-------
Figure 5-14 indicates that decreasing amounts of secondary solids in
the mixture produce drier dewatered cake. This would be expected since
primary solids are gritty and fibrous, which compact better than gelati-
nous secondary solids.
70
V)
-------
The balance of the dewatered raw sludge is trenched. Hauling and
disposal cost are approximately $35 per wet ton.
5.8. SUMMARY
The discussions of changes in solids production per MGIF caused by the
various processing operations are summarized in Table 5-2. Table 5-3 pre-
sents the various limitations noted for the processing steps.
57
-------
TABLE 5-2. SUMMARY OF ADDITION (REDUCTION) IN SOLIDS PRODUCTION DUE TO VARIOUS
SOLIDS PROCESSING STEPS
Processing operation
Current sludge generation,
dry tons (pounds)
per million gallons
of influent flow
Future sludge generation
dry tons (pounds)
per million gallons
of influent flow
00
Gravity Thickening
Dissolved air flotation
thickening
Anaerobic digestion
Elutriation
Digested sludge dewatering
o Ferric chloride
Raw sludge dewatering
o Ferric chloride
0 Lime
None
0.001 ( 2 )
0.256 ± 0.042 ((512 ± 84))
None
0.043 ± 0.009 ( 86 1 18)
0.049 ± 0.015 ( 98 ± 30)
0.223 ± 0.042 (446 ± 84)
None
0.002 ( 3 )
0.255 ± 0.042 ((510 ± 84))
None
0.049 ± 0.009 ( 98 ± 18)
0.044 ± 0.015 ( 88 ± 30)
0.119 ± 0.040 (238 ± 80)
-------
TABLE 5-3. SUMMARY OF DISTRICT OF COI.UHUIA'S UwTF SLUDGE NANAGIIMFNT
PROCESS [.IMITATIONS UNDER CURRENT OPERATION
Process
Gravity thickening
Dissolved air flotation
thickening
Limitations
Average thickened primary sludge concentration is 7 0 i 0 5 percent
Average thickened primary sludge volume per MGIF is 1,236 ± 218 gallons
Average primary solids production per MfilF is O.377 i 0 1)60 ton-: (754 * 120
pounds) The average volatile content is 71 ± 5 I percent
Average thickened secondary sludge concentration is 4 I i 0 3 percent
Average current thickened secondary sludge volume per MGIF is 1,644 i 239
gallons; in 1981, it will increase to 1,900 1 239 gallons
Average secondary solids production per MGIF is 0 284 i 0.034 tons
(568 ± 68 pounds) with an average volatile content of 65 percent;
in 1981, it will increase to 0 328 ± 0 034 tons (656 t 68 pounds)
with an average volatile content of 63 9 t 2.1 percent
Anaerobic digestion
o Tankage
Approximately 65 percent of the total volume available or 1,142,458
usahle cubic feet (8,545,587 usable gallons)
Ln
10
o Heating capacity
After meeting system radiation, losses at a 95°F operating temperalnie
available heating capacity is currently 9,800,000 RTU per hour during
the winter and 11,100,000 RTU per hour during the summer In 1981,
this will increase to 12,800,000 and 14,100,000 BTU per hour,
respectively
For maximum gas Maximum feed solids coiiccnliation to digestion uoL to exceed six
production pen en t solids.
Maximum volatile mailer loading not to exceed 0 14 pounds per usable
cubic feet per d«iy
F.lutnalion
Digested sludge
dnwalernig
Digested sludge flow rate to sysli-ra not to exceed 490,000 gallons
per day.
Feed sol ills coiiieiilralion to be a minimnnnf 2 7 penent
Maximum percent take solids achievable on a consistent basis 16 to 17
percent
Raw sludge dew.itering
Maximum current percent lake solids jclnev.ihle on a consistent h.isis
21 to 22 percent In the Fiiliue, tins may dui rease to IV to 2O
pel«enl
-------
SECTION 6
IMPROVING SLUDGE MANAGEMENT OPERATION USING ANAEROBIC DIGESTION
Table 6-1 summarizes expected sludge quantities at the current average
plant influent flow rate of 334 million gallons per day. The purpose of
this study was to evaluate the existing sludge processing operation with
the intent of determining if a new two-stage, mesophilic-thermophilic
anaerobic digestion process could be applied to digest all sludge produc-
tion using the existing equipment in conjunction with a minimal capital
expenditure. If possible, then sludge processing and disposal cost at
Blue Plains would be reduced by more than 50 percent. In addition, the
scope of work included recommendations to improve the current anaerobic
digestion operation and a brief evaluation of the use of thermophilic
digestion. This section of the report will discuss these three objectives
in the following order:
o Existing mesophilic system operation
o Evaluation of thermophilic system option
o Evaluation of mesophilic-thermophilic system option.
TABLE 6-1 EXPECTED PRIMARY AND SECOND-»RV SLUDGE QUANTITIES AT CURREVT 334 ,-ILLIOs GALLO.N PER DA}
INFLUENT FLOW3
Gallons of sludge per ia\ Pounds of sludge per das' \oiaiile pounds sludge pe- o-\
Minimum Average laximum *!inimao Average 'Idxuniift 'linimun Average Id* mi-.
Primary sluage 340,012 412,S2i 485,63c :il.'56 151.836 2»:,916 150,347 ITS 30; 2u7 :»C
Secondary sludge 55-.77. 634,600 71...-20 196.392 2:9.104 2-.l.?;t 12S.691 140^22^ 15- :«.-
TOTALS 394,786 1,047.424 L.200.062 iOS.143 470.940 53J.732 276.OSS 311.03., 3oi a::
Da-.« calculated from Table 5-3
60
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6.1. EXISTING MESOPHILIC SYSTEM OPERATION1
Evaluation of an existing anaerobic digestion process system for the
purpose of improving operations begins at the "end and works towards the
front." This is done to ensure that any individual process constraints,
which normally affect the output of the preceding process, can be identi-
fied and incorporated into the operation of the preceding process. In
addition, the evaluation will be made from the viewpoint that all the
sludge is to be processed through the present system. It is believed that
this is the only impartial way to compare all three digestion processes.
6.1.1. Ultimate Disposal
Ultimate disposal of anaerobically digested sludge is on the land. It
is desirable to have the driest cake possible to minimize the transpor-
tation costs.
6.1.2. Digested Sludge Vacuum Filter Operation
The constraint from ultimate disposal is to produce the driest sludge
cake possible. From the viewpoint of dewatering management, it is impor-
tant to minimize chemical additions (chemical cost and extra solids). In
Section 5.5, the data presented indicated that maximum cake solids and
minimum chemical usage occurred at the highest feed solids concentration.
The data in Section 5.5 also indicated that with proper operation of the
elutriation system, a minimum of five percent feed solids concentration
could be obtained on a regular basis. This would result in an average
16.5 percent cake solids concentration.
Current Operation--
There are four old drum vacuum filters, each with 500 square feet of
filtering area. In 1979 when the secondary to total sludge mass ratio of
the sludge being digested was between 0.4 to 0.5, the average calculated
yield was 2.41 pounds per square foot per hour. Assuming that all four
1 All supporting calculations for Section 6.1 are given in Appendix M.
61
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units were operating at the average yield, 115,680 pounds of anaerobically
digested sludge could be dewatared. At an average 16.5 percent cake
solids there would be 390.5 wet tons of sludge per day needing disposal.
At the present, the limited capacity of these facilities is a major
constraint in processing sludge through the digestion system. This will
change shortly with the start-up of six new and larger filters.
Future Operation—
Sometime in early 1981, six new cloth belt vacuum filters will become
operable for anaerobic sludge dewatering and the four existing units will
be abandoned. Each new unit will have 600 square feet of filtering area
and it is assumed the same yield. Under these conditions the digested
sludge dewatering capacity would increase to 208,224 pounds per day. With
these new filters in operation, dewatering capacity will no longer be the
rate-limiting process. In fact, elutriation will be the rate limiting
process and will limit digested solids requiring dewatering to 142,000
pounds per day (479 wet tons to disposal), which would mean only four of
the six filters would need to be operated at any one time.
It should be noted that if all primary and secondary sludge could be
mesophilically digested, 10 of the 15 vacuum filters currently being used to
dewater raw sludge could be used to dewater digested sludge, as piping and
valving exits for such a configuration.
6.1.3. Elutriation
The constraints from the dewatering operation are: (a) to produce a
solids concentration (elutriation underflow solids concentration) of at
least five percent solids; and, (b) the maximum amount of sludge capable of
being dewatered in early 1981 is 208,224 dry pounds per day.
In Section 5.4, the data presented indicated that in order to achieve
a constant five percent solids concentration in the elutriation underflow:
o The flow rate to the elutriation system from the digestion system
should not exceed 490,000 gallons per day.
o The solids concentration of the influent digested sludge stream to
elutriation had to be a minimum of 2.7 percent.
62
-------
With the start-up of the new digested sludge dewatering operation, the
existing elutriation system would become the next rate-limiting process,
limiting sludge processing to 490,000 gallons per day (40 to 55 percent of
the total sludge flow).
Consideration should be given to using some of the spare
dissolved air flotation tanks as elutriation tanks. Eight of the spare
tanks would provide an additional 880,000 gallons per day elutriation
capacity under the constraints specified. This additional capacity would
allow the elutriation system to process all sludge generated. Appropriate
charges would enable pumping digested sludge and washwater to the flotation
tanks.
6.1.4. Anaerobic Digestion
The constraints from the present elutriation facilities are:
(a) Digested solids concentration from the digesters to be a minimum
of 2.7 percent.
(b) The flow rate from the digestion system cannot exceed 490,000
gallons per day.
(c) The maximum sludge mass not to exceed 208,224 dry pounds per day.
From the viewpoint of digestion management it is important to maximize
flow rate, solids reduction, and gas production within the constraints
stated. In Section 5.3, the data presented indicated the following addi-
tional operating constraints:
(d) Approximately 35 percent of the existing tank volume—1,757,856
cubic feet (13,148,763 gallons)—is unusable, usable tank volume
is 1,142,606 cubic feet (8,546,693 gallons).
(e) Available sludge heating capacity after meeting system radiation
heat loss requirements is 9,800,000 BTU per hour during the
winter and 11,100,000 BTU per hour during the summer. In 1981,
this will increase to 12,800,000 and 14,100,000 BTU per hour.
(f) Maximum gas production achievable on a consistent basis required
that:
63
-------
o Maximum feed solids concentration to digestion not to exceed
six percent solids
o Maximum volatile matter loading not to exceed 0.14 pounds per
usable cubic foot per day
(g) Existing data indicate that hydraulic residence times of 16 days
present no problem over a wide range of feed combinations. Lower
detention times may be possible, but no operating data are avail-
able.
Since all digestion tanks are being mixed and no supernatant is re-
moved, the flow rate out of the digestion tanks should be approximately
equal to the flow into the tanks. The flow rate through the tanks is
governed by one of three constraints: the elutriation system, sludge
heating, and vacuum filtration capacity.
The calculations on sludge heating capabilities indicate that the
existing heat exchangers are capable of heating 683,700 gallons per day to
95°F during the 1980 winter and 1,549,000 gallons per day to 95°F during
the summer of 1981. When the new hot water boiler is put in service during
the summer of 1981, the winter capacity will increase to 893,000 gallons
per day and 1,967,000 gallons per day during the summer.
It should be noted that in order to process all sludge through diges-
tion, an additional 4,400,000 BTU per hour would be required during the
winter months. As explained in Appendix G, 17,000,000 BTU per hour of new
low pressure (9 psi) steam capacity is being interconnected with the exist-
ing sludge heat exchanger steam boilers. If the capacity is available, it
may be possible to place steam lines up to the top of the digestion tanks
and inject the steam directly into the digesters through the roof.
Based on a minimum 16-day hydraulic detention time and 65 percent
usable digester volume, the flow rate would be 534,000 gallons per day. If
the grit problem was solved and all existing tank capacity became avail-
able, then the flow rate would be 821,700 gallons per day.
64
-------
It may be possible to operate this mesophilic system at a lower
hydraulic detention time, but operating data do not currently exist to
verify this.
Both heating capacity and hydraulic detention time flow rate maximiuns
are above the elutriation operation 490,000 gallon per day constraint.
Therefore, total raw sludge flow rate through the existing anaerobic diges-
tion tanks should be and is limited to 490,000 gallons per day under the
present circumstances.
In addition to hydraulic flow rate restrictions on the digestion
tanks, volatile matter loading requirements must also be satisfied. Avail-
able data indicate that the system can be successfully operated at volatile
matter loading ratios of 0.16 to 0.17 pounds volatile matter per usable
cubic foot per day, though gas production seems to deteriorate over 0.14.
Based on 0.16 loading and 65 percent usable digester volume, the total
amount of volatile solids pumped to the system would be 183,000 pounds per
day. If the grit problem was solved and all existing tank capacity became
available, then the amount would be 281,000 pounds per day.
If all the existing digesters were utilizing full capacity, then at
least four more tanks identical to the existing 12 would be required to
meet volatile matter loading requirements.
6.1.5. Primary - Secondary Flow Rates To Digestion
The ratio of thickened primary to thickened secondary sludge volumes
is 0.65:1. At the current time, the ratio being processed through diges-
tion is 1.44:1 (288,000 gallons per day:200,000 gallons per day). As was
discussed in Section 5 of this report, operating at high primary sludge to
total sludge mass ratios leads to digester stress conditions. It is re-
commended that for better overall process operation the primary to secon-
dary flow rate volumes should be altered to 193,000 gallons per day:297,000
gallons per day (0.65:1).
65
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6.1.6. Digester Gas Production
Calculations in Appendix M show that at the 490,000 gallon per day
sludge processing rate under the conditions previously discussed, more gas
will be generated than required to meet total sludge heating requirements.
The average daily excess gas production is 658,000 cubic feet per day and
will range from 780,000 cubic feet per day during the summer to 537,000
cubic feet per day during the winter.
6.2. EVALUATION OF THERMOPHILIC SYSTEM OPTION2
Review of thermophilic anaerobic digestion clearly indicates that the
process should be seriously considered for the least cost, short term solu-
tion of the sludge processing and disposal problems of the District of
Columbia's Wastewater Treatment Facility. The three significant advantages
of the process (a) increased sludge processing capability, (b) improved
sludge dewatering, and (c) increased destruction of pathogens, are all
pertinent to the District's situation.
