Environmental Protection Technology Series
AN ALTERNATIVE SEPTAGE TREATMENT METHOD:
LIME STABILIZATION/SAND-BED DEWATERING
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-600/2-75-036
September 1975
AN ALTERNATIVE SEPTAGE TREATMENT METHOD:
LIME STABILIZATION/SAND-BED DEWATERING
by
W. A. Feige
E. T. Oppelt
J. F. Kreissl
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 Labora-
tory, U.S. Environmental Protection Agency, and approved for publication.
Mention of trade names or commercial products does not consititue endorsement
or recommendation for use.
11
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FOREWORD
Man and his environment must be protected from the adverse effects of pesti-
cides, radiation, noise, and other forms of pollution, and the unwise
management of solid waste. Efforts to protect the environment require a
focus that recognizes the interplay between the components of our physical
environmentair, water, and land. The Municipal Environmental Research
Laboratory contributes to this multidisciplinary focus through programs
engaged in
studies on the effects of environmental contaminants on the
biosphere, and
a search for ways to prevent contamination and to recycle
valuable resources.
Few desirable methods presently exist for the disposal of septic tank
sludge. Septic tank pumpouts must nevertheless be treated safely and
efficiently. This study provides one technically feasible and economically
competitive alternative.
A. W. Breidenbach, Ph.D.
Director
Municipal Environmental
Research Laboratory
111
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ABSTRACT
3
Approximately 5 billion gal (18,927,000 m ) of septage must be annually
disposed of in the United States, a volume that is nearly equal to that of
undigested raw and secondary municipal sludges. Few desirable methods
exist for disposing of the sludge that is periodically pumped from septic
tanks. This report describes the results obtained from a pilot study of
one alternative septage treatment method-lime stabilization followed by
covered sand-bed dewatering.
The study was conducted in two phases. Phase I (4 months) consisted of
the general, chemical, and biological characterizations of the incoming
septage. Attempts were made to thicken the material via stirring, poly-
electrolyte addition, and lime addition. Phase II (9 months) concerned
itself with the application of limed septage onto covered sand beds.
Four experimental runs were conducted to assess the feasibility of such
an approach. The septage was limed to pH 10.5, 11.0, and 11.5 and applied
at 8-in. (20.3-cm) depths. Underdrainage and cake characteristics were
monitored and practical sand-bed application rates were determined. A
materials balance of chemical constituents around the system was made.
A cost estimate for the treatment of septage at small treatment plants
via this method is included.
IV
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CONTENTS
Foreword ill
Abstract iv
List of Figures vi
List of Tables vii
Acknowledgments viii
Introduction 1
Literature Review 2
Description of the Study 3
Results 10
Cost Analysis 46
Recommendations 50
References 51
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FIGURES
No. Page
1 Pilot Study Facilities 6
2 Covered Sand Bed Construction 7
3 Septage Loading Pattern at Lebanon 11
4 Effect of Stirring on Septic Tank Waste Thickening 14
total solids, 3.04 percent; pH, 6.15.
5 Effect of Stirring on Septic Tank Waste Thickening 15
total solids, 8.86 percent; pH, 7.5.
6 Effect of Stirring on Septic Tank Waste Thickening 16
total solids, 2.14 percent; pH, 7.75
7 Effect of Lime Addition on Thickening 17
8 Sand-Bed Dewatering of Limed Septic Tank Waste, Run 2 23
9 Sand-Bed Dewatering Trend, Run 3 29
10 Sand-Bed Dewatering Trend, Run 4 32
11 Sand-Bed Dewatering of Limed (pH 11.5) Septic Tank 37
Waste, Run 5
12 Underdrainage Breakthrough, Run 5 39
13 Sand-Bed Dewatering Trend, Run 6 42
14 Underdrainage Breakthrough, Run 6 43
VI
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TABLES
No. Page
1 Sampling Schedule 8
2 Characterization of Septic Tank Wastes 12
3 Separation Efficiency as a Function of Degree of Settling 20
4 Bacterial Results, Run 2 24
5 Distribution of Chemical Constituents of Sand-Bed-Dried, 26
Limed Septage, Run 2
6 Bacterial Results, Run 3 30
7 Bacterial Results, Run 4 33
8 Distribution of Chemical Constituents of Sand-Bed-Dried, 35
Limed Septage, Run 4
9 Chemical Mass Balance, Run 5 40
10 Chemical Mass Balance, Run 6 45
vi i
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ACKNOWLEDGMENTS
The authors express their appreciation to the Waste Identification and
Analysis Section, Wastewater Research Division, MERL-Cincinnati for the
analytical work, and in particular, to Bernard Kenner for the micro-
biological analyses. Albert Oberschlake and George Morrison of the Lebanon
Pilot Plant also deserve special recognition for their contributions to the
study.
viii
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INTRODUCTION
Many households depend on individual waste treatment systems for wastewater
disposal. In the United States, approximately 126 million persons are
connected to central sewerage systems, and about 74 million persons are
served by other disposal methods. The most common of these methods is the
septic tank soil absorption system. The septic tank provides sedimentation
of raw wastewater solids that accumulate and undergo partial digestion in
the anaerobic mode. After a period of generally from 2 to 5 years, the tank
must be pumped of collected floatable (scum) and settleable (sludge) solids.
This step is necessary to prevent serious damage to the soil absorption
system. A common procedure is for a septic tank hauler to pump the tank
contents (septage) into a truck and to discharge the material at wastewater
treatment plants that accept such wastes. In some cases, disposal of septage
to municipal facilities is permitted. In many cases, however, treatment
plants do not allow septage disposal because of possible detrimental effects
on plant efficiency and pump clogging effects. As a result, unsafe and
illegal disposal of these wastes to streams and to the land frequently
occurs. For example, one frequently cited practice has been the disposal
of pumpings to open pits, which pose health and safety hazards.2
Septic tank pumpouts must be treated and disposed of safely and efficiently.
The easiest disposal method is to discharge septage at controlled rates to
large-capacity waste treatment facilities where dilution with the incoming
sewage is available. However, in areas where numerous individual home
systems exist, the municipal treatment facilities most readily available are
usually of a relatively small capacity. Small plants generally operate
under conditions of highly variable flow and frequent hydraulic surges.
Peak flows usually occur during the daylight hours, the same time period
when septage dumpings are usually permitted. Unless some form of receiving
station is available at the plant to permit holding the septage and releasing
it to the plant in a controlled manner, the likelihood of upsetting the
plant is greatly increased. As a result, many of the smaller plants refuse
to accept these discharges, and truckers are often forced to find other
dumping locations. Other alternatives for treating these wastes must be
investigated and adopted to prevent the haphazard and dangerous release of
these discharges to the environment.
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LITERATURE REVIEW
Limited background information is available regarding the treatment and dis-
posal of septic tank pumpouts. Kolega et al.^,3,4 have described land
applications of septage and characterized the material biologically and
chemically. Smith and Wilson^ have discussed the design of septage receiving
facilities at treatment plants with emphasis on the importance of properly
handling these discharges. Jewell et al." have investigated the dewatering
rates of septic tank sludge after aerobic and anaerobic digestion and after
sand-bed dewatering. A description of a commercially available system for
septage treatment also appears in the literature. This process utilizes
chlorine oxidation under pressure, with the end product being dewatered on
sand beds or other dewatering devices. The use of lime as an effective
bactericidal agent is well documented. Buzzell and Sawyer" added lime to
raw wastewater and found that a pH of 10.9 initially killed all of the
coliform bacteria. A study of lime disinfection of raw sewage at low
temperatures showed that significant bacterial kill was achieved.^ Lime
stabilization of sewage sludges was investigated by Farrell et al.-*-" and
more recently by Battelle Northwest Laboratories.H The disposal and
recycling of lime-containing wastewater sludges has been discussed by Dean
and Smith.12 A very recent report concerns itself with the septage problem
in Norway."
Computer searches were also made, but no information relating to methods
of treating septic tank pumpouts was found. The following data bases were
used: Lehigh University, Medline, Civil Engineering, Chemical Abstracts,
and Engineering Index. A request to the Water Resources Scientific Infor-
mation Center (WRSIC) resulted in more than 100 references, but were con-
cerned with treatment of household wastes via septic tanks and not with
the problem of sludge disposal.
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DESCRIPTION OF THE STUDY
OBJECTIVES
The objective of this study was to examine some alternative treatment
possibilities for septic tank pumpings. One major treatment alternative,
lime stabilization followed by sand-bed dewatering, is described in this
report. The terms "pumpout," "dumpings," "pumpings," and "septage" are
all used throughout the paper to denote the material pumped from septic
tanks. During the course of this study, several related tasks were carried
out:
1. To define the nature and frequency of septic tank dumpings.
2. To characterize the general, chemical, and biological makeup
of the septage.
3. To determine optimum pH conditions for effective lime
stabilization.
4. To determine practical sand-bed application rates for limed
septage.
5. To determine the fate of chemical and biological pollutants.
APPROACH
Before any pilot scale investigations were made, it was necessary to
characterize the incoming material (Phase I). Thus, the initial 2 months
of the study were spent collecting and analyzing septage received at the
Lebanon, Ohio, Municipal Sewage Treatment Plant from local haulers. The
following 2 months were used in attempts to thicken the septage. Jar tests
were conducted to evaluate the effects of stirring, polyelectrolyte addition,
and lime addition. Results obtained from 4 months of bench testing pro-
vided the basis for deciding to study the lime stabilization and sand-
drying-bed treatment sequence (Phase II). Sand-bed dewatering of lime-
treated septage was then investigated for 9 months. The first 6 months
were devoted to assessing the effects of liming raw septage to three
different initial pH levels before applying it to sand drying beds. The
septage for stabilization was limed to pH 10.5, 11.0, and 11.5 and dis-
charged to a covered bed sectioned off to accommodate each batch. Four
experimental runs were conducted during this period to determine the
feasibility of such an approach. Eight-in. (20.3-cm) application depths
of the septage were made during these runs. Drainage and cake character-
istics were monitored during three of the runs. The final 2 months were
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spent varying bed application rates to determine the maximum practical level.
