SEPIAGE TREATMENT
AND DISPOSAL
by
I. A. Cooper1 and J. W. Rezek2
Prepared for the
Environmental Protection Agency
Technology Transfer
Seminar Program
on
Small Wastewater Treatment Systems
1977
-Senior Project Manager; and
President, Rezek, Henry, Meisenhelmer & Gende, Inc.,
an HMG Group Affiliate
Colorado, Illinois and Missouri
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GENERAL
The first priority of the Environmental Protection Agency's program
to abate water pollution has been focused on providing adequate waste-
water treatment for sewered communities. However, results of the 1970
census inform us that 16.6 million housing units, or over 24.5 percent of
the total housing units in the United States, relied on septic systems for
wastewater disposal.
The geographical distribution of the use of septic systems, as seen
in Figure No. 1 and Table 1, shows states with over 35 percent usage
located in New England, the Southeast, and the Pacific Northwest. Most
North Central, Northeastern, and Southeastern states have only a slightly
lower usage of these on-site disposal facilities. The Southwestern states'
usage of septic tanks is between 10 and 20 percent. On a local level,
many counties in New Jersey, New York, California, and other states
have over 50,000 housing units which use on-site waste disposal systems,
while their statewide usage appears less significant. Areas with over
100,000 housing units using on-site waste disposal systems include
suburban New York, Los Angeles, and Miami .
The use of a septic system requires periodic maintenance, which
includes pumping out the accumulated scum and sludge called septage.
Kolega^ has reported a septage buildup of between 65 and 70 gallons per
capita per year in properly functioning septic systems.
Various recommendations exist for time periods between pumping out
a septic tank, most between two and five years. After a hauler pumps
out the homeowner's septage, this highly offensive sludge must be disposed
of in a safe, cost-effective, and convenient manner. Table 2 shows the
estimated statewide septage generation per year based on pumping the
average 1000-gallon septic tank once every four years.
Septaqe Characteristics
Septage is a highly variable anaerobic slurry with characteristics
that include large quantities of grit, grease, highly offensive odor, the
ability to foam, poor settling and dewatering, high solids and organic
content, and quite often, an accumulation of heavy metals. Tables 3,
4, and 5 are the result of previous research work compiled by the U .S. EPA's
Cincinnati research group, as well as extreme values as reported in the
literature.
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PERCENT OF
HOUSEHOLDS USING
SEPTIC TANKS
OVER 35%
Y///////A 25% TO 35%
j j UNDER 25%
(SOURCE: 1970
CENSUS)
Figure 1. Distribution of On-Site Septic Systems, by State, in the United States
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Table 1. Sewage Disposal Characteristics for the United States
from 1970 Census3
Housing Units
on Public Sewers
Housing Units
with Septic Tanks
Housing Units
with Other
State
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Conn.
Delaware
Wash.D.C .
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Mass.
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
N.Hampshire
N. Jersey
N .Mexico
New York
N.Carolina
N. Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Number
566,307
55,511
446,304
355,684
6,084,632
612,659
608,603
130,259
277,068
1,509,682
848,516
161,438
137,891
3,072,266
1,060,942
662,320
594,758
536,388
778,247
169,975
953,470
1,339,304
1,947,137
864,984
338,581
1,173,688
154,581
r-385,860
14 7,, 74 3
132,475
1,890,977
230,737
4,824,525
733,848
128,967
2,565,317
686,240
448,967
2,798,522
% of
Total
50.80
62.69
77.11
52.85
87.22
82.47
62.82
74.44
99.52
60.61
57.85
74.78
57.87
83.20
61.97
69.35
75.52
50.57
67.90
50.11
77.23
72.83
68.43
70.92
48.56
70.47
64.21
75.44
86.07
53.26
82.03
71.60
98.34
45.32
64.32
74.41
73.17
61.04
72.13
Number
385,345
18,629
114,433
220,287
853,013
113,290
354,585
39,860
454
938,352
474,455
50,558
93,146
554,603
589,794
257,889
163,918
312,856
287,481
140,409
243,728
490,365
847,433
307,441
209,115
359,278
74,198
105,320
21,988
109,015
404,241
65,781
1,289,253
687,572
53,074
779,510
203,174
275,944
985,014
% of
Total
34.56
21.03
19.77
32.73
12.23
15.25
36.60
22.78
0.16
37.67
32.35
23.42
39.09
15.02
34.45
27.00
20.82
29.50
25.. 08
41.39
19.74
26.67
29.78
,25.21
30.00
21.57
30.82
20.59
12.81
43.83
17.53
20.42
20.93
42.46
26.47
22.61
21.66
37.52
25,39
Number
163,139
14,423
18,013
96,999
38,324
16,689
5,633
4,870
- 871
42,743
143,654
3,844
7,266
65,080
61,061
34,829
28,808
211,328
80,245
28,817
37,271
9,120
50,509
47,070
149,514
132,617
11,974
20,266
1,951
7,231
10,123
25,722
44,883
197,859
18,457
102,566
48,413
10,559
96,502
% of
Total
14.63
16.29
3.11
14.41
0.55
2.25
0.58
2.78
0.31
1.72
9.79
1.78
3.05
1.76
3.57
3.65
3.66
19.93
7.01
8.50
3.02
0.50
1.78
3.86
21.44
7.96
4.97
3.96
1.13
2.91
0.44
7.98
0.73
12.22
9.21
2.98
5.16
1.44
2.48
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Table 1. Sewage Disposal Characteristics for the United States
from 1970 Census3 (Continued)
Housing Units
on Public Sewers
Housing Units
with Septic Tanks
Housing Units
with Other
State
Rhode Island
S. C arolina
S. Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
W .Virginia
Wisconsin
Wyoming
Total U.S.
Total Housing
Number
197,947
363,611
140,258
671,248
2,989,684
258,649
72,264
906,030
786,551
304,151
994,926
86.983
48,187,675
Units = 67,
% of
Total
64.41
45.18
63.30
51.76
78.49
82.93
48.23
71.02
65.28
51.31
70.26
75.94
71.18
693,842
Number
107,544
334,210
62,366
457,008
654,283
49,249
68,265
408,213
403,909
187,028
: 371,567
23,349
16,601,792
(100%)
% of
Total
34.99
41.53
28.14
35.24
17.18
15.79
45.56
27.49
33.52
31.55
26.24
20.38
24.52
Number
1,843
106,996
18,970
168,672
'164,950
3,976
9,315
170,580
14,464
101,600
49,549
4,217
2,904,375
% of
Total
0.60
13.29
8.56
13.00
4.33
1.28
6.21
11.49
1.20
17.14
, 3.50
3.68
4.30
Gra'ner^ reports septage characteristics in Nassau and Suffolk counties
as low as medium to strong wastewater, while Goodenow^ in Maine found
some samples with total solids and suspended solids over 130,000 mg/1
and 93,000 mg/1, respectively. Tilsworth in Alaska obtained some sep-
tage samples with BOD5 over 78,000 mg/1 andCOD's over 700,000 mg/1.
The EPA mean concentrations are good indicators of septage concentrations
when compared to other researcher's data.
The geometric mean heavy metal content of residential septage from
Lebanon, Ohio was compared to geometric means found in raw and digested
sludge from 33 U .S. sewage treatment plants, and Danish and Swedish
sludge metal content in Table 5. On a mg/kg dry weight basis, domestic
septage contains one-half to two orders of magnitude less heavy metal
than does municipal sludge7.
Bacteriology
Bacteriologically, septage contains predominately gram-negative, non-
lactose fermenters. Many of these micro-organisms, such as Pseudomonas,
are considered aerobic and have been found in septic tanks. Numerous
obligate anaerobes are present, but only spore-forming types, including
Clostridium lituseburence and Clostridium perfringens have been recovered.
4
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Table 2. Estimated Household Septage Generation
by State*
State
M3Ar. Gal.Yr.
(Millions)
M3Ar. Gal". Air.
(Millions)
State
Montana
Nebraska
Nevada
N.Hampshire
N Jersey
N. Mexico
New York
N.Carolina
N. Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
S. Carolina
S. Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
W.Virginia
Wisconsin
Wyoming
Total U.S.
*Based on pumping a 1,000-gallon septic tank every four years.
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Conn.
Delaware
Wash.D.C.
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Mass.