More detailed checks should be made on a number of items prior to
deciding to convert the existing digesters to thermophilic operation.
These include (a) amount and type of additional sludge heating required,
(b) structural competency of existing digesters and piping at thermophilic
temperatures, (c) needed improvements in the temperature control system,
(d) equipment needed to remove the increased amounts of moisture to be
expected from the digester gas, and (e) how to avoid possible inhibition
by ammonia.
2A11 supporting calculations for Section 6.2 are given in Appendix N.
66
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6.2.1. Ulitmate Disposal
Thermophilically digested sludge is generated under conditions that
approach disinfection, thus allowing for acceptable final disposal to the
land. As with the current mesophilic operation, it would be important to
minimize transportation cost, therefore, the driest cake possible is
desirable.
6.2.2. Digested Sludge Vacuum Filter Operation
Thermophilically digested sludge exhibits better filterability than
straight mesophilically digested sludge—some times as much as double. In
Appendix N, the analysis used a 25 percent improvement in yield resulting
from thermophilic digestion, a value considered conservative. Calculations
indicate that thermophilic digestion of all Blue Plains sludge would re-
quire the use of 8 of the 21 new vacuum filters for dewatering of the
digested sludge.
Another advantage would be the elimination of the need for sludge
conditioning by elutriation or by added iron salts. Thermophilically
digested sludges can be conditioned using a combination of anionic and
cationic polymers. This change alone would reduce the present amount of
solids to be disposed of by 94 pounds per million gallon of influent flow—
over 16 dry (96 wet) tons per day.
A disadvantage to dewatering this sludge is that the sludge must be
cooled to under 90°F. Calculations in Appendix N indicate that the exist-
ing elutriation tanks might be used as cooling tanks. Potential odor
problems may also be minimized by using the elutriation step because of
this liquid to liquid cooling.
6.2.3. Impact of Increased Heat Requirements
The thermophilic digestion process being evaluated operates at 122°F.
The existing heating capabilities at Blue Plains have been calculated to be
inadequate, with approximately 16.1 x 10 BTU per hour additional heating
67
-------
needed during the winter months. It is suggested that direct steam injec-
tion be considered for supplying the additional heat since this has been
used successfully in Los Angeles, Moscow, and the Canadian study. Struc-
tural competency should be checked by a structural engineer. A control
engineer should be engaged to look at the temperature control system
with a maximum variation of about ±1.5°F being permitted (at 120°F
operation).
6.2.4. Digestion Tanks
Calculations indicate that the existing digestion tanks are capable of
taking the full sludge load in the thermophilic range of operation if they
are cleaned and grit accumulation kept to a minimum.
6.2.5. Volatile Matter Reduction and Gas Production
Analysis indicates that the percentage volatile matter reduction in
the thermophilic system would be about the same as the mesophilic system
but at one half the time. Calculations in Appendix N show that more gas
will be generated than required to meet total sludge heating requirements.
The average daily excess gas production is 840,000 cubic feet per day and
will range from 1,000,000 cubic feet per day during the summer to 600,000
cubic feet per day during the winter.
6.2.6 Transition from Mesophilic to Thermophilic Operation
It would be desirable to make the transition from mesophilic to ther-
mophilic operation as rapidly as possible. However, caution should be
exercised in making this transition since very little information is
available on the maximum rate at which this transition can be effected.
In Garber's early work (4), he indicated that almost six months were needed
to establish the first thermophilic unit as a separate culture. By seeding
and more rapid increases in temperature, he was able to cut this time
to three months.
68
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In Garber's later work, he gave more details as to the transition
procedure. This time he increased the temperature from 96°F to 126°F at
the rate of 1°F per day while maintaining the load at approximately 0.1
pound volatile solids per cubic foot per day. This was not successful and
the digester turned "sour." He then reduced the loading to a minimum while
maintaining the temperature at the 126°F level but observed no change in
condition over a four month period. The temperature was then reduced to
120°F and over a three week period, satisfactory digestion commenced.
Because of Garber' experience, personnel in Chicago were more cautious
in raising the temperature. Their procedure was to raise the temperature
at a rate of 1°F per day for only five days and then to wait for two to
three weeks for the digester to stabilize before again increasing the
temperature 1°F per day until a final temperature of 127°F was attained.
During this period the loading on the digester was maintained at about 0.13
pounds volatile solids per cubic foot per day. Several surges (one up to
2,500 mg/liter) were observed during the transition period and it took
approximately one year for the digester to stabilize at consistently low
volatile acid concentrations.
From the above, it can be clearly seen that there is still much to be
learned about the correct procedure for making the transition from
mesophilic to thermophilic digestion. The three variables involved are (1)
rate of change of temperature, (2) rate of change of loading, and (3)
maximum temperature to be attained. Garber's experience indicates that, at
least inititally, the maximum temperature should be limited to 120°F.
In both the Los Angeles and Chicago experiences, the loading on the
digester was maintained at its normal value while the temperature was
gradually increased. An alternate approach would be to stop the loading to
the digester, bring it to the new temperature as rapidly as possible, and
then gradually increase the loading. Limited experience in Atlanta (12)
during the summer of 1980 indicates that the transition might be accom-
plished more rapidly by following the latter procedure.
69
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6.3. EVALUATION OF MESOPHI1IC - THERMOPHILIC SYSTEM OPTION3
As noted at the beginning of Chapter 6, the primary purpose of this
study was to evaluate the existing sludge processing operation with the
intent of determining if a new, two-stage, mesophilic-thermophilic anaero-
bic digestion process could be applied to digest all sludge production
using existing equipment and without substantial capital expenditures.
The mesophilic-thermophilic system offers all the advantages of
thermophilic digestion (disinfection, increased volatile matter reduction,
and improved dewatering) and produces an essentially innocuous sludge. In
addition, the system is simple to operate and has built in buffering
capacity to deal with unusual loading conditions. Disadvantages are that
it requires heating of two completely separate digestion processes (one at
95°F, the other at 122°F) and that there is only one operational plant,
handling 100,000 people, in the United States. Both the mesophilic-thermo-
philic and thermophilic processes will require that the sludge be cooled
before being dewatered.
6.3.1. Ultimate Disposal
The sludge from this process is extremely inert and looks very similar
to composted sludge. This quality should allow for disposal to both pri-
vate and public lands.
6.3.2. Digested Sludge Vacuum Filter Operation
The mesophilic-thermophilic process will have the same vacuum filter
operation requirements as for the thermophilic option.
All supporting calculations for Section 6.3 are given in Appendix 0.
70
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6.3.3. Impact of Increased and Dual Heat Requirements
The total sludge heating requirements for this process option are the
same as the previous thermophilic option. The major difference is that the
mesophilic digestion tanks are to be maintained at 95°F and the thermo-
philic tanks at 122°F. The suggested method of sludge heating is as
follows:
o For the mesophilic tanks, the existing sludge heat exchangers
would be used and steam (approximately 500,000 BTU per hour)
would be injected into each of the tanks.
o For the thermophilic tanks, all heating would be by direct steam
injection (approximately 5,000,000 BTU per hour per tank).
As was mentioned earlier, calculations indicate that the increased
temperature will have no significant impact on sludge piping and wall
structural integrity.
6.3.4. Digestion Tanks
Calculations indicate that even if all the existing tanks volume was
available, the hydraulic detention time under each process condition would
be inadequate. In order to process all of the currently generated sludge
through this process, four more digesters would be required.
6.3.5. Volatile Matter Reduction and Gas Production
Limited experience indicates that a 50 percent volatile matter
reduction can be expected from digesting the sludge. Calculations in
Appendix 0 show that more gas will be generated than required to meet total
sludge heating requirements. The average daily excess gas production is
1,109,000 cubic feet per day, and will range from 1,384,000 cubic feet per
day during the summer to 833,000 cubic feet during the winter.
71
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6.4. SUMMARY
Table 6-2 summarizes the major process considerations in implementing
either of the three anaerobic digestion alternatives to fully process the
maximum sludge quantities given in Table 6-1.
72
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TABLE 6-2. SUMMARY OF MAJOR PROCESS CONSIDERATIONS IN IMPLEMENTING FULL ANAEROBIC DIGESTION OF
BLUE PLAIN SLUDGES
Mesophilic
digestion
of all sludge
Additional heat requirements
BTU's x 106
4.4
Thermophilic
digestion
of all sludge
16.1
Mesophilic-thermophilic
digestion
of all sludge
Provisions for better grit removal
Digestion tanks required
yes
18
no
12
yes
16
16.1
Average daily revenues from excess
digestion gas production, dollars
Additional elutriation capacity
Vacuum filters required to be
operational
Maximum wet tons per day for disposal
1298
yes
10
1148
802
no
8
1033
1057
no
8
961
Excess gas production sold to Naval R&D at $.95 per 1,000 cubic feet.
Cake solids - 16.5 percent.
-------
SECTION 7
ECONOMIC IMPACT
Municipal sludge management is a challenging field. It is also an
expensive one. It is not unusual these days for a wastewater treatment
facility to devote over fifty percent of its capital and operational budget
to "managing" the steadily increasing amounts of wastewater sludge.
The Blue Plains Wastewater Treatment Plant is at a crossroads. The
Plant's current wastewater flow generates almost 500,000 pounds per day of
sludge. Several sludge treatment and disposal options are utilized:
o Dewatering of thickened raw sludge followed by land trenching
o Dewatering of thickened raw sludge followed by composting
o Mesophilic anaerobic digestion of thickened raw sludges followed
by dewatering and application to land.
In the near future, the land trenching alternative must be dis-
continued. Composting with its attendant problems and land requirements
is not practical. The third existing disposal scheme—mesophilic
anaerobic digestion—is a variable option.
This section of the report will not answer the question—what should
be done? What it will do is show how economically attractive anaerobic
digestion, in any of three process configurations, can be.
74
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7.1. OPERATIONAL COST IMPACT
Table 7-1 presents average sludge generation per million gallons of
influent flow for five different sludge management conditions.
CONDITION I - This is historical information and represents the situation
for the first six months of 1980. During this time period,
approximately 40 percent of the sludge was digested, 40 to
45 percent went to land trenching, and 15 to 20 percent to
composting.
CONDITION II - This is a projection of what the situation will be in late
1981 based on completion of current on-going process
changes. At this time, approximately 40 percent of the
sludge will be digested, the rest will be composted.
CONDITION III- This is a projection of what the situation would be if all
the sludge was processed through a mesophilic anaerobic
digestion system.
CONDITION IV - This is a projection of what the situation would be if all
the sludge was processed through a thermophilic anaerobic
digestion system.
CONDITION V - This is a projection of what the situation would be if all
the sludge was processed through a proposed new process
modification, mesophilic-thermophilic anaerobic digestion.
The economic impact of the numbers shown in Table 7-1 are better
illustrated in Figures 7-1 and 7-2.
In Figure 7-1 a comparison is made of the average cost for chemicals
and final disposal per million gallons of influent flow for the five condi-
tions given in Table 7-1. The 40 percent reduction in cost shown between
the existing 1980 and projected 1981 plan is solely due to eliminating land
trenching and replacing it with composting. The significant cost reduc-
tions shown between the projected 1981 plan and the three anaerobic diges-
75
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TABLE 7-1. SUMMARY OF AVERAGE SLUDGE GENERATION PER MILLION GALLONS OF INFLUENT FLOW
-vl
cr>
Based on
January to June 1980
Based on
completion of
current
on-going changes
Dlanning-iall 1981
Sludge Sludge
generated Cost generated Cost
per per per per
MGIF,0 MGIF,
Primary sludge
Secondary sludge
Gravity thickening
Dissolved air flotation
thickening
Anaerobic digestion
Eliilri.ition
pounds
696
568
0
2
dollars
3.83b
MGIF, MGIF,
pounds dollars
696
656
0
3
(512) (5.84)L (510)
0
De.walcring digested sludge
0 Iron salt
0 Polymer
Dewalered raw sludge
0 Iron salt
0 Lime
Disposal digested sludge
Disposal raw sludge
86
98
446
a MGIF = million gallons of
Polymer cost
C Based on 12
1 Based on $0.
Basprl on an
averaged $13.
cubic feet per
0685 per pound
average cost
A
5.B9d
6.71
37. 86*
38. IB1
147. 328
influent flow.
0
98
88
238
4.42
(5.81)
6.71
6.03
20.26
42.86
65.36
Based on
mesophil ic-
Based on Based on tliermopliil ir
mesophilic digestion thermophi lie digestion digestion
of all sludge of all sludge of all sludge
Sludge Sludge
generated Cost generated
per per per
MGIF, MGIF,
pounds dollars
696
656
0
3 4.42
(510) (5.81)
0
98 6.71
42.86
MGIF,
pounds
696
656
0
3
(510)
0
2
Sludge
Cost generated
per per
MGIF, MGIF,
dollars pounds
696
656
0
4.42 1
(5.81) (572)
0
8.00 2
38.50
Cost
per
MGIF,
dollars
4.42
(6.52)
8.00
35.54
50 per ton of dry feed solids.
pound volatile
of this sludge
of $0.0849 per
matter reduced
produced.
pound of this
and $0.95 per 1000 cubic feet.
sludge
produced.
8 Based on a $35 per wet ton composite cost (some composting, some trenching).
Based on a $24 per wet ton composting cost.
-------
118.35
100 -
80 -
5 1
a 2
2 U.
< =
SI
s-
— 1/1
II
§ ri
UJ
o oe
5 £
60 i
40 -
20 -
41.44
EXISTING
1980
CURRENT
PLAN
1981
ALL
HESOPHIL1C
ALL ALL
THERMOPHIUC HESOPHILIC-THERMOPHILIC
Figure 7-1. Average cost for chemicals and final disposal
per million gallons of influent flow for the
five conditions given in table 7-1.
tion alternatives are due to two items. First, in digestion approximately
37 to 40 percent of the raw solids generated are destroyed so that diges-
tion of all the sludge will significantly reduce the mass of solids that
requires disposal. Secondly, the dewatering operation for digested sludge
at Blue Plains does not require lime for conditioning: in the 1981 projec-
tion, the raw sludge dewatering operation will require a significant amount
of lime, which will increase solids by 238 pounds per million gallons of
influent flow. The higher unit cost of mesophilic over the other two
digestion alternatives is mainly because the other two digestion alterna-
tives do not require iron salts in the dewatering operation (equivalent to
96 pounds of solids per million gallons of influent flow). Meso-
thermophilic digestion has a lower overall cost than thermophilic digestion
because of a higher volatile matter reduction.