Limed septage depths introduced onto the sand beds were 8, 12, 16, and 24 in.
(20.3, 30.5, 40.6, and 60.9 cm). Drying bed performance evaluation was based
on dewaterability and ease of cake removal. Attempts were made to obtain
a materials balance of chemical constituents around the system.
STUDY SITE
The study was conducted at the Lebanon Pilot Plant, Lebanon, Ohio. This
facility is operated by the U. S. Environmental Protection Agency, Municipal
Environmental Research Laboratory (MERL)-Cincinnati, Wastewater Research
Division, and is situated adjacent to the Lebanon Municipal Sewage Treatment
Plant (LMSTP), which is a 1.15 mgd (4370 m3/day) activated sludge plant.
DUMPING PROCEDURE
The procedure required by LMSTP for all septic tank haulers is to discharge
1,000-to 2,000-gal (3.8-to 7.6-m3) loads of septage into the main interceptor
line located upstream from the comminutor. Other requirements imposed by
the City of Lebanon are:
1. Dumping is allowed at the LMSTP on weekdays between the hours of
7:30 AM and 4:30 PM only.
2. An attendant of the LMSTP must be on the site at the time of
dumping.
3. Haulers must show a valid license or permit issued by the Board
of Health.
4. Septage being dumped cannot contain any waste oil, kerosene,
gasoline, cleaning compound, or other substance obviously harmful
to plant operation.
5. Septage containing industrial wastes is not accepted.
6. Dumping fee is $5.00 per tank load up to 1,000-gal (3.8-m3) tank
capacity and $10.00 per tank load for larger capacities.
An important part of the study was having the cooperation of the septic tank
haulers. At the beginning, there were three septic tank services that
regularly discharged septage at the LMSTP. The septage consisted of house-
hold, school, and machine shop wastes. The latter contribution was dis-
allowed after a time because of its oily nature and detrimental effect on
plant operation. Sometimes a hauler had to be called on to deliver septage
needed for the study as the winter months approached and discharges to the
plant decreased.
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EQUIPMENT REQUIREMENTS
Phase I
During the bench-testing phase, little hardware was required. All thickening
runs took place in graduated cylinders: initially, 1-liter cylinders, and
later, 2-liter cylinders for jar tests with lime and polymers. Two- and
4-rpm stirrer-equipped motors adapted with shafts and wires to fit com-
fortably into the cylinders were used to evaluate stirring effects.
Phase II
Figure 1 shows the set-up used for the pilot phase. The lime slurry tank
consisted of a 1,750-rpm mixer fastened to the inside of a 30 gal (114-
liter) drum. The 25-percent-by-weight lime (Ca(OH)2) slurry was bucketed
from the drum and introduced into the holding tank, which was previously
filled with septage. The 4,500-gal (17-m^) tank was located outdoors and
above ground and modified to accept septage as directly pumped or gravity-
fed from the truck. The cylindrically shaped diffusers, each about 15 in.
(38 cm) long, were radially positioned 120ฐ apart on the floor of the tank
to air mix the lime with the septage. When the desired pH level was reached,
the mixture was allowed to flow by gravity through approximately 100 ft
(30.5 m) of 4-in. (10.2 cm) diameter flexible pipe to the covered sand bed.
Figure 2 shows a sectional view of the modified drying bed and the cover
over it. The bed was quartered off, with 64 ft^ (5.8 m ) of useable area
available in each section. The wood planking used was creosote-treated
to minimize attack by the lime. Heavy-duty plastic was draped over the
planks to prevent cross-septage of the waste. The access doors, located on
either side of the roof, served as entrances to the bed. At the end of each
test period, the septage cake was removed through these doors. Because it
was not possible to collect drainage separately from each of the bed sections,
three simulated sand beds were constructed from cylindrical fiberglass drums
2 ft (0.6 m) in diameter x 4 ft (1.2 m) deep, and each was equipped with
a bottom sample tap. The drums were also located in a section of the
covered structure and filled with 12 in. (30.5 cm) of sand, 15 in. (38.1 cm)
of #6 gravel, and 3 in. (7.6 cm) of #3 gravel (the same as the beds). Each
time limed septage was applied to a section of the big beds, a corresponding
depth was applied to one of the drums. In this way, the drainage from all
sections was monitored.
SAMPLING AND ANALYSIS
The sampling schedule for both phases of the study is outlined in Table 1.
Phase I
Samples for the characterization phase were taken directly from the dis-
charge line of the truck at the point before entering the manhole. Grab
samples were taken in 2 1/2-gal (9.0-liter) buckets near the beginning,
middle, and end of the approximately 20-min unloading time and composited
in a fourth bucket. Samples from 21 sources of domestic septage and five
machine shop loads were analyzed. Two-hr and 4-hr settleability tests
were run, with and without stirring, with lime addition, and with poly-
electrolyte addition.
5
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LIME SLURRY
SEPTAGE
FROM
TRUCK
COVERED SAND BEDS
-AIR
HOLDING
TANK
ooooooooo
oooooooo
O OOQOOOOO
LIMED WASTE
SIMULATED SAND
BEDS FOR
UNDERDRAINAGE
CAPTURE
Figure 1. PILOT STUDY FACILITIES
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CHICKEN
WIRE
I"x4
-5 mil
CLEAR
PLASTIC
PLASTIC/CHICKEN
WIRE COVERING
DETAIL -A-
FACING
BLOCK
ACCESS DOOR
WOOD
DIVIDING
WALLS '
GRAVEL
DRAIN
Figure 2. COVERED SAND BED CONSTRUCTION
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00
Table 1.
SAMPLING SCHEDULE
Phase I - Characterization
Daily
.Phase Ji,
Twice Weekly Three Times Weekly
pH X ....J
Total Solids (%) X X
Total Volatile Solids (%) X X
COD X X
TOC X
IV2 Series X X
Total Hydrolyzable Phosphorus X
Hexarte Extractable Materials X X
Heavy Metals (iron, manganese,
cadmium, nickel, and mercury) X
Settl eabi I i ty Tests X
Bacterial Analyses X
Covered Bed Temperature X
Relative Humidity X
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Phase II
Samples for the pilot study were taken from the holding tank after the
contents of two or three haulers were allowed to mix for about 1-hr. A
part of the sample was poured into a beaker and used to estimate the amount
of lime necessary to attain the desired pH level in the tank. A few
gallons less than the volume of lime slurry extrapolated from the bench
determination were added to the holding tank and allowed to mix for about
20 min before pH was measured. This procedure was repeated until the re-
quired pH was reached. Samples of the limed waste were taken from the
discharge line entering the sand bed. Subsequent representative samples
of the limed septage during each test period were taken from the respective
64-ft2 (5.8-m2) section of the bed by withdrawing samples from five places
in the section and compositing them. Drainage from each drum was collected
for chemical and bacterial analysis and, in later runs, drainage volumes
were also recorded so that material balances could be made.
All chemical and most bacteriological procedures were carried out in
accordance with the methods described in Standard Methods. -^ Bacteriological
methods for the determination of Salmonella species and Pseudomonas aeruginosa
were developed by
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RESULTS
PHASE I - SEPTAGE CHARACTERIZATION
Quantity Discharged
The results reported here reflect data accumulated from July 1972 to
September 1973. To quantify the extent to which septage was discharged
at the Lebanon site, a record was kept of the total volume unloaded each
month during 1972 and during the first few months of 1973 (Figure 3). As
the figure shows, most septic tanks are pumped during the warmer months.
From April to September, 550,000 gal (2,082 m3) , or about 75 percent of
the total 1972 volume of septage, was discharged to the treatment plant.
The total accountable quantity of septic tank wastes during 1972 was
717,000 gal (2,725 m3), and the average plant flow was 1.4 mgd (5,320 m3/day),
Assuming that 45 percent (230 million gal or 874,000 m3) of the yearly plant
flow entered the plant between 7:30 AM and 4:30 PM (allowable interval for
haulers to dump their loads), approximately 0.3 percent by volume of the
plant intake was septic tank waste (assuming all of it entered the plant).
Unfortunately, septage discharges are intermittent and constitute a greater
instantaneous portion of the total flow at the time of discharge. At an
average plant flow (7:30 AM to 4:30 PM) of 975 gpm, assuming that a hauler
dumps a 1,000 gal load in 15 min, the septage to sewage volume ratio
(Qseptage/Qsewage) would be approximately 0.07 or 7 percent of the total
influent flow. The result is a temporary overload and possible upset
of the plant.
Physical and Chemical Characterization
Results of the characterization phase are shown in Table 2. The data were
divided into two groups: domestic wastes (average pH 6.9) and machine shop
wastes (cutting oil) (average pH 9.6). The color of the domestic septage
varied from black to brownish-black, or gray, and the color of the oil was
cream. Odors were similar to those of sewage for the household wastes and
similar to kerosene for the cutting oil. Although these two types of wastes
were distinctly different in source and appearance, there was a surprising
similarity in content. It is unknown whether the presence of heavy metals
in the domestic septage originated in the septic tank or resulted from
previous truckloads.
Settling characteristics of the septic tank wastes were very erratic.
Samples were examined at 15-min intervals in 1-liter graduated cylinders
to determine settleability. The cutting oil waste did not settle at all.
Before the first domestic sample settled, 25 consecutive samples had not.
10
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120
Z
o
100
80
o
x^
Z
O
60
40
20
I I I
i i i i r
i I I i i i i I I I L
JFMAMJJASOND
MONTH, 1972
Figure 3. SEPTAGE LOADING PATTERN AT LEBANON
11
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Table 2.
