CLEAN
—SESSION Rr
REMOVAL of
SOLIDS &ORGANICS
ADVANCED WASTE TREATMENT
SEMINAR
San Francisco
October 28 &29
19 70
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ADVANCED WASTE TREATMENT SEMINAR
KABUKI THEATRE
1881 POST STREET
SAM FRANCISCO
OCTOBER 28-29, 1970
JOINTLY SPONSORED BY
CALIFORNIA STATE WATER RESOURCES CONTROL BOARD
AND
PACIFIC SOUTHWEST REGIONAL OFFICE
FEDERAL WATER QUALITY ADMINISTRATION
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PROGRAM
OCTOBER 29 MORNING
SESSION III REMOVAL UP SOLIDS AND ORGANICS
Moderator: Professor Ray B. Krone
9:00 AM Solids Removal Processes ~ Jesse M. Cohen
9:30 AM New Developments in Sludge Handling - Robert B. Dean
10:15 AM Removal of Soluble Organics on Carbon - John N. English
10:45 AM Use of Pure Oxygen in Biological Treatment
Edwin F. Barth
11:15 AM Summary - Professor Krone
mUTFIlT
Solids Removal Processes Jesse M. Cohen
New Developments in Sludge Handling and Disposal Robert B. Dean
Removal of Organics from Wastewater by Activated Carbon
English, Masse# Carry, Pitkin and Haskins
Investigation of the Use of High Purity Oxygen Aeration in the
Conventional Activated Sludge Process (Summary) Edwin F, Barth
The Seminar also included the below sessions:
Session I Nitrogen Removal
Session II Phosphorus Removal
Session IV Combined Treatment and Application
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SOLIDS REMOVAL PROCESSES
Jesse M. Cohen
If one were t
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- 2 -
(*)
/r/ \\jl7 wJy XAjgy \»JJ/ vV/
£/ vSy v%y vS/ V^y V*j;
(»)
fi(tm l—S*4imtnuti*i tank of hwtxontol-flow t/p* yndar difftrtnt tofidilbnt of rtlotivt ttmptritmn.
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- 3 -
Vertical-Upflow Design
The improved performance obtained in upflow tanks has led to a variety
of new designq, incorporating variants of the upflow principle. These
new designs are designated by various proprietary names - Accelator,
Clarifow, Floosettler, Reactor-Clarifier, etc. One of the earliest of
the upflow taflks was the Spaulding Precipitator, shown in Fig. 2. In
this design, tyie flow is introduced into the center of the tank and
flows upward through a blanket of previously formed solids.
The principal advantages of the upflow versus the horizontal tanks are
(l) improved flow control, and (2) sludge blanket effect. Salt-injection
tests performed on a variety of tank designs clearly show the superior
efficiency of the upflow principle in the matter of flow control. The
radial-flow still largely used in sewage treatment is distinctly inferior,
being subject:to short-circuiting.
Tube and Lamella Settlers
In an ideal settling basin, as defined by Camp, the paths of all discrete
particles will be straight lines, and all particles with the same settling
velocity will move in parallel paths. The settling pattern shown in Fig. 3
would be the same for all longitudinal sections. It is apparent from this
that as the interval (h) is reduced, the size of the basin required to
remove a given percentage of the incoming settleable material decreases.
Many devices have been proposed since this principle was first proposed
by Hazen in 1904. and further developed by Camp in 194-6. None of the
proposed devices were accepted commercially until the recent introduction
of the device called the tube settler. These consist essentially of
closely packed smal1 diameter tubes, 1-4. inches in diameter and 2-4 feet
in length, inclined at some angle to provide for removal of sludge as the
water flows upward through the tubes. Detention times are in the order of
6 minutes and less. The tubes provide as much as 24. hours of sludge stor-
age, depending of course, on the amount of suspended solids, and sludge
is readily removed by gravity drainage. A schematic diagram of the tube
settler integrated into a complete clarification device which consists
of coagulation-flocculation, a tube settler unit and a mixed media filter
is shown in Fig. 4* More recently, a device consisting of parallel plates
rather than tubes has become available. The device is called a lamella.
Flow is co-current in contrast to the countercurrent flow of the tube
settlers. The plate arrangement in a tank is shown in Fig. 5.
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- u -
<=> Stirrer
I | Motor
ft
v\
Approximate toy
fovsJ cf Sudca
Drain •*—=
rV^1' L
FIG. 2 —Spaulding frteipHctor
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- 5 -
Surface Area ^4
T
\
V
Vs
X
V
Direction of Flow Q
i Fo
-L ~
Lo
FIG. 3 Idealized Settling Paths of Dis-
crete Particles in a Horizontal Flow Tank
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Alum
Mechanical
Floccutator
/ Mixed Media
// Fitter/>
Finished
Fig- 4u Schematic Diagram of Apparatus Used in Tield Tests of Tubs Settler
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- 8 -
DISSOLVED AIR FLOTATION
The use of dissolved air to float suspended solids was first used in
industrial operations. In recent years, the process has been adapted
to domestic wastewater and particularly to sludge thickening. The
process achieves the separation of suspended particles by attachment
of gas bubbles to the suspended particles, thereby reducing the effective
specific gravity of the particles to less than that of the water.
A. A flotation system using the pressurization and de-pressurization
sequence consists of the following elements (Fig. 6).
1. Pressurizing pump
2. Air injection facilities
3. Retention tank or contact vessel
4.. Back-pressure regulating device
5. Flotation device
6. Facility for addition of chemicals if needed
B. Advantages and Disadvantages
1. Much reduced retention time - 10-20 minutes
2. Greatjer solids concentration in float than in settled sludge
3. Greater efficiency of solids recovery
A- Offers mechanical control over the process
5. Increased cost of operation for pumping, etc.
6. Need to remove top and bottom solids
SCREENING DEVICES
Microscreening is a form of simple filtration by straining (Fig. 7).
These mechanical filters consist of a rotary drum which revolves on a
horizontal axis. The peripheral surface of the drum is covered with
a stainless sjteel fabric. The effectiveness of the woven mesh screen
for retaining fine particles is dependent on the size of the openings
in the screen; and on the pattern of the weave. Influent enters the
open end of the drum and is filtered through the fabric with the inter-
cepted solidq being retained on the inside surface of the fabric. As
the drum rotates, the solids are transported and continuously removed
at the top of the drum by pumping strained effluent, under pressure,
through a series of spray nozzles which extend the length of the drum.
The solids and wash water are collected in a central trough within the
drum and discharged through a hollow axle. The microstraining device
is avail able in several unit sizes ranging from 5' in diameter and l1
width with a capacity of 0.05 to 0.5 mgd to 10' diameter and 10* wide
with a capacity of 3-10 mgd.
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Effluent
'Pressurized Feed
Total Pr«ssurlzfttloo
Uopresaurlxed Portion of Feed
'Flo* by Gravity
Portion of
Feed which has
bsso preasurlzsd
lack Pressur*
Yalve
"1 I ?•*>—gf fluent
Partial Pressurlzatioo of Feed
Dopressurlzod Feod
lov by Gravity
Puap
Pressurized
titluent
Effluent
Preva ure
Valve
A Pressurl-
satloo
Sequence
Partial Prensurlzatlon of Effluent
Methods employed fur partial and total pressurizatlons.
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1.
2.
3.
4.
i 5.
t
Not Shown 6.
7.
Wastewater Hopper
Ultra-violet Lamp
Wash-water Pump
Drive Unit
Rotating Drum
Wash-water Jets
Micro-fabric
Influent Chamber
Effluent Chamber
Effluent Weir
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-11 -
Microscreening devices have found their greatest application to treat-
ment of river waters, and information on their performance on wastewaters
is quite scarce. The effect of aperture size on removal efficiencies and
flow rate is shown below.
Fabric Removal Efficiency Flow
Solids BOD gals/hr/ft^
Mark 0 (23 microns) 70-80/6 60-70# 4.00
Mark 1 (35 microns) 50-60% 40-50% 600
The advantages of microstraining are the low initial capital cost and
ease of operation. The disadvantages are the incomplete solids removal
and the inability to handle solids fluctuations.