77
-------
1173
1129
1100
1000 •
I I
§
I
785
1980
RENT
PLAN 1981
ALL
MESOPHILIC
ALL MESOPHUIC-THERMOPHILIC
THERMOPH1LIC DIGESTION
Figure 7-2. Average wet tons of sludge produced per day for
the five conditions given in table 7-1.
Figure 7-2 shows the difference in wet tons generated by the five
different conditions given in Table 7-1. The large reduction in wet tons
is due to two items. First, in the digestion alternatives approximately 37
to 40 percent of the raw solids are destroyed (converted into methane gas,
carbon dioxide, and water); secondly, significantly less chemicals are
required in the dewatering operations. The difference in wet tons between
the three digestion alternatives is due to lower chemical conditioning
requirements for the thermophilic and meso-thermophilic options, and the
higher volatile matter reduction achieved by the meso-thermophilic option.
For every million gallons of flow into the plant, the raw sludge
dewatering option must dispose of 738 more pounds of solids. This is
equivalent to 3432 wet pounds or 1.72 wet tons.
78
-------
Of the three anaerobic digestion alternatives, the mesophilic-ther-
mophilic option is shown to have the lowest operational cost. In addition,
of the three digestion alternatives only the mesophilic-thermophilic option
produces a sludge that is extremely inert, with essentially no pathogens
and little to no odor potential. These benefits should allow the District
of Columbia to develop a strong marketing campaign to allow disposal of
dewatered digested sludge on public and private lands.
7.2. CAPITAL COST IMPACT
In order for any of the three anaerobic systems to process all the
sludge currently being generated at Blue Plains, some capital expenditures
would be required to expand and upgrade existing equipment. A detailed
cost analysis was not performed. However, the following unit operation
analysis indicates that the capital improvement cost would be the greatest
for the mesophilic system and the least for the thermophilic system. The
mesophilic-thermophilic system would lie between the two.
7.2.1. Improvements in Grit Removal
The analyses in Sections 4 and 5 indicated that 1.4 to 2.0 cubic feet
of grit per million gallons of influent flow is contained in the sludge
stream. Grit is inert, but it reduces the anaerobic digestion process
capacity by occupying tank volume. The calculations of tank volume (in
Section 6) assume minimal grit accumulation, but at the current time
approximately 25 to 30 percent of the existing digestion tank capacity
is occupied by grit. The best options are to increase grit removal before
the influent flow reaches the digesters or to increase digestor capacity
to allow for accumulation. The capital expenditures for grit removal
equipment are approximately equal for all digestion processes.
The cost for the necessary grit removal equipment has not been esti-
mated in this study, but it should be approximately equal for all three
digestion options. However, if grit removal is not provided, then the
digestion capacity would have to be increased by about 25% to allow for
accumulation.
79
-------
7.2.2. Digestion Tanks
Assuming that grit is removed upstream of the digestors, the need for
additional digestion tanks to handle the entire sludge stream is approxi-
mately six for mesophilic, four for the raesophilic-thermophilic, and none
for the thermophilic process. A preliminary analysis indicated that
operating the digesters at the thermophilic temperature would not cause
structural problems.
7.2.3. Sludge Heating Requirements
All three processes would require additional heating capacity to
handle the entire sludge stream. The mesophilic option may be satisfied
by existing in-house heat generation. The other two options would require
auxiliary steam generating equipment to allow direct steam injection
into each digestion tank operating at thermophilic temperatures.
7.2.4. Improvements in Gas Piping
The existing gas collection piping and safety devices need to be
replaced or upgraded for any of the anaerobic digestion processes. The
piping shows corrosion damage in places, and some of the gas protection
equipment is not functional.
7.2.5. Improvements in Mixing
The existing digestor mixing is believed to be deficient for several
reasons. First, the majority of the existing gas-mixing equipment was
originally installed in 1960 on a temporary basis and was not designed as a
complete tank mixing system. Secondly, the existing internal heating coils
allow build up of grit and inert material not capable of being mixed.
Improvements in grit removal, removal of internal heating coils, and an up-
80
-------
grade of the gas-mixing system to current standards would significantly
improve the mixing operation and, hence, improve the tank utilization.
7.2.6. Elutriation Capacity
The mesophilic system would require a 200 percent increase in elutria-
tion tank capacity. The mesophilic-thermophilic and thermophilic processes
both could not require elutriation.
7.3. SUMMARIZED ECONOMIC IMPACT
The operating cost analysis has developed a sludge handling unit cost
for the five options considered in this study. The developed costs are not
necessarily "accurate" (in the sense that all minor cost factors have been
included), but they are consistent and reflect the comparative costs of the
options. The unit costs are presented in Table 7-2, which also includes a
comparative presentation of capital costs for the five options.
A qualitative analysis of the disposal factors also is summarized in
Table 7-2. This analysis is reflected to some extent in the disposal cost
analysis for the current and projected 1981 options, in that disposal costs
of undigested sludge are included. The anaerobic digestion options for the
entire sludge stream will result in a reduced disposal cost. The charac-
teristics of the sludge product as indicated in the disposal factors in
Table 7-2 will determine the eventual disposal cost.
81
-------
TABLE 7-2. SUMMARY OF OPERATING AND CAPITAL COST REQUIREMENTS FOR SLUDGE HANDLING OPTIONS
00
to
Option Operating cost Capital cost items0
1.
2.
3.
4.
5.
($/MGIF) Grit removal Digestion tanks
Current 118.85 NA NA
(January to
June 1980)
Projected 72.12 NA NA
1981
Mesopliilic, 48.18 Yes, even Yes
all sludge
Mesophilie- 41.44 Yes, even Yes
thermopliilic,
all sludge
Thermophilic, 45.41 No No
all sludge
Sludge heating Gas piping Mixing Elutriation
NA NA NA NA
NA NA NA NA
Yes Yes Yes Yes
Yes, + Yes Yes No
Yes, + Yes Yes No
Current and projected options do not include the digestion of all sludge generated.
3
MGIF = million gallons of influent flow.
Yes = a capital expenditure is required or recommended to handle the entire sludge shown.
No = existing equipment is adequate or not required to treat the entire sludge stream
NA = not applicable to the evaluation.
Even = approximately the same capital would be required
Number = the number of digestors required.
+ = a significantly greater capital expense than for the other options is expected.
-------
REFERENCES
U.S. EPA 1979. Process design manual: sludge treatment and disposal.
EPA-625/1-79-001. U.S. Environmental Protection Agency, Cincinnati, Ohio.
83
-------
APPENDIX A
JANUARY TO JUNE 1980
SUMMARY OF AVERAGE MONTHLY OPERATING
DATA ON BLUE PLAINS SLUDGE MANAGEMENT OPERATIONS
The data shown in Appendix A were obtained from operating log sheets and
from conversations held with Mr. Ed Jones, Mr. Steve Bennett, and Mr. Walt
Baily.
The purpose of this analysis was to perform solids mass balances around each
unit process and to segregate the type of solids—primary, waste activated,
lime, ferric chloride—involved in each situation. This is possible at Blue
Plains since extensive process stream testing is conducted on a regular
basis. Analysis of six months of operating data indicates the following:
1. On a total solids basis, mass balance calculations around each unit
process are generally within 5 to 10 percent of closing.
2. Existing flow meters should be maintained and calibrated on a
regular basis. Many of the existing flow meters have been out of
service for some time. Flow calculations are approximated using
either pump strokes, pump curves, or changes in tank liquid levels.
This type of hydraulic data makes for difficult process control and
is believed to be responsible for some of the difficulty in closing
the mass balances around each process.
3. Numerous duplication of data on various log sheets is currently
required. In many cases different data are indicated for situa-
tions in which the data should be identical. It is recommended
that a review of all existing log sheets be conducted, that they be
consolidated where possible, and that better quality control be
maintained over the logging of data.
4. Some of the solids analyses are done by total solids and some by
total suspended solids. Since total solids is equivalent to dis-
solved solids plus suspended solids, a difficulty exists in doing
solids mass balances.
This difficulty arises for several reasons:
o Dissolved solids do not concentrate, but do increase in con-
centration as the sludge moves through the sludge treatment
process.
o Analyses of thickened or dewatered sludges show that the
amount of dissolved solids is almost insignificant compared to
the suspended solids.
A-l
-------
Analyses of clarified liquors, filtrates, or elutriates show
that suspended solids normally comprise only 15 to 50 percent
of the total solids, while dissolved solids normally comprise
the majority.
A-2
-------
TABLE A-l. SUMMARY OF RECENT AVERAGE MONTHLY HISTORICAL DATA ON RAW SLUDGE QUANTITIES
Year
1980
Primary sludge
Total dry sol ids
r Month
) Jan
Fob
Mar
Api
May
Jllll
Vo 1 ume ,
MGD
4 2
3.8
3 7
4.4
4 5
3 0
Percent
0.55
0.72
0.61
0 78
0 62
0.92
Tons .per
day
98
116
96
146
119
117
Total dry
volatile sol ids
Percent
volati le
77
81
78
78
79
85
Tons per
day
75
94
75
114
94
99
Volume,
MOD
2.7
3 1
2.9
3.4
2.8
2.7
Waste activated
Total dry sol idsc
Percent
dry
sol ids
0.91
0.72
0.67
0.73
0.68
0.88
Tons per
day
103
94
82
104
80
101
sludge
Total
volatile
PC remit
volatile
66
68
66
66
62
64
dry
sol ids
Tons per
djy
68
63
r,4
69
65
65
Data obtained from Mr Walt Rally and Blue Plains operating records.
There .ire strong indications that significant amounts of grit are in the primary sludge. Detailed analysis ol volume w.is
not made, but currently is estimated at 300 to 350 cubic feet per day or approximately 30,000 to 35,000 pounds per day
Iron is added for phosphorus removal. The iron - phosphate sludge contribution is between It to 15.5 percent of the total
mass
Density of this material is 8 5 pounds per gallon
Density of this material is 8.39 pounds per gallon.
-------
TABLE A-2. SUMMARY OF RECENT AVERAGE MONTHLY DATA ON GRAVITY Til ICKEN1NO"
Total gravity thickener inflow
Tul.il dry solids0
Year
I'J80
HoiiLh
.Lin
Fell
Mai
A,..
May
Jim
.liil
Vo 1 time ,
MOD
16 0
15. Q
15.7
15 7
15.3
16.0
16.9
mg/l
1600
1915
1600
2350
I960
184-i
Tons
per day
107
127
105
154
125
123
Total
volatile
Percent
volatile
74. /
67 4
69.4
66 5
72.0
69.7
67.6
dry
solids
Tons
per day
74 7
82.2
70.8
99.1
83.5
82.8
Gravity thickener under (low
To La I dry sol ids
Vo 1 nme .
HGI)
328
437
.165
.521
.135
370
Percent
7.3
6.7
6.7
6 9
6 4
7.9
'Inns .
l>er_da/
105
129
IOR
158
120
129
Tnt a 1
vnl.il I In
Pcrrriil
volatile
79
75
70
65
66
71
dry
sol ior ilny
74
97
7f.
101
70
92
. .
Data obtained from Mr. Steve Bennett and Blue Plains operating data. Data jre not avail.ilile on gravity thickener ovetflow
Tnl.il gravity lliirkrncr inflow consiits of flow Irom primary danders, dilution water, approximately 50 percent ol UIK eliitrialiou tank ovcillnw
C Existing d.ila arc* tnnsidered lo be incorrect because they indicate a sludge oass greater th.in the output being disposed ol At this Unit,
tin: niiinlicrs hliown liir tons per day arc based on primary sludge production (Table- A-1) * the suspended solids LontrilmLion of
the dilution w.-iter (0.17 to 1 0 tons per day) + one half of the total solids in the elutriate overflow (Table A-5)
•
Density of this material is 8.B pounds per gallon.
-------
TABLE A-3. SUMMARY OF RECENT AVERAGE MONTHLY DATA OH DISSOLVED AIR FLOTATION THICKENING
Total dissolved air notation
Year
i?8o
Mould
Jan
Nar
A|ir
H.iy
Jim
Volume,
MCI)
2 7
3 1
2 9
3 4
2 8
2.7
Toldl dry
PcrrenL
dry solids
0 91
0 72
0 70
0.71
0 68
0.89
sol ids
Tons
per day
101
91
85
103
79
100
Lliickc-iicr inflow
Total
volatile
Pcrn-iil
vo 1 a 1 1 1 e
66.0
67 7
65 9
66.0
62 0
64.0
dry
sol ids
Tons
per day
6B
63
56
f.R
49
64
Volume,
MCI)
0 665
0.5/0
0.496
0.582
0.448
0.508
Thickened m.ilciial
Total dry
Percj-iil
diy solids
3.7
3.9
4.1
4.2
4 2
4.7
solids
Tons
per day
102 7
92 7
84.8
101 9
78 4
-------
TABLE A-3.
SUMMARY OF RECENT AVERAGE MONTHLY DMA OH DISSOLVED AIR FLOTATION THICKENING0 (continued)
Subnatant Flow
Total dry
suspended solids,
Year Month
1080 Jan
Feb
Hat
Apr
May
Jun
Volume,
HOD
Z 6
2.9
2.2
7 7
3.1
S.5
EB/I
28
21
21
37
'•4
17
Tons
per day
0.3
0.3
0.3
1.2
0.6
0.4
Data obtained from Mr. Steve Bennett and Blue Plains operating data.