CHARACTERIZATION OF SEPTIC TANK WASTES
LEBANON, OHIO*
Parameter (mg/l)
Domestic Waste
(21 Samples)
Machine Shop Waste
(5 Samples)
PH
Total Solids (%)
Range 0
Volatile Solids (%)
6.9
3.95
.68 - 10.6
69.3
Total COD 60,582
Hexane Extractable
Materials
Total Kjeldahl Nitrogen
NH3-N
N02-N
N03-N
Tot. P
Fe
Mn
Zn
Cd
Ni
Hg
9,561
650
120
1.3
1.2
214
163
5.4
62
0.2
<1.0
0.022
9.6
4.14
2.57 - 10.0
54.3
63,750
10,377
446
143
0.8
1.7
107
103
3.6
89
<1.0
0.043
Mn mg/l unless otherwise noted.
12
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A settling curve for the 26th sample is represented by the control line of
Figure 4. The figure shows that approximately 15 percent settling occurred
after 2 hr, 25 percent after 4 hr, and only 46 percent after 24 hr. The
term "percent settling" is defined as the ratio of the graduated cylinder
interface height difference (in ml) between the beginning and ending
settling points divided by the interface height beginning point multiplied
by 100. Results from two other occasions when some natural settling took
place are shown in Figure 5 and 6; they also indicate relatively poor
settling (10 and 40 percent after 2 hr).
Because minimal thickening took place, attempts were made to bring about
liquid-solid separation of the septage via stirring. Stirring tests at
rates of 2 rpm and 4 rpm showed that in cases where no thickening occurred,
stirring did not help; but when some thickening was possible, it was promoted
by stirring. The curves in Figures 4 through 6 show the positive results of
stirring. Stirring speed apparently did not effect the thickening rate.
Despite the benefits of stirring, additional thickening was considered
mandatory for good separation, and the use of lime and polyelectrolytes
was next investigated. No further research was done with the cutting oils,
and in fact, their discharge to the Lebanon Plant was no longer permitted
after November 19-72.
Jar Tests
Jar tests with lime were conducted in the following way: Based on the total
soilds content of the septage, dosages of 5 to 20 percent lime were made.
The lime was introduced into 2-liter graduated cylinders in a 25-percent
slurry. Figure 7 shows the results of one of these tests and is typical
of other test results. A maximum of only 38 percent thickening occurred
after 2 hr and 50 percent after 4 hr with lime addition. Stirring of the
limed samples showed increased settling over the unstirred limed samples,
but still a maximum of only 50 percent thickening was achieved.
Six cationic polyelectrolytes* (Calgon 2600, 2640, and 2660; Purifloc C31
and C41; and Ionic NC721) were used in the jar tests, as well as three
anionic polymers (Calgon 2690A, Magnifloc 835A, and Magnifloc 837A). Total
solids concentrations of the tested septage ranged from 0.8 to 4.6 percent.
Standard jar test procedure was to introduce each polymer at a dosage of
10 milligrams of polymer per gram of sludge solids. Samples were allowed
to settle in the graduated cylinders for 2 hr, with readings taken at
15-min intervals. Results were inconsistent. In two cases (sample total
solids concentrations of 4.6 and 3.6 percent), virtually no thickening took
place with any of the polymers even after 4 hr of settling. When the
polymer dosages were doubled to 20 mg per g of dry sludge solids for
samples containing 3.6 percent solids, the sample with cationic polymer
C2600 resulted in 23 percent settling after 1 hr. An equivalent amount of
settling resulted after 1 hr with stirring (2 rpm) plus 10 mg C2600 per g
*Mention of a proprietary product does not constitute an endorsement or
recommendation by the Federal Government.
13
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1000
- 800
E
I
ฎ 600
LU
I
LU
u
< 400
LU
1
z
~ 200
0
C
//
1 1 1 11 1 1 1 1 Iff
^^^^-^.^.^.^^ :
^^^^ft-^c * -* "
ffl- ^B
m
(
A = Control TOTAL SOLIDS - = 3.04%
= 2 rpm stirring pH = 6.15 -
D- 4 rpm stirring
III 1 1 1 1 \j (1 I,*
0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 3*0 4.0^724
TIME, hours
Figure 4. EFFECT OF STIRRING ON SEPTIC TANK WASTE THICKENING
-------
1000
I: 600
u
ฃ 400
UJ
I
z
200
1
A - Control
= 2 rpm stirring
D= 4 rpm stirring
TOTAL SOLIDS = 8.86%
pH= 7.5
I
I
I
I
I
I
0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0
TIME, hours
Figure 5. EFFECT OF STIRRING ON SEPTIC TANK WASTE THICKENING
-------
1000
80ฐ
600
< 400
- 200
I = Control
= 2 rpm stirring
D - 4 rpm stirring
I I
TOTAL SOLIDS - 2.14%
pH = 7.75
I I I I
I
0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0
TIME, hours
Figure 6. EFFECT OF STIRRING ON SEPTIC TANK WASTE THICKENING
-------
E
t-^
O
<
LL.
ฃ*
pH
2000
1500
1000
500
0
7.1
-*-
Control
T.S.
= 2.2%
8.5
.ime
ป
/O 2
9.1
10%
Lime
ป
10.8
11.3
12.5% \ 15%
Lime \ Lime \Lime
0 2 4
11.5
20%
,0 2 4N
024 024 024
THICKENING TIME, hours
Figure 7. EFFECT OF UME ADDITION ON THICKENING
-------
of solids, indicating that stirring may reduce the amount of polyelectrolyte
required to accomplish equivalent amounts of thickening. In two other
cases, the C2600 polymer resulted in almost 75 percent settling without
stirring and almost 85 percent with stirring. Tests with a range of
dosages (2-15 mg C2600 per g of solids) showed that the use of 2 mg per g
effectively resulted in as much settling as with the higher dosages,
although the clarity of the supernatant was not as good. The anionic
polymer C2690A was the next most effective polymer. The other anionic
polymers brought about virtually no settling.
The importance of good separation is shown in Table 3, where the heavy
metal distribution between phases is compared for septage samples with
and without polymer addition. The use of polymer substantially increased
the capture of materials in the underflow. The supernatant concentration
values were obtained from supernatant samples decanted from the graduated
cylinder and were directly analyzed, rather than first having been filtered.
Table 3 also shows the distribution of other materials present in the
untreated septage samples. Most of the COD and TOC and much of the
phosphorus and Total Kjeldahl Nitrogen appeared in the solid phase.
Conclusions
Tests were conducted to determine whether septage would effectively separate
into solid and liquid fractions for the purpose of treating each phase
individually. Neither natural settling, lime addition, nor polyelectrolyte
introduction resulted in consistent separation. Even though one polymer
proved optimum most of the time, the thickening that resulted fluctuated
from 25 to 75 percent. The separation approach was therefore considered
technically unfeasible and impractical for implementation at the average
sewage treatment plant. A decision was thus made that pilot plant investi-
gations of septage treatment alternatives would involve only approaches
where the septage is treated as a whole. Two avenues were considered:
studying the effects on the biological treatment plant of discharging
the material at controlled rates and treating the septage independently
of the plant. The latter approach, utilizing lime stabilization followed
by sand-bed dewatering, was chosen for several reasons: (1) total solids
concentrations as great as 10 percent were present in the septage and would
be kept out of the treatment plant, (2) heavy metal constituents could be
complexed by the lime, (3) bacterial kills could potentially result from
lime addition, (4) lime is a relatively low-cost chemical, (5) sand beds
are available at many small treatment plants, (6) drainage from the sand
beds should be of better quality than the septage, (7) if workable, the
procedure could be easily implemented by sewage treatment plant personnel
and, (8) if workable, the process may not have to be dependent on the
presence of a sewage treatment plant.
18
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PHASE II - PILOT STUDIES
Experimental Runs I through 4: Lime Stabilization
3
Run 1 Approximately 2,100 gal (8.0 m ) of septage from two haulers were
pumped into the holding tank, air-mixed, limed, and applied to the sand beds
for further study. The air-mixing system provided adequate mixing, even
though distribution was not equal among the three diff users used. Other
investigations have documented the advantages of air-mixing over mechanical
mixing. -*-!
The general, chemical, and biological characteristics of the raw septage
tested are shown below:
General :
Color ----------------------------- dark brown
pH -------------------------------- 6.5
Total solids ---------------- % --- 3.2
Total volatile solids ------- % --- 63.4
Biological:
Fecal coliforms
Fecal streptococci
Pseudomonas aeruginosa
Salmonella species
Chemical:
Counts /100 ml
TOG
NH3-N
N02-N
NO^-N
6.1 x
1.8 x 106
6.0
0.3
Chemical continued
mg/1
Cu 0.3
Ni
Hg
0.7
52.0
0.6
0.2
4.4
0.154
Odors were initially present, but they improved with air-mixing and lime
addition. The true ammonia and TKN concentrations were probably higher
than those shown, because a portion of the ammonia was stripped during
air-mixing. The contribution of heavy metals in the septage is important
to note. Whether they were actually present in the septic tank or appeared
as a result of cross-contamination in the tank truck was not apparent. In
any event, septage treatment methods must consider the fate and effects of
heavy metals.
The intended limed pH values for sand-bed dewatering studies were pH 10.5,
11.0, 11.5, and 12.0. Unfortunately, the pH 11.0 value was exceeded, and
therefore limed septage was applied to three sections of the sand drying
bed. Loading depth to each section (area, 64 ft^ or 5.95 m^) was 8 in.
(20.3 cm), which corresponded to a volume of 320 gal (1.21 up). The actual
pH values introduced onto the beds and the amounts of lime required to
reach those values are tabulated as follows:
19
-------
TABLE 3. SEPARATION EFFICIENCY AS A FUNCTION OF DEGREE OF SETTLING
No Polymer (50% Settling)'
Polymer (70% Settling)
t-o
o
Parameter Supernatant
(mg/1)
Fe
Mn
Cu
Zn
Cr
Cd
Ni
Hg (yg/1)
Total P
Total COD
Total TOC
TKN
NH3-N
N02-N
30
3.0
3.0
6.2
4.4
0.5
3.0
.002
70
4,728
1,910
410
220
Solid Phase
215
4.6
5.4
11.2
5.6
0.8
4.0
15.8
173
33,458
8,460
844
215
Solid Phase
88
61
64
64
56
61
55
88
71
88
82
68
50
Supernatant
(mg/1)
1.
