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-------
Excellent treatment is provided by overland flow systems and at the Melbourne and Ada,
Oklahoma, systems, BOD5 and suspended solids removals of 95-99% have been obtained. Nitrogen
removals have ranged between 70-90% arid phosphorus removals from 50-60%. The Paris, Texas,
facility treating industrial wastewater has shown equal treatment efficiencies. All of the performance
data presented are site specific to some degree but do indicate the type performance and cost that
could be expected at most locations throughout the United States.
INTERMITTENT SAND FILTRATION
General
Intermittent sand filtration is not a new technique. Rather, it is the application of an old
technique to the problem of upgrading lagoon effluents. Intermittent sand filtration is similar to
the practice of slow sand filtration in potable water treatment or the slow sand filtration of raw
sewage which was practiced during the early 1900's. Intermittent sand filtration of lagoon effluents
is the application of lagoon effluent to a sand filter bed on a periodic or intermittent basis. Sus-
pended solids and organic matter are removed through a combination of physical straining and
biological degradation as the wastewater passes through the sand filter bed. The particulate matter
collects in the (op 5 to 7.5 cm (2 to 3 inches) of the sand filter bed. This buildup of organic matter
eventual]) clogs the sand filter bed and prevents the passage of effluent through the sand filter. The
sand filter is then taken out of service and the top layer of clogged sand is removed. The sand filter
is then put back into service and the spent sand is either discarded or washed and used as replace-
ment media for the sand filter.
Single Stage Filtration
The development of intermittent sand filtration to upgrade lagoon effluents has been con-
ducted primarily at Utah State University \Wnrshall and Middlebrooks, 1974; Reynolds, et al.,
1974a: Ham's, et al, 1975; Reynolds, et al, \ 974b; Hill, et al, 1976; Messinge.r, et al, 1977J.
The work at Utah State University has been conducted on laboratory scale, pilot scale and field
scale filters. The principal work was conducted on six prototype filter scale filters as shown in
Figure 16. Each of these filters was operated at a different hydraulic loading rate for twelve months.
The filter sand employed in the study was ungraded pit run sand with an effective size of 0.17 mm
(0.007 inches) and a uniformity coefficient of 9.74 (see Table 6).
The biochemical oxygen demand (BO1)5 ) removal performance for each of the six filters is
shown irt Figure 17.
The overall average influent BOD5 concentration was 19 mg/1. The influent BOD5 concen-
tration ranged for 3.5 mg/1 to over 288 mg/1, exceeding 5 mg/1 94% of the time.
Figure 17 shows the consistently high quality of filter effluent, which was unaffected by
influent B()l)5 fluctuations. Effluent quality was below 5 mg/1 93% of the time (except filter
number 2 during the winter). The effluent BOD5 concentration never exceeded 11.8 mg/I and ex-
ceeded 7 mg/1 only 4 times during the study.
The operation of filter number 2 was hampered by constant flooding during winter opera-
tions. The anaerobic conditions that developed due to this flooding greatly reduced the filtration
-------
SCALE: i = 6 -o
[ VAX DIA ROCK
I/O," WAX DIA ROCK
I i/
-------
to exceed 5 mg/1 83% of the time. The suspended solids concentrations from eaeh filter were con-
sistently low.
The length of filter runs achieved during this study was a function of the hydraulic loading
rate and the influent suspended solids concentration. Filter run lengths ranged from 8 days at a
hy draulie loading rate of 9,360 m3/h'd (0.2 MGAD) during the winter months.
The results of these studies [Harris, el, al., 1975; Reynolds, el al., 1974; Reynolds. <>t al..
1975) clearly indicate that intermittent sand filtration of lagoon effluents can produce a final
effluent with a H()T)5 concentration and a suspended solids concentration of less than 10 to 15 rng/l
consistently throughout the entire year even during periods of sub-zero temperatures. Intermittent
sand filters should be similar in design to those illustrated in Figure 16 with hydraulic loading rates
of 2744 to 5616 m3/h-d (0.4 to 0.6 MGAD). Filter sands should have an effective. si/,e of 0.1 5 to
0.25 mm (0.006 to 0.010 inches) with a uniformity coefficient [Fair, Geycrand Okarn, I968|
from 1.5 to 10. The expected filter run length from intermittent sand filters designed on the above
criteria will depend on the filter influent quality, but should he a minimum of approximately 30
to 60 day s.
Series Intermittent Sand Filtration
In an attempt to increase the, length of filter runs achievable with intermittent sand filtration
of lagoon effluent, /////, cl uL, [1977], conducted laboratory and pilot scale studies on a scries ar-
rangement of intermittent sand filters. The experimental design employed in these studies is shown
in Figure 19. Series intermittent sand filtration involves the passage of lagoon effluent through two
or three intermittent sand filters arranged in series with progressively smaller effective si/.e sands.
Hill, ft al. [ 1977] investigated three different hydraulic loading rates on a pilot scale basis.
The weekly Biochemical Oxygen Demand (HOI)5) removal performance of the pilot scale
series intermittent sand filters is illustrated in Figure 20. The influent BOD5 concentration varied
from 4.1 mg/I to 24.0 mg/1 and averaged 10.7 rng/l during the study. The final effluent BOI)5
concentration varied from 0.6 mg/1 at the 14,031 rn3/lrd(1.5 MGAD) hydraulic loading rate to
Table 6. Sieve analysis of filtor sand. [Kjynolds, et c,l., 1974]
U. S. Sieve
Designation
Number
Size of
Opening
(mm)
Percent
Passing
(')
,V8"
4
10
40
100
200
9.5 1
4.76
0.42
0.149
0.074
e * 0.170 mm; u - 9.74
29
-------
C INFLUENT
A EFFLUENT
5.
o
o
o
UJ
52
X
o
o
s
LJ
X
o
o
03
JUL AUC SEP OCT KOV ' DEC ' JAN T FEB MAR ' APR ' MAY ' JUN
TIME IN) MONTHS ('974 - 1975)
Hgure 17. Single stage intermittent sand filtration Biochemical Oxygen
Demand (BOD5) removal performance [Harris, et a/., 1975].
4.2 mg/1 at the 9.353 m3/h-d (1.0 MGAD) hydraulic loading rate. At no time did the final effluent
BOD5 concentration from the operation exceed 5.0 mg/1. Statistical analysis at the 1% level reveal-
ed that the effluent BOD5 concentration was statistically identical at all three hydraulic loading
rates for the 0.72 mm (0.0284 inch) and 0.40 mm (0.0158 inch) effective size sand filters. The efflu-
ent BOD5 concentration from the 0.17 mm (0.0067 inch) effective size sand filter at the 14,031
m3/h-d (1.5 MGAD) hydraulic loading rate was significantly higher (1% level) than from the
9,353.9 m3/h-d (1.0 MGAD) and 4,677 rn3/h-d (0.5 MGAD) hydraulic loading rates. However
the differences were small.
30
-------
The weekly suspended solids removal performance of the pilot scale field filters is shown in
Figure 21. The influent suspended solids concentration ranged from 12.5 mg/1 to 69.4 mg/1 and
averaged 32.4 mg/1 for the - tudy. The final average effluent suspended solids concentration ranged
from 8.6 mg/1 for the 4,677 m3 /h-d (0.5 MGAD) hydraulic loading rate to 6.4 mg/1 for the 14,031
m3/h-d (1.5 MG AD) hydraulic loading rate. There was no significant difference (1% level) between
the final effluent suspended solids concentrations among the different hydraulic loading rates.
O JNFtUtNT
A CFILUCNT
JUL ' 1UG ' S
TIMF IN MONTHS (1974-1975)
Figure 18. Single stage intermittent sand filtration suspended solids
removal performance {Harm, el al.. 1975].
31
-------
0.5 mgod
Figure 19. Series intermittent sand filtration of lagoon effluents
[Hill etal, 1977).
Figure 21 indicates that at the beginning of the study, the final effluent suspended solids con-
centration was dependent upon the influent concentration. At the end of the experimental phase,
when removals were exceptional, the 0.17 mm (0.0067 inch) effective size sand filter effluent sus-
pended solids concentration was essentially independent of the influent concentration. The effi-
ciency of removal of intermittent sand filters is increased as the "schmutzdecke" (filtering skin)
builds up on the surface of the filters. During the month of August, the suspended solids concen-
tration actually rose between the 0.72 mm (0.0294 inch) and 0.40 mm (0.0158 inch) effective
size sand filters. This was due to the "filter washing" effect which takes place during the initial
start-up of intermittent sand filters when inert fines must be washed from the filter. When this
washing was completed, excellent removals were obtained.
One of the main advantages obtained with the use of a series intermittent sand filtration
operation is the increased length of the filter runs. At the time operations were suspended due to
freezing conditions (December 2, 1974), all three filter systems had operated for 131 consecutive
days without plugging (Table 6). Until the time operations ceased, the applied influent loading
passed completely through all three filters in the series within four hours. It is difficult to esti-
mate the length of filter run which could have resulted if freezing had not occurred; however,
based on the data available, filter runs of at least 131 days may be obtained with a hydraulic load-
ing between 4,677 m3/h-d (0.5 MGAD) and 14,031 m3/h-d(1.5 MGAD).
Hill, et al, [1977] conducted a series of both laboratory arid pilot scale studies of series
intermittent sand filtration to determine the effect of hydraulic loading rates on the length of filter
run achievable with three stage series intermittent sand filtration. The results are summarized in
32
-------
Q
O
m
25
20
IO
0
25
20
15
10
O
25
20
15
10
INFLUENT
0 72 mm Effluent
0 40 mm Effluent
0 17 mm Effluent
0.5 MGAD
4676.96 ra3/li-d
1.0 MGAD
9353.92 m3/h
i r
1.5 MGAD
14030.89 m'/h-d
JUL AUG
SEP
OCT
NOV
Figure 20. Weekly B()I)5 removal performance of pilot scale scries
intermittent sand filtration [/////. el al, 1977].
Figure 22. The results indicate that hydraulic loading rates greater than 38,080 m3/h-d (3.0 MGAD)
significantly reduce (he length of filtration run. However. Figure 22 neglects the effect of influent
suspended solids concentration on filter run length. Thus, variations to Figure 22 will occur as the
influent suspended solid.s concentration varies.
The results of these studies indicate thai a three stage series intermittent sand filtration sys-
tem should be designed with filter sands of effective sizes between 0.72 mm (0.0284 inch) and
0.17 mm (0.007 inch) arranged according to Figure 19. Hydraulic loading rates should not exceed
28,080 m3/h-d (3.0 MGAD) and preferably should be in the 14,031 m3/h-d (1.5 MGAD) range.
Using this criteria, filler run lengths in excess of 131 da) s should be possible.
33
-------
to
g
_i
o
to
o
UJ
o
z
UJ
0-
co
75
60
45
30
15
0
75
60
45
30
15
0
75
60
4b
30
Ib
0
INFLUENT
0.72 mm Effluent
04Omm Effluent
0 17 mm Effluent
0.5 MGAD
467S.96 m3/h-d
1.0 MGAD
9353.92 mVh-d
1.5 MGAD
14030.89 m'/h-d
JUL
/\UG
SFP
OCT
NOV
Figure 21. Weekly suspended solids removal performance of pilot scale
series intermittent sand filtration [Hill, et al, 19771.
Filtration of Aerated Lagoon Effluent
Bishop, et al., [ 1977] and Bishop, et al., [ 1976] conducted a pilot scale single stage inter-
mittent sand filtration study to determine the feasibility of upgrading aerated lagoon effluent with
intermittent sand filters. The result of the study clearly indicates that although BOD5 removal
was acceptable (i.e., effluent concentrations less than 30.0 mg/1) suspended solids concentrations
were not significantly reduced. Thus, direct intermittent sand filtration of aerated lagoon effluent
appears not to be feasible. The aerated lagoon was treating wastewater from a milk processing and
chesse manufacturing plant. Whether the passing of the solids through the intermittent sand filter
was attributable to the type wastewater being treated is unknown. However, activated sludge pro-
cesses treating milk wastewater produce fluffy, low density solids which are easily dispersed when
agitated. Therefore, it is possible for the solids in aerated lagoons treating other types of wastewater
would not pass the intermittent sand filter.
34
-------
o
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Q
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cc
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ft:
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in
ex
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h
150
120-
6C
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LOfdinq
3ote
i-6-4 mgod
IT-6-3 mg.,-1
12 mgaci
? mgad
^-4-? nigi"1
6-'M.S
4 "T^r*
<* n j d
i i fv
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36
-------
service for a long period of time. The time required to manual!» ''i-vs, .1 Mow sand filter was 75
man-hours. \ filter of 2000 m2 (0.494 acres) surface area loaded at a : \ maulic loading rate of
0.6 MGA1) (5.616 m3/h-d) would (real a flow rale of 0.30 M(, i) (U " ; '''as), \s-uminglbat
labor costs including benefits will be $7.50 per hour and that i< \\;:'i !>; . <. > --ary to clean the, fillers
once each month, it will cost $6,750 per year or $6 I/million g.dfo,'- ' is!, isater treated.
Experience at existing sites indicates thai less than 2 hours per day throughout the, year will
be required to operate tin' intermittent sand filter. Operational costs would result in an additional
$5.475 per year or $5(Vmillion gallons ($0.0 132/m3 ) of wastewater treated, Therefore, the o\erall
operation and maintenance costs would be approximately $1 I I/MO ($0.293/m3) of wastewalcr
treated or $0.1 1/1.000 gallons.
The application of tractor scrapers would decrease the labor cosls by a factor of 4 or 5 and
the capital costs would be increased by approximately $12.000 or $1,709 per year amorti/ed at
1% for a 10 year useful life. Using 20 man-hours of labor and assuming a cleaning once per month.
the cleaning costs would be $1,800 for labor plus $ 1,70() additional charge lor the amorli/alion of
the tractor, or $3,509 per year for a filler \\ilh 2000 n\2 of ,-urfaec area. 'I he costs per volume of
wastewater treated would be $32AIO ($0.008 1/nr1) or SO.03;' 1,000 gallons. Opera! ing costs would
be (he same as reported above. $50/M(; ($0.0 i 32/m 3) or 0.05/1.000 gallon,-. The total OK M costs
for a 0.3 \\(',l) (1.136 m'Vday) ititermiltc'i! -ami fill. ; -s-i- n uonM be >'02/Mf, ($U.0216/m3 ) or
$0.08/1,000 gallons of uasleuater (rcaf-d.
\ summary of (lie costs for a 0.3 M(J|J (!. I 3o m 'd;u ) in term it leu! -and filter -A stem is
shown in Table 8 using manual and trader scrapi r < leaning technique- and -and washing. Manual
and tractor scraping are probably the oni\ tuo \ iable cleaning alternatives foi small (1))
wasleuater treatment plants. (Capital cost.- ate based on 1('73 ( . ,s. dollar- and I'or a 0.3 M(l!)
(1,1 36 m3/day ) facility \\ere estimated to be $ I 90,000 in< ludin" sand washing equipment.
\mor(i/.ed at lf/f for 20 y ears yields a cost of $I7.<'3! peryiar. 01 $|6|/M(; ($0.0433/tn3) or
SO. I ()/ 1,000 gallons, \llocating an additional 2 man hour- pei -lay to \\a-h sand to pro\ ide a \ cry
conservative estimate for labor, the labor co
($0.0 132/m3). \dding the capi I a I co-Is and the variou- () \ M i o-^ls \ iehis a total coM for intermit-
tent sand filtration of $0.33 per 1.000 gallons ($0.()H7/'m ') > ilh manual < leaning and $0.30 per
1.000 gallons ($0.()79/m3) with tractor scraf).-r eh , ning.
\ recently constructed (completed. l)e< cmh. , ! '.'76) lagoon-infermitlent sand filler system
located in JIunlinglon. I'lab. and d('signed at a h\ m aulii- loading rale of 0.3 M(i/\l) (2,808 m3/lrd)
u ith four feel (I 22 cm) of sand and 1.8 feet (.'>,!. < >u} of gravel with two 0.67 acre (0.27 h) fillers
in parallel was constructed at a total cost of $(>(: '..C>8. The filter costs $214.134 or $3.67 per ft2
($362/m2). Therefore, it is obvious that the estu-.i ics shown in Table 8 arc ver\ coti.-er\ali\c and
will vary considerably \\ilh location.
The above operation and maintenance < o-l.- .ire cornpch!i\c when compared with other
polishing techniques available. However, these cosls are liberal because performance data from
several existing wasteuater stabilisation ponds indicates Ilia! lor most times of the year filter runs
would be long enough to reduce the number of cleanings per year to 6 or less. \lso in rrianv rural
an as. labor i osts are It ,-,- lii an i he v ,,iue used a bin e.
-------
Table 8. Summary of the costs to construct and operate a 0.3 MGD
intermittent sand filter system expressed in 1973 U.S. dollars,
MANUAL CLEANING
Capital Costs
Filter System and Sand Washing Equipment3 $ 190,000
Operation & Maintenance
Routine Maintenance, 2m-hrs/day $ 5,475
Sand Washing, 2 tn-hrs/day 5,475
Filter Cleaning, 75 m/hr/cleaning,
12 cleaning/yr 6,750
Annual Costs
Amortization of Filter & Washing Equip.
20 years I? 7% 190,000 (0.09439) $ 17,934
0 & M 17,700
$/MG = $325
$/l,000 gallons = $0.33
$/MG = $296
$/1,000 gallons = $0.30
35,634
TRACTOR SCRAPER CLEANING
Capital Costs
Filter System and Sand Washing Equipment3 $ 190,000
Tractor Scraper Equipment 12,000
$ 202,000
Operation & Maintenance
Routine Maintenance, 2 m-hrs/day $ 5,475
Sand Washing, 2 m-hrs/day 5,475
Filter Cleaning, 20 m-hrs/cleaning,
12 cleaning/yr 1,800
$ 12,750
Annual Costs
Amortization of Filter & Washing Equip.,
20 yrs @ 7% 190,000 (0.09439) $ 17,934
Amortization of Tractor Scraper Equip.,
10 yrs 6> 7% 12,000 (0.14238) 1,709
0 & M 12,750
32,393
Metoalf & Eddy, Inc. [1975]
38
-------
Controlled Discharge
Controlled discharge is defined as limiting the discharge from a lagoon system to those
periods when the effluent quality will satisfy existing discharge requirements. The usual practice
is to prevent discharge from the lagoon during the winter period and during the spring and fall
overturn period. Many states currently do not permit lagoon discharges during winter months.
Pierce [1974] has reported on the quality of lagoon effluent obtained from 49 lagoon install-
ations in Michigan which practice controlled discharge. Of these 49 lagoon systems, 27 have 2 cells,
19 have 3 cells, 2 have 4 cells and 1 has 5 cells. Discharge from these systems is generally limited to
late spring and early fall. However, several of the systems discharged at various times throughout
the year. The period of discharge varied from less than 5 days to greater than 31 days. The lagoons
were emptied to a minimum depth of approximately 0.46 m (18 inches) during each controlled
discharge to provide storage capacity for the non-discharge periods.
During the discharge period, the lagoon effluent was monitored for Biochemical Oxygen
Demand (BOD5), suspended solids, and fecal coliform. The effluent BOD5 and suspended solids
concentrations measured during the stud) are illustrated in terms of probability of occurrence in
Figure 23. All values are arranged in order of magnitude and plotted on normal probability paper
with concentration (mg/1) plotted against the probability that the value would not be exceeded
under similar conditions. The plot compares the performance of two cell lagoon systems versus
three or more cell lagoon systems. The results of Figure 23 are summarized in Table 9.
£
>
90-
80-
70-
60-
50
20-
SUSPENDED SOLIDS
'3 or mo't CELLS
. SUSPENDED SOLIDS
E_LS
BOD - 3 or mor«
E f"> .5 - 2 C f L L S
01 ) 10 50 90
(X) PROBABILITY OF NOT EXCEEDING Y
S99
Figure 23. Comparison of effluent quality 2-cell systems vs. 3 or more with
long period storage before discharge, Michigan [Pierce, 1974J.
39
-------
Table 9. Effluent quality resulting from controlled discharge operation
of 49 Michigan lagoon installations [Pierce, 1974].
Percent Probability
of Occurrence
50% Probability
(i.e. Most Probable)
90% Probability
(i.e. will not be
exceeded 9 out
of 10 samples)
Effluent BOD 5
Concentration
(mg/£)
2 Cells
17
27
3 or more
cells
14
27
Effluent Suspended
Solids Concentration
(mg/£)
2 Cells
30
46
3 or more
cells
27
47
The study indicated that the most probable effluent Biochemical Oxygen Demand (BOD5)
concentration for controlled discharge systems was 17 mg/1 for two cell lagoon systems and 14 mg/1
for three or more cell lagoon systems. There was a ninety percent probability that the effluent
BOB5 concentration from both 2 cell and 3 or more cell lagoon systems would not exceed 27 mg/1.
This value is slightly less than the 30.0 mg/1 BOD5 Federal Secondary Treatment Standard.
The most probable effluent suspended solids concentration was found to be 30 mg/1 for two
cell lagoon systems and 27 mg/1 for three or more cell lagoon systems. However, the ninety percent
probability level for effluent suspended solids concentration was 46 mg/1 for 2 cell lagoon systems
and 47 mg/1 for 3 or more cell lagoon systems.
The results of the study also indicated that the fecal coliform levels were generally less than
200 per 100 ml, although this standard was exceeded on several occasions when chlorination was not
employed.
A similar study of controlled discharge lagoon systems was conducted in Minnesota |Pierce.
1974J. The discharge practices of the thirty nine installations studied were similar to those em-
ployed in Michigan. The results of that study from the fall discharge period indicated that the efflu-
ent BOD5 concentrations for 36 of 39 installations sampled were less than 25 mg/1 and the effluent
suspended solids concentrations were less than 30 mg/1. In addition, effluent fecal coliform concen-
trations were measured at 1 7 of the lagoon installations studied. All of the installations reported
effluent fecal coliform concentrations of less than 200 per ]()0 ml.
During the spring discharge period, 49 municipal lagoon installations were monitored. Ef-
fluent BOD5 concentrations exceeded 30 mg/1 at only three installations, while the maximum efflu-
40
-------
ent BOD5 concentration reported was only 39.0 mg/1. However, effluent suspended solids concen-
trations ranged from 7 mg/1 to ] 28 mg/1 with 16 of the 49 installations reporting effluent suspended
solids concentrations greater than 30.0 mg/1. Only 3 of the 45 installations monitored for effluent
fecal coliform concentrations exceeded 200 per J 00 ml.
An evaluation of the four facultative lagoon systems described earlier in this report [J.B.F.
Scientific Corp., 1976; Hill and Shindala, 1976; McKinney, 1976; and Reynolds, et al, 1976]
indicates that all of these systems could satisfy the 30.0 mg/1 BOD5 Federal Secondary Treatment
Standard throughout the entire year with the adoption of controlled discharge operations (see
Figures 1, 2, 3, 4, 5, and Table A-l). There were only four of the twelve months studied during
which the Peterborough site did not produce a final effluent BOD5 and suspended solids concen-
tration of less than 30.0 mg/1. Because this system practiced chlorination, the geometric mean fecal
coliform concentration never exceeded 200 per 100 ml. The Eudora, Kansas, and Kilmichael,
Mississippi, systems' monthly average effluent BOD5 concentration exceeded 30 mg/1 during only
two of the twelve months studied. However, monthly average effluent suspended solids concentra-
tions were often greater than 30.0 mg/1. Thus, controlled discharge at these two sites would be
possible to implement, but would require a ver\ limited discharge and large storage volume.
The Corinne site is an excellent example of where controlled discharge could be imple-
mented. The monthly average effluent BOD5 concentration of this system never exceeded 30.0
mg/1 and during only 3 of the 13 months studied did the monthly average effluent suspended
solids concentration exceed 20.0 mg/1. In addition, fecal coliform concentrations were never greater
than 200 per 100 ml.
In conclusion, controlled discharge of lagoon effluent is a simple, economical, and practical
method of achieving a high degree of treatment. Experience indicates that routine monitoring of
the lagoon effluent is necessary to determine the proper discharge period. However, these discharge
periods may extend through the major portion of the year. It will be necessary to increase the
storage capacity of certain lagoon systems which employ controlled discharge. However, many
lagoon systems already have additional freeboard and storage capacity which could be utilized
without significant modification.
Total Containment
In areas with inexpensive land and high evaporation rates, total containment lagoons are a
viable alternative for wastewater disposal. Fluctuating water levels can produce odor problems, but
limited experience indicates that normal isolation practices for lagoons are adequate. Salt buildup
may eventually produce a limited growth which could result in poor degradation of the organics.
Because of the limited operating experience, it is difficult to predict what problems might occur.
From an economic standpoint, total containment is competitive when applicable.
IN POND REMOVAL OF PARTICIPATE MATTER
General
There are several problems associated with the in-pond removal of participate matter:
41
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1. The subsequent decay of settled matter and degradation of microorganisms to produce
dissolved BOD5 , which would then have an effect on the receiving water;
2. The possibility that settled material will not remain settled;
3. The lack of positive control of effluent participate matter;
4. The problem of eventually filling in the oxidation pond; and
5. The possibility that anaerobic reactions within the settled material will produce
malodors.
At first glance, it seems that some of these problems could be resolved by rather simple
changes in operation. For example, in ponds that are in series, possibly all of the settled material
could be removed from the bottom of the last pond and transferred to the anaerobic pond or
primary pond in which biological degradation is encouraged and malodors are not such a problem.
Positive control could be achieved by adding material to the final pond to ensure that settling takes
place and remains in place. For example, chemicals such as lime, ferric chloride, and alum might be
used in this manner. Filling in a pond is not necessarily as much of a problem as one might think
unless chemicals are to be added. Generally, ponds that are used for complete containment have a
life expectancy of about 20 years [Oswald, 1968]. In areas short of land, filling could be a problem,
but it might be possible to dredge and remove the solid material after 1 to 2 decades have elapsed
and to restore the pond to its initial status. In areas where land is available and cost is not prohibi-
tive, filling would not be a problem.
Specific in-pond mechanisms of particulate removal include complete containment, biologi-
cal disks, baffles or raceways, chemical additions for precipitation, autoflocculation, and biological
harvesting. Some of the more practical mechanisms are discussed below.
Biological Harvesting
The use of biological systems to harvest algae from wastewater stabilization pond effluents
appears reasonable and would have tremendous economic advantage if the processes were control-
lable. Most of the studies which have been conducted have concentrated on the production of high
concentrations of algae rather than attempting to develop design and operating procedures. How-
ever, there are currently several studies being conducted throughout the United States which may
eventually lead to a well-designed and easily operated and controlled biological system for produc-
ing high quality effluents. Duffer [1974] presented an effective summary of projects being conduct-
ed throughout the world where the principal objective is the removal of algae from lagoon effluents.
This reference is still relatively current and should be consulted if additional information is desired.
The most promising work toward developing a biological harvesting system is being conducted
at the Woods Hole Oceanographic Institute in Woods Hole, Massachusetts [Rytlc.r, 1973]. Experi-
ments were very successful and prototype processes were developed around this concept. Several
growth systems involving marine phytoplankton, oysters, deposit feeders and seaweed were com-
bined in series to treat secondary effluent diluted with filtered seawater. A large scale multi-species
food chain concept has been in operation at Woods Hole for several years now. The results continue
to be encouraging, but are limited to areas where seawater is available [Goldman, 1976].
Fish culture in enriched waters is a verv old practice of treating wastewater employing prin-
cipally fish of the carp family. The silver carp is the most frequently employed fish used to consume
phytoplankton. There are studies in the United States being conducted to determine its effective-
ness as a means of consuming algae from wastewater stabilization pond effluents [Duffer, 1974].
42
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Other types of fish have been employed successfully in removing algae from wastewater stabiliza-
tion ponds. But control of the system still remains a principal problem. This is particularly true
when the possibility of introducing toxicants to the lagoon system occurs.
Two vascular plants, water hyacinths and alligator weeds, have been used to polish waste-
water stabilization pond effluents on a laboratory scale, and excellent results have been obtained
[ Wolverton, et ai, 1975 a, 1975bJ. However, the process remains experimental and requires con-
siderable evaluation before it will become a viable alternative to polish lagoon effluents.
Several "natural" recycling systems are being evaluated and incorporate lagoon systems or
other holding and treatment systems which arc followed by marshes and ponds or meadows,
marshes, and pond [Small, ] 977J. The City of Arcata, California, is evaluating a wastewater treat-
ment facility which includes existing primary treatment, lagoons, and a freshwater marsh operated
in conjunction with ocean ranching. The first released salmon returned to the Arcata lagoons in
the fall of 1977 \Klopp. 1977J.
Results from carefully controlled experiments such as those being conducted are required
before it will become feasible to recommend biological harvesting as an alternative in the control
of algae from small wastewater stabilization systems. In addition the lack of data substantiating
the reliability and performance of such systems, there are no cost data available upon which
economic comparisons could be made. Presently, it appears to be unfeasible to incorporate bio-
logical harvesting into small wastewater stabilization pond systems, but it is an idea which holds
some promise and should be considered as more research results become available.
Intermittent Discharge Lagoons with Chemical Addition
A series of reports distributed by the Canadian government [Graham and JIunsinger, un-
dated:/'o//« tech Pollution Advisor Services, \975;ar,(\Polletech Pollution Advisor Services, un-
dated | have reported success with the treatment of intermittent discharge lagoons by adding
various coagulants from a motorboat. Excellent quality effluents are produced, and the costs are
relatively inexpensive. The, cost of in-pond treatment and the long detention times required must
be balanced against the, alternatives available to an engineer. Man-hour requirements for the full-
scale batch treatment systems employed in Canada are summarized in Table 10.
In addition to the usual design considerations applied to intermittent discharge lagoons, the
following physical design requirements were recommended by Graham and JIunsinger [undated].
1. A roadway to the edge of each cell with a turn-about area sufficient to carry 50 tons (45
metric tons) in early spring and late fall or a piping system to deliver the chemical to each
cell and a road adequate enough to get the boats to the lagoon edge.
2. A boat ramp and a small dock installed in each cell.
3. Separate feed and outlet facilities to allow diversion of raw sewage during treatment and
draw-down in multiple cell installations for maintaining optimum effluent quality.
4. A low-level outlet pipe in the lagoon to allow complete drainage of the cell contents.
43
-------
5. A discharge pipe from the lagoon of sufficient size and design to allow drainage of the treated
area over a 5-10 day period.
6. In new large installations, a number of medium sized cells of 30-15 acres (4-6 ha) would be
better suited to this type of treatment than one or two large cells. These medium sized cells
could be treated individually and drawn down over a relatively short period of time, thus
maintaining optimum water quality in the effluent.
Table 10 . Labor requirements for full scale batch treatments [Graham and
Hunsinger, undated].
Man-hours Man-hours Man-hours
per acre per million gallons for set-up and
clean-up
per application
Alum, liquid 2 1.6 16
Ferric Chloride,
liquid 1.5 1.2 16
powder 13 9.6 16
Lime,
dry chemical method 24 17.7 12^
Haliburton method 1.7 1.4 16
Notes: 1 acre = 0.4047 ha, 1 million gallons = 3,785 m3 .
Using the typical wastewater stabilization pond design required in the State of Utah with 120
days retention time for cold weather storage, three chemical treatments per year would be required.
Designing a system for 0.3 MGD (1,136 m3/day) operation would result in approximately 136 mil-
lion liters of stored wastewater per treatment. Applying alum at a rate of 150 mg/1 would result in
20,400 kilograms (44,900 pounds) of alum required per treatment assuming that the hydraulic de-
sign would control the sizing of the storage ponds and neglecting evaporation. The installations
would require approximately 20 acres (8.09 ha) of lagoon surface with a depth of 6 feet (1.83 m).
Assuming that a relatively small boat and supply system would be adequate to distribute and mix
the chemicals with the lagoon water, a capital investment of approximately $33,000 would be re-
quired to obtain the tank trucks, storage facilities, boat and motor to carry out the operation.
Amortizing the equipment for a useful life of ten years and assuming 7% interest, it would cost
$4,700 per year. Liquid alum costs approximately $105/ton (equivalent dry) and using 68 tons
annually would cost $7,140. Approximately 36 MG (136,363 m3) of wastewater would be treated
before each discharge. Using the labor requirements shown in Table 10 of 1.6 man-hours per MG
and 16 man-hours for set-up and clean-up per application results in a total labor requirement of
221 man-hours per year. At labor costs of $7.5()/hour, the cost would be $1,658. Adding all of the
44
-------
above, costs, exclusive of Hie capital cost of the lagoon system, results in an annual rosf of $13,500
or$123/M(; (S0.0:i25/m3) of wastewater irealed (SO. 12/1.000 Bailout-).
The above eosls do not include storage facilities for the alum and (he additional design re-
quirements to accommodate the alum handling equipment and the boats. However, even doubling
the estimated costs it is apparent that intermittent discharge with chemical treatment is a viable
alternative where applicable.
In addition to (lie cost advantages outlined abo\e. batch chemical treatment of intermittent
discharge lagoons can produce an effluent containing less than 1 rng/1 of total phosphorus. Suspend-
ed solid and BOD5 concentrations of less than 20 rng/1 can be produced consistent!} and onl\
occasional!} did a bloom occur during drau down of the lagoon. Rapid draw down would overcome
this disadvantage. Sludge buildup was insignificant and would require vcars of operation before
cleaning would be required.
The KPA is supporting a study of chemical addition to poli.-h lagoon effluents at St. Charles,
South Carolina, and results are promising; however, (he project lias been in operation for onK four
months (January 1977). Vs this work progresses, more control and cost data will be available to the
design community.
In-Pond Treatment with Chlorination
('.nldirell \ 1946 | reported (he use of chlorine to kill algae and clarify the effluent from a
four-cells-in-a-series oxidation pond in California. \ 13.5 hour detention time chlorine contact pond
followed the four-cell oxidation pond sv stern, and when I 2 mg/'l of chlorine were added, all of the
algae were killed. BOD5 concentrations were reduced from 4," to 25 nig/I, suspended solids con-
centrations were reduced from I 10 mg/I to H) mg/1. and lurhidih was reduced from 70 to 40 units.
In a later stud), Dinges and Rust \ I960) reported similar resulls.
Recent studies at I'tah Stale University on the chlorinalion of lagoon effluent indicate (hat
the concern expressed in earlier articles bv EchcUn'rger, i'l til. ( 1971 | and llom \ I972| is not con-
firmed, and that the destruction of algae and the lysis of cells with high doses of chlorine occur only
when free residual chlorine is available ( Wight, 1976; and Johnson. 1976]. These studies have
shown relatively little COD released to the effluent In the chlorination of alaie laden walers with
V V ~
chlorine dosages adequate for disinfection. Dosages of chlorine as high as 30 mg/1 with 63 mg/I of
suspended solids have produced very little change in the chemical oxygen demand of lagoon efflu-
ents. Figure 24 shows the net change in soluble COD in (be lagoon (-('fluents in the Logan, Utah.
wastevvater stabilization pond effluents over a one-vear period for various free chlorine residuals.
The majority of the ^SCOD vales show an increase with free chlorine residual available, but
at residual concentrations less than 2 rng/1 there appears to be no consislent pattern. With a reason-
able degree of control, disinfection of the algae to improve settling should produce an effluent
meeting the. requirement of 30 mg/I of IU)I)5 and SS concentrations.
Baffles
The encouragement of attached biological growth in oxidation ponds is an apparent practical
solution for maintaining biloogical populations while still obtaining (he (reatment desired, \llhough
-------
+ 30-
24
Q
O
O
to
-16
j
-30-f
0
EsHSlisn si iLisj
Y = 4GD2 X - 2.948
R« .547
2 3
FREE CHLORINE RESIDUAL (mg/l)
Figure 24. Changes in soluble COD when free chlorine residual is present
in unfiltered lagoon effluent \Wight, 1976].
baffles are considered useful primarily to ensure good mixing and to eliminate the problem of short-
circuiting, they behave similarly to the biological disks in that they provide a substrate on which
bacteria, algae, and other microorganisms can grow [Reynolds, I971;Nielson, 1973]. In general,
attached growth surpasses suspended growth if sufficient surface area is available. In anaerobic or
facultative ponds with baffling or biological disks, the microbiological community consists of a
gradient of algae to photosynthetic, chromogenic bacteria and. finally, to nonphotosynthetic, non-
chromogenic bacteria [Reynolds, 1971; Niehon, 1973]. In these baffles experiments, the presence
of attached growth to the baffles was the reason for the higher efficiency of treatment than that in
the nonbaffled systems.
Whereas an attached growth system has the advantage of requiring little maintenance in terms
of the biological operations, its initial cost, subsequent treatment requirement, and unproven capa-
bility seem to preclude serious consideration at this time.
Rock Filter
General
The rock filter [O'Brien, 1974, 1975a, 1975b] is essentially a porous rock wall or rock em-
bankment located at the end of a lagoon system through which the lagoon effluent is allowed to
flow. As the lagoon effluent flows through the void space within the rock filter, suspended solids
46
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settle out in the voids and onto the rock surfaces. The accumulated suspended solids are then bio-
logically degraded. This biological degradation process is generally aerobic during warm months and
anaerobic during cooler periods.
Laboratory scale studies on rock filters have, been conducted by Martin [1970] and O'Brien,
et al. [1973]. In addition, pilot scale rock filter studies have been conducted by Martin and Wetter
[1973). However, the principal full scale rock filter research has been conducted by O'Brien [1974,
1975a, 1975b].
Eudora, Kansas
O'Brien's work (1974, 1975a, 1975b] was conducted at Eudora, Kansas, during 1974-1975.
The study was conducted on both a large rock filter and a small rock filter (Table 11). A cross sec-
tion of the filter is shown in Figure 25. The hydraulic loading of the large rock filter ranged from
2977.8 l/m3/day (22.3 gal/ft3 /day) to 535.6 l/m3/day (4.0 gal/ft3/day) and on the small rock
filter from 62.0 l/m3/day (0.5 gal/ft3/day) to 2187.9 l/m3/day (16.4 gal/ft3/day). After approxi-
mately 11 months of operation, the small rock filter ceased to function due to the growth of a
dense algal mat on the downstream side of the filter face.
Table 11. Size gradation of the rock used in the large and small
filters at Eudora, Kansas [O'Brien, 1975a].
rock
Sieve Opening
cm
5.08
3.81
2.54
1.91
1.27
0.95
0.67
0.47
Porosity
% Weight
Large Rock
7.4
28.8
52.0
10.4
1.3
0.1
0.44
Retained
Small Rock
13.4
33.1
29.0
10.4
3.2
0.9
0.44
47
-------
WALJOWtr
SAMPLING TUBES
1 I
-2JTin4
OUTLET STRUCTURE
O
SCALE
I 2 3
METERS
Figure 25. Cross section of rock filter at Eudora. Kansas 11 >"Bn>«. 1975a |.
The Biochemical Oxygen Demand performance (BODS ) of the large rock filter is shown in
Figure 26. In general the roek filter did not receive BOD5 loadings which exceeded 20.0 mg/1.
However, rock filter effluent BO1>5 concentrations were generally less than 20.0 mg/1. During the
winter months of February. JAaveh and April mflaent BOD5 concentrations to the large rock filter
did exceed 20.0 mg/1 and during these months the rock filler effluent BQD5 concentrations were
generally between 25 JO and 3O.O mg/L
The suspended sofids performance of the large rock filter is illustrated in Figure 27. In
general, influent suspended sefids concentrations were apparently 50.0 to 60.0 mg/1- Rock filter
effluent suspended sofidk concentrations were senexanV less than 3O.O we/I during the warm sum-
IT n (1975a) recommended
that rock filters should be constructed with rocks greater than ±54 cm (1 inch) and less than 12.70
cm (5 inches) with most of the roek being approximately 5.1 em (2 inches) in diameter. Recom-
mended hydraufic loading rates range from 401X9 l/m3/day (3 gat/ft3/dav) during cold weather
periods to 1203 l/n3/day (9 gal/ft3 /day) during warm weather periods.
California. Ifeffiami
Lane-Riddle Engineers., Inc. designed a rock filler for the town of California. Missouri
[O'Brien, 1975a}, in June 1974, to upgrade an existing lagoon. This was placed along one side of a
tertiary lagoon as illustrated in Figure 28. The roek fiber was designed for a hydraulic loading rate
of 400.9 l/m3 (3.0 gal/ft3/day). The gradation of roek employed in the filter is reported in Table
12. The fitter was constructed by city employees in August of 1974.
48
-------
I I I I I
LAGOON INFLUENT
FILTER EFFLUENT
LARGE ROCK FILTER
FMAMJJ ASONDJFMAM
00
Figure 26. Biochemical Oxygen Demand (HOD5 ) performance of large rock
filter at Eudora, Kansas [O'Brian* 197,ia].
i i i
i i I I I
LAGOON INFLUENT
FILTER EFFLUENT
LARGE ROCK FILTER
MAM
CO
F M A M
Figure 27. Suspended solids performance of large rock filter at Eudora. Kansas
[O'Brien, 197.r)aj.
49
-------
A performance evaluation of the California, Missouri, rock filter was conducted by the Sur-
veillance and Analysis Division, Region 7, U.S. Environmental Protection Agency during March and
April 1975. The results of that evaluation indicated that the actual average hydraulic load on the
filter was 250.7 l/m3/day (1.9 gal/ft3/day). A summary of the rock filter performance is reported
in Table 13. During the evaluation period, the rock filter average effluent BOD5 concentration was
12 mg/1; however, the average rock filter influent BOD5 concentration was only 21 mg/1. The rock
filter average influent suspended solids concentration was 69 mg/1 while the rock filter average
effluent suspended solids concentration was 22 mg/1.