Capital and Operating Costs
The capital and operating costs associated with microstraining have been
prepared by Smith and are shown in Fig. 8. For a 10 mgd plant, total cost
for microstraining is calculated to cost about 1.5^/1000 gallon.
In-Depth Filtration
In-depth filtration is the passage of a fluid through a bed of granular
media designed to permit the captured particles to be retained within
the filter. The degree of penetration and solids removal efficiency can
be altered by changing the size and character of the particulates to be
removed as well as the size and composition of the filter media itself.
A basic prerequisite for the operation of rapid sand filters is that good
coagulation and flocculation must be obtained. Barring adequate pretreat-
ment of the wastewater, filtration efficiency is decreased as evidenced
by "breakthrough" of floe. With good pretreatment by coagulation, higher
filtration rates are attainable while still maintaining clarity of the
effluent.
It is beyond the scope of this talk to discuss the subject of coagulation
and flocculation. A variety of coagulants and flocculants are available
including various salts of aluminum and iron, lime and organic polymeric
flocculants. The former inorganic salts, in the proper dosages can also
provide for precipitation of phosphate in addition to clarification.
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WO*OCTAVO > c
ETLLT*.?
Capital Coat. Cper at t s\ • :, K.^lrxcnance "oat, Debt Servlea
vb .
15: ' -;r Capacity
Coat Adjusted to J-.™?, i '
M-U44^
^mn
u
3r.|rr| *'|x|£|
Figure 13
1-fl
1.0
I
H
U
*
0.10 S
1
r*i
3
I
• • • »•»»»* i > • t • t ( i 't
,1.0 ?0 0 100.
DeeLgr) Cwpacit , ca;lllona of gallona per day
0.01
C • Capital Coat,
A • D»bt 0®rvVc«i. - •-«
0 i K • Oparatlrs®
T » Tot® I fire«tc*&t -
of dollar#
E>?r *.000 ^allona(W l/21l • 25 yr.)
wrv:< Coffit, centa p«r 1000 *ellone
carta par 1000 «allona
FIG. 8
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- 13 -
In the past 70 or 80. years there has been a gradual improvement in the
basic process of media filtration. Some of the earlier work centered
on increasing the filtration rates of slow sand filters to the modern
rapid sand filter rates. Various cleaning methods were also developed
including backwashing and surface scouring. More recently, the engineer-
ing advances have been concerned with modifications of filter media that
would allow greater production of high quality water from a given filter
area.
The evolution,of filter design is illustrated in Fig. 9. The cross-
section shown at the top represents the rapid-sand filter which is in
common use in many filter plants today. Typical effective size of the
media used is 0.5 mm although effective sizes from 0.35 to 1.0 mm have
been used. During filter backwashing, the sand grades hydraulically
with the finest particles rising to the top of the bed. As a result,
most of the material removed by the filter is removed at very near the
surface of the bed. Only a small part of the total voids in the bed
are used to store particulates and headloss increases very rapidly.
When secondary effluent is being processed, the high solids concentration
will blind the surface in a very short time. As much as 75-95% of the
headloss, under these conditions, will occur at the upper 1-inch layer
of the filter. Filter runs will be so short as to be prohibitive. Further,
floe breaking through the topmost layers, have increased opportunity to
pass through the entire filter since voids become increasingly larger with
increase in depth.
One approach to increasing the effective filter depth is the use of a
dual media bed using a discrete layer of coarse coal above a layer of
fine sand. The filter provides basically a two-layer effect to achieve
increased penetration of particles. The amount of sand is reduced to
afford lower headlosses at the higher throughput rates used. Normally,
such a bed is designed so that 24 inches of anthracite coal, with a
nominal size of about 1 mm, overlays a 6 inch sand layer with a size of
about 0.4-5 mm. Hydraulic stratification still occurs following back-
washing but the difference of specific gravity is such that the larger
coal remains on top of the sand. The bulk of filtration is accomplished
in the upper layers of the coal and at the top inch or two of the sand
bed.
With low applied turbidities and constant rate operation, the coal-sand
media bed has demonstrated an ability to operate in the range of
U-5 gal/min/sq/ft of filter surface area. A defect in this design is
that if a flow change occurs, the particles held in the relatively large
void volume of a coal bed, can become dislodged and will be captured by
the fine layer of sand and the filtration run would have to be terminated
either because of high head loss at the coal-sand interface or because of
breakthrough of particles through the relatively shallow sand bed. This
design, then, presents a serious inconsistency in design.
Ideally, the effluent should pass through as fine a filter material as
is feasible. This ideal design is illustrated in the bottom cross-
section of a filter uniformly graded from coarse to fine from top to bottom.
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- H -
Figure 1
Croaa-Sactlon Through
Single-Media B«d
Such •• Conventional
lUpld Sand Filter
Figure 2
Crosa-Sectlon Through
dual-Madia Bad
Coaree Coal Above
Flna Sand
Figure }
Croaa-Sectlon Through
Ideal Filter
Unlfornly Graded Froo
Coarae to Flna
froa Top to Bottoo
FIG. 9
Or&ln slsa
Oraln site
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- 15 -
One solution is the use of three materials of differing specific gravity
of such size gradation that some intermixing of the materials occur at
the interfaces of the bed layers. The third media material is garnet
which has a specific gravity of about 4*2. An ideal filter bed, then,
would consist of about 60% of anthracite with a size of 1.0 to 1.5 mm at
the top, 30% s&nd with a size of 0.4 to 0.5 mm at the middle and 10% of
garnet with a size of about 0.15 nim. The materials are so sized that
intermixing ocpurs at the interfaces. In this ideal filter, the effluent
is passed through increasingly finer media. The unifonn decrease in media
particle size With filter depth allows the entire filter depth to be used
for floe remov&l and storage.
Cost of the filtration step is shown in Fig. 10. For a 10 mgd plant this
cost amounts to about 3.5^/1000 galIon, when operating the filter at
k gpm/sq ft. {Further economy, of course, can be obtained at higher rates.
Rates as high as 6-8 gpm/sq ft have been shown to be feasible when proper
pretreatment oif coagulation-flocculation followed by sedimentation is
practiced.
Moving Bed Filter Technique
A new filtering technique has been evaluated by Johns-Manville under
contract with FWQA. The technique is designed to overcome the problem
of surface clogging and to achieve what is obtainable by multi-media
filtration. A schematic diagram of the moving bed filter is shown in
Fig. 11.
The unit is basically a sand filter. Particulate matter is removed as
the water passes through the sand (0.6 to 0.8 mm). As the filter surface
becomes clogged, the filter media is moved forward by means of a mechan-
cal diaphragm. The clogged filter surface is removed either hydraulically
or, as shown, mechanically thereby exposing a clean filter surface. The
sand and accumulated sludge is collected and washed. The sand is returned
via a hopper to the base of the bed. The unit is thus a form of counter-
current extraction device feeding sand countercurrent to the water being
filtered. The moving bed filter has a renewable filter surface analogous
to the microstrainer'and the advantage of depth filtration comparable to
the coarse media filter. The unit does not have to be taken off-stream
for backwashing. In theory, 1% of the filter is being backwashed 100/6
of the time compared to the conventional practice of backwashing 100% of
the filter 1% of the time.
Several pilot MBF units have been built to date and used to treat settled
and non-settled trickling filter effluents and primary effluent. The
system lends itself well to the use of chemical aids ahead of filtration
because of designed flexibility to handle high solids loadings.
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FILTRATION THROUGH SAND OR GRADED MEDIA - 1+GFM/SQ F"
Capital Cost, Operating & Maintenance Cost, Debt Service
V s.
Design Capacity
1.0
0.1
.01
1.0 10.0 100.
Design Capacity, millions of gallons per day
C = Capital Cost, millions of dollars
A =» Debt Service, cents per 1000 gallons(U l/2# - 25 yr.)
