
tions, the dilution air inlet valve was maintained in a closed position.
However, when the baghouse temperature increased beyond 163°C (325°F), which
could have been triggered by a disruption of the carbon feed rate and/or
plugging of the quench tank screen, the dilution air valve was manually
opened for such a duration as needed to restore the temperature to about
163°C (325°F).
During the first carbon regeneration, the performance of the various
components of the air pollution control system was evaluated by test
engineers from a local testing laboratory. In evaluating the system, the
flue gases at the inlet and outlet of the baghouse and at the outlet of the
afterburner were tested for flow rate, temperature, particulate matter,
volatile hydrocarbons, oxygen, carbon dioxide, carbon monoxide, water vapor,
oxides of nitrogen, and oxides of sulfur. The odor number was determined on
the integrated flue gas samples collected in 8.2-liter cylinders at the
inlet to the baghouse and at the outlet of the afterburner.
Gas flow measurements were made with a standard pi tot tube and a
magnehelic draft gauge. Temperatures were measured with a Chromel-Alumel
thermocouple and a portable potentiometer. The test for particulate matter
was performed using a wet impingement method. Samples for the determination
of oxides of sulfur were collected by an impinger train containing hydrogen
peroxide. An Orsat analysis was performed to determine the carbon dioxide
and oxygen concentrations. The phenol-disulfonic acid method was employed
for the determination of the oxides of nitrogen. A gas-chromatogwaph-comb-
ustion-infrared technique was used to determine the concentration of carbon
monoxide and volatile hydrocarbons.
During regeneration, odors were detected and this was confirmed by the
relatively high odor number of 3 odor units/1 (90 odor units/SCF). Particu-
late emission was also high and averaged 0.30 kg/hr (0.64 Ib/hr). Based on
the particulate emission rate data, the baghouse removed only about 26
percent of the incoming dust load, which was indeed significantly below the
82
-------
design removal efficiency of 99 percent. It should be pointed out, however,
that the emission data represented samples collected over 45 to 60 minutes
sampling period. The total actual weight of dust collected from the bag-
house over the 53-hour regeneration period was only 14.7 Kg (32.5 Ibs.),
which represented about 56 percent of the calculated dust removed.
In Table 11 is presented a summary of the emission data from the various
components of the air pollution control system. For purposes of comparison,
the emission data obtained during the third regeneration of the lead con-
tactor of the tertiary two-stage carbon adsorption system is also included
in this table. It is apparent from the data in Table 11 that the emission
parameters evaluated were significantly higher in the IPC carbon regeneration
than in the carbon column III 3A. This observation was expected, considering
that the IPC carbon column was subjected to a much heavier load of organic
matter than column III 3A. At the time the IPC column was taken off-stream
for regeneration, it had processed 113,550 m3 (30 million gallons) of alum-
polymer treated raw sewage with an equivalent total organic loading of 4.6
kg TCOD applied/kg carbon and 2.3 kg DCOD applied/kg carbon. The correspond-
ing carbon capacity in the virgin cycle was 3.54 kg TCOD removed/kg carbon
and 1.54 kg DCOD removed/kg carbon. On the other hand, when column III 3A
was regenerated it had treated 108,000 m3(28.48 million gallons) of activated
sludge plant effluent with a total applied organic loading of 1.0 kg TCOD/
kg carbon and 0.65 kg DCOD/kg carbon. The COD removal capacity was .65 kg
TCOD/kg carbon and .29 kg DCOD/kg carbon. The results of the air pollution
control system evaluation thus demonstrate that, the air pollutants eventual-
ly discharged to the atmosphere during carbon regeneration, depend on the
amount and composition of the adsorbate.
DISCUSSION OF THE IPC SYSTEM PERFORMANCE
As discussed in previous sections the chemical clarification step provided
the major bulk of the pollutant's removal in the IPC system. In addition to
the anticipated high degree of suspended solids and phosphate removal, sig-
nificant removal of suspended organic material was obtained. The dissolved
organic removal, however, which was measured by DCOD was only marginal, indi-
cating that the alum-polymer treatment was not effective in the coagulation
of impurities in the wastewater filterable through a 0.45y filter used in the
DCOD determination. This observation is contrary to what other investigators
(3,12) reported, which suggests that the type of wastewater treated affects
the degree of soluble organics removal by the chemical clarification process.