-------
TABLE A-4. SUMMARY OF RECENT AVERAGE MONTHLY DATA ON ANAEROBIC DIGESTION
Year
1979
1980
Primary slmlee
Ion th
J a n
Fell
Mar
Apr
Hay
Inn
Jill
A"g
Sept
OiL
Nov
lire
.Ian
Full
Mnr
Apr
May
.Inn
Vi> 1 nine ,
MCI)
0.242
0. 188
0 . 284
0 301
0. 199
0 225
0 194
0.216
0 177
0 U>6
0 177
0 195
0.228
0.227
0.228
0. 196
0 222
0.169
Tula I dry
IVrtenl
dry solids
8 0
8 6
8 1
7.3
9.8
8 8
7 3
7 8
7
69.2
66 9
63.8
63.7
66 3
,lry
sol nls
Tons
JKT d.iy
29 4
2r> 0
IS 4
20 4
IS 4
28 i
28 8
»2 1
17 1
35 1
_ _ — —
18 5
14 0
il 1
1J.S
10 6
27 0
41 1
Data olitJincil from Mr Steve Bennett and Blue Plains operating data.
(continued)
-------
TABLE A-4. SUMMARY OF RKCENT AVERAGE MONTHLY DATA ON ANAEROBIC DIGESTION3 (continued)
Year_
1970
f
CO
1980
Hniith_
.Lin
Krl>
M.II
Apr
H.iy
Jim
In I
AiiR
Sopl
Oct.
Nov
l)er
liin
Fel>
Mar
Ap.
May
Jim
Coinliincil digester input
Vn 1 nine ,
MGD
0 416
0 158
0.384
0 461
0.442
0 431
0 42.)
0 455
0.460
0.441
0.357
0.364
0 503
0 521
0.465
0.464
0 485
Total
Percent
diy solids
7.1
7.0
7.6
6.3
7 4
7 1
6.0
6.4
5.9
5 6
5.4
5.9
5.2
5 2
5.3
5.2
5.8
dry solids
'Inns
per il.iy
123.5
104.3
121.6
122.0
116.0
127.3
105. R
121. 1
113.6
102 6
79.7
90.4
108.3
113.8
103.5
101 6
117.7
Total
volatile
IVrcrnL
volatile
67 6
71 6
71.7
73.0
69.1
67 9
64. 1
64 2
62.1
65. J
70.5
75.8
72.6
68. 4
65.2
65.1
68.5
dry
solids
Tuns
per day
83.5
74 7
87.2
89 1
94.0
86.4
6/ 8
77 7
70.6
67.0
56.2
68.5
78.7
77.8
67.5
66.2
80.6
W.isLc activiitril
sludge
I'tirrcnl
by weight
35
35
19
25
40
35
44
42
52
51
15
23
41
44
46
42
51
t ruction
Price-ill
liy vii 1 Hint:
42
48
26
15
55
48
54
51
62
(>t
45
17
r>r>
56
58
52
f>5
Dal.i nhi nineil From Mr Steve lleimrlt jnd Blue Plains operating data
(cniiLiiiucil)
-------
TABLE A-4. SUMMARY OF RECENT AVERAGE MONTHLY DATA ON ANAEROBIC DIGESTION (continued)
Digested sLmlge
Year Mon III
1979 )7
0 364
0 S03
O.S2I
0 465
0 464
0 485
Total dry
Percent
dry solids
3.3
3 3
3.4
2 9
3 2
3.8
3.8
3.6
3 9
3.6
3.6
2 7
2 3
2.6
2.6
2.8
3.1
3.1
3.1
sol ids
Tons
per day
57.2
49.3
54 4
56.0
59.0
68 3
67.0
68.3
74.8
66 2
47.7
40.2
34.9
54.5
56 5
54 3
60.0
62.5
Total
volali le
Percent
volatile
54 2
54.6
54.2
55.7
55 5
53.3
55.3
54.3
52.3
53.8
56 5
56.6
57.6
55.3
55 1
56.1
55.5
54.8
55.3
dry
solids
Tons
per day
31.0
26.9
29.5
11.2
32.7
36.4
37.1
37 1
39 1
35 6
27.0
22.7
20 1
30 2
31 1
30.5
33.3
34.2
Togo.."
95
96
94
95
96
95
95
95
94
95
95
94
92
91
93
90
9J
95
93
Volatile
acids,
mg/l
168
233
204
158
172
260
207
183
176
166
180
225
142
126
284
338
371
323
329
Alk.C
nig/1
5629
6229
5')56
5313
5868
6488
657H
5742
5238
5209
5099
7272
6784
7624
8403
8914
8328
8366
8140
Nil -N
rag/1
1107
1451
1428
1374
1400
1568
1302
Gns j
produced ,'
cubic feet
xlOOO
912
846
834
999
12)6
1205
R86
749
797
849
808
879
1061
1246
1123
888
906
994
928
Digester gas
co2
rontent ,
percent
32.7
31 4
34.4
31 8
32 6
32.6
12.8
29. 1
33 0
31.9
34.9
35.0
35.5
34.3
35 I
34 6
34.2
34.9
34.8
lias prodiHcd
per pound of
void I lie snl ids
reduced
8 7
8.8
7 2
8 6
9.9
12 (I
14 4
9 I
12 6
11 5
9 6
1 1 0
12 8
12 0
12 0
13 8
10.7
Data obtained from Sieve Bennett and Blue (Mains operating data.
Tempornture measured on recycle sludge before entering heat exchanger.
AIK - alkalinity. Alkalinity is measured on entire solids mass rather than on sulinatant of sludge.
Blue Plains is in the process of signing » contract with Naval Research to sell all excess digester gas for $0.95 per 1000 rnliir Icet.
-------
TABI.K A-5. SUMMARY OF RECENT AVERAGE MONTHLY HISTORICAL DATA ON ELUTRIATION TANK OPERATIONS
Anacrnhic ill (jesters
ToLal dry solids
Year Nonlli
I'JHO J.in
Kcl)
Mm
Apr
May
Illll
Dnld oli I aincd from
A|i|>rox mini <:!y hall
!*• C Data indicate LliaL
Vo 1 lino ,
NCI)
0.397
0.509
o 509
0.666
0.448
0 492
Percent
dry solids
2.6
2.4
2.4
2 7
3 0
3 3
Tons
per
-------
TABLE A-5. SUMMARY OF RECENT AVERAGE MONTHLY HISTORICAL DATA ON ELUTRIAT10N TANK OPERATIONS0 (continued)
Elutriation underflow Lo dewatoring
Elutriation overflow
Total diy solids
Year
19 BO
" Data
b TI..I,
HonLh
Jan
Krl>
Mar
A|>r
Nay
Jun
obtained from Mr.
Volume,
MGU
0.227
0 279
0.309
0 187
0 207
0.241
Steve Bennett and
nrmallv in fsunnnfipl
Percent
dry solids
5.4
4.8
3 6
5.5
5.4
5.2
Blue Plains operating
1 to return to nnmarv
Tons d
per day
54
59
49
46
52
55
records.
treatment bv eravitv
Volume,
MGD
2 44
2.57
2.52
2.56
2.41
2.46
' flow. At the preset
h
Total dry
sol ids
n-B/1
1800
I'J74
1652
1517
12f>4
1208
it tune, only par
Tons
per day
IR 3
21 1
17 4
16 2
12.6
12.4
t of
the overflow flows by gravity to primary treatment The other part is pumped to gravity thickening. Theie are no flow meters
on cither line, and it is not possible to tell how much flow is going to gravity thickening or to primary treatment.
c Suspended solids for the same time period in mg/1 were: Jan-295; Feb-874; Mar-1048; Apr-684; May-479; Jnne-559.
Density of this material is 8 85 pounds per gallon.
-------
TABLF. A-6. SUMMARY OF RECENT AVERAGE MONTHLY DATA ON RAW SLUDGE DEUATEKING°
M
Primary sludge
From gravity thickener
Waste activated sludge from 1,
dissolved air flotation thickeners a
Total dry solids
Year Month
1980 Inn
rcl>
Mar
Apr
May
Jim
a
b
c
-------
TABLE A-6. SUMMARY OF RECENT AVERAGE MONTHLY DATA ON RAW SLUDGE DBWATERJNG (continued)
Uewatered raw sludge off vacuum filler
Yeor
1979
1980
Non Hi
Aug
Sept
Oct
Nov
Dec
Jan
Mar
Apr
May
.Inn
Jill
Wei ions
per day
948
490
910
635
695
Total dry
Pei cenl
dry solids
19 6
20 7
19.9
17.6
17.2
21.6
21.1
21 1
22.6
22 1
sol ids
Tons .
, d
per day
163
106
192
134
157
Tolal
volali Ic
Percent
volatile
44 6
43.3
44 8
48. 1
46.2
41.0
40.9
40 2
42 1
41 4
vacuum filler fillralc
dry
solids Total dry solids
Tons Volumu, Tons ,
per day MOD mg/1 per day
75 0.499
44
78 0.574
54
66 0 440
washwalui
Tolal diy solids
Volume-, 'Ions
MGD nig/I per day
I _ _ .-...— ...--. __.
1-1 a
l*J Da la obtained from Mr. Steve Bennett and Blue Plains operating data.
Data base is extremely limited.
Wasliwater volume is significant but no data are taken on this stream Suspended solids are not believed to be significant
See footnote c on Table A-8.
Analysis based on several samples indicated that total solids were about 500 ing/1 and that suspended solids about 250 mg/l.
llascd on limited data, it is estimated that the total solids in the filtiate average 2 tons per day and can be considered insignificant.
-------
TABLE A-7. SUMMARY OF RECKNT AVERAGE MONTHLY DATA OM DIGESTED SLUDGE DBUATERING*
From clutnation
Vn 1 nine ,
Year Month MCI)
Total (ley
Percent
Dry Solids
solids,
Tons
per day
Dry ferric
chloride added
Tons
per day
I'm Ang
Sept
On
Nov
Her
1980 .Ian 0 227
a
b
c
d
c
Fch 0.279
Mar 0 309
Apr 0.187
May 0 207
.Inn 0.241
Jill
Data obtained from
Data indicate that
5 4
It 8
3 6
5.5
5.4
5.2
54
59
49
46
52
55
Mr. Steve Bennett and
solids contributed by
Density of tins material is 8.83
Sunnier of 1980 Blue Plains pays
pounds
$0.0825
10.2
11.9
10.8
10.0
10.7
10.3
Blue Plains
filtrate are
per gallon.
per pound of
Dewatered digested sludge to disposal
Total
to
dry solids
disposal
Total dry
volatile solids
To disposal
Vacuum liltei filtrate
Total diy
so 1 ids
Dollars. Wet tons Percent Tons Perrent Tons Volume, _ Tons
per day per day dry solids per day volatile per day MGD UIR/ 1 per day
740
864
784
726
777
748
operating data
insignificant
368
361
345
290
289
293
395
337
302
314
328
294
.
compa red
17.8
17.9
16.3
16 1
16.0
15 8
15.6
16.7
16.8
16.9
16.8
65.5
64.6
56.2
46.5
49.9
62.4
52.6
50.4
52.7
55.4
49.4
to total mass of
iron (Fe), which comprises 44
percent of
49.5 32
47 . 7 30
49 6 27
54.3 25
56.3 26
57.2 35
54.1 28
51.6 26
51.9 27
52.5 29
53.8 26
solids included.
.4
.8
9
0
4
.7
.4
.0
.4
.1
.6
0.136
0 205 9600 8.2
0.192 8800 7.0
0.130 12000 6.5
0.144 9200 5.5
0.175 8200 6 0
ferric chloride (Fe CI2).
Suspended solids [or this same time period in ng/1 were: Jan-185; Feb-66; Mar-110; Apr-103; June-270.
-------
TABLE A-8. SUMMARY OF RECENT AVERAGE MONTHLY HISTORICAL DATA ON RAW SLUDGE DISPOSAL
\Jl
Break down of total dry solids to disposal
Year
1980
Month
Jan
Feb
Mar
Apr
Hay
Jim
Jill
Raw sludge
hauled from
plant. D'c
Wet tons
per day
1153
1047
758
1004
862
762
716
Trucking and ,
disposal cost,
Dollars
per day
41,175
37,200
26,362
35,587
30,262
26,512
24,787
Total dry solids,
to disposal ,
Percent
dry solids
as trucked6
14.1
14.5
14.0
19.1
15.5
20.6
Tons
per day
163
152
106
192
134
157
Raw
sludge
solids.
tons
per day
112
106
72
150
93
104
From
lime addition
tons ,
per day
41
36
28
36
35
36
From
ferric chloride addition
tons
per day
11
10
6
6
6
17
Data obtained from Mr. Ed Jones, Mr. Steve Bennett, and Blue Plains operating records.
At the time of this report - Sept. 1980 - dewatered raw sludge was being disposed of as follows:
o Approximately 100 wet tons per day to Beltsville at an approximate trucking cost of $30/wet ton.
o Between ISO to 200 wet tons per day to HT1 for composting at an approximate trucking cost of $30/wet ton. Contract on a
yeai to year basis. Could possibly go up to 400 wet tons per
-------
TAIII.E A-9 SUMMARY OF KKCKNT AVF.RAKK MUNTII1.Y HISTORICAL DATA ON I)IfiKSTKI) SI.UUGK DISPOSAL
Total dry sol ids
lo disposal
Break down of_ |-oLJlJ_|lr.y sojids
Year
1979
1980
HonLli
Ang
Sept
Oct
Nov
Dec
Jan
K.-l.
Mar
A|ir
Mjy
Jim
.liil
Deviate red
digested
slmlgp,
we I Lous
|ici day
168
361
145
290
28V
291
395
337
302
116
128
294
Triu king and .
disposal cost,
do 1 1 a rs
per
4.395
5,925
5,055
4,510
4,710
4,920
4,410
pert nil
dry solids
17.8
17.9 '
16.3
16 1
16 0
15 8
15 6
16.7
16 8
16.9
16 8
tons
pi>r day
65.5
64.6
56 2
46.5
49 9
62.4
52.6
50.4
52.7
55.4
49.4
Digested Sol i
-------
APPENDIX B
ANALYSIS OF AVERAGE PRIMARY AND SECONDARY SLUDGE PRODUCTION
PER MILLION GALLONS OF INFLUENT FLOW
B.I. PRIMARY SLUDGE
TABLE B-l. ANALYSIS OF AVERAGE SLUDGE
PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW3
(January through June 1980)
Primary sludge. Primary sludge
production, 'C volatile solids,
Month T/MGIF0 percent
January
February
March
April
May
June
Average
Standard deviation
98/331
116/325
96/345
146/332
119/327
117/330
= 0.296
= 0.357
= 0.278
= 0.440
= 0.364
= 0.355
0.348
0.057
77
81
78
78
79
85
79.7
2.9
Average dry ton of volatile primary sludge production per MGIF is:
(0.348 ± 0.057) T/MGIF (0.797 ± 0.029) percent volatile
= (0.348)(0.797) ± (0.797) (0.057) + (0.348)2(0.029)2
= 0.277 ± 0.047 VT/MGIF
All data taken from Appendix A, Table A-l.