0 & M « Operating and Maintenance Cost, cents per 1000 gallons
T ¦ Total Treatment Cost, cents per 1000 gallons
Cost Adjusted to June, l$6f
~rmtrtTTtT1~t
Figure 4,
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BASC (mCEPT OF MOVING BED MITER
INFLUENT
CHEMICALS
(OPTIONAL)
FEED
HOPPER
DIAPHRAGM
HYDRAULIC
SYSTEM
SAND
RECYCLE
CUTTER
p.lCDUCi
WATERL
SAND
WASHING
WASH_
WATER
EDUCTOR^Jr
SLUDGE
WASTE
SLUDGE
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- 18 -
Fig. 12 shows some data with the MBF treating non-settled trickling
filter effluent with various dosages of alum and coagulant aid. Product
quality was maintained at about 10 BOD while being fed an influent with
a widely varying BOD content of=»40 to as high as 180 BOD.
It is too premature to talk about cost of this method of filtration.
Design and performance information developed from these pilot units
will be used tio obtain these costs.
ULTRAFILTRATION
One of the newest unit processes to separate solids from liquids is the
operation known as ultrafiltration. While this method has been under
development over the past 10 years, it is only within the past two-
three years that has seen the commercial development of this process.
Ultrafiltration is closely related to reverse osmosis with the distinction
generally made on the basis of size of particle separated. Reverse osmosis
removes all molecular sizes including inorganic salts. Ultrafiltration
generally will not separate molecules smaller than ^500-1000 MW, thus
inorganic salts are not separated from solution. Ultrafiltration uses
pressures of about 50 psi in contrast to reverse osmosis where pressures
in excess of 500 psi are generally used.
Membrane ultrafiltration is a pressure activated process using semi-
permeable membranes which act as molecular screens to separate molecular
and colloidal materials dissolved or suspended in a liquid phase.
Thus far, the principal commercial applications of the process have been
in (l) industrial operations where valuable products can be recovered by
separation from a bulk solution, (2) analytical application which provides
a new method to separate molecules according to size and molecular weight,
and (3) in a package waste treatment plant which separates mixed-liquor
solids from a biological reactor. Solids are returned to the aerator and
clarified product water is discharged.
A plant employing ultrafiltration has been installed on Pikes Peak to
provide waste treatment and water reuse. The essentials of the process
are shown in Fig. 13. The 15,000 gpd plant treats wastewater by high-
solids activated sludge. The solids are separated in an ultrafiltration
unit. Solids are returned to the aerator. Product water is excellent.
Some typical removals are shown below.
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0GB wmToi s i# m-
0OD>-i'C>t r.
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ENZYME REACTOR
CONCENTRATE
RECYCLE LINE
MEMBRANE
PRODUCT
FEED
CONCENTRATE
y BYPASS
V LINE
REACTOR
iaawJT n-'-gu*
UNIT
PUMP
FIG. 13 REACTION SYSTEM
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Removals by Activated Sludge and Ultrafiltration
Influent
Effluent
% Removal
BOD
382
<1
>99
COD
678
20
97
Turbidity
-
<0.1
-
SS
323
0
100
P0.-P
12.2
7.7
37
These result^ emphasize that only molecules or particles greater than
500-1000 MW iare separated. Inorganic ions such as phosphate are not
retained, lihe 37/6 reduction of phosphate was due to biological uptake
in cells which were removed.
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- 22 -
REFERENCES
Evans, G. R., "Microstraining Tests on Trickling Filter Effluents
in the Clean Creek Watershed Area, Texas," Public Works, October 1965).
Bodien, D. Q., and Stenburg, R. L., "Microscreening of Effluent from
a Municipal Activated Sludge Treatment Plant," Water and Wastes Eng.,
(September 1966).
Truesdale, G. A., Birkbeck, A. E., and Shaw, D., "A Critical Examina-
tion of Some Methods of Further Treatment of Effluents from Percolat-
ing Filters," Conference Paper No. 4, Water Pollution Research
Laboratory, Stevenage, England (July 1963).
Diaper, E. W., "Microstraining and Ozonation of Sewage Effluents,"
Presented at the 41st Annual Conference of the WPCF, Chicago,
Illinois ( September 1968).
Truesdale, G. A., and Birkbeck, A. E., "Tertiary Treatment of Activated
Sludge Effluent," Reprint No. 520, Water Pollution Research Laboratory,
Stevenage, Herts, England (1967).
Smith, R., "Cost of Conventional and Advanced Treatment of Wastewaters,"
Jour. Water Pollution Control Federation, 40, 1546- ;574 (September 1968).
Rich, Linvil G., Unit Operations of Sanitary Engineering, John Wiley
and Sons, Inc., New York, 1961.
Camp, T. R., and Stein, P. C., "Velocity Gradients and Internal Works
in Fluid Motion," Jour. Boston Soc. Civ. Engrs., 30, 219 (1943).
Robeck, G. G., "High Rate Filtration Study at Gaffney, South Carolina,
Hater Plant," USPHS, R. A. Taft Sanitary Engineering Center,
Cincinnati, Ohio (1963).
Craft, T. F., "Review of Rapid Sand Filtration Theory," JAWWA, p.428-439,
April 1966.
O'Melia, Charles R., and Crapps, David K.., "Some Chemical Aspects of
Rapid Sand Filtration, JAWWA, 56, 1326 (1964).
Hudson, H. E., Jr., "Physical Aspects of Flocculation," JAWWA,July 1965.
Gurnham, C. F., Industrial Wastewater Control, Academic Press,Inc.,
New York, 1965.
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- 23 -
Katz, W. J., and Wullschleger, R., "Studies of Some Variables Which
Affect Chemical Flocculation When Used with Dissolved-Air Flotation,"
Proc. 12th Purdue Industrial Waste Conference (1957).
van Vuuren, L. R. J., et al., "Dispersed Air Flocculation/Flotation
for Stripping of Organic Pollutants from Effluents," Water Research,
Pergamon Press, 2^ 177-183 (1968).
Vrablik. E. R., "Fundamental Principles of Dissolved-Air Flotation of
Industrial Wastes," Proc. 14th Purdue Industrial Waste Conference (1959).
MLchaels, A. S., "New Separation Technique for the CPI," Chemical
Engineering Progress, 64, December 1968.
Weissman, B. J., Smith, C. V. Jr., and Okey, R. W./'Performance of
Membrane Systems in Treating Water and Sewage," Water - 1968, 64,
Chemical Engineering Progress Symposium Series.
Mohanka, S. S., "Multilayer Filtration," JAWWA, 61, 504-511 (Oct. 1969).
Ives, K. J., and Gregory, J., "Basic Concepts of Filtration,"
Proc. Society for Water Treatment & Examination, 16, Part 3 (1967).
Boby, W. M. T., and Alpe, G., "Practical Experiences Using Upward
Flow Filtration," Proc. Society for Water Treatment & Examination,
16, Part 3 (1967).
Rimer, A. E., "Filtration Through a Trimedia Filter," Jour. San Eng.Div.,
ASCE, SA 3, June 1968.
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HEW DEVELOPMENTS IN SLUDGE HANDLING AHD DISPOSAL
Robert B. Dean
Z. IHTHODOCHON
A. Pollutants removed ffrm wastewaters must "be treated in
such a "way that they vlll not pollute the environment
1. dnly three places to put polluting substances. Air,
land, ocean. Hot In surface waters.
B. Ocean Disposal
1. Ocean can oxidize wastes if kept aerobic.
a. Grease should "be removed "by aerobic treatment.
2. Food chains may concentrate poisons killing larger
species.
C. Land Disposal.- Fill.
1. pot suitable for soluble substances such as salts.
2. Needs dewatering to produce solid that vlll bear a
load. Useful for Insoluble inorganic wastes.
D. Land ffl-sposal. Surface.
1. Not suitable for solubles except nutrients in quanti-
ties utilized by plants.