The chemical clarification of raw sewage using alum at an average dosage
of 25 mg/1 Al (275 mg/1 alum) with 0.3 mg/1 of anionic polymer (Calgon WT-
3000) was very effective throughout the study in producing good quality
clarified effluent. The clarified effluent had an average turbidity, suspend-
ed solids and TCOD concentration of 22.9 JTU, 28.3 mg/1 and 95.8 mg/1, respec-
tively. The total phosphate in the raw sewage, which had averaged 11.1 mg/1
P was reduced about 88 percent, resulting in a clarified effluent with an
average total phosphate concentration of 1.3 mg/1 P.
The economics of any chemical clarification system is influenced
a great deal by the cost involved in the treatment'and subsequent disposal
83
-------
TABLE 11. SUMMARY OF AIR POLLUTION CONTROL SYSTEM PERFORMANCE
Parameters
Parti cul ate Matter
Concentration, mg/1
Emission Rate, kg/hr
. Oxides of Nitrogen ,(NOV)
A
Concentration, mg/1 dry
Emission Rate, kg/hr
. Oxides of Sulfur (S02)
Concentration, mg/1 S02
Emission Rate, kg/hr
. Hydrocarbons
Concentration, mg/1 C
Emission Rate, kg/hr
. Carbon Monoxide (CO)
Concentration, % vol. dry
. Odor
Odor Units/1
*
Gas Flow
Temp. ,° C
Rate, I/sec
APCD
Emission
Limit
0.46
0.45
225.00
2000.00
1st Regeneration of
IPC Carbon Column
Baghouse
Inlet Outlet
7.82 3.57
2.11 1 . 44
49.00 120.00
0.016 0.068
Nil
Nil
5530.00 2800.00
0.74 0.56
5.00 1.7
777.00
271.00 121.00
75.00 112.00
Afterburner
Outlet
0.48
0.30
423.00
0.49
729.00
1.17
221.00
0.066
0.47
3.00
665.60
167.00
3rd Regeneration of Two-
Stage Carbon Column (III 3A)
Baghouse
Inlet Outlet
4.16 1.08
0.98 0.36
40.00
0.012
Nil Nil
740.00 561.00
0.09 0.095
1.36 0.86
706.00
177.80 70.60
66.00 93.00
Afterburner
Outlet
0.017
0.11
180.00
0.18
149.00
0.26
Nil
0.11
0.70
620
177.4
co
-------
of the chemical-sewage sludge produced. In this study, the flow of the
alum-sewage sludge produced, which was about 1.2 percent of the pilot
plant flow, was of the same level as that normally obtained for waste
activated sludge. Results of bench-scale studies performed in the course
of the study showed that the alum-sewage sludge was difficult to dewater
and that chemical conditioning at a cost of $15-$17 per ton dry solids was
required to achieve a yield of 4.9-9.8 kg/m -hr (1-2 Ib/ft -hr) with cake
solids of 18 percent. The economic analysis, which is discussed in subse-
quent sections, showed that the sludge treatment accounts for about 59 per-
cent of the capital cost of the chemical clarification system.
The function of the subsequent carbon adsorption step is the removal of
residual dissolved organics from the chemical clarification system. Since
inert media filtration was not provided, the carbon contactor also served as
a deep bed filter for the removal of suspended solids from the clarified
effluent feed. Because of the suspended solids load as well as the biologi-
cal growths produced within the column, daily backwashing was required to
relieve the column of excessive headless and to minimize septicity in the
column. Despite the daily backwashing, sulfide generation still occurred
in the column. Of the various sulfide control methods evaluated, continuous
sodium nitrate addition to the column at a dosage of about 5.4 mg/1 N was
found to be the most effective. Moreover, the sodium nitrate added to the
column enhanced the biological activity within the column resulting in
improved overall dissolved organics removal. In comparing the organic
removal before and after sodium nitrate addition, it was demonstrated that,
indeed, nitrate addition brought about a significant increase in the
capacity of the carbon for DCOD removal. While the carbon DCOD removal
capacity tends to decrease with repeated thermal regeneration as had been
shown from previous study at Pomona (7), results from the current study has
demonstrated higher carbon capacity of the regenerated carbon compared to
that of virgin carbon. This result may be due to enhanced biological
activity within the column brought about by the nitrate addition, rather
than a change in the carbon adsorptive property.
A summary of the overall performance of the IPC pilot plant is present-
ed in Table 12. The values shown in the table are the average effluent
quality characteristics and removal efficiencies obtained during the entire
27 months of the study. For purposes of comparison, the effluent quality
from a 30,280 cu m/day (8 mgd) activated sludge plant treating the same raw
sewage is also included in Table 12. The data clearly demonstrate the
superiority of the IPC system effluent quality over that of the secondary
effluents.