<0.
2.
5.
1.
<0.
<0.
<0.
3
1
1
1
2
1
5
2
Solid Phase
(mg/1)
850
26.6
13.8
140
8.3
0.4
14.2
44
Solid Phase
99+
99+
85
97
86
-
96+
99+
1.0
1.0
50
settling time 4 hours, untreated septage
settling time 2 hours, 10 mg/g C2600 polymer added
-------
Actual
PH
10.4
11.6
12.0
Gal (liters) of 25%
lime slurry required
12 (45)
20 (76)
21.8 (83)
Ib (kg) of lime
required
25 (11.4)
41.6 (18.8)
45.2 (20.5)
Ib of lime/ton
(kg/metric ton)
of dry solids
92 (46)
180 (91)
240 (120)
After the first day on the beds, the pH of all wastes dropped 0.4 to 0.5 pH
units. The nature of the samples taken showed that sampling techniques would
become the most critical part of the study. Despite precautions taken to
even out the sand level in each section of the bed, application of the waste
resulted in uneven distribution in some places; floating solids were noticed,
and in others, most of the solids had settled onto the sand. After the second
day, only 1 1/2 in. (3.8 cm) of the original 8 in. of waste remained; yet
only a slight increase, and in one case a decrease, in total solids concen-
tration from the original 3.2 percent was measured. This result was
undoubtedly an error in sampling and was alleviated beginning with Run 2
by sampling from several points within the same section, thus assuring that
samples were as representative as possible. Although the sampling procedures
used were not completely satisfactory, a general trend in the dewatering
characteristics of each of the sludges was observed. After 6 days, the cakes
all thickened to approximately 28 percent solids; after 19 days, all cakes
dewatered to greater than 38 percent solids. The dewatering times were
reasonably short compared to the times normally required for the sand bed
drying of municipal sludges. It is further encouraging in that the ambient
temperature and relative humidity in the enclosure averaged, respectively,
5ฐC and nearly 100 percent during the run. Volatile solids measurements
remained about 63 percent for all pH levels. A decision was made to sample
daily the total solids levels of future batches until concentrations of
20 to 30 percent were reached. At that time, the sludge cake could be
hauled away and preparations made to receive a new load.
Run 1 served to point out sampling and operational problems to be expected
during the study. The rapid drying times and ease of cake removal for each
batch of limed septage were encouraging. The presence of heavy metals
and the importance of tracing their paths were made evident. Also, pH
levels could be expected to decrease as a function of time, regardless
of initial pH. No intolerable odors in the bed enclosure were detected,
however.
Run 2 After the septage was removed from the sand beds, new sand was
added, and the three sections were raked evenly to receive the next batch.
The holding tank was cleaned of residual septage, rags, grit, etc. from
the previous experimental run.
Run 2 was conducted for 16 days, at which time the cake was considered
truckable and was removed. General and chemical characteristics of the
unlimed septage are as follows:
21
-------
General :
Col
pH
Chemical :
COD
TOG
TKN
NH
To
Fe
Cu
Although the initial pH of the waste was abnormally high, all indications
were that the source was domestic sewage and not cutting oil. The organic
concentrations were significantly higher than in the previous batch, but
the inorganic concentrations were generally lower. Total and volatile
solids levels were the same, however.
The septage was limed to pH 10.4, 10.9, and 11.5 for discharge to the
sand drying beds. The amounts of lime required are tabulated below:
.UL
:al
:al
i
i
-
-N
:al
volatile solids
mg/1
sv 700
17 nnn
Ionn
, zuu
}Qr>
joU
P 24
979
. - - 8.8
aarK
8Q
. o
"/ "\ \
la J . J.
% 63.0
Chemical -
AT-f
r-r-
\ji
Mn
TJfY
ttg
gray
- continued
mg/1
07
1 L
J-. f
00
. Z
fi S
n HI
Actual
PH
10.4
10.9
11.5
Gal (liters) of 25%
lime slurry required
19.5 (74)
21.5 (81)
24.0 (91)
Ib (kg) of lime
required
40.6 (18.4)
44.8 (20.3)
50.0 (22.7)
Ib of lime/ton
(kg/metric ton)
of dry solids
131 (66)
167 (85)
219 (110)
As in Run 1, the pH of the waste in all sections decreased about 0.5 pH units
after the first day and continued to decrease linearly throughout the remain-
der of the run. Regardless of initial pH, the final pH of the 16-day run
was 8.5 to 8.7 for each limed waste. The underdrainage pH fell to a constant
value of 8.2 within 2 to 4 days of application.
The dewatering trend for each bed during Run 2 appears in Figure 8. The
original waste contained slightly greater than 3 percent total solids, and
the lime addition increased the solids level to 4.5 percent. An interesting
note is that the low-limed waste dried the quickest and the high-limed
waste the slowest of the three batches. One explanation of this trend may
be that magnesium hydroxide precipitated as the pH increased, thereby slowing
the draining process.
The effects of lime on the fecal bacterial population during Run 2 are shown
in Table 4. The table traces the fates of the fecal coliform and fecal
streptocci organisms in the septage on the sand beds and in the under-
drainage. Samples were taken every few days throughout the experimental
22
-------
6 8 10
TIME, days
Figure 8.
SAND BED DEWATERING OF LIMED SEPTIC TANK WASTE - RUN 2
LEBANON, OHIO
23
-------
Table 4.
BACTERIAL RESULTS - RUN 2
Septage
Underdrainage (counts/100 ml)
SEPTAGE
DAY PHASE
HIGH
RAW L|ME
MEDIUM
LIME
Fecal Coliform
0 Liquid*
1 Liquid
5 Solid**
7 Solid
12 Solid
16 Solid
0 Liquid
1 Liquid
5 Solid
7 Solid
12 Solid
16 Solid
1.7x106 <5 x 103
<1 x103
00
^10
Oo
(10
2.2 x107 9.2 x
1.5 x
2.9 x
1.6 x
5 x
2.65 x
10s
106
104
105
103
103
<5x
O x
<50
' <50
<50
<50
Fecal
6.4 x
8.8 x
1.0 x
5.6 x
4.1 x
103
103
LOW
LIME
Population
<5x103 1
<1 x 103
<50
<50
<50
00
1.
<
HIGH
LIME
I x105
4 x105
6 x 103
1 x103
MEDIUM
LIME
2.5
1.7
<1
<1
<1 x 103 <1
1.2 x103
x105
x104
I x 103
x103
t x103
<40
LOW
LIME
600
2.8 x 103
1.1 x 104
<1 x 103
<1 x 103
<40
Streptococci Population
106
106
104
105
105
1.2 x 106
1.2 x107
1.4 x107
3
.Ox 10s
2.8 x 106
1.
1.
2 x 105
5x106
1
1
4
1
1
.1 x 106
.8 x 106
.2 x 105
.5x 10*
.4 x 103
400
9.
3.
2 x105
8 x 10s
3.3x106
8.5 x 105
3.
3.
4 x 104
0 x 103
3.5 x 104
6.2 x 105
5.7 x 105
3.5 x104
2.0 x 103
720
* Liquid phase expressed as counts/100 ml
'* Solid phase expressed as counts/gram
-------
run. Fundamental considerations were (1) the amount of kill effected by
the lime, (2) the quality of the material shoveled from the beds, (3)
indications of regrowth, and (4) the quality of the underdrainage.
The fecal coliform count in the septage was reduced about 3 logs (-99
percent) on contact with the lime for all pH levels. After 5 days, the
septage was in the solid phase, and less than 50 counts per g were present
in each batch. When the experimental run ended after 16 days, the fecal
coliform population in the septage remained low, and no sign of regrowth
appeared for any of the three lime concentrations. In some cases, the
underdrainage initially contained high amounts of fecal coliforms, but
after 7 days, relatively low levels were observed.
The fecal streptococci appeared to be more resistant to lime than the
fecal coliforms, and the amount of resistance appeared to be related to the
initial pH. About a 95-percent fecal streptococci reduction took place
on contact with the lime at pH 11.5, about a 73-percent reduction at pH
10.9, and about a 45-percent reduction at pH 10.4. Even though 95 percent
of the fecal streptococci population was reduced at the high lime dosage,
it is important to note that a large number of organisms remained. By the
12th day of the run, the high-limed batch effected a 1-log indicator reduc-
tion from the first day in the solid phase versus no reduction for the
medium- and low-limed batches. At the end of the run, the difference
in qualities was even greater: signs of regrowth were present for the two
lower dosages, but a further organism reduction was observed for the high
dosage. The underdrainage contained high amounts of fecal streptococci
for several days before a tailing-off occurred.
The pathogenic content of the waste was also monitored. No Salmonella
species were detected in any of the raw or treated wastes or in the under-
drainages. Pseudomonas aeruginosa was present in the unlimed waste in
small numbers (3.6 counts per 100 ml), but did not appear in any of the
limed wastes.