A routine monitoring program for the California, Missouri rock filter was initiated by the
Missouri Department of Natural Resources in March 1975 and the results of this work are sum-
marized in Figure 29. All solids determinations were made on grab samples. The performance of
the rock filter was sporadic and failed to meet the federal discharge standard of 30 mg/1 of sus-
pended solids in the effluent on 11 of the 19 sampling dates. Further work is currently being con-
ducted in Oregon on the performance of the rock filter. Results are expected from the Oregon
study in early 1978.
DOUBLE PER-
FORATED PIPE
EFFLUENT STRUCTURE
SECTION A~A
Figure 28. Rock filter installation at California, Missouri
[O'Dea, 1975a].
50
-------
Table 12. Size gradation of the rock used in the rock filter at
California, Missouri [O'Brien, 1975a]
% Passing Screen
by Weight
85 - 100
0 - 15
0 - 5
Screen Size
cm
7.62 - 12.70
6.35 - 7.62
below 6.35
FEDERAL DISCHARGE
STANDARD
Figure 29. Suspended solids concentrations in lagoon effluent applied (o the California,
Missouri, rock filter and the rock filter effluent | Forcsfcr, 1977J.
51
-------
Table 13. Performance of rock filter at California, Missouri [O'Brien, 1975a]
Date
March 5, 1975
March 13, 1975
March 19, 1975
March 26, 1975
April 2, 1975
Average
BOD5 (
-------
in the literature and are not corrected for changes in value of the dollar. This was done to allow the
reader to use the system appropriate for his area to adjust the costs to a current base. Corrections
were made to all capital costs to reflect a 1% interest rate and a 20-year life except for systems
known to have shorter operating periods. The exceptions are identified in Table 14.
The selection of the cost-effective alternative must be made based upon good engineering
judgment and local economic conditions. Cost variations in one item, such as filter sand or land,
can change the relative position of a process dramatically. In brief, Table ]4 cannot be substituted
for good engineering.
All of the processes listed in Table 14 arc, capable of meeting secondary standards, and sev-
eral are capable of producing an effluent superior to 30 mg/1 of B01)5 and suspended solids. Varia-
tions in design and operation also alter the quality of the effluent dramatically in most of the pro-
cesses. A careful study of all alternatives must be made before selecting a system. The literature
referenced herein will provide all details needed, but a firm should remain aware of current devel-
opments and use other alternatives as more information becomes available.
53
-------
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62
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APPENDIX
63
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-------
SMALL COMMUNITY WASTEWATER
TREATMENT FACILITIES-
BIOLOGICAL TREATMENT SYSTEMS
by
Henry H. Benjes, Jr. '
Prepared for the
Environmental Protection Agency
Technology Transfer
National Seminar
on
Small Wastewater Treatment Systems
1 Chief Engineer,Culp/Wesner/Culp, Box 40, El Dorado Hills, California 95630
-------
TABLE OF CONTENTS
INTRODUCTION 1
Plant Operation 1
Wastewater Character 1
Wastewater Process 1
GENERAL DESIGN CONSIDERATIONS 2
Flow Measurement 2
Sampling 2
Mechanical Equipment Access 3
Buildings 3
Plant Site and Landscape 4
TREATMENT UNITS 4
Grit & Screening 4
Primary Treatment 5
Anaerobic Digestion 5
Aerobic Digestion 8
Sludge Disposal 10
BIOLOGICAL TREATMENT 11
Suspended Growth Biological Treatment 14
Conventional Activated Sludge 20
Extended Aeration Activated Sludge 21
Oxidation Ditch Activated Sludge 23
Comparison of Extended Aeration & Conventional
Activated Sludge 23
Attached Growth Biological Treatment 27
Rational Design Basis for Attached Growth Systems 29
Rock Media Trickling Filters 32
Plastic and Redwood Media Trickling Filters 34
Rotating Biological Media 34
Temperature 43
Nitrification 44
Solids Production 49
PROCESS PERFORMANCE 52
Extended Aeration and Conventional Activated Sludge 52
Oxidation Ditch 56
Trickling Filters 56
Rotating Biological Media 56
ESTIMATING PROJECT COSTS AND OPERATING & MAINTENANCE
REQUIREMENTS 63
Raw Wastewater Pumping 65
Preliminary Treatment 65
Sedimentation Basins 65
Waste Sludge Pumping Stations 66
Prefabricated Extended Aeration Plants 66
Prefabricated "Contact Stabilization" Plants 67
Custom Designed Extended Aeration Basins 67
Oxidation Ditch Aeration Basins 67
Mechanical Aeration Equipment 67
Diffused Aeration Equipment 68
Recirculation Pumping Stations 68
-------
TABLE OF CONTENTS
(continued)
Trickling Filters 68
Rotating Biological Disks 68
Sludge Treatment 68
Disinfection 69
OPERATION & MAINTENANCE REQUIREMENTS 70
Comparison of Alternative Processes 72
CHANGES TO CASE I CONDITIONS FOR NITRIFICATION 86
-------
LIST OF TABLES
Table NO.
1 Example Wastewater Characteristics 20
2 Comparison of Trickling Filter Models With Data 33
3 Rock Media Biofilters - Data Evaluation for
Depth and Volume Effects 35
4 Plastic and Redwood Media Biofilters - Data
Evaluation of Equations (4) and (5) 36
5 Rotating Biological Media - Performance Data 41
6 Extended Aeration Performance 55
7 Oxidation Ditch Performance 57
8 Example Process Design Basis Summary 74
9 Prefabricated Extended Aeration Plant 79
10 Prefabricated Contact Stabilization Plants 80
11 Conventional Activated Sludge 81
12 Custom Built Extended Aerat-'on 82
13 Extended Aeration Oxidation Ditch Plant 83
14 Rock Media Trickling Filters 84
15 Rotating Biological Media 85
16 Process Advantages and Disadvantages of Biological
Treatment Alternatives for Small Community
Applications 87
-------
LIST OF FIGURES
Figure No. Page
1 Hydroscreen Primary Treatment 6
2 Sludge Treatment Schematic Using Anaerobic
& Aerobic Digestion 9
3 Land Spreading of Sludge 12
4 Hose Delivery System for Sludge Injector 12
5 Sand Drying Beds 13
6 Activated Sludge Process 13
7 Oxygen Requirements 17
8 Required Aeration Time for Varying SRT Values 19
9 Suspended Growth Typical Sludge Production 18
10 Biodegradable Fraction of Waste Sludge 19
11 Effect of Organic Load Variations, Conventional
& Extended Aeration Activated Sludge 25
12 Effect of Hydraulic Variations, Conventional &
Extended Aeration Activated Sludge 26
13 Rock Media Trickling Filters, Effect of Wetting
Rate on Evaluation Constants 37
14 Redwood & Plastic Media, Trickling Filters Soluble
BOD Removal Efficiency 38
15 Rotating Biological Media, Manufacturer's Design
Approach 39
16 Rotating Biological Media Temperature Effects 45
17 Effect of Organic Load on Nitrification Efficiency
of Rock Media Trickling Filters 46
18 Plastic Media Trickling Filter Loading - Temperature
Performance Relationship of a Nitrifying
Trickling Filter 48
19 RBM Process, Nitrification - Hydraulic Load
Relationship 50
20 RBM Process, Nitrification - Temperature
Relationship 51
21 Activated S ludge Effluent Quality 54
22 Activated Sludge Effluent Quality, Dallas, Texas
Nitrification Pilot Plant 58
23 Trickling Filter Effluent Quality, Two Texas Plants 59
24 Effluent Quality, Trickling Filters 60
25 RBM Effluent Quality, Gladstone, Michigan 61
26 Process Schematic - Extended Aeration Process 75
27 Process Schematic - Prefabricated Contact
Stabilization Plants 75
28 Process Schematic - Prefabricated Contact
Stabilization Plant 76
29 Process Schematic - Custom Designed Extended
Aeration Plants 76
30 Process Schematic - Oxidation Ditch Extended
Aeration Plant 77
31 Process Schematic - Conventional Activated Sludge 77
32 Process Schematic - Stationary Media Trickling Filters 78
33 Process Schematic - Rotating Biological Media System 78
-------
LIST OF FIGURES
(continued)
Figure No. Pac
34 Case I - Estimated Cost Comparison,
Nitrification Not Required 91
35 Case II - Estimated Cost Comparison,
Nitrification Required 92
36 Case I - Alternative Comparison,
Nitrification Not Required 93
37 Case II - Alternative Comparison,
Nitrification Required 94
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SMALL COMMUNITY WASTEWATER
TREATMENT FACILITIES
INTRODUCTION
The facilities provided for treatment of domestic wastewaters from
small communities require some significantly different considerations
than those encountered when designing large plants. The overall facility
design concept of simplicity is much more important than in larger plants.
The factors which are generally prevalent and must be considered in
design for small plants include:
Plant Operation
Available operator time will be minimal because of restrictive small
community budgets.
Available operator skills will be restrictive since the skills re-
side with one or two individuals rather than a large staff.
Capital improvements will be a minimal or nonexistent budget item.
The plant will not be manned during night time or weekend shifts.
Preventative maintenance will be practiced as an exception rather
than a rule.
Wastewater Character
Variations in hydraulic and organic loads will be greater.
Night time flows for very small plants may be near zero.
Wastewater Process
Plant operating data will be less oriented to design needs but more
oriented to operational needs.
Some process alternatives may be more applicable to smaller plants
than larger ones.
Process units such as sedimentation basins are smaller than those
used for larger plants and the design parameters may be different than
for larger plants.
The topic which this presentation reviews in detail is biological
treatment systems for small community treatment plants; however other
-------
phases of the design for these plants are equally important insofar as
providing acceptable design practice and economical construction and
operating costs.
Other presentations included in this Small Wastewater Treatment
Systems Seminar do not include the considerations given to facilities for
mechanically oriented wastewater treatment systems; therefore, this pre-
sentation will include a brief discussion of the design approach of plant
functional units which are adjunctive to the biological treatment process.
GENERAL DESIGN CONSIDERATIONS
For the purposes of this presentation, small community plants are
considered to be those having a capacity of less than 2 mgd. The design
of small plants has many considerations which are common with larger
plants. Many of these considerations are outlined in EPA guidelines;
however, the features required by the guidelines have been neglected in
the past and bear repeating.
Flow Measurement
Every plant should provide flow measurement of the incoming wastes
and a record of the flow rate. Many small plant flow meters are inac-
curate because they are infrequently checked or provide little means to
permit the operator to check the flow to know if the equipment requires
service. For this reason, the use of an open channel flow measurement
device, such as a Parshall flume is convenient, to permit the operator
to zero the meter and to manually check the depth, calculate the flow,
and compare it to the metered reading. The operator can also check the
hourly flow and with a few calculations determine if the totalizer is
working properly. The author's experience with in-channel level measure-
ment devices is poor and stilling wells connected to the Parshall channel
are preferable.
Sampling
Almost all small plants use manual sampling to obtain performance
results and operational monitoring, and for this reason it is usual that
only 8 hour composites are obtained. Because of the time consuming chore
of collecting samples, the opportunity for error in compositing, and the
lack of a total picture of the waste character, the use of automatic com-
positing samplers is justifiable for at least the plant influent and
effluent samples. There are many compositing samplers on the market to-
day in the cost range of from $2,000-$5,000 per sample point which, when
interconnected with the flowmeter, produce an excellent composite sample.
The use of these devices not only relieves the operator for other duties,
but results in more accurate data than manual sampling.
-------
Mechanical Equipment Access
There are many examples of extraordinarily poor layout design of
mechanical equipment and mechanical equipment access in small communi-
ty plants. Tt appears at times that no thought is given to removal of
pumps, valves, or other equipment, let alone access by maintenance
personnel.
During design the designer should keep in mind minimum aisle
clearances, adequate spacing between equipment, and other passage access
space required for personnel.
It is also important to work out procedures which would be employed
to remove equipment from structures or basins in the event replacement is
required. The life of the structure probably exceeds the equipment life
by 4 times and future plant expansions may require upsizing equipment and
retaining the use of the structure.
Buildings
Recently more attention by designers has been directed to building
layout and design; however, it is worthwhile to reiterate certain of the
more salient features which should be included.
Laboratory. Many past designs of laboratories for wastewater utili-
ties were perfunctory. The lab design should be based on establishing
work areas for the various analyses; counting the numbers of tests, bottles
and equipment required to establish space and lab utility requirements;
and, placing equipment in logical groupings to prevent the operator from
wandering from one end to the other to perform one analysis. Good light-
ing and ventilation also are necessary. Even in small labs, safety equip-
ment should be provided, such as fire extinguishers, eyewashes, emergency
showers, etc.
A great percentage of the operator's time at a small community plant
is required for performing lab abalyses and a thoughtfully planned lab
will contribute significantly to the savings in time spent for this opera-
tor function.
Maintenance Shop. A place for repair of equipment should be pro-
vided commensurate with the organizational setup of the utility. If
maintenance and repair of small parts is to be performed at the plant,
a workshop area should be provided.
Office/Lunchroom/Records. A room, even though it may be small should
be provided to permit storage of records and a place to make out reports.
This space also provides a location where the operator(s) may have lunch
and coffee breaks away from the lab. A bacteriological/chemical labora-
tory is no place for lunch.
-------
Plant Site and Landscape
The planning of the plant site and landscaping also provides the
designer an opportunity to minimize maintenance and operation labor and
facilitate future expansion of plant facilities.
The plant site should be as compact as possible, but retaining
access by cranes or other lifting equipment between structures and re-
taining access to buried piping for future expansions. A compact plant
layout will cost less for connecting piping, sidewalks, driveways and
will be more convenient during operation.
Roadways into the plant and to unloading facilities (such as chlor-
ine cylinders) and to loading facilities (such as grit and screenings
containers) should be based on the appropriate truck and turning radius.
This may seem to be obvious; however, the numbers of small community
plants with inadequate vehicle access provisions are legion.
The plant site and associated yard work are poorly planned as a
general rule. It is typical for small community plant designs to fence
the entire property and plant grass in the enclosed area. The size of
the yard and the maintenance required either results in a hit and miss
maintenance program or a considerable amount of maintenance labor to
retain a presentable site. As a rule-of-thumb, it takes about 30 MH/year/
acre to maintain a lawn. A 5 acre site will require a man-month/year.
Therefore, it is thoughtful to minimize the portion of the site which is
maintained in lawn. One alternative to a lawn may be ground covers which
do not require mowing. Automatic irrigation systems in many climates are
also a labor saving device.
TREATMENT UNITS
Grit &_Screenin_g
There are many approaches to grit and screening of wastewater, most
of which are applicable to small plants. Light duty equipment has been
used in many small plants with limited success. It must be remembered
that even though the smaller plants are subjected to less severe condi-
tions that larger plants, almost everything can, and does, come down the
sewer. The use of articulating arm grit channel collectors, or grit
channels not preceded by screening devices cause the operators many prob-
lems during peak wet weather flow conditions. It is important to precede
the grit collecting device with a screening device and to provide heavy
duty grit removal equipment that will not bog down when slugs of gravel
come to the plant during peak wet weather flows. Consideration should
be given to screening the wastes and collection of the debris, rather
than subsequent grinding and placing the shredded debris back in the flow.
The small amount of debris and grit at smaller plants permits direct bur-
ial rather than maintaining a shredder and coping with the problems of
-------
debris with downstream equipment. Of course two sets of grit and screen-
ing equipment are required, even though the standby set may require manual
cleaning.
Primary Treatment
The use of primary treatment facilities in small community wastewater
treatment plants is prevalent. Primary treatment affords a means of remov-
ing settleable solids, some of which are biodegradable, providing protection
for equipment downstream from dense solids and reducing the size of second-
ary treatment facilities. Since the advantages afforded to the secondary process
may be offset by the added primary facilities (primary sedimentation basins,
scum wells, sludge pumping, solids treatment and disposal), elimination of
primary treatment facilities may be advantageous. Small community wastewater
treatment plants, however, have smaller pumps and piping and potential plug-
gage of these units should be carefully considered.
Attached growth processes require primary treatment to prevent
pluggage of small openings in the media. Primary treatment may be pro-
vided in the conventional manner, using a basin, or alternatively using
a fine mesh hydroscreen, as shown on Figure 1. The hydroscreen generally
requires less capital expenditure and provides the necessary protection
required for downstream processes. The solids removed from the hydro-
screen are much more concentrated than from settling basins and either
must be diluted for subsequent treatment, unless dewatering and compost-
ing or chemical stabilization is provided.
Anaerobic Digestion
One area of poor design for most small community plants is sludge treat-
ment and disposal. This function is also the most costly unit at most plants and
requires the greatest operator effort in terms of labor and skill. A successful
small community plant design will result in the simplest and most direct means
of sludge treatment and disposal.
Anaerobic digestion has been used extensively in small community
wastewater treatment plants. The use of anaerobic digesters is usually
associated with primary treatment facilities. The general lack of suc-
cess of this process at small plants is partially caused by gross over-
design, lack of proper mixing, lack of monitoring, and lack of control
facilities for upset.
A recent review of plant facilities for a small California waste-
water treatment plant revealed the anaerobic digester had over 400 days
storage capacity for solids. It is not unusual to find anaerobic diges-
ters designed for 40 to 60 days detention. Many digesters are provided
with small gas recirculation systems predesigned by manufacturers. The
usual design basis is about 5 to 10 CFM/1,000 cubic feet. This level of
mixing is generally adequate to maintain some of the solids in suspension
-------
FIGURE 1 - HYDROSCREEN PRIMARY TREATMENT
-------
and control the scum blanket but is insufficient to provide proper mixing
for a complex biological reactor. In aerobic systems, at least 20 CFM/
1,000 cubic feet is considered necessary to approach complete mixing.
The anaerobic system, to perform as well as aerobic systems, should be
mixed equally well. Anaerobic bacteria gain about 1/5 the energy from
a unit of organics as compared to aerobic bacteria. Anaerobic digesters
designed at about 0.1 Ib of volatile solids/cubic feet per day are loaded
at about 50 pounds of BOD/1,000 cubic feet. This is similar to loadings
used for aerobic processes. Therefore, considerably less bacteria are
present in an anaerobic digester as compared to an aerobic system. The
methane bacteria are very sensitive to changes in pH. A sudden addition
of organic matter first causes formation of volatile acids and can result
in retardation of the methane bacteria if pH is depressed.
If used, anaerobic digesters should be completely mixed, continuous-
ly fed, or fed frequently at small doses, loaded higher than convention
to result in greater concentrations of bacteria, and routinely monitored
for volatile acids and alkalinity.
Many plants recycle waste activated sludge to the primary or add the
waste activated sludge to the anaerobic digester. Either of these actions
frequently proves to be unsatisfactory. Placing a large quantity of bacteria
with a large quantity of organics for cosettling in the primary basin can
only lead to the lower efficiency of this unit process. The bacteria will
liquefy the organics; the added organic material will tend to disperse
the bacteria; and it is not unusual to find the primary effluent BOD
equal to or greater than the influent BOD.
Addition of waste activated sludge to an anaerobic digester results in poor
supernatant separation for the same reasons. Waste activated sludge and raw
sludge codigested in an anaerobic digester will typically result in very high
solids and BOD in the supernatant return to the plant.
On the other hand, the cosettling or the codigestion of primary waste
and waste sludge from attached growth biological processes has a higher
degree of success. The lower activity and more stable sludge, from attached
growth systems often will permit cotreatinent of these sludges although there
are instances where poor results have been obtained.
Even properly designed anaerobic systems applied only to raw waste-
water solids result in supernatant return to the liquid process which has
a high BOD and is odorous. Preaeration or judicial selection of the return
point for this liquor is necessary to prevent odorous conditions or
effluent quality deterioration.
Anaerobic digestion, although an extremely efficient process, should be
applied to small plants only when operator skills are suitable; the process
will be routinely monitored; external means are provided for chemical (sodium
bicarbonate or lime) additions for pH control; the process is provided with
-------
means to continuously feed organics, or for frequent feeding in small doses;
complete mixing is provided; and initial organic loads are above 75 pounds
per 1, 000 cu ft/day in the primary digester. Otherwise, other means of
sludge treatment which require less precise operator control should be used.
Aerobic Digestion
Aerobic digestion when properly designed is an extremely simple pro-
cess which is applicable to all biological or organic sludges and in any com-
bination. Unfortunately, it is a poorly understood process and inadequate
designs are prevalent. Aerobic digestion will require more energy than
anaerobic digestion because of the energy requirements for oxygen transfer.
Whereas a proper design for anaerobic digestion may require 0.4 kwh/lb
BOD5 and produce energy in the form of methane gas, an aerobic digester
will generally require from 1.1 to 1.6 kwh/lb BOD5.
The aerobic digestion process provides a stable supernatant and a
stable sludge. A combination of the anaerobic and aerobic process for
digestion has been successfully applied. Using the anaerobic digester
for raw sludge stabilization and the aerobic digester for waste activated
sludge and anaerobic digester supernatant stabilization as shown on
Figure 2 provides the advantage of separate treatment of incompatible
sludges, stabilization of anaerobic digester supernatant, which is often
a problem when returned to the liquid process, and compromises on the
energy savings by using the anaerobic digester for the greatest share of
the organic sludge.
The proper design of an aerobic digester is not complex; however,
many of the approaches used to date have erroneously been based on solids
destruction or solids loadings from which empirical factors are applied.
Solids destruction, although a desireable goal is limited in biological
unit processes. It is fundamental that only the biodegradable fraction
can enter into the biological reaction. The biodegradable fraction is
measured by the BOD test. The stabilization in an aerobic digester can
be predicted by the following equation:
BOD out 1
BOD in KTKet-l
Where Ke is the endogenous respiration rate
K is the temperature effect modifier
t is the sludge detention time In days
The "constants" in fact are not constant and are determined from the
following equations:
K = 1.072(2°-T)
T
Ke = 0.5 (0.66lnT)
where T is temperature, celcius
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The oxygen uptake rate in the aerobic digester may be determined by
the following equations:
do 1.3 (BOD in - BOD out)
dT T x 24
Where do/dt = oxygen uptake rate mg/l/hr
BOD = 5 day BOD of waste activated sludge, rng/1
T = aerobic digester detention, days
The above equations and the combined effect of including raw sludge or
anaerobic digester supernatant have been developed previously").
Sludge Disposal
The disposal of the stabilized sludge is an onerous problem. There
are many combinations of processes available which may be used. However,
especially for small community wastewater treatment plants, most of the
available alternatives may be eliminated from consideration upon cursory
review.
Disposal of sludge to natural watercourses may be eliminated as a
viable alternative for almost any plant because of regulatory resistance
to this alternative. Disposal of sludge by incineration for small plants
is uneconomical. For large community plants these disposal alternatives
may be economically attractive and worthy of further pursuit, but for small
community plants they may be eliminated summarily.
The sludge for small community plants will, with few exception, be
discharged to the land.
Liquid Sludge Disposal
Transport
Pipeline
Truck
Application
Injection
Spraying
Storage
Dewatered Sludge Disposal
Dewatering
Sand Drying Beds
Mechanical Dewatering
Removal/Transport
Truck
Community Removal
Disposal
Landfill
Land Spreading
The selection of the method of disposal is primarily one of economics.
For small community plants, the considerations of operational simplicity,
flexibility and reduction of the number of times the sludge is handled
will generally result in the most economical solution.
It is not intended to explore the advantages and disadvantages or
design approach of the above alternatives. A few out-of-the-ordinary
10
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successful sludge disposal practices are presented below as examples of
successful practice for small community plants.
Trinity River Authority, Texas. The 6 mgd TRA Ten Mile Creek plant
was originally equipped with centrifuge dewatering for the anaerobic-ally
digested sludge. The large chemical demands and mechanical operating
problems associated with the centrifuge led the authority to pursue land
disposal of the sludge on an adjacent site. The land being uniformly and
gently sloped led the authority to use a land spreading application method.
Figure 3 shows the land disposal site.
Corpus Christi, Texas. Corpus Christi has 6 plants many of which are
located in developed areas. At their Westside plant a program of sludge
disposal by shallow injection was piloted to ascertain adverse environ-
mental effects from this procedure. The impetus to investigate this pro-
cedure came from the previous practice of the City to heat dry their
sludge in rotary driers, a costly procedure requiring large amounts of
fuel.
Figure 4 shows the tractor and sludge supply hose in operation. The
equipment has the capacity to inject liquid sludge at 400 gpm at a depth of
4 inches below the soil. At this rate, one week's accumulation of sludge is
disposed of in less than 2 hours for the 1. 5 mgd plant. The sludge is pumped
directly from the secondary digester. The lack of odors and savings in energy
and mechanical equipment resulted in a successful pilot operation.
Placerville, California. Placerville, California operates a 0.75
mgd plant and anaerobically digests the sludge. The digested sludge is
dewatered on sand drying beds. See Figure 5. The demand by private
individuals for the dried sludge is so great, that the City permits only
those individuals who are willing to remove the sludge from the beds to
use the sludge. For the past several years, the City has had no require-
ments for labor to remove the sludge from the beds and no sludge haul
requirements.
The above examples present sludge disposal practices at small commun-
ities which represent a practice which logically evolved in each community
to find an easier and more economical method for sludge disposal.
Design practice should emphasize simplicity in disposal procedures
and avoid complex processes that may be abandoned by the operating
agency in favor of simpler procedures.
BIOLOGICAL TREATMENT
This section will review performance problems and costs of selected
biological treatment processes. The processes selected for presentation
are those that appear particularly well suited for application to small
11
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FIGURE 3 - LAND SPREADING OF SLUDGE
FIGURE 4 - HOSE DELIVERY SYSTEM FOR SLUDGE INJECTOR
12
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FIGURE 5 - SAND DRYING BEDS
Fj mg/l
AERATION
t, hrs
V, mg
Ma - mg/l
Me mg/l
F, mg/l
WAS
FIGURE 6 - ACTIVATED SLUDGE PROCESS
13
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community wastewater treatment processes and include:
Suspended Growth Biological Treatment
Conventional Activated Sludge
Extended Aeration Activated Sludge
Oxidation Ditch Activated Sludge
Attached Growth Biological Treatment
Rock Media Trickling Filters
Plastic or Redwood Media Trickling Filters
Rotating Biological Media
Suspended Growth Biological Treatment
Design Approach. The design approach to suspended growth biological
treatment systems has been outlined by several researchers ' ' and
presented in a unified model by Goodman "' . The proper usage of any of
these procedures will result in sufficiently accurate designs.
It will be helpful to review one of these models from which certain
observations may be made concerning the differences in design of the.
selected alternative suspended growth systems. The McKinney model is
used extensively in the midwest and is presented below. Refer to Figure 6
for a schematic of the process which parallels the following model.
F =
Fi
Kmt+1
ts = SRT =
# solids in aeration and sedimentation basins
# solids wasted and lost in effluent per day
Ma =
Ks F
Ke+l/ts
Me = 0.2 Ke Ma ts
do/dt = l.S(Fi-F) - 1.42(Ma+Me)
t ts x 24
Where Fi = influent BOD , mg/1
F = effluent unmetabolized BOD , mg/1
t = aeration, detention time, hours
Ma = active cell mass in MLSS, mg/1
Me = endogenous mass in MLSS, mg/1
ts = SRT, days
do/dt = oxygen demand in aeration basin, mg/1 hr
Km = metabolism rate constant = 7.2/hr @ 20C
14
-------
Ks = synthesis rate constant = 120/day @ 20C
Ke = endogenous rate constant = 0.48/day @ 20C
The constants may be adjusted for temperature variations from the
20C base by:
Where T = temperature, degrees Celcius
The MLSS may be estimated by the sum of the bacterial mass (Ma+Me)
plus the buildup of the inert solids which are in the incoming sewage.
The inert solids include the nonvolatile solids plus the fraction of
the volatile solids which are not biodegradable. The inert sewage solids
accumulate in the MLSS in proportion to the SRT.
A portion of cell mass generated is nonvolatile. This fraction may
be estimated as being 0.1 (Ma+Me). Therefore, the total MLSS may be
calculated as follows:
Solids Source MLVSS MLSS
Ma Ma Ma
Me Me Me
Inert nonvolatile sewage
solids, ISS 0 ISSxtsx24
t
Inert volatile sewage
solids, IVS IVSxtsx24 IVSxtsx24
t t
Nonvolatile cell mass 0 0.1(Ma+Me)
SUM Ma+Me+IVSxtsx24 1.1(Ma+Me)+(IVS+ISS)tsx24
The sludge production is calculated by the pounds of solids in the
system divided by the SRT or:
Sludge Production = MLSSxVxS.33
t
s
Where V = aeration basin volume, mg
Based on the above, several general relationships may be derived to
review process differences between the three suspended growth systems
selected.
The key design parameters for sizing basins and equipment are:
Oxygen Requirements. An adequate oxygen supply must be provided for
conversion of the organics to bacterial cells and the stabilization of the
15
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bacterial cells to result in a readily settleable sludge. The oxygen
demand rate also influences the size of the aeration basin. Large demand
rates (in excess of 60-70 mg/l/hr) are usually beyond the capability of
conventional aeration devices. Therefore, peak demand rates should be
maintained below this level. One means of controlling the peak rate dur-
ing design is to increase the aeration basin size.
MLSS. The concentration of MLSS in the aeration basin is determined
by the food supplied and the SRT. The physical limitation on the MLSS
concentration is the compactability of the sludge in the final sedimenta-
tion basin. For a conventional design based on 50 percent recycle and a
settled sludge or return sludge concentration of 10,000 mg/1 (SVI = 100),
the solids balance for the final sedimentation basin may be stated:
Solids In = Solids Out
(Qi+0)xMLSS = Q C
R R R
If: QR = 0.5 Q.
Then: 1.5 p.MLSS = 0.5 Q.C
~i. 1 R
And: MLSS = C
-3 R
If: CR = 10,000 mg/1
Then: MLSS = 3,333 mg/1
Therefore, conventional design indicates a. practical design upper limit
for the MLSS of about 3, 000 mg/1. Higher MLSS concentrations may be
attained in operation; however, to provide a design for a stable opera-
ting system, the author recommends a design based on a MLSS not to
exceed 3, 500 mg/1 at the desired SRT.
Sludge Production. The amount of the sludge produced from the pro-
cess is a kay parameter for subsequent design of sludge handling/treatment/
disposal facilities.
Nitrification. Where effluent requirements include nitrification,
the operating characteristics and oxygen requirements to achieve nitri-
fication must be considered.
The key design parameters described above have been generalized on
Figures 7, 8, and 9 based upon an influent waste having the characteristics
defined in Table 1. The cases presented include:
1. Raw wastewater directly to aeration
2. Primary treatment preceding aeration
3. Nitrification required
16
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SLUDGE RETENTION TIME, days
OXYGEN REQUIREMENTS
17
FIGURE 7
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RAW WASTEWATER
PRIMARY SETTLED WASTEWATER
T
SLUDGE PRODUCTION
QUANTITIES
20C
10
12 14
16 18
20
SRT,days
SUSPENDED GROWTH
TYPICAL SLUDGE PRODUCTION
18
FIGURE 9
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RAW WASTE
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PRIMARY SETTLED WASTE
NOTE: BASED ON MAXIMUM
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DESIRED SRT, days
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20
22
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REQUIRED AERATION TIME
FOR VARYING SRT VALUES
FIGURE 8
PRIMARY SETTLED WASTE
10°C
RAW WASTEWATER
20'
8 10 12 14 16 18 20 22 24
SRT, days
BIODEGRADABLE FRACTION
OF WASTE SLUDGE
19
FIGURE 10
-------
TABLE 1. EXAMPLE WASTEWATER CHARACTERISTICS
Raw Settled
BOD mg/1 200 133
TSS mg/1 200 100
NH -N mg/1 30 30
Inert nonvolatile solids,
ISS, mg/1 40 20
Inert volatile solids,
IVS, mg/1 60 30
The general relationships presented on the figures clearly depict
the practical design basis of the various suspended growth systems.
Conventional Activated Sludge
The conventional activated sludge system, which operates at an average
detention time of 6 hours has a practical design limitation of an SRT of
4-5 days when treating raw wastewater (Figure 8). The limitation is based
on the presumption of not exceeding 3,000 mg/1 in the MLSS. The average
oxygen demand of 1.1 Ib/lb of BOD (Figure 7) represents an uptake rate
of 37 mg/1/hour at the 6 hour detention. For small flow plants, it is
typical to provide 2 times the average oxygen demand rate to enable meet-
ing peak demand rates. The oxygen transfer capacity would need to be
nearly 74 mg/1/hour. This will exceed the capacity of many conventional
aeration devices. Mechanical aeration will meet this demand; however,
the power requirement will be about 3 HP/1,000 cu ft which will cause
spray and mist problems.
Using conservative design, if a 6 hour detention period, conventional
activated sludge process is to work properly on normal domestic waste,
primary sedimentation will be required. At 6 hours on settled wastewater
input, a 7 day SRT can be attained at average conditions (Figure 8) assum-
ing the same design limitations previously expressed. An oxygen supply
of 1.13 Ib of oxygen/lb BOD (Figure 7) at average loadings is required
which represents an average oxygen uptake rate of 22 mg/1/hour and a peak
oxygen uptake rate of 44 mg/1/hour. This is within the capability of
conventional aeration devices.
If nitrification is required, an average oxygen uptake rate of 39
mg/1/hour is indicated, and a peak oxygen uptake rate of 78 mg/1 would
be required assuming the 7 day SRT is adequate for the nitrifiers.
Therefore, the conventional 6 hour aeration period would necessarily be
extended to be suitable for conventional aeration devices.
Figure 10 presents a relationship showing the fraction of biodegradable
20
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solids in the waste activated sludge (WAS) for various SRT values. The
conventional activated sludge process treating primary settled wastewater
results in a biological sludge having about 30 percent biodegradable
material. From experience at many plants, this sludge when placed on
drying beds or on the land, is odorous and dewaters poorly. Sludge diges-
tion or other means of treatment is necessary to produce a sludge suitable
for dispsoal.
Extended Aeration Activated Sludge
Extended aeration plants have been used for treatment of small flows
to overcome some of the limitations associated with the conventional
activated sludge. The design formulae for extended aeration plants are
the same as for conventional activated sludge.
Extended aeration activated sludge plants are typically based on 24
hours aeration, and rarely are accompanied by primary sedimentation.
From Figure 8, a 24 hour detention period and 3,000 mg/1 of MLSS results
in an SRT of 20-22 days. The carbonaceous oxygen demand (Figure 7) is
nearly 1.25 Ib/lb BOD . Nitrification will occur if sufficient oxygen is
available. In fact, if sufficient oxygen is not available, partial nitri-
fication will occur to the limits of the available oxygen, depleting the
dissolved oxygen to less than 1 mg/1. If sufficient oxygen is not made
available at the high SRT values, there may be problems in operation
associated with filimentous growths. Therefore, even when not required
by effluent criteria, it is important to provide sufficient oxygen trans-
fer capability in extended aeration plants to meet nitrification reuqire-
ments. Therefore, at average conditions, the oxygen requirements are
about 1.85 Ib/lb BOD , assuming the 30 mg/1 NH -N used in the example
waste.
Oxygen requirements for nitrificatuon are about 4. 5 Ibs oxygen/lb NH^-N.
The raw wastewater will contain organic nitrogen and ammonia nitrogen. Only
in the coldest climates does raw domestic wastewater contain nitrite or nitrate
nitroten. The organ nitrogen is mostly in an insoluble for. Conventional acti
activated sludge plants operated at moderate to low SRT's result in the in-
soluble organic nitrogen being enmeshed in the activated sludge floe and to
the greatest part removed from the waste sludge. However, in extended
aeration plants, the high SRT's afford the bacteria time to convert organic
nitrogen to the ammonia form. The design of the oxygen resources for ex-
tended aeration should include the organic nitrogen as well as the ammonia
nitrogen. A typical domestic wastewater will have about 10 mg/1 or organic
nitrogen.
Also, the nitrogen in the activated sludge must be considered in
evaluating nitrification requirements. About 9 percent of bacterial cell
mass is nitrogen. The bacteria will convert the raw wastewater nitrogen
to cell mass and, upon endogenous respiration, will release the nitrogen.
At an SRT approaching zero, about 0.7 Ib of bacterial cells are formed
per pound of BOD stabilized. At an SRT approaching infinity, the residual
cell mass approaches 0.15 Ib/lb BOD stabilized. The associated nitrogen
21
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in cell mass is 0.07 Ib/lb BOD at zero SRT and 0.015 Ib/lb BOD at an
5 5
infinite SRT. For typical extended aeration plants, the nitrogen in
bacterial cell mass will be about 0.02 Ib/lb BOD stabilized. For the
example waste, the percent nitrogen associated with bacterial cell mass,
and that available for nitrification is as follows:
Influent Effluent
Ib per mgd Ib per mgd
BOD, 200 mg/1 1,670 50
NH -N, 30 mg/1 250 300
OrgN, 10 mg/1 83 33 (Cell Mass)
Total N, 40 mg/1 333 333
Therefore, the nitrogen which may be nitrified in this example
exceeds the influent ammonia by 20%. This example is somewhat overstated
because a fraction of the organic nitrogen is not degradable (1 to 3 mg/1).
In the example, the oxygen required for nitrification will be 1,350
Ib/mg (4.5 x 300 Ib). The oxygen required for carbonaceous BOD stabiliza-
tion will be 2,100 Ib/mg (1.25 x 1,670 Ib). The peak oxygen demand for
small plants is about 2 times the average demand. The peak daily demand
is about 1.5 to 1.6 times the average demand based on loading variations.
Measured hourly variations in oxygen demand are less than the variations
in raw waste loadings and a peak hour demand of about 1.25 x times the
average during the peak day is appropriate for small plants.
Therefore, the average oxygen supply, for the example, would be 3,450
Ib/day/mgd, and the peak oxygen supply would be 6,900 Ib/day/mgd. The
corresponding oxygen uptake rates for a 24 hour extended aeration plant
would be 17 mg/1/hour and 34 mg/1/hour.
From Figure 9, the sludge production for the extended aeration plant
approaches 0.68 Ib/lb BOD . of this quantity, 0.5 Ib/lb BOD are associated
with nonbiodegradable raw sewage solids. Therefore, only 0.18 Ib/lb BOD
are associated with bacterial solids. From Figure 10, 8 to 15 percent of
the solids are biodegradable. The low percentage of biodegradable solids
is indicative of a sludge which will dewater readily if placed on drying
beds or the land, and will not be malodorous. If the plant effluent solids
were 25 mg/1 or 210 Ib/mg, the waste sludge quantity would be 930 Ib/mg
(solids production = 1,140 Ib/mg).
Nitrification causes a reduction in alkalinity and potentially may
depress the pH. In the conversion of 1 pound of ammonia nitrogen to 1
pound of nitrate nitrogen, about 7 pounds of alkalinity are destroyed.
Thirty mg/1 of ammonia nitrogen reduced to 1 mg/1 of ammonia nitrogen
will destroy 203 mg/1 of alkalinity. For low alkalinity wastewaters, the
pH will drop to harmful levels and chemical addition will be necessary.
22
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Oxidation Ditch Activated Sludge
Whereas, a typical extended aeration plant is urually a prefabri-
cated tank using diffused aeration, the oxj.dat id Aitc'-, is an extended
aeration process using a long narrow continuous, typically oval or cir-
cular, channel and paddlewheel type irp-zhari1'c aerator.
The long, narrow, continuous aeration basin associated with the oxi-
dation ditch may lead some to believe the piocess is "plug flow", however,
the minimum velocity of 1 fps will result in a cycle time of less than 15
minutes, even in the longest channels used. Compared to the typical 24
hour detention time, the cycle time becomes insignificant. Therefore,
the oxidation ditch may be considered to be an extended aeration, completely
mixed, activated sludge process.
The extended aeration process design example presented above is
applicable for determining the oxygen supply for the oxidation ditch. The
peak oxygen supply was determined to be 6,900 pounds of oxygen per million
gallons.
Assuming the following design conditions were established for peak
conditions:
Minimum Basin Dissolved Oxygen O.'j mg/1
Elevation 500 ft
Alpha oe 0,9
Beta 6 0.yr->
T 20C
The oxygen transfer capability to pure water at standard conditions
(20C, sea level), which is the normal ratinq condition for aeration devices,
would need to be approximately 8,500 pounds of oxygen per million gallons-
Mechanical aeration devices are generally rated in pure water at stand-
ard conditions at about 3 to 3. 5 Ib/hp hr. One hundred hp 01 mechanical aera-
tion is indicated, having a transfer capability of .-..c,si! '/, ZOf to 8, 400 pounds
per day.
The above design approach for oxidation ditches is typical. Oxygen
is provided for both carbonaceous BOD removal and nitrification at peak
demands. A combination of using a conservative design d.nd a basically
simple process for small communities is Vindicated ,.-./ t.;,e excelJent
results obtained by operating oxidation ditch plctJits.
Comparison of Extended Aeration ^Conventional Activated Sludge
The extended aeration process and conventional activated sludge
plants differ in aspects of particular significance _LII sa.al^ plants such
as :
1. Process stability
2. Stability of waste sludge
23
-------
Stability is achieved by providing a sufficiently large aeration
basin to dampen variations in oxygen demand and unusual shifts in solids
inventory between the aeration basin and sedimentation basin.
For small plants receiving less than 2 mgd, variations in organic
and hydraulic loading are more extreme than for larger plants. A com-
parison between a conventionally designed 6 hour detention aeration basin
and a 24 hour detention aeration basin is shown on Figure 11 for an average
and a short term peak load condition. The short term peak load imposed
represents a sudden doubling of BOD and ammonia mass loading.