Effect of Copper Waste on IPC System
One of the main advantages of the physical-chemical treatment system
over biological secondary treatment processes is the ability of the IPC
system to consistently produce good quality effluent even in the presence
of toxic industrial wastes. The stability of the IPC system operation was
85
-------
TABLE 12. SUMMARY OF IPC SYSTEM PERFORMANCE'
Parameters
Suspended Solids, mg/1
Turbidity, JTU
TCOD, mg/1
gDCOD, mg/1
BOD5, mg/1
Total Phosphate, mg/1 P
Nitrate, mg/1 N
Color
PH
Raw
Sewage
199
321
49.4
11.1
7.7
Clarified
Effluent
28.3
22.9
95.8
48.6
36.2
1.3
0.90
20.0
6.8
Carbon
Effluent
6.7
6.3
19.3
13.5
7.8
0.90
1.3
7.8
6.8
Average
Chemical
Treatment
85.8
70.2
1.6
88.3
Percent Removal
Carbon
Treatment Overall
76.3 96.6
72.5
79.9 94.0
72.2 72.7
78.5
30.8 91.9
61.0
Activated
Sludge
Plant
Effluent
11.6
7.7
39.5
25.7
8.0
33.1
* Average alum dosage = 25 mg/1 Al (275 mg/1 alum); Average polymer dosage = 0.3 mg/1 Calgon WT-3000-
-------
indeed demonstrated during a one-week period when the Pomona activated
sludge plant suffered a severe upset caused by a discharge of copper-
bearing wastes. The measured copper concentration in the sewage for the
24-hour period from March 13 to March 14, 1972 was 1.2 mg/1 Cu. As
expected, the activated sludge plant effluent quality deteriorated, as
shown by the high levels of suspended solids and COD, whereas, the IPC
effluent quality remained essentially unchanged. Figures 34 through 36
clearly demonstrate the superiority of theIPC system performance over
that of the activated sludge process especially during periods when copper
wastes were present in the incoming raw sewage.
Metals and Miscellaneous Analyses
Periodically during the course of the study, determination of heavy
metals and other chemical analyses were performed on the various waste
streams on the IPC system. The results of the metal analyses are present-
ed in Table 13. The data indicate that the metal constitutents in the
carbon effluent were generally low except for iron and zinc which were
significantly higher than those present in the chemically clarified effl-
uent. The agressive environment within the carbon column produced by ana-
erobic conditions, and the presence of organic sulfides and sulfate-reducing
bacteria could have contributed to the process of corrosion. Although the
interior of the column was initially coated with coal tar epoxy to inhibit
corrosion, there could have been some areas which were not properly coated.
In fact, when the column was taken off stream for repairs as discussed
previously, (Dec. 1972 - Jan. 1973), there were some parts where the coat-
ing separated from the column exposing the metal. This exposed metal was
covered with heavy brush-on coat of bitumastic coal tar epoxy before the
column operation was resumed. In subsequent periods, the concentrations
of zinc and iron were still high indicating active corrosion taking place
within the column. The extent of corrosion within the column became
evident in the last two months of the study when leaks occurred at several
places along the carbon column.
Table 14 presents the results of mineral analyses and other determina-
tions. As indicated in the table, the alkalinity, sulfate, total dissolved
solids and conductivity of the wastewater showed significant changes in
passing through the various stages of the IPC system. As a result of the
alum addition, sulfate was added to the wastewater in an amount equivalent
to 5.2 mg/1 SOLf per mg/1 Al added compared to the theoretical value of 5.4
Other soluble wastewater components, however, such as phosphate and alka-
linity were reduced in concentration, the net effect of which was a slight
increase in the clarified effluent total dissolved solids (TDS) concen-
tration. A slight increase in the TDS concentration occurred in the carbon
effluent as a result of sodium nitrate addition to the column for sulfide
control. As indicated in the table, the conductivity of the effluents also
increased correspondingly.
Although a high alum dosage ranging from 22-25 mg/1 Al (242-275 mg/1
87
-------
120
co
co
100
80
e
~ eo
Q
O
o
40
20
ACTIVATED SLUDGE EFFLUENT
TCOD
IPC EFFLUENT TCOD
ACTIVATED SLUDGE EFFLUENT
DCOD
J_
IPC EFFLUENT DCOD
__1 I
I
10
15 20
MARCH 72
25
DATE
30 5 10
-H-* —APRIL'
15
Figure 34. Effect of copper waste on the COD removal.
-------
CO
to
•ACTIVATED SLUDGE EFFLUENT
b-cf
IPC EFFLUENT
DATE
Figure 35. Effect of copper waste on suspended solids removal.
