EPA-600/2-77-141
August 1977
Environmental Protection Technology Series
FEASIBILITY OF TREATING
SEPTIC TANK WASTE BY
ACTIVATED SLUDGE
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.'
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EPA-600/2-77-141
August 1977
FEASIBILITY OF TREATING SEPTIC TANK WASTE
BY
ACTIVATED SLUDGE
by
Stephen M. Bennett and James A. Heidman
EPA-DC Pilot Plant
Washington, D.C. 20032
and
James F. Kreissl
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
Contract No. 68-03-0349
Project Officers
Irwin J. Kugelman
Thomas P. O'Farrell
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 publica-
tion. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
ii
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled
land are tragic testimony to the deterioration of our natural environment.
The complexity of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem
solution and it involves defining the problem, measuring its impact, and
searching for solutions. The Municipal Environmental 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.
The study described in this report assesses the ability of a municipal
wastewater activated sludge treatment plant to treat domestic septic tank
pumpage on a continuous or intermittent basis. Such treatment provides a
viable methodology for the disposal of this highly concentrated waste.
Francis T. Mayo
Director, Municipal Environmental
Research Laboratory
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ABSTRACT
The objective of the study reported herein was to evaluate the impact
of household septic tank wastes on municipal activated sludge treatment plants.
Septage addition was evaluated on a continuous basis over a four-month period
in a 7500 I/day (1980 gpd) pilot plant. The septage was combined with munici-
pal wastewater primary effluent in a series of increasing loadings to the
activated sludge unit. Results were compared to a control unit receiving
primary effluent only. Shock load studies were also conducted in the pilot
plant system and with a series of batch aeration tests.
Septage addition was found to be feasible on either a continuous or
intermittent basis. The response during the continuous feeding studies
depended upon the organic loading and the septage characteristics. COD
loadings below 3 g COD/g MLVSS/day could be handled without severe upset.
Unacclimated systems also responded well when septage was added, and sub-
stantial organic removals were obtained within a relatively short time.
This report covers a period from February 1974 to November 1974 and
work was completed as of September 1975.
IV
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CONTENTS
Page
Foreword i i i
Abstract iv
List of Figures vi
List of Tables vii
Acknowledgment viii
I Introduction 1
II Summary 3
III Conclusions 4
IV Recommendations 5
V Experimental Facility 6
Continuous Feed Study 6
Shock Load Study 9
VI Septage Characteristics 10
VII Analytical Procedures 13
VIII Continuous Feed Study 14
Operation 14
Performance 18
IX Shock Load Studies 32
Batch Aeration Test-Procedure and Results 32
Pilot Plant Shock Loadings-Procedure and Results 44
X Discussion 53
XI References 59
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LIST OF FIGURES
iNumoe
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
r
Schematic of Parallel Plug Flow Activated Sludge Pilot Plant. .
Septage Feed Mechanism
Variation of Mixed Liquor Suspended Solids
Variation of Influent and Effluent Suspended Solids
Variation of Influent and Effluent BOD and BOD: MLVSS Ratio . .
Variation of Influent and Effluent COD and COD: MLVSS Ratio . .
Variation of Influent and Effluent TOC
Variation of Effluent (N02+N03)-N
Effect of Loading On Effluent COD at Various Aeration Times and
Septage Loads
Effect of Loading On Effluent BOD at Various Aeration Times and
Septage Loads
Effect of Loading On Effluent TOC at Various Aeration Times and
Septage Loads
COD Reduction for Various Mixtures of Septage and Primary
Effluent, Septage Load No. 10
COD Reduction for Various Mixtures of Septage and Primary . . .
Effluent, Septage Load No. 11
COD Reduction for Various Mixtures of Septage and Primary . . .
Effluent, Septage Load No. 12
Effect of Shockload to the Pilot Activated Sludge Unit Using. .
.Septage Load No. 13
Effect of Shockload On Effluent Suspended Solids and COD Using.
Septage Load No. 14
Effect of Shockload On Effluent TOC and BOD and Variation of. .
Page
«?
7
8
17
19
20
21
22
23
35
36
37
38
39
40
; 49
50
MLSS Using Septage Load No. 14 51
vi
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LIST OF TABLES
Number Page
1 Septage Characteristics 11
2 Heavy Metal Concentrations In Septage 12
3 Comparison of the Feed to the Parallel Plug Flow Activated. . .
Sludge Systems without Septage Addition 15
4 Operation of Plug Flow Activated Sludge System with Septage . .
Addition 24
5 Comparison of the Septage System with the Control System. ... 25
6 Characteristics of Primary Effluent-Septage Mixtures and. . . .
Reactor Solids Concentrations Used In Batch Shock Loads .... 34
7 Suspended Solids Concentration of Clarified Effluents from. . .
Batch Aeration Studies 42
8 Initial BODc Concentrations and BODc Concentrations of
Clarified Effluents from Batch Aeration Studies 43
9 Effluent Quality Following Addition of Shock Loads to the ...
Pilot Activated Sludge System ... 46
10 Characteristics of Influents to Parallel Activated Sludge . . .
System During Shock Loads 47
11 Oxygen Uptake Values in the Control and Shocked Systems ....
(Septage Load 14) 52
12 Average SVI for the Control and Septage Systems During the. . .
Continuous Feed Study 55
VII
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ACKNOWLEDGMENT
The pilot system was maintained and operated by the EPA-DC Pilot Plant staff
under the direction of Calvin Taylor, chief operator, and Paul Ragsdale, head
of instrumentation and mechanical repair. Laboratory analyses except for
trace metal concentrations were performed in the EPA-DC Pilot Plant laboratory
under the direction of David Rubis. Trace metal concentrations were
determined by MERL Laboratories, Cincinnati, Ohio under the direction of
Robert Williams.
The assistance offered by Thomas 0'Parrel!, chief of the pilot plant, in
organizing and performing this study is gratefully acknowledged.
vm
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SECTION I
INTRODUCTION
Approximately 17,500,000 septic tanks are in use in the United States at this
time (1). Of this number, a significant percentage are pumped each year to
remove the accumulated sludge and scum. Because the behavior of these tanks
is not predictable, there is no rational method for calculating the number of
pumpings which might be expected in a single year. For the purpose of
estimation, the frequency of pumping will be assumed as once every four years.
An additional assumption will be that the average septic tank volume is 3 m3
(793 gal). Since these assumptions are reasonably representative of the
realities of today, the volume of septic tank pumpings (septage) which must
be disposed of in this country each year is roughly 13,000,000 m3 (3.5 billion
gallons).
Most of the pumpings are transferred from the septic tank to trucks with
varying capacities, but usually about 3.8 m3 (1000 gal). The pumpers must
then dispose of this particularly offensive material. In recent years,
health authorities have imposed regulations which require that septage disposal
be accomplished in a controlled manner at sanitary landfills, other approved
disposal areas, central septage handling facilities and sewage treatment
plants (STP). At a STP, the septage has often been added directly to the
wetwell where it is mixed with the incoming raw sewage prior to the treatment
processing.
Tales of problems caused by this form of septage disposal at small STP's
abound. Plants have reportedly been upset for periods from a few hours to a
few months by this practice. As a result, many (if not most) small treatment
plants have banned septage disposal for all but that generated within the
political boundaries of the authority served. The difficulties created by
such bans can be manifold, but primary among them are higher costs to the
septic tank owners due to additional time and travel requirements on the part
of the pumpers. A secondary (and more serious) effect is the increased
reluctance on the part of the septic tank owner to request pumping services
until absolutely necessary, a condition which is generally exhibited by "day-
lighting" or appearance of effluent at the ground surface above the leaching
area. This condition usually means that the soil disposal field has failed
and a new one must be excavated - a costly situation at best.
Since the bans are often based on hearsay evidence or effects only partially
related to septage addition, there is a significant need to determine why
plants may be upset and what safe limits of septage can be handled by a plant
of a given configuration and capacity when septage is added to the wetwell.
In order to fully appreciate the problem, it must be broken down and analyzed.
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The trucked septage should be received at the treatment plant in a special
handling facility, or receiving station, which may employ coarse screening,
rock traps, comminution or maceration, and odor control. Unfortunately, many
existing plants do not have these receiving stations and use the aforemention-
ed wetwells as the receiving locations. In these cases, the septage becomes
a shock load to the treatment facility. In smaller plants this shock load
can be overpowering. For example a 3.8 m3 (1000 gal) truck emptying its
contents in 10 to 20 minutes represents a hydraulic surge of 6.3 to 3.2 1/s
(100 to 50 gpm). At a 760 nr/day (0.2 mgd) STP, this would represent an
instantaneous increase in flow of between 36 and 72 percent. This hydraulic
surge, when coupled with the concentrated suspended solids, BOD and other
pollutants of septage, represents a major shock load on the treatment plant.
The ability of a plant to handle a given shock loading is a function of its
design. Obviously, a plant which has primary sedimentation would be better
protected than one which does not. The ability of a trickling filter plant
or an aerated lagoon to handle such a shock would be different from that of
an activated sludge plant, and each modification of the latter would also
exhibit differences in resistance to upset by these shock loadings. An
additional factor is the actual vs. design loading on the plant (load factor).
Also, the solids handling capacity of the STP must be capable of processing
the additional sludges which will be produced by septage addition.
Smith and Wilson (2) indicate that three factors must be considered in deter-
mining the capacity of handling trucked wastes at an activated sludge plant.
These factors are the additional organic solids load, the reserve oxygenation
capacity of the plant, and the toxicity. Although toxicity might be a factor
in some cases of upsets by septage addition due to cross contamination of
domestic septage in the pumpers tank from a previous load of industrial waste,
it is less likely to be a factor if proper maintenance procedures are employed
by the pumper. The toxicity factor becomes most important when dealing with
boat or trailer holding tank wastes where zinc and formaldehyde compounds are
employed in great concentrations for odor control. The reserve oxygenation
capacity of a plant is a function of the design and the load factor. Since
the loading of a plant and the design oxygenation capacity are known, the
reserve capacity can be calculated and compared to the oxygen demand of the
trucked wastes. Since these wastes are arriving at the STP in varying fre-
quencies, the most important factor according to Smith and Wilson would be
the effects of influent solids and solids synthesized from the oxidation of
soluble organic matter.
If a properly designed receiving station and holding tank are available,
numerous alternatives are possible. The most obvious one would permit a
controlled discharge to the treatment facility in order to minimize the
hydraulic and organic shocks. This continuous "bleeding" of septage to the
treatment system is commonly recommended as good design procedure. However,
little data exist on the performance of STP's receiving septage in controlled
or uncontrolled modes.
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SECTION II
SUMMARY
The objective of the experimental program summarized in this report was to
determine the feasibility of treating material pumped from domestic septic
tanks (septage) in activated sludge sewage treatment plants. Two approaches
for adding septage were evaluated. Septage was added: (1) on a continuous
basis to a system receiving a combination of septage and sewage in varying
ratios and (2) on a shock load basis to a system treating municipal waste
only. The continuous feed studies were conducted on a 7500 1/d (1980 gpd)
pilot plant. The shock load studies employed both the pilot plant facilities
and a series of batch aeration tests. In both approaches, primary sedi-
mentation was simulated prior to adding septage to the activated sludge. In
both approaches a control unit receiving only municipal waste was operated
for comparative purposes.
Septage addition was found to be feasible on either a continuous or inter-
mittent basis. The particular response of the continuous flow activated
sludge system receiving septage depended upon organic loading and septage
characteristics. Unacclimated systems were not unduly upset by septage
addition and substantial removals of septage were obtained within a relatively
short time.