An attempt to determine the fate of the individual chemical constituents
in the septage as it dried was made during Run 2. Points of interest
were whether these materials would be located in the cake or in the under-
drainage and what the effects of higher lime dosages would be. Results
of this investigation appear in Table 5. All data related to the cakes
are expressed on a weight-to-weight basis (mg of constituent per g of
solids) , and underdrainage data are expressed on a weight-to-volume basis
(mg/1). The limed septage concentrations in Table 5 represent average
daily values computed over the duration of the experimental run, whereas
the underdrainage values are expressed as ranges. It should be further
noted that the cake data were obtained by normalizing the daily total
solids data and averaging the results. The following general conclusions
can be drawn from the information presented: (1) the majority of the heavy
metals remained with the cakes, (2) the high-limed cake (pH 11.5) retained
slightly more of the heavy metals than the medium- (pH 10.9) and low^limed
(pH 10.4) cakes, (3) nearly all of the organic content was found in the cake,
and (4) the underdrainage contained much reduced amounts of chemical
constitutents relative to those present in the raw waste. An encouraging
25
-------
Table 5. Distribution of Chemical Constituents of
Sand-Bed-Dried Limed Septage - Run 2
Concentration (mg/g solids)
Limed Septage
High
1327
319
26
3.0
12.6
7.0
1.2
0.13
0.36
0.047
0.037
0.013
0.36
Medium
1272
324
24
2.2
10.8
6.3
1.02
0.08
0.29
0.034
0.028
0.011
0.29
Low
1288
282
26
2.4
10.8
6.8
0.92
0.10
0.33
0.036
0.030
0.009
0.33
Unlimed
Septage
1860
548
39
12
7.2
6.8
1.06
0.30
0.21
0.045
0.022
0.006
0.21
Parameter
COD
TOG
Total N
(Org N, NH3
2NH33
Fe
Total P
Zn
Cu
Mn
Cr
Ni
Cd
Hg (vg/g)
Concentration Range (mg/1)
Unlimed
Septage
57,000
17,000
1,202
380
222
210
33.0
8.8
6.5
1.4
0.7
0.2
6.5
Limed Septage Underdrains
High
224-1610
84-375
32-41
15-24
4-10
1-3
0.1-1.2
0.1-0.3
0.9-1.2
0.0-0.1
0.1-0.2
0.06-0.1
0.9-1.2
Medium
2030-3100
400-900
15-150
18-91
4-67
1-7
0.8-1.9
0.2-0.5
0.2-2.4
0.1-0.2
0.1-0.2
0.06-0.1
0.2-2.4
Low
1080-2540
320-840
7-110
8-73
1-62
2-8
0.5-1.0
0.1-0.14
0.9-1.9
0.0-0.1
0.1-0.3
0.06-0.1
0.9-1.9
i
!
-------
fact was that despite pH decreases of daily monitored samples during the
run, resolubilization of the metals did not occur. This suggests that
the underdrainage from the sand beds at a conventional biological treatment
plant can be recycled to the headworks of the plant with little additional
metal contributions. The marked increase in iron levels of the limed
septage was noted, but no explanation was apparent.
Results from Run 2 indicated that sand-bed dewatering of lime-treated
septage is a potentially viable method of septage treatment that results
in a good quality underdrainage amenable to conventional biological
treatment.
Run 3 About 3,300 gal (12.5 m^) of septage from two haulers were limed
to pH 10.4, 11.0, and 11.5, and sand-bed dewatering studies were conducted
for 5 days, the shortest duration of any of the experimental runs.
General and chemical characteristics of the septage as received appear as
follows:
General:
Color
pH
Total solids %
brownish-gray
7.15
4.08
Total volatile solids % 71.2
Chemical:
mg/1
COD 28,400
TOC 96,000
TKN 340
NHo-N 89
Chemical continued
Total P
Fe
Cu
77
600
23
\T-i _
7-n
ft- _
CA
\jQ. ~
Mi-i
Hrr _
mg/1
98
-1C.
1 J
i r>
11
. -L
1 C
J.J
n m ^
This batch of septage was different than any previously observed in that
it possessed a fuel oil or gasoline odor and had a nearly neutral pH. The
abnormally high TOC concentration probably reflected the fuel oil con-
tribution to the waste. Also unique to Run 3 was that only about half
of the lime requirement previously used was needed to stabilize the
septage:
Actual
PH
10.4
11.0
11.5
Gal (liters) of 25%
lime slurry required
15 (57)
18 (68)
22 (83)
Ib (kg) of lime
required
31.2 (14.2)
37.4 (17.0)
45.7 (20.7)
Ib of lime/ton
(kg/metric ton)
of dry solids
55 (28)
74 (37)
102 (53)
27
-------
The pH trend witnessed during Runs 1 and 2 was once again evident during
Run 3. The pH of the cakes in all sections decreased 0.5 to 1.0 pH units
after the first day. The final pH of the 5-day run was 2.0 to 2.5 pH units
units lower than the starting pH for each limed waste. The pH of the under-
drainage from each bed ranged from 7.5 to 8.0, with minimal variance.
The dewatering trend for each bed appears in Figure 9. After 5 days, the
septage on each of the beds thickened to greater than 32 percent. Unlike
Run 2, there was no clear-cut relationship between the rate of dewatering
and the lime dosage. A total volatile solids reduction from 71 to 41
percent took place during this run, probably because of the atypical organic
nature of the waste.
The effects of lime on the fecal bacterial population for Run 3 are shown
in Table 6.
Fecal coliform reduction of about 3 logs resulted when the septage was
initially limed to pH 11.5 and 11.0, and 2 logs when limed to pH 10.4.
Regrowth appeared to occur only in the cake originally limed to pH 10.4,
and therefore the fecal coliform population of the low-limed cake was not
stabilized by the end of the 6-day run. The underdrainage contained low
populations of the indicator organism by the end of the run in each case,
but the die-off was slower at the lower pH.
As in Run 2, the fecal streptococci were generally more resistant to lime
than the fecal coliforms, and there was a relationship between initial
lime dosage and the efficiency of kill. When the septage was limed to
pH 11.5, 99 percent of the fecal streptococci population was destroyed;
when limed to pH 11.0, 72 percent were killed; and when limed to pH 10.4,
virtually no kill took place. By the end of the run, the number of counts
per gram remaining in the high-limed cake was 1 to 3 logs fewer than the
others. Whether or not regrowth occurred during the run was unclear.
The underdrainage showed minimal reduction in fecal streptococci count
by the end of the experimental run.
Results of the samples taken for pathogenic analyses were as follows: No
Salmonella species were detected in any of the raw or treated wastes or
in the underdrainages. Pseudomonas aeruginosa organisms were present in
the unlimed waste in small numbers (7.3 counts/100 ml) but did not appear
in any of the limed wastes.
Results from Run 3 indicated that sand-bed dewatering of limed septage
can be accomplished in a few days under certain conditions. Also, bacterial
reduction appeared to occur more consistently at pH 11.5 than at lower pH
values, with fecal coliform removals being nuch greater than fecal strep-
tococci removals.
Run 4 Because the septage used during Run 3 was not of a purely domestic
source, it was decided to conduct one more experimental run of varying
lime dosages and a single application depth.
28
-------
42
40
38
36
34
32
30
28
c 26
o>
oi 24
a
ซn 22
to
< 18
O '6
I
14
12
10
8
6
4
2
0
TOTAL SOLIDS = 4.08% -
I
1
2345
TIME , days
Figure 9. SAND BED DEWATERING TREND - RUN 3
29
-------
Table 6.
BACTERIAL RESULTS - RUN 3
Septage
Underdrainage (counts/100 ml)
DAY
SEPTAGE
PHASE
, ... HIGH
RAW LIME
MEDIUM
LIME
LOW
LIME
HIGH
LIME
MEDIUM
LIME
LOW
LIME
Fecal Coliform Population
0
1
5
6
Liquid *
Liquid
Solid**
Solid
3.3 x 106 <1 X103
<1 x 103
<10
<5x103
<1 x 103
<10
1 x 104
3x104
1.5 x103
320
_
<8
16
5.9 x103
_ _
<40
<8
3 x 10s
2.2 x 104
1.76 x103
40
Fecal Streptococci Population
0
1
5
6
Liquid
Liquid
Solid
Solid
3.0 x106 2.5x10"
2.5 x104
7 x 103
8,5 x 10s
1.1 x 106
1.1 x 105
1 x107
5.4 x107
2.8 x106
2.3 x104
_
3x104
7.5 x103
2.0 x 10s
_
1.9 x 106
1.5x105
2.8 x105
1.3x104
1 x107
6 x105
*Liquid phase expressed as counts/100 ml
**Solid phase expressed as counts/gram
-------
Run 4 was conducted for 11 days. General and chemical characteristics of the
of the unlimed septage as received appear below:
General:
Color brown
pH 7.4
Total solids % 4.5
Total volatile solids % 76
Chemical:
Chemical continued
rrvn
Tnr __ _
TTTNT
TVTH M
Tnl-al P
T?Q
mg/1
CQ onn
TO /, nn
i ion
j- , jyv
90
*7n
Pn _
W-i _
7n
PT
CA -.
Mr.
mg/1
n 8
n 8
u. o
70
/ y
n s
n "}
9 Q
This batch contained a higher total and volatile solids content than any of
the previous loads.
The septage was limed once again to pH 10.5, 11.0, and 11.5 and discharged
to the respective sections of the covered bed. Lime requirements for Run
4 were the following:
Actual
PH
10.4
10.95
11.5
Gal (liters) of 25%
lime slurry required
14 (53)
16.5 (62)
18.5 (70)
Ib (kg) of lime
required
29.0 (13.2)
34.2 (15.5)
38.4 (17.6)
Ib of lime/ton
(kg/metric ton)
of dry solids
82 (41)
115 (58)
163 (82)
Consistent with prior experimental runs, the pH of each limed waste decreased
on the sand beds. A 0.5 to 1.0 pH drop was observed in each section after
the first day. The final pH of the 11-day run was 2 to 3 pH units lower
than the initial pH for each limed waste. The pH of the underdrainage from
each bed remained essentially constant between 7.6 and 8.0.
The dewatering trend for each bed appears in Figure 10. The original waste
contained almost 4.5 percent total solids. After 11 days, the septage
on each of the beds thickened to at least 20 percent solids, and the run
was ended. All septage was truckable at that point. The high-limed
septage thickened in the shortest time and the low-limed material in the
longest time. This order of thickening was the reverse of Run 2, showing
that there was no consistent pattern to the rate of dewatering.
The effects of lime on the fecal bacterial population for Run 4 are shown
in Table 7.
31
-------
TIME, days
Figure 10. SAND BED DEWATERING TREND - RUN 4
-------
Table 7.