-------
60
50
40
' 30
Q
GO
20
10
ACTIVATED SLUDGE EFFLUENT
10 15 20
MARCH 72
25
30 5 10
3^U APRIL-
DATE
Figure 36. Effect of copper waste on turbidity removal.
-------
TABLE 13. HEAVY METAL ANALYSES
Constituents
(ug/D
Aluminum
Arsenic
Boron
Cadmi urn
Chromium (Hex. )
Chromium (Total )
Copper
Cyanide
Fluoride
Iron
Lead
Manganese
Mercury
Nickel
Silver
Zinc
Raw
Sewage
70.0
22.0
720.0
4.0
45.0
238.0
830.00
25.0
890.0
880.0
185.0
16.0
0.8
190.0
4.2
217.0
Clarified
Effluent
336.0
9.1
429.0
2.9
36.0
110.0
275.0
19.1
303.0
228.0
366.0
17.5
0.3
182.0
1.8
257.0
Carbon
Effluent
50.0
7.0
610.0
2.6
2.3
25.0
71.0
11.5
290.0
928.0
28.5
20.0
0
105.0
6.7
587.0
Average Removal , %
Chemical
Treatment
--
58.6
40.4
27.5
20.0
53.8
66.9
23.6
66.0
74.1
80.2
—
66.7
4.2
57-1
--
Carbon
Column
85.1
23.1
--
10.3
93.6
77.3
74.2
39.8
4.3
--
22.1
—
100.0
42.3
--
--
91
-------
TABLE 14. MINERAL AND MISCELLANEOUS ANALYSES
Constituents
Alkalinity, mg/1 CaC03
Calcium, mg/1 Ca
Chloride, mg/1 Cl
Magnesium, mg/1 Mg
Nitrate, mg/1 N
Potassium, mg/1 K
Sodium, mg/1 Na
Sulfate, mg/1 SO^
MBAS, mg/1
Phenols, mg/1 phenol
2
Conductivity, umhos/cm
Total dissolved solids, mg/1
PH
Raw Sewage
217.00
51.30
104.40
10.90
10.50
100.00
95.00
1.96
0.17
573.00
7.68
Clarified
Effluent
130.00
52.8
105.40
11.20
0.90
10.80
101.00
225.00
2.42
0.055
1046.00
618.00
6.75
Carbon
Effluent
169.00
52.4
96.20
11.00
1.32
11.40
113.00
219.00
0.43
0.005
1089.00
627.00
6.80
92
-------
alum) was used in the chemical clarification of the raw sewage, the clar-
ified effluent and carbon effluent contained only 0.31 and 0.05 mg/1 Al,
respectively. The alum floe in the clarified effluent was effectively
filtered out in the carbon column. While most of the trapped floe was
removed from the carbon column during the routine backwash operation,
invariably some floe adhered tenaciously to the carbon granules.
In an effort to determine the fate of various metals present in the
chemically clarified effluent in passing through the carbon column,
samples of virgin carbon, spent carbon and quench water were collected
during the first carbon regeneration. These samples were analyzed for
various metal constituents at the Municipal Environment Research Lab-
oratory of the U.S. EPA in Cincinnati, Ohio. The summary of the test
results are presented in Table 15. In evaluating the data from this table,
the following general observations can be drawn:
(1) The spent carbon contained considerably larger concentrations of Cd,
Cr, Cu, Ni and Zn than were present in the virgin carbon. Analyses
of spent carbon taken at various depths of the column showed the
amount of Cd, Cr, Cu and Zn were highest at the top 30.5 cm
(12 in.) of the carbon bed with the concentration of nickel about
evenly distributed throughout the bed. The concentrations of Hg,
Ti, Be, As and Sr in the spent carbon were lower than that in the
virgin carbon.
(2) The concentrations of Zn3 Cr, Cu and Ni in the regenerated carbon
were much higher than those of virgin carbon. In comparing the
metal contents of the spent carbon composite samples with those
of the 12-hr.regenerated carbon composite samples, it is apparent
that a high loss of Cd and small losses of Zn, Crs Cu, As, Fe
and Pb occurred on regeneration.
(3) The baghouse dust contained considerably higher levels of Ca, Cd,
Cu, Cr, Al, Fe, Sr, Sn, Pb, Ni,and Zn than virgin carbon.
(4) The metal constitutents in the quench water were found generally
near background levels.
(5) Unlike the other metals, Cd was almost completely stripped from
the carbon during regeneration and ended up in the baghouse.