The 24 hour detention basin (at average flow) experiences a 63
percent increase in oxygen demand from 16 mg/l/hr to 26 mg/l/hr. If
the oxygen concentration in the basin was 4 mg/1, it would eventually
drop to 1 mg/1 at the higher uptake rate and have a 3 mg/1 (4-1) buffer,
or at least 18 minutes at the increased uptake rate from the excess basin
dissolved oxygen to absorb the added load.
The 6 hour detention basin (at average flow) experiences a 70 per-
cent increase in oxygen demand from 56 mg/l/hr to 95 mg/l/hr. If the
oxygen concentration in the basin was 4 mg/1, it would eventually drop
to 0.2 mg/1; and would have 3.8 mg/1 buffer (4-0.2) which only represents
6 minute buffer at the increased uptake rate to absorb the added load.
So, it can be concluded that a greater detention period will result
in a slightly more stable system for variations in organic load.
Many plant upsets are caused by loss of solids from the final clari-
fier either by poor solids inventory management or marginal designs. The
use of longer detention periods provides significant advantages in main-
taining good quality under variations in hydraulic load. An example is
shown on Figure 12.
The comparison shown is between an aeration basin having 24 hours de-
tention and a conventionally designed sedimentation basin versus an aeration
basin having 6 hours detention and a conventionally designed sedimentation
basin.
Most small plants will operate with a set, or fixed, recycle flow
rate. At night, when inflow rates are low, the system solids will tend
to shift to the aeration basin since the solids flux to the sedimentation
basin is low and the recycle rate is constant. When the daily peak flows
occur, the solids will shift to the sedimentation basin. The critical
consideration is preventing the solids to fill the final basin and spill-
ing over into the effluent. The example on Figure 12 depicts the percen-
tage of the sedimentation basin which is used for solids storage.
The 24 hour detention aeration basir. under typical operating condi-
tions will result in only 18 percent of the volume of the final basin
occupied by sludge. A sudden increase in flow (2 times average) will
cause a greater influx of solids to the final basin and a dilution of
24
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EFFECT OF ORGANIC LOAD VARIATIONS
CONVENTIONAL & EXTENDED AERATION ACTIVATED SLUDGE
25
FIGURE 11
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CONVENTIONAL & EXTENDED AERATION ACTIVATED SLUDGE
26
FIGURE 12
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the solids concentration in the aeration basin. After about 1 hour under
this condition the amount of solids in the aeration basin for the example
will decrease from 16,660 pounds to 16,000 pounds.
The loss of solids from the aeration basin, of course, will be added
to the sedimentation basin, increasing the inventory from 740 pounds to
1,400 pounds. The volume occupied by the solids will approach 34 percent
of the sedimentation basin volume. The solids flux rate will increase
from 13 Ib/day/sq ft to 24 Ib/day/sq ft.
In the conventionally designed plant, the same circumstances will
cause the volume occupied by the sludge in the final basin to increase
from 36 percent to 63 percent. The solids flux rate increases from 27
Ib/day/sq ft to 43 Ib/day/sq ft.
Therefore, as the extended aeration plant remains within reasonable
operating parameters for high quality treatment, the conventionally
designed plant approaches marginally acceptable conditions. In effect
the conventionally designed plant would require operational procedures
to adjust for the change in hydraulic load, such as increasing the recycle
rate.
The shift in solids inventory is actually more pronounced than the
example depicts since the peak daily hydraulic load does not occur upon
onset of equilibrium conditions dictated by the average hydraulic load,
but occurs after the night-time minimum hydraulic conditions which cause
the solids inventory to shift to the aeration basin. The greater solids
concentration in the aeration basin at onset of peak hydraulic load causes
higher sedimentation basin solids influx than depicted. The management
of solids inventory for the conventionally designed plant is as important
during the minimum flows as during the maximum flows to compensate for
this effect.
Any biological design is concerned with the amount of sludge produc-
tion and disposal procedures. The extended aeration activated sludge
process has certain inherent advantages. The long SRT's at which these
plants operate (20-30 days) results in a well stabilized, aerobically
digested sludge. In a conventional plant having an SRT of from 4 to 10
days, the sludge, if placed on drying beds or on the land, will be odorous
and objectionable because of the relatively high biodegradable organic
content of the sludge. Aerobic digestion of the sludge for 7 to 15 days
will result in a stable product suitable for disposal on drying beds or
the land. The total sludge age prior to disposal will be from 15 to 20
days. In effect then, the extended aeration process itself provides a
sludge stability comparable to that from conventional activated sludge
and separate aerobic digestion.
Attached Growth Biological Treatment
Processes which may be categorized under the general heading of
attached growth biological treatment include:
27
-------
Trickling Filters - or biofilters wherein stationary media is
arranged over an underdrain system and the wastewater is distributed
over the media. Various media used include rock, plastic, and redwood.
Rock media trickling filters flow schematics have been highly
variable insofar as staging of filters, the presence or absence of inter-
mediate clarification, and the source and quantity of recycle water.
The array of alternative flow schemes which the rock media trick-
ling filter system may be applied, reflects the uncertainty of the cri-
tical parameters which determine the trickling filter performance.
Plastic media trickling filters are most commonly a single stage
process. The media is piled or stacked to a greater depth than rock
media and recirculation is commonly taken directly from the trickling
filter underflow, but in instances is taken from the clarifier underflow.
Plastic media is manufactured in various forms. Plastic media manufac-
turers strive to obtain large surface areas per cubic foot on the premise
that media surface area is a prime performance parameter. Another sub-
stitute for rock media in trickling filters is redwood media. The red-
wood media is manufactured in the form of slats which are fabricated in
the form of pallets which are stacked in the trickling filter.
Rotating Biological Media - where the media is rotated slowly
through a bath of the wastewater. The media is almost universally con-
structed of synthetic materials and is available in the form of discs
or a structural lattice.
Rotating biological media systems were developed in Europe and
recently have been applied in the United States. There are several
domestic manufacturers. The process differs from the concept used for
trickling filters by moving the media through the waste (in a bath) in-
stead of passing the waste through the media. The media rotates slowly
through the bath exposing the attached growth to the wastes, and through
the atmosphere for oxygen supply. Recirculation of liquid around the
rotating media unit process is not practiced.
The media originally introduced into the United States was a series
of closely spaced, parallel, flat discs. This media is still commonly
used in Europe. The major manufacturers in the United States currently
offer a lattice structured media, made of thinner plastic sheets, but
structurally supported by closely spaced intermediate bracing. The
current design offers about 50 percent more available surface area
per unit volume.
Full scale installations to date (1976) use mechanical rotational drives;
however, one manufacturer offers an "air drive" system which has been tested
in pilot and bench scale units. Several projects currently under design are
reportedly intending to incorporate the "air drive". Air is injected below the
media causing a combination of an off-center buoyancy of the media and an
air lifting of the liquid which effects media rotation. The air also provides
added oxygenation. Design and operating data for this type of rotating bio-
28
-------
logical media systems are not established sufficiently to include in this
report.
The media is almost always externally protected by constructing a
superstructure over the rotating biological media system or by covering
each shaft with an individual cover specially constructed and provided
by the manufacturer. Media construction by one manufacturer is offered
with larger specific surface areas (square feet of exposed media per cubic
foot) intended for use in second stage systems or nitrification where
solid pluggage is less likely.
The application of attached growth systems generally requires pretreat-
ment, including screening of debris from the waste stream and primary sedi-
mentation. The attached growth system as applied to organic removal, requires
subsequent sedimentation to remove synthesized bacteria and accumulated
inert sewage solids.
Rational Design Basis for Attached Gro..ch Systems
A sound design for attached growth biological systems requires the
designer to be familiar with the basis of the design procedures employed,
the adequacy of these procedures to predict performance, and the differences
between real data and procedural predictions.
The rational design of attached growth biological systems has been
elusive. Empirical curve fitting has been substituted for a rational
design basis with limited success requiring the design for a specific
effluent condition to be conservative.
Traditionally the concept of attached growth systems has been
visualized as a decreasing concentration of organics passing over a film
of attached bacterial growth. The organics move from the carriage water
to the growth in proportion to the organic concentration. Likewise
oxygen in the air is transferred to the carriage water and then to the
bacterial growth. Theoretically then, the surface area of the media
should have a major effect on performance. The greater surface area
per unit volume will support more bacterial growth, cause a thinner film
of carriage water per unit flow of water, thus increasing oxygen transfer
and slow the rate of carriage water over the bacterial growth.
The predictive techniques used for design of attached growth systems
may be categorized into empirical models and rational models. Empirical
models comprise the vast majority of techniques available for attached
growth system design and are the procedures used by almost all design
engineers. These procedures are based on statistical curve fitting of
plant data to variations in plant operating conditions and physical
facilities. Since the many available models tend to give varying results,
it is likely that they do not express the true removal phenomena.
Recently many investigators ' ' have attempted rational develop-
ment of attached growth design conditions. The Williamson and McCarty
biofilm model is a well presented sample representing the rational
29
-------
approach. This model considers many factors which describe substrate
utilization by biofilms but may be too complex for general usage by design
engineers. Basically, the model predicts soluble substrate removal from
limitations of diffusion of oxygen and substrate through the liquid and the
biofilm to the bacteria and the simultaneous effects of biochemical reac-
tions. The surface area of biofilm becomes a key design parameter.
The limitations on the usage of the model may include the absence of the
effect of suspended biological growths in the bulk liquid, the absorption/ad-
sorption of substrate, and the physical removal of insoluble substrate. The
degree of influence of these potential limitations is not known; however, there
is indication that the influence is significant. GulpO^) fn comparing two simi-
lar trickling filter systems, one recycling plant (secondary clarifier) efflu-
ent and the other recycling trickling filter flowunder directly showed that the
improved treatment resulted from recycling directly. It may be hypothesized
that improved treatment resulted from recycling suspended biological growth.
Slechta '**) reported on pilot studies where comparative parallel tests were
conducted. One system used a trickling filter with direct recycle (trickling
filter underflow) and the second system used final clarifier underflow. The
system using final clarifier underflow showed almost twice the removal capa-
bility as the direct recycle system. The conclusion is that the amount of sus-
pended biological growth in the bulk liquid will significantly affect the perform-
ance of the attached growth system.
The "rational approach" exemplified by the Williamson-McCarty biofilm
model may be limited in its predictive capability for carbonaceous removal;
however, the investigators do make observations from their model which are
useful to a better understanding of the removal phenomena in an attached
growth system.
1. "Any change in environmental conditions that encourages biofilm
growth such as an increase in k (Monod maximum utilization rate) , DC
(diffusion coefficient in biofilm), Xc (bacterial concentration within
biofilm), or So (bulk liquid substrate concentration) will not result in
as large an increase in the substrate removal rate. The k value would
have to be increased by a factor of 2...One implication is the under
adverse environmental conditions, the substrate removal rate is not de-
creased as drastically for biofilms as it is for dispersed growth systems."
2. "On the basis of...(the model and certain rate assumptions) sub-
strate utilization in these two reactors (trickling filters and rotating
biological media) are predicted to be dependent on D.O. concentrations
for all cases in which the soluble BOD exceeds approximately 40 mg/1."
3. "...The D.O. concentration required to avoid oxygen flux limi-
tation would have to be 2.7 times the ammonia-N concentration (for nitri-
fication in attached growth systems)."
These conclusions represent a portion of the removal phenomena
because they relate only to attached growth. If significant suspended
biological growth is carried in the bulk liquid, the limitation imposed
30
-------
by oxygen concentration is lower than in attached growth systems. Also
significant suspended growth in the bulk liquid will reduce the soluble
substrate concentration and reduce the level of effort by the attached
biofilm.
Although the biofilm kinetic models are enlightening, insofar as the
removal phenomena of the attached growth is concerned, the use of these
models may be limited to conditions wherein suspended growth is dispersed
or is not significant. For real systems this confines the evaluation of
attached growth systems to previously developed empirical relationships.
There is a large school of thought that the surface area of media is
the primary criteria for trickling filter sizing. That is, a media having
more surface area per unit volume may permit a smaller volume than a media
having less surface area per unit volume. The complicating multiple
conditions which occur in an attached growth system makes such a simple
premise doubtful. From the previous discussion, it was stated that the
specific surface area will have less effect on the design when greater
concentrations of suspended growths are carried in the bulk liquid. On
the other hand when suspended growth concentrations are minimal in the
bulk liquid, specific surface area may have greater effect on the design.
A later section reviews available data on various media to ascertain
the difference in treatment capability associated with greater unit
specific surface area.
Empirical predictive techniques for the attached growth biological
process have been presented by several investigators. The more generally
used formulae are presented in this section. More complete reviews of
attached growth biological system models are presented elsewhere ' '
Of the more commonly used formulae, the earliest was developed by the
National Research Council (NRC), where:
E = 1 for first stage (1)
1 + 0.0561 W__ h
VF
Where E = fraction of BOD removed
W/V = Ib BOD /day/1,000 ft
F = (1+R)/(1+0.1R)2
R = ratio of recirculation to influent flow
Following several formulae based on estimation of fluid travel time
through attached growth systems, Eckenfelder presented the formulae:
Le_ = 1 (2)
Lo 1 + 2.5D2/-Y(Q/A)15
31
-------
Where: Le = BOD out
Lo = (Li + RLe)/(l + R)
Li = BOD in
D = filter depth, ft
Q = hydraulic flow to filter, mgd
A = filter area, acres
R = recycle ratio
(16)
Caller and Gotaas later proposed a formula incorporating more
variables and fitted by regression analysis to existing trickling filter
plants:
0.13
Le = 0.464 Lo1'19 (1 + R)°'2B (A) (3)
0.67 0.15
(1 + D) T
Where: T = temperature, C
Manufacturers of plastic media trickling filters increased the general
usage of the Velz equation in the following form:
(4)
.LJJ-
Where: q = flow rate gpm/sq ft excluding recycle flows
A similar equation form has been developed during this study for
general usage with all attached growth media systems. This equation was
developed primarily to assess the removal phenomena as a function of
hydraulic loading rate per unit volume.
T p T*C (~\f I (~} \ f
Lo
Rock Media Trickling Filters
Considerable data are available to judge the accuracy of design for-
mulae. Most data reported represent averages and certain of the parame-
ters must be assumed in order to calculate values from the various models.
A summary of data is shown on Table 2. Using physical description and
operating parameters given, the predicted values for the several more fre-
quently used empirical formulae have been calculated.
Equations (4) and (5) are generally not applied to rock media trick-
ling filters. Because these equations are in general usage for media other
32
-------
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Dayton, Ohio
Durham, N.C.
Madison, Wise.
Richardson, Tx.
Plain fie Id, N.J.
Great Neck, N.Y.
Oklahoma City, Ok
Freemont , Ohio
Storm Lake , Iowa
Richland, Wa.
Alisal, Ca.
Chapel Hill, N.C.
Dallas, Texas
B ri dgepo rt , Mi .
Cass City, Mi.
Charlotte, Mi.
Hillsdale, Mi.
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33
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than rock, the applicability has been reviewed for data from rock media bio-
filters as shown in Table 3. The value of k (Equation 4) and K (Equation 5)
is dependent upon the surface wetting rate as shown on Figure 13. Also the
effect of depth does not seem to affect the results more so than volume.
Plastic and Redwood Media Trickling Filters
The several forms of fabricated media available include:
Plastic media - stacked
Plastic media - random dumped
Redwood Media - stacked
The data on Table 4 indicate that both k and K are variable, imply-
ing factors other than flow will influence the predictability of the
degree of treatment. However, the domestic waste treatment as represented
by Chipperfield imply media volume is as representative of a treatment
parameter as is depth. The application of formulae developed for rock
media trickling filters to the plastic media trickling filters will not
produce successful predictions. For instance, as a general rule, the
Galler/Gotaas equation (Equation 3) which is successful with rock media
trickling filters, will predict a much lower effluent BOD from plastic
media trickling filters than is experienced.
Tne data on Table 4 imply that the capability of the plastic media
with an effective surface area of 25-30 square feet/cubic foot is about
the same as the redwood media having an effective surface area of about
14 square feet/cubic foot. A more direct comparison of the capability
of the two media was made in Salem, Oregon and is shown on Figure 14.
These data indicate little difference in capability of the two media,
and in this presentation no differentiation will be made in the design
procedures. Furthermore, when compared to performance of rock media having
a surface wetting rate above 0.35 gpm/sq ft, the plastic or redwood media
trickling filters appear to provide equal treatment per unit volume.
Rotating Biological Media
The design approach for rotating biological media has been a graphical
relationship between the effective surface area of the media and the per-
cent removal efficiency as shown on Figure 15. Basically this relationship
implies beneficial results for higher specific unit surface areas. Media
is manufactured in the form of discs which have a specific unit surface
area of 20-25 sq ft per cubic feet and in the form of lattice structure
which has a specific unit surface area of 30-35 sq ft per cubic foot,
A higher specific unit surface area is available (45-50 sq ft/cu ft) for
use in the latter stages of the system which purportedly reduces the over-
all volume of the media. The usage of the high specific surface area media
in early stages of the rotating biological media system often results in
clogging due to the smaller clearances and is not recommended. As men-
tioned in previous sections of this report, the disc type media is no
longer available from the two major domestic manufacturers; however, a
34
-------
TABLE 3
ROCK MEDIA BIOFILTERS
DATA EVALUATION FOR DEPTH AND VOLUME EFFECTS
Plant Location
Aurora, 111.
Dayton, Ohio
Durham, N.C.
Madison, Wise.
Richardson, Texas
Plainfield, N.J.
Great Neck, N.Y.
Oklahoma City, Okla.
Freemont, Ohio
Storm Lake , Iowa
Rich land, Washington
Alisal, Calif.
Chapel Hill, N.C.
Dallas, Texas
Bridgeport, Mich.
Cass City, Mich.
Charlotte, Mich.
Hillsdale, Mich.
Lapler, Mich.
State Prison, Mich.
Vassar, Mich.
Depth
(ft)
6
7.5
7
10
6.5
6
4
6
3.3
8
4.5
3.2
4.25
7.5
6
6
6
6
5.8
8
5.6
q
(gpm/sqft)
0.034
0.056
0.030
0.038
0.062
0.024
0.062
0.130
0.121
0.111
0.082
0.081
0.087
0.090
0.15
0.07
0.214
0.057
0.160
0.050
0.090
Wetting
Rate
(gpm/sqft)
0.034
0.056
0.030
0.038
0.062
0.038
0.125
0.260
0.30
0.34
0.31
0.33
0.26
0.13
0.329
0.160
0.214
0.057
0.214
0.060
0.231
BOD
in
(mg/1)
70
137
261
138
118
76
117
300
95
381
118
185
77
130
99
152
119
91
65
153
59
Average
BOD
out
(mg/1)
14
33
68
33
20
13
20
66
21
61
20
24
44
37
42
33
63
32
23
17
29
Depth
k
0.05
0.04
0.03
0.03
0.07
0.06
0.11
0.09
0.16
0.08
0.11
0.18
0.04
0.05
0.07
0.09
0.06
0.052
0.09
0.06
0.05
0.07
Volume
K
0.12
0.12
0.09
0.09
0.17
0.11
0.22
0.22
0.29
0.21
0.24
0.32
0.09
0.14
0.16
0.1V
0.21
0.13
0.16
0.17
0.13
0.17
35
-------
TABLE 4
PLASTIC AND REDWOOD MEDIA BIOFILTERS
DATA EVALUATION OF EQUATIONS (4) AND (5)
Location
Indianapolis, IN
14
Stockton, CA
15
Wiskeywaste
15
Domestic
. 15
Domestic
16
Corvallis, OR
16
Corvallis, OR
Idaho Falls,
Idaho
Madera, Calif.
1 8
Akron, Ohio
Buena Vista,
Mich.19
19
Bay City, Mich.
Essexville,
Mich.1
Greenville,
Mich.19
19
Rockwood, Mich.
Media
Plastic
Plastic
Plastic
Plastic
Plastic
Redwood
Redwood
Redwood
Redwood
Plastic
Dumped
Plastic
Plastic
Plastic
Plastic
Plastic
Depth
(ft)
21.5
21.5
34
6
18
14
14
21.5
12
25.5
20
21.5
21.5
21.5
22
q
Wetting
Rate
(gpm/sqft) (gpm/sqft)
2.
0.
NA
0.2-0
0.6-2
0.
1.
0.
0.
0.
0.
0.
0.
0.
0.
0
28
.8
.3
94
12
34
20
36
46
90
75
46
32
2.
0.
NA
0.2-0.
0.6-2.
3.
4.
1.
3.
0.
1.
1.
1.
0.
0.
0
71
8
3
3
3
0
2
75
20
1
50
50
97
BODIn
(mg/1)
112
240
950
a
a
100
192
60
220
120
54
79
23
62
61
BODout
(mg/1)
57
40
65
a
a
24
72
9
25
20
21
18
11
15
23
De
pth
k
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
04
04
04
11
06
10
07
05
08
48
03
005
03
05
03
Volume
K
0.20
0.20
0.20
0.28
0.25
0.37
0.28
0.24
0.28
0.22
0.14
0.31
0.15
0.21
0.12
36
-------
0.3
(K')-
0.2
£
o
0.1 -
KB)
0.1
0.2
0.3
0.4
WETTING RATE, gpm/sq ft
ROCK MEDIA TRICKLING FILTERS
EFFECT OF WETTING RATE
ON EVALUATION CONSTANTS
37
FIGURE 13
-------
100 -,
80
>
o
u
IT
D
O
CD
HI
CO
O
3=
60
40
REDWOOD MEDIA - 21 ft a D
A PLASTIC MEDIA-21 ft « D
NOTE: *DENOTES DATA WITH 1:1 RECYCLE
(2GPM/SQ FT) ALL OTHER DATA HAS NO
RECYCLE (1 GPM/SQ FT)
20
20 40 60 80 100 120 140
160
180
BOD LOADING, (lb/day/1,000 cu ft)
REDWOOD & PLASTIC MEDIA
TRICKLING FILTERS
SOLUBLE BOD REMOVAL EFFICIENCY
38
FIGURE 14
-------
30
BIO-SURF PROCESS DESIGN CRITERIA
DOMESTIC WASTEWATER TREATMENT
Wastewater Temperature = 13 C
4Stage Operation
INFLUENT SOLUBLE BOD, mg/l
150 120 100
80
25
20
en
Q"
O
m
11J
m
D
H
Z
LLJ
3
U.
U.
LU
15
10
70
60
50
40
30
20
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
HYDRAULIC LOADING, gpd/sq ft
ROTATING BIOLOGICAL MEDIA
MANUFACTURER'S DESIGN APPROACH
FIGURE 15
39
-------
review of data from existing installations is helpful to assess the effects
of varying specific surface areas.
One manufacturer's (Autotrol) design approach is based on soluble
BOD in the influent and effluent. Much of the existing data indicates
the effluent BOD from the RBM final clarifier will be 50 percent soluble
and 50 percent suspended material. This is consistent with the limited
data from other attached growth systems. However, the influent soluble
BOD portion is highly variable. For example, the following results have
been reported for primary effluent at various locations.
Plant Percent Soluble
Pewaukee, Wisconsin 66
Seattle, Washington 31-50 (41 average)
Tucson, Arizona 50-75 (67 average)
The use of soluble influent BOD as a critical design parameter, if
applicable, will be unwieldy because of the general lack of data for this
parameter and the variability even at a single plant location.
To provide a more consistent design approach with other attached
growth systems and to enable realistic data evaluation, equation (5) has
been applied to the RBM systems. It is impractical to attempt to evaluate
the manufacturer's design approach unless data are generated for soluble
influent BOD .
The data which are available are evaluated and summarized on Table 5.
These data are from discs and lattice type RBM systems and represent full
scale and pilot plant installations. Individual data have been shown to
indicate the range of calculated K values.
A probability distribution of the calculated K values is shown graphically
on Figure 16. The data plotting indicates that the lattic shuchure media per-
forms better than the disc media. Using a relationship of treatment to sur-
face area as follows:
Le _ -s(As/Q)1/2 (6)
Lo "6
where: As = media surface area; and S = treatability factor as a function of
surface area, the performance data on Table 5 has been evaluated to calculate
S. Figure 17 presents a probability distribution plotting of calculated S values.
Comparing the relationships shown on Figures 16 and 17, the rotating biologi-
cal media systems do perform as a function of the available surface area.
The conclusions which may tentatively be made from the available RBM
data are:
1. The Pewaukee pilot plant data and full scale data, as well as
the Gladstone pilot plant data and full scale data may be correlated
reasonably well by use of equation (6) .
2. For BOD5 removal, a design value for S20 of 0. 055 appears appro-
priate.
Field data from other RBM installations are limited and are presented
below:
40
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Location
Plant
Design Current Volume
Flow
Media
BOD BOD
BOD
K
Flow of Media Description Raw Primary Final T
(mgd) (mgd) (cu ft) (lattice) (mg/1) (mg/1) (mg/1)
Woodland,
Washington 0.45 0.15
Kirksville,
Missouri 5.0 1.30
Georgetown,
Kentucky 3.0 1.10
2,413 12 ft diam 270 175* 28 0.38
63,100 12 ft diam 252 164* 15 0.29
25,240 12 ft diam 230 150* 21 0.34
*Estimated,- BOD is not measured on primary effluent.
These data generally confirm the conclusions reached concerning BOD
removal relationships for the RBM system.
There are many European manufacturers of rotating biological media
systems (primarily discs). The design relationships presented by Schuler/
Stengelin' "' have been evaluated in terms of equations (5) and (6) and an
average K value of 0. 30 and an average S value of 0. 06 were obtained.
Temperature
The temperature effects on effluent quality and system design require-
ments for attached growth systems are usually critical for cold weather
conditions. For a year-around effluent quality criteria, the cold weather
conditions will determine the size of the attached growth reactor because
the lower biological reaction rate. An extensive evaluation of data which
assesses temperature effects was made by Caller/Gotaas. In their formulae,
temperature affects on effluent quality may be stated:
Le
Le
20
= 20
T
0.15
Where: T
Le
"20
= temperature, celcius
= effluent BOD mg/1 at
effluent BOD mg/1 at temperature 20C
Le = effluent BOD mg/1 at temperature T
For example: To obtain an effluent BOD at 30 mg/1 at a temperature
of IOC, the effluent BOD at 20C would need to be 27 mg/1.
Eckenfelder states the effect of temperature as:
(T-20)
E = E x 9
T 20
Where: 9 = 1.035 to 1.040
(21)
In a presentation of actual data, Benzie, et al provided a basis
to evaluate 9.
43
-------
Of the 17 plants reported, 6 plants had a value for 9 exceeding that
predicted by Galler/Gotaas (1.011). Of these 6 plants, 5 plants employed
recirculation, whereas, of the eleven plants having a calculated 9 value
below 1.01, only two plants employeed a 1:1 recirculation.
A comparison of plants employing recirculation from different sources
by Gulp indicates that the location of the source of recirculation
effects the results. The calculated 9 value are as follows:
Warm Weather Cold Weather
T-C E T-C E 9
Direct Filter Recirculation 18.3° 60.5 10.4 56.2 1.009
Recirculation from Final Effluent 18.6 51.4 9.4 38.6 1.032
Where high recirculation rates are employed, a greater cooling effect
on the wastewater occurs. For plants using high recirculation rates, lower
wastewater temperatures at the trickling filter will occur. If the waste -
water temperatures reported reflect incoming raw wastewater the actual 0
value may well be closer to the 1. 01 predicted by Galler Gotaas.
The temperature effect in plastic media biofilters has been calcu-
lated from plastic media manufacturer's literature on a common basis and
a 9 value of 1.018 appears to have been used widely.
RBM data evaluated in this report are shown on Figure 18 and indicate
temperature has no apparent effect above 13C. Below 13C, the relation-
ship shown on Figure 18 would be appropriate.
Nitrification
The conventional design of an attached growth biological system for
nitrification has been based on experience and empirical relationships. The
EPA, Technology Transfer Process Design Manual for Nitrogen Control(22)
reports that in rock media trickling filters, the organic load must be limited
to 10-12 pounds per day per 1, 000 cubic feet to obtain efficient nitrification.
From the same reference data were collected from the literature
relating nitrification efficiency to organic loading (lb/day/1, 000 cu ft). The
relationship shown is reprinted as Figure 19.
The reported data from second stage trickling filters shows mixed
results which defy confident prediction of results from one plant to the
next. Data which have been reported are shown below.
Second Stage Filter Nitrification Efficiency
Location BOD Load Effluent NH -N NH -N Removal
(lb/day/1,000 cu ft) (mg/1) (mg/1) (%)
Johannesburg, SA 3.4 4.4 20.8 83
4.3 9.1 12.9 59
6.3 8.3 15.6 65
Northhampton, E 3.7 11.2 21.8 66
44
-------
O PEWAUKEE FULL SCALE
PEWAUKEE PILOT PLANT
EDGEWATER FULL SCALE
A GLADSTONE PILOT PLANT
GLADSTONE FULL SCALE
0.5 1
0.4
0.3
0.2
SUPERIMPOSED TEMPERATURE
CORRECTION RELATIONSHIP
AFTER ANTONIE (18)
0.1
10
15
20
25
TEMPERATURE,C
ROTATING BIOLOGICAL MEDIA
TEMPERATURE EFFECTS
45
FIGURE 16
-------
100
80
01
o
I
O
z
UJ
O
u.
IL
UJ
z
O
I-
o
DC
I-
60
40
20
NO RECIRCULATION
RECIRCULATION
10
20
30
40
50
60
BOD5 LOAD, lb/1,000 cu ft/day
EFFECT OF ORGANIC LOAD ON
NITRIFICATION EFFICIENCY OF
ROCK MEDIA TRICKLING FILTERS
46
FIGURE 19
-------
Organic nitrogen removals in rock media trickling filters are also
unpredictable. The organic nitrogen in biological waste treatment plant
effluents typically consists of 1-3 mg/1 of soluble refractory organic
nitrogen. Also, about 10 percent of the effluent suspended solids are
organic nitrogen. Raw waste organic nitrogen sources may cause an addi-
tional effluent organic nitrogen in attached growth processes. To attain
an organic nitrogen concentration of less than 3 mg/1, effluent filtration
is probably required.
Plastic media trickling filters have been proposed for nitrification.
Buddies, et al (^3) reported on a second stage plastic media trickling filter
with a loading rate of 0.5 gpm/sq ft treated waste flow. The typical influent
BOD5 was reported to be 20 mg/1. It can be calculated that the BOD5 loading
was 11 lb/1, 000 cubic feet per day for the 0. 5 gpm/ square foot loading.
Ammonia removals of 90 percent were achieved. Temperature effects at
these loadings were not influential as shown on Figure 20. Stenquist, et
reported that a single combined carbonaceous/nitrification trickling filter at
14 lb/1, 000 cubic feet per day, attained average effluent ammonia concen-
trations of 1 mg/1 at a pilot plant in Stockton. Raw waste flow application
rates were 0. 15 to 0.20 gpm/sq ft. Temperatures were always in excess of
20C during the pilot work. Both plants used a 21. 5 feet deep medium. Re-
ports of the full scale Stockton plant indicate that at 14 pounds of BOD5/
1, 000 cubic feet, effluent ammonia concentrations are 4-5 mg/1.
The above studies show effluent organic nitrogen concentrations to
be 0.9-2.7 mg/1 and 7.2-12.7 . Filtered effluents from these
studies showed the soluble effluent organic nitrogen to be 0.8-2.0
mg/1 and 2.1-3.0 mg/1 . The Stockton plant receives canning wastes
containing higher than normal organic nitrogen concentrations; therefore,
it is likely that this organic nitrogen data are not typical.
It appears that to attain 90 percent, plus, nitrification efficiency,
BOD loadings must be maintained below 10 pounds per 1,000 cu ft in a
single stage plastic media trickling filter, or below 10 pounds per 1,000
cu ft and 0.5 gpm/sq ft in a second stage plastic media trickling filter.
At these low loading rates, temperatures above IOC do not appear to
influence the degree of nitrification.
Rotating biological media ^ysterns have also been proposed for nitri-
fication. The Gladstone, Michigan plant data indicate that flow applica-
tion rates of 1.0 to 2.0 gpd/sq ft and BOD loadings of from 24-76 pounds/
1,000 cubic feet resulted in ammonia removals of from 0-96 percent with an
average of 66 percent. Temperatures varied from 8C to 20C. Effluent pH
varied from 6.5-7.4 and is influenced by alum feed of about 60 mg/1 as well
as the nitrification effect.
/ o c^ \
Pilot plant studies were conducted at Belmont, Indiana using the
RBM unit as a nitrification unit preceded by a carbonaceous waste treatment
process. With BOD loadings of 5-14 lb/day/1,000 cubic feet and hydraulic
loadings of 1.8-3.0 gpd/sq ft ammonia removals ranged from 60-94 percent.
47
-------
90
z
O
35
oc
IU
>
O
O
CO
Z
80
70
SUMMER
WASTE TEMPERATURE
WINTER
WASTE TEMPERATURE
0 LA/-
0.5
1.0
RAW INFLUENT HYDRAULIC APPLICATION RATE, gpm/sq ft
PLASTIC MEDIA TRICKLING FILTER
LOADING - TEMPERATURE - PERFORMANCE RELATIONSHIP
OF A NITRIFYING TRICKLING FILTER (22)
48
FIGURE 20
-------
Date
3/23-3/27
3/28-4/30
5/1-5/13
5/17-5/26
T
14. 3C
16.4
19.1
20.0
V
/Q
(cu ft/gpm)
17.5
15.1
23.9
25.2
g-gpd/
sq ft BOD
2.6
3.0
1.9
1.8
in-mg/1
8
17
18
16
NH -N in
mg/1
11
14
12
8
NH -N out
mg/1
1.4
5.7
1.9
0.5
5/27-6/17 21.8 15.6 2.9 18 12 1.9
At Saline, Michigan, pilot plant studies of disc type RBM have been
conducted to determine nitrification capabilities. These data are shown
on Figure 21. Also shown are the Belmont data. From these data, the
hydraulic loading must be below 35 cu ft/gpm or 24, 300 cu ft/million
gallons to obtain 90 percent nitrification. This corresponds to a unit hydrau-
lic loading of about 2. 0 gpd/sq ft of effective surface area for lattice type
RBM media and about 3. 0 gpd/sq ft of effective surface area for disc type
RBM media. The data from the disc media used at Saline, Michigan, and
the lattice media used at Gladstone, Michigan and Belmont, Indiana indicate
that unit surface area has a little effect on the nitrification results. It ap-
pears that hydraulic loads, even with low influent BOD concentrations in-
fluence the nitrification efficiency. Sufficient data to assess the tempera-
ture effects are available only from Gladstone. Figure 22 presents the
relationship developed by Antonie to fit the data available from Gladstone'^ *'.
The Saline data indicate that at lower loadings than those experienced at
Gladstone, temperature has less effect on nitrification efficiency.
Solids Production
Field data for solids production are always subject to errors in
sampling, measurement and system storage complications. Solids production
is an important design consideration for all wastewater treatment schemes.
The wastewater applied to the attached growth biological system will be
composed of biodegradable organics which will be in the solid and soluble
form and non-biodegradable volatile and nonvolatile solids. The portion
of influent settled sewage non-biodegradable solids were presented pre-
viously and for the typical waste represent about 0.38 Ib/lb BOD .
The theoretical range of solids production from organic synthesis
is from 0.15-0.75 pound per pound of BOD . The "normal" value of bio-
logical cell production is about 0.3 pound per pound BOD . Therefore, a
typical total solids production (including solids lost in the effluent)
would be 0.68 pound per pound BOD . If the effluent solids were 30 mg/1,
the waste solids production would be about 0.45 pound per pound BOD for
a typical domestic waste.
Data are shown in the following tabulation for sludge production from
attached growth plants. The variability of the sludge production figures
are typical. However, note that three of the total solids production
values are near the typical solids production value. The waste sludge
production values are calculated based on reported solids production and
the solids leaving the system.
49
-------
z
o
o
E
t-
z
K
Z
UJ
o
Ul
Q.
100
90
80
70 '
60
50 .
40
30
20
10
GLADSTONE
TEMPERATURE RANGE* 52-70*F
20-50 mg/l (except Gladstone)
10 20 30 40 SO 60 70 SO
FLOW, gpm/1,000 cu ft
RBM PROCESS
NITRIFICATION - HYDRAULIC LOAD RELATIONSHIP
50
FIGURE 21
-------
100
90
80
70
Z
o
H
O
u.
£
60
SO
BOD5 LOADING = 35-60 ppd/1,000 cu ft
a 46 ppd/1,000 cu ft ave.
HYDRAULIC LOADING 1.5 gpd/sq ft effective
surface area
> 30 cu ft/gpm
Z
UJ
u
DC
UJ
0.
40
30
20
10
10
15
TEMPERATURE - C
20
RBM PROCESS
NITRIFICATION - TEMPERATURE RELATIONSHIP
51
FIGURE 22
-------
Total Waste
Solids Production Sludge Production
Process
Rock Media
Rock Media
RBM
ABF
ABF
Location
Dallas, Tx.
North Plant
Dallas, Tx.
South Plant
Pewaukee, Wise.
Corvallis, Ore.
Rochester, Minn.
(Ib solids/lb
BOD Applied
0.42
0.65
0.62
0.67*
0.47*
(Ib solids/lb
BOD Applied
0.22
0.33
0.43
0.39
0.39
Effluent
Solids
(mg/D
40
43
30
34
17
*Estimated from volatile solids data.
For nitrification, solids production values are very low. The theore-
tical solids production is 15 percent of the dry weight of ammonia nitrogen
nitrified. For example, a waste having an influent ammonia nitrogen con-
centration of 20 mg/1 will produce 3 mg/1 of solids. This is a small
quantity and is lost in the significance of the carbonaceous solids
production values.
PROCESS PERFORMANCE
The characteristic capability and reliability of various processes
is an important consideration in meeting effluent criteria. Not only is
the average effluent quality important, the extremes must be considered
to assure meeting the criteria imposed on most all plants. This section
will review reported data for the various processes discussed.
Extended Aeration and Conventional Activated Sludge
The activated sludge process has the capability of converting essen-
tially all influent soluble organic matter to solids. It is necessary to
efficiently remove the solids in order to attain high quality effluents
in terms of organics. Unfortunately, plain sedimentation of flocculant
solids is not easily predicted. When dealing with large input solids
quantities, density currents, and thickening considerations, careful
operational consideration of solids balances is necessary to attain good
effluent quality consistently.
The data from activated sludge processes reflect the problems in
attaining consistently good effluent quality. The Deeds and Data section
of the JWPCF reports data from 20 plants during the period from 1960 to
1965. Plant BOD loadings ranging from 18 to 74 pounds BOD /I,000 cubic
feet resulted in average effluent BOD values of 3 to 86 mg/1 with 8 of
the 20 plants reporting average BOD values of less than 20 mg/1.
52
-------
Data are shown on Figure 23. Data has been selected to exemplify
representative experience and potential process capability. The data in
each case represents daily data for an entire year. The plants selected
experience a range of loadings. Also, shown on Figure 23 are typical data
for oxidation ditch plants which will be discussed later. The conclusions
which may be made from these data are:
1. Two plants shown have significant industrial waste flows.
The High Point, North Carolina Eastside plant receives textile dye
wastes and the Grand Island, Nebraska plant received slaughter-house
wastes. Both plants perform as well as the domestic waste plants.
2. The loadings on the plants range from 20 to 80 pounds of BOD
per 1,000 cubic feet of aeration capacity. The performance of the plants
are not related to unit organic loading to the aeration basin.
3. The Grand Island plant data are presented for the best one
year of data (1968) and the worst one year of data (1965) from the same
plant. A long period of operator training by the consulting engineer and
continual data monitoring on this plant is part of the reason for the
excellent improvement in effluent quality.
4. Whereas all of the plants shown are considered to have good
operational control and design, the Grand Island plant, for one year,
produced an effluent BOD significantly better than 10 mg/1, 70 percent
of the time. Four of the plants produced an effluent better than 35 mg/1,
90 percent of the time. This level of treatment is a fair representation
of current activated sludge process capability and reliability under
typical conditions.
Many extended aeration plants do not practice good sludge inventory
and wasting management and periodic discharges of high solids concentra-
tions are experienced. Extended aeration plants typically will "burp"
the solids upon high, flows to the plant. The results of a plant study
by Morris, et al are shown on Table 6 which emphasize poor solids
management.
The potential for the activated sludge process is better exemplified
by the Grand Island plant producing a quality better than 5 mg/1, 50
percent of the time and 20 mg/1, 90 percent of the time.
Biological nitrification of ammonia to nitrate is a well established
phenomenon and several bench scale processes and demonstration processes
have shown virtually complete conversion is possible if sufficient oxygen
transfer is available. Several activated sludge plants having excess
oxygen transfer capability do nitrify; however, until the past few years,
few plants routinely monitored effluent ammonia.
A source of good data suitable for probability analysis on activated
sludge nitrification is available from the Dallas demonstration pilot
plant. The plant was a constant flow (150 gpm) plant receiving trickling
filter effluent having an average BOD of 60 mg/1. The aeration basin was
loaded at 20 pounds/1,000 cubic feet and had an average hydraulic detention
53
-------
AUSTIN. TEXAS
PLANT D
_ PLUG FLOW
20-25 lb/1,000cu. ft.
GRAND ISLAND, NEBRASKA
CMAS PLANT 80 lb/1.000 cu. ft. -t
AUSTIN, TEXAS
PLANTS A, B, C
DALLAS. TEXAS
CMAS 40 lb/1,000 cu. ft.