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SECTION III
CONCLUSIONS
1. Septage disposal to sewage treatment plants employing primary clarifi-
cation and conventional activated sludge processing is feasible when
sufficient excess aeration and sludge handling capacities are available.
2. Continuous addition of septage upstream of the primary clarifier could
be handled without severe upsets when the COD loading was below 3 g COD/
g MLVSS/day.
3. Conversion of maximum COD loadings to maximum acceptable hydraulic flows
of strong septage allows a treatment plant operator to determine the
maximum number of septage loads his plant can handle without being upset,
if all other factors are favorable.
4. Batch shock load studies indicated that domestic septage is not toxic
and that extended aeration times may be required for sufficient septage
stabilization.
5. The residual COD in the activated sludge effluent was found to increase
with the COD loading added to the plant.
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SECTION IV
RECOMMENDATIONS
1. All future studies of the effects of septage addition on an activated
sludge facility should include material balances to determine the
quantities of the additional sludges produced and should include an
analytical method for quantifying the biodegradable fraction of septage
sol i ds.
2. Future studies should be performed to characterize the sludge produced
after septage addition so that the affect on the solids handling facility
may be fully evaluated.
3. Further studies of septage addition to activated sludge facilities are
necessary, preferably at a somewhat larger scale. These studies should
consider several activated sludge modifications to determine the cap-
abilities of each to handle septage additions in both shock and continuous
modes.
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SECTION V
EXPERIMENTAL FACILITY
Continuous Feed Study
The experimental pilot plant system consisted of two 7500 1/d (1980 gpd)
activated sludge systems operating in parallel as indicated in Figure 1.
Primary effluent from the District of Columbia primary clarifiers'was
pumped to a splitter box at 15,000 1/d (3960 gpd). The flow was split equally
with half passing directly into the first stage of the control activated
sludge system and half passing into a clarifier where septage was also added.
The purpose of the second clarifier was to simulate septage addition into a
primary clarifier since this would probably be the normal operating procedure
at most plants receiving septage.
The septage was stored in two 9100 1 (2400 gal) covered and vented storage
tanks. One tank was kept on standby while the contents of the other were
added to the activated sludge system. When a truckload of septage was received,
it was pumped to a storage tank. Next the septage was continuously pumped in
a closed-loop manner through a Moyno "maz-o-rator" and back into the storage
tank. The pumping time was approximately 8 hours at a 38 1/min (10 gpm) flow.
The macerated septage was then held in the storage tank until needed.
When the contents of one of the storage tanks were exhausted, the feed was
changed to the standby storage tank and a new truckload of septage was procured
for the empty tank. The feed tank was continuously mixed with a 2.2 kw (3 hp)
Lightnin mixer equipped with a 61 cm (24 in) diameter impeller. In addition,
the septage was continuously recycled from the bottom of the storage tank.
That portion of the cycled septage which was not fed to the primary clarifier
was returned to the top of the storage tank. The mechanism which fed septage
into the primary clarifier is shown in Figure 2. It consisted of a piece of
5.1 cm (2 inch) PVC pipe with automatic valves at each end. The automatic
valves were operated by a timer. The valves were operated such that valve A-
would open while valve B remained closed allowing septage from the recycle
line to fill the pipe. After the pipe was filled, valve A closed and then
valve B opened discharging the contents by gravity into the primary clarifier.
To prevent air lock, a portion of the piping above the feed mechanism was
vented to atmosphere. A delay timer was used to assure that the pipe was full
before valve A closed. The frequency of fill and discharge was determined by
the timer setting. This feed sequence resulted in septage being added to the
clarifier every 1-7 minutes depending upon the particular loading being
investigated.
The septage discharged about 5.1 cm (2 in) above the surface of the clarifier.
A baffle was provided at the discharge point to distribute the septage
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D.C. PRIMARY EFFLUENT
SECONDARY EFFLUENT
Figure 1. Schematic of Parallel Plug Flow Activated Sludge Pilot Plant.
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SEPTAGE
RECYCLE
D.C. PRIMARY
EFFLUENT
TO SEPTAGE
AIR
VENT
VALVE
WASTE SOLIDS
Figure 2. Septage Feed Mechanism.
8
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throughout the clarifier. The clartfier was shaped like an inverted pyramid.
It was 1.22 m (4 ft) square at the top and tapered to a 1.52 m (5 ft) depth.
Solids were wasted from the bottom of the clarifier one or two times weekly to
prevent a backup of settled material. The mixture of primary effluent and
septage exiting the clarifier passed directly into the first stage of the
septage activated sludge system.
Each activated sludge system consisted of a series of eight 208 1 (55 gal)
drums connected in series and followed by a 0.76 m diameter x 1.49 m depth
(2.5 ft diameter x 4.9 ft depth) secondary clarifier. The 208 1 (55 gal)
drums were filled to a liquid depth of 66-74 cm (26-29 inches) with at least
25 cm (12 in) of freeboard to prevent solids loss during aeration. Compressed
air was supplied to the bottom of each of the drums with manual control of the
air flow rates. The reactor volumes of the control system and the septage
system were 1454 1 (384 gal) and 1340 1 (354 gal), respectively. This resulted
in corresponding hydraulic retention times based on the influent flow of D.C.
primary effluent of 4.7 and 4.3 hours. Both secondary clarifiers were equipped
with conical bottoms to facilitate solids recycle. Underflow solids from each
clarifier were recycled to the first pass of each system with a Milton Roy
positive displacement pump.
Shock Load Study
The shock load studies also employed the above pilot facility. In addition
the shock load studies employed a series of metal drums for aerating MLSS
and several containers for settling septage and mixing septage and primary
effluent. Further details are presented in the section describing the shock
load studies (Section IX).
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SECTION VI
SEPTAGE CHARACTERISTICS
The septic tank wastes employed in the study were obtained from household
sources. Each load of septage was delivered by "Potters Septic Tank Service",
a local hauler in the D.C. area, with the exception of the first load which
was delivered by "San-I-Kan", also a local hauler.
Characteristics of the septage used in both the continuous feed and shock load
studies are summarized in Tables 1 and 2. During-the course of the study,
14 different loads of septage were employed. Septage loads Nos. 1-9 were used
in the continuous feed studies. Each of these loads contained the combined
waste of two different household sources. Therefore the septage used in the
continuous feed studies represents septage from 18 different sources. Through-
out the entire study septage from 23 different sources was used.
The values presented in Table 1 for the continuous feed study are average
values of daily composite samples. There was some concern that the septage
characteristics could change during storage. Therefore, samples of septage
were taken from the continuous recycle line every 4 hours and composited over
a 24 hour period on Sunday thru Thursday to obtain the daily composite sample.
Throughout the continuous feed studies, the analytical results obtained from
the composited samples with any given load exhibited a random variation
because of the difficulty of keeping a homogenous septage feed. The values
for septage loads Nos. 10-14, shown in Table 1, were obtained by analysis of a
single grab sample of each load.
One grab sample from each load (Nos. 1-14) was collected in a one-liter
polyethylene cube container which was specially cleaned. The cube container was
rinsed with a 25% solution (by volume) of nitric acid followed by rinsing with
de-ionized water. This rinsing cycle was performed at least seven times. Ten
ml of concentrated nitric acid were added to the cube container before the
septage samples were taken. These samples were sent to the NERC Laboratory in
Cincinnati, Ohio for trace metal analysis. The results of these analyses are
presented in Table 2.
The septage characteristics varied widely from load to load. For example, COD
varied from 5,965 to 43,400 mg/1 and BOD varied from 1,460 to greater than
18,600 mg/1. The volatile suspended solids ranged from 59 to 85% of the
suspended solids and the Nfy-N ranged from 12 to 55% of the total nitrogen.
In addition the COD: BOD ratio for any given load varied from 2.7 to 8.4.
10
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Load No.
Continuous Feed
1
4
5
6
7
8
9
Shock Load
Batch
10
11
12
Pilot Plant
13
14
COD
mg/1
(D
22,800
7,340
21,980
6,880
21,480
13,870
14,870
43,400
12,260
5,965
12,920
11,450
TABLE :
BOD
mg/1
6,300
4,400
2,520
3,820
3,320
2,910
>18,600
1,460
1,780
--
1,870
L. Septage Characteristics
SS
mg/1
22,600
6,800
19,000
6,280
21,440
14,370
14,110
18,000
9,600
1,770
13,630
9,120
(Vol.)
(%)
(51)
(73)
(72)
(70)
(70)
(59)
(65)
(82)
(63)
(85)
(60)
(60)
P04
mg/1
760
190
390
140
390
370
290
515
184
166
502
322
TKN
mg/1
1250
190
490
200
560
460
390
750
216
346
493
316
(NH4-N)
(«)
(55)
(53)
(33)
(30)
(18)
(12)
(19)
(25)
(21)
(50)
(28)
(18)
TOC COD
mg/1 BOD
3.6
__
5.0
2.7
5.6
4.2
5.1
12,690 <2.3
3,470 8.4
1,316 3.4
4,000
3,330 6.1
(1) Results not presented for loads No. 2 and 3 because of sampling error
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TABLE 2.
Load No..
Continuous Feed
1
2
3
4
5
6
7
8
9
Shock Load
Batch
10
11
12
Pilot Plant
13
14
Fe
750
7
3
90
210
71
275
163
146
230
100
31
395
Mn
4.4
1.2
0.6
0.8
2.3
0.8
3.6
20.0
18.0
2.8
0.8
0.5
6.5
Heavy Metal Concentrations in Septage, mg/1 .
Hg
0.024
0.018
0.028
0.005
4.000
0.110
0.740
0.081
0.084
<0.001
0.200
0.055
O.OG2
Ni
0.4
0.3
0.2
0.3
0.9
0.5
1.2
1.2
1.2
0.9
0.4
0.3
1.2
Cd
0.2
0.2
0.2
<0.05
10.8
0.3
1.7
0.3
0.3
0.2
0.18
<0.05
0.21
As
__
<0.04
^0.04
0.4
0.5
0.05
0.08
0.20
0.03
0.40
<0.04
<0.04
<0.04
Zn
120
21
8
11
17
5
42
16
35
51
14
8
43
Cu
4.2
6.8
1.0
18.5
5.1
4.4
9.6
0.5
0.7
13.0
3.3
6.8
34.0
Al
40
--
2
17
50
37
68
3
18
--
200
Cr
0.4
--
--
0.3
1.5
1.8
1.0
1.5
1.3
0.3
2.2
Pb Se
1.8 0.30
0.20
0.20
-- <0.02
-- 0.05
- 0.05
- 0.05
<0.02
-- <0.02
5.2 <0.02
2.5 <0.02
1.5 <0.02
__
31.0 0.02
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SECTION VII
ANALYTICAL PROCEDURES
Total phosphorus was determined by the persulfate method (3) and total organic
carbon (TOC) was measured on a Beckman Carbonaceous Analyzer (4). The pro-
cedure specified in the EPA Manual (5) was used for determination of Nlfy-N
and (N02+N03)-N with a Technicon Autoanalyzer. Trace metal analyses at the
NERC-Cincinnati Laboratory were performed on a Perkin-Elmer Model 303 atomic
adsorption unit. Procedures specified in the Perkin-Elmer instruction manual
were employed. All other analyses were performed in accordance with Standard
Methods (6). Dissolved oxygen content in the aeration chambers was measured
with a model 1010 Delta Scientific field probe.