Michigan
Minnesota
Mississippi
Missouri
0.36
0.02
0.11
0.21
0.81
0.11
0.34
0.00
0.00
0.89
0.45
0.05
0.09
0.52
0.56
0.24
0.16
0.30
0.27
0.13
0.23
0.46
0.80
0.29
0.20
0.34
96.3
4.7
28.6
55.1
213.3
28.3
88.6
1.0
0.11
234.6
118.6
12.6
23.3
138.7
147.4
64.5
41.0
78.2
71.9
35.1
60.9
122.6
211.9
76.9
52.3
89.8
0.07
0.10
0.02
0.10
0.38
0.06
1.22
0.65
0.05
0.74
0.19
0.26
0.93
0.10
0.32
0.06
0.43
0.62
0.05
0.06
0.39
0.38
0.18
0.35
0.02
15.67
18.5
26.3
5.5
27.3
101. 1
16.4
322,.3
171.9
13.3
194.9
50.8
69.0
246.3
26.9
83.6
15.6
114.3
163.6
12.3
17.1
102.1
101.0
46.8
92.9
5.8
4,141.91
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Table 3. Septage Characteristics (All values in mg/1 except where noted)
EPA Mean
Cone.
Minimum
Reported
Maximum
Reported
Parameter
Total Solids
Total V.S.
Total S.S.
Volatile S.S.
BOD 5
COD
TOG
TKN
NH3-(N)
N02
NO3
Total P
PO4
Alkalinity
Grease
pH (units)
LAS
*Values represent ratio of maximum to minimum values.
40,000.0
26,000.0
15,000.0
18,100.0(46)
5,000.0
45,000.0
15,000.0
600.0
150.0
o 7(46)
3 '.2(46)
150.0
64.0(46)
1,020.0(46)
9,561.0
6-9
150.0
1132.o(4)
4500. 0(46)
310.0(6)
3660.0(46)
440. 0(4)
1500. 0(6)
1316. 0.(7)
66.0(7)
6.0(7)
<0.l(26)
<0.l(26)
2o!o(46)
10.0(46)
522.0(6)
604. 0(7)
1.5(4)
110.0(7)
130,475. 0(5)
71,402.0(5)
93,378.o(5)
51,500.0(33)
78, 600. 0(6)
703,000.0(6)
96,000.0(26)
1,900.0(46)
380.0(26)
1.3(26)
1,1.0(18)
760. 0(7)
170.0(46)
4,190.0(6)
23,368.0(7)
12.6(4)
200.0(7)
Variability*
115
16
301
14
179
469
73
29
63
13
110
38
17
8
39
8
2
Table 4. Septage Metal Concentrations (All values in mg/1)
EPA Mean
Cone .
50.0
0.1
. 0.5
1.0
8.5
200.0
0.1
5.0
1.0
2.0
0.1
50.0
Minimum
Reported
2.0 (7)
0.03 (7)
0.05 (7)
0.30 (7)
0.30 (26)
3.0 (7)
0.0002 (7)
0.50 (7)
0.20 (7)
1.50 (7)
0.02 (7)
33.00 (26)
Maximum
Reported
200.0(7)
0.5(7)
10.8(7)
3.0(26)
34.0(7)
750. 0(7)
4.0(7)
32.0(7)
28.0(26)
31.0(7)
0.3(7)
1 53.0(7)
Metal
Al
As
Cd
Cr
Cu
Fe
Hg
Mn
Ni
Pb
Se
Zn
*Values represent maximum to minimum values.
6
Variability*
100
17
216
10
113
250
20,000
64
140
21
15
5
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Table 5. Heavy Metal Content of Septage and Municipal Sludge^
(Mg/kg dry solids)
M etal
Cd
Cr
Cu
Hg
Mn
Ni
Zn
Lebanon, Ohio
Septage
5.5
21.0
28.1
0.24
106.0
28.5
43.0
1,050.0
1,270.0
6.5
475.0
530.0
1,280.0
Salotto Other U.S. Denmark Sweden
69
840
960
28
400
240
2,900.0 2,600
10.0
110.0
340.0
7.8
350.0
37.0
9.3
170.0
670.0
5.8
400-.0
65.0
2,600.0 1,900.0
Calabro was unsuccessful at isolating non-spore forming obligate anaerobes, such
asBacteriodes, since they are exceedingly oxygen-sensitive, the pumping operation
may expose them to incident oxygen, killing them. Figure No. 2 shows the
comparative enumeration of specific types of micro-organisms from 12 sep-
tage and septic tank sewage samples, with 95-percent confidence limits.
The standard plate count (SPC) per ml was determined after 48 hours incu-
bation in aerobic and anaerobic conditions at 24°C +1°. When the septic
tank is pumped, mixing of the bottom sludge, intermediate wastewater,
and upper layer of scum occurs, yielding both aerobes and anaerobes.
The presence of aerobic types in a septic tank can be explained by either
the dissolved oxygen of the incoming sewage providing sufficient oxygen
to allow limited aerobic growth, or by chemostatic displacement of effluent
by the influent furnishing a relatively constant number of aerobic micro-
organisms . It is fortunate that Pseudomonas and other similar aerobic bac-
teria are found in the septic tank, as they add limited lipid and detergent
degradation capabilities.
Calabro estimated the gross relative stability of septage, septic tank
sewage, and domestic wastewater using methylene blue as a redox indica-
tor of biological activity. Septage samples changed color in five hours,
septic tank sewage between 6 and 21 hours, and raw domestic sewage
between 17 and 21 hours45.
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CO
S A-Seplage
v> B- Septic Tank Sewage
o 8
% 7
E 6
"S 5
1 4-
2 3
V
O '
-J
:==
...
r—-«
b
c
...
>5
°X
r-i
> Confidence Li
-
m
...
it
s
i — i
r— n
.
AB AB AB
Aerobic Anaerobic Synthetic
A B A B A B
E.coli Lactose Non- Lactose
Fer menters Fermenters
Figure 2 Comparative Enumeration Of Specific Types Of
Microorganisms With 95 % Confidence Limits. (After Calabro)
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LAND DISPOSAL
Septage disposal on the land can include surface spreading and sub-
surface injection, spray irrigation, trench and fill, sanitary landfills,
and lagooning. Common requirements in all land disposal alternatives
are analyses of soil characteristics, seasonal groundwater levels, neigh-
boring land use, groundwater and surface water protection and monitoring,
climatological conditions, and site protection, such as signs and fencing.
Land spreading requires a knowledge of land slopes, often limited to
eight percent, and runoff conditions. Other requirements may include
storage facilities for times when land application is inadvisable, crop
management techniques, odor control procedures, and loading criteria.
Loading criteria generally are determined by agricultural considerations
which result in organic and heavy metals limitations.
Loading Factors
Nitrogen—
In most agricultural areas, available existing nitrogen is far below
levels needed for optimum crop yield. As a result, artificial sources of
nitrogen are generally added, such as commercial fertilizer. Nitrogen is
available as a plant nutrient in the form of the ammonium ion which is
retained on negatively charged soil particles^. Septage is rich in avail-
able ammonia, with about 25 percent of the total 5 to 8 pounds/1,000
gallons of nitrogen occurring in this form. Soil bacteria will transform
NH3~N to NO3~N, but much of this nitrogen may not be available for plant
use if hydraulic loadings cause the highly soluble NO3~N to be leached
below plant roots.
Nitrogen may be lost if poor drainage conditions exist. This causes
a rapid denitrification to occur, converting nitrate to nitrogen gas.
* v
Health aspects dictate nitrogen be applied at rates less than or equal
to plant nitrogen uptake requirements. Otherwise, excess nitrates could
form and contaminate groundwater or surface water through leaching or
runoff. Since it is generally recognized that nitrate concentrations above
10 mg/1 in drinking water may cause health problems, particularly infant
methemoglobinemia (nitrate cyanosis), concern is justified. Nitrate
pollution in surface waters also will lead to accelerated eutrophication, or
premature aging of lakes and streams.
-------
The State of Maine has reported in its Maine Guidelines for Septic
Tank Sludge Disposal on the Land that a loading criteria of 62,500 gallons/
acre/year on well-drained soils and 37,500 gallons/acre/year on moderately
well-drained soils will not result in pollution caused by excess nitrogen.
These loadings result in an application of 500 pounds/acre/year in well-
drained soils and 300 pounds/acre/year in moderately well-drained soils.
Maine officials report that monitoring wells at sites that follow these
criteria shows no signs of pollution.
Phosphorous and Potassium—
Both phosphorous and potassium are basic requirements for plant
growth. Land application of septage usually results in excess phosphor-
ous applied, compared to plant requirements, while a potassium "deficiency
will result at the same dosage. Both elements, however, tend to become
fixed in the soil and are not liable to leach out. For this reason, nitrogen
requirements usually govern the organic considerations in application rates.
Heavy Metals--
The phytotoxic metals (Zn, Ni, and Cu) and Cd are foliage-limiting
factors in the amount of sludge which may be applied to the land. How
these metals are retained in the soil is complex and poorly understood,
but workable estimates of limits based on soil cation exchange capacity
(CEC) have been proposed by researchers in Wisconsin^ .