WORST OXIDATION
OXIDATION DITCH
PLANTS - AVERAGE
HIGH POINT, NC
EASTSIDE '
GRAND ISLAND, NEBRASKA
CMAS 80 lb/1,000 cu. ft.
CONTACT STABILIZATION
40-50 lb/1,000 cu. ft:
BEST OXIDATION
DITCH PLANT*
HIGH POINT, NC
WESTSIDE
20 30 40 50 60 70 80 90
PERCENT OF TIME VALUE WAS LESS THAN
* OXIDATION DITCH PLANT DATA BASED ON 17 PLANTS.
95 98 99
ACTIVATED SLUDGE
EFFLUENT QUALITY
FIGURE 23
54
-------
TABLE 6
EXTENDED AERATION PERFORMANCE
(Reference: Morris, et. al)
Date
Aug. '61
8
9
10
11
12
13
14
Dec. '61
12
13
14
15
16
17
18
Mar. ' 62
6
7
8
9
10
11
12
May '62
14
15
16
17
18
19
20
Flow,
gpd
20,400
18,400
18,000
18,900
22,800
26,600
21,200
27,800
23,900
24,000
22,300
47,300
36,200
42,800
32,000
39,900
59,100
71,500
46,800
58,100
45,300
28,000
23,900
21,300
22,000
22,400
23,600
22,300
MLSS,
mg/1
6,580
5,480
6,000
5,910
6,090
6,440
6,380
6,580
7,240
6,260
6,220
6,600
6,480
4,640
4,440
5,360
5,340
5,180
5,180
5,380
8,000
7,860
8,320
7,980
7,900
8,220
7,960
Effluent
BOD,
mg/1
10
9
9
10
6
8
11
14
10
8
8
>71
24
34
21
100
34
210
34
43
50
26
27
28
34
27
18
19
Effluent
Suspended
Solids,
mg/1
17
30
20
12
12
14
14
15
69
20
1500
20
190
29
180
45
490
32
110
58
15
12
16
25
21
14
12
Effluent
NH3~N,
mg/1
0.48
0.46
0.42
0.48
0.62
0.44
0.44
0.54
0.42
0.54
0.48
3.00
1.06
0.54
1.06
2.72
1.30
1.74
2.04
1.16
2.48
7.06
6.70
5.96
6.00
3.20
2.50
2.70
55
-------
time of 4 hours. Sludge retention time (SFT) varied from 7 to 20 days.
The activated sludge effluent BOD and ammonia nitrogen are shown on
Figure 24.
The effluent BOD median value was less than 20 mg/1 and 50 percent
of the time a zero ammonia nitrogen value was obtained. Seventy percent
of the time an effluent ammonia value of less than 2 mg/1 was obtained.
Poorer results were obtained when SRI" s in excess of 15 days occurred.
Clarifier solids buildup associated with attempting to thicken sludge
in the clarifier resulted in denitrification and poorer quality. The
pilot plant was monitored continually and the operators were highly
skilled individuals who reacted quickly to ill effects.
The data for this study show that the activated sludge process may
produce an effluent quality of 2 mg/1 NH -N seventy percent of the time.
Oxidation Ditch
The oxidation ditch extended aeration process has enjoyed consistently
good results insofar as reliability and performance are concerned. Table 7
shows results of performance from several plants. Data is presented on
Figure 23 representing a recent survey of operating data from 17 plants.
The results show consistently low average effluent values, with peak
values which are typical of other activated sludge plants, but lower than
the poorly managed extended aeration or conventional activated sludge
plants. The one Texas plant, on Table 7, shows peak effluent BCD and TSS
values indicating the need for good solids management, which if not
practiced, will result in poorer effluent quality.
Trickling Filters
Selected trickling filter plant effluent data are presented in Figure 25
to indicate process reliability. Process capability heis been presented in
detail in earlier sections of this presentation. A guideline summary is
presented in Figure 26 relating approximate effluent quality to organic
loading. The data on Figure 25 indicate that the effluent quality variation
is probably no more than the influent quality variation.
Rotating Biological Media
Rotating biological media, as a secondary treatment alternative, is
relatively new and only a few plants have been in operation for more than
one year.
Very few full scale data are available.
Recently, the data from the Gladstone, Michigan plant have become
available affording a detailed analysis of the RBM process capability at
one plant. Return frequency data for the Gladstone plant are shown on
Figure 27.
56
-------
TABLE 7
OXIDATION DITCH PERFORMANCE
Period
of
Record (mgd)
months
Q
Ave. Effluent
Quality-mg/1
Peak Effluent
Values-mg/1
Glenwood, Minn.
Somerset, Ohio
W. Liberty, Ohio
Lucasville, Ohio
Sugar Creek, Ohio
Brookston, Ind.
Clayton Co., Ga.
Paris, Texas
2
9
12
12
2
1
12
18
0.34
0.10
0.20
0.20
0.8
0.20
0.44
3.90
BOD
7
7
2
3
12
7
5
17
TSS NH3 Qrg N
13 8.2 2.3
15 0.1
2 - -
8 - -
8
6 - -
10
14 - -
BOD5
18
19
3*
7*
14
12
15
60
TSS NH-
34
35
6*
10*
9
20
40
60
19
0.7
*Peak Month
57
-------
O)
E
50
45
40
35
30
UJ
U.
UL
LU
25
20
BOD,
15
10
NH3 -N
2 5 10 20 30 40 50 60 70 80 90 95 98 99
PERCENT OF TIME EQUAL TO OR LESS THAN
ACTIVATED SLUDGE EFFLUENT
QUALITY, DALLAS, TEXAS
NITRIFICATION PILOT PLANT
FIGURE 24
58
-------
80
70
^ 60
o>
O
§
z
Ul
LL
LL.
LU
50
40
30
20
10
AVERAGE LOAD
50#/1,000 CUBIC FEET
AVERAGE LOAD
-20#/1,000 CUBIC FEET
2 5 10 20 30 40 50 60 70 80 90 95 98 99
PERCENT OF TIME VALUE WAS LESS THAN
TRICKLING FILTER
EFFLUENT QUALITY
TWO TEXAS PLANTS
FIGURE 25
59
-------
130
120 '
110 '
100 '
90 '
£
I
in
80
70
IL
U.
UJ
60
50
40
30
20'
10-
0 10 20 30 40 50 60 70 80 90 100
- pounds per 1,000 cu ft/day
EFFLUENT QUALITY
TRICKLING FILTERS
FIGURE 26
60
-------
Ul
UJ
O
_l UJ
u. >
I-
3 u.
u.
UJ
2.0
1.0
50
40
~
D)
t 30
UJ
LL
LL
UJ
20
10
/^
SUSPENDED SOLIDS
BOD,
5 10 20 30 40 50 60 70 80 90 95 98 99
PERCENT OF TIME VALUE WAS LESS THAN
RBM EFFLUENT QUALITY
GLADSTONE,MICHIGAN
FIGURE 27
61
-------
The Gladstone, Michigan plant is a 1 mgd plant and consists of pri-
mary sedimentation, RBM's designed for 1.94 gpd/sq ft of effective surface
area, chemical addition, and final sedimentation. The plant started in
March of 1974 and reached stable operation by June of 1974. The manufac-
turer's literature would predict the following effluent quality based on
the operating data when chemicals were not added.
Predicted Removal Predicted Effl. Quality
BOD in Q BOD NH -N
Month mg/1 gpd/sq ft % %
June, 1974 99 1.5 97.5 99
July, 1974 105 1.7 92 97 8(19) 0.6(<1.0)
Aug., 1974 102 1.5 92.5 99 8(12) 0.2(<1.0)
(*) Actual values
The actual results are shown in parenthesis. For the three months
of operation when chemicals were not added, the effluent BOD averaged 16,
whereas a BOD of 8 mg/1 would be predicted by the manufacturer's
literature.
The conclusions which may be reached based on the Gladstone, Michigan
data are as follows:
At low unit flow rates (1.0-2.0 gpd/sq ft) effluent BOD
values from the RBM, will be comparable to activated sludge
processes.
Ammonia nitrogen concentrations in the Gladstone, Michigan
effluent exceeded 2 mg/1 consistently; however, good nitri-
fication was experienced during the warmer summer months.
A review of effluent data from various biological waste treatment pro-
cesses indicates that capability to achieve year round effluent BOD5 and
NH3-N criteria for well designed and operated plants may generally be
assigned as follows. Specific plants designed for unusual temperature and/
or industrial wastes may be assessed differently.
Effluent BOD or
Suspended Solids Ammonia N*-mg/l
50% of 90% of
Time Time 50% of Time
Conventional Activated Sludge 20 40 1
Extended Aeration 10 30 1
Oxidation Ditch 10 30 1
Trickling Filter 30 40 3
RBM 20 30 3
*If system is designed for nitrification
62
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ESTIMATING PROJECT COSTS AND OPERATING & MAINTENANCE REQUIREMENTS
The key area of alternative comparison is equitable cost comparisons.
In the facility planning stage of a project, the cost estimation is
necessarily based on generally defined facility components. To make
comparisons of costs of several alternatives, it is impractical to make
detailed lists of material and equipment components for each alternative;
therefore, the use of general cost estimating guides for the process
functional units are relied upon.
This section presents procedures which may be used to develop con-
struction costs and operating and maintenance requirements of the
alternative processes previously described. Estimates are presented for
construction costs as a function of appropriate capacity parameters for
the major plant components. The total initial investment, which includes
engineering, fiscal, administrative and land costs are not shown but may
be developed on the basis of these relationships.
To make planning cost estimates for a project, several techniques
are used. For conventional facilities, or often used unit processes,
the results of previously developed detailed cost estimates may be
extrapolated to the project at hand. Extrapolation of costs requires
consideration of different unit size, local variations in labor and
material costs, differences in site requirements, inflation, and added
or reduced ancillary systems. Although each consideration may be quanti-
fied, considerable judgement on the part of the estimator is required
offering potential error in the estimate.
Where extensive cost data are not available, other techniques must
be employed. Alternative procedures include a thorough takeoff of a
specific component and relating the cost of the facility to the component
by a factor. A procedure commonly used in chemical industry is to add
the costs of all major purchased equipment and multiply an appropriate
experience factor times the equipment purchase cost to determine the
overall facility cost; typically used factors range from 2.0 to 3.0,
depending on the equipment intensity. For example, experienced ratios
of equipment purchase cost to installed facility cost for vacuum filters
range from 2.2 to 2.7 based upon detailed estimates of cost of several
projects. Again this method is subject to considerable judgement and
may afford opportunity for significant error.
The most frequently used approach to estimate costs for facilities
which do not have significant historical cost background is to:
a. Define the facilities by dimensions, construction material,
equipment piping and valve requirements. A general plan of the facility
is drawn defining walls, overall dimensions, and structural requirements.
b. Estimate quantities of major cost components: Rules of thumb
are applied to derive quantities, e.g., concrete walls - 8 inch minimum,
or 1 inch per foot of height. Concrete footings - two thirds the quan-
tity of wall concrete.
63
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c. Estimate costs of major cost components including: concrete,
equipment, piping and valves, excavation, housing.
d. Add 10 to 20 percent of sum of cost for miscellaneous minor
cost components, which are not detected in the major cost items.
The use of any method of cost estimating requires careful considera-
tion of inflation. This has been especially true for the last 5 years
since inflation of construction costs have averaged about 9 percent per
year. The rapid change in costs effects both the use of previous cost
estimates to predict project costs and the planning for project cost
which may be 6 months to one year away from time the planning estimate
is prepared.
Many planners and engineers are accustomed to using cost indices
which track costs of specific items and proportion these costs in a pre-
determined mixture. Unfortunately, there is all too much evidence that
these time honored cost indices are not understood by the user, and/or
are inadequate for many specific applications.
The basis for all cost indices used in the construction industry
is to monitor the costs of specific construction material and labor
costs, proportion these costs by a predetermined factor and thereby
derive an index. The most frequently used indices are probably the
Engineering News Record's (ENR) Construction Cost Index and Building
Cost Index.
The ENR indices were started in 1921 and intended for general con-
struction cost monitoring. The large amount of labor included in the
construction cost index was appropriate prior to World War II; however,
on most all contemporary construction, the labor component is far in
excess of current labor usage. In fact, there should be little, if
any, application of the construction cost index to water utility plant
projects. This index does not include mechanical equipment, pipes and
valves, which are normally associated with water utility plant construc-
ton, and the proportional mix of materials and labor are not specific
to water utility construction.
To provide a more specific index the Environmental Protection Agency
developed a Sewage Treatment Cost Index. This index was based on the cost
components of a hypothetical 1 mgd trickling filter plant. The quantities
of labor, materials, construction equipment and contractor's overhead and
profit remain constant and the unit prices and price changes as derived
from the U.S. Bureau of Labor Statistics and Engineering News Record are
applied to the constant quantities to derive the index. Because this
index was specific to a single process and because more activated sludge
plants are being constructed currently, the EPA has developed a new index
based on the components of a hypothetical 5 mgd activated sludge plant
and 50 mgd activated sludge plant followed by chemical clarification and
filtration.
Obviously, the more specific an index is, the more accurately it
64
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will track cost change. The variation in inflation of various cost com-
ponents cannot be monitored by a single component index. If an index
is based on an improper mixture of several single component indices, it
also will fail. It is necessary for the planner to recognize the short-
comings of cost inflation and use judgement and the best data at hand in
deriving budget comparative estimates.
The cost estimating techniques used for the various unit processes
involved in this study are varied. Where detailed material and equipment
quantities are available, this information has been used with January 1977
unit costs. Where little or no detailed material and equipment quantities are
available, costs are developed by identifying costs of major components and
adding experience factors for miscellaneous unaccounted for features. The
basis of estimating each functional unit is described in the following para-
graphs. The cost relationships are shown graphically in Appendix A. The
costs presented include electrical work associated with the unit function and
a 15 percent contingency. The costs presented are applicable for January
1977 and have been found to be appropriate in the Colorado, Kansas, and
Missouri areas.
Raw Wastewater Pumping (Figure A-l)
Raw wastewater pumping stations are often incorporated into other
structures at small community wastewater treatment plants. When in-
appropriate to incorporate the pumping station into other structures at
the plant site, the use of package pumping stations is common. The
construction costs for the raw wastewater pumping station reflect con-
struction costs of both prefabricated and custom designed pumping stations
with a separate concrete wetwell and the use of manually cleaned basket
screens for pump protection.
Preliminary Treatment (Figure A-2)
Preliminary treatment includes screening, grit removal and flow
measurement. The provisions for screening are based on comminutors
for flows less than 0.5 mgd, and mechanically cleaned screens without
shredders for flows in excess of 0.5 mgd. A manually cleaned screen in
a bypass channel is provided. Grit removal is based on an aerated grit
basin with grit pumping to a grit washer. Flow measurement is based
upon a Parshall flume.
The design basis for these facilities is peak flow rate.
Sedimentation Basins (Figure A-3)
Costs for construction of plain sedimentation basins with sludge
collection equipment have been presented in earlier cost studies by
Black & Veatch . These cost estimates were made on the basis of
plants larger than 1 mgd. For plants smaller than 1 mgd, estimates of
quantities have been prepared during this study for selected sedimenta-
tion basin sizes. To provide updating of the previous information, the
cost data from the Black & Veatch study were used as well as quantity
takeoff information from several selected sedimentation basin sizes.
The cost data are presented as a function of the surface area
65
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provided, as was done in the earlier study. Costs are bsised on the use
of two basins. The basin depth will affect the cost of the sedimentation
basin; albeit, minor variations will not exceed the accuracy of the esti-
mate. The cost data presented have been based on a basin having 15 feet
side water depth and a 1.5 feet freeboard. Cost components are presented
on the basis of steel launders and weirs. The costs for basin surface
areas in excess of 1,500 sq ft are applicable to sedimentation basins
using circular sludge collection equipment in circular basins. Cost
data for basins less than 1,500 sq ft in surface area are applicable to
straight line sludge collection equipment in rectangular basins.
Waste Sludge Pumping Stations (Figure A-4)
Waste sludge pumping equipment is selected based on the sludge con-
centration to be pumped and the operation intended. Sludge pumping units
which operate continuously may be centrifugal pumps, so long as one avoids
high solids concentrations and large suction head losses. Normally better
control is established using intermittent sludge pumping and use of posi-
tive displacement pumps.
Positive displacement pumping units are more expensive than equal
capacity centrifugal pumping units.
The cost data presented in the earlier study by Black & Veatch were
based on positive displacement pumping units. This study updates those
costs. A practical limitation is imposed as to the minimum size of pump-
ing unit and sludge piping which can be used. This limitation is reflected
in the cost estimate by 10 gpm.
The station is based on an underground structure which houses pumping
units and piping, constructed adjacent to and having common walls with the
solids separation unit process. A superstructure is included to access the
station from the ground level and to house electrical control equipment.
Prefabricated Extended Aeration Plants (Including Aeration) (Figure A-5)
Prefabricated extended aeration plants are typically used for ex-
tremely small flows. Estimates for capacities from 10,000 to 90,000 gpd
were made. Costs are presented for shop fabricated units. At some point
the economics shift in favor of field fabricated units and the designer
should investigate this for each application. Air requirements are based
on 2,100 cubic feet per pound of BOD removed (2 Ibs BOD/1,000 gallons).
Aeration using positive displacement blowers with 100 percent standby are
provided. Prefabricated extended aeration plants include a sedimentation
zone, return sludge pumping, waste sludge storage, and chlorine contact
basin, but not chlorine feed equipment. The prefabricated plant is esti-
mated on the basis of an above ground unit installed on a concrete pad.
Freight costs are included at $15 per cwt. A contingency allowance of
15 percent was added to the manufacturer's estimate of the equipment
and erection costs. In addition, percentages of equipment costs were
used for electrical (15 percent) and contractor's overhead and profit
(25 percent).
66
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Prefabricated "Contact Stabilization" Plants (Including Aeration)
(Figure A-5)
Construction v.osts have been developed for prefabricated contact
stabilization plants although the specific design approach has not been
presented. The prefabricated plant for contact stabilization is more
closely akin to conventional activated sludge and is normally used with-
out primary sedimentation. Single stage systems are not normally
adaptable to situations requiring nitrification for the same reasons
explained for typical conventional activated sludge systems.
The prefabricated contact stabilization plant normally has a 3
hour contact zone and a reaeration zone. Although the flow path is iden-
tical to the true contact stabilization process, the contact zone is about
6 times larger. True contact stabilization relies on adsorption/absorp-
tion of organics in the contact zone with little or no real stabilization.
A reaeration zone is provided to condition the return activated sludge to
provide a suitable SRT. The prefabricated plant provides relatively short
term stabilization in the contact zone and further stabilization in the
stabilization zone.
Prefabricated contact stabilization plants are normally provided
with return sludge and waste sludge pumping, aerobic digestion of waste
activated sludge and a chlorine contact basin. The estimated prices shown
include blowers and blower housing.
Custom Designed Extended Aeration Basins (Figure A-6)
For plants larger than 100,000 pd, the use of prefabricated con-
struction becomes marginally economical. The use of either concrete
structures, steel basins, or concrete lined, earthen basins becomes
more desireable. The construction costs estimates presented for custom
designed aeration basins are based on construction with structural con-
crete and concrete lined earthen basins. Provisions are included for
walkways, supports, and handrails for the structural concrete basin.
The estimated costs reflect a square or circular geometry associated with
a completely mixed aeration basin in contrast to the long narrow basins
sometimes associated with plug flow.
Oxidation Ditch Aeration Basins (Figure A-7)
Oxidation ditch aeration basins have been estimated using vertical
structural walls and sloped concrete side walls. The costs for these
alternative construction systems are very close. The construction cost
estimates are shown for either construction system. Aeration equipment
is not included in the oxidation ditch basin costs.
Mechanical Aeration Equipment (Figure A-8)
Aeration equipment estimated construction costs include purchase
cost as quoted by manufacturers, installation, manufacturer's installa-'
tion check, and contractor's overhead and profit. Costs are based on
67
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fixed platform mounted surface aerators and paddle wheel type aerators.
Diffused Aeration Equipment (Figure A-9)
Diffused aeration equipment is based on the use of centrifugal
blowers, wherein two blowers are provided, one serving as a standby.
The blowers having inlet filter silencers are housed in a superstructure.
Air piping and sparger type diffusers are included.
Recirculation Pumping Stations (Figure A-10)
Recirculation pumping stations include the facilities for return
activated sludge pumping stations and similar uncomplicated pumping sta-
tions. The basis of the cost estimates shown are of the type of station
employing vertical diffusion vane pumping units with attendent valves,
piping and control facilities. The pump is suspended in the wetwell
and motors and motor control centers are housed in a superstructure.
The cost data base for recycle pumping stations is limited because these
facilities are normally constructed as part of other facilities.
The Black & Veatch report, "Estimating Costs and Manpower Require-
ments for Conventional Wastewater Treatment Facilities", presents cost
relationships for recycle pumping stations. The few data for recent
recycle pumping station costs have been reviewed in relationship to the
earlier Black & Veatch cost data. The recent cost data indicate the
influences on costs have approximately doubled the cost of recycle pump-
ing stations. These influences include inflation, OSHA regulations, and
EPA regulations on reliability which have been instituted since the
earlier B & V work.
Trickling Filters (Figure A-ll)
Costs for trickling filters were estimated on the basis of rock at
$12/cubic yard, redwood media at $2.75/cubic foot, and plastic media at
$2.75/cubic foot of media. Rock media trickling filters are based upon
a filter depth of 6 to 8 feet and plastic and redwood media filters are
based on a depth of 21 feet. Rotating distribution equipment costs were
obtained from manufacturers. The cost curves include the facilities
within the confines of the biocell foundation and do not include piping
to and from other functional units.
Rotating Biological Disks (Figure A-12)
Cost development procedures and unit costs for rotating biological
disks have been derived from Autotrol and from limited quantity take-off
information provided from recent construction projects.
The manufacturer's estimating cost for 100,000 sq ft (effective
area) have been used plus the estimated time associated with installation
and tankage as provided by the manufacturer.
Sludge Treatment (Figures A-13 and A-14)
Estimated costs for sludge treatment facilities are presented for
68
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anaerobic digestion and sludge drying beds. Aerobic digestion costs,
where applicable, may be derived from the construction cost estimates
for aeration basins and aeration equipment. The aerobic digester costs
derived would represent continuous flow designs, or designs which incor-
porate decanting provisions but may not represent batch operated systems.
Construction costs for anaerobic digestion have been derived, in
part, from the costs presented by Black & Veatch . The costs have
been updated by using limited number of costs experienced for recently
bid construction projects and inflating the cost relationship based on
these more recent costs. Anaerobic digesters represent two stage diges-
tion volume and include provisions for heating to 95F and mixing of the
primary digester and include an unheated, unmixed secondary digester of
equal size as the primary digester.
Sludge drying beds are based on jobs constructed during the past
year (1976) and estimates of intermediate sized installations. The
estimated costs include influent distribution piping and valves and
perforated underdrains.
Disinfection (Figures A-15 & A-16)
Feed Equipment & Storage. The most prevalent form of disinfection
is chlorine gas. The equipment and storage facilities requirements are
well known and commercial equipment is readily available. Construction
costs for chlorine feed equipment have been presented previously " .
The previous work cites the difficulty in isolating costs for the chlorine
feed and storage facilities. Most often, the chlorine feed and storage
facilities are combined with other sturctures, making analysis difficult.
Ton cylinders are shown; however, for less than 1,000 pounds per day feed
rate, 150 pound cylinders were used as a basis of storage requirements.
Several quantity take-offs of similar chlorine feed and storage
facilities were reviewed. Of seven installations, the installed chlor-
ination system facility was estimated to cost from 2,5 to 3,5 times the
purchase price of the chlorinators. The average estimated installed cost
of the seven installations was 3.0 times the quoted purchase price of the
chlorinators above.
The total installed cost includes distribution panels,, cylinder
chocks, installation, manufacturer's preparation of shop drawings, in-
stallation check and startup, and contractor's overhead and profit,
Chlorinator costs include one standby chlorinator.
Miscellaneous piping varies significantly depending on the layout,
Piping costs will vary from 5 to 10 percent of the installed chlorina-
tion equipment cost.
Hoist equipment will be essentially constant for electrically
operated, monorail trolley hoists. For large storage areas having long
rails and extensive duct-o-bar electrical systems, the costs will
approach 30,000 dollars for a 30 cylinder storage system or 1,000 dollars
69
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per cylinder. Manually operated hoists systems are less expensive (about
half) but require more labor for loading and unloading. For the purposes
of this analysis, hoisting equipment is estimated at 0.50 dollars per
pound of cylinder storage capacity.
Chlorine Contact Tanks. Contemporary chlorine contact tanks are
constructed to provide a serpentine flow path to enable maximum use of
the chlorine fed. The construction costs of these structures are much
more than single or double pass basins constructed in the past. The
costs for the multi-pass contact tanks are presented in this report to
reflect current practice. The cost estimates presented are based on 2
basins, and structural concrete construction.
OPERATION & MAINTENANCE REQUIREMENTS
Operation and maintenance requirements include:
Administration
Labor
Power Costs
Chemical Costs
Miscellaneous Supply Costs
For small plants the segregation of these total operation and
maintenance costs into the above categories is difficult. Small com-
munities often do not have detailed budgets and in many cases do not
maintain records of the total cost of wastewater treatment. Many large
utilities have extended their recordkeepirig to the costs associated for
the above categories by each unit process. Therefore, there are available
data to reasonably predict operation and maintenance requirements for
larger plants, but any attempt to accurately predict operation and main-
tenance requirements for small plants is subject to potentially large
errors.
The information presented in this section is based on distributing
experienced requirements for small community plants on the basis of pub-
lished information for operation and maintenance requirements from in-
dividual process units for larger plants.
The labor requirements are presented on the basis of manhours re-
quired. Miscellaneous supply costs are presented on the basis of annual
cost.
Labor requirements represent both operation and maintenance labor.
Most of the plants are not operated full time, and the plants are un-
attended at night and on weekends. In these instances, it is necessary
to provide alarm monitoring to a continuously manned site, such as the
police dispatcher.
Power and chemical requirements are not shown since these may be
70
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readily calculated from the system.connected and operating equipment and
on typical chemical dosage rates. Appropriate unit costs may be applied
to values determined.
Miscellaneous supply costs are variable and difficult to assign to indi-
vidual unit functions. These costs have been assigned in proportion to the
distribution found as larger utilities were more detailed records are main-
tained. Miscellaneous supply costs are based on January 1977 costs and
may be inflated in proportion to changes in the BLS, all commodities
-wholesale price index.
Requirements for site work and laboratory work are a function of
plant site size and number of analysis made, respectively, and are pre-
sented as such in the following operating and maintenance requirement
relationships.
The numbers of samples and laboratory analyses presumed to be per-
formed are outlined below. The unit time required for each analysis and
sample are obtained from information derived from the laboratory director
of Metropolitan Denver Sewer District No. 1 and from information presen-
ted in EPA's Handbook for Analytical Quality Control in Water and Waste-
water Laboratories"
PARAMETER UNIT TIME* (Hours)
BOD 0.24
TSS 0.36
COD 0.36
TKN 0.36
NO-NO 0.18
NH 0.18
PO 0.18
Dissolved Oxygen 0.12
pH 0.07
Conductivity 0.07
Turbidity 0.10
Alkalinity 0.18
Color 0.12
Automatic Sample Obtained 0.24
Manual Sample Obtained 0.60
Coliform 0.40
Cl Residual 0.20
*Based on 10 percent nonproductive time plus 5 percent standardization
and reagent preparation time plus 5 percent reporting time.
The laboratory and sampling requirements for various numbers of
samples and assuming one sample per sampling point per day of operation
are summarized below based on automatic samplers and the following
analysis per sample:
BOD, TSS, NH , pH, Coliform, Cl Residual
71
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LABORATORY MANHOURS REQUIRED PER YEAR
Number of Sampling
Points
2
4
6
8
10
No. of Days Analyses are Performed Per Year
40 60 80 100 200
130
260
387
520
650
194
387
580
774
970
260
520
774
1040
1300
324
648
970
1300
1630
648
1296
1940
2600
3240
The cost for laboratory supplies presented in the Black & Veatch
study were about 0.70 to 3.00 dollars per manhour required in the
laboratory per year. The larger plants required greater supply costs
than the smaller plants. The supply costs for small community plants
will likely be in the range of 1.00 dollar per manhour.
Yard Maintenance. If the land upon which the facilities are
located are landscaped and grassed, the labor and supplies associated
with maintenance and care of the yard may be a significant budget item.
The requirements for the care of the yardwork is dependent upon climate,
types of plantings and area of site. Therefore, the requirements for
yard maintenance are basically independent of the flw.capacity of the
plant. Guidelines are presented in the Dodge Guide which relate
yard maintenance to area and these are repeated here to arrive at a
basis for estimating yard maintenance.
Mowing
Fertilization
Crabgrass Control
Average
Frequency/
Year
30
2
1/3
Labor
(Hours /Year
1,000 sq ft)
0.5
0.1
0.05
0.65
Materials
(Dollars/Year
1,000 sq ft)
0.50
3.0
1.50
Equip-
ment*
(Dollars)
160
5
165
Area of Plantsite
50,000 sq ft
100,000 sq. ft
150,000 sq ft
250,000 sq ft
500,000 sq ft
1,000,000 sq ft
Maintenance/
Labor (Hours)
32.
65.
97.
162.
325.
650.0
Material & Equipment
Costs (Dollars)
415
665
915
1415
2665
5165
*Amortized over 5 years at 8 percent and independent of area.
Comparison of Alternative Processes
The primary purpose of this evaluation is to show examples of the
use of the cost data and to generally determine the relative economics
of alternative processes most likely to be used for small community
wastewater treatment. For secondary levels of treatment, the costs of
72
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the following competitive processes were evaluated.
Capacity, mgd Process
0.01, 0.1 Prefabricated extended aeration plants
0.1, 0.5, 2.0 Custom built extended aeration plants,
conventional activated sludge, trick-
ling filters, rotating biological media
systems and prefabricated contact
stabilization plants.
The applicability of individual processes for specific design flows
is not fixed nor representated to imply typical applicability. These
examples are merely presented to guide the reader through examples of
the use of information in this presentation.
The design conditions for the processes are as follows:
Raw Wastewater:
Suspended Solids 200 mg/1
Volatile Content 75 percent
BOD 200 mg/1
NH -N 30 mg/1
Temperature 20C
Peaking Factor (dry weather) 1.5
Peaking Factor (wet weather) 4.0
Effluent Quality Case I Case II
BOD 25 25
TSS 25 25
NH -N - 3
The secondary process design bases were developed as shown on
Table 8. The schematic process diagrams and unit processes are shown
on Figures 28 through 35. The examples shown may superficially appear to
represent conservative aeration capacities for the plant sizes shown. The
peaking capacity required for small plants and the author's opinion that
aeration capacity should be provided for peak hour conditions is reflected
in these values.
The Case II (nitrification requirement) requires increasing the bio-
logical treatment capabilities of all processes except the extended aeration
alternatives. Detention and oxygen supply have been included in the extended
aeration alternatives (Case I) to assure adequate dissolved oxygen concen-
trations at normal operating conditions. The modifications which are re-
quired to Tables 9-15 to provide for nitrification are as follows: (Go to page So)
73
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74
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PUMPING
STATION
AERATED
GRIT
CHAMBER
RAW
/SEDIMENTATION
( ZONE
^CHLORINE CONTACT
\ ZONE
TO RECEIVING
WATER
EXTENDED AERATION
PACKAGE PLANT
SLUDGE DRYING
BEDS
DRY SLUDGE
f STOCKPILE
FIGURE 28 - PROCESS SCHEMATIC - EXTENDED AERATION
PROCESS (0.01 to 0.1 mgd)
For cases requiring nitrification or not requiring
nitrification
PUMPING
STATION
AERATED
GRIT
CHAMBER
RAW
TO
RECEIVING'
WATER
' SCREENINGS
f TO LANDFILL
I
I
t
GRIT TO
LANDFILL
PACKAGE CONTACT
STABILIZATION PLANT
DR
S
Y SLUDGE
rOCKPILE
SLUDGE DRYING
BEDS
FIGURE 29 - PROCESS SCHEMATIC - FABRICATED
CONTACT STABILIZATION PLANTS (0.1 to 1.0 mgd)
For cases requiring nitrification or not requiring
nitrification
75
-------
PUMPING
STATION FLOW
. MFASHWh-
RAW S~^ AERATED MENT AERAT|ON
WASTE \^ / CHAMBER " *
. ] .
! i *
1 SCREENINGS I GRIT TO PFTIIDW QI nnrr
f TO LANDFILL « TO LANDFILL RETURN SLUDGE:
/\\ REAERATION \
/ /x ZONE \
\ xA. ZONE T^ZONE / WATER
^ N. AEROBIC DIGESTER\ /
\v ZONE /
PACKAGE CONTACT |
STABILIZATION PLANT \
t
SLUDGE DRYING
BEDS
1
4 DRY SLUDGE STOCKPILE
FIGURE 30 - PROCESS SCHEMATIC - PREFABRICATED CONTACT
STABILIZATION PLANT (0.1 to 1.0 mgd)
For cases requiring nitrification or not requiring
nitrification
p-*!
PUMPING \ If T
STATION pLOW \ 1 1 /
1 .MEASURE- \\ 1 /
RAW /" ^v AfcRATED MENJ ^ '
w V* GRIT *C><1 *
WASTE V / CHAMBER fc -
i ^ VTT\
! I /Li-
7 - CHLORINE
^_L^ CONTACT
/ >. BASIN
^ /SEDIMEN-N j 1 T0
< \ BASIN / WATPP
\ I
\ SCREENINGS 1 GRIT 1
T TO LANDFILL ' TO LANDFILL AERATION BASIN 'WASTE SLUDGE
i
] SLUDGE DRYING
BEDS
i
' DRY SLUDGE
T STOCKPILE
FIGURE 31 - PROCESS SCHEMATIC - CUTSTOM DESIGNED
EXTENDED AERATION PLANTS (0.1 to 2.0 mgd)
For cases requiring nitrification or not requiring
nitrification
76
-------
RETURN SLUDGE
n
SCREENINGS
TO LANDFILL
CHLORINE
CONTACT
SEDIMEN-X I1 T0
TATION W-s*M fi +
BASIN I ' J RECEIVING
/ WATER
WASTE SLUDGE
SLUDGE DRYING
BEDS
DRY SLUDGE STOCKPILE
FIGURE 32 - PROCESS SCHEMATIC - OXIDATION DiTCH
EXTENDED AERATION PLANT (0,1 to 2,0 mgd)
For cases requiring nitrification or not requiring
nitrification
PUMPING
STATION
CHLORINE
CONTACT
RECEIVING
STREAM
| SCREENINGS
J TO LANDFILL
PRIMARY
SEDIMEN-
TATION
ANAEROBIC!
DIGESTER
SLUDGE DRYING
BEDS
DRY SLUDGE STOCKPILE
FIGURE 33 - PROCESS SCHEMATIC - CONVENTIONAL ACTIVATED
SLUDGE (0.1 to 2.0 mgd)
For cases requiring nitrification or not requiring
nitrification
77
-------
PUMPING
STATION
FLOW
MEASURE
MENT
TRICKLING
FILTER
CHLORINE
CONTACT
TO
RECEIVING
WATER
SCREENINGS I GRIT TO
TO LANDFILL 4 LANDFILL
PRIMARY
SEDIMEN-
TATION
i _, I
SLUDGE
, DRYING
1_BEDS
PUMPING
STATION
FIGURE 34 - PROCESS SCHEMATIC - STATIONARY
MEDIA TRICKLING FILTERS (0.1 to 2.0 mgd)
For cases requiring nitrification or not requiring
nitrification
FLOW
MEASURE
MENT
DRY SLUDGE
STOCKPILE
CHLORINE
CONTACT
TO
ROTATING BIO
LOGICAL MEDIA
RECEIVING
WATER
SCREENINGS
1 TO LANDFILL
GRIT
TO LANDFILL
DECANT «
SLUDGE DRYING
BEDS
JDRY SLUDGE STOCKPILE
FIGURE 35 - PROCESS SCHEMATIC - ROTATIONAL BIOLOGICAL
MEDIA SYSTEM (0.1 to 2.0 mgd)
For cases requiring nitrification or not requiring
nitrification
78
-------
TABLE 9
PREFABRICATED EXTENDED AERATION PLANT
Unit Process/Function
Raw Sewage Pumping Station
Chlorine Contact
Chlorination
Drying Beds
Site Area
Lab Analysis
Unit
mgd
capacity
Plant Design Capacity - MGD
0.01 0.05 0.10
0.04
0.20
0.40
cu ft
volume
ppd
capacity
ppd
feed ave.
(sq ft)
acres
sampling points
days per year
120
10
1
400
0.5
2
40
560
25
1
1000
0.7
2
40
1200
50
3
2000
1.0
2
80
79
-------
TABLE 10
PREFABRICATED CONTACT STABILIZATION PLANTS
Plant Design Capacity - MGD
Unit Process/Function
Raw Sewage Pumping Station
Preliminary Treatment
Chlorination
Drying Beds
Site Area
Lab Analysis
Unit
mgd
capacity
mgd
capacity
ppd
capacity
ppd
feed ave.
(sq ft)
acres
sampling points
days per year
0.10
0.40
0.40
50
3
2000
1.0
2
80
0.5
2.0
2.0
250
15
10,000
2.0
2
80
1.0
4.0
4.0
500
30
20,000
3.0
2
120
80
-------
TABLE 11
CONVENTIONAL ACTIVATED SLUDGE
Unit Process/Function Unit
Raw Sewage Pumping Sta. mgd
capacity
Preliminary Treatment mgd
capacity
Primary Sedimentation sq ft
area
Sludge Pumping gpm
capacity
Aeration Basin cu ft
volume
Aeration Basin CFM AIR
Aeration Basin HP
(Alternative) aerators
Secondary Sedimentation sq ft
area
Sludge Pumping gpm
capacity
Recirculation Pumping mgd
capacity
Chlorine Contact cu ft
volume
Chlorination ppd
capacity
ppd
feed ave.
Aerobic Digester cu ft
volume
CFM AIR
(Alternative) HP aerators
Anaerobic Digester
(Primary) cu ft volume
(Secondary) cu ft volume
Drying Beds sq ft
Site Area acres
Lab Analysis sampling points
days per year
Plant
0.10
0.40
0.40
170
10
3000
180
10
170
15
0.05
1200
50
3
800
20
1
400
400
1800
1.0
3
80
Design
0.50
2.0
2.0
850
15
Capacity
1.0
4.0
4.0
1700
25
16,700 33,300
900
30
850
25
0.25
5600
250
15
4000
90
5
2000
2000
9000
2.5
3
80
1800
60
1700
50
0.5
11,000
5DO
25
8000
180
10
4000
4000
18,000
4.0
3
120
- MGD
2.0
8.0
8.0
3400
50
66,700
3600
120
3400
100
1.0
22,000
1000
50
16,000
360
20
8000
8000
36,000
6.0
3
200
81
-------
TABLE 12
CUSTOM BUILT EXTENDED AERATION
Unit Process/Function
Raw Sewage Pumping Sta.
Preliminary Treatment
Aeration Basin
Aeration Basin
Aeration Basin
(Alternative)
Secondary Sedimentation
Sludge Pumping
Recirculation Pumping
Chlorine Contact
Chlorination
Drying Beds
Site Area
Lab Analysis
Unit
mgd
capacity
mgd
capacity
cu ft
volume
CFM AIR
HP
aerators
sq ft
area
gpm
capacity
mgd
capacity
cu ft
volume
ppd
capacity
ppd
feed ave.
sq ft
acres
sampling points
days per year
Plant
0.10
0.40
0.40
13,300
600
20
170
10
0.05
1200
50
3
2000
1.0
2
80
Design
0.50
2.0
2.0
66,700
3000
100
850
30
0.25
5600
250
15
Capacity
1.0
4.0
4.0
133,300
5700
200
1700
60
0.5
11,100
500
25
10,000 20,000
2.5
2
80
4.0
2
120
- MGD
2.0
8.0
8.0
266,700
11,400
400
3400
120
1.0
22,200
1000
50
40,000
6.0
2
200
82
-------
TABLE 13
EXTENDED AERATION OXIDATION DITCH PLANT
Plant Design Capacity - MGD
Unit Process/Function
Raw Sewage Pumping Sta
Preliminary Treatment
Aeration Basin
Aeration Basin
Unit
mgd
capacity
mgd
capacity
cu ft
volume
HP
aerators
Secondary Sedimentation sq ft
area
Sludge Pumping
Recirculation Pumping
Chlorine Contact
Chlorination
Drying Beds
Site Area
Lab Analysis
gpm
capacity
mgd
capacity
cu ft
volume
ppd
capacity
ppd
feed ave.
sq ft
acres
sampling points
days per year
0.10
0.40
0.40
13,300
20
170
10
0.05
1200
50
3
2000
1.0
2
80
0.50
2.0
2.0
66,700
100
850
30
0.25
5600
250
15
10,000
2.5
2
80
1.0
4.0
4.0
133,300
200
1700
60
0.50
11,100
500
25
20,000
4.0
2
120
2.0
8.0
8.0
266,700
400
3400
120
1.0
22,200
1000
50
40,000
6.0
2
200
83
-------
TABLE 14
ROCK MEDIA TRICKLING FILTERS
Unit Process/Function
Raw Sewage Pumping Sta.