13
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SECTION VIII
CONTINUOUS FEED STUDY
Operation
The continuous feed studies were performed in the parallel activated sludge
systems previously described in Section V. The D.C. primary effluent to the
control activated sludge system was maintained at 5200 ml/min (1.4 gpm) and
the inlet flow to the septage system clarifier was also maintained at 5200 ml/
min. Grab samples of primary effluent were analyzed to determine if any
additional settling of the D.C. primary effluent occurred in the septage
system primary clarifier. As shown in Table 3, the septage system clarifier
did not noticeably alter the concentrations of COD, BOD, TOC and SS.
The rate of septage addition was a function of its organic strength and the
particular organic loading rate under investigation. Throughout the study, COD
was the parameter used for controlling the organic load applied. The particular
combination of primary effluent and septage was determined by attempting to
provide a fixed average influent COD concentration. Since the COD of each
septage load was variable, the rate of septage addition was adjusted to attempt
to maintain the fixed COD value with each change in the septage load. Initial-
ly the concentration was set at roughly twice that of primary effluent alone.
As the investigation progressed, the magnitude of the fixed COD level was
increased. During the course of the study, the septage flow to the septage
system clarifier varied from 2-14% of the primary effluent flow.
Samples for analyses (BOD, COD, TKN, Nfy-N, (N02+N03)-N, P, SS and VSS) in
the EPA-DC Pilot Plant Laboratory were manually taken every 4 hours and com-
posited over either 24 or 48 hours. All samples except those taken for BOD
and suspended solids analysis were preserved with 1 drop of ^04 per 30 ml
of sample while they were being held in storage. During storage all samples
were maintained at 3°C to minimize biological activity.
From April 1 until July 11, all samples except for the D.C. primary effluent
feed to the control system were composited over 24-hour periods on Sunday
through Thursday; no laboratory samples except D.C. primary effluent were
collected on Friday or Saturday. The D.C. primary effluent feed to the
control system was sampled every day and the non-acidified sample composited
over 24-hour periods only, while the acidified samples were composited over
24 hours on Tuesday, Wednesday and Thursday, and over 48 hours on Friday-
Saturday and Sunday-Monday. BODs analyses were performed on a seven-day-a-
week basis. Starting July 12, influent and effluent samples from both systems
were collected for BOD5 analysis every day and composited over 24 hours. Also
starting July 12, samples for all suspended solids analysis were composited
over 24 hours on Tuesday, Wednesday and Thursday, and over 48 hours on
14
-------
TABLE 3. Comparison of the Feed to the Parallel Plug Flow Activated Sludge Systems
without Septage Addition.
Date
03-25-74
03-26-74
03-27-74
03-28-74
10-19-74
10-20-74
11-12-74
System
Control
Septage
Control
Septage
Control
Septage
Control
Septage
Control
Septage
Control
Septage
Control
Septage
COD
mg/1
196
205
199
213
215
199
207
281
251
BOD
mg/1
113
119
113
125
105
129
115
100
--
--
--
--
131
141
TOC
mg/1
--
--
--
--
88
74
75
71
77
74
SS
mg/1
52
70
100
82
88
76
74
76
108
116
140
120
146
116
NOTE: All analyses were performed on grab samples.
-------
Friday-Saturday and Sunday-Monday.
The operators checked flow rates and dissolved oxygen levels every four hours
on a continuous seven-day-a-week basis. The solids recycle rate in both
systems was set at approximately 20% of the influent flow (1040 ml/min)
through most of the study. The dissolved oxygen content was maintained at
1-5 mg/1. Thirty minute sludge volumes in 1-liter cylinders were obtained
on recycle solids and mixed liquor from the second and eighth drums (Figure 1)
once every eight hours. The reactor sludge volumes and approximate mixed
liquor suspended solids analysis from the seventh drum were used to control
the wastage rate. The approximate solids analyses were performed Monday
through Friday on grab samples which were filtered and dried at 105°C for
30 minutes. Any upward or downward trend over several days of operation
resulted in an adjustment in the wastage rate. On weekends, the wastage rate
was not changed unless there was an abnormal change in sludge volumes.
Solids were manually wasted from the control system throughout the study. The
solids were wasted from a tee in the recycle line which was located ahead of
the recycle pump. The tee was located below the bottom of the clarifier and
flow was by gravity. Initially, 76-95 1 (20-25 gal) of waste solids were
removed from the system only once per day. It was visually apparent during
wasting that the waste solids concentration was decreasing considerably near
the end of the waste cycle. This indicated channelling in the clarifier
because of the high waste flow rate. Therefore, the frequency of wasting was
gradually increased until it reached once every 4 hours.
Channelling in the clarifier during wasting was more severe in the septage
system because the volume of waste was 2-5 times greater than in the control.
When solids were manually wasted every 4 hours, similar to the control system,
channelling still occurred. An automatic blow-down system operated by a tim-
ing mechanism was installed in June, and from that time onward the waste
frequency was approximately once per hour depending upon the particular waste
rate desired. Because of channelling and various mechanical problems, a
representative sample of the solids being wasted from the system was not
always obtained. Starting May 28, the operators obtained the sample to
determine waste solids concentration from the volume of sludge actually wasted
rather than from the sludge recycle line. The operators obtained the sample
during a regularly scheduled time of wasting. Each time the operators sampled
the system, the full volume of solids wasted at that time was collected,
mixed and sampled. Prior to May 28, the waste solids concentration was im-
properly sampled because of channelling during wasting. For this reason
sludge production data prior to May 28 are not available.
Throughout the study, the variability of the mixed liquor suspended solids con-
centration was greater in the septage system than in the control. Prior to
septage addition both systems were operated at a high (4000-5000 mg/1) MLSS
concentration. After septage addition commenced on April 10, the MLSS
concentrations in both systems were gradually reduced over approximately a
month's time to near 2000 mg/1, a value typical of a conventional activated
sludge system. From May 24 through August 12, the MLSS in the septage system
averaged 2050 mg/1. However,as shown in Figure 3, there was considerable
variation. The MLSS in the control system were generally maintained at 2000
16
-------
PERIOD
SEPTAGE LOAD NO.
SEPTAGE FLOW, %
Figure 3. Variation of Mixed Liquor Suspended Solids.
17
-------
mg/1 with only minor variations until July 22 when they were intentionally
reduced to approximately 1700 rag/1.
The variations in MLSS in the septage system can be attributed to erratic
fluctuations in influent SS and BOD, mechanical difficulties, and the frequen-
cy of changing loads of septage. The variability of the influent to the
septage system compared to the control is shown in Figures 4-A, 5-A, 6-A, and
7-A. Although the septage storage tank was equipped with a mixer and septage
was continually recycled, there was variability in the daily septage sample
being pumped to the primary clarifier as a result of insufficient mixing.
This variability was the primary reason for fluctuation in influent character-
istics.
Although the septage was macerated, the septage recycle line as well as the
feed mechanism periodically plugged (approximately once every week) with
septage solids consisting mainly of hair and fibrous material. Recurring
mechanical problems were also present in the automatic blow-down system.
Maintenance personnel were on call 24 hours a day to correct any malfunctions
which could not be handled by the normal operating crews.
Another factor which made maintaining a steady MLSS concentration difficult
was the frequency of changing loads of septage. With each load of septage,
the operators had to establish a new waste rate to attempt to maintain the
desired solids level. However, establishing the correct waste was a gradual
process. Several times before the waste rate could be accurately established,
a different load of septage was added requiring an immediate change in waste
rate. Consequently, maintaining a constant MLSS level was difficult. Even
during full scale operation, a constant MLSS concentration could be difficult
to maintain because of the changing nature of the septage,
Performance
The performance of the parallel activated sludge systems during continuous
addition of septage is summarized in Figures 3-8 and in Tables 4 and 5.
Because of the wide variation of the influent BOD and COD loadings to the
septage system and because of other day-to-day variations which occurred, it
is difficult to accurately characterize periods of average performance based
on uniform process loadings. Although the research plan called for stable
operation of the septage system with a series of increasing loading rates,
the variations in septage characteristics, etc. made the actual process
loadings different than desired at certain times. Another problem
experienced in the analysis of the data was that effluent suspended solids
from the control were very erratic (Figure 4-C), causing abnormal
fluctuations in effluent quality. The erratic variation of effluent
solids continued until period VI due to an excessive growth of Nocardia
organisms which floated to the surface of the secondary clarifier, causing
a mat of floating so.lids and an effluent.quality of marked variability.
During period VI, clarification and effluent quality improved considerably
and remained relatively stable for the balance of the study. Other studies
at the pilot plant have shown that the Nocardia growths are less competitive
at the higher loadings experienced in the latter phases of this study.
18
-------
PERIOD
SEPTAGE LOAD NO.
SEPTAGE FLOW, %\
1
1
2
II
2
6
3
13
III
4
IV
5
7 I 2
V
6
13
VI
7
VII
8
VIII
9
3| 4 | 5 | 7 1121611
SEPTAGE SYSTEM
CONTROL SYSTEM
EFFLUENT SEPTAGE SYSTEAA
Note: Shaded area indicates
periods of comparison,
Table 5
Figure 4. Variation of Influent and Effluent Suspended Solids,
19
-------
PERIOD
SEPT AGE LOAD NO.
SEPTAGE FLOW, %
500
INFLUENT BOD
EFFLUENT BOD - SEPTAGE SYSTEM
EFFLUENT BOD - CONTROL SYSTEM
Figure 5. Variation of Influent and Effluent BOD
and BOD: MLVSS Ratio.
20
-------
SEPTAGE LOAD NO.
SEPTAGE FLOW, %
1000 r-
RIOD
NO.
W, %
1
1
2
II
2
6
3
13
III
4
IV
5
7 1 2
V
6
13
VI
7
31 4 IS"
VII
8
VIM
T9
7 H216I14
SEPTAGE SYSTEM
CONTROL SYSTEM
5 15 25
APRIL
5 15 25 I 5 15 25
MAY
JUNE
5 15 25
JULY
5
AUG
Figure 6. Variation of Influent and Effluent COD
and COD: MLVSS Ratio.
21
-------
PERIOD
SEPTAGE LOAD NO.
SEPTAGE FLOW, %
o.
%
VI
7
3 | 4 |
VII
8
VIII
9 1
5 | 7 | 12 | 6 |14
0
o
O
200 -
100 -
O
SEPTAGE SYSTEM
CONTROL SYSTEM
*
Figure 7. Variation of Iififluent and Effluent TOC.
22
-------
PERIOD
SEPTAGE LOAD NO.
SEPTAGE FLOW %
1
1
2
II
2
6
3
13
III
4
IV
5
7 I 2
V
6
13
VI
7
3| 4 | 5 |
VII
8
VIII
9
7 |12|6|14
, , I , , , , , I , , , , , I ,
Figure 8. Variation of Effluent (N02 + N03)-N.
23
-------
TABLE 4. Operation of Plug Flow Activated Sludge System with Septage Addition.
Period
Septage Load No.
Time Period
MLSS-Reactor, mg/1
Volatiles, %
COD-Influent, mg/1 ,
COD:MLVSS, day"1'
Effluent, mg/1
* BOD-Influent, mg/1 ,
BOD:MLVSS, day"1
Effluent, mg/1
SS-Influent, mg/1
Effluent, mg/1
TOC-Influent, mg/1
Effluent, mg/1
(1) Average Values for 4/10-23 only.
(2) June 24, 25 and 26 only.
I
1
4/10-
4/30
4870
67.4
404
0.7
52
191(D
0.33
31
284^
25
__
II
2-3
5/01-
5/14
2800
64.8
w» ~
__
41
316
1.1
32
136
19
M
-_
III
4
5/15-
5/23
2510
71.6
557
1.8
43
415
1.4
22
252
13
«*
--
IV
5
5/24-
6/17
'1870
76.2
438
1.7
52
153
0.61
21
171
14
»
..