The changes in the various forms of nitrogen during chemical treat-
ment and subsequent carbon adsorption are presented in Table 16. The
ammonia concentration increased from 14.5 mg/1 N in the raw sewage to
21.2 mg/1 N after chemical clarification and remained essentially un-
changed in passing through the carbon column. However, the organic
nitrogen concentration showed a significant drop from 14.7 in the raw
sewage to 6.3 mg/1 N in the clarified effluent and to a level of 2.1
mg/1 N after carbon adsorption. The nitrate concentration in the
93
-------
TABLE 15. HEAVY METAL CONSTITUENTS OF QUENCH WATER AND CARBON SAMPLES
Metal
Hg
Se
Sb
Sn
Co
Tl
Mo
Ti
V
Be
Bi
Zn
Cr
Pb
Ni
Mn
Cu
Ba
Cd
As
Fe
Al
Sr
Ca
Virgin
Filtrasorb
300
1.92
<0.96
<7.20
<48.00
<4.80
<24.00
<12.00
240.00
24.00
2.40
<24.00
1.20
7.20
16.80
12.00
26.40
<1.20
50.40
1.20
108.00
617.00
1536.00
72.00
391.00
Spent Carbon
Composite
0.36
<.96
<7.20
72.00
14.40
<24.00
<12.00
96.00
24.00
<2.40
<24.00
132.00
658.00
19.20
816.00
1.20
444.00
76.80
26.40
57.60
1200.00
1920.00
|8. 40
3120.00
Avg. of 4-12 hr Composites
of Regenerated Carbon
0.45
9.84
<7.20
<48.00
24.00
<24.00
<12.00
216.00
24.00
<2.40
<24.00
102.00
559.80
13.80
936.00
30.60
286.30
79.20
<1.20
49.80
912.00
3162.00
80.40
4632.00
Avg. of 4-12 hr Composites
of Quench Water *
-------
TABLE 16. NITROGEN REMOVAL IN THE IPC SYSTEM
Nitrogen
Forms
(mg/1)
Organic N
NH -N
3
NO -N
2
NO -N
3
Total N
Raw
Sewage
14.7
14.5
0.8
2.6
32.6
Clarified
Effluent
6.3
21.2
0.4
0.9
28.8
Carbon
Effluent
2.1
21.3
0.2
(*)
1.31 '
24.9
Chemical
Treatment
57.1
__
50.0
65.4
11.7
Percent Removal
Carbon
Treatment
66.7
—
50.0
79.4 ^+>
27.2
Overall
85.7
—
75.0
1
1
* Sodium nitrate fed to carbon column = 4.5 - 5.8 mg/1 N
+ Based on an average sodium nitrate fed to column =5.4 mg/1
-------
carbon effluent averaged 1.3 mg/1 N which was slightly higher than that of
the clarified effluent. The nitrate, which was added to the carbon column
at dosages from 4.5 - 5.8 mg/1 N for sulfide control was completely reduced
presumably by biological denitrification in the carbon column. The
significant increase of the ammonia level in the clarified effluent was
probably due to the biological oxidation of the organic nitrogen in the
raw sewage and/or in the alum-sewage sludge.
96
-------
SECTION 6
ECONOMIC ANALYSIS
For convenience in the discussion of the economic analysis, the
estimated treatment cost for the IPC system is subdivided into three parts,
namely, chemical treatment costs, carbon treatment costs and total IPC
system costs. The economic analysis is based on the treatment of Pomona
wastewater for an average design flow of 0.44 m3/sec (10 mgd) and a peak
design flow of 0.61 m3/sec (14 mgd). The process design parameters for
sizing the various treatment units are presented in Table 17. The assumed
unit costs for chemicals and other direct costs for estimating the operation
and maintenance (0/M) costs are shown in Table 18. Figure 37 presents the
IPC system flowsheet, showing the various treatment components employed.
In the preparation of the economic analysis, various published reports
were consulted, particularly references (13,14) for the chemical treatment
system and reference ( 6) for the carbon contacting system. The capital
costs obtained from literature were adjusted to reflect the price levels
of March 1975, with an EPA sewage treatment plant construction cost index
of 232.1.
CHEMICAL TREATMENT COSTS
Table 19 presents a summary of the chemical treatment costs for a 0.44
m3/sec (10 mgd) plant. The estimated capital costs of the various treatment
components include allowance for instrumentation, pipings, appurtenances
and buildings. In addition, an allowance of 20 percent of the total capital
costs is included for engineering, legal and administrative costs. The
preliminary treatment costs include the costs for bar screening, comminution,
grit removal and flow measurement.