Sludge as withdrawn from the primary clarifiers and pumped to the
gravity thickeners.
Q
It is estimated that grit equal to 1.5 to 2.0 cubic feet per million
gallons of influent flow at 100 pounds per cubic foot is included with
the primary sludge.
B-l
-------
MGIF = million gallons influent flow.
T/NGIF = dry tons of solids per million gallons influent flow.
VT/MGIF = dry tons of volatile solids per million gallons influent
flow.
B.2. SECONDARY SLUDGE
B.2.1. Current Conditions
TABLE B-2. ANALYSIS OF AVERAGE SECONDARY SLUDGE
PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW3
(January to June 1980)
Secondary sludge Secondary sludge,
production, Volatile solids,
Month T/MGIF percent
January
February
March
April
May
June
Average
Standard deviation
103/331
94/325
82/345
104/332
80/327
101/330
= 0.311
= 0.289
= 0.238
= 0.313
= 0.245
= 0.306
0.284
0.034
66
68
66
66
62
64
65.3
2.1
Average dry tons secondary sludge, volatile solids production per MGIF
is:
(0.284 ± 0.034) T/MGIF (0.653 ± 0.021) percent volatile
= (0.284)(0.653) ± (0.653) (0.034) + (0.284) (0.021)
= 0.185 ± 0.022 VT/MGIF
a All data taken from Appendix A, Table A-l.
Sludge as withdrawn from the secondary clarifiers and pumped to the
dissolved air flotation thickeners.
B.2.2. Future Conditions
Increase Phosphorus Removal —
Effluent limitations on phosphorus will be reduced from the current 1.1
mg/1 average to the new NPDES permit requirement of 0.53 mg/1. This will
be accomplished by increasing the current iron dosage. Past records
indicate 3.8 pounds of chemical sludge produced per pound of P removed by
iron, therefore, every million gallons of influent will generate an
additional:
(1.1 - 0.53)»g/l P (8.34)(1 HC)
B-2
-------
It is assumed there are no volatile solids.
Multi-media Filters —
Within the year the new multi-media polishing filters will be in operation.
It is estimated that these filters will reduce the suspended solids being
discharged from an average of 15 to 7.5 mg/1. Therefore, every million
gallons of influent will generate an additional:
(15.0 - 7.5)mg/l (8.3A)(1 MG) = 0'°31 T/MGIF
It is assumed that 70 percent of the solids will be volatile.
Nitrification--
Within several months the nitrification system will be completely
operational. At a minimum, this system will have to reduce current total
kjeldahl nitrogen (TKN) levels in the plant effluent from an average of
13.8 mg/1 to the NFDES permit level of 5.3 mg/1. Assuming a biological
yield coefficient of 0.1 pounds of solids produced per pound of TKN
reduced, the additional dry solids generated would be:
(13.. - 3.MM/1 (..MXIW • °-0"
It is assumed that 70 percent of the solids will be volatile.
Assuming no change in the standard deviation, the new volatile solids
content would be:
(0.185 + 0 + 0.0313(0.7) + 0.0035(0.7) (100) ,. .
0.284+0.009+0.031+0.004 ~ J Percent
B-3
-------
APPENDIX C
ANALYSIS OF GRAVITY THICKENER OPERATION
There are six 65-foot diameter units. Surface area of each unit is 3,318
square feet. Surface area is 19,908 square feet. All operational data
taken from Appendix A, Table A-l and A-2.
TABLE C-l. AVERAGE MONTHLY HYDRAULIC AND SOLIDS LOADING RATES
AVERAGE MONTHLY HYDRAULIC AND SOLIDS LOADING RATES
(January through June 1980)
Month
Hydraulic loading rate,
gallons per day per square
foot of tank surface
Solids loading rate,
gallons per day per square
foot of tank surface
January
February
March
April
May
June
804
799
789
789
769
804
10.7
12.8
10.5
15.5
12.6
12.4
TABLE C-2. AVERAGE MONTHLY THICKENING PERFORMANCE
(January through June 1980)
Month
Thickened sludge volume,
gallons thickened sludge
per million gallons of
plant influent
Thickened sludge
concentration,
percent
solids
January
February
March
April
May
June
Average
Standard deviation
328,000/331 =
437,000/325 =
365,000/345 =
521,000/332 =
435,000/327 =
370,000/330 =
991
1,345
1,058
1,569
1,330
1,121
1,236
218
7.3
6.7
6.7
6.9
6.4
7.9
7.0
0.5
C-l
-------
No relationship between hydraulic loading rate or solids loading rate
versus thickened sludge concentration could be established.
TABLE C-3. ANALYSIS OF EFFECT OF GRAVITY THICKENING ON AVERAGE PRIMARY
SLUDGE PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW
(January through June 1980)
sludge. Thickened sludge
production, ' volatile solids,3
Month T/MGIF percent
January
February
March
April
May
June
Average
Standard
105/331
129/325
108/345
158/332
120/327
129/330
deviation
= 0.317
= 0.397
= 0.313
= 0.476
= 0.367
= 0.391
0.377
0.060
79
75
70
65
66
71
71
5.3
Average VT/MGIF as removed from the gravity thickener.
(0.377 ± 0.060) T/MGIF (0.71 ± 0.053) percent volatile
22 22
= (0.377K0.71) ± (0.71) (0.060) + (0.377) (0.053)
= 0.268 ± 0.047 VT/MGIF
Sludge as withdrawn from the gravity thickeners.
It is estimated that grit equal to 1.5 to 2.0 cubic feet per million
gallons of influent flow at 100 pounds per cubic foot is included with
the primary sludge.
MGIF = million gallons influent flow.
T/MGIF = dry ton of solids per million gallons influent flow.
VT/MGIF = dry ton of volatile solids per million gallons influent
flow.
C-2
-------
APPENDIX D
ANALYSIS OF DISSOLVED AIR FLOTATION (DAF) THICKENER OPERATION
There are 18, 20-foot wide by 55-foot long (effective length) units.
Effective thickening surface area of each unit is 1,100 square feet. Total
effective surface area is 19,800 square feet. These units operate
continuously at 30 to 34 pounds of secondary solids per day per square foot
of effective thickening area. Polymer is required to operate at this
loading rate. Polymer usage is 7 to 10 pounds of dry polymer per dry ton
of feed solids. All operational data taken from Appendix A, Table A-l and
A-3.
TABLE D-l. AVERAGE MONTHLY THICKENING PERFORMANCE
(January through June 1980)
Thickened sludge volume, Thickened sludge
gallons thickened sludge concentration,
per million gallons of percent
Month plant influent solids
January
February
March
April
May
June
Average
Standard
665,000/331 =
570,000/325 =
496,000/345 =
582,000/332 =
448,000/327 =
508,000/330 =
deviation
2,009
1,754
1,438
1,753
1,370
1,539
1,644
239
3.7
3.9
4.1
4.2
4.2
4.7
4.1
0.3
Since float concentration is not expected to change in the future, the
additional secondary solids generated in the future (Appendix B) will
increase thickened sludge volume by approximately the same amount or 15
percent (from 1,644 ± 239 to 1,900 ± 239 gallons per million gallons of
influent flow).
At 30 pounds of dry secondary solids per day per square foot of effective
thickening area, each DAF can thicken:
30 pounds 1100 square feet _ 33,000 pounds
day-square foot x unit day-unit
D-l
-------
In the future, each million gallons of influent flow will contribute
0.328 ± 0.034 tons (656 ± 68 pounds). Assuming a value of 656 + 68 or 724
pounds per million gallons of influent and an average daily flow of
334 million gallons per day (MOD), then the minimum number of DAF
thickeners required to be operating is:
1 unit 724 pounds 334 MOD _ g -t
33,000 pounds X 1 MGD X 1 "
D-2
-------
APPENDIX E
ANALYSIS OF LITHIUM CHLORIDE (LiCl) TRACER STUDIES
BLUE PLAINS DIGESTERS
E.I. MECHANICAL DATA
Inside diameter of each digester - 84 feet
Cone depth - 13 feet
Average cylindrical height - 22.1 feet
Theoretical tank volume
(42) (3.1416K22.1 + 13/3) = 146,488 cubic feet
= 1,096,000 gallons
Theoretical weight of digester fluid - 9,140,000 pounds
E.2. TEST PROCEDURE
Each day three digesters were taken off line and 6 pounds (Ibs) of
LiCl added in approximately four equal fractions at manholes spaced about
25 feet from the center of the digester. On digester No. 1, two of the
manholes could not be entered, so one-fourth of the LiCl was added at a
manhole located on a line between the two manholes that could not be used,
and one-fourth at a location adjacent to the wall of the digester. On
digester No. 9, one manhole could not be entered, so one-fourth of the LiCl
was added through a manhole at the center of the digester instead. Mixing
was accomplished by means of the regular gas-mixing system and with a
recycle of approximately 1,000 gallons per minute (GPM) by means of a pump
for one hour before the sampling time. Samples were taken before the
addition of the LiCl (0 time) and at 3, 6, and 8 hours after the addition.
Gas compressors were not available on digesters 9 and 10, so mixing in
these digesters was accomplished by means of the 1,000 GPM recycle pump
running continuously during the 8-hour test period.
Samples were analyzed for lithium by means of an atomic adsorption
instrument, using a graphite furnace. The available volume was calculated
from the difference in concentration between the 0-hour and 8-hour samples
resulting from the addition of the 6 Ib dose of LiCl.
E.3. RESULTS
The results of the tracer studies are presented in Table E-l.
E-l
-------
E.4. DISCUSSION
It is apparent that mixing was a problem, as indicated by the fact
that in digesters 3, 4, 6, 9, and 11, the 8-hour and 6-hour concentrations
differed by more than 10 percent, indicating that equilibrium may not have
been reached.
TABLE E-l. LITHIUM TRACER STUDY RESULTS
Lithium
Digester 0-hr
1
2
3
4
5
6
7
8
9
10
11
12
0.00
0.16
0.29
0.52
0.00
0.16
0.39
0.46
0.03
0.19
0.47
0.07
3-hr
0.95
1.15
2.11
4.15
1.50
1.16
2.37
2.17
14.13
1.09
18.20
7.15
Concentrations,
6-hr
0.59
1.13
1.64
1.82
1.20
1.14
1.57
1.00
3.00
0.96
1.50
1.73
mg/1
8-hr 8-hr - 0-hr
0.55
1.09
1.32
0.84
1.20
1.45
1.43
1.09
1.37
0.98
1.12
1.59
0.55
0.93
1.69
0.32
1.20
1.29
1.04
0.63
1.34
0.79
0.65
1.52
Volume ,
gallons
x 1000
1,310
775
699
2,251
600
558
693
1,143
538
912
1,108
474
Usable
volume,
percent
119
71
64
205
55
51
63
104
49
83
101
43
The value for digester No. 1 is also suspect. As discussed above, a
portion of the LiCl was added near the tank wall of the digester, rather
than at the more central addition points used in the other digesters. The
very low concentration of LiCl found in digester No. 1 would indicate that
mixing was not adequate in the area near the tank wall, and that a portion
of the LiCl was not recovered.
The distribution of recycle to the digesters appears to be good, based
on the 0-time readings for digesters 4, 8, and 11, the last three tested.
The content of LiCl in the digesters before addition of LiCl was 0.52,
carried to the digesters by the recycle from the other digesters.
The usable-volume values obtained in these tests exclude portions of
the tank volume occupied by grit and also those areas where mixing was so
poor that the LiCl never reached them. The results of digester No. 1
indicate that this may be a factor in the areas of the tanks near the
walls. It is also of note that 4 of the 9 gas-mixing tubes in the No. 1
digester were inoperative. It should also be noted that a scum layer,
which may range from 0 to 12 inches, will also be excluded from the usable
volume.
Lithium chloride appears to be quite satisfactory as a tracer material
for this test. More reliable results would be obtained if the digesters
E-2
-------
were kept off-line for a longer period to allow more complete mixing. A
test where one slug of LiCl was added to the recycle line would allow a
determination of the recycle distribution to all tanks, and a determination
of usable volume for the entire system, but a test of this type would also
have problems in distinguishing between areas occupied by grit and areas of
very poor mixing; to make this determination, longer-term off-line tests
are probably required.
The system was simulated by computer analysis, using an average usable
digester volume of 700,000 gallons. The values predicted by the simulation
agreed very well with the analyzed values through the end of the third day
of testing, but the analyzed values were about 20 percent low during the
fourth day. It is not known what problems could have caused this dis-
crepancy during the last tests, those of digesters 4, 8, and 11.
E.5. COMPUTER SIMULATION
A computer program was developed to simulate the behavior of lithium
chloride during the test period. For the purposes of the simulation, the
digesters were divided into four groups of three digesters each, in
accordance with the test procedure. Each group was assumed to have a total
volume of 2.1 million gallons (700,000 gallons per digester) and a recycle
rate of 1,500 gallons per minute, (500 GPM per digester). The flow of
fresh sludge into the group and treated sludge out of the tanks was assumed
to be 1/15 of the total volume per day. The program calculated the esti-
mated LiCl concentrations each half hour; a subroutine was set up to cal-
culate the changes in concentration that would take place because of the
removal of tank contents by the recycle, the addition of recycle sludge
that was composed of mixed sludge from all four groups, the removal of
treated sludge from the system, and the addition of fresh sludge. The main
program in turn applied this subroutine to each group of digesters for each
half-hour time period, noting the change in concentration of each group of
the combined recycle, taking into account the additions of LiCl to a dif-
ferent group each day, and the fact that one group was off-line for an
8-hour period each day. Results were printed out from 9:00 AM (time of
LiCl addition and removal of the group from line) and 5:00 PM (the time
that the group was placed back on-line).
The results of the simulation are presented in Table E-2. It can be
seen that there was good correlation between the concentrations predicted
by the model and the field results until Sunday at 5:00 PM.