2. Low cost de watering; can handle liquid sludges.
3. low cost oxidation of organic matter,
E. Disposal into Wells
1. Unsuitable if there is a chance that pollutants vlll
reach useful ground water or cause earthquakes.
ZZ. ORGANIC SUBSTANCES
A. Principal problem in disposal of organic sludges is water.
Twenty to fifty times as much water as all other substances
in waste.
1. Oxidation of 1 lb. of organic sludges is sufficient
to evaporate about 2 lb. of water.
4.1
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2. Economics of incineration are therefore closely tied
to dewaterlng "by sedimentation, filtration and dry-
ing.
B. Treatment of wet sludge to aid further processing
1. Anaerobi$ digestion. Reduces solids about 50$ by hy-
drolysis and fomentation to methane gas which is
burned to 00^ and water. Produces foul supernatant
liquor which returns organics and nutrients to the
plant for recycle.
2. Sludge cooking at 370 °F. Improves fllterability of
solids. Returns 10-20$ of the SOD and 60-80$ of the
nitrogen.
3. Wet oxidation - Zimpro at 350°F removes 15$ of 00D by
oxidation; dissolves 25$ of solids and 90$ of nitro-
gen. Higher temperatures destroy more solids. Im-
proves filtration, produces a foul supernatant liquor.
4. Aerobic Stabilication.
a. Stabilizes solids, oxidizes oil and grease, re-
tains nutrients.
b. Can reduce nitrogen levels by nitrification-denitri-
fication.
c. Does not aid dewaterlng.
C. Oxidation and dewaterlng on land surfaces. An "old-fash-
ioned" process.
1. Low cost dewaterlng on land.
2. Ammonia, phosphate and pesticides fixed on soil minerals.
3. Soil organisns destroy pollutants.
a. Organics go to 00g.
b. Ammonia converted to nitrates.
4. Soil improved for agriculture and forestry.
4.2
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III. CHE'GCAL SIUDGES
A. Lime
1. CaCO^, Ca^OI^FO^)^ Mg(0H)2> CaSO^, Ca(OH)gDewater in lagoon
01; • vacmrn filter.
2. L^nd fill
a. Alkaline due to excess Ca(0H)2
b „ Non-leachable F0"£
c. SOJ leaches out, 1300 mg/l
3. Recovery of CaO from CaOO^ by "burning.
B. Iron
1. Fe(OH)v- Fe+2. 2 Pe+3 (OH)q, FePO^, CaOCK, CaSO^ ~
Dewatering more difficult.
2. Land fill.
3. Iron recovery rarely worthwhile.
C. Aluminum
1. A1(0H)^ A1 PO^, CaC03.
2. Very difficult to dewater; freezing.
3. Aluminate recovery may be practical.
4. 3
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IV. SPECIAL DEWATERING T£CKTII*UES
A. Freezing — Destroys colloidal structure; gives good filtration
1. Needs slov freezing over several hours after thawing.
2. Complete freezing and minimal mechanical agitation.
3. Most pxtamise for Activated Sludge and Aluminum Hydroxide.
4. Does not increase strength of filtrate.
5. Does nqt kill organisms.
B. Radiation
1. Selectively attacks high polymers and may reduce water holding
capacity.
2. Does not disinfect. May kill microorganism.
3. Releases organics to filtrate.
k. Requires costly shielding.
C. Pressure Cooking — 250° C (480° F)
1. Gives good filterability.
2. Strong "soup" needs further treatment.
3. Disinfects.
D. Cooking with SO^ catalyst
1. Good filterability at lower temperatures and pressures.
2. Strong "soup" may have food value for livestock.
3. Disinfects-.
E. Cooking with Oxygen -- Zimpro
1. High temperature to destroy organic solids (^50° C)
2. Low temperature to get good filterability (250° C)
3. Produces "soup" that is difficult to treat.
4. Disinfects.
5. Power recovery not economical.
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LIST OF PERTINENT REFERENCES
1« Dean, R. B., "Ultimate Disposal of Waste Water Concentrates to the Environ-
ment/' Env. SCi. and Tech. 2(12), 1079-1086 (Dec. 1968).
2« Dalton, F. £•; Stein, J. E., and Lynam, B. T., "Land Reclamation—A Complete
Solution of tfie Sludge and Solids Waste Disposal Problem," J. Water Poll.
Control Federation jj0(5), 789-80U (1968) •
3. Warner, D. L., "Deep-Well Injection of Liquid Waste," EHS Pub. No. 999-WP-21
(1965).
4. Healy, J. H., Rubey, W. W., Griggs, D. T., and Raleigh, C. B., "The Denver
Earthquakes," Science l6l (3848), 1301-1310 (Sept. 27* 1968).
5. Owen, M. B., "Sludge Incineration," J. San. Eng. Div. Am. Soc. Civil Eng. 83,
Paper 1172 (Feb. 1957).
6* Evans, S. C., and Roberts, F. W., "Heat Treatment of Sewage Sludge," The
Surveyor, 9-12 (Jan. 3/ 19^7)*
7» Teletzlie, G. H., "Wet-Air Oxidation," Chem. Eng. Progr. 6o(l), 33-38 (1964).
8. Slechta, A. F., end Culp, G. L., "Water Reclamation Studies at the South
Tahoe Public Utility District," J. Water Poll. Control Federation 39(5)j
787-813 (1967).
9. Doe, P. W., Benn, D., and* Bays, L. R.. "The Disposal of Washwater Sludge
by Freezing," J. Inst. Water Eng. 12(*0> 251-291 (June 1965)*
4.5
-------
REMOVAL OF ORGAN ICS FROM WASTEWATER
BY ACTIVATED CARBON
John N. English, Arthur N. Masse,
Charles W. Carry, Jay B. Pitkin and James E. Haskins
Presented To
American Institute of Chemical Engineers
February, 1970
John N. English, Chief, Pomona Pilot Plant, Federal Water Quality
Administration, Pomona Advanced Waste Treatment Research Facility, Pomona,
California.
Arthur N. Masse, Chief, Municipal Treatment Research Program, Federal
Water Quality Administration, Advanced Waste Treatment Branch, Cincinnati,
Ohio.
Charles W. Carry, Division Head; and Jay B. Pitkin, formerly Project Engineer
for Research and Development, Sanitation Districts of Los Angeles County,
Los Angeles, California.
James E. Haskins, Research Chemist, Federal Water Quality Administration,
Pomona Advanced Waste Treatment Research Facility, Pomona, California.
-------
SUMMARY
A 0.3 mgd, four-stage, fixed bed granular activated carbon pilot
plant has continuously treated unfiltered activated sludge plant effluent
from tne Poinona Water Renovation Plant from June, 1965, through July, 1969.
Extensive opera:ing data collected during four adsorption cycles, which
required four years to complete, indicated that a high quality product
water, characterized by an average dissolved COD of 8 mg/1 was produced on
a routine basis. This water contained, on the average, a concentration of
carbon chloroform extract (CCE) equivalent to 0.026 mg/1, which is signi-
ficantly less than that required by the Public Health Service standards
for potable water.
Successful backwashing of the first stage carbon, which serves as
a filter and an adsorbor, made pretreatment of the secondary effluent un-
necessary. The filtering action of the carbon readily removed the 9 mg/1
of suspended solids present in the activated sludge plant effluent. This
filtration causes, on the average, a 10 psi increase in the pressure loss
over a 24 hour service period. Partially due to filtration, 46 percent of
the total COD that is removed by the four stage column is removed in the
first stage. About equal removals of dissolved organic matter, represented
by dissolved COD, occur in each stage.
Removal efficiency of dissolved COD was greater than anticipated,
amounting to a carbon capacity of 59 pounds per 100 pounds of carbon during
ihe first cycle. A 17 percent decrease in the carbon capacity occurred
-1-
-------
betx/cctne first ar.d fourth cycles which resulted in a fourth cycle
c&pcC". -j of 49 pounds of dissolved COD per 100 pounds of carbon. The data
mencaics that a steady state-condition is being reached at a capacity of
45 zc 50 pcur.Gs 'per 100 pounds of carbon.