V
6
6/18-
6/26
2490
75.5
683
2.3
91
316
1.0
44(2)
394
27
__
__
VI
7
6/27-
7/21
2150
72.0
590
2.2
65
198
0.74
23
355
18
158
22
VII
8
7/22-
7/28
1790
75.4
730
3.2
94
282
1.3
41
480
36
208
30
VIII
9
8/02-
8/12
2300
71.3
755
2.8
83
225
0.84
19
480
24
196
30
-------
TABLE 5. Comparison of the Septage System with the Control System.
ro
01
System
Control
Septage
Control
Septage
Control
Septage
Control
Septage
Control
Septage
Control
Septage
Control
Septage
Time
Period
4/16-21
5/5-9
5/15-21
6/2-5
7/9-16
7/24-25
8/6-10
MLVSS
mg/1
2500
3600
1500
1750
1650
1900
1500
1550
1600
1650
1410
1170
1300
1900
BOD
Inf.
mg/1
113
172
123
336
111
419
102
138
130
200
124
301
106
231
Eff.
mg/1
28
22
36
33
24
24
32
18
18
25
14
43
13
18
COD
Inf.
mg/1
263
403
__
252
555
220
407
258
632
247
803
214
691
Eff.
mg/1
42
52
39
45
34
41
34
50
38
62
32
115
29
69
TOC
Inf.
mg/1
75
163
73
209
77
222
Eff.
mg/1
__
12
20
10
36
13
24
SS
Inf.
mg/1
133
281
119
170
107
264
106
117
105
305
102
460
115
479
Eff.
mg/1
37
25
29
21
17
11
15
11
14
19
11
34
6
12
Septage
Load No.
1
2-3
4
5
7
8
9
Period
I
II
III
IV
VI
VII
VIII
-------
Although the MLSS concentrations in the septage system were maintained
near 2000 mg/1 from period III to the end of the study, the SRT was
considerably less than in the control because of a greater sludge wasting
rate. For example, during period V the SRT in the septage system was
near 1 day. The Nocardia was never competitive at these low SRT values,
and therefore the effluent quality from the septage system represents a
more typical operation of the activated sludge process than does the control
system during periods I-VI.
Owing to the problems discussed above, it is.aooarent that any method
selected for presenting and analyzing the data must be somewhat arbitrary.
It was felt that the results from the septage system could best be
described by characterizing the operation of this system during eight
discrete time periods. The duration of each of these periods is shown
at the top of Figures 4 thru 8, and the average characteristics of the
septage system during these eight periods are summarized in Table 4.
Because of the highly erratic variability in the effluent suspended solids
from the control system during most of the study, it is not reasonable to
attempt to quantify any changes in effluent quality attributable to the
septage by making a direct comparison of the effluent qualities from the
septage and control systems for each of the eight periods shown. However,
by selecting relatively short periods of operation where the effluent
suspended solids concentrations from the control system were reasonably
uniform and relatively free of Nocardia organisms, it is possible to
compare the two effluent qualities in a manner which provides additional
useful information. A comparison of the two systems during seven of the
above short time periods is summarized in Table 5, and these periods are
indicated by the shaded areas in Figure 4. The particular reason for
selecting each of these seven short periods is included in the discussion
of system operation during each of the eight periods described below.
Period I
The first time period to be considered was from April 10-30. Septage addition
was initiated on April 10. During the period April 10-30, only one septage
load (load No. 1) was fed to the septage system at a constant flow rate of 2
percent of the D.C. primary effluent flow. Prior to April 10, the two parallel
systems had been operating for a period of approximately two months on primary
effluent only. When septage addition began, the MLSS concentrations in both
the septage system and in the control were considerably higher than the intend-
ed operating level of 2000 mg/1. Consequently, the waste rate in both systems
was increased to gradually reduce the reactor MLSS from 3000-4000 mg/1 to near
2000 mg.l. As shown in Figure 3, the MLSS in the control unit gradually
decreased to near 2000 mg/1 but the MLSS in the septage system increased and
remained high throughout the period averaging 4870 mg/1. This was the result
of insufficient wasting in the septage system. Examination of Figure 6-C
reveals that the average daily COD loadings (mass of daily COD/MLVSS mass of
reactor) for each of the two systems were similar although the MLSS in each
system were not equal. The average COD loading to the septage system was 0.70
g COD/g MLVSS/day and the average COD loading to the control system was 0.63 g
COD/g MLVSS/day. Over the entire period the influent COD to the septage system
averaged 404 mg/1 which was approximately 1.6 times that in the control. The
effluent COD, BOD and SS averaged 52, 31 and 25 mg/1, respectively.
26
-------
It should be noted that until clarification in the control system
improved during period VI, the BOD from the control (Figure 5-C) was
generally greater than that from the septage system (Figure 5-B). This
was due mainly to the BOD associated with the increased suspended solids
in the control effluent (Figure 4). In addition, since the control system
was nitrifying throughout the study (Figure 8), the effluent suspended
solids from the control contained nitrifying organisms which resulted in
nitrification in the BOD,- test. It is also apparent from Figure 8 that
septage addition did not prevent biological nitrification during the period
when the SRT was maintained at a sufficiently high level.
As indicated in Figures 6-C and 5-D, the COD and BOD loadings during period
I were relatively low. The performance of the septage system is compared
with the control system from April 16-21 in Table 5. Although the average
SS from the control system were higher than from the septage system, 37 mg/1
compared to 25 mg/1, the COD from the control system was less, 42 compared
with 52 mg/1. Based on this comparison, it appears that even at low loadings
there was a small increase in effluent COD attributable to the septage.
Additional laboratory analyses not shown in Table 4 revealed 10-11 mg/1
PO, in the effluent from each system, indicating that excess phosphorus
was present for biological growth.
Period II
The second period of system operation to be characterized is from May 1-14.
During this period septage loads No. 2 and No. 3 were added to the septage
system clarifier at flow rates of 6 and 13% of the influent flow of D.C.
primary effluent, respectively. Increased wasting reduced the MLSS in the
septage system during the addition of septage load No. 2 but they were
relatively stable during the addition of load No. 3. The intended influent
COD to the septage system during this period was 400-500 mg/1, but because
of sampling error with the acidified composite sample, neither the COD of the
influent nor the COD of the daily septage sample were accurately determined.
The BOD loading to the septage system averaged 1.1 g BOD/g MLVSS/day. This
was a considerable increase over period I, which averaged 0.33 g BOD/g MLVSS/
day. Although this was a substantial increase in BOD loading, the average
effluent BOD during periods I and II was essentially the same. Also, during
this period the COD and SS from the septage system averaged 41 and 19 mg/1,
respectively.
Comparison of effluent quality from the septage system with that fron the
control for the period of May 5-9(Toble 4) indicates that nearly the same
average effluent BOD and COD were obtained from both systems on the days
when the average effluent solids differed by only 8 mg/1. The systems
were both nitrifying at this time, and this is reflected in the effluent
BOD5 analysis.
Period III
The operation of the parallel activated sludge system from May 15-23 is
summarized as period III. During this period, the MLSS in both systems were
relatively stable (Figure 2) and averaged 2510 mg/1 in the septage system
27
-------
and 2110 mg/1 in the control system. Only one load of septage, load No. 4,
was added during this period. The influent COD to the septage system averaged
557 mg/1 resulting in a COD loading of 1.8 g COD/g MLVSS/day which was 2.0
times that in the control.
Although this was a relatively short period of operation, it was considered
separately because during this period the highest sustained BOD loading was
imposed on the septage system. The BOD5 loading for this period was 1.4 g
BOD/g MLVSS/day, while that in the control for the same period was only
0.4 g BOD/g MLVSS/day. During this period the effluent COD, BOD, SS from the
septage system averaged 43, 22, and 13 mg/1, respectively. As shown in
Figure 6-B, the effluent COD during this relatively short period was not
stable, and varied from roughly 20-60 mg/1.
The period May 15-21 was selected for comparing the septage system with the
control system because the effluent SS from both systems were relatively low
and stable during this time (Figures 4-C and 4-B). As shown in Table 5, there
was no difference in average effluent BODs between the two systems although
a much higher BOD loading was imposed on the septage system. It should be
kept in mind, however, that there was nitrification occuring in the BODs
tests of the control system effluent and, possibly, in the effluent from
the septage system. As in previous comparisons, a slight increase in COD
from the septage system was observed, and averaged 41 mg/1, compared to
34 mg/1 for the control system.
Period IV
Period IV covers 25 days of operation from May 24 to June 17. The reactor
MLSS in both systems were relatively stable and similar during this period
(Figure 3). The MLSS in the septage system averaged 1870 mg/1. This was
somewhat less than during the previous period, but similar to the control
system which averaged 1900 mg/1. Only one load of septage, load No. 5, was
added during this time.
The influent COD to the septage system averaged 438 mg/1. This was less than
in the previous period but the reduced MLSS level in the reactor produced a
COD loading of 1.7 g COD/g MLVSS/day. Although the COD loading was nearly
the same as the loading during Period III, the BOD loading was only 0.61 g
BOD/g MLVSS/day. In contrast, the COD and BOD loadings to the control system
at this time averaged 0.85 g COD/g MLVSS/day and 0.4 g BOD/g MLVSS/day. The
COD and BOD loadings to the control system were maintained close to these
values through the remainder of the continuous feed study.
During Period IV the septage system produced an effluent averaging 52 mg/1
COD, 21 mg/1 BOD and 14 mg/1 SS. As shown in Figure 6-B, the effluent COD
was stable except for one day where the effluent suspended solids were higher
than normal. The average effluent BOD and SS were similar to those values
in the previous period of operation (Period III) but the COD was 9 mg/1
greater.
28
-------
The period June 2-5 (Table 5) was selected for comparing the control and
septage systems because the effluent SS from the control were stable and
similar to those from the septage system during this time. The effluent COD
from the septage system was 50 mg/1 whereas that from the control was 34 mg/1.
Examination of the control system through Period IV (Figure 6-B) during times
of good clarification indicates an effluent COD which generally varied from
35-45 mg/1. Examination of the septage system through Period IV (Figure 6-B)
indicates an effluent COD of roughly 40-60 mg/1. Based on these ranges of
COD from the control and septage systems, it appears that with COD loadings
to 1.8 g COD/g MLVSS/day the effluent COD from the septage system was 10-15
mg/1 greater than from the control. During the June 2-5 period, the BOD in
the control system was greater than in the septage system, 32 mg/1 compared
to 18 mg/1, probably because of nitrification in the 6005 analysis as previous-
ly discussed. During this time period the high waste rate reduced the amount
of nitrification in the septage system considerably.
Period V
The fifth period of operation to be discussed covers the period from June 18-
26 when septage load No. 6 was added to the septage system clarifier at a rate
of 13 percent of the D.C. primary effluent flow. Because of a malfunctioning
of the automatic wasting mechanism and a sharp increase in the influent
suspended solids concentration over that observed with load No. 5, the MLSS in
the septage system increased from 1800 mg/1 on the 18th to 3500 mg/1 by the
23rd. A very high waste rate was then applied to the system and the MLSS were
reduced to 2100 mg/1 by the 26th of the month. This extreme variability makes
it unrealistic to compare the septage and control systems during this period.
The brief nine-day operating period in conjunction with the large variation
in reactor solids also makes it difficult to adequately summarize system
operation during this time. The COD loading averaged 2.3 g COD/g MLVSS/day,
and was as high as 2.6 g COD/g MLVSS/day. Other system parameters are sum-
marized in Table 4. Although the effluent COD and BOD values were somewhat
higher than normal, there was really no adverse affect on the system which can
be attributed to the septage per se. The absence of effluent BODs values
during the first six days of septage addition resulted from all oxygen being
depleted in the BOD test. These values were all in excess of 30 mg/1. Average
effluent BOD for the last three days during this period was 44 mg/1.