BACTERIAL RESULTS - RUN 4
Septage
Underdrainage (counts/100 ml)
SEPTAGE
DAY pHASE RAW
HIGH
LIME
MEDIUM
LIME
LOW
LIME
HIGH
LIME
MEDIUM
LIME
LOW
LIME
Fecal Coliform Population
0 Liquid* 1.1 x106
1 Liquid
2 Liquid
8 Solid**
11 Solid
<1 x 103
<1 x103
<1 x 103
<10
<10
<1 x 103
<1 x103
<1 x 103
1.15 x 103
350
1.2 x 104
4 x 103
2.5 x104
750
10
1.08 x 103
280
64
<8
464
2.2 x 104
1.68 x 103
360
440
128
3.9 x104
2.4 x 104
1.2 x 103
736
88
Fecal Streptococci Population
0 Liquid 4.8 x 105
1 Liquid
2 Liquid
8 Solid
11 Solid
2 x 10s
1.8 x 105
5x104
<50
<50
3.3 x 10s
1.6 x 10s
6 x 10s
<50
350
1.2 x 106
7.5 x105
1.7 x 107
2.3 x 104
4.8 x 10s
8.6 x 103
3.5 x 105
1.5x 105
2 x 103
3.3 x105
2.2 x 106
6.3x105
9.3 x105
6.8 x104
2 xlO4
9.6 x103
1.4 x 104
2.6 xlO4
1.1 xlO4
4.2 x 103
*Liquid phase expressed as counts/100 ml
**Solid phase expressed as counts/gram
-------
The previously observed trend for fecal coliform reduction was observed
again during Run 4. Greater than 3 logs of kill took place on direct
contact with the lime for the high- and medium-limed batches, and almost
2 logs for the low-limed batch. Regrowth appeared to occur for the septage
initially limed to pH 10.4; it may have occurred for the medium-limed
septage, and it did not occur for the high-limed septage. Underdrainage
fecal coliform population initially decreased about 3 logs and remained
low for the duration of the experimental run for the high-limed cake.
The lower-limed batches showed initial underdrainage population reductions
of approximately 1 log, with lower levels observed during the remainder
of the run.
The initial resistance of fecal streptococci to lime was again observed
during Run 4. About a 58-percent kill took place when the septage was
limed to pH 11.5, about a 31-percent kill occurred when limed to pH 11.0,
and no effect was observed at pH 10.5. By the end of the run, almost a
4-log difference existed in the number of organisms remaining in the cake
between the high- and low-limed batches. Indications of regrowth appeared
in the low-limed cake by the end of the experimental run, but the high-
limed cake showed no such signs. Underdrainage levels were generally
high in all cases.
Salmonella species were not found in any samples. Pseudomonas aeruginosa
appeared in the raw waste at a concentration of 150 counts per 100 ml, but
not in any of the limed septages. The underdrainage of the low-limed (pH
10.5) waste contained 150 counts per 100 ml the first day, but this figure
was reduced to fewer than 3 counts per 100 ml by the second day.
A second attempt was made to follow the path of the chemical constituents
as sand-bed dewatering was taking place. Table 8 shows the distribution
of some of the monitored chemical constituents during Run 4. Results
were similar to those obtained during Run 2, where it was observed that
most of the materials remained in the cake and that the high-limed cake
(pH 11.5) retained slightly more of the toxic metals than the lower-
limed cakes.
Results from Run 4 supported earlier findings that dewatering of limed
septage can take place in a few days with (1) good chemical capture and
retention in the cake, (2) good fecal coliform reduction, and (3) rather
good fecal streptococci reduction at high pH.
The four experimental runs brought to an end Phase I of the sand-bed
dewatering study. Limed septage was shown to dewater to truckable levels
in 5 to 16 days when 8-in. (20.3-cm) depths were applied. Each new load
of septage was limed to pH 10.5, 11.0, and 11.5, resulting in average
lime requirements of 90, 134, and 168 Ib of lime per ton (45, 68, and 83 kg
per metric ton) of dry solids, respectively. Fecal coliform reductions
were consistently more effective at pH 11.5 than at lower pH values.
Although fecal streptococci were more resistant to lime than the fecal
coliforms, removals of these organisms were better at pH 11.5, and evidence
of regrowth was least at the high pH. Chemical constituents were found
34
-------
Table 8. Distribution of Chemical Constituents of
Sand-Bed-Dried Limed Septage - Run 4
Concentration (mg/g solids)
Limed Septage
High
1518
291
6.4
1.7
0.066
0.016
0.016
0.010
0.006
Medium
1400
272
4.0
1.4
0.064
0.005
0.012
0.011
0.008
Low
994
268
3.3
1.2
0.054
0.006
0.010
0.012
0.004
Un limed
Septage
1320
408
8.2
1.75
0.064
0.016
0.016
0.011
0.007
Parameter
COD
TOC
Fe
Zn
Mn
Cu
Ni
Cr
Cd
Concentration Range (mg/1)
Un limed
Septage
59,200
18,400
370
79
2.9
0.8
0.8
0.5
0.3
Limed Septage Underdrains
High
148-1710
40-700
0.3-4.2
0.1-0.4
0.3-0.5
0.1-0.2
0.1-0.2
0.1-1.0
0.1-0.2
Medium
455-2020
128-680
0.6-3.2
0.1-1.0
0.1-0.5
0.1-0.2
0.1-0.2
0.1-0.2
0.1-0.2
Low
187-1110
84-340
0.4-6.0
0.1-2.0
0.8-1.3
0.1-0.2
0.1-0.4
0.1-0.4
0.1-0.2
Ul
-------
mostly in the cake, and although a 0.5 to 3.5-pH-unit drop took place on the
beds during any one run, resolubilization did not occur. COD/TOG ratios of
the unlimed domestic septages for Runs 1, 2, and 4 were 3.7S 3.4, and 3.2,
respectively.
Because of the relatively short dewatering times experienced during Phase II,
bed depths greater than 8 in. (20.3 cm) were felt to be worthy of evaluation.
For this reason, two more experimental runs were initiated. The purpose was
to examine the performance of high-limed septage on sand beds at application
depths up to 24 in. (60.9 cm). At the same time, greater effort was to be
devoted to conducting material balances on the system.
Experimental Runs 5 and 6: Application
Run 5 Domestic septage was limed to pH 12.3 in the holding tank and dis-
charged to the experimental sand beds. Application depths of 8 in. (20.3 cm),
16 in. (40.6 cm), and 24 in. (60.9 cm) were applied to the beds and to the
drums used to collect underdrainage. General and chemical characteristics
of the unlimed septic tank waste are shown below:
General:
pH 7.3
Total solids % 4.6
Total volatile solids % 59.0
Chemical: Chemical continued
mg/1
COD 68,490 Total P
TOG 18,000 Fe
TKN 1,560 Cu
NH -N 182 Zn
NO^-N 0.1 Mn
The dewatering pattern for each loading appears in Figure 11. If 23 percent
total solids concentration were considered an attainable point to truck the
wasฑe, the following drying times would be required: 6 days (8-in. or 20.3-
cm depth), 13 days (16-in. or 40.6-cm depth), and 20 days (24-in. or 60.9-
cm depth). Although the 24-in. application batch thickened to almost 24
percent, the consistency of the cake was of a nonuniform nature. Much of
the cake was water-bound, even after 35 days on the bed. The difficulties
in sampling such a mixture were evident from the apparent decrease in
solids concentration during the first 3 days of the run. Considerable
amounts of green algae were present by the end of the experimental run
for the 24-in. (60.9-cm) batch, and many flies were noted.
The pH drop after the first day was 0.1 to 0.2 pH units, as compared to
0.5 to 1.0 pH units during the previous experimental runs. This
difference may be explained by the higher initial pH during Run 5. An
interesting note is that the pH decrease was less rapid with the greater
application depths. For example, pH 9.4 was reached after 9 days in the
8-in. (20.3-cm) bed, whereas pH 10.0 was reached after 21 days in the
36
-------
S.
ซ,"
Q
<
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
"A,
D
a:
8", 16", 24" - Application depths _
Total solids = 4.6%
1 i I
8 10 12
TIME, days
14 16
18 20
Figure 11. SAND BED DEWATERING OF LIMED (pH 11.5) SEPTIC TANK WASTE - RUN 5
LEBANON, OHIO
-------
24-in. (60.9-cm) bed. This result indicates that the longer the septage
remained liquid, the more gradual the ptt loss was. Measurements of pH
became more difficult as the septage approached the solid phase. Under-
drainage pH remained constant at pH 7.4 in all cases.
The nature and volume of bed underdrainage from the three fiberglass drums
was closely monitored during Run 5. The results of the volume determinations
appear in Figure 12. For the shallowest application depth, increasing
breakthrough was observed for the first 2 days, after which decreasing
volumes were collected until the eighth day, when virtually no more under-
drainage was present. For the 16-in. (40.6-cm) depth of applied waste,
underdrainage volume increased until the third day and then gradually
decreased to almost zero on the tenth day. The deepest (24-in. or 60.9-cm)
septage application produced increasing underdrainage volumes until the
fifth day. About 75 percent of the total underdrainage from both the
8-in. (20.3-cm) and 16-in. (40.6-cm) batches of septage was collected
within the initial 3 days of the experimental run. About 9 days were
required to collect a comparable percentage for the 24-in. (60.9-cm)
batch. Evaporation and sand-bed retention took place and accounted for
a 40-percent volume loss at 16- and 24-in. (40.6- and 60.9-cm) depths
and a 50-percent volume loss at the 8-in. (20.3-cm) depth when average bed
temperature was 28ฐC and average relative humidity was 80-percent. The
importance of these two variables has been emphasized in the literature.1"
An additional purpose for the use of the drums during Run 5 was to determine
the fate of chemical constituents in the septage after their application
onto the sand beds. The results are summarized in Table 9. Daily
measurements of underdrainage concentration and volume were made; total
mass for each constituent leaving the drum was computed and compared to
the mass initially applied to the drum. Table 9 indicates that in all
cases, the major portion of the organics (COD and TOG), heavy metals, and
phosphorus remained in the cake. Iron and zinc were complexed most
effectively. Copper and manganese were better retained in the cake at
the 8-in. (20.3-cm) depth than at the greater depths. Even though a 2-
to 3-pH-unit decrease occurred during the run, the phosphorus content of the
septage remained in the cake, with very little lost to the underdrainage.