Routine column performance data show that 89 percent of the
secondary effluent dissolved COD was removed during the first cycle, which
decreased to 71 percent during the second cycle after which the removal
approacned a steady state condition. Following an increase in the carbon
dosage from 250 pounds of carbon per million gallons during the first cycle,
the dosage remained constant during both the third and fourth cycles at 350
pounds per million gallons.
Regeneration of the carbon was shown to be a feasible process and
has beer, routinely accomplished. Iodine number determinations confirm
that a decrease in adsorptive capacity takes place and that the micropores
(less than 20 A0) in the carbon cannot be completely cleared of adsorbed
organics by thermal regeneration. However, the iodine molecule is not
characteristic of typical organic matter in secondary effluent and conse-
quently, as the data show, is not a satisfactory parameter for determining
the effect of repeated adsorption cycles on the capacity of carbon for
dissolved COD.
Data collected from a separate, parallel, single stage column
Gesigr.e- to provide supplementary information to that collected from the
four-s;;ge column indicated a 13 perci": decrease in the mean particle
diameter of the carbon after seven adsorption cycles at which time a steady
state condition existed. No significant differences in column operation or
-2-
-------
in pressure loss in the carbon resulted due to the decrease in particle
size from 0.90 to 0.79 mm.
An estimate for a 10 mgd, four-stage carbon pilot plant designed
to produce a product water with a dissolved COD of 8 mg/1 was made. The
estimated cost of $86 per million gallons is based on a fourth cycle carbon
dosage of 350 pounds per million gallons of water and a conservative carbon
loss of 10 percent per cycle.
-3-
-------
INTRODUCTION
The Federal Water Pollution Control Administration and the Los
Angeles County Sanitation Districts, through a contractual agreement,
operate an advanced waste treatment research facility on the grounds of
ihe Po~ona Water Renovation Plant in Pomona, California. The over-all
objective at Pomona is the development of the minimum cost technology
capable of renovating wastewater. In order to attain this objective, the
most promising available treatment processes are being field tested and
evaluated on a pilot plant scale.
The removal of residual dissolved and suspended organic matter
from municipal waste water treatment plant effluents is a necessary step
if this water is to be reused. It has been demonstrated at Pomona that the
use of a granular activated carbon column is a feasible process for
accomplishing this removal.
Since June of 1965, an o.3 mgd, four-stage, fixed bed, granular
activated carbon pilot plant, complete with thermal regeneration facilities,
has been continuously treating unfiltered activated sludge plant effluent
from tre Pomona Water Renovation Plant. The objective is to obtain reliable
cost and operating data on the use of granular carbon and to establish
its effectiveness, after repeated adsorption cycles, in removing dissolved
and suspended organic matter that vary in type and concentration due to
the conditions of daily and seasonal flow fluctuations that occur in municipa-1
waste streams.
-4-
-------
PILOT PLANT DESCRIPTION
The pi 1 ox plant components include five carbon vessels or contactors,
influent and product water storage tanks, a carbon dewatering bin, a quench
tank, and a regeneration furnace, all mounted on a concrete slab with related
piping, pumps and controls. The slab 'is 44 feet square and sloped to drain
into the quench tank pit in order to facilitate the recovery of any acci-
dentally spilled carbon. A photograph of the carbon pilot plant is presented
in Figure 1. (omitted from this seminar paper)
A schematic flow diagram for the pilot plant is shown in Figure 2.
Initially, chlorinated secondary effluent was used since it was more
conveniently available from the water renovation plant. However, during
the course of the study the plant was enlarged by the construction of a new
parallel treatment plant and both chlorinated and unchlorinated secondary
effluent from either the old or new treatment plants has been used without
any significant differences in operation of the carbon columns.
The secondary effluent is directed to the storage tank from where
it is pumped into the carbon columns. The pilot plant is composed of two
columns, a single stage and a four stage; each of the stages or contactors
is identical in design and contains 6,700 pounds of 16 x 40 mesh granular
carbon having characteristics as shown in Table I. The contactors are 6
feet in diameter, have an overall height of 16 feet, and are designed for
a working pressure of 50 psi. The detailed design is shown in Figure 3.
The carbon bed is supported on a Neva-Clog screen system consisting of the
-5-
-------
Neva-Clog screen, an expanded metal backing, and a series of concentric
annular rings which are an integral part of the contactors for structural
support. The screen is comprised of two layers of stainless steel perfor-
ated with 1/32" diameter holes and spot-welded together with holes off-set
from each other
The interiors of the contactors are coated with a coal-tar epoxy
compound designed to withstand the corrosive action of the carbon-water
environment. One-inch couplings are welded in the contactor walls for
sampler connections and pressure taps.
The liqund enters at the top from an annular ring through twenty 1"
holes around thfc circumference of each contactor. This ring is also used to
remove liquid during backwashing. A distance of 3-1/2 feet between the
entrance ring and the top of the carbon bed provides room for a 35% to 40%
bed expansion during backwashing.
The single stage column was designed to provide supplementary data
to that obtained from the main four stage column pilot plant and is operated
O
at 200 gpm, or a hydraulic loading of 7 gpm/ftS which results in an empty
bed detention time of 10 minutes. The water leaves the column and is
discharged to the nearby San Jose Creek.
The four'stage column also operates at 200 gpm and has an empty
bed detention time of 40 minutes with the secondary effluent passing, in
series, through each of the stages and thence to the product water storage
tank with overflow entering the creek. As the carbon becomes exhausted,
the level of organic matter in the effluent increases and, when it reaches
a COD of 12 mg/1, the first stage is removed from service and the carbon is
-6-
-------
transferred as a slurry into the dewatering bin. The carbon, with a 40
percent moisture content, is conveyed into the multiple hearth furnace
where it is regenerated at 1,650° to 1,700°F.
The furnace is a 30 inch I.D., vertical, refractory-lined, 6
hearth unit, complete with air pollution control equipment. It is natural
gas fired and steam is added to enhance the regeneration. Carbon leaves
the furnace at 90 lbs/hr and is discharged, under water, into the quench
tank from where it is educted into the contactor. Regeneration of one
stage requires about 75 hours to complete.
Carbon losses during regeneration, which average 8-1/2 percent,
are made up with virgin carbon and the contactor is returned to service as
the fourth stage of the column. Through valving, the other stages are
moved forward qne position, thus approaching a counter-current flow of
carbon and water.
Repeatecj exhaustions and regenerations of the carbon are defined as
adsorption cycles. In the four stage column an adsorption cycle for the
column is completed when all of the stages have been exhausted and regen-
erated once, that is, each contactor has seen service in each stage position.
Experience has indicated that regeneration of the first stage is required
every 75 days-*equivalent to treating about 20 mg of secondary effluent.
On this basis, exhaustion of each of the four stages requires almost one
year. At this rate four cycles have been obtained during the period of this
study.
In the single stage column, four adsorption cycles are completed in
a year's time. This has allowed evaluation of the effect of 9 cycles on
-7-
-------
carbon efficiency and 11 cycles on carbon attrition and regeneration
characteristics. During the last two cycles, special studies were conducted
with secondary effluent which did not include the monitoring of dissolved
COD removal, but did require carbon regeneration. Though its operation is
different from that of the main four-stage pilot plant, the single stage
column has provided valuable additional supporting data.
-8-
-------
PILOT PLANT PERFORMANCE
Operation
Backwashing of both the single stage column and the first stage of
the four stage column is performed on a daily basis to free the carbon bed
of trapped suspended solids removed by filtration from the secondary effluent.
Backwashing is accomplished using secondary effluent at hydraulic loading
rates up to 7 gpm/ft^ and a volume of water equivalent to 3 to 4% of the
daily column flow.
Pressure loss data in the carbon for each stage of the four stage
column, before and after backwashing the first stage, is shown in Table 2.
After backwashing the first stage, the column has a total pressure drop of
about 21 psi which increases to 32 psi over an average 24 hour period. This
increase, as presented in Table 2, is due to filtration of suspended solids
by the first stage carbon resulting in a 10 psi pressure loss increase in
this stage.