Period VI
Septage load No. 7 was added to the septage system clarifier during the period
of June 27-July 21 and this operation will be summarized as Period VI. Although
the septage flow was increased from 3 to 7 percent of the flow of D.C. primary
effluent during this period, there was also a general trend towards increasing
MLSS concentrations in the septage system. As a result the organic loading to
the septage system during this period exhibited a rather random variation about
the average value. The COD loading averaged 2.2 g COD/g MLVSS/day and the BOD
loading was 0.74 g BOD/g MLVSS/day.
29
-------
The process performance of the septage system was entirely satisfactory. The
influent COD was reduced from an average of 590 mg/1 to 65 mg/1. The effluent
BOD5 averaged 23 mg/1. There was some nitrification in the septage system
during much of this period and thus the BOD5 values probably also represent
some nitrogenous demand. TOC analyses were initiated at the beginning of this
period and these values are presented in Figure 7.
The effluent suspended solids from the septage and control systems were
similar and reasonably stable during the period of July 9-16, and the results
obtained from each of the two systems during this period are compared in
Table 5. The COD loading was 2.7 times greater and the BOD loading 1.7 times
greater in the septage system than in the control system. During this period
the septage feed was only varied from 4 to 5 percent of the influent flow of
D.C. primary effluent. The effluent COD from the septage system was 24 mg/1
higher and the TOC 8 mg/1 higher than the corresponding values in the control
system. The effluent BOD5 values differed by 7 mg/1. Once again the differ-
ence in effluent quality of the two systems was small.
Period VII
Period VII describes the operation from July 22-August 1 when septage load
No. 8 was added. With the exception of one day, July 24, the MLSS in the
septage system were reasonably stable for the 11 days of operation. During
the first seven days of operation, the influent COD, BOD and SS were high and
relatively stable but they decreased sharply on succeeding days because of
operational problems with the septage feed mechanism. For example, the
influent COD decreased from 600-800 mg/1 to near 400 mg/1 and the BOD
decreased from roughly 300 to 100 mg/1 by the 30th of the month. Because of
the decrease in organic concentrations, only the first seven days of the
operation with load No. 8 have been summarized in Table 4. As shown in
Figure 6-C and 5-D the daily COD and BOD loadings to the septage system
during the first seven days of operation were not uniform because of a sharp
increase in COD and BOD loadings on July 24 when the MLSS were lowest (1300
mg/1) and the influent COD was highest (890 mg/1). During the seven day
period, the influent COD, BOD, TOC and SS averaged 730, 282, 208 and 480 mg/1,
respectively. This influent COD was the highest average COD thus far in the
study. The corresponding COD and BOD loading averaged 3.2 g COD/g MLVSS/day
and 1.3 g BOD/g MLVSS/day. The day of the sharp increase in loading, July 24,
is considered in these averages, and it is emphasized that the average
effluent characteristics do not represent the results of a uniform loading.
The effluent from the septage system averaged 94 mg/1 COD, 41 mg/1 BOD,
30 mg/1 TOC and 36 mg/1 SS during this time. There were the highest average
concentrations of pollutants in the effluent thus far. The deterioration of
effluent quality appeared to be related to clarification efficiency since
there was an increase in effluent SS at this time. The poor clarification
was the result of the high organic and solids loading to the aeration system.
The influent and effluent characteristics of the septage system are compared
with those from the control during July 24-25, in Table 5. Of course, a
comparison based on 2, 24-hour composite samples can hardly be considered a
definitive evaluation, but the data are useful in showing that the septage
system responded well to a temporary very high loading. The loading on
30
-------
July 24 was about 5 g COD/g MLVSS/day and the BOD loading, 1.9 g BOD/g MLVSS/
day. The effluent quality on the 25th was somewhat worse than measured on the
24th and therefore the 2-day average was presented in Table 5. By the 29th of
the month, the effluent BOD from the septage system was only 7 mg/1 which
shows that there were no long-term effects on the septage system.
Period VIII
The operation of the septage system from August 2-12 is described as Period
VIII. As shown in Figure 2, the MLSS were unstable during this period varying
from near 1800 mg/1 during the beginning of the period to as high as 2900 mg/1.
The average MLSS for the period were 2300 mg/1. Because of the variation in
MLSS and influent COD, the daily COD loadings to the septage system were
erratic during this period (Figure 6-C). The effluent characteristics are not
typical of operation with a uniform COD loading.
Although the COD loading to the septage system was similar to that maintained
during operation with septage load No. 8, the BOD loading only averaged 0.84 g
BODc/g MLVSS/day. The effluent quality was very good with a carbonaceous
effluent BOD5 of just 19 mg/1 and average effluent suspended solids of 24 mg/1.
The effluent quality from the septage system is compared with that from the
control system from August 6-10 in Table 5. During this time the effluent SS
from both systems were relatively stable and similar (Figures 4-B and 4-C).
The effluent quality from the control system was similar to that in the
previous period with load No. 8. During both septage loads No. 8 and No. 9,
the control system operated well with steady MLSS concentrations in the
reactor and an average SVI of 110. Fluctuations in effluent SS were minor and
clarification was good. Operating with an average influent COD of 691 mg/1
during the 5 days of comparison, the septage system produced an effluent with
a COD 40 mg/1 greater than the control, a BODs only 5 mg/1 greater, a TOC
11 mg/1 greater and SS only 6 mg/1 greater.
31
-------
SECTION IX
SHOCK LOAD STUDIES
Since the continuous flow studies did not indicate any significant problems
with septage addition to an acclimated system, several shock load studies
were performed to assess the potential impact on an unacclimated system.
Both batch aeration tests and the 7500 I/day (1980 gpd) pilot plant system
were used in these evaluations.
Batch Aeration Test - Procedure and Results
The experimental procedure for each batch aeration test was as follows.
Approximately 150 1 (40 gal) of septage were placed in a 190 1 (50 gal) drum,
mixed, and sampled for laboratory analysis. The contents of the drum were
then allowed to settle under quiescent conditions for a period of one hour.
Next, the top third of the settled septage was siphoned off and different
volumes of the siphoned septage were added to 38 1 (10 gal) containers.
Primary effluent was also added to each of the containers to produce a total
liquid volume of 30 1 (8 gal). The contents of each container were then mixed
and samples were withdrawn for laboratory analysis. The liquid volume was
then adjusted to 27 1 (7 gal).
For each test a total of six containers was used. One of the containers
received only primary effluent and served as a control. The other five
containers contained varying ratios of septage to primary effluent.
o
Approximately 8 1 (2 gal) of recycle solids from a 189 m /day (50,000 gpd)
plug flow activated sludge system operating at a 3-4 day SRT and treating
D.C. primary effluent were added to each of the six containers. The D.O.
was then quickly adjusted to between 2-5 mg/1 by throttling the air line to
each container and maintained within this range. Mixed liquor samples were
withdrawn from each of the drums after 0.5, 2.0, 4.0 and 24 hours. The
samples were settled in a two-liter graduate cylinder for 30 minutes and
then approximately 1300 ml of the clarified supernatant were siphoned off
for laboratory analysis. Supernatant samples taken for soluble COD analysis
were filtered immediately through a Reeve Angel-Grade 934 AH glass fiber
filter. TOC analysis was performed on the same day each sample was taken.
Samples which were stored overnight were refrigerated at 3°C.
Three separate batch aeration tests were performed. A different source of
septage was used for each test. The septage characteristics are presented
in Tables 1 and 2 (Load Nos. 10, 11 and 12). It can be seen that each of
the septage loads was considerably different. Load No. 10 was the strongest
32
-------
organic load encountered both in terms of COD and BOD. Load No. 11 had a
typical COD value, but was the weakest load encountered with respect to BOD.
This septaqe had the highest COD to BOD ratio. Load No. 12 had the lowest
COD value of any septage investigated, but the COD to BOD ratio was typical
of several other septage loads.
Characteristics of the primary effluent-settled septage mixture used in the
batch shock load studies are presented in Table 6. During the studies with
load Nos. 10 and 12, the maximum COD of the mixture was near 2400 mg/1
(approximately ten times that of D.C. primary effluent). However during the
addition of load No. 11, the maximum COD was only 915 mg/1. The reduction
in organic strength with load Mo. 11 was the result of much better solids
removal than anticipated during the one-hour septage settling period. With
load Nos. 10 and 12, only 10-15% of the solids were removed during settling
but during load No. 11 nearly 90% of the solids were removed.
The organic loading to each batch activated sludge unit was calculated in
terms of the COD: MLVSS, BOD: MLVSS and TOC: MLVSS ratios. In all cases the
MLVSS concentrations measured in the control unit were used in these calcu-
lations. This was done because the increased reactor MLVSS indicated in
Table 6 resulted from solids which were introduced by the septage as the
percent of septage was increased. The calculated loading represents an
instantaneous loading and was determined as follows:
V
(vs + vp
where;
L = organic loading (COD, BOD or TOC)
V = volume of septage
V = volume of primary
V = volume of recycle
C . = concentration of septage-primary mixture
X = VSS concentration in the control unit
C
The effect of organic loading on effluent quality for the various loads of
septage at aeration times at 0.5, 2, 4 and 24 hours is shown in Figures 9,
10 and 11. Unless otherwise noted, the values plotted for the least organic
loading represent the results from the control units where no septage was
added. Also the effluent COD values and soluble COD values obtained during
the studies with load Nos. 10, 11 and 12 are shown in Figures 12, 13 and 14,
respectively. The initial values shown were calculated as follows:
33
-------
TABLE 6. Characteristics of Primary Effluent-Septage Mixtures and
Reactor Solids Concentrations used in Batch Shock Loads.
00
Septage
%
Load No. 10
0.0 (Control)
0.7
2.1
3.4
4.8
6.7
Load No. 11
0..0 (Control)
4.4
14.5
26.8
42.0
61.3
Load No. 12
0.0 (Control)
5.3
19.1
36.4
59.7
92.7
COD
mg/1
161
428
981
1330
1880
2390
191
279
434
582
786
915
297
480
892
1370
1810
2390
TOC
mg/1
84
175
283
375
556
693
75
108
139
197
247
309
90
151
258
400
460
640
BOD
mg/1
73
205
550
666
982
1220
80
95
96
110
110
120
144
215
408
625
777
1050
SS
mg/1
94
184
400
730
850
800
122
128
180
290
370
450
162
244
380
570
740
770
Reactor Solids
MLSS
mg/1
1460
1490
1680
1730
1710
2070
1360
1290
1480
1550
1610
1680
1520
1520
1540
1740
1860
1880
MLVSS
mg/1
1100
1100
1250
1330
1300
1630
1070
1030
1190
1220
1270
1360
1300
1280
1320
1460
1620
1560
-------
1200
1000
^ 800
O
S 600
o
O
400
200
0
0.5 HRS
© LOAD NO. 10
LOAD NO. 11
A LOAD NO. 12
2 HRS
oo
en
500
^ 400
O
.. 300
Q
O
u
200
100
4 HRS
(817 MG/L)
0 .2 .4 .6 .8 1-0 1.2 1.4 1.6 1.8
COD: AALVSS RATIO
24 HRS
I i i i
0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8
COD: MLVSS RATIO
Figure 9. Effect of Loading On Effluent COD at Various
Aeration Times and Septage Loads.