Preliminary Treatment
Primary Sedimentation
Sludge Pumping
Secondary Sedimentation
Sludge Pumping
Recirculation Pumping
Trickling Filter
Chlorine Contact
Chlorination
Anaerobic Digester
(Primary)
(Secondary)
Drying Beds
Site Area Rock Media
Plastic Media
Lab Analysis
Plant Design Capacity
Unit
mgd
capacity
mgd
capacity
sq ft
area
gpm
capacity
sq ft
area
gpm
capacity
mgd
capacity
cu ft
volume
cu ft
volume
ppd
capacity
ppd
feed ave.
cu ft
volume
cu ft
volume
sq ft
acres
acres
iling points
s per year
0.10
0.40
0.40
170
10
170
10
0.. 10
7150
1200
50
3
700
700
1400
1.5
1.0
3
80
0.50
2.0
2.0
850
15
850
25
0.50
35,750
5600
250
15
3400
3400
7000
3
2.5
3
80
1.0
4.0
4.0
1700
25
1700
50
1.0
71,500
11,100
500
25
6700
6700
14,000
5
4
3
120
- MGD
2.0
8.0
8.0
3400
50
3400
100
2.0
143,000
22,200
1000
50
13,400
13,400
28,000
7
6
3
200
84
-------
TABLE 15
ROTATING BIOLOGICAL MEDIA
Plant Design Capacity - MGD
Unit Process/Function
Raw Sewage Pumping Sta
Preliminary Treatment
Primary Sedimentation
Sludge Pumping
Unit
mgd
capacity
mgd
capacity
sq ft
area
gpm
capacity
Secondary Sedimentation sq ft
area
Sludge Pumping
RBM System
Chlorine Contact
Chlorination
Anaerobic Digester
(Primary)
(Secondary)
Drying Beds
Site Area
Lab Analysis
gpm
capacity
cu ft
volume
cu ft
volume
Ppd
capacity
ppd
feed ave.
cu ft
volume
cu ft
volume
sq ft
acres
sampling points
days per year
0.10
0.40
0.40
170
10
170
10
3700
1200
50
3
700
700
1400
1.5
3
80
0.50
2.0
2.0
850
15
850
30
18,000
5600
250
15
3400
3400
7000
3
3
80
1.0
4.0
4.0
1700
35
1700
60
32,000
11,000
500
25
6700
6700
14,000
5
3
120
2.0
8.0
8.0
3400
50
3400
120
74,000
22,200
1000
50
13,400
13,400
28,000
7
3
200
85
-------
CHANGES TO CASE I CONDITIONS FOR NITRIFICATION
PLANT DESIGN CAPACITY - MGD
ALTERNATIVE
Prefabricated Extended Aeration
Prefabricated Contact Stabilization
Add: Preceding Aeration Basin
(cu ft)
Surface Aerators (hp)
Recycle Pumping
Station mgd
Conventional Activated Sludge
Increase: Aeration Basin Size
to (cu ft)
Aeration Capacity
to (CFM)
or (HP)
Custom Built Extended Aeration
Oxidation Ditch
Rock Media Trickling Filters,
Increase Media Volume To
Rotating Biological Media
Increase Media Volume To
0.1
0.5
1.0
NO CHANGE
3,000 15,000 30,000
10 40 80
0.05
0.25
5,700 28,500
380
15
1,900
60
3,750
120
2.0
0.5
57,000 114,000
7,500
240
NO CHANGE
NO CHANGE
11,300 56,500 113,000 226,000
7,400 37,000 74,000 148,000
Other factors, besides economics, which affect the selection of
alternative processes include the ease of operation, process reliability,
process and mechanical reliability and the effect of sludge treatment
process alternatives on the overall process. Table 16 presents general
advantages and disadvantages of the alternative secondary treatment processes
which may or may not be reflected in the economic analysis.
Construction costs and operating and maintenance requirements were
developed from the relationships shown in Appendix A. In addition to
the construction costs for the unit processes for which the cost curves
include electrical work and contingencies, costs are provided for the
following:
Site Improvements
Engineering, Legal, Administrative
Interest During Construction
15 percent of subtotal of
unit process costs
25 percent of construction costs
5 percent of subtotal of
projections
86
-------
TABLE 16
PROCESS ADVANTAGES AND DISADVANTAGES OF BIOLOGICAL
TREATMENT ALTERNATIVES FOR SMALL COMMUNITY APPLICATIONS
Prefabricated Extended
Aeration Plants:
Prefabricated Contact
Stabilization Plants:
Custom Designed
Extended Aeration Using
Low Speed Surface
Aerators:
Advantages
1. Stable process when
proper sludge
management is
performed.
2. Standardized design
and components
readily available.
3. Package design per-
mits relocation, if
necessary, for grow-
ing metro areas.
4. High quality
effluent.
5. Predictable process.
Disadvantages
1. Small air lift
pumps clog often,
at specific plants.
2. Requires good
operator skills
and routine monitoring
to assure continuing
high quality effluents.
3. Sufficient oxygen
supply should be
provided for nitri-
fication and pH may
need to be controlled.
1. Two basins of active 1.
sludge provide
opportunity for
fast recovery after 2.
upsets caused by
hydraulic peak
loads or toxic
loads.
2. Standardized design
and components
readily available.
3. Can be re-erected
at other sites,
with difficulty for
growing metro areas.
4. High quality effluent.
5. Predictable process.
1. Stable process when 1.
proper sludge manage-
ment is performed.
2. High quality effluent 2.
3. Many types of al-
ternative aeration
devices may be 3.
considered.
4. Predictable process.
Small air lift pumps
clog often, at
specific plants.
Requires good
operator skills and
routine monitoring.
Icing in cold weather
climates must be
considered.
Major maintenance
requires crane to
remove equipment.
Drive units afford
higher mechanical
maintenance.
Requires good opera-
tor skills and routine
monitoring.
Sufficient oxygon
supply should be
provided for nitrifi-
cation and pH may need
to be controlled.
87
-------
TABLE 16
(continued)
Oxidation Ditches:
Conventional Activated
Sludge:
Trickling Filter:
Advantages
1. Stable process
when proper sludge
management is
performed.
2. High quality
effluent.
3. Predictable process.
1. High quality
effluent.
2. Predictable
process.
3. Many types of
aeration devices
may be considered.
1. Stable process.
2. Operator skills
and monitoring
requirements less
than suspended
growth systems.
3. Energy requirements
less than suspended
growth systems.
Pis advant age s
1. Icing of aerator
supports and nearby
area must be considered.
2. Major maintenance
requires crane to
remove equipment.
3. Drive units require
higher maintenance
frequency.
4. Requires good operator
skills and routine
monitoring.
5. Sufficient oxygen
supply should be pro-
vided for nitrification
and pH may need to be
controlled.
6. Only one type of
aeration device is
applicable.
1. Requires good operator
skills.
2. Requires frequent
monitoring.
3. Daily variation in
flows cause significant
shift in sludge
inventory.
4. Mechanical aeration
may cause spray and
mist problems.
5. More subprocesses
complicate overall plant.
1. Effluent quality is
not as predictable as
suspended growth
processes.
2. Filter flys, snails
are problem at some
locations.
3. High quality effluents
are difficult to
achieve.
4. More space required
than suspended growth
systems.
88
-------
TABLE 16
(continued)
Rotating Biological Media
Advantages
1. Stable process.
2. Good quality
effluent.
3. Simple operation.
4. Low maintenance,
as a general rule.
Pisadvantage s
1. Effluent quality is
not as predictable as
suspended growth
process.
2. Heavy load on first
cell may cause odors.
3. Multiple drives at
larger plants affords
proportionally higher
maintenance requirements.
4. Shaft and drive failures
have been experienced
and require major
maintenance.
5. Oil leaks from drive
units are common.
6. Larger plants require
more space than equal
size suspended growth
systems.
89
-------
Inflation Allowance 8 percent of subtotal of project
costs
Land Not included
Based on the unit process sizes, cost relationships, and operating and
maintenance requirements shown, the construction and operating costs for
Case I and Case II conditions are developed on Figures 36 and 37. The pro-
ject costs have been amortized at 6. 5 percent interest and 25 years to devel-
ope a total annual cost which has been converted to a unit cost on the basis cf
cost/1, 000 gallons treated at the design flow condition. The relationships com-
paring unit costs for the various processes are shown on Figures 38 and 39.
Labor has been charged at $9/hour, power at $0. 03/kwh, and chlorine at
$250/ton.
A summary of capital costs and operating costs are tabulated in
Appendix B.
The cost comparison of the various alternatives as mentioned, are
not the "bottom line". When cost estimates for facility planning purposes
are within 10 percent, the accuracy of the estimate may not permit a clear
cut advantage. It may be necessary to eliminate costs of common functions
and reflect upon the costs of dissimilar functions.
For situations where dissimilar functions for alternative pirocesses
are estimated to cause less than 10 percent difference in costs (during
the facility planning stage), the best answer might be more reasonably
chosen from considerations other than the cost analysis.
The cost value is not absolute. The methods used in arriving at the
costs are general. They are not intended for precision but are intended
to fairly and conservatively arrive at a project cost. The estimated costs
derived in the manner presented should not arbitrarily be reduced unless
detailed layout, quantity and unit price tabulation and more rigorous
analysis indicate reduction in cost is appropriate.
Operating and maintenance requirements for small community plants
developed in the example cost analysis, are; typical but the unit costs
used for the labor ($9/hour) are not typical. For instance, in a recent
survey by the author's firm, principal labor costs (including fringe
benefits) were found to be $3.50-$5.00 per hour at small communities and
$8.00-$11.00 for larger communities. Because small community plants have
a higher proportionate cost associated with labor costs, the unit cost
used will heavily influence the total operation and maintenance costs.
The relationship of equivalent unit costs shown on Figures 38 and 39
emphasizes that for small community wastewater treatment plants, less
complex and fewer unit processes provide a facility that is not only less
difficult to operate, they generally provide a higher reliability in effluent
quality and are more economical.
90
-------
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NITRIFICATION NOT REQUIRED
FIGURE 36
91
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4 56789
0.1
4 56789
1.0
PLANT CAPACITY, mgd
3456 789
10
CASE II - ESTIMATED COST COMPARISON
NITRIFICATION REQUIRED
FIGURE 37
92
-------
*
(B
£
(0
O)
o
O
o
8
o
100
9
8
7
6
5
4
3
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0.1
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1.0
3456 789
10
PLANT CAPACITY, mgd
CASE I - ALTERNATIVE COMPARISON
NITRIFICATION NOT REQUIRED
FIGURE 38
93
-------
re
01
re
O)
§
o
H
Z
100
9
S
7
6
5
10
9
8
7
6
5
7
6
5
4
0.1
PACKAGE
AERATION
CONVENTIONAL ACTIVATED SLUDGE
STATIONARY TRICKLING
FILTER
I I I I I
PACKAGE CONTACT STABILIZATION
ROTATING BIOLOGICAL MEDIA
V CUSTOM BUILT
EXTENDED AERATION OR
OXIDATION DITCH
0.01
4 56789
0.1
4 56789
1.0
3456 789
10
PLANT CAPACITY, mgd
CASE II - ALTERNATIVE COMPARISON
NITRIFICATION REQUIRED
FIGURE 39
94
-------
APPENDIX A
CONSTRUCTION COST RELATIONSHIPS
OPERATING & MAINTENANCE REQUIREMENTS
-------
CONSTRUCTION COST, 1,000 dollars
' ° C
c, o INJ oj 4k 01 o> -JOKD0 ro w 4* UICHHOXOC
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1 2 3456789]0 2 3 4 5 6 7 89](
FIRM PUMPING CAPACITY, mgd
ESTIMATED CONSTRUCTION COST
RAW WASTEWATER PUMPING
FIGURE A-1
-------
a
o
o
1/1
o
U
z
o
H-
u
ID
0£.
O
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1,000
9
8
7
6
5
4
3
2
100
7
6
5
4
3
2
10
0
^
x^
x
x'
2 3 4 5 67 89
1
j^
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X"
X
X"
X
X
,X
x
/
x
Q 2 3 4 5 6 789,,-
PEAK DESIGN FLOW RATE, mgd
ESTIMATED CONSTRUCTION COSTS
PRELIMINARY TREATMENT
(Screening, Grit removal & Flow measurement)
FIGURE A-2
-------
ESTIMATED CONSTRUCTION COST, 1,000 dollars
- o 8
ro oJ * oio^Jaxo0 ro c*i * oicn-^aoio0
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^^
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s
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s
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0.1
3 456789
1.0
SURFACE AREA, 1,000 sq ft
3 4 5 6 789
10
ESTIMATED CONSTRUCTION COST
SEDIMENTATION BASINS
FIGURE A-3
-------
s
ars
o
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111
^
0
0
4
0
2 3 456789
10
2 3 456789
100
FIRM PUMPING CAPACITY, gpm
ESTIMATED CONSTRUCTION COSTS
SLUDGE PUMPING STATIONS
FIGURE A-4
-------
1,000
_o
~o
O
U
2
g
i-
u
13
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o
o
o
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I-
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4
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0.01
3 456789
0.1
3 4 56789
1.0
PLANT CAPACITY, mgd
ESTIMATED CONSTRUCTION COSTS
PREFABRICATED ACTIVATED SLUDGE PLANTS
FIGURE A-5
-------
V)
o
o
-a
o
U
2
g
H-
U
oo
Z
O
U
Q
LU
UJ
9
8
7
6
5
4
3
2
100
9
8
7
6
5
4
3
2
in
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x
EARTH
1EN
3AS
IN
0.1
3 4 5 67 89
1.0
3 456789.
10
VOLUME, mg
ESTIMATED CONSTUCTION COSTS
CUSTOM BUILT AERATION BASINS
FIGURE A-6
-------
to
o
o
o
o
U
g
(-
u
o;
o
U
o
HI
LLI
9
8
7
6
5
4
3
2
100
7
6
5
4
3
2
in
ST
x
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^
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X
x
^ SLOPED
r
SIDE'
/ALL
.S
0.1
3 456789
1.0
VOLUME, mg
3 4 5 6 789
10
ESTIMATED CONSTRUCTION COSTS
OXIDATION DITCH AERATION BASINS
FIGURE A-7
-------
1,000
o
-o
o
o
o
U
2
O
H-
U
QL
H-
Z
O
U
LU
111
9
8
7
6
5
4
3
2
0
7
6
5
4
3
2
0
1
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X
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X
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/
/
/
^
HORIZONTAL SHAFT AERATORS
2 3456789 2 3456789
0 100 1,
000
INSTALLED HORSEPOWER, hp
ESTIMATED CONSTRUCTION COSTS
MECHANICAL AERATION
FIGURE A-a
-------
1,000
o
-o
o
u
z
g
h-
u
a:
O
u
o
UJ
UJ
3 456789
3 4 5 6 7 89
FIRM BLOWER CAPACITY, 1,000 cfm
ESTIMATED CONSTRUCTION COSTS
DIFFUSED AERATION
FIGURE A-9
-------
1,000
o
-a
O
U
U
13
DC.
O
U
o
HI
H
Ul
9
8
7
6
5
4
3
100
9
8
7
6
5
10
0.1
3 4 5 6789
1.0
FIRM CAPACITY, mgd
3 456789
10
ESTIMATED CONSTRUCTION COSTS
RECIRCULATION PUMPING
FIGURE A-10
-------
1,000
9
8
7
6
5
1/1
i-
o
~o
-o
CD
O
C3
O
u
u
O
u
o
Ul
111
100
9
8
7
6
5
10
-REDWOOD OR PLASTIC MEDIA -
/A
ROCK MEDIA
10
3 456789
100
3 456789
1,000
VOLUME, 1,000 cuft
ESTIMATED CONSTRUCTION COSTS
TRICKLING FILTERS
FIGURE A-11
-------
ESTIMATED CONSTRUCTION COSTS, 1,000 dollars _
__, o
£ g §
_ o N c*i * oi cn^axos ro ai & 01 cn-^axoo
/
/
/
/
/
/
/
jt
/
/
/
/
/
/
/
/
/
/
/
/
s
2 3456789 2 34567 8«
) 100 1
,000
MEDIA VOLUME, 1,000 cu ft
ESTIMATED CONSTRUCTION COSTS
ROTATING BIOLOGICAL MEDIA
FIGURE A-12
-------
8
0
ars
oo
I-
t/>
O
U
Z
g
i-
u
ID
oc
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h-
oo
UJ
ro w
0
en (o0
0
1.0
2 3456789
10
2 3 4 5 6 7 89
100
VOLUME, 1,000 cu ft
ESTIMATED CONSTRUCTION COSTS
ANAEROBIC DIGESTION
FIGURE A-13
-------
100
4
o
"o »
-o O
a
9
c.
£
0
U
o 10
|_ Q
u 5
:D o
ry; -7
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r
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X
J
/
/
/
/
X^
/
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3 456789
10
AREA, 1,000 sq ft
3 456789.
100
ESTIMATED CONSTRUCTION COSTS
SLUDGE DRYING BEDS
FIGURE A-14
-------
100
I/)
^.
o
o
o
o
o
U
U
^
Qi
I-
O
U
o
LU
III
9
8
7
6
5
4
10
9
8
7
6
5
4
3
10
3 4 5 67 89
100
DESIGN FEED RATE, Ibs per day
3 4 5 6 7 89
1,000
ESTIMATED CONSTRUCTION COSTS
CHLORINE FEED EQUIPMENT
FIGURE A-15
-------
ESTIMATED CONSTRUCTION COSTS, 1,000 dollars
*,
_| O C
0 ro OJ * 01 o^JOBCO0 ro w & 01 cn^a>toc
/
X
X
X
X
X
X
'
X
X
/
^
/
/
x
/
2 3 456789
10
2 3 4 5 6 7 89
100
VOLUME, 1,000 cuft
ESTIMATED CONSTRUCTION COSTS
CHLORINE CONTACT BASINS
FIGURE A-16
-------
o
Q:
>-
Q_
_J
<
1,000
9
8
7
6
5
100
7
6
5
4
10
0.1
3 456789
1.0
FIRM PUMPING CAPACITY, mgd
3 4 5 6 7 89
10
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
WASTEWATER PUMPING
FIGURE A-17
-------
10,000
9
8
7
6
5
in
b.
0
o
-o
8
1,000
7
6
4
3
100
0.1
X
2 3 456789
1.0
2 3 456789
10
FIRM PUMPING CAPACITY, mgd
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
WASTEWATER PUMPING
FIGURE A-18
-------
>-
<
a.
1,000
9
8
7
6
5
4
3
100
1
8
7
6
5
10
0.1
s
3 456789
1.0
3 4 5 6 789
10
AVERAGE PLANT FLOW RATE, mgd
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
PRELIMINARY TREATMENT
FIGURE A-19
-------
o
-a
O
U
10,000
9
8
7
6
5
1,000
9
8
I
»
4
3
100
0.1
3456789 2
1.0
AVERAGE PLANT FLOW RATE, mgd
3 4 56789
10
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
PRELIMINARY TREATMENT
FIGURE A-20
-------
10,000
9
8
7
6
5
4
3
^ 2
_c
E
_f
_J
O
* 1,000
* 1
^ 7
i e
5 5
4
3
2
100
^^
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^
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x
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X
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0.1
2 3 456789
1.0
2 3456789
10
SURFACE AREA, sq ft
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
SEDIMENTATION
FIGURE A-21
-------
10,000
9
8
7
6
5
4
3
£ 2
to
o
"o
-c
g ^
<-» 8
^ 7
i e
^ 5
4
3
2
100
^
X
X
X
X
X
x
X
,
.X
^x
x
s
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X
X
^
x
/
0.1
3 456789
1.0
SURFACE AREA, 1,000 sq ft
3 456789
10
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
SEDIMENTATION
FIGURE A-22
-------
1,000
9
8
7
6
5
o
on
z
z
<
100
f»
8
7
6
5
4
10
2 3 456789
10
2 3456789
100
FIRM PUMPING CAPACITY, gpm
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
SLUDGE PUMPING
FIGURE A-23
-------
o
-a
O
O
<
13
10,000
9
8
7
6
5
1,000
0
7
6
5
4
100
3 4 5 67 89
3 456789
10
FIRM PUMPING CAPACITY, gpm
100
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
SLUDGE PUMPING
FIGURE A-24
-------
10,000
9
8
7
6
5
4
3
^ 2
-E
E
_j"
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O
£ 1,000
o. |
^ 7
i e
5 5
4
3
2
100
_^
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^
x
^
^
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v
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^
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^
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-^
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^
0.01
3 456789
0.1
PLANT CAPACITY, mgd
3 456789
1.0
Note:
Extended Aeration
Includes labor for sedimentation zone and aeration equipment.
Contact Stabilization
Includes labor for sedimentation basin, aeration equipment, aerobic
digester
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
PREFABRICATED ACTIVATED SLUDGE PLANTS
FIGURE A-25
-------
o
T3
O
U
9
8
7
6
5
4
3
2
1,000
7
6
5
4
3
2
100
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yl
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^^
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3 456789
0.1
PLANT CAPACITY, mgd
3 456789
1.0
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
PREFABRICATED ACTIVATED SLUDGE PLANTS
FIGURE A-26
-------
>v
_n
E
10,000
9
8
7
6
5
1,000
7
6
5
100
10
3 4 5 67 89
100
2 3456789
1,000
INSTALLED HORSEPOWER, hp
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
CUSTOM BUILT AERATION BASINS USING
MECHANICAL AERATION
FIGURE A-27
-------
10,000
9
8
7
6
5
4
3
^ 2
_c
_r
_j
S 1,000
Q- 8
i S
^ 5
4
3
2
100
^^
.
(^
/
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x
X
'
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X
S
/
^
f
/
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/
x
^
0.1
3 456789
1.0
3 4 5 6 789
10
FIRM BLOWER CAPACITY , 1,000 cfm
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
CUSTOM BUILT AERATION BASINS USING
DIFFUSED AERATION
FIGURE A-28
-------
a
~o
ts>
O
z
z
10,000
9
8
7
6
5
4
3
2
1,000
7
6
5
4
3
2
100
0
^?
^^^
*^^
^
^
^
^
^
s*
^
^
^
**"
^
^
^
X
2 3456789 2 34567 89
,1 1.0 1C
VOLUME, mg
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
CUSTOM BUILT AERATION BASINS
FIGURE A-29
-------
E
_J
_l
O
<
Q_
* f W W
9
8
7
6
5
4
3
2
1,000
9
8
7
6
5
4
3
2
inn
X
xx
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X
X
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ING
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x
y
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10
3 456789
100
3 4 5 6 789
1,000
VOLUME, 1,000 cu ft
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
TRICKLING FILTERS
FIGURE A-30
-------
10,000
9
8
7
6
5
4
3
o
-o
O
O
_J
<
ID
2
Z
1,000
7
6
5
4
100
10
ROTATING MEDIA
STATIONARY MEDIA
3 456789
3 456789
100
VOLUME, 1,000 cu ft
1,000
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
TRICKLING FILTERS
FIGURE A-31
-------
10,000
9
8
7
6
5
O
o;
1,000
7
6
5
4
100
X
X
2 3456789 2 3456789
10 100
VOLUME, 1,000 cuft
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
ANAEROBIC DIGESTION
FIGURE A-32
-------
10,000
9
8
7
6
5
D
o
-a
o
o
<
ID
Z
1,000
8
?
6
5
4
100
3 456789
10
VO LUME, 1,000 cu ft
3 4 5 6 7 89
100
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
ANAEROBIC DIGESTION
FIGURE A-33
-------
10,000
9
8
7
6
5
4
o
(X
<
z
1,000
8
7
6
5
4
3
100
100
3 4 5 6789
1,000
3 4 5 6 7 89
10,000
DRIED SOLIDS APPLIED, IBs/day
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
SLUDGE DRYING BEDS
FIGURE A-34
-------
O
-o
U
9
8
7
6
5
4
3
2
1,000
9
8
6
5
4
3
2
100
X
X
/
/
/
/
/
/
y
X'
y'
/
f
'
/
/
,
100
3 456789
2 3456789
1,000 10,OOC
DRIED SOLIDS APPLIED, Ibs/doy
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
SLUDGE DRYING BEDS
FIGURE A-3S
-------
1,000
9
8
7
6
5
4
3
i_
x
-= 2
E £-
_f
_i
o
Q£
< 100^
< 8
I z
5
4
3
2
10
/
^
.s^
^
/
-X
S
s
X
X"
^
^x-
X
x
X
X1
x
X
X
3 456789
3 4 5 6 789
10
CHLORINE USE, IBs/day
100
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
CHLORINATION
FIGURE A-36
-------
10,000
9
8
7
6
5
O
-o
8 1,000
U 9
7
6
5
4
100
3 456789
10
CHLORINE USE,lbs/day
3 456789
100
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQIUREMENTS
CHLORINATION
FIGURE A-37
-------
-C
E
9
8
7
6
5
4
3
2
1,000
9
8
7
6
5
4
3
2
100
x-
[X
X
X
>
^
/
/
/
s
/
/
/
f
s
/
s
/
/
/
/
/
/
/
0.1
2 3 4 5 67 89
1.0
PLANT SIZE, mgd
2 3 4 5 6 789
10
LABOR
OPERATION & MAINTENANCE REQUIREMENTS
ADMINISTRATION
FIGURE A-38
-------
10,000
9
8
7
6
5
o
-a
«/>
8
«j
<
ID
1,000
A
5
4
TOO
0.1
3 456789
1.0
PLANT SIZE, mgd
3 4 56789
10
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
ADMINISTRATION
FIGURE A-39
-------
NUMBER OF SAMPLING
POINTS
Q.
Z
Z
4200
3800
3400
3000
2600
2200
1800
1400 '
1000 -
600
200 '
40
60
80
100
120
140
160
180
200
NUMBER OF DAYS SAMPLES COLLECTED PER YEAR
LABORATORY MAN-HOUR REQUIREMENTS
FIGURE A-40
-------
12,000
NUMBER OF SAMPLING
POINTS
_
O
D
I
O
Z
Z
11,000
10,000 '
9,000 '
8,000
7,000
6,000-
5,000-
4,000'
3,000-
2,000'
1,000'
40
60
80
100
120
140
160
180
200
NUMBER OF DAYS OF SAMPLES COLLECTED PER YEAR
LABORATORY, MISCELLANEOUS SUPPLY COSTS
FIGURE A-41
-------
1,000
9
8
7
6
5
4
3
E
_r
_i
o
(£
100
9
8
7
6
5
in
3 456789
10
PLANT SITE SIZE, acres
3 456789
100
OPERATION & MAINTENANCE LABOR REQUIREMENTS
YARDWORK
FIGURE A-42
-------
_0
"o
O
U
10,000
9
8
7
6
5
1,000
9
8
7
6
5
4
3
TOO
3 456789
10
PLANT SITE SIZE, acres
3 456789
100
MISCELLANEOUS SUPPLY COSTS
OPERATION & MAINTENANCE REQUIREMENTS
YARDWORK
FIGURE A-43
-------
APPENDIX B
COST COMPARISON SUMMARY
PREFABRICATED EXTENDED AERATION - CASES I & II
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual 0 & M $/YEAR
Amortised Capital
(6^% - 25 YRS)
Equivalent Annual Cost
Unit Cost ($/1000 GAL)
Plant
0.01
144,400
7,281
531
47
2,400
10,259
11,838
22,097
6.05
PREFABRICATED CONTACT STABILIZATION - CASE
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual O & M $/YEAR
Amortised Capital
(6^5% - 25 YRS)
Equivalent Annual Cost
Plant
0.10
463,700
20,160
2,850
143
7,720
30,873
38,015
68,887
Capacity
0.05
277,400
10,845
1,005
47
3,880
15,777
22,741
38,518
2.11
I
Capacity
0.50
988,500
36,360
13,410
712
14,720
65,202
81,039
146,511
- mgd
0.10
422,500
17,550
4,170
143
6,170
28,033
34,637
62,670
1.72
- mgd
1.0
1,578,300
53,280
26,580
1,186
18,970
100,016
129,391
229,407
Unit Cost ($/1000 GAL)
1.89
0.80
0.63
B-l
-------
PREFABRICATED CONTACT STABILIZATION - CASE II
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual O & M $/YEAR
Amortised Capital
(6% - 25 YRS)
Equivalent Annual Cost
Unit Cost ($/1000 GAL)
CONVENTIONAL ACTIVATED SLUDGE -
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual O & M $/YEAR
Amortised Capital
(6*5% - 25 YRS)
Equivalent Annual Cost
Unit Cost ($/1000 GAL)
CONVENTIONAL ACTIVATED SLUDGE -
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual 0 & M $/YEAR
Amortised Capital
(6% - 25 YRS)
Equivalent Annual Cost
Plant
0.10
596,450 1
23,310
5,910
143
8,440
37,803
48,900
86,703
2.38
CASE I
Plant
0.10
695,500 1
23,400
3,570
143
6,500
33,613
57,018
90,631
2.48
CASE II
Plant
0.10
753,740 1
23,760
7,530
143
6,550
37,983
61,800
99,783
Capacity
0.50
,343,100
42,300
25,710
712
16,040
84,672
110,110
194,872
1.07
Capacity
0.50
,472,900
37,935
11,610
712
10,690
60,947
120,750
181,697
1.00
Capacity
0.50
,611,200
40,365
19,500
712
10,890
71,467
132,100
203,567
- mgd
1.0
2,107,500
62,550
57,030
1,186
20,770
141,536
172,780
314,316
0.86
- mgd
1.0
2,355,000
55,305
22,920
1,186
15,150
94 , 561
193,066
287,627
0.79
- mgd
1.0
2,537,000
70,305
27,654
1.186
15,350
114,495
208,000
322,495
Unit Cost ($/1000 GAL)
2.73
1.12
0.89
2.0
3,835,100
93,870
45,750
2,373
25,720
167,713
314,407
482,120
0.66
2.0
4,162,700
101,970
77,280
2,373
26,120
207,743
341,300
549,043
0.75
B-2
-------
CUSTOM BUILT EXTENDED AERATION - CASES I & II
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual O & M $/YEAR
Amortised Capital
(6h% - 25 YRS)
Equivalent Annual Cost
Unit Cost ($/1000 GAL)
OXIDATION DITCH - CASES I & II
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual O & M $/YEAR
Amortised Capital
(6^% - 25 YRS)
Equivalent Annual Cost
Unit Cost ($/1000 GAL)
ROCK MEDIA TRICKLING FILTERS -
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual O & M $/YEAR
Amortised Capital
(6^5% - 25 YRS)
Equivalent Annual Cost
Plant
0.10
424,300 1
15,660
4,020
143
5,290
25,113
34,784
59,897
1.64
Plant
0.10
432,400 1
15,660
4,020
143
5,290
25,113
34,784
59,897
1.64
CASE I
Plant
0.10
768,600 1
18,450
930
143
6,120
25,643
63,011
88,654
Capacity
0.50
,008,800
32,445
19,410
712
9,770
62,337
82,702
145,039
0.79
Capacity
0.50
,029,900
32,445
19,410
712
9,770
62,337
82,702
145,039
0.79
Capacity
0.50
,583,600
26,955
3,780
712
10,300
41,747
129,826
171,573
- mgd
1.0
1,696,800
52,110
38,640
1,186
13,480
105,416
139,106
244,522
0.67
- mgd
1.0
1,732,500
52,110
38,640
1,186
13,480
105,416
139,106
244,522
0.67
- mgd
1.0
2,570,900
45,855
7,380
1,186
14,300
68,721
210,766
279,487
Unit Cost ($/1000 GAL)
2.43
0.94
0.77
2.0
2,898,600
92,160
77,130
2,373
20,900
192,563
237,632
430,195
0.59
2.0
2,816,100
92,160
77,130
2,373
20,900
192,563
237,632
430,195
0.59
2.0
4,375,500
79,560
14,550
2,373
22,270
118,753
358,710
477,463
0.65
B-3
-------
ROCK MEDIA TRICKLING FILTER - CASE II
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual 0 & M $/YEAR
Amortised Capital
(6% - 25 YRS)
Equivalent Annual Cost
Unit Cost ($/1000 GAL)
ROTATING BIOLOGICAL MEDIA -
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual O & M $/YEAR
Amortised Capital
(6*2% - 25 YRS)
Equivalent Annual Cost
Unit Cost ($/1000 GAL)
ROTATING BIOLOGICAL MEDIA -
Capital Cost $
Operating Cost - $/Year
Labor @ $9/MH
Power @ 3C/KWH
Chlorine @ $250/TON
Misc. Supply
Annual O & M $/YEAR
Amortised Capital
(6% - 25 YRS)
Equivalent Annual Cost
Plant
0.10
790,440 1
18,540
930
143
6,200
25,813
64,800
90,613
2.48
CASE I
Plant
0.10
596,900 1
17,280
1,950
143
5,870
25,243
48,900
74,143
2.03
CASE II
Plant
0.10
678,900 1
18,000
3,390
143
6,080
27,613
55,700
83,313
Capacity
0.50
,747,400
27,585
3,780
712
10,390
42,467
143,250
185,717
1.02
Capacity
0.50
,501,900
26,505
8,280
712
9,740
45,237
123,100
168,337
0.92
Capacity
0.50
,941,900
29,115
14,880
712
9,840
54,547
159,200
213,747
- mgd
1.0
2,989,500
47,025
7,380
1 , 186
14,300
69,891
245,100
314,991
0.86
- ingd
1.0
2,531,000
46,755
16 , 980
1,186
13,410
78,331
207,500
285,831
0.78
- mgd
1.0
3,265,000
52,245
30,780
1,186
13,580
97,791
267,700
365,491
Unit Cost ($/1000 GAL)
2.28
1.17
1.00
2.0
5,194,500
81,360
14,550
2,373
30,190
128,473
425,850
554,323
0.76
2.0
4,325,000
83,700
33,150
2,373
20,770
139,993
354,600
454,593
0.62
2.0
5,629,000
90,000
60,150
2,373
21,020
173,543
461,500
635,043
0.87
B-4
-------
APPENDIX C
BIBLIOGRAPHY
1. Benjes, H. H., "Aerobic Digestion", Presented at the Culp-Wesner-
Culp Seminar, South Lake Tahoe, 1975.
2. Monod, J. , "Research on Crossing of Bacteria Cultures", Herman
et Cie, Paris, (1942).
3. McKinney, R. E., "Mathematics of Complete Mixing Activated Sludge",
Trans. Amer. Soc. Civil Eng., 128, Paper No. 3516 (1963).
4. Eckenfelder, W. W., Jr., and O'Connor, D. J., "Biological Waste
Treatment", Pergamon Press, Oxford, England, (1961).
5. Goodman, B. L., and Englande, A. J. , "A Unified Model of the Acti-
vated Sludge Process", JWPCF, 46, 2, p. 312, February, 1974.
6. Goodman, B. L., "Monod Type Relationships Applied to Complete
Mixing Activated Sludge", Unpublished, January 25, 1973.
7. Process Design Manual for Upgrading Wastewater Treatment Plants,
U.S. EPA, Environmental Research Information Center, Cincinnati,
Ohio, October, 1974.
8. Baker, J. M. and Graves, Q. B., "Recent Approaches for Trickling
Filter Design", Journal of the Sanitary Engineering Division,
ASCE, 94, SA1, p. 65, February, 1968.
9. Gotaas, H. B., and Galler, W. S., "Design Optimization for Biologi-
cal Filter Models", Journal of the Environmental Engineering Division,
ASCE, 99, EE6, p. 831.
10. Gulp, Gordon, "Direct Recirculation of High Rate Trickling Filter
Effluent", JWPCF, 35, 6, p. 742 (1963).
11. 1971 Pilot Plant at the Willow Lake Sewage Treatment Plant, Salem,
Oregon, CH2M/Hill Engineers (March, 1972).
12. Williamson, K., McCarty, P. L., "A Model of Substrate Utilization
by Bacterial Films", JWPCF, 48. No. 1, p. 9, January, 1976.
13. Harremb'es, Poul, "Biofilm Kinetics", Submitted to Water Pollution
Microbiology for Publication, 1976.
C-l
-------
14. Atkinson, Bernard and Howell, J. A., "Slime Holdup, Influent BOD,
and Mass Transfer in Trickling Filters", Journal of the Environ-
mental Engineering Division, ASCE, 101, EE4, p. 585, August, 1975.
15. Eckenfelder, W. W., "Trickling Filter Design and Performance".
Transactions of the American Society of Civil Engineers, 128,
pp. 371-398 (1963).
16. Caller, W. S., and Gotaas, H. B., "Analysis of Biological Filter
Variables". Journal of the Sanitary Engineering Division, ASCE,
90, No. 6, pp. 59-79 (1964).
17. Germain, James E., "Economical Treatment of Domestic Waste by
Plaster-Medium Trickling Filters", JWPCF, _38_, 2, p. 192, (Feb. 1966).
18. Chipperfield, P. N. J., "Performance of Plastic Media in Industrial
and Domestic Waste Treatment", JWPCF, 39, 11, p. 1860, November, 1967.
19. Unpublished data from University of Michigan at Saline, Michigan
plant.
20. Hartmann, H., "The Biodisk Filter", Oesterreichische Wasserwirtschaft,
11/12, 1965.
21. Benzie, W., "Effects of Climatic and Loading Factors on Trickling
Filter Performance", JWPCF, 35, No. 4, pp. 445-455 (1963).
22. Process Design Manual for Nitrogen Control, U.S. EPA, Environmental
Research Information Center, Cincinnati, Ohio, October, 1975.
23. Duddles, G. A., and Stevens, E. R. , "Application of Plastic Media
Trickling Filters for Biological Nitrification Systems", Environ-
mental Protection Technology Series, U. S. EPA Contract No, 14-12-
900 (June, 1973).
24. Stenquist, R. J., Parker, D. S., and Dosh, T. J., "Carbon Oxidation-
Nitrification in Synthetic Media Trickling Filters", JWPCF, 46, 10,
p. 2327 (October, 1974).
25. Antonie, R. L., "Nitrification and Denitrification With the Bio-
Surf Process", presented at the Annual Meeting of the New England
W.P.C. Association in Kennebunkport, Maine, June 10-12, 1974.
26. Reid, Quebe, Allison, Wilcox, and Associates, "Advanced Wastewater
Treatment Studies for the Consolidated City of Indianapolis,
Indiana, January, 1975.
27. Antonie, R. L., "Rotating Biological Contacts for Secondary Waste-
water Treatment", Presented at Culp-Wesner-Culp Seminar, South
Lake Tahoe, October, 1976.
C-2
-------
28. Morris, G. L., et al., "Extended Aeration Plants and Intermittent
Watercourses" Environmental Health Series Publication, U. S. Dept.
of HEW, July, 1963.
29. Black & Veatch, "Estimating Costs and Manpower Requirements for
Conventional Wastewater Treatment Plants", EPA Project 17090DAN,
October, 1971.
30. "Handbook for Analytical Quality Control in Water and Wastewater
Laboratories", U. S. EPA, Environmental Research Information Center,
Cincinnati, Ohio, 1972.
31. 1975 Dodge Guide, 7th Edition, McGraw Hill, 1975.
C-3
-------
TREATMENT AND DISPOSAL OF SEPTIC TANK SLUDGES
A STATUS REPORT
MAY 1977
by
Robert P. G. Bowker
Sanitary Engineer, Urban Systems Management Section, Systems and Engineering
Evaluation Branch, Wastewater Research Division, Municipal Environmental
Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio
45268
-------
TREATMENT AND DISPOSAL OF SEPTIC TANK SLUDGES
A STATUS REPORT
by
Robert P.G. Bowker
INTRODUCTION
It has been estimated that twenty-nine percent of the United States
population disposes of domestic wastes through on-site disposal units, of which
eighty-five percent are septic tanks and cesspools (1). To ensure proper
operation of these systems, it is necessary to periodically remove and dispose
of the contents of the septic tank. The frequency of such maintenance is high-
ly variable and dependent upon a host of factors, although 2-5 years is often
recommended for minimization of failure rates in the soil absorption system.
Kolega has reported that, in Connecticut, septic tank waste (septage)
generation from unsewered areas amounts to approximately 70 gallons per
capita per year (2). Using this figure, the annual national volume of septage
slated for disposal exceeds four billion gallons, rivaling in magnitude that
of undigested primary and secondary municipal sludges. Due to the offensive
nature of this material and its potential threat to public health, providing
environmentally sound, cost-effective methods of disposal poses a formidable
dilemma.
This paper provides an overview of septage treatment and disposal options,
with particular emphasis on addition to municipal wastewater treatment facili-
ties .
CHARACTERIZATION OF SEPTAGE
Definition
Domestic septic tank wastes (septage) may be defined as the partially
digested combination of liquid and solid material originating as waterborne
wastes from the household and accumulating over a period of several months
to years in a septic tank or cesspool. Normally, household wastes derive
from the toilet, bath or shower, sink, garbage disposal, dishwasher, and
washing machine. Consequently, septage may contain significant amounts of
soluble and solid or^anics, grease, detergents, grit, and oLhtj.
-------
Chemical Characterization
Studies dealing with the chemical characterization of septage are well
documented (3,4,5,6,7). Table 1 summarizes the work by EPA at the Lebanon
and Blue Plains Pilot Plants. Of particular interest is the variability in
characteristics of septage, with some parameters varying in concentration by
greater than two orders of magnitude. It has been suggested that such
differences may be attributed to user behavior, cleaning frequency and
procedure, tank design, sampling procedure, and presence of household garbage
grinding devices (8).
Microbiological Characterization
The microbiology of septage has been examined by Kolega et al.(9) who
found a predominance of gram negative non-lactose fermenters. Both aerobic
and anaerobic organisms were isolated. Of the anaerobic sporeformers
recovered, most were obligate anaerobes of the species Clostridium
lituseburense and Clostridium perfringens. In general, the microbiology of
septage and septic tank effluent was found to be quite similar.