Both the 9:00 AM and the 5:00 PM results on Monday, the last day of
the test, indicated that actual results were substantially lower than those
predicted by the model. We are unable to explain the apparent loss of LiCl
from the system indicated by the 5:00 PM, Monday recycle sample. In order
to make the computer simulation agree with the field results, it was
necessary to postulate a withdrawal of treated sludge and replacement with
fresh sludge of 3,300 GPM starting at 5:00 PM on Sunday and continuing
through 5:00 PM on Monday or some other addition of several million gallons
of fresh sludge to the system. There are no such upsets reported from the
plant. One of the digesters did overflow, but this accident took place the
next day. The weight of LiCl left (23 Ibs) from the original 100 Ib drum
E-3
-------
TABLE E-2. MODEL SIMULATION OF DIGESTER ANALYSIS
Lithium concentrations, mg/1
Day Time
Friday 5 PM
Saturday 9 AM
Saturday 5 PM
Sunday 9 AM
Sunday 5 PM
Monday 9 AM
Monday 5 PM
Digester
1 2
i'°
-------
Ibs of LiCl in the system, as compared to a total weight of 56 Ibs pre-
dicted by the model. Various explanations are possible:
o There was a large influx of fresh sludge to the system, flushing
out the LiCl. As discussed earlier, this would have had to have
been on the order of several million gallons, and no such upset
occurred.
o A mistake was made in the addition of LiCl. As discussed above,
a check of the remaining LiCl indicates that the proper amount
was added.
o The average volumes of the digesters are nearer to the theoreti-
cal 1,096,000 gallons than the assumed 700,000 gallons. This
does not appear reasonable, in that if this assumption is made,
all of the analyses for the first three days would have been in
poor agreement with the model, and such an assumption does not
fit with the individual test results.
o The missing 12 pounds of LiCl, which cannot be accounted for by
the analyses, may be concentrated in areas of poor mixing so that
the tracer, or portion of it, never entered the system.
E.6. COMPARISON OF RESULTS WITH CANADIAN TRACER STUDIES
It is of interest to compare results with those obtained by J. Smart
(1978) (An Assessment of the Mixing Performance of Several Digesters Using
Tracer Response Techniques, Research Publication No. 72, Dec. 1978, Ontario
Ministry of the Environment.) He used fluoride as a tracer on 10 anaerobic
digesters ranging from 165,900 to 1,690,000 gallons in size, using both
mechanical and gas mixing with mixing power ranging from 0.02 to 0.25
HP/1,000 gallons.
Smart found mixing to be a problem, with an average of 55 percent
usable volume, as compared to 65 percent found in our study. He found that
the tracer concentration leveled out in 4 to 6 hours, which agrees well
with our finding that in most cases the tracer leveled out in 4 to 8 hours.
He could find no correlation between the amount of dead space and the size,
age, condition, applied mixing power, or type of mixing used in the
digester.
E.7 CONCLUSIONS
The results are consistent with an average usable volume of about 65
percent of theoretical, with the dead space consisting of the grit layer,
the scum layer, and areas where there is little or no mixing.
A tracer study where the tracer is added to the recycle line, thus
feeding all 12 digesters at once, will help to resolve some of the ques-
tions about short-circuting and total hydraulic detention time.
E-5
-------
APPENDIX F
ANALYSIS OF GRIT ENTRY INTO ANAEROBIC DIGESTERS PER
MILLION GALLONS OF PLANT INTLUENT FLOW
Based on discussions with anaerobic system operating personnel:
o It takes 2 to 3 years for a digester to accumulate grit to a point
of equilibrium, that is grit no longer accumulates but passes
through the digestion tanks.
o Grit in the tank was estimated to occupy 15 to 20 percent of the
total tank volume. Since each tank has a theoretical volume of
146,469 cubic feet, then grit occupies 21,970 to 29,294 cubic feet
of tank volume.
Assuming three years for grit build-up within a tank to reach equilibrium
then:
21 970 cubic feet off grit = 2Q
(365 day/year) (3 years)
or
29,294 cubxc feet of grit cub-c d
(365 days/year) (3 years) & *
Approximately half the daily sludge production goes to anaerobic digestion
or the plant influent flow equivalent of 167 million gallons per day (MGD).
There are 12 digestion tanks and it is assumed that sludge is pumped
uniformly to all of them, therefore each tank receives raw sluge generated
from:
12?tanks = 13'9 MGD °f plant influent flow
At 20 cubic feet of grit per day per tank, each MGD of plant influent flow
is contributing:
20 cu^c feet 8rit per tank = :.4 cubic feet per HGD
13.9 MGD per tank r
At 100 pounds per cubic foot, 140 pounds or 0.07 tons of dry solids per
million gallons of plant influent flow (T/MGIF) is being contributed.
At 26.8 cubic feet it is 2.0 cubic feet per MGD, which at 100 pounds per
cubic foot is 200 pounds or 0.1 T/MGIF.
F-l
-------
APPENDIX G
ANAEROBIC DIGESTION HEAT AVAILABILITY AND SYSTEM HEAT REQUIREMENTS
G.I. DIGESTER HEATING CAPABILITIES
There are six double inlet, double outlet, 6 inch by 8 inch, tube and
tube heat exchangers each with a heated exterior sludge tube surface of 360
square feet. Each unit is specified as originally having a rated output
capacity of 3,000,000 BTU per hour. The original design criteria could not
be found, but knowing how the heat exchanger supplier would have designed
the units, it is believed that the 3,000,000 BTU per hour output was predi-
cated on the following:
o Sludge at each inlet (there are 12) would be at an average tempera-
ture of 80°F at a flow rate of 350 gallons per minute (gpm).
o Sludge at each outlet (there are 12) would be at an average tem-
perature of 95°F at a flow rate of 350 gpm.
o Hot water at each inlet (there are 12) would be at 180°F at a flow
rate of 200 gpm.
o Hot water at each outlet (there are 12) would be at 160°F at a flow
rate of 200 gpm.
The source of hot water was to be provided by two, 250 horsepower, low
pressure steam boilers; one, 150 horsepower, hot water boiler; and engine
jacket cooling water.
Through the years since the sludge heating system was first conceived
and installed, changes have taken place that have altered the heating
capabilities as follows:
o Sludge at each inlet averages 92 to 95°F at a flow rate of 500 gpm.
The higher than expected sludge temperature decreases the expected
thermal gradient and therefore decreases heat transfer capabili-
ties. However, the higher flow rate tends to increase heat trans-
fer capabilities.
The original heat exchanger design would have been predicated on
two standard industry assumptions:
- Sludge flow through a 6-inch sludge tube would be approximately
350 gpm.
G-l
-------
- Sludge flow into the heat exchanger would have consisted of 2
parts digested, recirculated sludge at 95°F and 1 part raw sludge
at 50°F (assumed winter conditions).
At Blue Plains raw sludge is added after the heat exchangers rather
than before. The addition is downstream because of a historical
problem with heat exchanger plugging due to rags in the primary
sludge. The required screening of plant influent, to eliminate
rags in the raw sludge has only recently been accomplished.
Even if all the available raw sludge (approximately 600 gpm) was
added upstream, the average inlet temperature would be reduced by
4°F during the winter and by 2°F during the summer. This small
decrease is due to the high digested sludge recycle flow, which is
10 times the raw sludge flow instead of the 2 times originally
envisioned.
It is not known why the recycle flow rate was increased to 500 gpm
per sludge inlet. It has a beneficial effect on the heat exchanger
in that the high velocity (5.7 feet per second) through the sludge
tubes prevents tube fouling.*
o Hot water at each inlet is at 195°F. The higher hot water tempera-
ture tends to increase the thermal gradient, therefore increasing
heat transfer capabilities.
Plant operating experience indicated that the hot water being
utilized could be increased to 195°F without causing any scaling
problems within the heat exchanger.*
o At the present time the source of hot water is provided by two, 250
horsepower, low pressure steam boilers and one, 150 horsepower, hot
water boiler. Engine jacket cooling water is no longer available.
The 150 horsepower hot water boiler is in poor condition and is
scheduled to be replaced within the next couple of years. Assuming
an overall efficiency of 80 percent for the steam boilers and heat
exchangers, about 13,200,000 BTU per hour are available. The new
hot water boiler would add an additional 3,000,000 BTU per hour.
In addition, the current construction contract calls for linking
together the steam boilers in the heat exchanger building with the
three 150 horsepower, low pressure steam boilers in the power house
and the two 100 horsepower, low pressure steam boilers in the new
grit chamber structure being built. These changes would produce an
additional 17,000,000 BTU per hour availability, but how much could
be used for sludge heating is not known at this time.
G.2. DIGESTION SYSTEM HEAT REQUIREMENTS
Digestion system heat requirements consist of two components: heat
required for raw sludge addition and heat required for radiation losses.
* Inspection of one unit during this study showed no scaling on either
sludge or hot water side of 6 inch sludge tube.
G-2
-------
G.2.1. Heat Required For Raw Sludge Addition
The amount of heat required for raw sludge addition per million
gallons of plant influent flow can be calculated as follows:
(gallons of sludge/MGIF)(Density)(T2 - T^
where:
gallons of sludge/MGIF = gallons of raw sludge per million gallons of plant
influent flow
density = density of the liquid sludge stream, pounds per
gallon
T_ = temperature to which the raw sludge stream is to
be raised, °F
TI = expected temperature of the raw sludge stream, °F
G.2.2. Heat Required For Primary Sludge Addition Only
From Appendix C, the primary sludge volume expected per MGIF is
1236 ± 218 gallons. The highest value or 1454 gallons is used for the
following calculations. Density of primary sludge stream is 8.8 pounds per
gallon. Sludge temperature to be raised to 95°F. During the winter
season, the coldest primary sludge temperature is 55°F. During summer
operation, the primary sludge temperature is 75°F.
Winter operation:
1454 gallons 8.8 pounds (95 - 55)°F
MGIF X gallon X 1
= 511,808 BTU's per MGIF
Summer operation:
1454 gallons 8.8 pounds (95 - 75)°F
MGIF X gallon X 1
= 255,904 BTU's per MGIF
G.2.3. Heat Required For Secondary Sludge Addition Only
From Appendix D, the future secondary sludge volume expected per MGIF
is 1900 ± 239 gallons. The highest value or 2139 gallons is used for the
following calculations. Density of secondary sludge stream is 8.5 pounds
per gallon. Sludge temperature to be raised to 95°F. During the winter
G-3
-------
season, the coldest secondary sludge temperature expected is 60°F. During
summer operation, the secondary sludge temperature expected is 80°F.
Winter operation:
2139 gallons 8.5 pounds (95 - 60)°F
MGIF X gallon X I
= 636,353 BTU's per MGIF
Summer operation:
2139 gallons 8.5 pounds (95 - 80)°F
MGIF X gallon X 1
= 272,723 BTU's per MGIF
G.2.4. Heat Required For All Sludge Addition
The heat input required for all sludge per MGIF is calculated by
totaling the primary and secondary requirements as follows:
Winter Summer
operation, operation,
BTU's per MGIF BTU's per MGIF
Primary sludge 511,808 255,904
Secondary sludge 636,353 272.723
TOTAL 1,148,161 528,627
G.2.5. Heat Required For Conductive/Convective Losses
The amount of heat required for conductive and convective losses from
the digestor equipment can be calculated as follows:
(U)(Area)(T3 - T^)
where:
i
U = -5=
^ = Conductance for a certain thickness of material
BTU
hour-square foot-°F
x. = Thickness of material in inches
k. = Thermal conductivity of material
BTU - inch
hour-square foot-°F
G-4
-------
A = Area of material normal to direction of heat flow in square feet
T_ = Temperature of inside boundary, °F
T, = Temperature of outside boundary, °F
Figure G-l shows a cross sectional view of one of the 12 existing anaerobic
digestion tanks. In the following analysis the assumptions made are:
Earth Cover
T
24"
_L
*'-l*
.»? Concrete Roof 10.25"
Moving, Heated, VJater
Saturated Air Space
..
,. -.1 . • ,
Liquid at 35°F
>
•V '.
'
Concrete Tank Wall
Concrete Floor
FIGURE G-l. Cross sectional view of existing anaerobic digesters
G-5
-------
1. The liquid contents of the tank are being mixed and maintained
at an inside boundry temperature of 95°F.
2. The average (several weeks) coldest outside temperature (winter
operation) is 0°F.
3. The average (several weeks) warmest outside temperature (summer
operation) is 60°F.
4. All earth is considered to be wet (worst condition).
5. The average temperature of the soil underneath the digestion
tanks is 40°F.
G.2.6. Heat Loss Through Roof
T_ is 95°F; T^ for winter is 0°F and for summer is 60°F; area normal to
heat flow is:
CTT)(one internal tank diameter)2 (12 tanks)
4
= (JT)(84)2 (12) = ^
4
U can be calculated as follows:
o liquid-air space interface, 1/C = 0
o air space (as indicated), 1/C = 0.5
o air space - concrete interface, 1/C = 0.33
10 25
o concrete 10.25 inches thick, x/k = —^ = 0.854
o concrete - earth interface, 1/C =1.0
24
o wet earth 24 inches thick, X/T6= — = 1-5
U =
o earth - atmosphere interface, 1/C = 0.167
1
(0 + 0.50 + 0.33 + 1.00 + 0.167) + (0.854 + 1.50)
1 _ 0.23 BTU
4.35 ~ hour-square foot-°F
Winter operation:
(0.23 BTU)(66,501 square feet)(95-0)°F = BTU
hour-square foot-°F ' ' *
G-6
-------
Summer operation:
(0.23 BTU)(66,501 square feet)(95-60)°F _
hour-square foot-°F
G.2.7. Heat Loss Through Walls
= 535,333 BTU per hour
T« is 95°; T, for winter is 0°F and for summer is 60°F; area normal to heat
flow is:
(TT)(one mean tank diameter) (12 tanks) (vertical wall height)
= (TT)(84 + ^)(12)(22) = 71,154 square feet.
All vertical surface is not exposed to the outside. As shown in
Figure G-2, the grouping of the existing digestion tanks only allows part
of each tank to be exposed to the outside environment, the rest is exposed
to each other. The wide dark lines in Figure G-2 indicate the part of the
circumference (59 percent) that is considered exposed to the outside. The
other 41 percent is exposed to a protected environment with an average year
round temperature of 70°F.