-------
CO
0 LOAD NU. IU
LOAD NO. 11 ,
A LOAD NO 12 (BOD OF CONTROL IS NOT SHOWN FOR 0.5 AND
2 HR AERATION TIME)
.3 .4 .5 .6
BOD: MLVSS RATIO
.1 .2
.3 .4 .5 .6
BOD: MLVSS RATIO
.7 .8 1.0
Figure 10. Effect of Loading On Effluent BOD at Various
Aeration Times and Septage Loads.
-------
300
O
u
O
200
100
00
120
100
80
60
40
20
0
u
0.5 HRS
O LOAD NO. 10 LOAD NO. 11 A LOAD NO. 12
2 HRS
4 HRS
I i
i I I I
24 HRS
i i
.2 .3
TOC: MLVSS
.2 .3
TOC: MLVSS
.4 .5
Figure 11. Effect of Loading on Effluent TOC at Various Aeration Times
and Septage Loads.
-------
0 6.7% SEPT AGE
A 4.8% SEPT AGE
a 2.1% SEPTAGE
CO
00
1800
1600
1400
O 1200
5
g 1000
u
55 80°
8 600 y
400
200
O 6.7% SEPTAGE
A 4.8% SEPTAGE
e 2.1% SEPTAGE
8 12 16
TIME, HOURS
8 12 16 20
TIME, HOURS
Figure 12. COD Reduction for Various Mixtures of Septage
and Primary Effluent, Septage Load No. 10.
-------
800
700
600
^ 500
O ^
400
6
O
O
CO
300
200
100
O 61.3% SEPTAGE
A 26.8% SEPTAGE
O 14.5% SEPTAGE
O 61.3% SEPTAGE
A 26.8% SEPTAGE
O 14.5% SEPTAGE
8 12 16
TIME, HOURS
20 24
8 12 16
TIME, HOURS
20 24
Figure 13. COD Reduction for Various Mixtures of Septage
and Primary Effluent, Septage Load No. 11.
-------
O
A
92.7% SEPTAGE
59.7% SEPTAGE
36.4% SEPTAGE
19.1% SEPTAGE
V 5.3% SEPTAGE
Q CONTROL UNIT
O
a
8
1600
1400
1200
1000
800
~, 600
8 12 16
TIME,HOURS
20 24
O 92.7% SEPTAGE
A 59.7% SEPTAGE
^ 36.4% SEPTAGE
O 19.1% SEPTAGE
V 5.3% SEPTAGE
Q CONTROL UNIT
8 12 16 20
TIME.HOURS
Figure 14. COD Reduction for Various Mixtures of Septage
and Primary Effluent, Septage Load No. 12.
-------
(V, + V ) (C )
Initial Organic Concentration = -n+ vp + v p
s p r
The effluent SS concentrations of the clarified effluent samples are presented
in Table 7. The calculated initial BODs concentrations and the effluent BOD5
concentrations are presented in Table 8. Since each load of septage has its
own unique characteristics, the results from each test need to be considered
in relation to these characteristics.
As shown in Table 1, septage load No. 10 was quite high in COD and BOD. A
significant portion of the organic material was in soluble form. The
suspended solids fraction was not high when considered in relation to the
other septage loads which were examined.
Septage removal from all units shocked with the settled "supernatant" from
load No. 10 was extremely rapid. As shown in Figure 12, the soluble component
was readily removed along with the non-settleable suspended organic material
present in the septage "supernatant." The use of settled septage was intended
to maximize the removal of the suspended organic materials as a result of
sorption/degradation reactions with the mixed liquor biomass. Only the results
of three shock load studies are shown in Figure 12 for clarity. The perform-
ance of all five shock systems can be compared to the control unit in Figures
9-11. The effect of the shock loads on the effluent suspended solids con-
centrations is shown in Table 7. This study clearly showed that most of the
septage "supernatant" from septage load No. 10 was readily removed by an
unacclimated culture. Most of the soluble material was assimilated quite
rapidly as shown in Figure 12. A small component of the soluble material was
resistant to rapid degradation, however, and the differences in soluble COD
values between the control and shocked units after 24 hours were 2.8, 11.0,
13.0, 20.8 and 30.6 mg/1. These concentrations correspond to the increased
amount of septage addition. An acceptable "effluent" quality (30 SS and
30 6005) was obtained with 0.7% septage after 2 hours, with 2.1% septage after
4 hours, and with all septage loadings after 24 hours.
Examination of Table 1 shows that septage load No. 11 contained a large
percentage of chemically oxidizable organic matter which was resistant to
biodegradation as measured by the BODc analysis. Most of the chemically
oxidizable material was associated with the suspended solids and most of this
material was removed in the one-hour settling period prior to mixing the
septage "supernatant" with primary effluent. The results of the shock load
studies with the settled septage from load No. 11 are presented in Figures 9-
11 and Figure 13. Even at the highest loading the initial COD was only 915
mg/1 which was barely 4 times the value in the control. Once again both the
nonsettleable suspended organic and soluble COD in the septage-sewage mixture
were rapidly removed from the shocked units. After two hours of aeration an
acceptable effluent quality was obtained from the units receiving up to 26.8%
septage. Within four hours all units produced an effluent of acceptable
quality. After 24 hours the difference in soluble COD between the units
receiving 4.4% septage and 61.3% septage was only 14 mg/1.
41
-------
TABLE 7. Suspended Solids Concentrations of Clarified Effluents
from Batch Aeration Studies.
Load No. 10
Load No. 11
Load No. 12
O.W
94
184
400
730
850
800
122
128
180
290
370
450
162
244
380
570
740
770
Aeration
0.5
12
26
48
108
170
260
24
28
55
56
74
104
39
62
184
260
340
990
Time,
2.0
11
16
30
72
104
150
11
11
14
24
32
42
26
33
73
162
200
320
Hrs.
4.0
10
14
11
52
86
128
7
9
10
14
14
23
11
20
38
54
132
308
24.0
13
11
7
11
13
21
6
10
11
11
13
12
13
9
28
54
166
Settled
Septage
%
0.0
0.7
2.1
3.4
4.8
6.7
0.0
4.4
14.5
26.8
42.0
61.3
0.0
5.3
19.1
36.4
59.7
92.7
(1) Initial Value of Primary Eff1uent-Septage Mixture. All
concentrations are given in mg/1.
42
-------
TABLE 8. Initial BOD,- Concentrations and BOD5 Concentrations of
Clarified Effluents from Batch Aeration Studies.
BOD Concentrations, mg/1
Load No. 10
Load No. 11
Load No. 12
Aeration Time, Mrs.
0.0
57*
160*
428*
519*
765*
953*
62*
74*
75*
86*
86*
93*
115*
171*
324*
497*
620*
830*
0.5
27.1
36.7
74
129
247
404
22.4
30.2
41.5
67
65
83
> 44
91
197
340
466
830
2.0
19.8
18.5
43
90
129
209
11.3
10.2
14.8
26.4
30.4
36.7
> 36
44.5
175
258
468
4.0
11.6
11.8
22.1
87
93
89
10.9
12.8
9.4
8.9
9.6
19.0
15.4
22.6
48.8
97
163
376
24.0
7.5
6.9
5.9
10.1
10.6
18.4
11.6
12.0
11.5
12.6
13.2
13.0
17.9
18.8
25.6
30.2
84
202
Settled
Septage
%
0.0
0.7
2.1
3.4
4.8
6.7
0.0
4.4
14.5
26.8
42.0
61.3
0.0
5.3
19.1
36.4
59.7
92.7
Calculated Initial Concentrations
43
-------
Septage load No. 12 had the lowest COD of any load characterized, but the COD
to BOD ratio indicated that much of the material was biologically degradable.
The ratio of COD to suspended solids was the highest of any load investigated.
Results of the shock load studies with the settled septage from load No. 12
are presented in Figures 9-11 and in Figure 14. It can be seen that the
residual COD, BOD or TOC was higher at any given loading and time than was
the case for the shock loading with loads Nos. 10 and 11. The reasons for
this are two-fold. First, the soluble COD fraction consisted of a component
which was fairly difficult to degrade. As indicated in Figure 14, the
residual soluble COD after 24 hours increased in each unit in proportion to
the percentage of septage present. The difference between the control unit
and the unit receiving 92.7% septage was 153 mg/1 of soluble COD after the
24 hour period. By comparison, the soluble residuals with the units shocked
with septage load No. 10 were quite similar after 24 hours, even in the
system with a higher initial soluble COD content than present with load No. 12.
Also, load No. 12 contained a non-settleable suspended COD fraction which was
more resistant to degradation/sorption than the other loads. This is apparent
when comparing the soluble and total "effluent" COD values in Figure 14 as
well as the clarified suspended solids concentrations shown in Table 7.
Although the "effluent" residuals were higher than encountered with the other
two shock load studies, there was no indication of any inhibition or toxicity
with the unacclimated activated sludge system.
Pilot Plant Shock Loadings - Procedure and Results
The three batch aeration tests indicated that an unacclimated activated sludge
system treating domestic wastewater could readily accept shock loadings of
septage without any apparent long-term deleterious effects. The temporary
affect on effluent quality was obviously dependent on loading, septage
characteristics, etc.
To further evaluate the transient response of an activated sludge system
receiving a shock load of septage as well as to evaluate any possible longer
term effects on effluent quality, two additional shock load studies were
performed on the previously described parallel activated sludge systems
(Section V). Prior to these shock load studies, both parallel systems were
operated on a feed of just D.C. primary effluent for a period of 2.0 months.
The flow rates to the systems were the same during this time period 7500 I/day
(1980 gpd) and the MLSS were maintained as close to the same level as possible,
The procedure for these shock load studies was as follows:
(1) Septage and primary effluent were mixed in a 1140 1
(300 gal) drum and then allowed to settle quiescently
for a period of one hour.
(2) Approximately 757 1 (200 gal) of the settled mixture
was carefully siphoned into a separate tank where it
was continually mixed.
44
-------
(3) This mixture was used to shock load one of the two
parallel activated sludge systems for a period of
one hour duration. During this period the normal
flow of D.C. primary effluent was applied to the
control unit only.
(4) The flow rate of the mixture of septage and primary
effluent was maintained identical to that of the
control unit, 5200 ml/min.
(5) The recycle rate in both activated sludge units was
50% of the influent flow. The hydraulic retention time
in each unit including recycle flow was approximately
3 hours.
(6) After one hour the shock load was discontinued and the
flow of the primary effluent returned to the shocked
system.
The influent to both the control and shocked systems was sampled two hours
prior to the addition of the shock load. During each study, the shock began
near 0930 hours. After initiating the shock, both systems were sampled
intensively. After the intensive grab sampling, additional effluent samples
were collected from each of the two systems and composited for various time
periods. The compositing period varied with each study and the exact schedule
is presented in Table 9. Grab samples collected on the day of the shock load
were stored at 3°C and all laboratory analyses except for TOC were performed
the following day. The TOC concentration of samples taken before 1630 hours
on the day of the shock load study was determined immediately. Samples col-
lected for TOC after this time were analyzed the following day. No acid was
added to the grab samples. The composite samples were treated as in the
continuous feed study.
Septage load Nos. 13 and 14 (Table 1 and 2) were used to prepare the mixtures
of primary effluent and septage for the shock load studies in the pilot
system. The two septage loads were similar with a COD near 12,000 mg/1 and
a TOC near 3500 mg/1,.
The septage-sewage mixture consisted of 20% septage with load No. 13 and 50%
septage with load No. 14. The characteristics of the influent fed to each of
the pilot activated sludge units during both shock load studies are summarized
in Table 10.