The CEC can be estimated by a displacement procedure which yields
an exchange capacity in milligram equivalents (meq) per 100 g of soil.
A lifetime application load to any soil has been proposed" which limits
the amounts of phytotoxic metal applied in terms of Zn equivalent. Fur-
ther search on lifetime metal loading limits is indicated and, in fact,
underway, as it has been observed that some heavy metals may become
tied up in the soil structure over a period of time. This is the result of
a reversion effect linked with a solid state diffusion of metal into crystal-
line soil structures. Attenuation of the effects of overapplication of phy-
totoxic metals in sludges to the land may be attributed to this mechanism.
The Wisconsin metal loading criterion limits the Zn equivalents to 10
percent of the CEC . Zn equivalents are based on Cu being thought of as
twice as toxic as Zn and Ni four times as toxic as Zn, although other
researchers have proposed relative toxication other than 1:2:4.
10
-------
The calculation of permitted lifetime loading of metal from septage is
expressed as:°
ML =
where:
ML = maximum loading to soil, tons sludge/acre
CEC = cation exchange capacity of soil, meq/100 g
Zn = Zinc content of sludge, mg/1
Cu = Copper content of sludge, mg/1
Ni = Nickel content of sludge, mg/1
Cd toxicity presents a special problem in its mobility and its potential
in accumulating in the edible portions of plants. Effects are cumulative
and insidious. For example, excessive alimentary cadmium intake mani-
fests itself in humans as Itai-Itai disease^. This hazard is endemic to
the Jintsu River Region in Japan. The affected area is situated below the
Kamioka mine. High concentrations of cadmium, lead, and zinc have been
traced to this mine's effluent, which drains into the Jintsu River. This
area has shown high concentrations of cadmium in rice, fish, and river
water. Drainage from the mine varied from 0.005 mg/1 to 0.6 mg/1 Cd at
a pH of 7 to 8. Further downstream, the river water contained.almost no
cadmium, yet suspended material had concentrated the cadmium, showing
a concentration of between 363 ppm to 382 ppm. Solids had carried over
into the rice paddies where rice roots concentrated the cadmium* * . Rice
roots were analyzed and found to contain up to 1300 ppm Cdr^. People
complaining of renal dysfunctions were diagnosed as having Itai-Itai
(Ouch-Ouch) disease. Other symptoms include advanced skeletal de-
formations with weakened bones which fracture easily. Friberg^ hypothe-
sized that bone structure weakness was experienced through decalcifica-
tion of bone material by cadmium replacement.
Q
One recommendation for Cd limits is based on work in Wisconsin
whichijound that two pounds/acre and above showed a significant increase
in metal concentration of plants over control plants. The proposed limits
are two pounds/acre/year with a total lifetime loading of 20 pounds/acre^.
The proposed limits of phytotoxic metals and cadmium are reported to
be low enough to protect reasonably well chosen disposal sites.
Based on Lebanon, Ohio septage and Salotto findings, as shown in
Table 5, approximately eight times as much septage could be applied to
the land as could municipal sludge, using Cd as the limiting factor. Using
11
-------
the phytotoxic metals limit, approximately five times as much septage
could be applied as could municipal sludge. ?
An example calculation for septage application rates based on a com-
bination of phytotoxic metals and Cd, again assuming average Lebanon,
Ohio septage and a soil CEC of 10 meq/lOOg, is presented.
P
Metal Loading Calculation — °
Septage Concentration: Zn = 50 mg/1
Cu = 8.5 mg/1
Ni = 1.0 mg/1
Cd = 0.5 mg/1
1 . Total Metal Equivalent Loading: 65 x CEC =650 Ib./Ac .
2. Septage metal equivalent per ton:
50 + 2(8.5) +4(1.0) _ 71.0 n 1/I9l, ,. . . .
- ' - : — "~ — ~7m — * *• Iks. metal equiv. /ton septage
3. Total lifetime loading permitted:
-SSQ- = 4577.5 tons/acre
0.142
4 . Yearly loading limit due to Cd:
2 x 5°° = TT^ = 2000.0 tons septage/acre for 2 Ibs. Cd
ppm Cd U.5
5. - Total lifetime Cd loading permitted:
2000.0
20 pounds/acre x - = 20,000.0 tons/acre
Therefore, Cd loading is limiting on a yearly basis (2000.0 tons/A/year),
while phytotoxic metal equivalents are limiting on the lifetime of the site
(4577.5 tons/A/year).
It is interesting to note that the yearly loading based on Cd of 2000
ton/A/year translates to 0.469 million gallons/acre/year, or 4.8 times
the application rate based on the limiting nitrogen loading in this example
of 500 pounds/acre/year. A well-drained site receiving this septage would
have a phytotoxic metal loading lifetime of 11 years at the nitrogen appli-
cation rate.
12
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Pathogens—
The natural digestion process in a septic tank does not always result
in a pathogen-free material, as related by Calabro, who found salmonella
and other potentially dangerous organisms in septage. For this reason,
care must always be taken in handling this material.
Evidence for pathogen reduction when septage is exposed to atmospheric
conditions is based on work performed by the MSDGC and others. In
Table 6, after seven days only one percent of the original coliforms sur-
vived. Table 7 shows basically the same reduction for sludge cake applied
to the land. From a laboratory study, Table 8 shows the number of days of
storage required to reduce several viruses and bacteria to 99 .9 percent of
the original values at different temperatures .
Table 6. Fecal Coliform Counts of Stored Digester Supernatant
Exposed to Atmospheric Conditions ^
Fecal Coliform Counts Percent
Days (per 100 ml) Survival
0 800,000* 100.00
2 20,000** 2.50
7 8,000 1.00
14 6,000 0.75
21 <2,000 <0.25
35 <20 <0.01
*Fecal coliform count just prior to lagooning.
**Fecal coliform count after lagooning.
Table 7. Disappearance of Fecal Coliforms in Sludge Cake
Covering a Soil Surface* 3
No. of Fecal Goliforms/
^ No. Days after Gm sludge Cake
Sludge Application (Dry Weight)
1 3,680,000
2 655,000
3 590,000
5 45,000
7 30,000
12 700
13
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Table 8. Laboratory Study on Days of Storage Required for 99 .9 Percent
Reduction of Virus and Bacteria in Sludge^
No. of Days at
Organism 40(, 2o;Oc 2goc
Poliovirus 1 110 23 17
Echo virus 7 130 41 28
Echovirus 12 60 32 20
Coxsackievirus A9 12 — 6
Aerobacter aerogenes 56 21 10
Escherichia coli 48 20 12
Streptococcus faecalis 48 26 14
Pathogens reportedly have been removed by the soil structure by various
mechanisms, predominately filtration, soil inactivation, and die-off. Patho-
gen travel is usually restricted to the order of feet from point of application
unless runoff or channeling occur, potentially polluting surface and ground-
water.
8
While the Wisconsin guidelines for sludge disposal on agricultural land
do not recommend raw sludge spread without treatment, the partially digested
septage may be applied if some preventive measures are followed, such as
lagooning prior to land disposal, or immediate liming of septage into the
ground.
Disposal Methods
Septage disposal techniques include surface application on the land by
spreading from septage hauler trucks, transfer vehicles such as tank wagons,
ridge and furrow practices, and spray irrigation. Subsurface application
techniques include Plow Furrow Cover (PFC) and Subsurface Injection (SSI)
alternates. Placement intrenches, lagoons, and Sanitary Landfills (SLF)
are classified as burial practices.
Surface Application—
This method of septage disposal is perhaps the most frequently used
technique in the United States today. Future studies should give consider-
ation to stabilization and additional pathogen reduction before surface
application of septage on the land, as no discussion of septage health
hazards in this respect is available.
14
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With any surface application technique, some nitrogen loss occurs
through ammonia volatilization, with the highest losses occurring with
spray irrigation.
Land Spreading—The hauler truck which pumps out the septic tank is
frequently the vehicle that applies septage to the land. Consideration
should be given to intermediate holding facilities before application to
the land. Storage is necessary during or imminent to precipitation in order
to prevent runoff of contaminated water. In colder climates, land appli-
cation should be limited to non-frozen surfaces to prevent runoff during
thaw conditions . Pathogen die-off with storage, presented under the
previous heading, is also a factor indicating the necessity of storage.
With a storage facility, disposal can be performed either by the hauler
truck or by a tank wagon usually pulled by a farm tractor. The choice
between the two is one of economics . £ larger operation may choose to
have its trucks on the road, with septage spreading being performed by
a separate spreading crew, thus freeing the more expensive tank truck to
perform the cleanout functions. A smaller septage hauler may prefer to
use one vehicle to perform both tasks, thus leveling his work load by
spreading septage during slack hauling time periods. In some instances,
soil conditions may require the use of flotation-type tires which are not
suitable'for long-distance highway use. This would dictate the use of
separate collection and spreading vehicles.