Feige et al.(6) reported significant numbers of both fecal coliforms
and fecal streptococci in septage, in the order of 2 x 10^ counts per 100 ml.
Using this as an indicator of the presence of pathogenic organisms, the
public health concern regarding the disposal of these wastes becomes readily
apparent.
General Characteristics
In addition to the measured parameters listed in Table 1, other}less
quantitative, septage characteristics have been noted by many investigators.
These include: (1) a highly offensive odor; (2) poor dewatering and settling
characteristics; and (3) a tremendous foaming potential. The latter is
often attributed to the presence of detergents in the septage, since LAS is
not readily biodegraded under the anaerobic conditions normally found in a
septic tank.
Due to the variable nature of septage, prediction of dewaterability or
settleability is virtually impossible. Tawa (10), while at the University
of Massachusetts, classified septage into three categories. Type I, which
he found in 25% of his samples, was of a watery nature and readily settled to
20-50% of the original solids volume in 30 minutes. Type II, found in
approximately 50% of his samples, was intermediate in settleability (60-88%
of original solids volume), and Type III, found in 25% of the samples, was a
heavy, putrescible septage of 4-7% solids content which exhibited little
settling tendency. Tawa also investigated the use of ferric chloride, lime,
alum, and cationic, anionic, and non-ionic polymers with varying degress of
success. Feige et al. (6) conducted a series of jar tests utilizing lime and
polyelectrolytes as coagulants. His conclusion was that neither natural
settling, lime addition, nor polyelectrolyte introduction resulted in
consistent separation, and that the approach was "technically infeasible and
impractical for implementation at the average sewage treatment plant".
-------
TABLE 1
CHARACTERISTICS OF DOMESTIC SEPTAGE (6,7,11,41)
- All Values in mg/1 Unless Otherwise Indicated -
Parameter
TS
TVS, % of TS
SS
VSS, % of SS
BOD5
CODT
CODS
TOC
TKN
NH3-N
Total P
pH (units)
Grease
LAS
Fe
Zn
Al
Pb
Cu
Mn
Cr
Ni
Cd
Hg
As
Se
Mean
38,800
65.1
13,014
67.0
5,000
42,850
2,570 (.06 CODT)
9,930
677
157
253
6.9 (median)
9,090
157
205
49.0
48
8.4
6.4
5.02
1.07
0.90
0.71
0.28
0.16
0.076
Std. Dev.
23,700
11.3
6,020
9.3
4,570
36,950
-
6,990
427
120
178
-
6,530
45
184
40.2
61
12.7
8.3
6.25
0.64
0.59
2.17
0.79
0.18
0.074
Range
3,600-106,000
32-81
1,770-22,600
51-85
1,460-18,600
2,200-190,000
-
1,316-18,400
66-1,560
6-385
24-760
6.0-8.8
604-23,468
110-200
3-750
4.5-153
2-200
1.5-31
0.3-38
0.5-32
0.3-2.2
0.2-3.7
<. 05-10. 8
<. 0002-4.0
0.03-0.5
<0.02-0.3
No. Samples
25
22
15
15
13
37
21
9
37
25
37
25
17
3
37
38
9
5
19
38
12
34
24
35
12
13
-------
Tilsworth (26) found a high degree of variation in settleability. Jewell (4),
using the Capillary Suction Time (CST) device as a measure of dewaterability,
found an average CST of 223 seconds from 24 samples of raw septage. Typical
values for sewage sludge that can be dewatered in a reasonable period on sand
beds vary up to a maximum of about 70 seconds.
ALTERNATIVES FOR SEPTAGE HANDLING
Treatment and disposal of septage falls into three broad categories:
(1) direct land application; (2) treatment at a separate septage facility;
and (3) addition to a sewage treatment plant. These three alternatives are
briefly discussed below.
Land_Application of Septage
Application of septage to the land is by far the most widely used means
of septage disposal. Estimates regarding the fraction of septage disposed
of on the land range from 60-90% of the total septage generated.
Disposal of septage on the land may be effected by various forms of
surface spreading, subsurface application, or landfills.
Surface Application of Septage - -
Surface spreading of septage is quite common in remote areas where
human contact is minimal and land is readily available. In many cases,
arrangements may be made between the landowner and septage hauler for
spreading of the waste over unused portions of the land. The benefits to
the landowner derive from the value of septage as a fertilizer and soil
conditioner. However, certain health and environmental hazards exist with
surface spreading because of the potential for direct human contact, odor
and vector problems, and contamination of both ground and surface waters.
In Maine, most septage disposal occurs by direct land application on
open fields. All disposal sites must first be approved by the Maine
Department of Environmental Protection (DEP), Since septage generally
contains low metal concentrations relative to municipal sewage sludge, the
University of Maine Life Sciences and Agricultural Experiment Station has
recommended that land application rates be limited by nitrogen considerations,
Rates vary from 62,500 gal/acre/yr for well drained soils to 37,000 gal/acre/
yr for moderately well drained soils, equivalent to nitrogen loadings of
500 Ib N/acre/yr and 300 Ib N/acre/yr, respectively (39).
Subsurface Application of Septage - -
Soil injection and trench and fill methods are perhaps more desirable
forms of land disposal in that the possibility of human contact is reduced
considerably. In addition, these options are more aesthetically acceptable
with respect to odor generation. However, caution must be exercised to
prevent contamination of surface and ground waters by organics, nutrients,
-------
metals, and pathogens. Unless the septage is well stabilized, the presence
of pathogenic organisms precludes utilization of the cover crop for food
production or for grazing by domestic livestock. Although these land disposal
methods are more environmentally acceptable, they generally involve greater
costs.
Lagoons--
Lagoons enjoy widespread use throughout many areas of the country as a
means of septage disposal. These vary from "seepage pits", lacking any
rational engineering design, to anaerobic lagoons with or without spray
irrigation or subsurface disposal of the effluent or supernatant. Proper
design of these facilities is a paramount consideration in minimizing their
impact on the environment, e.g., groundwater contamination and odor
generation.
While the State of Maine does not consider the use of lagoon disposal
systems to be a viable solution, Connecticut has approved simple anaerobic
cells or lagoons (two or more in series) for handling septage. These
facilities are 3-5 feet deep, with a minimum of 1 foot of bottom sand to
enhance percolation of the liquid fraction. Operational problems, such as
clogging of the sand layer, have been reported (40).
Massachusetts has also recommended anaerobic lagoons as an interim
solution to the dilemma of septage disposal. A series of two 20 day detention
lagoons are required, with percolation beds (1 gpd/ft^) for disposal of the
supernatant.
Landfills--
In some areas, septage is hauled to a sanitary landfill and mixed with
solid waste. Many landfill operators are reluctant to accept septage,
however, due to its potential leachate production. In a survey of landfill
operators, septage was rated 5 and sewage sludge 2 (median values) on a
0-10 scale of increasing potential hazard (12) . Approximately one-third of
the surveyed landfills which accepted sewage sludge also allowed septage dis-
posal. In New Jersey, suggested rates of septage application in landfills
generally do not exceed 10 gal per cubic yard of solid waste (14).
Prime considerations governing the utilization of any of the afore-
mentioned land disposal alternatives include climate, topography, soil
characteristics, groundwater levels, surrounding land use, odor and vector
control, septage loading rates, and protection of surface and groundwaters.
Septage Treatment Facilities
In areas where high densities of septic tank systems exist, regional
facilities have been constructed for the sole purpose of septage treatment.
Process types currently in operation include chemical precipitation,
high-dosage chlorine oxidation, multi-stage aerboic/facultative lagoons,
and composting. In addition, septage treatment research has been
-------
conducted on an anaerobic-aerobic process, a treatment sequence employing ro-
tating biological contactors (RBC), and a modified physical-chemical system.
Separate septage treatment facilities are used to treat only a small
portion (approximately 1 percent) of the total septage generated. Economic
feasibility considerations dictate that a high density of septic tanks be
present within a reasonable distance of such an installation. Such conditions,
although somewhat unique, are found in such areas as Long Island, New York,
and suburban Boston, Massachusetts.
Chemical Precipitation--
Islip, Long Island, utilizes chemical precipitation of septage at a
facility with a design capacity of 120,000 gpd. The process consists of
screening, grit removal, equalization, chemical clarification, chlorination,
and groundwater recharge (sand beds) with vacuum filtration of the underflow
solids (13). Chemical dosages are as follows: lime - 190 Ib/ton of dry solids;
40% ferric chloride - 50 gal/ton of dry solids (14). Assuming a typical total
solids content of 0.5 percent in Islip scavenger waste (38), equivalent dosages
expressed as mass/volume would be 430 mg/1 lime and 533 mg/1 ferric chloride.
The plant has experienced difficulty in producing an effluent of consistently
good quality (14, 15). A similar facility which will eventually replace the
Islip plant is currently under construction, designed for a 500,000 gpd peak
septage flow. The effluent will be discharged to a 30 mgd activated sludge
plant. Sludges from septage and sewage treatment processes will be blended
and subjected to wet air oxidation, vacuum filtration, and multiple hearth
incineration (15).
Chlorine Oxidation--
A number of Purifax units exist throughout the country for treatment of
septic tank sludges or combinations of septic tank and sewage sludges. These
sites include Ventura, California, East Hampton, Massachusetts, and Putman and
Plainfield, Connecticut. Two Rhode Island facilities (Kingstown and Woonsocket)
are still in the construction phase. In Babylon, Long Island, the Purifax septage
treatment complex has recently been taken out of operation. The normal Purifax
treatment sequence involves screening, grit removal, and equalization, followed
by chlorine oxidation (at 700-2000 mg/1 Cl2) and subsequent dewatering, often
accomplished in a lagoon or on sand drying beds. The Purifax process is capable
of producing a biologically stable, easily dewatered sludge, effecting high solids
removal efficiencies through the dewatering process. If mechanical dewatering is
contemplated, pH adjustment is required, since the oxidized product is generally
in a pH range of 1.7-3.8 (14). Recently there has been concern regarding the
potential production of chlorinated organic compounds by the Purifax process.
Facilities plans considering the use of this process must rigorously examine the
potential environmental and health effects associated with discharge of these
compounds into the natural environment.
Aerobic Lagoons--
The town of Brookhaven, Long Island, installed a septage treatment
system which consisted of raw septage discharge to an aerated lagoon,
followed by settling in a second lagoon, with chlorination of the effluent
and subsequent groundwater recharge via sand beds. Unfortunately, the
-------
system was very susceptible to biological upsets due to lack of flow
equalization. The sequence has now been modified to include screening, grit
and scum traps, three settling lagoons in series, an aerated lagoon, a final
settling lagoon with sludge return to the aerated lagoon, effluent chlorin-
ation, and groundwater recharge. The 50,000 gpd system has suffered opera-
tional difficulties, primarily due to clogging of the sand recharge basins
by solids in the effluent (14, 15).
Composting--
In South Tacoma, Washington, a composting facility employing the "Lebo"
process treats approximately 10,000 gpd of septage. The system involves
vigorous aeration of the septage, spray application to a layer of sawdust,
followed by alternating applications of sawdust and septage. The claimed
advantages include maintenance of aerobic conditions without turning,
consistently high temperatures (160°F) during decomposition, and no leachate
production (16). However, at this time, ~ittle scientific data is available
to support such claims.
Composting of raw and digested sewage sludges has been closely examined
at Beltsville, Maryland. Sludges are mixed with wood chips and arranged
into windrows with aerobic conditions maintained by a forced-draft reversible
aeration system. Although septage addition was not studied, excellent
results were obtained with undigested primary and secondary sewage sludges.
Other Septage Treatment Methods--
A septage treatment facility has been designed to serve the towns of
Wayland and Sudbury, Massachusetts. Capable of treating up to 25,000 gpd
of septic tank wastes, the preliminary design employs screening, grit
removal, equalization with aeration, chemical clarification, biological
treatment with rotating biological contactors (RBC), final clarification,
rapid sand filtration, chlorination, and groundwater recharge. It has been
estimated that the total cost of treatment, including capital amortization,
would be $23 per 1000 gal (19).
Research has been conducted in Fitchburg, Massachusetts on a pilot
system that treats septage lagoon supernatant. The process, originally
conceived for treatment of combined sewer overflows, provides holding,
chemical addition, high rate settling, equalization, and "flash disinfection"
by the "Dynactor" process (20).
An anaerobic-aerobic digestion sequence followed by sand filtration has
been investigated by Chuang (21) on a laboratory and pilot scale. Excellent
removal of BOD, COD, PO^, NH -N, and TKN was effected, although high effluent
NO^-N values were reported, as would be expected.
Septage Disposal at Wastewater Treatment Plants
Disposal at wastewater treatment plants is estimated to account for up
to 25 percent of the total septage slated for disposal. In most of these
-------
cases, disposal is by addition to the liquid stream; however, in some
instances, septage is considered a sludge and is handled accordingly - either
alone or in combination with sewage treatment plant sludge. Both modes of
addition have experienced various degrees of success.
Addition to the Liquid Stream--
Addition of septage to the liquid stream of a wastewater treatment plant
may be accomplished through discharging to a manhole upstream in the
collection system, slug addition at the headworks, or controlled metering
of the septage to the influent stream.
Disposal at an upstream manhole is preferable to slug addition at the
headworks in many cases. By the time the septage reaches the plant,
considerable dilution often will have been effected, thus minimizing organic
shock to the biological processes and possible upset of the plant. However,
this method is not easily controlled or regulated. During the spring and
summer, when the magnitude of septage disposal is greatest, uncontrolled
upstream dumping may have a deleterious impact on plant operation and
effluent quality. In addition, incidences of sewer clogging due to the high
septage grit/trash content have been reported (8).
Direct slug addition of septage to the headworks has been practiced at
many plants throughout the country. This is undoubtedly the least desirable
method of addition to the liquid stream. Unless the plant is operating far
below design capacity, or the volumetric ratio of septage to sewage is
sufficiently small, significant problems may result. Some types of plants,
such as contact stabilization, have been found to be highly sensitive to this
mode of septage addition to the influent stream, even when operating at as
little as 10 percent of design flow (19).
The third and most highly recommended method of septage addition to the
liquid stream is controlled addition through the use of a holding tank. This
allows slow introduction of septage into the mainstream, thereby minimizing
the impact on the plant. Addition of septage to the liquid stream will, in
all cases, exert additional loadings upon the plant. These loadings can be
generally classified as being due to solids, oxygen demanding substances,
toxic materials, and nutrients.
Solids LoadingThe additional solids loading due to septage addition
to the liquid stream may result in detrimental effects on primary and
secondary settling as well as dewatering of undigested underflow solids.
Sludge production can be expected to increase substantially.
In primary clarifiers with sufficient solids loading design capacity,
satisfactory separation may occur. Bennet et al. (7) reported suspended
solids removal of 55-65 percent in a pilot scale septage-fed primary
clarifier preceding a 1980 gpd activated sludge system. BOD removals,
however, were only 15-20 percent. The impact of a slug load upon the
primary clarifier of a small plant can be significant, as the following
calculations show:
-------
Assume: SS sewage = 200 mg/1
SS septage = 10,000 mg/1
Plant flow =0.5 mgd = 350 gpm
Septage flow = 1000 gal/20 min (1 truck load)
= 50 gpm
350 gpm (200 mg/1) + 50 gpm (10,000 mg/1) = 400 gpm (X mg/1)
X = 1420 mg/1 SS in combined
waste
Thus, an instantaneous increase in hydraulic load of almost 15 percent and
an increase in suspended solids concentration of seven-fold can be expected.
If the clarifier is overdesigned and solids carryover is not a problem, scum
and grit accumulation may well be a cause for concern, particularly if grit
removal of the septage is not practiced.
Septage addition to the influent stream may have an effect on the
settleability of biological (secondary) sludges. Bulking has been reported,
as well as production of pin point floe in the effluent. The latter was
found to be true at a 0.6 mgd oxidation ditch in Farmington, Maine. Despite
the presence of an aerated 7400-gal holding tank with options for C\2 an^
lime addition, upsets in plant operation were common, resulting in an
attempt by the operator to discourage any septage addition (22). Bulking
occurred at an extended aeration plant in Kittery, Maine where septage was
slowly fed to the process after 2-3 days of stabilization in an aerated
holding tank (23). Little work has been done to adequately characterize
secondary settling problems resulting from septage addition, or to attempt to
determine control strategies to prevent such upsets. In general, potential
problems exist in (1) floe formation, (2) sludge density, and (3) bulking (34).
A myriad of factors may be responsible for the solids separation dilemma,
including organic overloading causing D.O. depression, grease, the septicity
of the septage, the presence of simple, soluble organic compounds which favor
filamentous proliferation, toxics, shifts in microbial populations due to
shock organic loadings, etc. (34). One or more of the above problems are
often present and can be of considerable magnitude.
Dewaterability of underflow sludges may be adversely affected by septage
addition to the liquid stream. The effect on dewatering characteristics of
primary sludge would, perhaps, warrant the greater cause for concern, since
raw septage itself dewaters poorly. At a high rate trickling filter plant
in Shrewsbury, Massachusetts, operating at 1.2 mgd (1.75 mgd design),
problems in primary clarification and vacuum filtration of the sludge were
encountered when the septage/sewage hydraulic ratio exceeded about 0.0033.
The facility was equipped with a 6000-gal holding tank for slowly
introducing the septage into the plant flow (24). Small rural treatment
plants, such as extended aeration systems, typically do not employ primary
clarification, and thus do not enjoy the considerable buffering capacity
afforded by such units. These plants, which may often receive substantial
quantities of septage, can be heavily stressed by loadings associated with
solids and oxygen demanding materials, and, in some cases, toxic substances
or heavy metals.
-------
Consideration must also be given to the increase in sludge production
accompanying septage addition. At the EPA-DC Pilot Plant (7), it was found
that the solids production (per mass of total BOD applied) from a system
receiving septage was approximately twice that of a conventional biological
system operating at the same SRT. This was due to the greater fraction of
inert solids in the septage system feed (1.3-2.0 gSS/g BOD) than in the con-
trol system influent (1.0 g SS/g BOD). Thus, it is extremely important that
a plant receiving septage have sufficient solids handling capacity to accomo-
date the additional sludge.
Oxygen Demanding SubstancesThe importance of the additional oxygen de-
manding load imposed upon a plant accepting septage in the liquid stream
should not be underestimated. This characteristic of septage probably
accounts for the most incidences of plant upset due to septage addition. It
is mandatory that the plant have sufficient reserve aeration capacity to
accommodate the increased oxygen demand associated with septage. Shock loads
of septage may have disastrous consequences for biological populations, many
times due to depression of the dissolved oxygen level to zero. The following
calculations illustrate the effects of a 1000 gal shock load of septage to a
0.5 mgd plant with no primary sedimentation or nitrification.
Plant flow = 0.5 mgd = 350 gpm
Septage flow = 1000 gal/20 rain = 50 gpm (1 truck
Sewage BOD = 200 mg/1 load)
Septage BOD = 5000 mg/1
BOD concentration in shock load:
(350 gpm) (200 mg/1) + (50 gpm) (5000 mg/1) = (400 gpm) (X)
X = 800 mg/1 BOD
With primary clarification, the effects of such a shock on oxygen demand
would be somewhat buffered. At the EPA-DC Pilot Plant, primary clarification
resulted in BOD removals in the order of 15 to 20 percent (7). It should be
noted that in the previous example, the additional nitrogenous oxygen demand
exerted on a nitrifying mixed liquor was not considered. As discussed in
Section 4, this demand may be significant.
Several investigators have attempted to establish recommendations for
septage loadings to biological treatment processes. Spohr (18), assuming
primary clarification is employed, developed volumetric loadings based on
plant design capacity and percent utilization of that capacity (see Table 2).
Carroll (25) has based slug septage loadings on limiting the resultant in-
crease in MLSS to 10 percent. The design curves of Carroll have been sum-
marized for septage by Cooper (14) in Figure 1. Figure 2 shows estimates of
allowable septage loadings to plants having holding facilities, as a function
of the excess design capacity inherent to the plant. These curves represent a
10
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TABLE 2
ALLOWABLE VOLUMETRIC SEPTAGE LOADINGS
FOR PLANTS EMPLOYING
PRIMARY CLARIFICATION (18)
Plant Capacity
Plant Design Capacity
Pop Equiv
20,000
20,000
30,000
30,000
40,000
40,000
50,000
50,000
100,000
100,000
200,000
200,000
300,000
300,000
400,000
400,000
500,000
500,000
Flow
(100 gpcd)
mgd
2
2
3
3
4
4
5
5
10
10
20
20
30
30
40
40
50
50
Utilization
Percent
50
80
50
80
50
80
50
80
50
80
50
80
50
80
50
80
50
80
Septage Added, gpd
Without
Holding
2,642
1,057
3,963
1,321
5,284
2,114
7,926
2,642
13,210
5,284
26,420
10,568
39,630
15,582
52,840
21,136
66,050
26,420
With
Holding
7,926
3,171
11,889
3,963
15,652
6,342
23,778
7,926
39,630
15,852
79,260
31,704
118,890
36,746
158,520
63,408
198,150
79,260
11
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reasonable judgement based on additional organic loadings resulting from
septage addition as well as actual field experience from plants receiving
septage (14).
A study at the EPA-DC Pilot Plant investigated septage addition to a
1980 gpd plug flow activated sludge system on both a controlled and shock
load basis. It was concluded that "continuous addition of septage upstream
of the primary clarifier could be handled without severe upsets when the COD
loading was below 3 g COD/g MLVSS" (7). For the wastewater and septage
studied, this translated into septage loadings of slightly greater than 3
percent of the average daily sewage flow, but assumes the presence of suf-
ficient aeration and solids handling capacity. As the quantity of added
septage increased, the COD of the effluent correspondingly increased in value.
However, effluent BOD and SS remained similar to those of the control system.
During the shock load studies, which utilized both the 1980 gpd pilot system
and batch aeration tests, upsets in effluent quality were realized. However,
recovery was effected within 2 to 24 hours after addition, depending on the
severity of the insult.
Toxic Materials and Nutrients -- Secondary loading considerations
applicable to septage addition to the liquid stream include toxic materials
and nutrients. Substances potentially toxic to the biomass, such as heavy
metals, are commonly found in septage. In domestic septage, the concen-
trations are such that they pose relatively little danger, although these
concentrations are highly variable [see Table 1). Problems may arise from
contamination of septage with toxic materials, e.g., hauling of metal plating
wastes prior to transporting septage, or mixing of industrial and domestic
wastes to ensure the hauler of a "full load" for the trip to the treatment
facility. The presence of a septage holding tank for controlled addition
to the plant would provide, in most cases, a safeguard against upsets due to
toxic substances. However, it is necessary to segregate industrial holding
tank wastes from domestic septage and provide an alternative means of treat-
ment and/or disposal.
In plants where limitations are imposed upon effluent nutrient concen-
trations, the additional loading due to septage addition should be considered.
Mean values for TKN and total P in septage (from Tab]e 1) are 677 and 253 mg/1,
respectively. Controlled addition to the liquid stream should provide adequate
dilution of these nutrients such that they can be handled effectively by the
removal mechanism employed. This topic is further discussed in a later
section. In the EPA-DC Pilot Plant study, there was no indication of in-
hibition of nitrification due to controlled septage addition (7).
Addition to the Solids Handling Sequence --
A number of treatment plant operators and researchers have applied con-
ventional sludge treatment technology for stabilization, conditioning, and/or
dewatering of septage or septage/sewage sludge combinations. These options
include aerobic and anaerobic digestion, and chemical conditioning/stabili-
zation followed by mechanical or sand-bed dewatering.
14
-------
Aerobic Digestion -- Jewell et al. (4) investigated bench-scale batch and
continuous feed aerobic digestion of septage at detention periods of 1-30
days. He noted high removals of soluble organics, but limited reduction of
particulate organic material. Removal efficiencies varied widely. Two
problems which continue to affect aerobic septage stabilization, odor and
foaming, were eliminated in batch units in 5 and 11 days, respectively.
Foaming persisted in the continually fed reactors, but odors were not a
problem in these units after an acclimation period of 3-4 days. Settleability
(zone settling velocity) and dewaterability (CST) were improved considerably
after aerobic stabilization at loadings of 0.03 to 1.3 Ib VSS/ft /day and
detention times of greater than 30 days (4).
A preliminary study at the EPA-Lebanon Pilot Plant was hampered by
serious foaming problems during batch aerobic digestion of septage. Odors
were eliminated and settleability improved in 7 and 13 days, respectively,
at air flow rates of 0.5 scfm/ft3. Supernatant quality improved sharply from
COD values of 31,200 and 26,830 mg/1 on days 1 and 12, respectively, to 2,270
mg/1 on day 13. However, supernatant quality did not improve after a 31-day
batch aeration study at 0.25 scfm/ft3. At the latter air flowrate, 55 percent
reductions of volatile solids were observed, while 70 percent reductions were
achieved at 0.5 scfm/ft3, both over 31-day periods (27).
Perrin, in his work on chemical treatment of septage, concluded that the
use of short hydraulic detention, aerated lagoons for odor reduction and partial
stabilization, followed by chemical conditioning and sand bed dewatering, was
a workable alternative for handling septic tank sludges (41).
Tilsworth noted 80 percent BOD reductions and 41 percent VSS reductions
after ten days of aeration (26).
A number of treatment facilities throughout the country utilize aerobic
digestion of septage-sewage sludge mixtures at various volatile solids load-
ings with generally satisfactory results. However, many appear to be plagued
with foam and odor problems (4, 27, 36).
Jewell (31) has investigated the use of a high temperature digestion
process for treatment of dairy cattle waste, and has made preliminary tests
on septage. The unit provides approximately 3 days of aeration, with auto-
oxidation raising the temperature into the thermophilic range (65-70°C). The
process has successfully yielded a stable, virtually pathogen-free material.
The application of this process for treatment of septic tank wastes may be
promising.
Anaerobic Digestion -- Chuang (21) reported BOD and TVS reductions of
75 percent and 94 percent, respectively, during bench-scale anaerobic
digestion of septage at a detention time of 15 days.
Howley (36) was able to load a laboratory-scale anaerobic digester at
rates of up to 0.1 Ib VSS/ft3/day before failure was realized. At lower
15
-------
loadings, the removal efficiencies were similar to those of the batch aerobic
unit. Howley concluded that anaerobic digestion was not effective for handling
specifically septage due to the sensitivity of the process to upsets.
In Tallahassee, Florida, septage is added to an unheated, uncovered an-
aerobic digester at the rate of 0.01 lb/VSS/ft^/day. Volatile solids reduc-
tions of over 50 percent were reported at an 82-day, retention time (14).
Future work in Tallahassee will investigate utilization of a second, covered
digester for further stabilization of the septage (28).
In Westport, Connecticut, septage was added directly to the primary
clarifier, resulting in highly variable effluent BOD and SS concentrations
and production of obnoxious odors. Consequently, septage receiving, screen-
ing, grit removal, and holding facilities were installed. The 5000-gal
septage storage tank was designed so that the settled solids could be pumped
to the anaerobic digester, with the supernatant slowly introduced into the
liquid stream. Good results were observed (37).
Chemical Conditioning/Stabilization Followed by Dewatering -- Lime
stabilization at pH 11.5, followed by covered sand bed dewatering, was found
to be a technically and economically feasible method of septage handling at
the EPA-Lebanon Pilot Plant (6). At lime dosages of 8.3 percent of dry solids
(pH 11.5), 99 percent reductions in fecal coliforms and 95 percent fecal
streptococci reductions were achieved. Cake solids of 20-25 percent were
realized in less than one week with application depths of 8 inches, and almost
all of the organics and heavy metals were complexed in the cake. At appli-
cation depths greater than 8 inches, both dewatering rates and underdrainage
quality deteriorated.
Vacuum filtration of chemically conditioned septage has been practiced
at the Islip, Long Island, septage treatment facility at loading rates of
6 Ib/hr/ft . Ferric chloride and lime originally were used both as coagulants
for flocculation and as sludge conditioning agents. However, the vacuum
filter filtrate contained a fine floe difficult to settle, leading to the use
of polymers for sludge conditioning (13).
Using specific resistance and capillary suction time as indicators of
filterability, Crowe found that chemical dosages required to optimally dewater
septage were less than those dosages required for digested municipal sludge
(32). However, a number of investigators have indicated that unconditioned
septage is extremely difficult to dewater (4, 26, 32).
General Considerations --
For any septage handling operation at a wastewater treatment plant, con-
sideration should be given to the installation and maintenance of adequate
septage receiving facilities. These facilities should incorporate the
following (29, 30):
(1) A truck discharge station that is easily accessible, with
adequate facilities for cleanup.
(2) A mixed holding tank capable of storing a volume equivalent
to two days peak septage flow.
16
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(3) Odor control in the holding tank.
(4) Screening and grit removal facilities.
(5) A variable-speed pump for introduction of septage into
the desired process.
(6) Flexibility in the point of septage addition.
Potential Effects of Septage Addition on Biological Processes --
Biological treatment sequences vary as to their sensitivity to high organic
and solids loadings. The potential problems associated with septage addition
to several types of biological treatment processes are discussed below. Since
each treatment plant is unique with respect to design and operation, it is
difficult to quantitatively predict the effects of septage addition. However,
the spectrum of problems encountered are often common to many facilities.
Extended Aeration Since extended aeration plants often serve rural
communities, they are likely to handle significant volumes of septic tank
wastes. Because such plants usually do not enjoy the benefits of primary
clarification, those receiving septage must handle high organic and solids
loadings as well as objectionable amounts of grease and scum. Table 3 gives
the expected characterization of various combinations of sewage and septage
resulting from controlled metering of the septage into the influent stream.
Due to the long hydraulic and solids retention times inherent to the
process (18-36 hours and 20-30 days, respectively), biological assimilation
of organics would not appear to pose a problem, provided that sufficient
aeration capacity is available. Studies at the EPA-DC pilot plant investi-
gated batch aeration of septage-sewage mixtures at various ratios. The mix-
tures were composed of settled septage, primary sewage effluent and unaccli-
mated recycle activated sludge. The results of these batch aeration studies
are presented in Tables 4 and 5. Although the EPA studies utilized primary
effluent and "settled" septage mixtures, it can be seen that acceptable
effluent BOD and suspended solids values were realized after 24 hours of
aeration, even at extremely high influent organic loadings. Some deterior-
ation of effluent quality did occur with load No. 2 (see Tables 4 and 5).
This is believed to be due to the poor settleability of the concentrated
septage-sewage combinations, resulting in high effluent SS and correspondingly
high effluent BOD values. In general, however, at septage loadings typically
employed at wastewater treatment plants (up to 5% of the sewage flow), the
24-36 hr aeration time would provide ample reductions in BOD and SS for meeting
these effluent quality criteria.
Since nitrification commonly occurs in the extended aeration process, it
is useful to examine the additional nitrogen loadings due to controlled
septage addition. Table 3 shows average expected TKN and NH_-N values in the
combined waste. At a rate of septage addition equal to 3 percent of the
influent sewage flow, TKN and NH_-N concentrations can be expected to increase
by 48% and 2%, respectively. Since sufficient aeration capacity is assumed,
17
-------
TABLE 3
RESULTANT WASTEWATER CHARACTERISTICS
DUE TO CONTROLLED SEPTAGE ADDITION TO TREATMENT
PLANT INFLUENT
(Septage Characteristics From Table 1)
(Sewage Characteristics From Ref. 33, 42)
PARAMETER
TS
TVS
SS
VSS
BOD
CODT
CODS
TKN
NH3-N
TOTAL P
GREASE
RESULTANT CONCENTRATION mg/1
Septage Added (% of Plant Flow)
0
700
500
200
150
200
500
100
40
25
10
100
0.5
890
623
264
193
224
711
112
43
25
12
145
1
1077
745
327
235
248
919
124
46
26
15
185
2
1447
985
451
318
294
1330
148
53
28
17
247
3
1810
1221
573
400
340
1733
172
59
29
20
360
18
-------
TABLE 4
BOD REDUCTION DURING BATCH AERATION OF SETTLED SEPTAGE
- PRIMARY EFFLUENT MIXTURES (7)
Septage % Settled
Load No. Septage
] 0.0
0,7
2.1
3.4
4.8
6 . 7
2 0.0
5 , 5
19. 1
36.4
59.7
92. 7
BOD5
0.0
57
160
-J28
319
765
953
i!3
L? i
32;
6 2 0
830
Concentrations (Settled)
Aeration Time, Hrs.
0.
27
37
74
129
247
404
44
91
197
340
466
830
5 2.0
20
19
"< 5
99
129
209
36
'15
173
258
468
4.0 2
12
12
22
87
93
89
15
23
19
97
163
,mg/l
4.0
8
7
6
10
11
18
18
19
26
30
84
376 202
-------
TABLE 5
SS REDUCTION DURING BATCH AERATION OF SETTLED SEPTAGE
- PRIMARY EFFLUENT MIXTURES (7)
Septage % Settled
Load No. Septage
1 0.0
0.7
2.1
3.4
4.8
6.7
2 0.0
5.3
19.1
36.4
59.7
92.7
SS Concentrations (Settled), rag/1
Aeration Time, Hrs.
0.0
94
184
400
730
850
800
162
244
380
570
740
770
0.5
12
26
48
108
170
260
39
62
184
260
340
990
2.0
11
16
30
72
104
150
26
33
73
162
200
320
4.0
10
14
11
52
86
128
11
20
38
54
132
308
24.0
13
11
7
11
13
21
13
9
28
54
--
166
20
-------
the impact of the additional NH,-N on nitrification would be relatively small,
although slightly higher effluent NO -N values would be expected. However,
since the extended aeration process operates in the endogeneous phase of
respiration, auto-oxidation of cellular material would release additional
NH-N. Thus, organic nitrogen that is hydrolyzed and then utilized by bacteria
for cellular synthesis would ultimately result in a higher NH_-N loading.
Assuming a volumetric rate of septage addition of 3% of the plant flow, the
nitrogen content of cells at 8% by weight, and that approximately 2/3 of the
cellular material undergoes auto-oxidation, the additional NH--N load can be
estimated to be:
340 rag/1 combined BOD x 1 rag/1 cells x .08 mg N x _2_
rag/1 BOD mg cell 3
= 18 mg/1 additional NH -N
(maximum) from auto-oxidation of cells
This somewhat crude calculation represents the maximum additional NH -N
loading from auto-oxidation of cellular material under extended aeration.
Thus the total additional oxygen demand resulting from a rate of septage
addition equal to 3% of the plant flow may be determined as follows:
Source of Q? Demand Q_ Requirement
(BOD ) : (200) (1.5) = 300 mg/1
1 sewage ^ 6/
(NH_-N) : (25)(4.57) = 114
v 3 J sewage *- J * }
*(Org-N * NH-N) : (200) (. 08) (. 67) (4.57) = 49
6 3 sewage J ^
(BOD >septage' (14°)(1-5) = 21°
NH-N) + : (140) (. 08) (.67) (4.57) = 34
6 3 'septage v J ^ J ^ J ^ }
(SUBTOTAL) = 463
'sewage
(SUBTOTAL) = 262
septage
TOTAL 0 Requirement = 725 mg/1
Additional percent contribution to
0_ demand due to septage (at Q
2 r & i. xseptage
= 0.03 Q ) = 57%
^sewage
* For purposes of this calculation, it is assumed that the NH4+ for cellular
synthesis is derived from the hydrolysis of 27 of the 30 mg/1 of influent
organic N, with the remaining 3 mg/1 being refractory. It is further
assumed that all influent NIty is oxidized to NO^".
21
-------
Table 6 gives the breakdown of oxygen requirement by source for four
levels of septage addition to an extended aeration process.
The occurrence of nitrification in the extended aeration process requires
consideration of buffering capacity and potential depression of pH, since the
conversion of 1 rag/1 of NH +-N to NO ~-N will result in the destruction of
approximately 7.2 rag/1 of bicarbonate alkalinity (as CaCCL) as described by:
NH* + 2HC03" + 202 »- NO " + 2C02 + 3^0 (45)
Thus at a level of septage addition equal to 3% of the plant
flow, complete nitrification of the 29 mg/1 NH -N in the combined waste
would result in the destruction of over 200 mg/1 of bicarbonate alkalinity.
If one considers the possible release of additional NH_-N from cellular
auto-oxidation, the potential for destruction of buffer capacity becomes
greater. Sodium bicarbonate addition may be required if the alkalinity
of the mixed liquor supernatant drops below 20-25 mg/1 (45).
Effluent COD values can be expected to increase in proportion to the
rate of septage input (7). Howley (36) found that, on the average, approxi-
mately 25% of the soluble COD (COD ) in septage is refractory. In conventional
activated sludge processes treating solely sewage, one could expect an ef-
fluent refractory COD of about 30 mg/1 (43). Thus at a level of septage
addition equal to 1% of the plant flow, the effluent refractory COD would
increase to 36 mg/1; and at septage additions of 2% and 3%, expected effluent
refractory COD values would be 42 mg/1 and 48 mg/1, respectively.
Due to the increased organic and solids loading to plants receiving
septage, sludge production can be expected to increase significantly. Table
7 presents an estimation of the additional sludge production in an extended
aeration plant resulting from rates of septage addition of 0-3% of the plant
flow. It is assumed that sludge produced in an activated sludge process is
of two types: 1) nonbiodegradable suspended solids present in the influent
wastewater, and 2) biological cells synthesized under aeration. The follow-
ing modified sludge production formula will be used to predict the quantity
of sludge produced from an aerobic suspended growth system..
P =8.34 YQ(SQ-S1*) + 8.34 Q SS
nd
l+b9
c
where
P = total secondary sludge production, Ib/million gallons
j\.
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Q = total flowrate, mgd
S = influent BOD, mg/1
S *= effluent soluble BOD, mg/1
* i
b = decay coefficient, day
0 = solids retention time, days
SS , = nondegradable influent suspended solids, mg/1
22
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It is assumed that approximately 60% of the SS in raw sewage are non-
degradable (48), and that about 70% of the SS in septage are nondegradable
(36). Table 8 presents the combined wastewater characteristics used for
calculating estimates of sludge production. Values for Y and b are 0.63
Ib SS/lb BOD and 0.075 day"1, respectively (48). Since a portion of the
total sludge produced will pass into the effluent, an arbitrary value of
25 mg/1 has been selected to represent the effluent SS. For the extended
aeration process, an effluent soluble BOD (S,*) of 5 rag/1 has been chosen,
while for conventional activated sludge, S * = 10 mg/1.
The following example illustrates the procedure used for estimating
sludge production from an extended aeration plant.
For Q = 0.01 Q
septage sewage
P = 8.34YQ(S -S *) + 8.34 Q SS ,
x x^ o 1 x nd
1+bO
c
= 8.34Q63) (248-5) + 8.34(209)
1+C.075) (25)
= 444 + 1743
= 2187 Ib/million gallons total sludge production
Subtract sludge in effluent = (8.34)(25) = 209 Ib/million gallons
Waste sludge production =
2187 - 209 = 1978 Ib/million gallons
Due to the long solids retention time in extended aeration plants
(20-30 days), mixed liquor solids may become deflocculated, resulting in
the production of "pin-point" floe, often exhibiting poor settling character-
istics (46). In addition, denitrification in the final clarifier due to
excessive detention times and loss of D.O. may cause entrainment of nitrogen
gas bubbles in the sludge particles, producing rising sludge. Septage
addition may potentially aggravate solids separation problems. As previously
discussed, factors responsible for poor secondary settling characteristics
include organic overloading and D.O. depression, grease, the septicity of
the septage, the presence of simple, soluble organic compounds which favor
filamentous growth, toxics, and microbial population shifts from shock organic
loadings (34).
Perhaps the greatest cause for concern in clarification of extended
aeration MLSS is the increased solids loading due to septage addition. The
clarifier must be of sufficient design capacity to handle this additional
sludge. If sludge wasting facilities are not included in the design of the
plant, excessive accumulation of solids may result. It is therefore recom-
mended that extended aeration plants receiving septage incorporate the
flexibility of variable sludge wasting to prevent solids overloading.
25
-------
TABLE 8
WASTEWATER CHARACTERISTICS USED FOR CALCULATING ESTIMATES OF SLUDGE
PRODUCTION
COMBINED WASTE CHARACT
%
Septage BOD
0 200
0.5 224
1 248
2 294
3 340
Raw
SS
200
264
327
451
573
ERISTICS
Primary Effluent**
SS *
nd
120
165
209
296
381
BOD
140
158
175
203
238
SS
80
106
130
180
230
SS ,
nd
48
66
83
118
153
*non-degradable SS
Assume: 1) for sewage: SS = 0.6 SS
2) for septage: SS"^ - 0.7 SS
**primary clarification provides 1) 30% BOD removal
2) 60% SS removal
26
-------
Separate sludge wasting from extended aeration plants is often followed
by aerobic digestion and sand-bed dewatering (33). Since it has been shown
that sufficient aerobic digestion of septage results in a readily dewatered,
stabilized sludge (4, 27, 36), it would appear that such a treatment sequence
would be effective in processing sludge from an extended aeration plant
receiving septage. The design of such facilities should consider the in-
creased sludge production due to septage addition.
Plug Flow, Complete Mix, and Step Aeration Activated Sludge (with
Primary Clarification) -- In most modifications of the activated sludge
process, primary clarification is included in the treatment sequence, thus
providing considerable buffering capacity for the additional solids and
organic loadings. However, problems in primary clarification may arise due
to (1) the poor settling characteristics of septage, (2) the high grease
content (see Table 3), (3) solids overloading, and (4) increased septicity
and odor production. The use of efficient surface skimmer mechanisms on
primary clarifiers is recommended for removal of grease and floatable
solids accompanying septage addition. Anaerobic conditions in the clarifier,
supposedly due to septage addition, have been reported (24). Possible
solutions to this problem include (1) increased underflow sludge withdrawal
rates to minimize residence times, (2) preaeration of the septage, and (3)
volumetric reduction of septage input.