The first shock load study was conducted with septage load No. 13. As shown
in Table 10, the influent COD to the shocked system was approximately 3 times
that applied in the control unit. The one-hour shock loading was equivalent
to a loading of 3.5 g COD/g MLVSS/day. This increase was almost entirely
attributable to non-settleable suspended material since the increased soluble
COD of the sewage-septage mixture was only 37 mg/1 higher than in the primary
effluent alone. Since the unsettled mixture can be calculated to have a COD
of about 2,800 mg/1, the measured influent COD of 790 mg/1 represents a COD
45
-------
TABLE 9. Effluent Quality Following Addition of Shock Loads
to the Pilot Activated Sludge System.
CT>
Time
After Shock
Load No. 13
8. 5-20.5^
20.5-44.5^
44.5-68. 5^
Load No. 14
11.3
14.3
17.3
20.3-44.3^
44.3-68.3^
80.3
104.3
SS
mg/1
22
18
34
54
73
43
30
31
75
35
Shocked
COD
mg/1
40.4
35.9
35.5
93.9
95.5
83.5
63.4
65.6
87.2
__
System
TOC
mg/1
14
14
13
32.5
32.8
27.5
20.2 .
33.0
21.0
Control
BOD
mg/1
25
27
23
40.7
45.5
32.1
29.5
36.9
23.3
SS
mg/1
__
23
10
35
42
36
40
33
27
40
COD
mg/1
36.4
30.8
66.6
89.6
65.9
61.1
49.3
63.2
59.7
TOC
mg/1
12
15
11
26.2
27.8
23.5
20.0
16.0
21.0
21.0
BOD
mg/1
22
30
18
30.7
40.1
30.9
37.0
33.6
22.7
--
(1) Represents composite sample of 4-hour grab samples taken between times indicated.
-------
TABLE 10.
Characteristics of Influents to Parallel Activated Sludge Systems
During Shock Loads.
Shocked System
Control System
Time
Hrs.
Septage
-2U)
0.5<2>
x(2)
2
4
6
Septage
_2uJ
0.5(2)
1(2)
2
4
6
SS
mg/1
Load No. 13
128
640
590*
670
92
102
94
Load No. 14
228
2,100
2,060
2,080
164
128
124
COD
mg/1
230
791
788
791
191
215
267
346
3,110
3,080
3,050
264
236
242
TOC
mg/1
75
225
220
230
61
67
86
116
880
824
884
84
83
84
BOD
mg/1
104
131
133
132
85
86
136
116
571
501
114
108
113
SS
mg/1
128
112
--
92
102
94
228
190
164
128
124
COD
mg/1
230
216
--
191
215
267
346
307
264
236
242
TOC
mg/1
75
65
--
61
67
86
116
98
84
83
84
BOD
mg/1
104
92
--
85
86
136
116
141
114
108
113
(1) Shock load added at time "0".
shock load was applied.
(2) Shock Load Applied.
A '-2" designation indicates samples taken 2 hours before the
-------
removal of almost 75 percent during settling. This very high removal cannot
normally be expected in a conventional primary sedimentation tank, especially
in view of only 20-45% COD removal in the primary during the continuous
addition studies. The increase in BOD applied to the shocked system was only
about 40 rng/1 over that applied to the control unit.
The response of the shocked and control systems is indicated in Figure 15 and
Table 9. The reactor MLSS concentrations shown in Figure 15 represent the
average of the values obtained from the first and fourth drum in the respec-
tive systems at the times indicated. The sampling times and locations
essentially avoided including the suspended solids contributed from the
septage-sewage mixture. The effluent samples were obtained from the clarifier
overflow. It is apparent that the shock loading.had no measurable impact on
the product quality as the septage component moved through the reactor and
into the final effluent. Furthermore there were no longer-term effects on
effluent quality as indicated by the similarity of the three composite samples
from the shocked system in relation to the results obtained from the control
system (Table 9).
The second shock load study was conducted 30 days after the first study.
During this interim period the previously shocked unit was fed primary
effluent only. The strength of the settled septage-sewage mixture in the
second study was considerably higher than in the previous investigation. The
COD was about 3100 mg/1 with a soluble COD of 320 mg/1. The average BOD was
536 mg/1. Suspended solids were approximately 2100 mg/1. The impact of the
shock loading (equivalent to a one-hour loading of 8 g COD/g MLVSS/day) is
summarized in Figures 16 and 17 and Table 9. There was a noticeable break-
through of organic material in the shocked system. Approximately 4.5 hours
after applying the shock load, the effluent COD, BOD and TOC reached peak
values of 302, 81 and 95 mg/1, respectively. Most of this material was
associated with colloidal and suspended particulates. This is apparent by
examining the differences in the soluble and total COD in the effluent from
the shocked and control units as well as by the large rise in effluent
suspended solids in the shocked unit (Figure 16). Visual examination of the
clarified effluent from the shocked unit during the period of breakthrough
revealed that it was very "murky" and "dirty". Once the rather severe shock
load passed through the system, the effluent quality rapidly returned to
normal. As indicated in Table 9, there were no apparent delayed effects on
the effluent quality from the shock-loaded system, with the possible exception
of a slightly higher COD concentration.
Samples of mixed liquor were periodically withdrawn during the second shock
load study and the oxygen uptake rates were measured with a Model 1010
Delta Scientific dissolved oxygen meter in a stirred BOD bottle. The results
are presented in Table 11. There was no indication of any toxic effects or
inhibition in the shocked unit. The number of measurements is insufficient
to carefully compare the oxygen uptake rates in the two systems, but, there
are certainly no noticeable large differences in oxygen demand. This would
indicate that a substantial part of the shock load was apparently either
adsorbed onto the floe and/or converted into cellular storage products.
48
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o
30
20
10
0
©--r - - H*IM: --«--©.
jit-'. ' '' ': A
*-'.''. \
A
~GK*^ 2^^*^^"
A__ &£ Q
l.l.i
O
Q
o
m
3000i-
O
, 2000
to
to
1000
-2
2 4
TIME, HOURS
Figure 15. Effect of Shock!oad to the Pilot Activated Sludge Unit
Using Septage Load No. 13.
49
-------
EFFLUENT QUALITY
SS
o
CO
CO
160
120
80
40
0
LOAD
- APPLIED /
AA CONTROL SYSTEM
OO SEPTAGE SYSTEM
4UU
300
\
O
S- 200
O
O
u
100
<
i
0
COD
A A CONTROL
V *7 CONTROL
Q O O SEPTAGE S
r \ B-0 SEPTAGE I
I \
i \
1 $
A \
/ \
I \
I &
i ^
tm i \
m 1
: :. ::_ Q Q^
li / ""^^^
^-^&T jzjur^-v
H SOLUBLE COD 37
;S;: T^jp-S?^^* SOLUBLE COD
|:S i 1 1 1 1 1 1 1 1 1
.2
6 8 10 12 14 16 18
TIME,HOURS
Figure 16. Effect of Shockload On Effluent Suspended Solids
and COD Using Septage Load No. 14.
50
-------
EFFLUENT QUALITY
O
5
O
Q
O
CD
100
80
60
40
TOC
©
SHOCK ,
LOAD ' ^
APPLIED <£ v
M / ^
i
A CONTROL SYSTEM
© SEPTAGE SYSTEM
\
^
20^
0
100
80
-------
TABLE 11. Oxygen Uptake Values
in the Control and Shocked System
(Septage Load 14)
Time Pass No. 1 Pass No. 4 Pass No. 7
After Shock mg02/l/hr mg02/l/hr ingCL/l/hr
Mrs. Control Shock Control Shock Control Shock
0 70 74
0.3 58 52
0.4 -- - - - - 21
0.5 ~ 80
0.6 - -- -- -- 32
0.9 -- 77
1.8 91 87
!.g - - 67 69
2.3 ._ __ .. 37
3.0 .. _. 56 31
4<1 _. _. - 44 - 30
4.5 _. ._ - 30
5.0 - -- - " 21 29
52
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SECTION X
DISCUSSION
Although the septage used in these studies was obtained entirely from domestic
sources, the composition varied considerably from load to load. The organic
concentrations were quite variable as were the ratios of BOD/COD/SS. For
example, the COD of load No. 10 was approximately 7 times that of load No. 12
and the COD/BOD ratio of load No. 11 was 3 times that of load No. 6 (Table 1).
This variability has been observed by others (7, 8) and is basically what
would be expected. The large variation in COD/BOD ratio is an indication of
the difference in the degree of stabilization of each septage load. Some
loads, such as Load No. 11, contained a lot of organic material which was well
stabilized while in other loads, such as load No. 6, a substantial portion of
the organic material was more readily degradable.
As shown in Table 1, all loads were sufficiently high in nitrogen and phospho-
rus for biological growth. Therefore, there was no need to be concerned about
nutrient deficiency as a possible cause for impairment of the biological
processes. In addition, the concentrations .of heavy metals also varied
considerably from load to load (Table 2) but at no time were any results
obtained which suggested toxicity or inhibition of the activated sludge process.
Septage was fed on a continuous basis over a four month period without any
significant problems related to the performance of the activated sludge system.
The organic load to the activated sludge process receiving septage was
controlled by changing the COD concentration of the influent septage-sewage
mixture. The influent COD ranged from an average of 404 mg/1 during Period I
to 755 mg/1 during Period VIII. These values are approximately 1.6 and 3.6
times that of D.C. primary effluent, respectively.
By gradually increasing the influent COD, relatively uniform COD loadings
were obtained at 0.7 (Period I), 1.7-1.8 (Periods III-IV) and 2.2-2.3 (Periods
(Periods V-VI) g COD/g MLVSS/day. These loadings were approximately 1.1, 2.0
and 2.8 times those in the control unit. Higher loadings of 3.2-2.8 g COD/g
MLVSS/day were obtained during Periods VII-VIII. These loadings were 3.3 and
4.0 times those in the control, but they were non-uniform.
The increase in effluent COD above that from the control during periods when
the COD loading was equal to or twice that in the control was roughly 10-15
mg/1. At higher loadings the increase was 20-80 mg/1 greater than the control
depending on the characteristics of the particular load of septage. To
illustrate the role of septage characteristics on effluent COD, the perform-
ance during Periods V and VI can be compared. The COD loadings, in terms of
g COD/g MLVSS/day, were nearly the same and were roughly 2.8 times the control,
but in Period V the effluent COD averaged 91 mg/1 while in Period VI the
53
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effluent COD averaged 65 mg/1 for a difference of 26 mg/1.
The increase in effluent COD with increasing COD loading may not represent a
serious deterioration in effluent quality since there was not a corresponding
increase in biologically oxidizable material (as measured by the BODc
analysis). Considering the nature of septage, it is not surprising that the
effluent COD values were higher than the control system since one would expect
the presence of some stabilized material in septage which was quite resistant
to further degradation. Therefore, it appears that 6005 is probably the best
indicator of the strength of a load of septage and its probable effects on the
effluent quality.
Throughout the study, as the effluent COD increased, there was no
sustained increase in effluent BOD. It is difficult to compare the
effluent BOD from the control and septage systems because most of the
time the control system nitrified and the septage system did not. There
was also the difficulty with the high effluent suspended solids concen-
trations occurring in the control system effluent during periods when
Nocardia covered the final clarifiers and influenced the effluent total
BOD values. Both systems were nitrifying to nearly the same degree during
the addition of septage loads Nos. 1-4 (Figure 8). The effluent BOD
values in Table 5, corresponding to the periods when these loads were added,
were not significantly different. With two septage loads (Nos. 6 and 8),
there was a slight increase in effluent BOD above 40 mg/1 (Figure 5B).
The influent BOD was near 300 mg/1 during this time. The increase in
effluent BOD, however, was probably related to the nature of the septage
and not excessive BOD loading, since with similarly high loadings during
periods II and III, the effluent BOD was only 32 and 22 mg/1, respectively.