Ridge and Furrow—Ridge and furrow disposal method has been used
to dispose of sludges on relatively level land, usually limited to 1.5-
percent slopes. No instances of septage disposal by this practice were
found during the course of this study. While this method can be used to
distribute septage to row crops during their growth, care should be taken
to ensure these crops are not for human consumption.
Spray Irrigation—Spray irrigation of septage necessitates a storage
lagoon prior to disposal. Portable pipes and nozzle guns are used rather
than fixed or solid sets. Since the septage must be pumped at 80 to 100
psi through 3/4-inch to 2-inch nozzle openings, a screening device at
the lagoon's'pump suction is mandatory. Since spray irrigation also offers
the greatest potential for offensive odors, knowledge of wind patterns and
a well-located site are important during design stages.
Subsurface Application—
Soil incorporation techniques offer better odor and pest control than
surface spreading techniques, plus likelihood of inadvertent pathogen
15
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contamination to humans is greatly reduced. Disadvantages include full
incorporation of all nitrogen, since ammonia volatilization is eliminated,
which reduces any nitrogen-loading safety factor from ammonia loss in
surface spreading. Costs increase over surface spreading, because a
storage lagoon or tank becomes mandatory, and capital is required for the
subsurface injection equipment. A resting period of one to two weeks is
required before equipment can be driven over the waste-incorporated
land.8
Three methods have been used to inject septage into the land, in-
cluding Plow-Furrow-Cover (PFC), Sub-Sod Injection (SSI), and a Terre-
ator1 5.
Plow-Furrow-Cover (PFC)—A typical setup using this method*consists
of a single mold-board plow, a furrow wheel, and a coulter. Septage is
applied to the land in a narrow furrow and immediately covered with a
following plow.
Sub-Sod Injection (SSI)—This technique employs a device which in-
jects a wide band or several narrow bands of septage into a cavity six
to eight inches below the surface. Some equipment uses a forced closure
of the injection swath.
Terreator—This is a patented device which opens a 9.5-cm, mole-type
hole with an oscillating chisel point. A tube then places the septage up
to 50 cm below the surface at a rate of 24.8 liters/linear meter (2 gallons/
linear foot)15. Kolega15 found that subsurface application of 300 pounds
of nitrogen per year in a well-drained soil did not produce any noticeable
groundwater quality variation with either PFC, SSI, or Terreator methods.
Burial—Broad forms of septage burial include disposal intrenches,
sanitary landfills, leaching lagoons, or settling lagoons followed by in-
filtration-percolation beds. Foul odors are endemic to these operations
until a final soil cover is placed over the open surfaces of trenches or
landfills. Lagoon management practices, such as inlet design, location,
or liming, minimize these problems.
Site selection is important, not only for odor control but also to mini-
mize potential groundwater and surface water pollution problems . Many
states require sampling wells and groundwater monitoring as an operational
check.
Trenches—Septage disposal in trenches is similar to disposal in lagoons,
except trenches are usually a smaller scale alternative than the lagoon.
16
-------
Septage is placed sequentially in one of many trenches in small lifts,
six to eight inches, to minimize drying time1^. When the trench is filled
with septage, two feet of soil should be placed as a final covering, and
new trenches opened. New York recommends trenches be a maximum of
seven feet deep. Sufficient room must be left between trenches'for move-
ment of heavy equipment. The trench and fill technique is quite often used
at sanitary landfills.
Sanitary Landfills—When a sanitary landfill accepts septage, leachate
production and treatment must be investigated. For moisture absorption,
New Jersey recommends a starting value of ten gallons of septage to each
cubic yard of solid wastes. Septage should be prevented from entering
landfills in areas with over 35 inches/year rainfall if leachate prevention
and control facilities are absent, or if an isolated hydrogeological under-
lying rock strata is not present.
A six-inch earth cover should be applied daily to each area that was
dosed with septage. A two-foot final cover should be placed within a
week after the placement of the final lift*?. Many designers suggest max-
imum cell height of a cell should be eight feet^. Using the New Jersey
criterion and an eight-foot cell height, 1000 gallons of septage could be
distributed on 340 square feet.
1 7
Leaching Lagoons—Connecticut has been advocating leaching lagoon
systems consisting of earthen anaerobic-aerobic sludge digestion cells.
Septage is discharged into a vertical manhole at the edge of a lagoon and
exits about one-third the distance into the cell near the bottom. The
lagoon bottom is not sealed, and at least one-third of the lagoon is above
ground level to facilitate liquid removal by hydrologic gradient and enviro-
transpiration. The minimum depth of the lagoon is three to five feet. Sludge
is periodically removed, and effluent from this anaerobic lagoon flows
through a controlled outlet to an aerobic leaching lagoon. Lime addition
is suggested to maintain pH between 6.8 and 7.2. When lime is introduced
into the influent manhole with the septage, the lime settles at the end of
thetanaerobic leaching lagoon influent pipe and exerts little or no effect
on lagoon pH^. Parallel sets of these series lagoons are recommended.
The capacity of each cell is equal to 0.1 of yearly volume, based on 50 •
70 gallons per capita per year of contributing population.
Massachusetts^? requires a minimum six-foot deep anaerobic lagoon,
followed by at least six percolation beds having one square foot per gallon
per day of design capacity. The lagoon design requirements call for a
sizing of one gallon per capita per day, with a minimum of 20 days'
17
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retention at average flow. The recommended discharge below the liquid
level has caused problems by stirring up bottom sediments and releasing
foul odors. Acton, Massachusetts now allows haulers to discharge over
rip-rap into the lagoon, which, they report, lessens odor problems.
Disposal Lagoons
Disposal lagoons are usually a maximum of six feet deep and allow
no effluent or underdrain system. These disposal lagoons require small
(six to twelve inches') application rates and sequential loading of lagoons
for optimum drying. Series or series parallel lagoons with two years
capacity each and a two-foot maximum depth are called for in New York
State Guidelines18. After drying, solids may"Be bucketed out^for disposal
in a sanitary landfill, with use of the lagoon for further applications; or
two feet of soil may be placed over the solids as a final cover. Many
states repprt odors may be controlled by placing the lagoon inlet pipe
below the liquid level and having water available for haulers to immedi-
ately wash any spills into the lagoon inlet line.
Comparative Land Disposal Practices
The land disposal methods previous discussed in this section are
compared in Table 9. This matrix assumes a moderately well-drained
soil, nitrogen loading requirements, northern climatic conditions (requiring
use of holding tanks or lagoons over inclement weather). In surface spread-
ing techniques, approximately 1/4 to 1/2 the ammonia nitrogen may be lost,
raising the amount of nitrogen that can be added.
Cost comparisons were not included here, as only very limited in-
formation is available, and cost variations in existing systems vary
widely depending on whether land must be bought and amortized over the
life of the project, rented, or already municipally owned; the amount of
regrading, clearing and grubbing, if necessary, and access requirements.
SEPARATE TREATMENT FACILITIES - SEPTAGE ONLY
Alternatives for treating septage at a separate treatment facility include
aerated lagoons, anaerobic/aerobic processing, composting, the BIF Purifax
Process, and chemical Treatment.
Aerated Lagoon
Aerated lagoons may be employed for treating septage if the aerators
have the required oxygen transfer capacity and impart sufficient turbulence
18
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Table 9 . Land Disposal Characteristics
Land Disposal
Method
Surface
Application
Spray Irrigation
Acreage Required
@ 10,000 gpd
250 days/year
370 + Storage +
Buffer Zone
Ridge & Furrow 400 + Storage
Hauler Truck
Spreading
400 + Storage
Farm Tractor 400 + Storage
w/ Tank Wagon
spreading
Sub-Surf ace
Application
Tank Truck w/ 420
Plow
F urrow-C over
C haracteristic s
Large orifices for
nozzle
Irrigation lines
to be drained
after irrigation
season
Land preparation
Larger volume
trucks require
flotation tires.