The second stage must also be backwashed to maintain the column
operating pressures within the capacity of the pumping system. This is
required, on the average, once or twice per month.
The use of granular activated carbon in a column system requires
that it be regenerated, transported to and from the regeneration facilities,
and routinely backwashed. As a result of those operations, attrition of the
carbon particles occurs. Data showing the effects of carbon regeneration and
handling on the mean particle diameter is presented in Figure 4. A 13
-9-
-------
percent decrease in the particle diameter of the carbon in the single stage
column occurred after 7 adsorption cycles, at which time no further signi-
ficant changes in the size took place. This is primarily caused by the
addition to the column of virgin make-up carbon, which has a mean particle
diameter of 0.9 mm, after each regeneration to replace losses. Also, as
the supply of the original 16 x 40 mesh carbon was depleted, Filtrasorb 400
(12 x 40 mesh carbon having a mean particle diameter of about 1 mm) was purch-
ased and used as make-up after the seventh cycle.
In addition to the reduction in the carbon particle size previously
described, which has not cuased any significant difference in the carbon
column operatipn or pressure drop, a loss of carbon occurs during the re-
generation process. This loss has ranged from 11 percent during the first
cycle to 7 percent during the fourth and has averaged 8-1/2 percent during
the four year study.
Adsorptive Capacity
The COD test has been used as the primary parameter for determining
the efficiency of the carbon columns in removing both suspended and dissolved
organic matter. Since carbon serves as a filtration media as well as an
adsorbant, the COD of the secondary effluent and carbon effluent was
determined on both unfiltered and filtered (0.45 micron, membrane filter)
samples and values for total COD and dissolved COD (filtered) are reported.
The data in Figure 5 show the distribution of COO removal in the
four stage column. The dissolved COD data indicate about equivalent removal
in each of the stages. However, the total COD data show 46 percent is removed
in the first stage. This difference is due to filtration of suspended COD
-10-
-------
which accounts, on the average, for 20 to 30 percent of the total COD.
Therefore, when monitoring the effect of repeated adsorption cycles on
the carbon efficiency it is necessary that a measurement of the dissolved
organic matter be made. A carbon column even after its adsorptive capacity
is exhausted wjll continue to remove suspended COO.
The effect of adsorption cycle on the dissolved COD removal per-
formance of th6 four stage column is shown by the data in Figure 6. Each
of the data points represents a regeneration of the first stage column;
four such regenerations are equivalent to an adsorption cycle. The data
clearly indicate that a reduction in COD removal occurs from an initial level
of 89 percent to 71 percent after 1-1/2 adsorption cycles, and that the
removal remain$ constant through the remaining cycles.
Comparable data for the single stage column are presented in
Figure 7. The dissolved COD removal decreased from an initial value
of 53 percent to 40 percent during the sixth cycle after which time the
removal stabilized at the 40 percent level. The addition of 8-1/2% virgin
make-up to replace losses during each cycle has had the effect of upgrading
the adsorption capacity of the carbon. If this loss rate is decreased, the
loss in capacity with adsorption cycle will be greater.
The effect of repeated adsorption cycles on the adsorptive capacity
of carbon can |>e expressed in terms of its capacity for a given adsorbate
under specific laboratory conditions. One of the adsorbates used to charac-
terize the adsorptive properties of activated carbon is iodine. The standard
iodine number test is used to measure the extent of recovery of the adsorptive
capacity or the extent to which the micropores (less than 20 A°) have been
-11-
-------
cleared of adsorbed organics by regeneration. Data in Figure 8 show the
iodine number for both spent (exhausted) and regenerated carbons from the
single and four stage columns after repeated cycles.
The initiial iodine number of the virgin carbon was 1100 and after
eleven adsorption cycles in the single stage column the iodine number was
reduced to 608 which is a 45 percent decrease with every indication that
further reductions will take place. An even greater decrease with adsorp-
tion cycle is noted in the iodine number of the regenerated carbon in the
four stage column. This continuous decrease in the adsorptive capacity of
the carbon for iodine indicates the micropores have not been cleared of
adsorbates duriing regeneration. However, previous data shown in Figures 6
and 7 relate CQD removal to adsorption cycle and indicates a 20 percent
reduction in efficiency in the four stage column during the first two cycles
after which time the removal remains constant. Iodine is therefore not
typical of the organic matter in secondary effluent and although the surface
area in the micropores has continued to decrease, the capacity of the carbon
for organic matter as measured by dissolved COD has not followed suit.
The iodine number of spent carbon as shown in Figure 8 also shows
a steady decrease forth both single stage and four stage columns. The differ
ence between the regenerated and spent iodine numbers, or iodine capacity
used, is due tq the presence of substances in the micropores that were re-
moved from the water during operation of the column. The data indicate
the amount of capacity used reaches a steady state condition after the third
cycle.
Since carbon capacity can have a significant effect on the economical
-12-
-------
feasibility of carbon adsorption as a process for removing organic matter
from secondary effluent, it is necessary to ascertain the effect of repeated
adsorption cycles on the virgin or original capacity. Data showing this
effect are presented in Figure 9. The total COD capacity is somewhat
variable and is primarily due to the variability of the suspended solids in
the secondary effluent which accounts for 20 to 30 percent of the total COD.
The dissolved GOD in the secondary effluent, which is significantly less
variable, shows a more consistent relationship between capacity and adsorptii
cycle. It has been previously mentioned that dissolved COD was chosen as
the primary parameter to measure the change in adsorptive capacity. The
capacity is expressed in pounds of COD adsorbed per 100 pounds of carbon
and has decreased 17 percent after four adsorption cycles. The change in
capacity between the third and fourth cycles has decreased less than that
of the early cycles indicating a steady state condition is being reached at
45 to 50 lbs/100 lbs.
It has been established through operating experience at Pomona that
biological oxidation of organic matter takes place in carbon. The single
stage column during a special long term study was never completely exhausted
and continued to remove 2 to 4 mg/1 of dissolved COD at the end of a nine
month period; for this reason biological action undoubtedly contributes
to increasing the carbon capacity above that occurring from true adsorption
phenomena.
The relationship between carbon dosage and adsorption cycle is shown
in Figure 10 and indicates a steady state condition was reached after the
third cycle at 350 lbs of carbon per million gallons.
-------
Water Quality
The average quality characteristics of the four stage column influent
and effluent from June, 1965, to July, 1969, are shown in Table 3. The
total COD of the effluent has averaged 10 mg/1 during this period with yearly
averages ranging from 9.3 to 10.5 mg/1. In order to evaluate the performance
of the column affter repeated adsorption cycles it was necessary to maintain a
constant effluent quality in order to eliminate this as a variable in
determining car.bon dosage and capacity.
The Unitjed States Public Health Service Drinking Water Standards
for 1962 limit the concentration of carbon chloroform extract (CCE) in a
water supply to 0.2 mg/1. The CCE present in the carbon effluent has
averaged 0.026 mg/1, which is an order of magnitude less than that required
for potable water.
The removal of turbidity and suspended solids is due to filtration by
the carbon and takes place primarily in the first stage.
A limited quality of nitrate is removed in the column and, at an
influent concentration of 8.1 mg/1 (NOyN), amounts to a 19 percent
reduction and is due to biological denitrification in the carbon.
Cost Estimate
A cost estimate for a 10 mgd, four-stage carbon plant based on
the operating results obtained during the four year pilot plant study is de-
tailed in Table 4. The capital equipment cost of $1.86 x 10® was amortized
over 20 years at 5% interest and amounts to 48 percent of the total cost of
$86 per million gallons for carbon treatment. This estimate is based on a
plant that would provide product water having the quality characteristic
-14-
-------
shown in Table 3. Cost and quality are inter-related variables and must be
considered together. For example, if a product water with an average total
COO of 15 mg/1 was desired it could be provided at a cost less than $86
per million gallons.