A study at the Hyannis Water Pollution Control Facility in Massachusetts
investigated the effects of septage addition on primary clarification (47).
For raw sewage alone, BOD and SS removals of 29 and 51 percent, respectively,
were reported. These value.: compare favorably with anticipated reductions
for raw sewage subjected to primary clarification. During septage addition,
however, reported removals of BOD and SS were 69 and 81%, respectively. These
high removal rates reflect the fact that septage was added to the plant at
a rate of 24 percent of the influent sewage flow, resulting in a combined
waste having an average BOD of over 500 mg/1 and an average SS concentration
exceeding 600 mg/1. This rate of septage addition is considerably higher
than what typically would be found in secondary treatment plants. These
data appear to indicate only a slight deterioration in primary effluent
quality at increasing rates of septage addition. However, before extrapo-
lation of these results, it would be necessary to scrutinize hydraulic and
solids loading capacities of the clarifier which resulted in these high
removal efficiencies.
Plug flow, complete mix, and step aeration activated sludge systems
normally provide a solids retention time of 4-10 days and a hydraulic reten-
tion time of 3-8 hours. Using Tables 4 and 5 to gain an estimate of effluent
quality after an aeration time of 4 hours, it can be seen that acceptable
effluent qualities were realized except at very high BOD and SS loadings.
For a relatively high septage input (Q ^ - 0.05 0 ), and assuming
1 septage 'sewage 6
30 percent BOD removal and 60 percent SS removal in primary clarification,
the resultant aeration tank influent BOD and SS concentrations (using values
from Table 1 and 3) would be 300 mg/1 and 325 mg/1, respectively. From
inspection of Tables 4 and 5, it would appear that such a waste would be
27
-------
amenable to oxidation at a hydraulic detention time of 4 hours. It must be
noted, however, that the values presented in Tables 4 and 5 represent the
results of unacclimated batch aeration studies, which may be of limited value
in attempting to predict effluent quality under actual field conditions.
It is important to examine the additional oxygen requirements for an
activated sludge system receiving septage. Table 9 presents estimated oxygen
requirements, assuming the combined waste characteristics in Table 3, and that
1.0 g of Q? is required to remove 1 g of BOD. These calculations also assume
a consistent BOD removal efficiency of 30 percent in primary clarification.
Table 10 yields estimates of primary and secondary sludge production at
various levels of septage addition. Again, BOD and SS removal efficiencies
in primary clarification were assumed to be 30 percent and 60 percent,
respectively. The procedure used for estimating secondary sludge production
is the same as that used for the extended aeration process. An example
follows.
For 0 . = 0.01 Q
^septage xsewage
A. Primary sludge production
(327-130) 8.34 = 1643 Ib/million gallons
B. Secondary sludge production
P =8.34 YQ(S -S *) + 8.34 OSS ,
x x^ o 1 J x nd
1 + be
c
= 8.54(.63)(175-10) (
1 + (.075) (5) + 8'34 (83j
= 630 + 692 = 1322
TOTAL = 1643 + 1322 = 2965 Ib/million gallons
Subtract sludge in effluent = 8.34(25) = 209 Ib/million gallons
Waste sludge production = 2756 Ib/million gallons
Since many states have imposed effluent standards for phosphorus (P), the
effect of septage addition on phosphorus removal processes should not be
neglected. Phosphorus removal at an activated sludge plant is normally ac-
complished by (1) mineral (Al, Fe) or lime (Ca) addition before primary clarifi-
cation, (2) mineral addition to the aeration basin, and (3) mineral or lime
addition to the secondary effluent followed by filtration. Coagulant aids are
often employed in conjunction with iron and alum. Although specific chemical
requirements for the additional phosphorus loadings will not be discussed,
several generalizations may be made regarding effects of septage addition.
Inspection of Table 3 shows that the influent concentration of phosphorus may
be expected to double when Q = 0.03 Q . Since phosphorus removal
o (2iJ L £*->} *~ S 6 W3.26
28
-------
TABLE 9
ESTIMATED ADDITIONAL OXYGEN REQUIREMENTS DUE TO SEPTAGE ADDITION TO A
CONVENTIONAL ACTIVATED SLUDGE SYSTEM WITH PRIMARY CLARIFICATION
n.
0
Septage
Addition
0
0.5
1.0
2.0
3.0
BOD of
Combined
raw waste,
mg/1
200
225
250
290
340
*BOD of
Primary
Effluent,
mg/1
140
158
175
203
238
0 Required
Ib/million
gallons
1168
1318
1460
1693
1985
% Increase
due to Septage
Addition
0
13
25
45
70
*Assumes BOD removal = 30%
SS removal = 60%
for all levels of septage addition
29
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using Al salts (alum, sodium aluminate) and Fe salts (ferric chloride, ferric
sulfate, ferrous sulfate) is dependent on the metal/P ratio, the increase in
influent P concentration will require increased metal addition. When lime is
employed for phosphorus precipitation, lime dosage is virtually independent
of phosphorus concentration at typical alkalinities, and is governed by the
desired pH for optimal precipitation. When iron or aluminum salts are used
for P precipitation, both minerals will destroy alkalinity and depress the
pH, while lime addition results in pH elevation. Therefore, pH adjustment
may be required, as in the case of nitrification following chemical addition.
Sludge production from mineral precipitation of P can be expected to increase
proportionately with chemical dosage.
Anaerobic digestion is commonly employed at activated sludge plants for
stabilization of primary and secondary sludges prior to dewatering and/or
disposal. Consideration must be given to the solids handling capacity of the
digester for plants receiving septage, since sludge production will increase
significantly. At typical rates of septage addition to the raw wastewater
(3 percent by volume), little impact on anaerobic digestion should occur.
Septage has been added directly to anaerobic digesters with good results (37).
Toxic effects from metals would be unlikely, due to the relatively low metal
content of septage. However, because of the variable character of septic tank
sludge and the potentiality of cross contamination from hauling industrial
sludges, high metal concentrations are possible.
Problems in dewatering of underflow sludges in plants receiving septage
have been reported. Whether or not these problems are directly attributable
to septage addition remains undetermined, as little or no data are available.
Septage addition could cause potential problems of this nature due to such
factors as grease, the inherent resistance of septage to dewatering, changes
in character of the secondary sludge due to mixed liquor population shifts,
etc. Although the effects of septage addition on dewaterability of underflow
sludges are not well known, consideration should be given to the additional
sludge production, which most likely will require an increase in the frequency
of dewatering operations or capital expenditures for additional dewatering
equipment.
Contact Stabilization -- Contact stabilization would appear to be the
least amenable of the aerobic suspended growth treatment processes for treating
septic tank wastes by addition to the influent stream. This is primarily
due to the short retention time (30-60 min) in the contact chamber. Success-
ful operation of the process is largely dependent on the removal of colloidal
and finely suspended organic matter by sorption on to sludge floe in the
contact tank, and subsequent synthesis and oxidation reactions in the
stabilization tank. Since contact stabilization systems are generally not
recommended for wastes with a high soluble organic content, it is useful
to examine the additional soluble COD (CODS) loading due to septage addition.
Assuming CODS = 0.2 CODT for sewage (42), and CODS = 0=06 CODT for septage
(36,41), controlled metering of septage into the influent stream at 1% of the
plant flow would increase the CODS contribution by 24% (see Table 3). Simi-
larly, at controlled septage additions of 2% and 3%, the corresponding CODS
of the combined waste would be increased by increments of 48% and 72%,
31
-------
respectively, over raw sewage alone. It is difficult to estimate what fraction
of the soluble organic load would be sorbed by the mixed liquor in the contact
tank. Since it has been suggested that the contact stabilization process
is most efficient in handling wastes in which the organic load is primarily
colloidal or particulate, it is unlikely that the additional soluble organic
contribution would be removed in the contact tank.
Using Tables 4 and 5, the effluent values for aeration times of 0.5 hr
may be considered to be rough estimates of the effluent quality from a contact
stabilization plant. Several differences exist in actual practice which would
limit the utility of these estimates: 1] the values presented in Table 4 are
for mixtures of primary effluent and settled septage (to simulate removal
during primary clarification which normally would not be employed at a contact
stabilization plant), 2) the waste activated sludge added to the units was not
reaerated, as it would be in a stabilization basin, and 3) the waste activated
sludge was not "acclimated" to septage. Note that as the organic loading in-
creases, the effluent quality deteriorates significantly at an aeration time
of 30 minutes. As would be expected, longer aeration times provide a greater
buffering capacity for the additional organic loadings.
Another important consideration in determining potential effects of
septage addition to contact stabilization plants is the contribution of grease
(hexane solubles) by septage. Grease removal pretreatment is recommended for
high-rate activated sludge and contact stabilization systems when the grease
concentration is between 75 and 200 mg/1 (44).. Since medium strength sewage
normally has a grease content of about 100 mg/1 (33), any significant increase
over this value may be deleterious to plant performance. From Table 3, it is
found that a rate of septage addition at 1% of the plant flow results in an
incremental increase in grease concentration of about 85%. At 2% of plant
flow, septage addition will result in a grease content in the combined waste
of about 250 mg/1.
In light of the above considerations, septage addition to the raw waste-
water flow at a contact stabilization plant would not be recommended. An
alternative to this mode of addition would be to add degritted septage to the
stabilization basin under controlled conditions. Normally, this unit would
provide 3-6 hours of retention, maintaining a MLSS of 4000-10,000 mg/1, with
underflow sludge recycle rates varying from 25-100% of the plant flow (33).
Overall solids retention times for the contact stabilization process are in
the range of 5-15 days.
Factors to be considered under this mode of addition include: 1) the
possibility of upsets in the stabilization basin due to toxics, 2) the recycle
ratio employed, which would affect the actual septage loadings to the stabili-
zation tank, 3) additional oxygen requirements, 4) additional sludge
production, and 5) the effect of the increased loadings on the oxidation and
synthesis reactions that normally occur in a well operated contact stabili-
zation plant.
32
-------
Estimated total oxygen requirements for a contact stabilization plant
receiving septage in the stabilization basin are presented in Table 11.
These values represent the overall combined oxygen requirements of the contact
and stabilization basins, based on total BOD loadings to the plant. No
attempt was made to differentiate between oxygen requirements in the separate
units, since this will depend largely upon recycle ratios employed and the
distribution of MLVSS between the reactors.
Estimates of sludge production at various levels of septage addition
are presented in Table 12. For these calculations, it was assumed that the
process operates at a solids retention time of 5 days, with an effluent
soluble BOD of 10 mg/1, and an effluent SS of 25 rag/1. A sample calculation
follows.
For Q , = Q.01 Q
^septage %sewage
Px = 8.34 YQCS^S^) + 8.34 QSSnd
= (8. 34) (0.63) (248-10] + 8.34 (209)
1 +(.075) (5)
= 2652 Ib/million gallons total sludge production
Subtract sludge in effluent = 25(8.34) = 209 Ib/million gallons
Waste sludge production = 2443 Ib/million gallons
Many "package" contact stabilization plants employ aerobic digestion for
treatment of waste solids. This would appear to be a viable sludge treatment
process for a contact stabilization plant receiving septage in the stabili-
zation basin, since septage itself is amenable to aerobic digestion. It is
imperative that in the design of such a plant, consideration be given to the
increased sludge production resulting from septage addition as it affects
solids handling capacity.
Although it appears that addition to the stabilization basin would be a
feasible strategy for handling septage at a contact stabilization plant,
several factors require scrutinization. For example, if a recycle ratio
(Q /Q ) of 0.5 is used, the septage hydraulic loading based on 0 would be
twice the hydraulic loading based on Q . Thus, the potential for upsets due
to toxics or organic overload increases at lower recycle ratios. Of particular
concern is that the organic loading may exceed the aeration capacity of the
stabilization tank. Loss of dissolved oxygen in this reactor may result in
demise of the biological population and subsequent total upset of the contact
stabilization process. In addition, consideration should be given to the
decrease in the volatile fraction of suspended solids due to septage addition,
resulting in decreased oxidation capability. The high grease contribution
may also impact system performance.
33
-------
TABLE 11
ESTIMATED ADDITIONAL OXYGEN REQUIREMENTS DUE TO SEPTAGE ADDITION
TO THE STABILIZATION BASIN OF A CONTACT STABILIZATION PLANT
,,,. . Total (Contact £ Stabilization) % Increase
Septage Addition Required Ib/million gallons Due to
Septage Addition
0 1834 0
0.5 2064 13
1.0 2293 25
2.0 2660 45
3.0 3120 70
34
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Trickling Filters In assessing the feasibility of employing trickling
filters for treatment of septic tank wastes, one must consider (1) design
organic loading, (2) increased sludge production, and (3) potential odor and
filter fly (Psychoda) generation.
Trickling filters are often classified as being low-rate (1-4 mgad,
300-1000 Ib BOD/acre-ft/day, no recirculation) or high-rate (10-40 mgad,
1000-5000 Ib BOD/acre-ft/day, recirculation ratio of 1:1 to 4:1) (33). Low-
rate trickling filters generally yield a fully nitrified effluent, while
nitrification in high-rate filters occurs only at low loadings. Most trick-
ling filters are preceded by primary clarification to reduce the organic
loading and to minimize clogging of the media. However, in some cases, com-
minuted wastewater has been applied directly to trickling filters employing
plastic media with a large void volume. In the following discussion, it will
be assumed that the treatment sequence includes primary clarification.
Two major problems with low rate trickling filters are odor generation
and filter fly proliferation. Odor problems generally result from stale or
septic wastewater, particularly during warm weather, and thus may be aggra-
vated by the addition of septage. For this reason, septage pretreatment may
be desirable. This might include (in addition to grit; removal) preaeration
and/or pretreatment with chlorine or hydrogen peroxide. Although odor may
remain a problem in high-rate trickling filters, filter flies are controlled
due to continuous sloughing of the organic growth and removal of the Psychoda
larvae.
The overriding consideration in determining the amenability of a trick-
ling filter process for treating septage is that of organic loading. As
shown by Table 13, the BOD loading to a trickling filter can be expected to
increase substantially with increasing rates of septage addition. Thus, in
estimating whether or not trickling filters could effectively handle the
additional loadings, consideration must be given to present organic loading
and the design capacity of the filter(s) on a case-by--case basis.
Care must be exercised to prevent clogging of the media, particularly
when rock is employed as a filter material. Clogging is mainly caused by
grease or excessive organic growth accumulation. Since the grease content
of septage is high, primary clarifiers should be equipped with efficient
surface skimmers. Clogging due to excessive stimulation of organic growth
appears to be a major problem with rock trickling filters of the 4-10 mgad
hydraulic loading range (44). One can only speculate as to the effect of
additional organic loadings from septage on media plugging potential. There
would appear to be a potential for clogging of rock media at the higher
organic and solids loadings shown in Table 13. Plastic media is less sus-
ceptible to clogging, due to the greater percentage of void space (93-97
percent for plastic versus 40-60 percent for rock). A clear opening of
0.7-0.8 inches is recommended to avoid media clogging by biological slime.
This limits the maximum specific surface area (surface to volume ratio), to
about 70 ft2/ft3 (48).
Increases in primary and secondary sludge production will occur at a
trickling filter installation receiving septage. Estimation of sludge pro-
36
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has been assumed that constant BOD and SS removal efficiencies are effected at
all levels of septage addition, despite indications that the removal efficien-
cies of primary clarifiers may increase at higher septage loadings (47).
Estimates of secondary sludge production due to sloughing of biological slimes
(humus) from the media vary considerably. Production of humus sludge is
dependent on waste characteristics, hydraulic and organic loading, the type
of medium employed, temperature, and other conditions within the filter
environment. Based on BOD removal, estimates of sludge production from high
rate filters vary from 0.2-0.3 Ib sludge solids/lb BOD removed (49) to
0.7-0.8 Ib sludge solids/lb BOD removed (50). Alternatively, one may use the
following equation to predict the concentration of suspended solids in a
high-rate trickling filter effluent prior to clarification (48), from which
estimates of sludge production can be easily generated.
X =0.5 (BOD + SS) - 0.5 VA
e * J y_
Q
where X = trickling filter effluent SS, mg/1
BOD = influent BOD to filter, mg/1
SS = influent SS to filter, mg/1
V = trickling filter volume, ft
A = media specific surface area, ft /ft
Q = flowrate, ft /day
Since the preceding equation does account for the SS in the influent
wastewater, it will be used here to estimate sludge production. For the low-
rate trickling filter case, however, the equation will be modified to the
following:
VA
X =0.35 (BOD+SS) - 0.5 ( v)
Q
The selection of this lower coefficient is somewhat arbitrary and is tailored
to yield estimates approximating those from actual installations. Unfortun-
ately, measurement of sludge production from trickling filters is difficult,
resulting in the wide variation in reported values. The second term of the
sludge production equation is dependent on filter volume and specific surface
area, and thus will vary for each specific case. The magnitude of this term
is small, however, in relation to o. 35 (BOD+SS). The examples on pages 40
and 41 illustrate the calculation of sludge production from low-and high-rate
trickling filters.
Due to its greater density, trickling filter sludge (humus) settles
more readily than activated sludge (48). In many cases, underflow sludge
concentrations in the final clarifier of 3-4 percent solids can be obtained.
The effect of septage addition on humus settleability is unknown, however.
38
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Calculation of Sludge Production
I. Low-rate trickling filter
Q = 1 mgd
Septage addition = 1% of plant flow
Assume rock media; A = 15 ft /ft
Assume conservative design organic
loading of 5 Ib BOD/1000 ft3
Primary effluent BOD = 140 mg/1 (no septage)
Filter volume = 140(8.54) = 233.52xl03ft3
5
A. Primary sludge production
(327-130) 8.34 = 1643 Ib/million gallons
B. Secondary sludge production
X = 0.35C175+130) -Q.5 [233.5x10 ) (15) =106.8-13.1 = 93.7 mg/1
133.7x10-*
Trickling filter sludge production == 8.34(93.7) = 781 Ib/inillion
gallons.
Total sludge production = 1643+781 = 2424 Ib/million gallons
Subtract sludge in final effluent
= 25(8.34) = 209 Ib/million gallons
Waste sludge production = 2215 Ib/mLllion gallons
40
-------
Calculation of Sludge Production
II. High-rate trickling filter
Q = 1 mgd
Septage addition = 1% of plant flow
Assume plastic media; A = 30 ft /ft
Assume conservative design organic
loading of 30 Ib BOD/1000 ft-5
Primary effluent BOD = 140 mg/1 (no septage)
Filter volume = 140(8.34) = 38.92xl03ft3
30
A. Primary sludge production
(327-130)8.34 = 1643 Ib/million gallons
B. Secondary sludge production ,
X = 0.5(175 + 130) - 0.5 (38.92x10 ) (.30) = 152.5-4.4 = 148.1 mg/1
6 (133.7x10-*)
Trickling filter sludge production = 8.34(148.1) = 1235 Ib/million
gallons.
Total sludge production - 1643+1235 = 2878 Ib/million gallons
Subtract sludge in final effluent
= 25(8.34) = 209 Ib/million gallons
Waste sludge production = 2669 Ib/million gallons
41
-------
Septage addition may aggravate dewatering of underflow sludges at a
trickling filter plant. The main factor responsible for such aggravation
would appear to be related to the character of the primary sludge, since
large amounts of raw septage solids would become incorporated into this
material. The dewaterability of the trickling filter humus may also be ad-
versely affected.
Oxidation Ponds -- Oxidation ponds account for about 32 percent of the
secondary treatment facilities in the United States. Approximately 78 percent
of these oxidation ponds have flows less than 0.5 mgd (35). Due to their low
capital and maintenance costs, ease of operation, and large land requirement,
oxidation ponds are an attractive alternative for rural communities. Conse-
quently, as waste treatment facilities, they are potential receptors of
significant volumes of septic tank wastes.
Classifications of wastewater treatment ponds vary considerably. For
the purposes of this discussion, ponds will be considered to be aerated or
nonaerated. Nonaerated ponds would include anaerobic, facultative, aerobic,
and polishing or maturation ponds. Nonaerated ponds treating raw domestic
wastewater (facultative/aerobic) often operate with marginal efficiency, and
are often hampered with odors associated with anaerobiosis. In northern
climates, ice cover aggravates these problems. Due to the high oxygen
demand of septage and its grease and solids content, addition to a nonaerated
pond normally treating domestic wastewater must be practiced with caution.
Provided that the pond is meeting secondary standards and has sufficient
design capacity (Ib BOD/acre/day) , continuous septage addition would be
feasible. Shock addition of septage to an oxidation pond should be dis-
couraged.
Aerated ponds can be classified as completely mixed or partially
mixed. The degree of mixing has the greatest effect on treatment efficiency.
Facultative partially mixed ponds are often preferable to completely mixed
aerated ponds due to (1) lower equipment and power costs for aeration,
(2) less sludge handling due to settling and digestion of solids within the
pond, and (3) less operational control. Energy requirements for completely
mixed ponds are 2-4 times greater than for facultative ponds
As the organic load to the pond increases, the power level necessary to
satisfy oxygen uptake requirements becomes greater. An increase in detention
time, however, will decrease the power requirements. Figure 3 indicates ex-
pected power requirements for an aerated pond, based on the relationship (48) :
P , 1>7S][10-4 (_!f20_ - j (fc,_)(^ .15J(1
S rj, O
where P = power level required to satisfy oxygen uptake,
v hp/103 gal of basin volume
C = D.O. concentration at saturation, mg/1
C = Desired D.O. concentration in pond, mg/1
42
-------
1VO NOiniW
43
-------
S = influent BOD, mg/1
N = oxygen transfer efficiency, Ib/HP-hr
t = detention time, days
T = pond temperature, C
The values in Figure 3 were obtained by assuming:
T = 20°C
Cs = 9.0 mg/1
C = 2.0 mg/1
N = 1.7 Ib HP-hr
o
It is generally agreed that, in an aerated pond, a completely mixed re-
gime can be achieved only at power levels in excess of 30 HP/10^ gal. Thus,
in Figure 3, the energy required for mixing exceeds that for satisfaction of
oxygen uptake requirements at a detention time between one and two days.
The soluble BOD in the effluent from an aerated lagoon will be largely
dependent on the degree of mixing and the detention time employed. Detention
times in excess of three days are recommended. Overall effluent quality is
largely a function of the efficiency of solids separation, provided that the
detention time and degree of mixing are sufficient. Longer detention times
often favor proliferation of algae which may be difficult to settle, thus
resulting in a significant oxygen demand in the receiving water.
Provided that an acceptable effluent quality is maintained, the remaining
considerations for an aerated pond treating septage are (1) oxygen uptake
requirements, (2) solids deposition, and (3) grease and scum accumulation.
Oxygen uptake requirements and power levels necessary for mixing have been
discussed previously. The increased organic and solids loading from septage
would obviously result in the generation of greater quantities of sludge per
unit volume of wastewater treated. For the more common facultative aerated
pond, or for those systems employing a final settling pond, sludge disposal
is not a consideration. However, increased rates of solids deposition due to
septage addition should be expected. Grease and scum accumulation may pre-
sent a severe problem on pond surfaces. Although separate grease removal
facilities would not normally be considered, proper design of the ponds with
respect to wind direction, dike construction, and week control would
facilitate manual grease removal if the extent of grease accumulation
warranted such action.
CONCLUSIONS
Over four billion gallons of septic tank sludge (septage) require disposal
every year in the United States. Current disposal practices include land
application, separate treatment facilities, and addition to sewage treatment
plants.
44
-------
The great majority of the septage is disposed of on the land by various
methods. Since stabilisation of the waste is generally not effected prior to
disposal, potential public health and environmental hazards exist in the form
of groundwater, surface water, and soil contamination by pathogens, organics,
nutrients, and toxic substances, leading some states to discourage such dis-
posal practices.
Separate treatment facilities exist in a few areas of the country for
handling solely septic tank wastes. However, for construction of such
facilities to be justified, it is necessary that a high concentration of sep-
tic tanks be present in the immediate locale to minimize hauling distances
and to take advantage of economies of scale. Such facilities currently in
use have often experienced operational problems. Regional systems which do
not employ land disposal methods are generally costly to construct and operate.
Utilization of existing wastewater treatment plants for handling of
septage has been practiced throughout the country, mostly via slug addition
of septage to the liquid stream. Such plants have experienced a wide spectrum
of problems, ranging from grit accumulation and foaming to the loss of biomass
and complete system failure. This has resulted in reluctance on the part of
many operators to accept septage, often unjustifiably so. Unfortunately,
little data exists on which to base loading guidelines for septage addition
to biological treatment processes. In addition, relatively little work has
been done regarding alternative methods of handling septage at the treatment
plant, e.g., receiving and pretreatment facilities, flexible piping arrange-
ments, treatment by solids handling processes, etc.
For small treatment plants in rural areas, which are likely to handle
significant quantities of septage, the presence of a septage receiving/holding
facility appears to be almost a necessity. Slug addition to the liquid stream,
except in cases where the septage/sewage volumetric ratio is small, or where
the plant has significant excess capacity, does not appear to be a viable
alternative for septage treatment.
Many unknowns still exist regarding septage addition to secondary bio-
logical treatment systems. Areas of interest which are in need of further
quantification include allowable septage loading rates, effects of septage
addition on sludge production and dewaterability, effects on primary and
secondary clarification, and control of foam and odor. Figures 4 and 5 sum-
marize estimates of sludge production and oxygen requirements for several
biological treatment processes receiving septage. A rational program of
research into septage addition to wastewater treatment plants would allow
development of operational guidelines and control strategies that could
minimize plant upsets and dispel the myths and fears of plant operators
across the country.
45
-------
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a.
O
o
z
o
3
O
P 1
o
o
ACTIVATED SLUDGE WITH
PRIMARY CLARIFICATION (PC)
HIGH-RATE TRICKLING FILTER
WITH PC
CONTACT STABILIZATION
WITHOUT PC
LOW-RATE TRICKLING
FILTER WITH PC
EXTENDED AERATION
WITHOUT PC
_L
1
1.0 2.0
RATE OF SEPTAGE ADDITION, % OF PLANT FLOW
3.0
FIGURE 4. ESTIMATED WASTE SLUDGE PRODUCTION FROM
BIOLOGICAL TREATMENT PROCESSES
RECEIVING SEPTAGE
46
-------
o
z
o
ae
LLJ
GO
o
o
2 3
i-^
Z
UJ
f.
UJ
O
UJ
QL
Z
UJ
o
X
o
1 -
EXTENDED AERATION
0e= 25 DAYS
(NITRIFICATION)
CONTACT STABILIZATION
0C = 5 DAYS
(NO NITRIFICATION)
ACTIVATED SLUDGE
WITH PRIMARY CLARIFICATION
0=5 DAYS
(NOC NITRIFICATION)
I
1.0 2.0
RATE OF SEPTAGE ADDITION, % OF PLANT FLOW
3.0
FIGURE 5. ESTIMATED OXYGEN REQUIREMENTS FOR
BIOLOGICAL TREATMENT PROCESSES
RECEIVING SEPTAGE
47
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REFERENCES
1. EPA, Robert S. Kerr Environmental Research Laboratory and Municipal
Environmental Research Laboratory, "Environmental Effects of Septic
Tank Systems" September 1976.
2. Kolega, J. J., Dewey, A. W., "Septage Disposal Practices," paper
presented at the National Home Sewage Disposal Symposium, Chicago,
Illinois, December 9-10, 1974.
3. Kolega, J. J., "Design Curves for Septage," Water and Sewage Works,
May 1971.
4. Jewell, W. J., Howley, J. B., Perrin D. R., "Design Guidelines for
Septic Tank Sludge Treatment and Disposal," paper presented at the
7th Internationl Conference on Water Pollution Research, Paris,
September 9-13, 1974.
5. Goodenow, R., "Study of Processing Septic Tank Pumpings at Brunswick
Treatment Plant," Journal of Maine Wastewater Control Assoc., Vol. 1,
No. 2, September 1972.
6. Feige, W. A., Oppelt, E. T., Kreissl, J. F., "An Alternative Septage
Treatment Method: Lime Stabilization/Sand-Bed Dewatering," Environmental
Protection Technology Series, EPA-600/2-75-036, September 1975.
7. Bennett, S. M., Heidman, J. A., Kreissl, J. F., "Feasibility of Treating
Septic Tank Waste by Activated Sludge," Environmental Protection Technology
Series, in press, 1977.
8. New England Interstate Water Pollution Control Commission, "Guidelines
for Septage Handling and Disposal," August 1976.
9. Kolega, J. J., Cosenza, B. J., Dewey, A. W., Leonard, R. L., "Septage:
Wastes Pumped from Septic Tanks," paper presented at the 1971 Annual
Meeting of ASAE, Washington State University, Pullman, Washington,
June 27-30, 1971.
10. Tawa, A. J., "Chemical Treatment of Septage," M.S. Thesis, University
of Massachusetts, August 1976.
11. Kreissl, J. F., "Septage Analysis," U. S. EPA Memorandum, February 2, 1976.
12. Stone, R., "Practices in Disposal of Sewage Sludge by Landfill," Pub1ic
Works, August 1972.
13. Graner, W. F., "Scavenger Waste Disposal Problems on Long Island," Report
to Suffolk County Dept. of Health, 1969.
48
-------
14. Cooper, I. A., "Septage Disposal in Wastewater Treatment Plants,"
paper presented at the 3rd National Conference on Individual On-
Site Wastewater Treatment Systems, sponsored by NSF and EPA, November
16-18, 1976.
15. Pirn, James., Suffolk County Department of Environmental Control,
Personal Communication.
16. Cooper, I.A., Memorandum: Meeting in Tacoma, Washington, February
4, 1976 in Monthly Progress Report #6, EPA Contract No. 68-03-2231.
17. Epstein, E., Wilson, G. B., Burge, W. D., Mullen, D. C., and Enkiri,
N. K., "A Forced Aeration System for Composting Wastewater Sludge,"
Journal Water Pollution Control Federation, April 1976.
18. Spohr, G. W., "Municipal Disposal and Treatment of Septic Tank
Sludge," Public Works, December 1974.
19. DeFilippi, J. A., "Preliminary Engineers Report, Septage Disposal
Facility, Town of Sudbury and Wayland, Massachusetts," Roy F. Weston,
December 1973.
20. Schauffler, F.K., New England Interstate Water Pollution Control
Commission, Personal Communication.
21. Chuang, F. S., "Treatment of Septic Tank Wastes by an Anaerobic-
Aerobic Process," Deeds and Data Supplement, W.P.C.F. Highlights,
13, 7, 3 (1976).
22. Chandler, D., Operator, Farmington, Maine STP, Personal Communication.
23. Tapley, Operator, Kittery, Maine STP, Personal Communication.
24. Segall, B. A., University of Lowell, Personal Communication.
25. Carroll, R. G., "Planning Guidelines for Sanitary Waste Facilities,"
Report to U.S.D.A. Forest Service, California Region, Ch7M/Hill,
January 1972.
26. Tilsworth, T., "The Characteristics and Ultimate Disposal of Waste
Septic Tank Sludge," Report No. 1WR-56, Institute of Water Resources,
University of Alaska, Fairbanks, November 1974.
27. Bender, J. H., Monthly Report, EPA Lebanon Pilot Plant, March/April 1976.
28. Lessaman, W. G., Laboratory Director, City of Tallahassee Wastewater
Treatment Plant, Personal Communication.
49
-------
29. Kolega, J.J. Dewey, A.W., Shu, C.S., "Streamline Septage Receiving
Stations," Water and Wastes Engineering, July 1971.
30. Smith, S.A., Wilson, J.C., "Trucked Wastes: More Uniform Approach
Needed" Water and Wastes Engineering, March 1973.
31. Cooper, I.A., Memorandum: Meeting in Ithaca, New York with William
Jewell, March 22, 1976. In Monthly Progress Report #7, EPA Contract
No. 68-03-2231.
32. Crowe, T.L., "Dewatering of Septage by Vacuum Filtration," M.S. Thesis,
Clarkson College of Technology, August 1975.
33. Metcalf and Eddy, Wastewater Engineering, McGraw-Hill, New York, 1972.
34. Pipes, W.O., "Bulking of Activated Sludge," Advances in Applied
Microbiology, 9: 185-232, 1967.
35. EPA, OWP, "Municipal Waste Facilities Inventory - Summary Table,"
STORET System, April 1976.
36. Howley, J.B., "Biological Treatment of Septic Tank Sludge," M.S. Thesis,
University of Vermont, October 1973.
37. Rotondo, V.J., '"Honey Wagon' Sludge Disposal," Water Works and Wastes
Engineering, August 1964.
38. Suffolk County Department of Environmental Control, "Scavenger Waste
Treatment and Disposal, Suffolk County Sewer District No. 1, Port
Jefferson and Adjacent Areas," December 1976.
39. Life Sciences and Agriculture Experiment Station and Cooperative
Extension Service, University of Maine, and Maine Soil and Water
Conservation Commission, "Maine Guidelines for Septic Tank Sludge
Disposal on the Land," Misc. Report 155, April 1974.
40. Whitman and Howard, Inc., "A Study of Waste Septic Tank Sludge Disposal
in Massachusetts," report to the Division of Water Pollution Control,
Commonwealth of Massachusetts, December 1976.
41. Perrin, D.R., "Physical and Chemical Treatment of Septic Tank Sludge,"
M.S. Thesis, University of Vermont, February 1974.
42. Weber, W.J., Physicochemical Processes for Water Quality Control,
Wiley-Interscience, New York 1972.
43. Heidman, J.A., "Pilot Plant Evaluation of Alternative Activated Sludge
Systems," EPA, Environmental Protection Technology Series, 1977, in
press.
50
-------
44. "Process Design Manual-Wastewater Treatment for Small Municipalities,"
prepared for EPA, Office of Technology Transfer by Camp, Dresser §
McKee, Inc., EPA-625/1-77-008, February 1977, DRAFT.
45. Salvador, M.E., O'Brien, J., "Importance of Bicarbonate Alkalinity in
Extended Aeration Plants," Deeds and Data, JWPCF, vol. 49, No. 2,
February 1977.
46. Bisogni, J.J., Lawrence, A.W., "Relationships between Biological Solids
Retention Time and Settling Characteristics of Activated Sludge,"
Water Research 5:755, 1971.
47. Guttenplan, S.D., "The Establishment of a Septage Receiving and Handling
Program for the Town of Barnstable, Massachusetts," Appendix E in "A
Study of Waste Septic Tank Sludge Disposal in Massachusetts," Whitman
and Howard, Inc., December 1976.
48. "Design Guides for Biological Wastewater Treatment Processes," prepared
for the U.S. EPA by the City of Austin, Texas and the Center for
Research in Water Resources, University of Texas; EPA Water Pollution
Control Research Series, 11010 ESQ 08/71, 1971.
49. Askew, M.W., "High-Rate Biofiltration: Past and Future," Water Pollution
Control, Vol. 69, No. 4, p. 445, 1970.
50. Bruce, A.M., Merkens, J.C., MacMillan, S.C., "Research Development in
High-Rate Biological Filtration," The Institute of Public Health
Engineers Journal, July 1970. "
51
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OVERLAND FLOW OF OXIDATION POND EFFLUENT
AT DAVIS, CALIFORNIA
by
Sch
and R.J . Stenquist^
D.L. Tucker,1 E.D. Schroeder,2 D.B. Pelz,3
prepared for the
Environmental Protection Agency
Technology Transfer Program
Project Engineer, Brown and Caldwell, Walnut Creek, California
Chairperson, Department of Civil Engineering, University of California, Davis,
California
Director of Public Works, City of Davis, California
it
Project Engineer, Brown and Caldwell, Walnut Creek, California
-------
OVERLAND FLOW OF OXIDATION POND EFFLUENT
AT DAVIS, CALIFORNIA
Oxidation ponds are one of the most commonly employed secondary wastewater
treatment systems in the United States for systems with average dry weather flows of
approximately 0.2 cu m/sec (5 mgd) and less. Oxidation pond systems are generally
easy and inexpensive to operate and maintain but require larger land areas than
conventional systems . Thus, they are cost-effective for smaller communities where
land is usually less costly than in urban areas.
Oxidation ponds are an effective method of waste stabilization except for the
large concentrations of algae carryover in the effluent. This algae is the source of
high suspended solids measurements, and decomposition results in oxygen demand
in the receiving waters. The EPA definition of secondary treatment requires a
30-day average value of 30 mg/1 or less for suspended solids and BOD^. A process
for algae removal will enable oxidation pond systems to meet secondary treatment
requirements.
This paper reviews the analysis of algae re .oval alternatives examined for Davis,
California, and describes pilot studies of overland flow as a new approach to algae
removal. The pilot study was a crucial part of the selection process leading to
recommendation of an alternative.
BACKGROUND
The original sewerage system in Davis discharged effluent, after treatment in an
Imhoff tank and rock filter, to the old Putah Creek channel approximately 600 m (2,000
ft) south of the city. In 1950 trunk sewers and pumping stations were constructed
and a new plant was constructed about three kilometers (two miles) north of Davis.
This plant had primary facilities for domestic flow with a capacity of 0.048 cu m/sec
(1.1 mgd) and a total of approximately nine hectares (22 acres) of oxidation ponds.
The primary facilities consisted of preaeration and sedimentation tanks, a sludge
digester and digested sludge drying beds .
In 1958 separate industrial waste treatment facilities were constructed at this
same location to handle tomato and peach processing wastes generated by a local
cannery, Hunt-Wesson. These facilities included a 0.6-m (24-in.) industrial waste
sewer from the cannery to the treatment plant, a separate industrial waste pumping
station, and 50 hectares (122 acres) of waste stabilization ponds.
A 1961 survey of the sewerage system by Brown and Caldwell indicated that
the domestic wastewater treatment facilities had reached capacity. In addition to
a series of trunk sewer system improvements, a staged expansion of the treatment
plant was recommended. However, these improvements were not undertaken.
In 1968 a new sewerage study was prepared by Brown and Caldwell for the City
of Davis.2 In the interim period, both the domestic facilities and the cannery stabi-
lization ponds of the existing 77-hectare (186-acre) site had become significantly
overloaded. Because of disadvantages of the existing site and the inability to
-------
incorporate existing facilities in alternative treatment plans, the 1968 report recom-
mended a site about eight kilometers (five miles) northeast of downtown Davis.
At the time of the 1968 study, consideration was being given to consolidation of
sewerage from the El Macero District, located to the southeast, with that of Davis.
Analysis indicated that it would be less costly for both Davis and El Macero to treat
their combined flow at this eastern site.
Soon after the 1968 report was issued, the only major industrial contributor,
Hunt's Cannery, elected to provide their own separate treatment facilities near the
location of the recommended site for the Davis facility. The new Hunt's facility
provides screening of raw wastewater at the cannery. Screened waste is conveyed
to a 91-hectare (220-acre) overland flow site and applied directly through 1.6 cm
(5/8-in.) spray irrigation nozzles . Overland flow effluent from the Hunt's facilities
is collected in open ditches at the bottom of terraces and discharged to the Willow
Slough Bypass. This facility operates about four months per year. Well water is
used for irrigation in other months to maintain the grass. The Hunt's facility has
experienced difficulty in meeting effluent limitations during the initial part of their
yearly operation because of inherent start-up problems in the overland flow scheme.
Design data for the present Davis treatment plant, completed in 1974, are given
in Table 1 and the plant layout is shown in Figure 1. The plant was constructed to
accommodate a population of 45,000 with an initial average dry weather flow of
0.22 cu m/sec (5 mgd) and a maximum dry weather flow of 0.44 cu m/sec (10 mgd) .
The plant is designed for a peak wet weather flow of 0.88 cu m/sec (20 mgd) .
Provision was envisioned during the 1970 design studies for the site to be able to
eventually accommodate a design population of 240,000 by replacing the oxidation
ponds with an activated sludge secondary treatment facility.
The initial treatment facilities include coarse screening, prechlorination, influent
pumping, comminution, preaeration and grit removal and primary sedimentation.
Secondary treatment is provided by three oxidation ponds operated in parallel. Final
effluent disposal is through an outfall to Willow Slough Bypass after the oxidation
pond effluent is chlorinated. Sludge digestion, with dewatering and disposal in
holding basins, is provided for sludge from the primary sedimentation basins.
Pumping units are provided for effluent pumping during extreme flooding in Willow
Slough Bypass, and postchlorination facilities are available if required.
The three-pond system of 50 hectares (120 acres) includes circulation channels
to provide for load distribution as well as initial mixing. Return flow through the ponds
of up to six times the influent volume can be attained. With the influent discharged
to the channel ahead of the recirculation pumps, intimate mixing is immediately
achieved. Both pond inlets from the channel and outlets to the channel are through
grated culvert type ports operating partly full so that scum does not accumulate.
Outlet ports are downwind so that scum is effectively prevented from forming on the
pond and any that does form is redispersed in the circulating water by the pumps.
Provision is made so that effluent can be discharged either from the return channel
or from the final pond if the ponds are operated in series. The ponds provide a
minimum of 39 days detention for design flow conditions.