500- to 2000-
gal. trucks ok
800- to 3000-
gal. capacity
Requires addi-
tional equipment
Single furrow plow
mounted on truck
Not usable on wet
or frozen ground
Advantages
Use on steep or
rough land
Lower power re-
quirements than
spray irrigation
Use in furrows on
crops not grown for
human consumption
Same truck can be
used for transport
and disposal
Frees hauler truck
during high usage
periods
Minimal odor
Storage lagoon op-
tional for pathogen
control
Disadvantages
High power requirements
Odor problems
Possible pathogen dis-
persal
Storage lagoon for patho-
gen destruction and wet
or frozen ground
Limited to 1.5% slopes
Storage lagoon
Some odor
Some odor immediately
after spreading
Storage lagoon
Slopes limited to 8%
Some odor immediately
after dispersal
Storage lagoon
Slopes limited to 8%
Limit slopes to 8%
Longer time needed for
disposal operation than
surface disposal
-------
Land Disposal
Method
Farm Tractor
w/Plow-
Furrow-Cover
Table 9 . Land Disposal Characteristics (Continued)
Characteristics Advantages
Acreage Required
@ 10,000 gpd
250 days/year
420
Sub-Surf ace
Injection
420
to
o
Other Methods
Trench
15
Lagoon
30
Septage discharge
into furrow be-
hind single plow
Septage spread in
narrow swath &
immediately
covered w/plow
Not usable on wet
or frozen ground
Septage placed in
opening created
by tillage tool
Not usable in wet,
frozen or hard
ground
New trenches
opened when old
ones filled
Long-term land
commitment after
operations end
Sludge bucketed
out to landfill from
bottom of septage
lagoon
Settled water usu-
ally flows to per-
c olation/inf iltra-
tion beds
Minimal odor
Storage lagoon op-
tional for pathogen
control
Injector can mount
on rear of some
trucks
Minimal odor
Storage lagoon op-
tionalfor pathogen
control
Simplest operation
No slope limits
No climatological
limits
No slope limits
No climatological
limits
Disadvantages
Limit slopes to 8%
More time used for appli-
cation than surface dis-
posal
Limit land to 8%
More time used for appli-
cation than surface dis-
posal
Keep vehicles off area for
1-2 weeks after injection
Odor problems
High groundwater restric-
tions
Vector problem
Odor problems
High groundwater restric-
tions
Vector problem
-------
Land Disposal
Method
Sanitary Land
Fill
Table 9 . Land Disposal Characteristics (Continued)
Acreage Required
@.10,000 gpd Characteristics Advantages
250 days/year
195; acres of
Working surface
Septage mixed w/
garbage at con-
trolled rates
Consider leachate
& collection
requirements
No topographic
limits
Simple operation
Disadvantages
Odor problems
Rodent and vector problem
Limit to areas less than
35 inches yearly rainfall
or have leachate collec-
tion or isolate from
groundwater
to
-------
to prevent solids deposition. Howley^^ reported severe foaming problems,
but he did obtain a VSS reduction of 23.8 percent and a COD reduction of
73.9 percent using various hydraulic retention times of 1 to 30 days in
bench scale units. Howley found 1.8 pounds oxygen was required to
destroy one pound of VSS at loadings between 0.08 and 1.3 pounds VSS/
C.F./day19. He reported that 18,500 gpd/million gallons of aerated lagoon
design capacity operating at 50 percent design sewage flow should not
cause an overload condition.
Brookhaven, Long Island, using lagoon treatment of septage, exper-
ienced reductions of 62.5 percent in BOD, 51 percent in total solids,
49 percent in suspended solids from influent strengths averaging 5600 mg/1,
3700 mg/1, and 2700 mg/1, respectively. Without equalization facilities,
this process was prone to biological upsets. Grit and scum chambers and
three large settling lagoons now buffer flow to the 50,000-gpd septage
system. The effluent from a final settling lagoon is chlorinated and dis-
charged to sand recharge beds. Accumulated sludge is removed to a nearby
landfill.
Anaerobic/Aerobic Proce s s
The anaerobic/aerobic process uses an anaerobic lagoon or digester
prior to an aerated lagoon. A pilot plant anaerobic/aerobic treatment pro-
cess with sand beds for filtering final effluent reported 99 percent BOD,
COD, and SS removal, and 90 percent removal of total nitrogen and total
phosphbrous^O. Anaerobic digesters are useful in reducing high concentra-
tions of volatile solids and BOD and are addressed later in this section.
Composting
Composting is an alternate septage disposal technique offering a
potential for good bactericidal action^ *22,23 ancj a 25 percent reduction
in organic carbon.
Aerobic composting operations mix septage with dry organic matter for
moisture control and for easier air penetration to allow aerobic conditions
to be maintained. Aerobic composting is generally recognized as superior
to anaerobic composting due to odor control, higher temperatures for pathogen
control, and shorter periods necessary for stabilization.
Process Stages—
Three stages exist in composting. A process initiation stage passes
from cryophilic (5°C - 10°C) to mesophilic (10°C - 40°C) regions. Active
composting can begin within days and operates in the thermophilic (40°C -
22
-------
80°C) region. This temperature region tends to be self-limiting by competing
mechanisms. With an abundance of substrate, bacterial populations increase,
raising temperatures. Above 60°C, temperatures inhibit microbial growth,
lowering population and temperatures until the point where optimum temper-
atures exist for the occurrence of renewed growth. The third stage is sub-
strate limiting. This curing stage operates under two successive temper-
ature regions, mesophilic (40°C - 10°C) and then cryophilic (10°C - 5°C) .
Design—
Composting areas should have ample room on site for movement of heavy
equipment, as well as facilities for a receiving tank for septage equaliza-
tion and for collection of leachate and surface water. Primary screening
for removal of larger unwanted material is advised. Compost piles are
shaped into windrows or other shapes, such as cubes or hemispheres,
after mixing with dry organic matter. Moisture control is achieved with
either control of dry organic material/septage ratios, or with aeration.
Pile aeration can be achieved through either natural draft, mechanical
mixing, forced (bottom) aeration, or by turning compost piles.
Lebo System—
The Lebo System has been composting septage in South Tacoma, Wash-
ington and Bremerton, Washington, and is being constructed for Lewis
County, Washington and in Kent, Washington. The Lebo method uses a
patented preaeration process prior to spraying septage on piles of sawdust,
wood shavings, or other dry organic material. A one- to two-inch applica-
tion is covered with additional sawdust, and the mixture is formed with
front-end loaders into piles to minimize heat loss. Natural draft aeration
is possible because of the bulky nature of this mixture, eliminating the
need for turning or forced aeration. The 50 to 60-percent moisture content
material is said to attain a pile temperature of 150°F24. The pile is cured
by the end of three months.
Bel\syille System—
* * • •
The Beltsville System, devised by USDA, is operating in Washington,
D.C.; Bangor, Maine; Durham, New Hampshire; Orange County, California;
and Johnson City, Tennessee on dewatered sludge. Camden, New Jersey
will use the Beltsville forced aeration system on 8-percent sewage sludge
using licorice root as the bulking. The Beltsville System usually mixes
sludge with wood chips in long windrows and has piping facilities to
alternately blow and pull air through 0.66-cm (0.25-inch) holes in 15-cm
(6-inch) pipe covered by 30 cm (1 foot) of wood chips or screened compost
23
-------
21 22
to maintain aerobic bacterial action ' . Some turning of the windrows
is suggested. After several weeks, the compost can be screened, recycling
the wood chips for further composting.
End Use--
Some composting facilities attempt to market their end product. This
method has rarely been successful, due to lack of public acceptance and
other factors . In a municipal facility, end product usage on parks and
golf courses as a soil conditioner has been acceptable.
In a study conducted by Western Washington Research ;and Extension
Center^, Lebo compost applied to sweet corn produced no significant
change in yield; however, an increased yield in subsequent years was
noted when compost and fertilizer were added over only commercial fer-
tilizer.
Purifax
The BIF-Purifax process oxidizes screened, degritted and equalized
septage with dosages of chlorine from 700 mg/1 to 3000 mg/1 under moder-
ate pressure. Chlorine replaces oxygen in organic molecules, rendering
this material unavailable to bacteria as a food source, thereby stabilizing
and deodorizing the septage. The purifaxed septage changes color from
black or deep brown to straw color. The process initially releases CC^
gas which separates liquids and solids quickly by the resulting flotation
of solids.
Purifax treatment results in a highly acidic slurry, pH 1.7 - 3.8 . If
mechanical dewatering or lagoon separation of the liquids or solids is
contemplated, chemical addition for pH control of the resultant liquid
fraction should be included.
Locations which use the Purifax process treating septage and/or sludge
with lagoons for liquid-solid separation have had periodic solids separa-
tion and odor problems . Sand drying beds appear to be the most efficient
method of liquid solids separation of purifaxed septage. Adequate venti-
lation of covered sand drying beds is mandatory to eliminate operator health
hazards from inhalation of any NClg released subsequent to the Purifax
process*^.
Chemical Treatment
Raw septage is chemically treated with lime and ferric chloride at an
Islip, Long Island facility. After screening, degritting, and equalization,
24
-------
about 190 pounds lime/ton dry solids and 50 gallons/ton dry solids of a
standard strength ferric chloride solution is flash-mixed with the septage.