During the continuous feed study the wastewater temperatures varied from
around 18 C during the addition of load No. 1 to around 26 C during July and
August. As shown in Table 12, the SVI tended to be higher in both systems
during operation at the colder temperatures. Overall, there was no notice-
able impact one way or the other regarding the effect of septage addition
on process SVI.
Similarly there is no indication that septage addition inhibited nitrification.
The effluent (N02 + NOs)-N levels shown in Figure 8 differed for the two
systems because the SRT in the septage system was less than in the control
during the latter part of the study. For instance, in Periods V, VII and VIII
the SRT was 0.7-1.0 days compared to 3-4 days for the control system. Poduska
(9) summarized the results of several studies on the growth rate of nitrifying
organisms and showed that at these lower SRT's nitrification is limited.
Therefore the lack of nitrification can not be attributed to the characteristics
of the septage. Septage addition does not necessarily require SRT's below the
range for nitrification since the system could be operated with higher MLSS to
increase the SRT. During Period I when the MLSS in the septage system were
high and the loadings to both systems were similar the effluent (N0£ + NOaJ-N
concentrations were quite comparable. Prior to Period V sludge production
data were not available because of improper sampling of the waste sludge.
During Periods V, VII and VIII the solids production was 1.6-1.7 g SS/g BOD5
applied. During Period VI a higher value of 2.0 g SS/g BOD5 applied was
obtained. These sludge production values correspond to SRT's of 0.7-1.0 days.
Figure 8 indicates that during Period VI nitrification was occurring; therefore,
54
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TABLE 12. Average SVI for the Control and Septage Systems
During the Continuous Feed Study.
Period SVI, ml/gm
Control System Septage System
4/10-4/30
5/01-5/14
5/15-5/23
5/24-6/17
6/18-6/26
6/27-7/21
7/22-7/28
8/02-8/12
130
185
190
95
95
85
100
115
140
145
155
160
130
85
80
75
55
-------
based on Poduska's summary of data (9) it is questionable that an SRT of 1.0
day is accurate for this period. The SRT was probably/-* 2 days. Because of
this apparent error in SRT the high sludge production value for Period VI
(2.0 g SS/g 8005) is questionable. These sludge production values obviously
do not represent long term operation with steady state wasting. The solids
production from the control system was 0.85 g SS/g BOD5 applied.
On the basis of solids production per mass of BOD applied the sludge production
values from the septage system are approximately twice those which are
expected from a conventional biological system treating domestic sewage and
operating with a similar SRT. This is the result of a large fraction of inert
solids in the influent to the septage system. The BOD/SS ratio in the control
system averaged 1.0 g BOD/g SS while that in the septage system (Periods V-
VIII) was 0.5-0.8 g BOD/g SS.
Since the sludge production values from the septage system were so high, the
results from the septage system were compared with the results from conven-
tional systems where the influent SS were also considered. Sludge production
was calculated on the basis of mass of (BOD + SS) applied based on the
following relationship (10):
1 0.6 (BOD + SS) -0.075
SRT Xt
where X is the MLSS concentration and t is the hydraulic detention time. The
sludge production values from both the septage system and the control are in
good agreement with the results of others (10). Therefore the sludge production
values observed do not seem unreasonable.
The effect of primary clarification as a means of protecting the plug-flow
activated sludge system was not investigated. However, removals of SS varied
from 55 to 65 percent in the primary clarifier, which is about what would
normally be expected. Removals of BOD, however, were only about 15 to 25
percent. This might suggest that heavier inorganic solids were preferentially
removed in the primary settler. In any event, it is reasonable to suggest
that primary clarification provides significant protection for the activated
sludge system when septage is added ahead of this unit. However, the
additional primary sludge along with the increased waste activated sludge due
to increased loading constitute a significant additional burden on the sludge
handling facilities of a treatment plant.
The shock load studies yielded little evidence of toxicity or any lasting
affect on an unacclimated sludge process as a result of a transient septage
loading. Much of the soluble and non-settleable organic material was very
readily adsorbed/metabolized. The exact response depended on the character-
istics of the particular load of septage. For example, with septage loads
No. 10 and No. 11 most of the soluble and non-settleable suspended fraction of
COD was removed after 24 hours aeration, but with load No. 12 a portion
remained after this time. Furthermore, the portion remaining was proportional
to the septage concentration. Even when the activated sludge process was
56
-------
severly shocked, such that sufficient aeration time was not available for
satisfactory removals, the process returned to normal in less than 18 hours
after the shock loading commenced.
The results obtained here are not consistent with the numerous stories and
rumors of septage addition "wiping out a plant." Many operators, however,
feel that this is the inevitable result of septage addition, and the accept-
ance of septage loads is a controversial issue in many locations. The results
obtained here do not indicate that reasonable septage addition need be a
problem provided that: (a) the septage does not contain any industrial waste
which contains toxic or unusual materials, and (b) the plant has adequate
aeration, settling and sludge handling capacity to handle the increased load.
In most small plants, facilities are not available for adding septage based
on organic (BOD or COD) loading. This would require laboratory facilities
for analyzing the septage and several completely mixed storage tanks: one to
handle the incoming septage, at least one to hold full loads of septage while
strength is being determined, and one to hold septage being added to the
system. Since such arrangements are not practical for small treatment plants,
the next best arrangement would be an adequately sized and designed receiving
station with flexible pumping capabilities for controlling the rate and point
of septage addition. On the basis of this study a plant which includes primary
clarification may even accept some random septage loads if sufficient aeration,
settling and sludge handling capability exist. Since the small plant operator
has limited capability for laboratory assessment of septage strength, his most
logical method for controlling septage loading within the capabilities of his
plant is by determining maximum allowable flow (continuous) of septage or a
maximum number of septage loads per unit time.
This study indicates that if sufficient oxygenation and sludge handling
capacities are available and control of the waste MLSS is possible, the
activated sludge system can accept significant septage flows. Based on the
results of this study an activated sludge plant with 4-hours of aeration time
preceded by a primary clarifier can accept a COD loading of up to 3 g COD/g
MLVSS/day to the activated sludge unit. One way such a value can be used is
by picking the strongest load and converting this to a hydraulic loading from
the receiving station. For example consider a hypothetical case where a
MLVSS of 2000 mg/1 is to be maintained and the strongest load of septage is
similar to septage load No. 1. The potential maximum septage pumping rate
from the receiving station to the head of the plant can be calculated as
follows:
COD (CODW)QW+(CODS)QS
MLVSS (MLVSS) V
where: Q = flow, in 1/d
V = volume of aerator, in 1
w = subscript for wastewater
s = subscript of septage
57
-------
It is obvious that no credit is given to septage COD removal in the primary
clarifier in order to provide a sufficient factor of safety. Additional
assumptions are that the plant wastewater influent flow is 22 1/s (0.5 mgd),
and primary clarifier effluent (no septage), has a COD concentration of about
250 mg/1. Therefore, Qs can be approximated by:
. = (250) (22) (1440) (60) + (22,800) Qs
J (2000) (22) (14,400)
and
n 19 x IP8 - 4.75 x IP8
gs 2.28 x 10^
Qs = 62,500 1/d (16,500 gpd)
This septage flow is equivalent to about 3.3 percent of the average daily
flow and assumes that aeration capacity, sludge handling capacity and mixed
liquor solids control are sufficient to handle the additional loading.
Since contact stabilization (^ 0.5-hr, aeration) and extended aeration
(^24-hour aeration) systems are normally used in package plant designs
without primary clarification, the results have limited applicability for
package plant systems. However, these systems are usually quite small in
capacity and would be marginal choices to receive septage loads anyway. For
those small plants of sufficient size to consider seotage acceptance and
which have primary clarification, the following conclusions may be drawn:
1. Extended aeration systems provide the best assurance
of being able to handle septage shock loadings.
Nitrification should be considered, however, if that
is an effluent requirement of the system.
2. Contact stabilization systems represent the poorest
activated sludge modification for handling shock
loads due to septage addition.
3. BOD and SS effluent concentrations from units receiving
septage as a shock loading depend on the nature of the
septage, the septage flow/total flow, the reactor MLSS
concentration, and the length of the aeration period.
58
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SECTION XI
REFERENCES
1 Detailed Housing Characteristics. U.S. Department of Commerce, Social
and Economic Statistics Administration, Bureau of the Census Publication
HC (1)-B1, U.S.G.P.O., Washington, D.C. (1970).
2 Smith, S.A., and Wilson, J.C., "Trucked Wastes: More Uniform Approach
Needed," Water & Wastes Engineering, 10^ No. 3, 48 (1973).
3 Gales, M., Julian E., and Kroner, R. "Method for Quantitative Determination
of Total Phosphorus in Water." Jour. AWWA 58, No. 10, 1363, 1966.
4 Schaeffer, R.B., et al., "Application of a Carbon Analyzer in Waste
Treatment," Jour. WPCF, 37^ 1545, 1969.
5 Method for Chemical Analysis of Water and Waste, EPA, 1971.
6 Standard Methods for the Examination of Water and Wastewater,
Thirteenth Edition, 1971.
7 Fiege, W.A., Oppelt, E.T., and Kreissl, J.F., An Alternative Method of
Septage Treatment: Lime Stabilization-Sand Bed Dewatering. EPA Report
No. 600/2-75-036 (Sept. 1975).
8 Kolega, J.J. "Design Curves for Septage," Water and Sewage Works,
pg. 132, May, 1971.
9 Poduska, R.A., "A Dynamic Model of Nitrification for the Activated
Sludge Process." Ph.D. Thesis. Clemson University, Clemson,
South Carolina, 1973.
10 "Design Guides for Biological Wastewater Treatment Processes", Water
Pollution Control Research Series, 11010 ESQ 08/71, U.S. Environmental
Protection Agency, pg. 93, 1971.
59
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
1. REPORT NO.
EPA-600/2-77-141
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
FEASIBILITY OF TREATING SEPTIC TANK WASTE
BY
ACTIVATED SLUDGE
5. REPORT DATE
August 1977 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Stephen M. Bennett, James A. Heidman
and James F. Kreissl
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
Government of the District of Columbia
Department of Environmental Services
EPA-DC Pilot Plant
5000 Overlook Avenue S.W. Washington. D.C. 20032
1BC611
11. CONTRACT/OJX9W NO.
68-03-0349
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF REPORT AND PERIOD COVERED
U.S. Environmental Protection AgencyCin., OH
Office of Research and Development
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
Final Report
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer : Irwin J. Kugelman (513-684-7631)
16. ABSTRACT
The objective of the study reported herein was to evaluate the impact of household
septic tank wastes on municipal activated sludge treatment plants. Septage addition
was evaluated on a continuous basis over a four-month period in a 7500 I/day
(1980 gpd) pilot plant. The septage was combined with municipal wastewater primary
effluent in a series of increasing loadings to the activated sludge unit. Results
were compared to a control unit receiving primary effluent only. Shock load studies
were also conducted in the pilot plant system and with a series of batch aeration
tests.
Septage addition was found to be feasible on either a continuous or intermittent
basis. The response during the continuous feeding studies depended upon the
organic loading and the septage characteristics. COD loadings below 3 g COD/g
MLVSS/day could be handled without severe upset. Unacclimated systems also
responded well when septage was added, and substantial organic removals were
obtained within a relatively short time.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Activated Sludge Process
Sewage Treatment
Septage
Septic Tank Pumpings
Continuous Flow
Shock Loads
13B
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
68
20. SECURITY CLASS (Thispage)
Uncl assified
22. PRICE
EPA Form 2220-1 (9-73)
60
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