The cost of make-up carbon was determined using a dosage of 350
pounds of carbon per million gallons of water as shown in Figure 10. A
conservative loss of 10 percent was also applied to estimate a makeup carbon
cost of $11 per million gallons.
-15-
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TABLE 1
CARBON CHARACTERISTICS
IODINE NUMBER 1100
METHYLENE BLUE NUMBER 300
MOLASSES NUMBER 220
APPARENT DENSITY 0.47
ASH CONTENT 5%
MEAN PARTICLE DIAMETER 0.90
MESH SIZE 16 x 40
-------
TABLE 2
EFFECT OF STAGE A BACKWAS8*
ON PRESSURE LOSS
PRESS
URE LOS
• nr/nsrv-r-ri i-... • -t ¦?
3S (PSD
STAGE
A
STAGE
B
STAGE
c
STAGE
D
BEFORE
BACKWASH
16.8
4.0
AFTER
BACKWASH
6.6
4 9
4.0
5.2
TOT/'.L
rsoocawj.. > -
C'V.7}
3!
£
P
-------
TABLE 3
CARBON ADSORPTION PILOT PLANT
AVERAGE WATER QUALITY CHARACTERISTICS
JUNE 1965 to JULY 1969
PARAMETER INFLUENT EFFLUENT
SUSPENDED SOLIDS mg/1 9 0.6
COD mg/1 43 10
DISSOLVED COD mg/1 30 8
TOC mg/1 12 3
NITRATE as N mg/1 8.1 6.6
TURBIDITY (Jtu) 8.2 1.2
COLOR (Platinum-Cobalt) 28 3
ODOR (Ton) 12 1
CCE mg/1 - 0.026
BOD mg/1 3 1
-------
TABLE 4
CARBON ADSORPTION PROCESS
COST ESTIMATE - 10 MGD PLANT
AMORTIZATION OF CAPITAL $/106 GALLONS
$1,860,000; 20 years @ 5% 41.00
OPERATION AND MAINTENANCE
POWER $ 8.50
LABOR 18.00
MAINTENANCE MATERIALS 5.00
CARBON REGENERATION
POWER, GAS AND WATER 2.50
MAKEUP CARBON (10% Loss) 11.00
45.00
TOTAL $86.00
-------
SCHEMATIC FLOW DIAGRAM
I SECONDARY
CLARIFIER
Uu-L
CH10RINATI0N
v v V -<
(OPTIONAL)
TO
PRIMARY
OLAfrlFtERS
A
'^V/V ¦/'
SECONDARY
, EFFLUENT
SMSBT STORAGE
BACKWASH
TANK
P
;;Vi> iYi'ihIIII
BACKWASH WATER
CONTACTOR
ET
CARBON
n
¦SPENTI
T^rajfflww
CARBON
REGENERATED
CARBON
MM
FURNACE
SAN JOSE
CREEK
.PRODUCT
WATER
'STORAGE
TO
SAN JOSE
CREEK
QiJEKGH
TANK
DRAIN
BIN
-------
FULL
WITH
I
20-1"
WA$H
WATER
~
a
M
h-
Sjl
CD
h-
U_
I
SURFACE
O
WASH-
CARBON 6ED~ajRFACE~
CARBON
CHARGE
I
TAPS
IvI'Xwi
INEVA
CLOG
$>®5 ,.
: 3p?';
m
g
=>
tr
CARBON
DISCHARGE
^-.-^EFFLUENT
4-U$~ BACKWASH
erU LiUUUUUUUUUUUUUUU-
KVrFTrTri n^rinnnnrinnn Qjn
HOLES-
OPEN COVER
i5" PORTHOLE
BOLT RING
INFLUENT
BACKWASH
-------
FIGURE 4
FFECT OF ADSORPTION CYCLE
ON CARBON PARTICLE SIZE
©
SINGLE STAGE COLUMN
_j ^ . I . ,1 .*
2 3 4 5 6 7 8 910
ADSORPTION CYCLE
-------
50
>
O
bJ
QC
a
o
o
40
2
30
-J
O
o
«J
<
o
fr-
it.
o
&—
2
yj
o
o:
kJ
ou
20
10
-------
FIGURE 6
100
90
80
70
60
50
EFFECT OF ADSORPTION CYCLE
ON COD REMOVAL
-j r f 1 y -r . .....
©
O
FOUR STAGE COLUMN
^r.TssJrr^ry^rir-A-rrgTjw^-r
0 I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18
|<3 j ^ J>L^ ^ &>J<3 is|. ^»-j
ADSORPTION CYCLE
-------
FIGURE 7
60
50
40
30
20
10
FFECT
o
Hr
4
0W COD REMOVAL.
SINGLE STAG!! COLUMN
3 4 5
ADSORPTIO
6 7
CYCLE
G
9
10
-------
FIGURE 8
EFFECT OF ADSORPTION CYCLE
ON IODINE NUMBER
12001?
')
1
1000 s-
800
600
400
200
npss
T
u^ii i iTiagp
REGENERATED
SPENT
A
SINGLE STAGE COLUMN
FOUR STAGE COLUMN
Q * " ¦¦¦ S—i
2.
X
12 3 4 5 6 7 8
ADSORPTION CYCLE
-------
FIGURE 9
EFFECT OF ADSORPTION CYCLE OH CARBON CAPACIT
100
90
80
70
60
50
40
30
DISSOLVED COD
TOTAL COD
CS3323
FOUR STAGE COLUMN
W-- mr¦.l."
-------
FIGURE 10
EFFECT OF ADSORPTION CYCLE ON CARBON DOSAGE
m
o
s
CO
ja
I'J
o
CO
o
Q
o
os:
<
o
400
300
200
100
T
=o
FOUR STAGE C0LU
: ---rr?v^'r;-ryg-gr. . r-r r.\ w..ri - ^UGSuJ.!CY&-
4
ADSORPTION CYCLE
-------
f " t- \ *\
(. v-•**!'.-I WATER POLLUTION COXTRO- RESEARCH SERIES G '7C5GO.NW05/7O
\ - >
N.1,
IN VESVJG AT I OM OF T*\2 USE O?
HIGH PUS ITY OXYGc.M AZ3ATIOM
IN THE CONVENTIONAL ACTIVATED
SLUDGE PROCESS
&K.e.e<^e
-------
ABSTRACT
A full scale system designed to demonstrate the practical and
economical use of high purity oxygen gas in aeration of the conventional
activated sludge waste treatment process has been tested under a variety
of operating conditions in a direct performance comparison with a parallel
air aerated system. A sparged-turbine, gas-liquid contacting unit was
employed in covpred tanks of conventional design with discreet liquid
and gas staging for cocurrent flow of each phase. This oxygenation
system required very low power input for oxygen transfer and liquid
mixing (0.08 - 0.140 HP/1000 gal. mixed-liquor) to routinely operate
at dissolved oxygen concentrations of 8-10 mg/1 while achieving > 907.
utilization of feed oxygen gas. It was shown that the oxygenation
system could operate with MLVSS concentrations of as high as 4500 mg/1
achieving about 907. BOD removals at aeration detention times as low as
1.2 hours (raw flow + recycle flow) treating domestic waste of 220 mg/1
BOD. Under ott\er conditions and in direct comparison with air aeration,
the oxygenation system consistently exhibited treatment performance
superior to th4t achieved with air aeration even at uneconomically high
aeration rates (3-5 cf air/gal. waste treated). Biomass from the
oxygenation syatem is highly flocculent and readily settleable with
desirable handling characteristics. Recycle and waste activated sludge
suspended solids concentrations of about 3% were achieved.