Some nitrification took place through the sand in all cases. The increase
in ammonia levels present during the 16-in. (40.6-cm) and 24-in. (60.9-cm)
applications were probably due to hydrolysis of organic nitrogen.
Although the domestic septage was limed to pH 12.3 instead of pH 11.5,
no additional bacterial removals occurred in either the cake or the
underdrainage. The pathogens Salmonella species and Pseudomonas aeruginosa
were present in higher numbers (>1100 counts per 100 ml each) in the raw
septage than previously observed, but the amounts were reduced to <3 counts
per 100 ml upon contact with the lime. Some indications of Pseudomonas
regrowth appeared in the underdrainage.
38
-------
22
20
18
in
a 16
O
>
Q
z
14
12
10
8
~nn i i i i i i i r
8", 16", 24" -
Application depths
0 2 4 6 8 10 12 14 16 18 20 22
TIME, days
Figure 12. UNDERDRAINAGE BREAKTHROUGH - RUN 5
39
-------
Table 9.
CHEMICAL MASS BALANCE - RUN 5
INCHES Uh
SEPTAGE
APPLICATION
"~^-^.4cm)
PARAMETER**"-
TKN
IMH3-N
N03-N
Tot. P
COD
TOC
Fe
Cu
Zn
Mn
8 (20.3)
APPLIED *
72
4.2
0.006
16.3
3820
832
25.6
0.033
6.2
0.417
UNDER-
DRAINAGE*
1.71
1.16
2.21
0.117
20.7
6.0
0.014
0.006
0.004
0.035
16 (40.6)
APPLIED*
144
8.4
0.012
32.6
7640
1664
51.2
0.066
12.4
0.834
UNDER-
DRAINAGE*
13.1
10.6
1.4
0.055
172
65
0.124
0.030
0.016
0.142
24 (60.9)
APPLIED*
216
12.4
0.018
48.9
11,460
2,496
76.8
0.099
18.6
1.25
UNDER-
DRAINAGE*
22.2
18.6
2.3
0.092
299
110
0.147
0.032
0.050
0.284
"Total mass (grams)
40
-------
Results from Run 5 indicated that sand bed applications of limed septage
might be successfully made at depths greater than 8-in. (20.3-cm) but probably
less than 16-in. (40.6-cm) in the covered sand-bed environment. Satisfactory
dewatering was obtained in a reasonable period of time, and most of the
underdrainage was collected during the initial 3 days of the run for these
two application depths. A chemical mass balance around the drum verified
that most of the organics and inorganics remained with the limed cake,
even under conditions of decreasing pH. Evidence of nitrification through
the sand beds was also observed.
Run 6 A final experimental run was made to better quantify the loading
limits of septage discharges onto sand beds and to obtain additional data
on underdrainage characteristics.
3
Almost 2,500 gal (9.5 m ) of domestic septage was limed to pH 11.5, and
the required amounts were discharged to the sand beds and the underdrainage
collection drums. Application depths of 8-in. (20.3-cm), 12-in. (30.5-cm),
and 16-in. (40.6-cm) were examined. The chemical and general composition
of the trucked waste are shown below:
General:
Color
pH
Total solids
Total volatile solids
Chemical:
mg/1
COD 53,600
TKN 1,140
NH -N 48
brown
6.9
4.01
74.0
Chemical continued
0.3
Cu
Mn
The dewatering trend for Run 6 is shown in Figure 13. Total solids levels
of 20-percent were obtained after 5 days (8-in. or 20.3-cm depth), 12 days
(12-in. or 30.5-cm depth), and 17 days (16-in. or 40.6-cm depth). Once again,
the rate of dewatering was very much a function of the amount of septage
initially applied. Note that although the solids concentration of the
thickest batch eventually reached a truckable consistency, the process
was relatively slow and the mixture less homogenous than the others. The
8-in. (20.3-cm) application also appeared to be more effective than the
12-in. (30.5-cm) application; but the use of an intermediate application
may have been optimum. A major consideration, of course, is the frequency
of bed cleaning; application of incremental batches at various times may
be more desirable than only one loading.
Underdrainage volume was monitored for Run 6 in the same manner as for Run
5, and the results appear in Figure 14. As was the case previously, in-
creasing liquid breakthrough occurred for about 3 days, followed by very
little drainage for the remainder of the run. The dashed lines on the down
side of each curve in Figure 14 indicate that more than one day was
41
-------
I I I I I I I I I I I I I I 1 I I
8", 12", 16" - Application depths
TOTAL SOLIDS = 4.01%
I I I I I I I I I I I I I I I I i
8 10 12 14
TIME, days
20 22
Figure 13. SAND BED DEWATERING TREND - RUN 6
-------
30
28
26
24
22
20
i/>
^
o>
~ 18
LU
5 16
Z>
ฐ 14
? 12
ฃ 10
LU
Q
Z 8
1 T
I I
I
8", 12", 16" - Application depths -
I
I
024 6 8 10 12 14 16 18 20
TIME, days
Figure 14. UNDERDRAINAGE BREAKTHROUGH - RUN 6
43
-------
necessary to accumulate measurable volumes. Greater than 75-percent of the
total underdrainage was collected within the first 3 days for the 8-in.
(20.3-cm) and 12-in. (30.5-cm) applications and within the first 4 days
for the 16-in. (40.6-cm) application. Evaporation and sand-bed retention
once again accounted for significant volume losses and seemed to be
related to the depth of applied septage. Volume losses varied from 75-
percent for the 8-in. (20.3-cm) application, to 39.5-percent for the
12-in. (30.5-cm) application, to 34.6-percent for the 16-in. (40.6-cm)
application at an average sand-bed temperature of 21ฐC and an average
relative humidity of 70-percent.
Underdrainage characteristics were monitored as in Run 5. The results
appear in Table 10. Again, the great majority of pollutants was present
in the cake for each application. Similar trends to those experienced
during the previous run were observed for the fate of the heavy metals:
iron and zinc were better held in the cake than copper and manganese,
both of which were not appreciably retained in the 12-in. (30.5-cm) and
16-in. (40.6-cm) limed cakes. The phosphorus and organic contents of
the septage remained in the cake and were not lost to the underdrainage
during the run. Some nitrification through the sand beds also took place
in Run 6, although the amount was negligible for the 16-in. (40.6-cm)
depth.
Results from Run 6 confirmed much of the data obtained during Run 5.
They showed that lime-treated septage could be applied to sand beds at
a depth of 8 to 12-in. (20.3 to 30.5-cm), and that a truckable stage would
be reached between 6 and 13 days. Most of the septage chemical pollutants
remained in the cake throughout the experimental run. Most of the under-
drainage was collected in the first few days, and in most cases, it con-
tained relatively small amounts of organics and inorganics.
The study was ended after Run 6, but the sludges were allowed to remain on
the sand beds for several weeks following. No further monitoring was
made, but it was noted that (1) the cakes became detached from the sand
(i.e., they could be lifted off in sheets), and (2) no obnoxious odors
occurred.
44
-------
Table 10.
CHEMICAL MASS BALANCE - RUN 6
1 IV \j 1 1 k-O +-r 1
SEPTAGE
APPLICATION
^ป**^(cm)
PARAMETER*
TKN
IMH3-N
N03-N
Tot. P
COD
Fe
Cu
Zn
Mn
8 (20.3)
APPLIED*
59
8.75
0.012
10.8
3040
8.9
0.018
2.02
0.131
UNDER-
DRAINAGE*
0.75
0.30
2.02
0.005
7.0
0.028
0.002
0.002
0.026
12
APPLIED*
88.2
13.1
0.018
17.2
4560
13.4
0.027
3.04
0.196
(30.5)
UNDER-
DRAINAGE*
8.52
7.06
2.91
0.031
106
0.159
0.017
0.013
0.128
16 (40
APPLIED *
118
17.5
0.024
21.6
6080
17.8
0.036
4.04
0.262
6)
UNDER-
DRAINAGE*
14.3
12.7
0.026
0.050
162
0.341
0.014
0.020
0.198
"Total mass (grams)
-------
COST ANALYSIS
A cost estimate for the treatment of septage at small treatment plants via
the lime stabilization/sand-bed dewatering approach was made. The use
of covered sand drying beds was considered in the analysis. The following
assumptions have been made:
1. The average septic tank is pumped every 3 years and is of a
1000-gal (3.8 m3) capacity.
3
2. Each week day, 5,000 gal (19.0 m ) of septage is treated.
3. The average total solids content of the unlimed septage is 4.0
percent and requires 200 Ib lime per ton dry solids (100 kg
per metric ton) to raise the pH to 11.5.
3
4. The average drying time for each 5,000-gal (19.0 m ) limed batch
is 7 days based on an 8-in. (20.3-cm) applied depth.
5. Diffused air requirements to mix the septage and lime in the
holding tank is about 100 cfm per 1000 ft3., or 67 cfm based on
5,000 gal (19.0 m3).
6. A front-end loader would clear one bed after 7 days, the next
bed after 8 days, etc.
7. Labor is to be provided by sewage treatment plant personnel and
would require one man for 2 hr each day, or 10 man-hr per week,
to prepare and apply 25,000 gal (95.0 m3) per week to the beds.