The costs in Table 19 sJnow that about 59 percent of the total capital
costs is associated with the treatment and disposal of the alum-sewage
sludge produced in the chemical coagulation-sedimentation system. Of the
total chemical treatment cost of 5.29 i/m3 (19.81 <£/1000 gallons), 67
percent represents operation and maintenance (0/M) and only 33 percent for
capital amortization. Moreover, about 67 percent of the 0/M costs is
associated with the cost of alum and polymer used in the chemical
clarification of the raw sewage.
97
-------
TABLE 17. IPC SYSTEM DESIGN DATA
CHEMICAL TREATMENT SYSTEM
1. F1peculation:
Detention Time, minutes 45.0
Chemical Dosage
Alum, mg/1 Al 22.0
Polymer, mg/1 0.25
2. Sedimentation:
Detention Time, hours 1.5
Overflow Rate, cu m/day/m2 36.6
Underflow, % of plant flow 1.25
Underflow solids, % by weight 2.0
3. Gravity Thickening:
Solids Loading, kg/day-m2 58.0
Underflow solids, % by weight 4.0
4. Vacuum Filtration:
Yield,kg/hr-mz 9.8
Cake solids 18.0
5. Sludge Incineration:
Solids Loading, Kg/hr-m2 9.8
CARBON TREATMENT SYSTEM
1. Carbon Contacting (8 x 30 mesh carbon)
Empty-bed contact time 25.0
Hydraulic surface loading, 1/sec/m2 2.7
Backwash volume , % of plant flow 5.0
Sodium Nitrate Dosage, mg/1 N 5.5
Carbon Dosage, kg/m3 0.03
Carbon Regeneration loss, % 5.0
98
-------
TABLE 18. UNIT COSTS FOR OPERATION AND MAINTENANCE ESTIMATE
CHEMICALS
Alum, $/kg Al 1.00
Polymer, $/kg 4.40
Sludge conditioning polymer, $/Ton dry solids 15.00
Sodium nitrate, $/kg sodium nitrate 0.16
Granular activated carbon (8 x 30 mesh), $/kg 1.10
OPERATING COSTS
Power, tf/KWH 2.0
Fuel, <£/therm 10.0
Carbon regeneration fuel, Kj/kg 14,000.00
Sludge Incineration, $/ton dry solids 5.0
Backwash water, <£/m 0.8
Operating Labor, 5 at $12,000/yr. 60,000.00
Maintenance Labor, 2 at $10,000/yr. 20,000.00
Laboratory personnel, 1 at $14,000/yr. 14,000.00
Maintenance materials, $/yr
Chemical Treatment 20,000.00
Carbon Treatment 10,000.00
CAPITAL COSTS
All equipment costs were amortized at 6% for 25 years.
99
-------
RAW SEWAGE
o
o
I
BA(
|
s
s
1
1 so
!
PRELIMINARY TREATMENT
:iKWASH_RECYCLE
I
I
ALUM >•
POLYMER ^CHEMICAL TREATMENT
[>IUM NITF
1 SPENT
CARBO
CARBON
REGENERATION
PATF -. - ..
f
"~~ GRANULAR
fARRON "
N ^
REGENERATED \\
CARBON jl
t ,
VIRGIN |
MAKE-UP— -1 '
tARBON TRE>
EFFL
L
ACTIVATED
FREATMENT
i
^TED
UENT
THICKENER
ALUM-SEWAGE ^
1
1
L_F]LT RATJE __
GRAVITY
THICKENING
(
-*- POLYMER
VACUUM
FILTRATION
\
INCINERATION
I
DISPOSAL
Figure 37. Proposed IPC system-flow sheet.
-------
TABLE 19. ESTIMATED CHEMICAL TREATMENT COST*
CAPITAL COSTS (1000 of $)
Raw Sewage pumping station 388
Preliminary Treatment 85
Coagulation-Sedimentation 568
Gravity Thickening 94
Vacuum Filtration 584
Incineration 812
Total 2,531
Engineering, legal and administrative costs, (20%) 506
Total capital costs 3,037
Amortized cost, tf/m3 U/1000 gallons) 1.74 (6.50)
OPERATION AND MAINTENANCE COSTS l/m3 U/1000 gallons)
Treatment Chemicals (alum and polymer) 2.32 (8.86)
Sludge Conditioning Chemical (polymer) 0.42 (1.56)
Power and Fuel 0.28 (1.06)
Operating and maintenance labor 0.34 (1.28)
Maintenance material 0-15 _(0.55)_
Total operating and maintenance cost,
-------
CARBON TREATMENT COSTS
The carbon contacting system consists of 10 carbon columns operated
in parallel at a design flow of 0.44 m3/sec (1 mgd) per column. Two
carbon storage tanks, each of which has a capacity equal to that of a
carbon column, is also provided. One of these storage tanks is initially
charged with carbon while the other tank is reserved for spent carbon
storage. Thus, the initial carbon charge is equivalent to the effective
volume of 11 carbon contactors.