Process advantages recognized with the oxygenation system indicate
significant reductions in secondary waste treatment costs in comparison
to conventional diffused air aerated systems. These advantages are
principally reduced aeration tank volume requirements for equivalent
treatment and a reduced production of waste activated sludge, a result
of more efficient utilization of high purity oxygen than here-to-fore
possible. As an example, the total cost of treatment, including preliminary
treatment, witb air at 6 hours nominal detention time and a 1.6 cf air/
gal. aeration rate is estimated to be 15.1 cents, 13.0 cents and 11.0 cents/
1000 gal. for plant sizes of 6, 30, and 100 MGD respectively while these
costs are estimated to be reduced to 11.9 cents, 9.5 cents, and 7.8 cents/
1000 gal. for Respective 6, 30 and 100 MGD plant sizes with the use of an
oxygenation treatment system capable of equivalent BOD removal at 2 hours
nominal treatment detention time.
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CONCLUSIONS ANT) R:¦COMMENDATIONS
A practical and economically attractive means for use of high
purity oxygen gas in aeration of the conventional activated sludge
process has been tested over an eight month period of continuous
operation. This work was done using a temporarily installed
oxygenation system in the existing aeration tanks at the Batavia,
New York Municipal Pollution Control Plant. A sparged-turbine, gas-
liquid contacting unit was employed for oxygen transfer. The aeration
tanks,which were of conventional design,were covered and equipped
with gas-liquid staging baffles to provide a multistage oxygenation
system. This system functioned with co-current gas and liquid flow.
The test program was specifically planned to evaluate the following:
1. The feasibility and economics of high purity oxygen use in
aeration of the conventional activated sludge waste treatment process.
2. The comparison of oxygenation and air aeration in terms of
treatment performance.
3. The consistent operation of the oxygenation system at high
mixed-liquor suspended solids (MLSS) levels (6000-8000 mg/1), high
dissolved oxygen concentrations (8-10 mg/1) and high overall utilization
of feed oxygen gas ( >907„).
4. The operation and treatment performance of an oxygenation
system at low detention times (approximately 1.2 hours based on raw
wastewater + recycle sludge flow) and high organic loading conditions
considered economically desirable but impractical with air aeration.
5. The relative economics of domestic waste treatment comparing
the cost of oxygenation with conventional (diffused air) air aeration.
The work was conducted in three phases. In two phases,the performance
of the oxygenation system was compared to a parallel air aeration system.
In a third phase, the oxygenation system was used with one-fourth of the
plant aeration tankage to treat the entire wastewater flow to the plant.
A summary of results from each of the three phases of operation is shown
in Table 1.
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TABLE 1
SUMMARY COMPARISON OF AIR AND OXYGENATION SYSTEMS PERFORMANCE
PRASE I
OPERATION
PHASE II OPERATION
PHASE III
0P7-RAT I Oil
AIR
OXYGEN
OXYGEN
AIR
OXYGEN
Wastewater Feed Rate (MGD)
1.97
1.91
2.53
1.29
1.44
Aeration Detention Time (Hrs.)*
3.6
3.6
1.2
2.6
2.0
Nominal Aeration Detention Time (Hrs.)
4.0
4.1
1.5
3.0
2.8
MLSS Concentration (mg/1)
2440
3060
6980
3640
6190
MLVSS Concentration (mg/1)
1740
2210
4450
2580
4310
Recycle Sludge TSS (mg/1)
14,960
18,620
29,560
16,600
18,790
Volumetric Organic Loading
lbs. BOD/Day/lOOO ft3
60.0
57.9
212.5
128.9
144.8
Mixed-Liquor Dissolved Oxygen
Concentration (mg/1)
1.5
8.7
9.0
0.8
8.0
Ft3 Air Utilized/Gal Sewage Treated
2.89
-
-
4.32
-
% Feed Oxygen Utilized
95.5
92.7
-
91.4
% BOD Removed
90
92
90
88
94
% COD Removed
76
80
71
79
84
% TSS Removed
93
96
89
94
97
* Raw Flow I Recycle Flow
** Raw Flow Only
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The oxygenation system consistently exhibited superior treatment
performance in direct comparison to the parallel air aeration system
in spite of the fact that an impractically high air aeration rate was
used to insure optimum performance. The power required by the oxygena-
tion unit to accomplish high treatment efficiency was only 0.08 -
0.14 HP/1000 gal. of wastewater treated.
The biomass generated by the oxygenation system was highly
flocculant and rapidly settleable, yielding sludge volume index values
as low as an average of 36. The high recycle and waste solids total
suspended solids concentration achieved (approximately 3-47. when
clarifier operation was closely controlled) obviates the requirement
for thickening of the waste activated sludge prior to further processing
for disposal.
An extensive evaluation of the oxygenation system treatment costs
in comparison to conventional air aeration reveals significant potential
savings attributable to high purity oxygen use. These savings are due
to several characteristics of the oxygenation system, but the major
factors are reduced aeration tank volume requirements for equivalent
treatment and a reduced production of waste activated sludge. As an
example, the total cost of air aeration treatment at 6 hours nominal
detention time (based on raw wastewater flow) and a 1.6 cf/gal aeration
rate is estimated to be 15.1 cents, 13.0 cents, and 11.0 cents/1000 gal
for plant sizes treating 6, 30, and 100 MGD of wastewater. For equivalent
BOD removal with oxygen aeration at 2 hour nominal detention time (based
on raw wastewater flow) these total treatment costs are estimated to be
11.9 cents, 9.5 cents, and 7.8 cents/1000 gal for the respective 6, 30,
and 100 MGD plant sizes. Total treatment costs referred to here include
investment and operating costs associated with preliminary and primary
treatment as well as the investment and operating costs associated with
secondary treatment by the activated sludge process and the disposal of
primary and waste activated sludges.
The promising results of the work reported clearly indicate the
advisability o£ further work to evaluate in detail certain characteristics
of tlu.' oxygenation system noL yet. studied in sufficient depth. SpecificaLly,
viii
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the existing temporary installation should be used to evaluate the
following:
1. The biokinetics of the treatment process as revealed by
careful control of sludge wasting, frequent analysis of soluble BOD
and COD in fepd wastewater, mixed-liquor filtrate and final clarifier
effluent.
2. Flow control should be established for the system such that
the measurements in (1) above can be made under more nearly steady
state conditions.
3. The handling properties of the waste activated sludge should
be more fully elucidated by direct vacuum filtration tests.
4. System performance should be optimized by installation and
operation of a flow proportion controlled activated sludge return
system.
5. It would be desirable to evaluate oxygen aerated, aerobic
digestion of waste activated sludge and to establish the handling
characteristics of such stablized sludge by vacuum filtration tests.
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FIGURE I
SCHEMATIC DIAGRAM OF MULTI-STAGE
OXYGENATION SYSTEM
GAS RECIRCULATION
COMPRESSORS
AERATION
TANK COVER
AGITATOR
OXYGEN .. _
FEED GAS
EXHAUST
GAS
MIXED LIQUOR
EFFLUENT TO
CLARIFIER
WASTE
LIQUOR
FEED
STAGE
BAFFLE
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ACKNOWLEDGEMENTS
This prpject was conducted under the auspices of the Linde
Division's Process and Product Development Department at Tonawanda,
New York (M. L. Kasbohm - Director). The technical efforts were
a part_of the Division's Wastewater Treatment Technology program
and involved direct contributions by the following personnel;
J. R. McWhirter
Product Manager, New Products
F. W. Bonnet
Technology Manager
E. K. Robinson
Contract Manager
J. G. Albertsson
Supervisor
N. P. Vahldieck
Senior Engineer
R. J. Grader
Staff Engineer
D. V. Daly
Technician
J."R. Duemmer
Technician
S. E. Faruga
Technician
E. H. Kremer
Technician
P. F. Layer
Technician
Appreciation is expressed to the City of Batavia, New York
for permission to conduct the work described here at their
Municipal Pollution Control Plant. The enthusiastic attitude
displayed toward this experimental program by Ira M. Gates, City
Manager; Robert Lawrence, Superintendent of water and Sewage Works
and his competent staff contributed greatly to the successful
completion of the program.
In the course of the project work, the efforts of Richard C.
Brenner, Charles L. Swanson, Robert L. Bunch, and Lawrence J.
Karaphake, of the Advanced Waste Treatment Research Laboratory of
the Federal Water Quality Administration were also greatly
appreciated.
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