FIGURE G-2. Plan view of existing anaerobic digestion tanks.
G-7
-------
U can be calculated as follows:
o liquid - concrete interface, 1/C = 0
21 5
o concrete 21.5 inches thick, x/k = —=--j- =1.79
o concrete - earth interface, 1/C = 1.0
o wet earth 72 inches thick, x/k = || = 4.5*
U ~
o earth - atmosphere interface, 1/C = 0.167
1
(0 + 1.00 + 0.167) + (1.79 + 4.5)
1 0.13 BTU
7.46 hour-square feet-°F
Winter operation:
(0.13 BTU)(71.154 square feet)[(0.59)(95-0)°F + (0.41)(95-70)°F]
hour-square foot-°F
= 613,276 BTU per hour
Summer operation:
(0.13 BTU)(71.154 square feet)1(0.59)(95-60)°F + (0.41)(95-70)°F]
hour-square foot-°F
= 285,826 BTU per hour
— £OJ,O£U O1U pel. 11UUI.
G.2.8. Heat Loss Through Floor
T,. is 95°F; T, is 40°F for both winter and summer; area normal to heat flow
is:
,__w one mean w one mean . vertical height, ,.., ,.__.-*
[III! II . ,. T f. Jll£ UanKS 1
^ yvtank radius 'vtank radius of cone
= 90,391 square feet
* In reality, the factor is larger since the earth cover is becoming
thicker. In calculating heat loss, the effective protection of an earth
cover is never used as more than 10 feet; therefore the maximum value
is 7.5.
G-8
-------
U can be calculated as follows:
o liquid - concrete interface, 1/C = 0
12
o concrete 12 inches thick, x/k = -r = 1.0
o concrete - earth interface, 1/C = 1.0
120
o wet earth 120 inches thick*, x/k = -rr =7.5
U =
(0 + 1.0) + (1.0 + 7.5)
1 0.11 BTU
9.5 hour-square foot-°F
Winter and summer operation:
(0.11 BTU)(90,391 square feet) (95-40)°F = ^ ^
hour-square foot-°F
G.2.9. Heat Losses Through Sludge Piping
All sludge piping involved in transporting sludge from the sludge heat
exchangers to the digesters and from the digesters back to the heat ex-
changers is made of steel pipe of various diameters. It is estimated that
approximately 600 linear feet (6,000 square feet of surface area) of this
pipe is buried in shallow concrete galleries located between the digestion
tanks and heat exchanger complexes. The U factor for this pipe was esti-
mated at 0.32 BTU per hour-square foot-°F. It is estimated that another
3,600 linear feet (10,000 square feet of surface area) is located in
several building structures, where the temperature stays about 70°F all
year long. The U factor for this pipe is estimated at 1.6 BTU per hour-
square foot-°F.
Winter operation:
(0.32 BTU)(6000 sq. feet)(95-0)°F + (1.6 BTU)(10000 sq. feet)(95-70)°F
hour-square foot - °F hour-square foot-°F
= 182,400 + 400,000 = 582,400 BTU per hour
Summer operation:
(0.32 BTU)(6000 sq. feet)(95-60)°F + (1.6 BTU)(10000 sq. feet)(95-70)°F
hour-square foot-°F hour-square foot-°F
= 67,200 + 400,000 = 467,200 BTU per hour
In calculating heat loss, the effective protection of an earth cover is
never used as more than 10 feet.
G-9
-------
G.2.10. Summary of Heat Requirements
Winter Summer
operation operation
For raw sludge addition in BTU's per MGIF:
o Primary sludge only 511,808 255,904
o Secondary sludge only 636,353 272,723
TOTAL PRIMARY & SECONDARY SLUDGE 1,148,161 528,627
For system conductive/convective heat loss in BTU's
per hour:
o Roof 1,453,112 535,358
o Walls 613,276 285,826
o Floor 546,866 546,866
o Sludge piping 582,400 467,200
TOTAL HEAT LOSSES 3,195,654 1,835,250
G-10
-------
APPENDIX H
ANAEROBIC DIGESTION PIPING SCHEMATIC
In order to perform this study an up-to-date piping schematic of the
anaerobic digestion system was required. Enclosed in this appendix are
the following three drawings:
Drawing 117-1-1 Existing Piping Schematic Digesters 1-8
Drawing 117-1-2 Existing Piping Schematic Digesters 9-12
Drawing 117-1-3 Existing Exterior Solids Processing Piping
H-l
-------
AVAILABLE
DIGITALLY
-------
APPENDIX I
ANALYSIS OF ANAEROBIC SYSTEM
VOLATILE MATTER REDUCTION AND GAS PRODUCTION3
I.I. VOLATILE MATTER REDUCTION
Table 1-1 lists historical volatile matter reduction and several possible
related variables. Data are plotted in Figures 5-2, 5-3, and 5-4 in Section
5.3.6 of this report.
TABLE 1-1. LISTING OF AVERAGE VOLATILE MATTER REDUCTION AND SEVERAL RELATED VARIABLES
Year
1979
1980
Month
January
February
. March
April
May
June
July
August
September
October
Noveober
December
January
February
March
April
May
June
Average volatile.
matter reduction,
percent
62.9
64.0
66.2
65.0
65.2
57.9
45.3
52.2
. 44.6
46.9
—
59.6
70.7
61.6
60.0
54.8
49.7
57.6
Secondary sludge
fraction,
percent by weight
35
35
19
25
40
35
44
42
52
51
—
35
23
41
44
46
42
53
Volatile matter
loading
pounds volatile
matter per
usable cubicc
foot per day
0.15
0.13
0.15
0.16
0.17
0.15
0.12
0.14
0.12
0.12
—
0.10
0.12
0.14
0.14
0.12
0.12
0.14
Hydraulic
detention
time .
days*
20.5
23.9
22.3
18.5
19.3
19.8
20.2
18.8
18.6
19.4
26.9
23.9
23.6
17.0
16.4
18.4
18.4
17.6
a All data taken from Appendix A, Table A-4.
b Calculated as follows:
avg tons volatile solids in - avg tons volatile solids out
avg tons volatile solids in X
c Based on the information in Appendix E, it was assumed that only 65
percent of the total 1,757,628 cubic feet of digestion tank volume
was usuable.
d Based on the information in Appendix E, it was assumed that only
65 percent of the total 13,152,000 gallons of digestion tank was
usuable.
1-1
-------
1.2. ANALYSIS OF ANAEROBIC DIGESTION ON AVERAGE VOLATILE MATTER REDUCTION
PER MILLION GALLONS OF INFLUENT FLOW*
1.2.1. Current Conditions - All Sludge To Digestion
Primary sludge to anaerobic digestion:
0.377 ± 0.060 T/MGIF** 0.268 ± 0.047 VT/MGIF
Secondary sludge to anaerobic digestion:
0.284 ± 0.034 T/MGIF 0.185 ± 0.023 VT/MGIF
Summation of primary and secondary T/MGIF and VT/MGIF:
(0.377 + 0.284) ± (0.060) + (0.034) = 0.661 ± 0.069 T/MGIF
2 2
(0.268 + 0.185) ± (0.047) + (0.023) = 0.453+0.052 VT/MGIF
Ratio of secondary sludge to total sludge mass:
(0.284) T (0.661) = 0.43
From Figure 5-2, Section 5.3.6, the average volatile solids reduction
expected is 56.5 ± 6.5 percent or:
(0.453)(0.565) ± (0.565) (0.052) + (0.453) (0.065)
=0.256 ± 0.042 VT/MGIF
The VT/MGIF reduction would be equivalent to the T/MGIF reduced for
the total sludge mass.
1.2.2. Future Conditions - All Sludge To Digestion
Primary sludge to anaerobic digestion:
0.377 ± 0.060 T/MGIF 0.268 ± 0.047 VT/MGIF
Secondary sludge to anaerobic digestion:
0.328 ± 0.034 T/MGIF 0.209 ± 0.023 VT/MGIF
* Data taken from Appendix B, Tables B-l through B-3.
** T/MGIF = dry ton of solids per million gallons influent flow.
VT/MGIF = dry ton of volatile solids per million gallons influent
flow.
1-2
-------
Summation of primary and secondary T/MGIF and VT/MGIF:
(0.377 + 0.328) ± (0.060) + (0.034) = 0.705 ± 0.069 T/MGIF
2 2
(0.268 + 0.209) ± (0.047) + (0.023) = 0.477 ± 0.052 VT/MGIF
Ratio of secondary sludge to total sludge mass:
(0.328) -=- (0.705) = 0.465
From Figure 5-2, Section 5.3.6, the average volatile solids reduction
expected is 53.5 ± 6.5 percent or:
(0.477)(0.535) ± (0.535)2 (0.052)2 + (0.477)2 (0.065)2
= 0.255 ± 0.042 VT/MGIF
The VT/MGIF reduction would be equivalent to the T/MGIF reduced for
the total sludge mass.
1-3
-------
1.3. GAS PRODUCTION
Table 1-2 lists historical gas production and several possible related
variables. Data are plotted in Figures 5-5, 5-6, and 5-7 in Section 5.3.7
of the report.
TABLE 1-2. LISTING OF AVERAGE GAS PRODUCTION AND SEVERAL RELATED VARIABLES
Gas production,
cubic feet
per pound of
volatile natter
\ear Month
1979 January
Februarv
.larch
April
Hay
June
July
August
Septenaer
October
N'ovemoer
December
1980 January
February
ttarcb
April
May
June
reduced
8.7
8.S
7.2
8.6
9.9
12.0
14.4
9 2
12 6
13.5
«
9.6
11.0
12 8
12.0
U.O
13.8
10 7
Volatile matter
Fsed to digestion.
solids,
percent
7.1
7 0
7 6
6.3
7 4
7.1
6.0
6.4
5 9
5.6
..
5.4
5.9
5.2
5.2
5.3
5.2
5.S
tons
per day
83.5
J4.7
87.2
89.1
94.0
86.4
67 8
77.7
'0.6
67.0
..
56.2
o8.5
78.7
77.8
67. S
66.2
3C.6
Volatile matter
loading.
pounds volatile Secondary
natter per sludge fraction.
usable cubic
feet per day3
0.15
0.13
0 15
0 16
0.17
0.15
0.12
0.14
0.12
0.12
..
0.10
0.12
0.14
0.14
0 12
0 12
0.14
percent by
weight
35
35
19
25
40
35
44
42
52
51
..
35
:3
to»»
to
42
53
Hydraulic
detention
time,..
days "
20 S
23.9
:2.3
18 5
19 3
19 8
20.:
18 S
-.8.6
19 4
26 9
23.9
23.o
17.0
16 •
IB.i
18 -
17 0
3 Based on the information in Appendix E, it was assumed that only 65
percent of the total 1,757,628 cubic feet of digestion tank volume was
usuable.
Based on the information in Appendix E, it was assumed that only 65
percent of the total 13,152,000 gallons of digestion tank volume was
usuable.
NOTE: The existing hot water source for the heat exchangers are two steam
and one hot water boiler (Appendix G). To allow the boilers to
operate at maximum output, approximately 20,250,000 BTU per hour of
energy is required. Assuming digester gas at 600 BTU's per cubic
foot, then the amount of digester gas needed is:
20,250,000 BTU per hour required
600 BTU per cubic foot
= 33,750 cubic feet per hour
= 810,000 cubic feet per day
1-4
-------
APPENDIX J
ANALYSIS OF ELUTRIATION SYSTEM OPERATION
Table J-l lists historical 1980 elutriation underflow to dewatering solids
concentration and several possible related variables. Data are plotted in
Figures 5-8 through 5-10 in Section 5.4 of this report. All data taken
from Appendix A, Table A-5.
TABLE J-l. LISTING OF ELUTRIATION UNDERFLOW TO DEWATERING SOLIDS
CONCENTRATION AND SEVERAL POSSIBLE RELATED VARIABLES
Elutciatioo. Total dry Solids loading
underflow to solids to Volume of rate, Ratio of
dewacenag solids elutriation, digested sludge feed solids pounds per tasn water flow
concentration, cons CO elutriacion, concentration, day per h Co digested
Month percent solids per day MOD* percent solids square toot sludge flow
January
Feoruarv
Marci
April
May
June
5 i
i 3
3 6
5 5
3.i
5.2
45
53
S3
54
SB
70
0 397
0.509
0.509
0 4o6
0.448
0 492
2.6
2.4
2.4
2.7
3.0
3-3
36.7
43.2
43.3
44.1
47.4
57 I
5.7
4 6
4 b
4 9
4 3
i.5
a MGD - million gallons per day.
b There are two elutriation tanks each 35-feet wide by 70-feet long
operated in series; therefore the first tank receives the entire solids
load. Loading rate calculated as follows:
(tons dry solids to elutriation per day) (2000 pounds per ton)
(35) (70) square feet of tank
J-l
-------
APPENDIX K
ANALYSIS OF DIGESTED SLUDGE DEWATERING ON AVERAGE
SLUDGE PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW*
TABLE K-l.
Ferric chloride usage
Month
January
February
March
April
May
June
Average
Standard
Tons per
day
10.2
11 9
10.8
10. 0
10.7
10. 1
deviation
Tons per day of dry
solids to filter
10.2/54 = 0.189
11.9/59 s 0.202
10.8/49 = 0 220
10 0/46 = 0.217
10.7/52 = 0.206
10.3/55 - 0.187
0.204
0.014
Feed solids
concentration.
percent
5.4
4.3
3.6
5.5
5.4
5.2
ftetatered cake
percent
solids
16 0
15 8
15.6
16.7
16.6
16 9
16.2
0 6
Secondary sludge
fraction,
percent by weight
23
41
44
46
42
53
The amount of solids contributed by ferric chloride per million
gallons of influent flow is estimated below.