A summary of the estimated carbon treatment costs is presented in Table
20, As indicated in the cost breakdown, the amortized cost represents
about 2.04 <£/m3 (7.62 it/1000 gallons). The costs of sulfide control in the
carbon column accounts for 37.5 percent of the total 0/M costs. The
operating and maintenance labor costs of 0.34 i/m3 (1.28 <£/1000 gallons), is
assumed to be one-half of that of the complete IPC system.
IPC SYSTEM COST
In Table 21 is shown the complete cost breakdown of the IPC system.
The total treatment cost to produce carbon treated effluent with character-
istics similar to that presented in Table 8 from 0.44 m3/sec (10 mgd) of
raw sewage is estimated at 8.69 <£/m3 (32.57 <£/1000 gallons). The effluent
quality from the IPC system would be about equal to or slightly better than
that obtained from a secondary biological treatment system for all the
parameters evaluated. Moreover, the IPC system has the added advantage
of not only providing stable effluent quality but also effluent with total
phosphate concentration of 0.9 to 1 mg/1 P.
The cost data in Table 21 show that the chemical treatment system cost,
which includes the cost for the treatment and disposal of the alum-sewage
sludge, represents about 61 percent of the total IPC system process costs.
If regeneration facilities were not required, the total treatment cost
is reduced to 7.92 i/m3 (29.68 <£/1000 gallons). This 9 percent cost
reduction is important especially in small plants where the regeneration
cost represents a significant portion of the overall cost.
102
-------
TABLE 20. ESTIMATED GRANULAR ACTIVATED CARBON TREATMENT COSTS*
CAPITAL COSTS (1000 of $)
Influent Pumping 219
Initial Carbon Charge 331
Carbon Contacting System 1,766
Carbon Regeneration System 650
Total 2,966
Engineering, legal and administrative costs (20%) 593
Total capital cost 3,559
Amortized cost, tf/m3 U/1000 gallons) 2.04 (7.62)
OPERATING AND MAINTENANCE COSTS j/m3 (6/1000 gallons)
Carbon make-up 0.16 ( -62)
Backwash water 0.04 ( .15)
Power and Fuel 0.24 ( .89)
Sulfide control (sodium nitrate) 0.51 (1.93)
Operating and maintenance labor 0.34 (1.28)
Maintenance material 0,-QZ ( -27)_
Total operating and maintenance cost,
<£/m3 U/1000 gallons) 1-36 ( 5.14)
Total treatment cost, <£/m3 U/1000 gallons) 3.40 (12.76)
* Based on EPA sewage treatment plant construction cost index
of 232.1 (March 1975) for a 37,850 cu m/day (10 mgd) plant.
103
-------
TABLE 21. ESTIMATED IPC SYSTEM COSTS*
CAPITAL COSTS (1000 of $)
Chemical Treatment System 3,037
Carbon Treatment System 3,559
Total Capital Cost 6,596
Amortized Cost,
-------
REFERENCES
1. Rizzo, J.L. and Schade, R.E., "Secondary Treatment with Granular
Activated Carbon", Water and Sewage Works, Vol. 116, No. 8, p 307
(Aug. 1969).
2. Hopkins, C.B., Weber, W.J., Jr., and Bloom, R., Jr., "Granular Carbon
Treatment of Raw Sewage", Water Pollution Control Research Series
ORD 17050 DAL 05/70, U.S. Department of Interior, Federal Water
Quality Administration (May 1970).
3. Friedman, L.D., Weber, W.J., Jr., Bloom, R., Jr., and Hopkins, C.B.,
"Improving Granular Carbon Treatment", Water Pollution Control
Research Series 17020 GDN 07/71, U.S. Environmental Protection
Agency, (July 1971).
4. "Standard Methods for the Examination of Water and Wastewater", 13th
Ed., American Public Health Association, New York, (1971).
5. "FWPCA Methods for Chemical Analysis of Water and Wastes", Federal
Water Quality Administration, Cincinnati, Ohio (Nov. 1969).
6. "Process Design Manual for Carbon Adsorption", U.S. Environmental
Protection Agency, (October 1973).
7. Parkhurst, J.D., Dryden, F.D., McDermott, G.N., and English, J.N.,
"Pomona Activated Carbon Pilot Plant", Journal Water Pollution
Control Federation, Vol. 39, No. 10, part 2, 1270 (October 1967).