The solids-liquid separation step occurs in a clarriflocculator. An ob-
served significant-solids carryover problem indicates the separation unit
may have been undersized. The liquid fraction is chlorinated and dis-
charged to ground water recharge beds. The underflow solids from the
clarriflocculator are vacuum filtered. Long-term relative stability of the
lime-ferric chloride-septage mixture is unknown.
Tilsworth found good liquid-solids separation only with huge additions
of chemicals. Separation occurred either 10,000 mg/1 lime, 10,000 mg/1
ferric sulfate, 4,000 mg/1 lime and ferric sulfate mixture, or a 3 percent
concentration of a cationic polymer.
Feige, et.al.^5, had to add similar quantities of lime (+180 Ib./ton
dry solids) to obtain acceptable septage dewatering on sand drying beds.
The long term fate of limed dewatered septage in landfills or on the land
still needs to be addressed.
SEPTAGE-SEWAGE TREATMENT FACILITIES
Sewage treatment plants are one of the most frequent acceptors of
septage, due to their number and location. Consequently, treatment at
this kind of facility must be included in any comprehensive study of
alternate treatment schemes. Septage can be disposed of in a treatment
facility by addition to either the liquid stream or the sludge stream. In
either case, a properly designed septage handling facility including
screening, degritting, and equalization are recommended.
Septage frequently is considered a high strength wastewater and is
dumped into an upstream sewer or placed directly into various unit pro-
cesses in a treatment plant (Figure No. 3). In several facilities, septage
is considered a sludge because it is the product of an anaerobic settling/
digestion tank, and it is approximately the same total solids concentration
as raw municipal sludge. The septage application points, if treated as a
sludge, may include sludge stabilization, sand bed drying, or the mech-
anical dewatering process. The decision of where to apply the septage
should be determined following a statistically significant sampling and
analysis program of a locale's septage, including:
solids loading
oxygen demand
toxic substances
foaming potential
nutrient loading (N and P), where required.
25
-------
o:
uj
LU
SEPTAGE
ADDITION PT.
*
AEROBIC DIG
ANAEROBIC
DIG.,PURIFAX
PROCESS,
ZIMPRO PRO-
CESS, LIME
CONDITIONING
OR OTHER
CLARIFIER]
AERATION
TANK/T.F.
PRIMARY
TANK
SOLIDS
CONDITIONING
STREAM
SAND DRYING
BEDS
MECHANICAL
DEWATERING
J
SOLIDS TO
LAND OR SEA
Figure 3." Septage Addition Points in Wastewater Treatment Plants
The preceding factors, combined with a plant's layout, design capacity,
and present loading, and the following design criteria provide the design
professional with sufficient information to arrive at a'reasonable septage
treatment scheme within a wastewater treatment facility.
When septage is added to an upstream sewer or discharged at a treat-
ment plant, a suitable hauler truck discharge facility should be provided.
This facility should include a hard surfaced, sloping ramp to an inlet port
to accept a quick-disconnect coupling directly attached to the hauler's
truck outlet. This will reduce odor problems significantly. Washdown
water should also be provided for the haulers© spills may be cleaned up.
A recording .of the time, volume, and name of the hauler is vital for both
operation and billing purposes. Portland, Oregon's Columbia Avenue Plant
and Seattle Metro's Renton facility use a plastic charge plate or magnetically
coded card and card reader to record this vital information.
26
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Pretreatment
Treatment plants handling septage have experienced better operation
when septage pretreatment is employed. Pretreatment generally includes
bar screens of 3/4- to 1-inch opening, grit removal, and pre-aeration or
prechlorination if added to an aerobic process. Grit removal by cyclone
classifiers has been done successfully in Babylon and is included in the
new Bay Shore plant, both on Long Island, New York. Usually separation
of inorganic matter larger than 150 mesh is sufficient. Equalization/
storage tanks for two days average septage flow and mixing capability
should also be provided. To further attenuate odors, enclosed storage
tanks and ozonation of tank vent lines may be considered. Pumping
equipment should be used to apply a continuous dose of septage into the
desired unit process. Operators report slug doses or intermittent doses
of septage are difficult to treat and may seriously upset biological
treatment systems .<
Primary Treatment
Feige's24 report for the U.S. EPA indicated that neither natural settling,
lime addition, nor polyelectrolyte addition resulted in consistent liquid-
solids septage separation. Tilsworth^ characterized raw septage as
relatively non-settleable, as determined by settleable-solids volume
test, from 0 to 90 percent with 24.7 percent as the average volume.
Tawa2^ found septage-settling characteristics could be divided into
three groups, types 1,2, and 3. Type 1, from septic tanks pumped before
necessary, settled well. Type 1 septage was found in 25 percent of his
samples. Type 2 septage, from normally operating systems, showed
intermediate settling characteristics and was found in 50 percent of his
samples. Type 3 septage exhibited poor settling, was found in 25 percent
of his samples, and was from tanks overdue for pumping. It was generally
found that poor settling characteristics can be expected from septage. All
samples were between one and six years of age.
U
It^is generally accepted that septage settles very poorly without
chemical addition. In a study on treatment of Alaskan septage, Tilsworth^
found that only 50 percent of the samples settled by more than 10 percent
after 30 minutes, as shown in Figure 4. About one-third of the data points
are not shown in the figure, because they settled by less than one percent
of the original height during the 30-minute test period.
Elutriation, or settling of septage in a septage-sewage mixture, is
reported to yield better results . Carroll2^ reports that up to 75 percent
of septage suspended solids can be expected to settle in a sewage treatment
27
-------
1,000
500
o
s
0)
(O
_ 100
g 50
10
5
I
0.01 O.I 125 10 20 40 60 8090959899 99.9
Probability Of Occurrence
Figure 4 Probability Of Reduction Of Solids-Liquid Interface
Heigth After 30 Min. Settling Of Alaskan Septage Samples
-------
plant's primary sedimentation basins. An EPA study found 55 to 65 percent
SS removals in a primary clarifier, while only 15 to 25 percent BOD re-
movals resulted in the same unit process^.
Activated Sludge
Septage may be added to the activated sludge process if 1) additional
aeration capacity is available, 2) the plant is organically and hydraulically
loaded below design capacity, 3) the septage metals content can be diluted
to a sufficiently low concentration, and 4) foaming potential is low or can
be controlled. Very limited quantities of septage may be added without
changing the sludge wasting rates .
At the Weaverville Wastewater Treatment Plant in Trinity County,
California, 400 gpd slug dumps were handled without significant upset
at a 0.5 MGD plant flowing at 40 percent capacity.
In a report to the Forest Service28, CI^M/Hill recommended various
levels of septage addition to differing types of activated sludge plants.
This information, modified by authors'field investigations16, is presented
in Figures 5 and 6.
tt 88
O 80
d 72
O
64
gu
oib
o 32,
<
ui 24
(9
< 16
*• ft
|X] O
(O
WITH PRIMARY
TREATMENT
(CARROL,1972)
NO PRIMARY-
TREATMENT"
PACKAGE PLANTS
I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16
WASTEWATER TREATMENT PLANT CAPACITY(M.G.D.)
Figure 5 . Septage Addition to Activated Sludge Wastewater
Treatment Plants (No Equalization Facilities)
29
-------
1.0
UJ
UJ
o;
Q.
O
z
U)
UJ
o
o
£
0
u.
UJ
o
§
UJ
.9
.8
.7
.6
.5
.4
.3
.2
.1
ACTIVATED SLUDGE
NO PRIMARY TREATMENT
PACKAGE
PLANTS.
8
-ACTIVATED SLUDGE
WITH PRIMARY |
^TREATMENT
AERATED
LAGOON
12
16 20 24 28 32
36
SEPTAGE ADDED (1,000 GAD PER MGD PLANT CAR
(PER DAY)
Figure 6. Septage Addition to Wastewater Treatment Plants
(with Equalization Facilities)
The use of slug dumping of septage may depend on limiting the increase
in MLSS to 10 percent per day to maintain a relatively stable sludge, as
seen in Figure 5. Higher loadings and wasting rates than the resident
aquatic biomass is acclimated to may result in a poor-settling sludge^
Severe temporary changes in loading beyond the 10-15 percent MESS
,29
increase may cause a total loss of the system's biomass
28
In the slug dumping mode, package treatment plants should not be
allowed to accept any septage if their design capacity is less than 100,000
gpd.28 In a study for the Forest Service, CH2M/Hill determined that pack-
age treatment plants can be expected to treat septage at approximately 0.1
percent of the plant design capacity, while modified activated sludge may
treat septage at twice the rate of a package plant. Conventional activated
sludge plants are able to treat septage at about four times the rate of
package plants^8.
30
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In plants with holding and metering facilities, septage may be bled
into the waste flow stream at considerably greater flows than would be
allowable if only slug dumping procedures were available.