Water level in the ponds is controlled by a weir in the plant effluent control
structure. Effluent spills over the weir and drops about eight feet where it
discharges through the outfall to Willow Slough Bypass. Discharging in this
-------
Table 1. Design Data for Existing Facilities
Design Factor
Design Flow
Average dry weather, myd
Maximum dry weather, mgd
Peak wet wather, mgd
Design Loadings
Design population, thousands
Biochemical oxygen demand, 10UO Ib/day
Suspended solids, 1000 Ib/day
Raw Sewage Pumps
Number
Capacity, each, mgd
Total dynamic head, PWWF, feet
Rated horsepower per unit
Raw Sewage Screening Equipment
Comminutors, number
Channel width, feet
Aerated Grit Tanks (preaeratlon tanks)
Number
Detention time at avg. dry weather flow, hrs
Air supplied, cfm to tanks
Air supplied, cfm to channels
Chlorlnators
Number
Capacity, each, Ib/day
Plant Outfall Sewer
Number
Size, Inch diameter
Emergency Generator
Number
Generator rating, kw
Engine horsepower
Sludge Digestion Facilities
Digesters
Number
Total volume, 1000 cu ft
Loading, 1000 Ibs dry solids per day
Detention at 4 percent solids, day
Gas produced, 1000 cu ft per day
Assumed solids reduction, percent
Digested sludge, 1000 Ibs dry
solids/day
Value
5
10
20
45
ay 11
11
2
20
40
200
2
4
1
v, hrs 0.48
300
360
2
2000
1
60
1
300
335
1
78.5
7.15
27
45
40
4.3
Design Factor
Sludge Holding Basins
Number
Net area , acres
Total volume, 10 ft depth, mil cu ft
Solids loading
Million Ib per year
Lb per cu ft
Capacity, solids, mil Ib
Primary Sedimentation Tanks
Number
Detention time at avg dry weather flow, hrs
Overflow rate at avg dry weather flow, gal/sq ft/day
Mean forward velocity, fpm
Maximum hydraulic capacity, mgd
Raw sludge pumps, number
Scum ejectors, number
Assumed Primary Treatment Efficiency
BOD removal, percent
Suspended solids removal, percent
Oxidation Ponds
Number
Total area , acres
Average depth, feet
Total volume, mil gal
Detention at avg dry weather flow, days
Pond Circulation Pumps
Number
Capacity, each, mgd
Total dynamic head, feet
Rated horsepower per unit
Chlorine Contact Tank
Total volume, 1000 cu ft
Contact time at avg dry weather flow, minutes
Value
2
2
0.85
1.55
18.5
15
2
1.5
1,060
1.36
10
2
1
35
65
3
120
5
196
39
2
15
3.5
15
9
20
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OXIDATIO^ POND
No I
TOPlNORTH LEVEE -PLANT ACCESS RU
1 SEE DETAIL A/SIS
Figure 1 Layout of Existing Davis Treatment Plant
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manner is intended to aid photosynthesis in the ponds and to maintain a near-
saturation DO in the effluent at all times. The effluent flows east in Willow Slough
Bypass a distance of about two miles to Yolo Bypass. The Willow Slough Bypass
does not receive flow from Willow Slough during dry weather. It is a shallow
ditch during dry weather receiving some agricultural runoff. Dissolved oxygen
downstream from the Davis discharges is generally not depleted but tends to remain
at near-saturation levels. The waste discharge requirements in effect at the time of
the existing treatment facilities design were adopted by the Central Valley Regional
Water Quality Control Board on December 1, 1969, by Resolution No. 70-104. The
applicable provisions include a receiving water limitation stating that discharge
shall not depress dissolved oxygen content of Yolo Bypass waters below 5 mg/1 at
any time.
The federal definition of secondary treatment was taken into consideration by the
Regional Board in establishing 1977 discharge requirements for Davis. The require-
ments include a limitation of BODg and suspended solids to a 30-day average of 30 mg/1.
The 30-day median total coliform organism concentration is limited to 23 MPN/100 ml.
Average daily dry weather discharge is limited to 18,700 cu m (five million gallons)
and pH must be between 6.5 and 8.5. Davis is required to limit mineralization to no
more than a reasonable increment and not to cause dissolved oxygen concentration in
Willow Slough Bypass to fall below 5.0 mg/1.
In 1975 the Davis pond effluent average suspended solids concentration was
74 mg/1. The average for the highest month (April) was 93 mg/1 and the low monthly
average (December) was 56 mg/1. Because a significant portion of the effluent BODg
from oxidation ponds is made up of biodegradable cell solids, the effluent BODg values
during 1975 were high, although they were still generally below the 30-mg/l level.
Average BOD5 for the maximum month was 27 mg/1. Average 1975 8005 was 19 mg/1
for the pond effluent.
For analysis of alternatives to meet the new discharge requirements, estimates of
primary treatment efficiency were based on the design assumptions for the existing
facilities, as developed in the 1970 design study. Estimated primary BODs removal
efficiency is 35 percent. Estimated primary suspended solids removal efficiency is
65 percent. For design conditions, the average peak month outflow at the Davis
facilities is estimated to be 0.21 cu m/sec (4.75 mgd), taking into consideration
oxidation pond evaporation. Under present conditions of an average dry weather
inflow of 0.12 cu m/sec (2.73 mgd), oxidation pond evaporation during much of the
late summer and fall allows zero discharge. At design inflow conditions, discharge
would occur year-round.
An operations staff of eight people is located at the treatment plant. All waste-
water management functions are the responsibility of the director of public works.
Total operation and maintenance cost for the 1975/76 fiscal year was $342,300, which
included costs for the collection system, treatment facilities, and general administra-
tion . Based on an average flow of 0.12 cu m/sec (2.73 mgd), this is a cost of 9.0 cents/
cu m (34 cents/1000 gallons). For the treatment facilities only, average operation and
maintenance cost for the 1975/76 fiscal year was 5.8 cents/cu m (22 cents/1000 gallons).
-------
ALTERNATIVES FOR IMPROVED TREATMENT
The principal objective of the planned facilities improvement at Davis is to provide
treatment which will produce an effluent suspended solids levels which meets the new
discharge requirements . Alternatives were considered under several categories
including replacement of existing treatment processes and additions to the existing
system.
Alternatives considered for implementation at Davis were compared in several
ways. A principal consideration was cost-effectiveness, which includes a monetary
cost analysis and an environmental and social impact analysis. Other important
factors may also affect an alternative's suitability. Two important categories of
criteria are "engineering effectiveness" and "conformance with identified constraints."
Engineering effectiveness concerns the ability of an alternative to perform as
planned and to be free of mechanical breakdowns. Identified constraints include
relevant local, state, and federal laws; administrative guidelines and regulations;
and the opinions and goals of the affected community.
Preliminary estimates of construction costs for the alternatives were developed
principally from the experience of Brown and Caldwell in designing similar facilities.
Supplemental cost information on overland flow and intermittent sand filtration was
taken, respectively, from "Costs of Wastewater Treatment by Land Application,1^
and "Intermittent Sand Filtration to Upgrade Existing Wastewater Treatment
Facilities."4
Construction cost estimates used in the Davis analysis were based on an ENR
Construction Cost Index of 3200, a value expected to be applicable in September,
1977 and which is equal to 97 percent of the San Francisco ENR Index projected for
September, 1977. Cost data given herein can be related to current price levels at
any time by applying the ratio of the ENR Index prevailing at the time to 3200.
A contingency allowance was also made for uncertainties unavoidably associated
with preliminary designs. Such factors as changes in design criteria, necessity for
special construction methods, or unusual foundation conditions may increase
construction costs, and some allowance must be made in preliminary design
estimates. The allowances used for construction contingencies and engineering
together were 30 percent of the basic construction cost for categories A and C
(described below), and 35 percent for category B alternatives, because less historic
cost data was available.
Annual operation and maintenance includes all costs for labor, power, chemical
supplies, laboratory control and monitoring, administration, and incidental costs
chargeable to various components of the system improvements. Estimates of annual
labor requirements for the various alternatives were based primarily on the
experience of Brown and Caldwell, with some information for the overland flow
alternatives taken from "Costs of Wastewater Treatment by Land Application." It
was assumed that the effective annual labor contribution of one man is 1,450 hr, or
6.5 hr per day, with 38 days off for vacation, sick leave, and holidays. The annual
cost of one employee was taken as $16,000 per year, including fringe benefits and
overhead. Electrical power costs were taken as $0.02 per kwh. Chemical costs
were based on current estimates escalated to projected 1978 values.
-------
The feasible alternatives considered for the Davis analysis fall into three main
categories The substitution of conventional secondary treatment processes was
considered under theiirst (category A) . The second category (B) considered addi-
tional treatment to polish oxidation pond effluent. Land disposal was considered as a
third category (C) . Ti, remainder of this paper is divided into sections dealing with
each category and a coi;.;luding section summarizing the comparison of alternatives.
Secondary Ti >,. itmeni Replacement
Under the iiist set of alternatives (category A) , abandoning the ponds and
substituting a new secondary treatment process, fall those solutions which can be
classified as "ticididonai" or "standard" approaches to wastewater treatment. These
are secondary biological treatment processes which usually follow primary sedi-
mentation; the present primary sedimentation tanks at Davis would be retained for
use in the treatment scheme. To fully meet all the discharge requirements at Davis,
chlorine disinfection and dechlorination for toxicity removal would follow the
biological treatment process. An important characteristic of these processes is
that most of them produce an additonal quantity of wastewater solids which must be
treated and disposed of. Solids removed in the primary sedimentation tanks at
Davis are presently treated by anaerobic digestion and then stored in sludge lagoons
before final disposal to land. Because present solids loadings at Davis are lower
than anticipated at the timo? of design, it is believed that the increased solids
prodiu.tix'j resulting from the addition of a biological treatment process could be
accnmr.v-dated by the existing digester. However, to provide for the slightly
increased solids loading, a third sludge lagoon would be added.
'Three alternatives were considered under category A. These were the conven-
tional activated sludge process, trickling filtration, and the extended aeration varia-
tion of the activated sludge process. Because a portion of the existing ponds could
be used for aeration basins, and because the extended aeration process produces a
very small quantity of biological solids, it was initially believed that this alternative
would show up well in the comparison.
Alternative A-lj_ /* ctivated Sludge. The analysis was based on an aeration
tank volume of 3,220 cu m (115,000 cu ft) which would provide a volumetric loading
of 0.64 kg SOD5/CU m/day (40 lb/1,000 cu ft per day) and an organic loading of
0,5 kg BODs/kg MLVSS per day at an MLSS concentration of 1,500 mg/1. Use of a
portion of the existing oxidation ponds for emergency and peak wet weather flow
storage would allow use of a single two-pass aeration tank and a single secondary
claiifier with an ADWF overflow rate of 21.4 cu m/day/sq m (525 gpd per sq ft) .
Avoiding duplicate, parallel units would reduce the costs for this portion of the
plant. It is anticipated that the storage basins could be used whenever the plant
flow exceeds 0.44 cu m/sec (10 mgd) or whenever a portion of the secondary
treatment process must be shut down.
A third sludge lagoon would be required in order to receive the increased
quantity of digested sludge. Capital and operating costs would be reduced sub-
stantially by avoiding construction of a second digester.
Estimated capital costs for Alternative A-l were $3.54 million. The capital cost
for the activated sludge process was the highest of the seven alternative . Additional
operation and maintenance (above that required for the existing plant) cost was
estimated at $172,000 per year.
-------
Alternative A-2: Trickling Filtration. The trickling filter system would replace
the oxidation ponds as the secondary treatment step and would consist of a trickling
filter and clarifier with clarifier underflow pumped to the digester. The existing
oxidation ponds would be retained to provide wet weather peak flow and emergency
storage of primary effluent. A plastic media trickling filter, sized for the average
design flow rate of 5 mgd with a 1: 1 recirculation, would be designed for an organic
loading rate of 1.0 kg BOD5/cu m/day (60 Ib per 1,000 cu ft per day) . The filter
would require a media volume of 3,640 cu m (130,000 cu ft); cost analysis was
based on a center shaft rotating distributor system.
The clarifier would be si zed for an average flow of 0.22 cu m/sec (5 mgd) , with
an average overflow rate of 40.7 cu m/day/sq m (1,000 gpd per sq ft). Capital
costs for the trickling filtration alternative were estimated at $2.91 million. Addi-
tional operation and maintenance costs were estimated at $90,000 per year.
Alternative A-3: Extended Aeration (Pond Modification-Aerated Lagoons) .
Oxidation pond No. 1 would be modified to contain three extended aeration basins.
The mid-depth area of each basin would be 3,260 sq m (35,000 sq ft) in order to
provide a total volume of 23,400 cu m (835,000 cu ft) . Aeration basins would be
situated in the oxidation pond so as to utilize a portion of the existing pond levee.
A portion of oxidation pond No. 1 would be used as a storage basin to regulate
peak wet weather flows and to provide emergency storage. Activated sludge would
be returned from the clarifier to the aeration basins to maintain desired mixed liquor
suspended solids concentration. Aeration and mixing in the ponds would be pro-
vided by floating surface aerators anchored to concrete pads in the basins. The
analysis was based on the assumption of a clarifier designed for an average flow of
0.22 cu m/sec (5 mgd) , with a peak overflow rate of 60 cu m/day/sq m (1,400 gpd
per sq ft) at 0.44 cu m/sec (10 mgd) . Because solids production from the extended
aeration process is low, additional anaerobic digestion capacity would not be pro-
vided. Sludge lagoon capacity would be increased to receive increased loadings.
Capital costs for Alternative A-3 were estimated at $2.38 million. Operation
and maintenance costs were estimated at $170,000 per year. An important component
of operating costs is for power to operate the mechanical aerators. In addition
to power for oxygenation, sufficient energy must be expended to prevent particles
from settling in the relatively large basins. This added requirement increases
power costs considerably.
Analysis. The category A alternatives would generally involve construction
within the boundaries of the existing treatment plant site, so that environmental
impact is localized. The major environmental impact of the alternatives in the A
category was a potential negative impact resulting from the reduction in a valuable
waterfowl sanctuary created by the oxidation ponds. Maintenance of pond capacity
for storm flows was a potential mitigating measure for winter conditions, but the
ponds might have had to be drained in the summer to prevent conditions conducive
to wild fowl botulism. These alternatives would have continued to support wildlife
habitat in Willow Slough Bypass through continued discharge to the bypass.
In terms of reliability to perform as planned, the group A alternatives were
rated highest. The activated sludge process, trickling filtration, and extended
aeration in aerated lagoons are all well-known conventional treatment processes for
which design criteria and operating procedures are well-established. They can be
expected to consistently meet the discharge requirements at Davis.
-------
The most likely future change in surface discharge requirements is the imposi-
tion of a requirement calling for nitrogen removal. This would occur if future studies
indicate that water quality in the Delta-Suisun Bay area is being impaired by high
nitrogen levels and that improvements would result from limiting municipal nitrogen
discharges. Although such a change may occur, it was considered improbable at
the time that the alternative analysis was undertaken.
Of the three group A alternatives, extended aeration/aerated lagoons (A-3) is
the one which can accommodate nitrogen removal with the least modification. Because
the extended aeration process normally produces a nitrified effluent (nitrogen in the
nitrate form) , only a denitrification step (conversion of nitrate to nitrogen gas) need
be added. For the activated sludge and trickling filtration alternatives, a nitrifica-
tion step (conversion of ammonia to nitrate) preceding denitrification would also need
to be added.
Upgrading of Oxidation Pond Effluent
The second set of alternatives (category B) considered for Davis involves the
reduction of the suspended solids level of the oxidation pond effluent. Most oxidation
ponds have difficulty meeting the 30~mg/l, 30-day average suspended solids require-
ment because of the presence of algal cells . Many techniques for algae removal have
been proposed. None has a long history of full-scale application, and some are still
in the early stages of experimental investigation and development. Nonetheless, in
situations where these techniques can be used effectively to reduce suspended solids
levels, their capital and operating costs may be significantly lower than for conven-
tional processes.
In category B, three processes were chosen for analysis: coagulation-flocculation-
sedimentation, overland flow, and intermittent sand filtration. Several additional
processes were evaluated before final selection of these three alternatives for
detailed analysis. An example was coagulation-dissolved air flotation. This is
similar in concept to coagulation-flocculation-sedimentation, except that finely
dispersed air bubbles are used to raise the algae-chemical floe to the water surface,
from where it is removed by skimming. Dissolved air flotation usually involves
lower capital costs because of shorter detention times and the resulting smaller
tanks. Because complicated air dissolution equipment is required, however, opera-
tion is more difficult, and this makes air flotation less suitable than sedimentation
for use in small and medium size communities. The high chemical costs associated
with coagulation-flocculation-sedimentation are also present with dissolved air
flotation, making total operation and maintenance costs for this process very high.
Other algae removal processes which have not been studied sufficiently or which
have proved unsatisfactory are submerged rock filtration, centrifugation, and
microstraining. in-pond removal systems which have been studied include series
pond arrangements, series ponds with intermediate chlorination, intermittent
discharge lagoons with chemical addition, and aquaculture, which is the use of an
ecological food chain that produces a useful product in the form of fish as opposed
to a material requiring further disposal. These in-pond systems also have not
been developed sir'' .cijntly or suffer from some dcf-jct in their operation which
would preclude their use at Davis .
Maximum performance and operational ease can be expected from algae removal
processes if influent (pond effluent) algae concentrations are minimized. The
-------
original plant design allowed simple conversion from parallel to series operation of
the oxidation ponds. Series arrangement of the ponds minimizes short-circuiting,
and provides about as good a prototype situation for minimizing effluent suspended
solids as can be expected.
Over the two-month period of the pilot study (9/9/75 to 11/7/75) discussed in
the overland flow section, conversion was made to series operation. However, no
evidence of significant autoflocculation was found. In addition, there was not a
significant difference in the suspended solids concentrations of the three ponds.
The conclusion reached was that autoflocculation would not be a viable process,
and that there was no advantage to other (tertiary) treatment processes in using
the ponds in series.
Alternative B-l: Coagulation-Flocculation-Sedimentation. In order to reduce
the size of the sedimentation tank required for the coagulation-clarification alterna-
tive, it was assumed that tube settlers would be utilized which allow a detention
time of one hour to be used in design. This reduces capital costs significantly.
Alum (A^ (804)0 ' 14H2O) would be used as the coagulant chemical. Adjust-
ment of pH through the addition of sulfuric acid (H2SO4) would be used to maximize
alum-algae floe precipitation. Conclusions reached from jar tests conducted in the
spring of 1976 were that an alum dose of approximately 125 mg/1, with acid addition
of 5 meq/1, would produce the greatest effuent clarity.
Main components of this system would be an influent pumping station, alum and
acid storage facilities, a flash mix unit for the addition of alum, flocculation com-
partments with a detention time of 20 min at design flow, and tube settling basin
with a detention time of 60 min. Chlorine disinfection in the existing facility and
dechlorination with sulfur dioxide would follow the coagulation-clarification process .
Sludge produced by the process would be returned to the oxidation ponds. It
is anticipated this would be the most cost-effective solids disposal method. Steps
would have to be taken to prevent autoflotation and to ensure that the sludge is
distributed fairly evenly throughout the pond area. Otherwise, no serious
operational problems would be anticipated.
Capital and annual operating costs were estimated at $1.51 million and $278,000
per year, respectively. A major fraction of the operating costs would be for
chemicals.
Alternative B-2: Overland Flow. For the overland flow alternative, approxi-
materly 83 hectares (200 acres) of land would be required. There are several
tenative sites close to the treatment plant. The 83 hectares (200 acres) include a
net application area of 66 hectares (158 acres) based on a loading rate of 2,700 cu
m/hectare/day (30,000 gallons per acre per day or gpad) plus additional land to
provide for roads, hay drying and buffer zones. A preliminary layout developed
for the most likely site would have 14 terraces 44 m (145 ft) wide by 1,070 m
(3,500 ft) long . The slope of each terrace would be 2 .5 percent. Seven maintenance
roads and eight drainage ditches would be included in the layout, with connecting
roads at each end and a main drainage ditch at the southern end. Orientation of the
terraces in a north-south direction would prevent the prevailing north wind from
blowing spray across the roads .
10
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The collection sump would be located at the southwest corner of the plot to
receive runoff prior to its discharge to Willow Slough Bypass. Provision would
be made to pump runoff back to the oxidation ponds when discharge requirements
were not being met. This could occur during start-up following grass harvest.
Costs were based on the assumption that oxidation pond effluent would be sprayed
through nozzles from a fixed sprinkler system located along a line near the top of
each terrace. Sprinkler spacings of 24 m (80 ft) with discharge pressures of
400,000 to 550,000 Pa (60 to 80 psi) and nozzle flows of 0.0025 cu m/sec (40 gpm)
would be typical operating parameters. This would allow for four hours operation
per sprinkler each day under design conditions of an application rate of 2,700 cu
m/hectare/day (30,000 gad), with the entire system designed to operate over a
24-hr period. A spray radius for the 180 degree nozzles of 152m (50ft) would
allow overlap and maximum terrace coverage. As a result of the analysis discussed
in this paper, overland flow was selected as the recommended project for meeting
the new requirements at Davis. When this project reaches the design stage, alter-
native delivery systems will be considered in more detail. The appendix to the
Davis project report contains a discussion by Donald M. Parmalee and Vaughan
Sparham of surface delivery systems for overland flow treatment based on experi-
ence in Australia and England.^ This experience will be taken into consideration
in optimizing the delivery system design.
Care in design and operation of the overland flow system will be required to
minimize conditions allowing mosquito propagation. For example, a thorough
dryout will be required prior to harvesting in order to prevent equipment ruts
which may become small breeding pools. Gambusia (mosquito fish) would be
planted in the runoff collection channels.
Costs for the overland flow alternative are presented in Table 2. Total costs
for this alternative were the lowest of the seven studied in detail.
Pilot Studies - As part of the concept development for improving wastewater
treatment at Davis, pilot studies of the overland flow process were undertaken.
The overland flow studies began one month after seeding of test plots located at
the Davis treatment plant. Data collection began on November 11, 1975, and
continued through March 27, 1976. The purpose of running the experiments during
the winter months was to develop data for the period of the year with the worst
operating conditions (maximum flow, lowest temperatures, and greatest precipita-
tion); for all practical purposes it does not rain in Davis during late spring to
early fall. Unfortunately, the year was a record drought and no effects of
precipitation were developed. This may be a reason for conservatism in scaling
up pilot data for design. Consideration of use of the ponds as temporary storage
tanks may eliminate the need for oversizing the system, however.
Three test plots, each 15 m (50 ft) wide and 31 m (100 ft) long with a 0.61-m
(2-ft) drop were constructed for the overland flow studies . Preparation of the plots
included grading, rototilling, flooding with digester supernatant and seeding with
annual rye grass. Annual rye grass was chosen because of the speed of germination
since plots were not seeded until late, October 1, 1975. Supernatant application
was not uniform, and the grass development was both faster and better on plots 1,
and 2 than on plot 3. Hiring the fiv° months of annhnna rwMstion nnnri <=ff!uont t^
the plots the grass grew continually, eventually reaching a height of 25 to 30 cm
(10 to 12 in.) .
11
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Table 2. Estimated Capital and Operating
Costs: Overland Flow
Alternative
Item
Capital costs3
Gravity Line to Sump
Distribution and Runoff
Collection Sump
Terrace Construction
Distribution System
Distribution Pumping
Runoff Collection
Electrical
Service Roads
Fencing
Subtotal
Engineering and
contingencies, 35%
Land (200 acres @
$l,800/acre)
Total capital cost
Operation and maintenance
costs"
Labor
Materials
Power
Total operation and
maintenance costs
Cost
$ 55,000
45,000
250,000
290,000
290,000
30,000
45,000
70,000
120,000
$1,195,000
420,000
360,000
$1,975,000
$ 48,000
per year
10,000
30,000
$ 88,000
per year
ENR Index = 3200
For additional facilities only
12
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Pond effluent was supplied from the chlorination basin effluent line at a nominal
pressure of 550,000 Pa (80 psig) . A separate pressure regulator and solenoid
valve was used to control the application rate to each plot. Five shrub type (two 90-
degree and three 180-degree) spray nozzles were installed on 0.6-m (24-in.) risers
at each plot. Initially the sprays were located on the uppet edg ^ of the plots, but
were later moved about three meters (10 ft) from the edge because a considerable
amount of spray was being blown behind the plots. Windy days are common in
Davis with the most common wind direction being from the north. On some days
most of the spray was directed off the plots. During these same periods dust was
blown off of the access road running below the plots into the sample containers.
This factor accounted for several very high suspended solids readings during
December, January, and February.
Although the spray heads were designed for use with tap water, very few
plugging problems occurred. Those problems that did occur were easily and
quickly handled.
From November 7 to February 7 the loading rates and application times were as
listed in Table 3. After the first week in February the loading times, and consequently
the hydraulic loading rates, were increased on plots 2 and 3. This change was in
part because of a desire to determine the effects of higher loading rates and in
part because of the lack of rainfall. Some method of estimating the probable
effect of rain was needed. Considerable difficulty accompanied this change because
of the coincidental plugging of the pressure regulators of plots 2 and 3. Although
the application periods were increased during this period the pressures were
greatly reduced. This situation was not fully corrected until February 27th.
Application rates for the period February 27th to March 28th are given in Table 4.
Plot effluent characteristics are summarized on a monthly basis in Figures 2
and 3. The monthly averages are useful in noting how the effluent quality changed
with season and with some of the operating parameter changes. Requirements set
on the discharge by the Regional Board are based on running 7~ and 30-day
averages, however. These values were calculated in the pilot study.
Several samples exceeded the 90-mg/l maximum set by the Regional Board. All
of these samples were taken on extremely windy days. In several cases it was noted
on the raw data sheet that there was considerable silt in the sample. Finally, if the
true suspended solids reading were high the BODs value should be correspondingly
high. This was not the case. It can therefore be concluded that wind-blown dust
was the cause of these extremely high suspended solids readings.
Limited nitrogen data was developed in the study. Some nitrogen was taken up
by the grass, but there is no clear evidence of the quantity. Because the 1977 dis-
charge requirements do not include any nitrogen limitation, it was decided to defer
those studies until such time as a limitation was imposed. Then, studies for optimum
nitrogen removal could be conducted using the full-scale system.
From the pilot studies, it was concluded that:
1. Loading rates up to 290 cu m/hectare/day (32,000 gal/acre/day) (3.00 cm/
day or 1.18 in./day) are suitable for process design. The data from
the pilot studies appear to be good, and support the above value for
design use.
13
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Tables. Pilot Study Application Kates, 11/7/75 through 2/7/76
Plot
Time of Application, hrs.
morning
afternoon
Application Rate
gal/acre/hr
Average Daily Flow
gal/acre day*3
in/da yc
1
3
3
3476
20,856
0.77
2
2
2
3350
13,400
0.49
3
1
1
3716
7430
0.27
gal/acre/hr x 0.0091 = cu m/hectare/hr
gal/acre/day x 0.0091 = cu m/hectare/day
»
'in/day x 2.54 = cm/day
Table 4. Pilot Study Application Rates, 2/27/76 through 3/28/76
Plot
Time of Application, hrs.
morning
afternoon
Application Rate
gal/acre/hr
Average Daily Flow
gal/acre/day
in/da yc
1
3
3
5530
32,000
1.18
2
4
4
5500
44,000
1.62
3
12
4630
56,000
2.07
gal/acre/hr x 0.0091 = cu m/hectare /hr
5ga I/a ere/day x 0.0091 = cu m/hectare/day
»
"in/day x 2. 54 = cm/day
14
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KEY
* Plot 1
« Plot 2
A Plot 3
50
en
9
.J
O
CO
Q
m
Ul
o_
CO
30
20
10
0
A
NOV
DEC
JAN
FEB
MAR
Figure 2 Effluent Suspended Solids Concentrations from Study Plots
50
40
30
o"
O
03
10
0
NOV
A
1
DEC
JAN
FEB
MAR
Figure 3 Effluent BOD Concentrations from Study Plots
15
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2. Loading rates studies above 290 cu m/hectare/day (32,000 gal/acre/day)
resulting in effluent quality very close to the minimum required. Using
these values would leave little margin (perhaps none) for natural process
variation.
3. Rye grass would be a suitable cover for prototype land treatment systems.
This conclusion was based upon the observations made in this study and
those reported in the literature.6
4. Application times up to 12 hours per day resulted in excellent grass growth.
Twelve hours was the maximum application period and it is not known if
longer periods would be satisfactory also.
5. Meeting BODg requirements with an overland flow treatment process de-
signed for suspended solids removal will not be a problem.
6. Chlorinated effluent will not damage the grass .
7. Data developed in the study provide conservative estimates of prototype
operation. As the grass root zone develops, effluent quality may continue
to improve and stabilize.
8. The fact that grass grows well in Davis during many winters may provide
a method of year-round nutrient removal from wastewater. Additional
studies need to be made year-round to determine the extent of possible
nutrient removal.
9. The effect of precipitation on the effectiveness of a prototype process
could not be predicted from the results of the study because there was
almost no precipitation during the study period. The response of the
plots to very large increases in loading during March was sluggish. This
leads to the conclusion that precipitation will not dramatically affect.
effluent quality from the prototype system unless the storm is very
intense.
Alternative B-3: Intermittent Sand Filtration. For the intermittent sand filter
alternative, a design application rate of 5,500 cu m/hectare/day (0.6 million gallons
per day or mgad) was assumed. Sixteen 0.21-hectare (0.5-acre) filter basins
would be required. It was assumed that each, basin would be 46 m (150 ft) square,
and the basins would be located in a double row in order to provide access for
cleaning. An area of approximately 10 hectares (25 acres), located along the east
side of the present treatment plant site, would be required if this alternative were
implemented.
In determining the intermittent sand filter design requirements, it was assumed
that a filter run would be 28 days. With 16 basins, one basin could be cleaned each
day during a regular five-day work week, with four days during each four-week
period allotted to other maintenance items. The influent supply line and main drain
would run along the spine between the rows of basins. The influent line would be
sized for hydraulic loading of each filter fcr two hours with a maximum of four
basins being loaded at a time. Loading would be rotated automatically by a timer-
controlled valve. Under design conditions it would be possible to load all the
basins within an eight-hour period. When the total amount of applied effluent
16
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fails to drain through the filter within 22 hr, the filter would be considered
plugged and would require cleaning.
It was assumed that the filters would be contained by soil embankments paved
with asphalt along the sides to facilitate cleaning, The basin tile drains would be
covered with about one-third meter (one foot) of graded gravel from 0 .6 cm (0.25 in.)
minimum diameter to a maximum diameter of 4.0 cm (1.5 in.) . The filter medium placed
on top of the gravel would consist of one meter (three feet) of sand with an effective
size approximately 0.50 to 0.75 mm. Cleaning would be accomplished by removing
the top two to five centimeters (one to two inches) of sand and replacing with clean
sand. Sand would be washed and reused. Sand wash water, after passing through
a sand sedimentation basin, would be returned to the oxidation pond. Effluent from
the intermittent sand filter basins would be drained to a sump and then pumped to
the chlorine contact tank before discharge to Willow Slough Bypass.
Capital costs for intermittent sand filtration were estimated at $3.52 million.
Operation and maintenance costs were estimated at $79,000 per year. The chief
uncertainty in the cost estimate was the amount of labor required for sand cleaning.
This results directly from the lack of adequate '^formation for designing intermittent
sand filters for wastewater characteristics and effluent quality requirements similar
to those at Davis .
Analysis. All the alternative methods of effluent improvement have similar
environmental impact on the service area. There are significant differences in the
immediate vicinity of the treatment plant. The overland flow alternative has a
favorable environmental impact. Wildlife habitats in the vicinity of Davis include
croplands, pasture, riparian and water surfaces. Rodents, small mammals and
birds use these habitats. Water surfaces are heavily used by both resident and
migratory waterfowl. Varying amounts of riparian habitat exist along the Yolo
Bypass, Willow Slough Bypass, Putah Creek and other stream and slough banks.
Riparian vegetation, considered one of the most valuable wildlife habitat types, is
a concentration point for a variety of game and nongame species and provides
excellent feed and cover. The Davis Audubon Society has identified the Hunt's
Cannery overland flow treatment site, located about two kilometers (one mile) east
of the central treatment plant, as one of the best wildlife habitats in the Davis area
and considers that the recommended overland flow project will significantly enhance
the wildlife habitat. A wildlife inventory from the vicinity of the treatment plant is
discussed in the summary section.
Because the group B alternatives all involve algae removal, all provide some
removal of nitrogen, which is incorporated into algal cells in the oxidation ponds.
Of the three group B alternatives, overland flow can be expected to provide the
greatest removal of unassimilated nitrogen. The principal mechanisms are crop
uptake and nitrification-denitrification in the soil.
Reclamation/Irrigation
The third major alternative investigated (category C) was to apply the effluent
to land, either as a reclamation program for crop irrigation or simply as a method
of disposal. Advantages to this approach are, in general, that crop irrigation is
a beneficial use (if reclamation is practiced) , less costly treatment is required,
and the possibility of future upgrading being required to meet more stringent
discharge requirements is less likely. Disadvantages are that large tracts of land
17
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are often required, wastewater storage during wet portions of the year is usually
required, and care must be taken to prevent degradation of groundwater aquifers.
Reuse of reclaimed wastewater for industrial purposes may be undertaken in some
situations, but the lack of industrial demand at Davis made this infeasible.
The wastewater effluent from the Davis facility has a sodium adsorption ratio
of 10. This high concentration of sodium in an irrigation supply can reduce soil
permeability by causing clay minerals to swell. The SAR value of 10 classifies
the plant effluent as potentially leading to severe soil permeability problems.
Using effluent as the source of water on soils around the treatment plant where
permeability is already low without any mitigating measures would, in time,
produce this sealing effect. This is unsuitable for irrigation but ideal for over-
land flow where water infiltration into the soil profile beyond the grass root zone
is not desirable. Due to the high SAR value, the wastewater must be blended at
a ratio of 1: 1 with local irrigation water for long-term irrigation. It is estimated
that an application area of 400 to 600 hectares (1,000 to 1,500 acres) would be
needed.
Because irrigation is a seasonal use at Dsvis, storage of effluent would be
required during the winter months. It was determined that a storage reservoir
with a capacity of approximately five million cubic meters (4,000 acre-ft) would
be required. A 200-hectare (500-acre) parcel, probably located to the east of the
existing plant site, would be purchased and used as the storage reservoir site.
Flow from the storage reservoir and existing ponds would be delivered by pressure
pipeline to the irrigation systems of local farmers .
In order to assure a reuse demand for the Davis effluent, it would be necessary
to develop long-term (e.g., 15-year) agreements with local farmers to receive the
effluent. An alternative would be to purchase land and lease it to farmers on the
condition that they use the effluent for irrigation. This would add $2,000,000 to
$2,500,000 to the capital cost. Resulting savings in other areas might result from
reduced storage and conveyance costs. Operating costs would be reduced by the
rent payments received for the leased land.
An important aspect of irrigation reuse is control of subsequent runoff from
irrigated fields. A probable Regional Board requirement would be that such drain-
age not reach surface waters (unless it has been treated to meet surface discharge
requirements) . This would require collection of drainage waters and return either
to the treatment plant or to the irrigation system. This could also add to the esti-
mated costs. Estimated capital costs were $3.24 million. Operation and maintenance
costs were estimated at $40,000 per year for the additional facilities.
Summary of Alternatives Analysis
Cost-effectiveness, including environmental and social impact analysis, and
project suitability were considered for the seven alternatives. Alternatives were
compared on the basis of equivalent annual cost, using a discount rate of 7 percent
and a 20-year planning period, conforming to state and federal guidelines for
cost-effectiveness analyses. The annual cost is computed by applying a capital
recovery factor, available from standard interest tables, after first taking into
account any facilities salvage value at the end of the 20-year planning period. No
depreciation was assumed for the value of land, so that capital recovery factor used
for land was equal to the interest rate. The results of the monetary cost analysis
is depicted graphically in Figure 4.
18
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ca
-------
The most notable aspect of the costs is range of values. The most costly
alternative, the actived sludge process (A-l) , is nearly 90 percent higher than
overland flow (B-2) . Overland flow and reclamation/irrigation (C-l) are the two
lowest-cost alternatives, and are significantly less expensive than the others.
In terms of operation and maintenance costs, which must all be borne locally,
reclamation/irrigation has the lowest cost, $40,000 per year, and trickling filtra-
tion (A-2) , overland flow (B-2) , and intermittent sand filtration (B-3) are in the
$48,000 to $90,000 per year range. The remaining three alternatives have much
higher operating costs. Activated sludge (A-l) has high labor and power costs.
The extended aeration alternative (A-3) has lower labor and materials cost, but
requires more power to keep all the particulate material in suspension in the
aerated lagoons . Coagulation-flocculation-sedimentation has the highest operating
costs; this results from the large quantities of alum and sulfuric acid which must
be used.
The alternatives have significantly different environmental impacts. Due to
the general dry ness of the area and the absence of major water bodies, aquatic
resources are limited within the study area. Water quality in Willow Slough Bypass
is poor, consisting in the summer of agricultural return flows and treated waste-
water effluent. Water quality in the fall, between the end of the irrigation season
and the beginning of the rainy season, is especially poor. Nutrients contained in
the agricultural runoff support excessive algae growth in the Bypass drainage;
algae decompositon consumes the oxygen supply. Most warm water fish species
are absent. California Department of Fish and Game personnel indicate that some
bluegill and catfish may inhabit the water course.
The major value of the Willow Slough Bypass is the riparian habitat it provides.
Vegetation in the vicinity of the treatment plant is sparce, reflecting the dry
climate. Most of the area is under cultivation. Dense primary riparian vegetation
along the Willow Slough Bypass provides food, nesting, dens and escape sites for
muskrats and other water-related mammals, amphibians, and ducks. Bottom lands
of the bypass provide habitat for rodents and upland birds such as pheasant. These
species attract and supply food to hawks and other raptors. Catec^y A and B
surface water disposal alternatives would support the continuation of tnis habitat.
The oxidation ponds are one of the most valuable wildlife habitats in the study
area. These ponds provide a sanctuary for several species of waterfowl and shore
birds. The treatment area is surrounded by a high chain link fence, and the opera-
tion of the oxidation ponds is automated so that the waterfowl are well isolated from
man's activities. These ponds are always occupied by large numbers of several
species of waterfowl. Category B and C alternatives would maintain this valuable
habitat.
The reclamation alternative, C, would involve irrigation during the summer
and storage of effluent during the winter. There would be no discharge to Willow
Slough Bypass. Storage would create 170 hectares (400 acres) of additional water-
fowl habitat from land currently devoted to irrigated agriculture.
The overland flow alternative would create 80 hectares (200 acres) of habitat
very favorable to wildlife, as indicated by the use of the Hunt's overland flow area.
Table 5 shows a wildlife inventory in the vicinity of the Davis treatment facility.
20
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The relative abilities of alternatives to meet engineering effectiveness criteria
and to conform to identified constraints may strongly affect selection of the recom-
mended plan. The effectiveness criteria include reliability, flexibility, flood
protection and bypass prevention. Constraints include ability to meet discharge
requirements, conformance with the basin plan, compatibility with "best practicable
treatment" requirements, reclamation potential, ability to implement, and public
acceptability. All of the alternatives were judged to be fairly reliable. None would
be affected greatly by power outages or process shutdowns. Retention of the
oxidation ponds, as emergency storage for the A alternatives and as part of the
treatment process for the B and C alternatives, would provide adequate storage
capacity for several days in the event of a process shutdown. Emergency power
for influent pumping is provided by gas engines. Resource commitments for the
various alternatives are summarized in Table 6.
Alternatives B-2 (overland flow) and C-l (reclamation/irrigation) were rated
as being the most flexible. They would be least affected by a future nitrogen
limitation, and both have low capital costs, a portion of which is for land, which
does not depreciate as structural or mechanical components do. In addition, the
reclamation/irrigation alternative would not be affected by any future requirement
mandating land disposal (although this was considered quite unlikely) . The
activated sludge (A-l) and trickling filtration (A-2) alternatives were rated the
least flexible: a high capital investment would be required, and major additions
would be needed to provide nitrogen removal.
As a result of the analysis, an overland flow system was recommended. A
summary of the project alternative analysis, taken from the Environmental Impact
Report,' is given in Table 7. A more detailed discussion of the alternatives is
contained in the EIR and in the Project Report. ^
The consideration of alternatives at Davis may be generally applicable to small
communities which have existing oxidation pond systems. This may be especially
true where existing capacity is sufficient to meet anticipated growth for the inter-
mediate future, but where upgrading of effluent quality is required. As more
experience is gained in the United States with overland flow systems, it is expected
that the positive environmental aspects will be recognized.
22
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24
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REFERENCES
1. Brown and Caldwell, City of Davis Sewerage Survey, December 1961.
2. Brown and Caldwell, City of Davis Sewerage Study, December 1968.
3. Pound, C .E., D.W. Crites and D .A. Griffes, Costs of Wastewater Treat-
ment by Land Application, U .S . EPA, Office of Water Program Operations,
Technical Report No. EPA-430/9-75-003, June 1975.
4. Marshall, G.R. andE.J. Middlebrooks, Intermittent Sand Filtra+ion to
Upgrade Existing Wastewater Treatment Facilities, Utah State University,
College of Engineering, Utah Water Research Laboratory, PRJEW115-2,
February 1974.
5. Brown and Caldwell, City of Davis, Project Report, Algae Removal
Facilities, February 1977.
6. Overman, A.R. and H.C. Ku, Effluent Irrigation of Rye and Ryegrass,
Proceedings ASCE, JEED, Vol. 102, 475 (April 1976) .
7. Brown and Caldwell, City of Davis, Draft Environmental Impact Report,
Algae Removal Facilities, February 1977.
25
ftUS GOVERNMENT PRINTING OFFICE 1977757-140/6605
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