8. Heukelekian, H. , "Some Bacteriological Aspects of Hydrogen Sulfide
Production from Sewage", Sewage Works Journal, Vol. 20, No. 3,
pp 490 (May 1948).
9. Dague, R.R., "Fundamentals of Odor Control", Journal Water Pollution
Control Federation, Vol. 44, No. 4, pp 583 (April 1972).
10. English, J.N., Carry, C.W., Masse, A.N., Pitkin, J.B., and Dryden, F.D.,
"Denitrification in Granular Carbon and Sand Columns", Journal Water
Pollution Control Federation, Vol. 46, No. 1, pp 28 (Jan. 1974).
105
-------
11. Juhola, A.J. and Tepper, F., "Regeneration of Spent Granular
Activated Carbon", Report No. TRWC-7, Robert A. Taft Water Research
Center, U.S. Dept. of Interior, Cincinnati, Ohio (Feb. 1969).
12. Burns, D.E. and Shell, G.L., "Physical-Chemical Treatment of
Municipal Wastewater using Powdered Carbon", Environmental Protection
Agency Technology Series, EPA, R2-73-264, U.S. Environmental
Protection Agency (August 1973).
13. Smith, R., "Electrical Power Consumption for Municipal Wastewater
Treatment", Environmental Protection Agency Technology Series,
EPA-R2-73-281, U.S. Environmental Protection Agency (July 1973).
14. Patterson, W.L., and Banker, R.F., "Estimating Cost and Manpower
Requirements for Conventional Wastewater Treatment Facilities",
Water Pollution Control Research Series, 17090 DAN 10/71,
U.S. Environmental Protection Agency (October 1971).
15. Lawrence, A.W, and McCarty, P.L. , "Unified Basis for Biological
Treatment Design and Operation", Journal Sanitary Engineering
Division, Proceedings American Society of Civil Engineering,
Vol. 96, SA 3, 757 (1970).
106
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-77-137
3. RECIPIENT'S ACCESSI ON" NO.
4. TITLE AND SUBTITLE
INDEPENDENT PHYSICAL-CHEMICAL TREATMENT OF RAW
SEWAGE
5. REPORT DATE
August 1977 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Leon S. Directo, Ching-Lin Chen, and Robert P. Miele
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Los Angeles County Sanitation Districts
Whittier, California 90607
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO.
14-12-150
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory--Cin., OH
Office of Research and Development
Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF RE PORT AND PERIOD COVERED
Final - Jan.1973-Aug.1975
14. SPONSORING AGENCY CODE
EPA/600/14
15.SUBP-LEMENTARY JSIOTES
Project Officer: Irwin J. Kugelman (513-684-7631)
A'3.T/l/sec(50 gpm)pilot plant evaluation of the independent physical-chemical treat-
ment (IPC)process was condicted for 27-months at Pomona, California. The pilot plant
consisted of chemical clarification w/alum at 25 mg/1 as Al and an
0.3 mg/1 followed by a single-stage, pressurized
hydraulic loading of 2.71 l/sec/m^(4 gpm/ft2)and
Performance data obtained have demonstrated the
as Al and an anionic polymer at
downflow carbon column operated at a
an empty-bed contact time of 30 min.
stability of the IPC system in produc-
ing effluent of excellent overall quality. The suspended solids, total COD and total
phosphate removals in the IPC system were 96.6%, 94%, & 92%, respectively. In the
course of the study, several methods of controlling sulfide generation in the carbon
column were evaluated. Continuous sodium nitrate addition to the carbon column at an
average dosage of 5.4 mg/1 N was found most effective in preventing sulfide generation.
The addition of nitrate had another favorable effect in that it permitted, through
enhancement of biological activity, a very high organic loading on the carbon column.
The carbon capacity was 3.54 Kg total COD removed/Kg carbon and 1.54 Kg dissolved COD
removed/Kg carbon. Although regeneration was not necessary, it was conducted in an
effort to obtain data on the effects of repeated regenerations on the carbon character-
istics. In all respects, the regenerations were as successful as those conducted on
granular activated carbon used in the tertiary treatment mode. The performance of the
regenerated carbon was found equal to or slightly better than that of the virgin carbon
bon
averaged 4.37; per
Ca
DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COS AT I Field/Group
Activated Carbon
Coagulation
Sedimentation
Treatment
Nitrate Treatment
Carbon Regeneration
Biological Activity
Sludge Dewatering
Physical-Chemical Treat-
ment
13B
13. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (This Report)'
Unclassified
21. NO. OF PAGES
119
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
107
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