A U .S. EPA study^ fed septage at a controlled rate of 2- to 13-percent
of the total influent flow to one of two activated sludge units . With a
control unit food-to-micro-organism ratio of 0.4 and a septage-sewage
unit F/M of 0.8, effluent BOD and SS characteristics were similar.
Effluent COD of the unit receiving septage increased when septage was
loaded at 10 to 13 percent of plant flow. When a lower F/M ratio of
0.5 to 0.6 was utilized in the septage unit, this unit had superior per-
formance due to control of Nocardia, a procaryotic filamentous actinomy-
cete, often associated with bulking.
Figure 6 was developed from various research reports in the literature,
plus field investigations16. Again, package plants with design capacities
under 100,000 gpd should not accept septage. Depending on the present
plant flow compared to the design plant flow, a biological treatment re-
serve can be estimated which will allow for a certain level of septage to
be adequately treated. Under identical loading conditions, the ratio of
septage addition to various types of treatment plants would be as follows:
Relative Volumes of
Septage Addition
Package Plants 1.00
Activated Sludge (no primary treatment) 2 .08
Activated Sludge (conventional) 4.83
Aerated Lagoons 6.00
Figure 6 is indicative of continuous septage addition to a facility for
a fully acclimated biomass. It is recommended that an initial septage
feed to an unacclimated system should be substantially less than shown
on the graph, e.g., on the order of 10 percent of the graph values. Fur-
ther gradual increases in daily septage loading should be made over a
two-vto three-week period up to the maximum amount shown in Figure 6.
Oxygen'capacity must be checked continuously and gradual changes made
in sludge age.
Figure 7 shows the additional oxygen requirements for septage addition
in activated sludge treatment plants and is modified upward from field
experience. Treatment facilities should be analyzed to determine if
oxygen requirements or mixing requirements are controlling factors.
31
-------
(0
"CD
g26
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O 22
£20
z 18
ui
o 16
X
o
z
o
hj
o
o
14
12
10
8
6
4
2
NO PRIMARY
TREATMENT
(CARROL.I972)
_WITH PRIMARY:
TREATMENT
I 2 3 4 5 6 7 8 9 10 II 12 13 14 15
SEPTAGE ADDED, 1,000'S GALLONS (PER DAY)
Figure 7 . Additional Oxygen Required for Septage Addition
in Activated Sludge Treatment Plants
Because of the higher oxygen demand for septage than for raw sewage
on a unit BODj- .basis, an additional oxygen supply for activated sludge
plants accepting septage having primary treatment would be 40 pounds of
02/1000 gallons septage added. For plants without primary treatment, an
additional 80 pounds of 02/1000 gallons septage added should be provided,
Package treatment plants will have an oxygen requirement similar to
plants without primary treatment.
. * Q 1 .
Feng*31 has shown higher sludge ages (10 days versus 4 days) result
in higher percentage BOD removal and less sludge production than at the
lower sludge age (Figure 8). Wasting must be adjusted gradually with
increased loads to obtain a sludge age which produces the optimum be-
tween aeration tank efficiency and good settling characteristics . A high
sludge age generally produces a light sludge with poor settling ability
but good substrate removal characteristics. The reverse is often true for
a very young sludge.
32
-------
100
90
8 0
< 70
060
£50
UJ
g30
LJ
a. 20
10
WEAK SEPTAGE BOD5«l,250mg/l _
STRONG SEPTAGE BOD^II,OOOmg/l
6C • SLUDGE AGE
(FENGJ975)
5 10 15 20 25 30 35 40 45 50 55 60 65 70
PERCENT SEPTAGE
Figure's,. BODg Removal from Septage-Sewage Mixtures
in Batch Activated Sludge Process
At one plant in New York, septage is bled into the liquid stream inversely
proportional to the sewage flow^, This procedure takes advantage of a
larger excess aeration capacity during lower loading times . Orange
County, Florida^ added septage proportionately with sewage flow rates.
Both plants have experienced some operational problems.
Some odor and foaming'problems have been reported in aeration systems;
however, the odor usually dissipated within 6 to 24 hours" '^ , and foaming
was not apparent in all cases. Commercial defoamers, such as decyl
alcohol, and aeration tank spray water have been used to reduce foaming.
Attached Growth Systems
Systems that employ attached growth aerobic treatment processes,
such as trickling filters and rotating biological contactors, are usually
more resistant to upsets from changes in organic or hydraulic loadings
and are suitable for septage treatment^7,34,35,
33
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In trickling filters , additional recirculation has been shown to ade-
quately dilute septage concentrations and diminish chances of plugging
the media. At Huntington, Long Island, 17 30,000 gpd septage is treated
at a 1 .9-MGD facility. BOD 5 reductions of 85 to 90 percent have been
observed concurrent with suspended solids reductions of 85 percent.
Rotating biological contactors utilize a long detention time and a
continually rotating biological media that is reportedly resistant to up-
sets. AtRidge, Long Island/ a BOD reduction of 90 percent, COD re-
duction of 67 percent, and a TSS reduction of 70 percent was reported.
This installation utilized flow equalization of a low strength septage.
A surface loading of 2 gpd/S .F . produced these results .
Aerobic Digestion
An alternative to considering septage as a concentrated wastewater
would be to assume septage is the product of an unheated digester and,
therefore, a sludge.
Many researchers have reported good results in aerobic digestion of
septage or septage-sewage sludge mixtures. Jewell33 reports odors
diminished, but time to produce an odor- free sludge varied up to seven
days.
Tils worth ^ reported a high degree of septage biodegradability at a
10-day aeration time, resulting in a BOD reduction of 80 percent and a
VSS reduction of 41 percent. Chuang^, treating anaerobically digested
septage with an aerobic digester, reported a 36-percent VS removal at a
40-day aeration time under a loading of 0.0016 pound VS/C .F ./day on
the aerobic digestion. After 22 to 63 days aeration, Howley^ found a
43- percent VSS reduction and a 75-percent COD reduction.
Orange County, Florida adds septage to aerobic digesters at the rate
of five percent of the total sludge flow and obtains good reductions at a
loading of 0.15 pound VS/C .F ./day. Bend, Oregon obtained good removal
adding 13 percent septage to 87 percent sludge at a loading of 0.02 pound
VS/C .F ./day, utilizing a 15- to 18-day aeration time36.
Tilsworth6 observed c\ and fi) gas transfer characteristics for
septage and found that both o^ , the ratio of gas transfer efficiency to
tap water, and A , the ratio of 0^ saturation concentration to tap water,
approached unity after one to two days' aeration. Prior to one day,
and / were in the range of 0 .4 to 0 .6 .
o 7
Jewell07 found both dewatering and settleability improved with aeration,
but the aeration time required to effect significant improvement varied.
34
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Prior to adding septage to the aerobic digestion process, aeration
capacity, toxic metal or chemical accumulations, and increased solids
to be disposed of should be investigated. All investigators consistently
have reported initial repulsive odors and foaming problems^* 19/20, 32 , 37^
Recommendations , when considering septage addition to aerobic di-
gesters , should include screening, degritting, flow equalization, an
analysis of excess digestion capacity, and peripheral effects to other
processes such as solids handling. An initial septage addition should
be limited to approximately five percent of the existing sludge flow .
Further septage additions should be gradual .
Studies in high temperature auto- oxidation of septage are planned^
and may prove promising as a low cost, efficient solids-destruction
technique.
Anaerobic Digestion
Septage in Tallahassee, Florida is treated in an unheated 20°C to
30°C anaerobic digester. With an influent septage concentration of
17,700 mg/1 total solids, a volatile solids reduction of 56 percent was
reported after an 82-day retention time at a loading of 0.01 pound VSS/
C .F ./day. Large quantities of grit in the septage required draining and
cleaning of the open digester after only three years in operation. Leseman
and Swanson^S analyzed volatile acid distribution concentrations in the
digester contents. The volatile acid-to-alkalinity ratio varied from 0.34
to 0.83. The eight-month volatile acid concentration averaged 703 mg/1
and ranged from 408 mg/1 to 1117 mg/1 at a consistent pH of 6.0 The
progression of volatile acid concentrations in the digester, from two to
five carbon acids, showed acetic =276 mg/1, propionic = 294 mg/1,
isobutyric = 14 mg/1, butyric = 49 mg/1, isovaleric = 28 mg/1, and
valeric = 42 mg/1. Since this digester had an open cover, gas production
could not be monitored. Supernatant from this digester is pumped to the
sewage sludge anaerobic digester.
reported a 45-percent reduction in VSS from a bench- scale
digester loaded at 0.05 pound VSS/C .F./day, with a 15-day hydraulic
retention time. Gas production varied from 4.2 to 7.6 ft^/lb COD up
to a loading of 0.08 pound VSS/C .F./day, where gas production fell off
dramatically, indicating a possible poisoning of the system by a toxic
chemical concentration of an unknown source.
reported a 92-percent VS removal from a heated anaerobic
digester loaded at 0.08 pound VSS/C .F./day with a 15-day hydraulic
retention time. Incoming solids ranged from 0.3 percent to 8 percent,
and total solids reduction was more than 93 percent. BOD reductions
averaged 75 percent, from 6100 mg/1 influent to 1500 mg/1 in the effluent.