Based on these assumptions, the following costs were computed:
Capital Costs:
Sand bed, 6,000-sq-ft (540 m2) $ 20,300
Bed cover @ $20/sq-ft ($220/m2) $120,000
Holding tank, 6,000-gal (22.8 m3), steel $ 2,100
Lime feeder and slurry mixer $ 2,100
Lime storage and handling building $ 20,000
Diffused air system, 67 cfm, or 100 cfm per 1000 ft3 $ 6,000
Yardwork $ 26,700
Front-end loader $ 11,000
Land (estimate 3 acres @ $1,000) $ 3,000
Total construction cost $211,200
46
-------
Capital Costs continued
Engineering, legal, fiscal and administrative cost
(22% of construction cost) $ 46,464
-Subtotal $257,654
Interest during construction $ 7,000
Initial investment cost : $264,664
Amortization (excluding land), 6%-25 yr $21,705/yr
Operation and maintenance costs:
Labor requirements:
Lime handling and mixing man-hr/yr 360
Sludge application man-hr/yr 520
Sludge removal and hauling man-hr/yr 230
Bed maintenance man-hr/yr 330
Diffused air system man-hr/yr 200
Total [Payroll Man-Hours] man-hr/yr 1,640
Labor costs:
Direct labor cost @ $4.70/hr $ 7,710
Indirect labor cost, 15% of above $ 1,160
Total labor cost/yr $ 8,870
Materials and supplies cost/yr:
Lime @ $4/cwt $ 350
Electric power @ 2c/kwh $ 410
Maintenance materials $ 3,420
Total materials and supplies $ 4,180
Amortization/yr $21,705
Total operation and maintenance cost/yr. $34,755
Households served/day 5
Total households served (assuming pumping every 3 yr) 3,900
Cost/yr/household $8.91
Note that more than 40-percent of the initial investment cost is contributed
by the purchase of the drying bed cover. Therefore, if open beds are used,
the annual cost per household would be considerably less than $8.91.
The cost of this septage treatment process appears to be competitive with
sludge handling costs at small activated sludge plants. For plants of the
1-mgd (3785-m^ per day) size, such costs vary between approximately $145
per dry ton($0.160 per dry kg) [for gravity thickening, anaerobic digestion,
and drying beds] and $360 per dry ton ($0.397 per dry kg) [for gravity
thickening, anaerobic digestion, sludge holding tanks, vacuum filtration,
and incineration]. Based on a total solids concentration of 4 percent, the
estimated cost of treatment by sand-bed dewatering of lime-treated septage
is $176 per dry ton ($0.194 per dry kg).
47
-------
CONCLUSIONS
1. Septic tank pumpouts are highly variable in their physical, chemical,
and biological characteristics.
2. The frequency of septage discharges to the treatment plant was greatest
during the summer months.
3. The septage contained high metal concentrations, and therefore any
effective treatment method must consider proper disposal of these
materials.
4. Poor settling characteristics were exhibited by the septage, even after
coagulant and polymer additions; therefore, separate treatment of super-
natant and sediment was not possible.
5. Results from this study have shown that lime stabilization of the
septage followed by sand-bed dewatering is a potentially feasible method
of septage treatment.
a) A holding tank equipped with air diffusers adequately mixed the
lime with the septage with little odor generation.
b) To achieve effective fecal coliform reduction, the septage must
be limed to a minimum pH of 11.5. Although fecal streptococci
were more resistant to lime than fecal coliforms, removals of
these organisms were also best at pH 11.5, and evidence of
regrowth was least at the high pH.
c) The pathogenic Salmonella species and Pseudomonas aeruginosa
in raw septage were destroyed by lime addition.
d) Septage applications of 8-in. (20.3-cm) on covered sand drying
beds can be made to achieve truckable cakes (20 to 25 percent
total solids concentrations) in less than 1 week in most cases.
e) Almost all of the organics and toxic metals were complexed in
the cake at pH 11.5; the underdrainage from the sand beds generally
contained low amounts of chemical pollutants.
f) The lime stabilization approach resulted in little volatile
solids reduction.
g) Average lime requirements to raise the septage to pH 11.5 were
168 lb per ton of dry solids (83 kg/metric ton).
h) Some nitrification took place through the sand beds.
i) Most of the underdrainage was collected in the first 3 to 4
days after application on the sand beds.
48
-------
j) Evaporation and sand-bed liquid retention contributed 35 to 75
percent of the underdrainage volume losses and was inversely
related to the application depth.
k) The economics of the process appear to be competitive with those
of sludge handling at 1-mgd (3785-m^ per day) activated sludge
plants.
49
-------
RECOMMENDATIONS
Though the results of this study have indicated that lime stabilization
followed by covered sand-bed dewatering offers a technically feasible and
cost-effective method of treatment for septic tank sludges, other methods
should also be evaluated. These methods include aerobic or anaerobic
digestion (either separately or in conjunction with treatment plant sludges),
or the commercially available Purifax system. In some instances it may be
feasible to hold intermittent septage discharges for continuous blending
with sewage treatment plant influent at rates that minimize plant upset.
Additional research that is necessary to better define the lime stabilization/
sand-bed dewatering concept includes:
(1) Examination of the performance of lime-stabilized septage on
uncovered sand beds over a variety of seasonal conditions to
determine:
a) typical drying rates to be expected;
b) the effect of prolonged drying times and intermittent wetting
on the cake, on the underdrainage quality, and on the re-
emergence of pathogens, pathogenic indicator organisms,
and odors; and
c) the long-term fate of cakes in landfill sites.
(2) Evaluation of the impact of underdrainage return on a sewage
treatment plant.
(3) Examination of the feasibility of land-spreading of limed septage
as a liquid and as a cake.
(4) Determination of the fate of viruses in the lime stabilization
of septage.
(5) Investigation of intermediate applications between 8-in. (20.3-cm)
and 12-in. (30.5-cm).
50
-------
REFERENCES
1. Bailey, James, and Harold Wallman, "A Survey of Household Waste
Treatment Systems," Jour. Water Poll. Control Fed., 43, 12, p. 2349,
December 1971.
2. Kolega, J. J., A. W. Dewey, R. L. Leonard, and B. J. Cosenza, "Land
Disposal of Septage," Paper No. NA-73-112, Proceedings of the First
International Meeting on Pollution held in Tel Aviv, Israel, June
12-17, 1972.
3. Kolega, J. J., B. J. Cosenza, A. W. Dewey, and R. L. Leonard,
"Septage: Wastes Pumped from Septic Tanks," Paper No. 71-411,
Presented at the 1971 Annual Meeting, American Society of Agricultural
Engineers, Washington State University, Pullman, Washington, June
27-30, 1971.
4. Kolega, J. J., "Design Curves for Septage," Water and Sewage Works,
118, 5:132-135, May 1971.
5. Smith, S. A., and J. C. Wilson, "Trucked Wastes: More Uniform
Approach Needed," Water and Wastes Engineering, 10, 3:48-57-
March 1973.
6. Jewell, William J., J. B. Howley, and D. A. Perrin, "Design Guidelines
for Septic Tank Sludge Treatment and Disposal," Presented at the
Seventh International Conference on Water Pollution Research, Paris,
France, September 9-13, 1974.
7. McCallum, Robert, "Treat Septic Tank Wastes Separately," The American
City, pp. 48-49, January 1971.
8. Buzzell, J. C. Jr., and C. N. Sawyer, "Removal of Algal Nutrients
from Raw Wastewater with Lime," Jour. Water Poll. Control Fed., 39,
10, R 16, 1967.
9. Colorado State University, "Lime Disinfection of Sewage Bacteria at
Low Temperatures," EPA Final Report No. 660/2-73-017, September 1973.
10. Farrell, J. B., J. E. Smith, Jr., S. W. Hathaway, and R. B. Dean,
"Lime Stabilization of Chemical-Primary Sludges at 1.15 MGD,"
Jour. Water Poll. Control Fed., 46, 1:113-122, January 1974.
51
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11. Battelle Pacific Northwest Laboratories, "Design, Development, and
Evaluation of a Lime Stabilization System to Prepare Municipal
Sewage Sludge for Land Disposal," EPA Final Report, No. 670/2-75-012,
In press.
12. Dean, Robert B., and James E. Smith, Jr., "Disposal and Recycling of
Wastewater Sludges Containing Lime," Proceedings of the 3rd Inter-
national Symposium on Lime, Berlin, Germany, May 1974.
13. Eikum, A. S., B. Paulsrud, and A. Lundar, Behandling av Septictankslam
(Treatment of Septic Tank Sludge), Interim Report No. 1, Norsk
Institut for Vannforskning Blindern (Oslo), PRAZ.8:0-58/74, March
1975.
14. Standard Methods for the Examination of Water and Wastewater, American
Public Health Association, New York, 13th Edition, 1971.
15. Kenner, B. A., and H. P. Clark, "Detection and Enumeration of
Salmonella and Pseudomonas Aeruginosa," Jour. Water Poll. Control
Fed., 4ฃ, 9:2163-2171, September 1974.
16. Burd, R. S., "A Study of Sludge Handling and Disposal," Water Pollution
Control Research Series, USDI, FWPCA, Publication WP-20-4, May 1968.
17. Internal EPA Memorandum from Walter McMichael to Water Feige, May
27, 1975.
52
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-75-036
3. RECIPIENT'S ACCESSIO!*NO.
4. TITLE AND SUBTITLE
AN ALTERNATIVE SEPTAGE TREATMENT METHOD:
LIME STABILIZATION/SAND-BED DEWATERING
5. REPORT DATE
September 1975 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
W. A. Feige, E. T. Oppelt, and J. F. Kreissl
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Municipal Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
In-house
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
3
Approximately 5 billion gal (18,927,000 m ) of septage must be annually disposed of
in the United States, a volume that is nearly equal to that of undigested raw and
secondary municipal sludges. Few desirable methods exist for disposing of the sludge
that is periodically pumped from septic tanks. This report describes the results
obtained from a pilot study of one alternative septage treatment method-lime
stabilization followed by covered sand-bed dewatering.
The study was conducted in two phases. Phase I (4 months) consisted of the general,
chemical, and biological characterizations of the incoming septage. Attempts were
made to thicken the material via stirring, polyelectrolyte addition, and lime
addition. Phase II (9 months) concerned itself with the application of lime septage
onto covered sand beds. Four experimental runs were conducted to assess the feasi-
bility of such an approach. The septage was limed to pH 10.5, 11.0, and 11.5 and
applied at 8-in (20.3-cm) depths. Underdrainage and cake characteristics were
monitored and practical sand-bed application rates were determined. A materials
balance of chemical constituents around the system was made.
A cost estimate for the treatment of septage at small treatment plants via this
method is included.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COS AT I Field/Group
*Septic tanks
Sludge disposal
Sand bed dewafceEing
Septage
Lime stabilization
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
61
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
53
iUSGPO: 1975 657-695/5309 Region 5-1
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