35
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Based on his research, Howley-'-^ recommends a maximum septage
addition of 2130 gpd to each 14',500 gallons sewage sludge added per
day per million gallons of digester capacity, with a detention time of
30 days and a loading of 0.08 pound VSS/ftvday. Good operation of
anaerobic digesters requires a limitation on toxic materials.
In treatment plants with single-stage digesters, septage treatment by
screening, grit removal, and equalization before digester addition is
necessary. Digesters should be cleaned on a regular schedule, such as
every two to three years, or as required.
Monitoring digester performance includes long term evaluation of
volatile acid/alkalinity ratios and gas production. Mixing is vital in
preventing a sour digester from the propagation of point-sourc^e*failure
from a septage load containing high volatile acid concentrations.
In systems with multiple tanks, all the preceding suggestions should
be followed. Spreading the septage load to many digesters will reduce
septage concentrations. Recycling from the bottom of a secondary digester
or from another well-buffered primary digester at a rate of up to 50 percent
of the raw feed per day has been helpful. Control of temperature and mix-
ing should also be adjusted for maximum performance^.
Mechanical Dewaterinq
Islip, Long Island, uses a vacuum filter to dewater 100,000 gpd of
chemically conditioned septage. A design basis of six pounds/hour/
S .F. of surface area was used and appears to be satisfactory^. A lime
addition of about 190 pounds/ton of dry solids and 50 gallons/ton of
dry solids standard concentration ferric chloride solution are added prior
to vacuum filtering.
In another study at Clarkson College, Crowe^2 obtained successful
results with vacuum filtration of mixtures of raw septage and digested
sludge with up to 20 percent raw septage by volume. Chemical condi-
tioning with lime, ferric chloride, and polymers was required beforehand
at chemical dosages typical of domestic sludge. Dewatering character-
istics were observed to be similar to those mixtures without septage
addition. The filtrate contained only 5 to 10 percent of the raw septage
COD.
Sand Drying Beds
Sand drying has been used to dewater septage, but with varying suc-
cess. Anaerobically digested septage is reported to require two to three
times the drying period of digested sludge^. After treatment in aerated
36
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lagoons and batch aerobic digesters, dewatering simulation studies
yielded a septage capillary suction time on the order of 200 seconds,
versus about 70 seconds for sewage treatment plant sludges. A lower
capillary suction time (CST) can be correlated to a faster dewatering
time. CST's of raw septage were found to range from 120 to 825 seconds,
with a mean of 450 seconds43. Lime addition of septage prior to sand
o c
bed dewatering vastly improved dewatering characteristics. Feige
found that an addition of 180 pounds lime/ton dry solids, or 30 pounds/
1000 gallons septage based on 40,000 mg/1 total solids, raised the pH
to 11.5 and dried to 25 percent solids in six days and 38 percent solids
in 19 days. An application depth of greater than eight inches is not
recommended, because it slowed the drying process. The filtrate analy-
sis showed that 1) most heavy metals were tied up in the solids; 2) fecal
coliform were killed effectively; 3) fecal streptococci were more resistant
than fecal coliforms; and 4) odors were significantly reduced. Filtrate
quality is generally good, but further treatment before discharge is
recommended-^.
Perrin found other chemicals worked well in modifying the ability of
septage to dewater. From a mean initial CST of 450 seconds, septage
showed a dewatering ability of 50 seconds after the addition of an average
of either 1360 mg/1 ferric chloride, 1260 mg/1 alum, 1360 mg/1 Purifloc
C-31, or 2480 mg/1 Purifloc C-41,43
Perrin also studied the affects of freezing on dewatered samples of
septage after treatment in aerated lagoons, or batch aerobic digestion.
Freezing lowered the CST from an initial 225 seconds to 42 seconds, an
80-percent decrease in dewatering time.
If septage is to be placed on sand drying beds, treatment to a consis-
tent CST range of 50 to 70 seconds is recommended. Further treatment
of underdrainage would be required in most cases.
COSTS
Of- all the alternatives investigated, land disposal has the lowest
associated operation and maintenance cost reported, from $1.50 to $5.00
per 1000 gallons, exclusive of the cost of the land. Various lagoon
systems report cost of treatment between $5.00 and $10.00 per 1000
gallons. The cost of septage treatment in sewage treatment plants varies
widely, but typically runs about $15.00 per 1000 gallons. Composting by
the Lebo process is reported to cost approximately the same as disposal
in wastewater treatment plants. Physical chemical treatment, such as
the Purifax process or chemical stabilization, range from similar average
costs found in disposal at treatment plants to double or triple that figure.
37
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A nationwide survey of 42 wastewater treatment plants^ determined
that only about half charged for septage disposal based on treatment
costs (Figure 9). Some charge prohibitive rates to avoid septage, while
others place a minimal charge on septage to ensure against illegal dump-
ing at an unauthorized site. For those plants surveyed, the average
charge surveyed for septage was $15.18 per 1000 gallons. However, an
additional 20 to 30 plants contacted either placed no charge on septage
disposal or levied only a yearly fee, most often in the range of $50 to
$300 per truck.
Many variables effect treatment costs, including local funding re-
quirements; eligibility for state or federal funds; necessity for industrial
cost recovery formats; local taxes assessed in lieu of, or to offset,
treatment plant expenses; level of pollutant removal capability; climate;
present loading versus design plant capacity; and cost of land. There-
fore, the broad range of charges for treatment plant septage disposal is
easily understood.
>- 30
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0)
Zzo
CO
i I5
Q.
u. 10
O
55 5
I
I'O *5 *IO *I5 '20 '25 '30 '35 +
42 PLANT AVERAGE CHARGE -*I5.I8/I,000 GALLONS
Figure 9 . Septage Disposal Charge at Wastewater Treatment Plants ,
$/1000 Gallons Septage
38
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An estimate was performed to determine a reasonable charge a home-
owner could expect to pay for having a 1000-gallon septic tank cleaned,
assuming no additional work was needed. It was based on a 15-mile
haul to the disposal point, two hours travel time per load, vehicle depre-
ciation and insurance of $4,000 per year, and estimated union wages.
Depending on the level of profit and a disposal cost not exceeding $15,
a reasonable charge would appear to be in the range of $40 to $60.
Fees charged to homeowners ranged from a low of $20 to $25 per 1000
gallons in parts of Long Island to around $100 per 1000 gallons in areas of
New Jersey, Connecticut, and Oregon. Rural areas in New England had
slightly lower charges, $25 to $40 per 1000 gallons, while in the rest
of the country, charges were mostly in the rangle of $40 to $60 per 1000
gallons. These charges are dependent on the distance from the septic
tank to the disposal point (especially pronounced if over 15 miles) and
the disposal fee charged.
SUMMARY AND CONCLUSIONS
We have presented various alternatives for septage disposal.- Good
design practices and conscientious operation are necessary to preclude
this material from polluting our environment.
The method of choice should depend on a local-need evaluation by
the design professional, cost effectiveness of particular solutions, and
environmental weighting of impact factors.
For example, while land disposal appears most cost effective, local
constraints in land use, nuisance odors, or poor soil may preclude this
option. Similarly, a more expensive option such as composting may prove
viable if it meets particular local requirements, such as land restrictions
or odor prevention, and conversion of excess wood waste into a market-
able product.
ACKNOWLEDGMENTS
Credits
Funding for this study was provided by the U.S. Environmental Pro-
tection Agency under Contract No. 68-03-2231 with the Municipal En-
vironmental Research Laboratory, Cincinnati, Ohio. We are grateful
to James F . Kreissl and Robert Bowker of the U .S .EPA for the information
and support they provided during the course of this study.
Authors
Ivan A. Cooper and Joseph W. Rezek are , respectively, Senior Project
Manager and President for the firm of Rezek, Henry, Meisenheimer &
Gende, Inc., Consulting Engineers, Libertyville, Illinois, an affiliate of
The HMG Group, with offices in Colorado, Illinois, and Missouri.
39
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1. "On-Site Domestic Waste Disposal", Draft Report for USEPA by
Miller, Inc., c. 1975
2. Kolega, J. J. andDewey, A. W. "Septage Disposal Practice",
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40
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41
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27. Tawa, Anthony, Research Asst. University of Massachusetts,
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42
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39. Leseman, Wm. and Swanson, Jerry, Lab. Director and Research
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43
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