The average amount of ferric chloride added per ton of dry solids
pumped to the vacuum filters is 0.204 ± 0.014 tons. It is assumed that all
iron solids (44 percent of the ferric chloride) and 16.3 ± 0.5 percent of
the chloride solids remain in the sludge (the remainder of the chlorides
leave with the filtrate). Therefore, the amount of solids contributed by
ferric chloride would be:
(0.44 + [0.163 ± 0.006][0.56])(dry weight ferric chloride added)
= (0.53 ± 0.003)(dry weight ferric chloride added)
= (0.53 ± 0.003)(0.204 ± 0.014)(dry solids to dewatering)
= (0.108 ± 0.007)(dry solids to dewatering)
For current conditions, sludge to digestion, each million gallons of
influent flow would contribute:
.063)2 + (0.04)
(0.661 - 0.256) ± s/XO.<
= 0.405 ± 0.075 dry tons to dewatering after anaerobic digestion.
All data taken from Appendix A, Table A-7 or Appendix I.
K-l
-------
The amount of solids contributed by ferric chloride addition would be:
(0.108 ± 0.007)(0.405 ± 0.075)
= (0.108X0.405) ± \A0.405)2(0.007)2 + (0.108)2(0.075)
= 0.043+0.009 T/MGIF*
For future conditions, sludge to digestion, each million gallons of
influent flow would contribute:
(0.705 - 0.255) ± xA°-063)2 + (0.04)2
= 0.450 ± 0.075 dry tons to dewatering after anaerobic
digestion.
The amount of solids contributed by ferric chloride addition
would be:
(0.108 ± 0.007)(0.450 ± 0.075)
= (0.108)(0.450) + \/0.450)2(0.007)2 + (0.108)2(0.075)2
= 0.049 ± 0.009 T/MGIF
For current and future conditions with only primary sludge
to digestion, each million gallons of influent flow would
contribute:
/i f
(0.377 - 0.188) ± V(0.055) + (0.035)
= 0.189 ± 0.065 dry tons to dewatering after anaerobic
digestion.
The amount of solids contributed by ferric chloride addition
would be:
(0.108 ± 0.007)(0.189 ± 0.066)
(0.108)(0.189) ± \/(0.189)2(0.007)2 + (0.108)2(0.065)2
= 0.020 ± 0.007 T/MGIF
For future conditions with only secondary sludge to digestion,
each million gallons of influent flow would contribute:
/ 2 r
(0.328 - 0.073) ± V(0.031) + (0.015)
= 0.255 ± 0.034 dry tons to dewatering after anaerobic
digestion.
* T/MGIF = Dry ton of solids per million gallons of influent flow.
K-2
-------
The amount of solids contributed by ferric chloride addition
would be:
(0.108 ± 0.007)(0.255 ± 0.034)
(0.108)(0.255) ± V/(0.255)2(0.007)2 + (0.108)2(0.065)2
0.028 ± 0.010 T/MGIF
K-3
-------
APPENDIX L
ANALYSIS OF RAW SLUDGE DEWATERING ON
AVERAGE SLUDGE PRODUCTION PER MILLION GALLONS OF INFLUENT FLOW*
TABLE L-l.
r«rrtc chloride usite
.Innch
faniuirv
February
March
April
•lav
June
Weraie
Standard
Tons
per
Tom per ton of dry
Tena per
d»» solids to filter dav
20
17
II
II
II
12
3
a
3
.3
3
3
20 5/114
17 8/1 10
11 5/73
II 3/134
II 5/96
12.5/108
deviation
0 180
0 162
0 133
0.073
0.12(1
0 116
0 134
0 031
55
48
38
i3
47
48
Line usage
Tons p«r ton
if dry
solids to filter
55/114
48/110
38/7S
18/134
47/96
48/108
0
a
a
0
0
!
0
0
482
4)6
307
312
490
_44i
443
071
feed soklda Oraatere-1 cake.
concentration, percent
percent solids
44 17
: 17
) :i
a 21
5 21
6 ZZ_
:o
2
2
9
6
1
1
_6
Z
2
Secondary sludge
fraction.
percent by 'eight
72
44
47
36
38
33
The amount of solids currently contributed by lime addition per
million gallons of influent flow is estimated below.
The average amount of lime (CaO) added per ton of dry solids pumped to
the vacuum filters is 0.445 t 0.065 tons. It is assumed that all calcium
solids (71.5 percent of the CaO) remain in the sludge and that there are 5
percent inerts associated with the high grade CaO utilized. Therefore, the
amount of solids contributed by lime addition would be:
(0.71 + 0.05)(dry weight CaO added)
= (0.76)(0.445 ± 0.071)(dry solids to dewatering)
= (0.338 ± 0.054)(dry solids to dewatering)
For current conditions, raw sludge to dewatering, the amount of solids
contributed by CaO addition per million gallons of influent flow would be:
(0.338 ± 0.054)(0.661 ± 0.063)
= (0.338)(0.661) ± (0.661) (0.054) + (0.338)2 (0.063)2
= 0.223+0.042 T/MGIF**
* All data taken from Appendix A, Table A-6
** T/MGIF = Dry ton of solids per million gallons of influent flow.
L-l
-------
In the future, CaO requirements per ton of dry solids pumped to the
vacuum filter are expected to drop by at least 50 percent. This reduction
is due to the current addition of lime in excess of conditioning require-
ments so that a high pH can be developed to meet land trenching require-
ments. In the near future, trenching will not be utilized and lime
requirements will decrease to that required to enhance dewatering opera-
tions only. This 50 percent reduction would change the amount of solids
contributed by lime addition from [(0.338 ± 0.054)(dry solids to
dewatering)] to [(0.169 ± 0.054)(dry solids to dewatering)].
For future conditions, if raw sludge to dewatering, the amount of
solids contributed by CaO addition per million gallons of influent flow
would be:
(0.169 ± 0.054X0.705 ± 0.063)
(0.169)(0.705) ± vAO.705)2 (0.054)2 + (0.169)2 (0.063)2
= 0.119 ± 0.040 T/MGIF
For future conditions, if only primary sludge to dewatering, the
amount of solids contributed by CaO addition per million gallons of
influent flow would be:
(0.169 ± 0.054)(0.377 ± 0.055)
(0.169)(0.377) ± \A0.377)2 (0.054)2 + (0.169)2 (0.055)2
0.064 ± 0.022 T/MGIF
For future conditions, if only secondary sludge to dewatering, the
amount of solids contributed by CaO addition per million gallons of
influent flow would be:
(0.169 ± 0.054)(0.328 ± 0.031)
(0.169)(0.328) ± x/(0.328)2 (0.054)2 + (0.169)2 (0.031)2
0.055+0.018 T/MGIF
The amount of solids currently contributed by ferric chloride per
million gallons of influent flow is estimated below.
The average amount of ferric chloride added per ton of dry solids
pumped to the vacuum filters is 0.134 ± 0.038 tons. It is assumed that all
iron solids (44 percent of the ferric chloride) and 20.2 ± 2.0 percent of
the chloride solids remain in the sludge (the remainder of the chlorides
L-2
-------
leaves with the filtrate). Therefore, the amount-of solids contributed by
ferric chloride would be:
(0.44 + [0.202 ± 0.02][0.56](dry weight ferric chloride added)
= (0.55 ± 0.011)(dry weight ferric chloride added)
= (0.55 ± 0.011)(0.134 + 0.038)(dry solids to dewatering)
= (0.074 ± 0.021)(dry solids to dewatering)
For current conditions, raw sludge to dewatering, the amount of solids
contributed by ferric chloride addition per million gallons of influent
flow would be:
(0.074 ± 0.021)(0.611 ± 0.063)
(0.074)(0.66l) ± \A0.66l)2 (0.021)2 + (0.074)2 (0.063)2
= 0.049+0.015 T/MGIF
In the future, ferric chloride requirements per ton of dry solids
pumped to the vacuum filter are expected to drop at least 15 percent. This
reduction is due to the significant reduction in lime requirement brought
about by elimination of the trenching operation. This 15 percent reduction
would change the amount of solids contributed by ferric chloride addition
from [(0.074 ± 0.021)(dry solids to dewatering)] to [(0.063 ± 0.021)(dry
solids to dewatering)].
For future conditions, if raw sludge to dewatering, the amount of
solids contributed by ferric chloride addition per million gallons of
influent flow would be:
(0.063 ± 0.021)(0.705 ± 0.063)
(0.063)(0.705) ± V(0.705)2 (0.021)2 + (0.063)2 (0.063)2
= 0.044+0.015 T/MGIF
For future conditions, if only primary sludge to dewatering, the
amount of solids contributed by ferric chloride addition per million
gallons of influent flow would be:
(0.063 ± 0.021)(0.377 ± 0.055)
(0.063X0.377) + \A0.377)2 (0.021)2 + (0.063)2 (0.055)2
0.024 ± 0.009 T/MGIF
L-3
-------
For future conditions, if only secondary sludge to dewatering, the
amount of solids contributed by ferric chloride addition per million
gallons of influent flow would be:
(0.063 ± 0.020(0.328 ± 0.031)
(0.063X0.328) ± v/0.328)2 (0.021)2 + (0.063)2 (0.031)2
0.021 ± 0.007 T/MGIF
L-4
-------
APPENDIX M
SECTION 6.1 SUPPORTING CALCULATIONS
M.I. DIGESTED SLUDGE VACUUM FILTER OPERATION
M.I.I. Current Operation
There are four existing units each having 500 square feet of filtering
area. Their yield depends upon the ratio of secondary and primary sludge.
In 1974 when the mixture was 40 to 50 percent secondary, the yield averaged
2.41 pounds per square foot per hour.
2.41 pounds 500 square feet 4 units 24 hours
square foot-hour X unit x 1 x day
= 115,680 pounds per day
Assuming an average feed solids concentration of five percent and a
density of 8.85 pounds per gallon, the volume of digested sludge capable of
being dewatered is:
115,680 pounds 1 gallon
x
day 8.85 pounds 0.05
= 261,423 gallons per day
Assuming an average cake solids of 16.5 percent, the number of wet
tons to be hauled away including the ferric chloride (FeCl_) conditioner
would be:
t 115,680 pounds sludge + 13,180 pounds Fed- , x 1 ton x 1
day day J 2000 pounds 0.165
= 390.5 wet tons per day
M.I.2. Future Operation
If six new filter units (600 square feet filtering area each with the same
yield of 2.41 pounds per square foot per hour) are placed into operation, then:
2.41 pounds 600 square feet 6 units 24 hours
square foot-hour unit 1 x day
= 208,224 pounds per day
M-l
-------
Assuming same feed solids concentration and density as before, the
volume of sludge capable of being dewatered is:
208.224 pounds 1 gallons „ 1
X
day 8.85 pounds 0.05
= 470,563 gallons per day
Assuming an average cake solids of 16.5 percent, the number of wet
tons to be hauled away including the ferric chloride (FeCl_) conditioner
would be:
r 208.224 pounds sludge + 23,725 pounds Fed. , x 1 ton x 1
day day J 2000 pounds 0.165
= 703 wet tons per day
If the maximum sludge production generated at 334 million gallons per
day influent flow was mesophilically digested under the conditions de-
scribed in Section M.5 of this Appendix, there would be 340,050 pounds per
day to dewater. The maximum number of filters required would be:
340,050 pounds 1 filter - day
day 34,704 pounds
= 9.8, or 10 filters required
Assuming an average cake solids at 16.5 percent, the maximum number of
wet tons to be hauled away including the ferric chloride (FeCl_) condi-
tioner would be:
340,050 pounds sludge + 38,744 pounds Fed, x 1 ton x 1
day day 2000 pounds 0.165
= 1,148 wet tons per day maximum
M.2. ELUTRIATION OPERATION
In order to generate 115,680 pounds of solids per day in the elutriate
underflow at a maximum hydraulic flow rate of 490,000 gallons per day and a
density of 8.64 pounds per gallon, the incoming digested solids concentra-
tion would have to be:
115,680 pounds 1 gallon 1 day 100
day X 8.64 pounds X 490,000 gallons X 1
= 2.7 percent solids
For any flow less than 490,000 gallons per day, the solids concentra-
tion would have to be proportionately higher.
M-2
-------
In order to generate 208,224 pounds of solids per day under the same
stated conditions, the incoming digested solids concentration would have to
be:
208,224 pounds 1 gallon 1 day 100
day x 8.64 pounds x 490,000 gallons x 1
= 4.9 percent solids
M.3. HEAT EXCHANGER OPERATION*
Available heating capacity limits the amount of sludge that can be
hydraulically processed. The maximum flow rate possible based solely on
sludge heating capacity is:
1980 winter operation
(9,800,000 BTU per hour) (24 hours)
(8.6 pounds per gallon)(95 - 55°F) (day)
= 683,721 gallons per day
1981 summer operation
(11.100,000 BTU per hour) (24 hours)
(8.6 pounds per gallon)(95 - 75°F) (day)
= 1,548,837 gallons per day
1981 winter operation
(12,800,000 BTU per hour) (24 hours)
(8.6 pounds per gallon)(95 - 55°F) (day)
= 893,023 gallons per day
1982 summer operation
(14.100.000 BTU per hour) (24 hours)
(8.6 pounds per gallon)(95 - 75°F) (day)
= 1,967,442 gallons per day
M.4. DIGESTION TANK OPERATION
The available data indicate that the system can be operated success-
fully at an average hydraulic residence time of 16 days. The maximum flow
rate possible based solely on usable tank capacity is:
* See Appendix G for discussion of calculation performed.
M-3
-------
8,545,581 gallons of usable tank volume
16 days
= 534,099 gallons per day
If the digestion tanks were cleaned and grit accumulation kept to a
minimum, the maximum flow rate possible would increase to:
13,147,055 gallons of usable tank volume
16 days
= 821,691 gallons per day
If the maximum sludge production generated at 334 million gallons per
day influent flow rate was mesophilically digested at a minimum hydraulic
detention time of 16 days, and if the existing digesters were clean of grit
and grit accumulation was kept to a minimum in the system, the maximum
number of digestion tanks required (all the same dimensions) would be:
1,200.062 gallons 16 days 1 digester
day 1 x 1,096,000 gallon capacity
= 17.5, or 18 tanks required; six new tanks would be required to meet
this condition.
Operating data at Blue Plains indicate that the system can be operated
successfully at volatile matter loading ratios averaging 0.16 to 0.17,
though gas production seems to deteriorate over 0.14. The maximum volatile
matter loading based on 0.16 pounds per usable cubic foot per day would be:
1.142,458 cubic feet of usable tank volume 0.16 pound volatile matter
1 usable cubic foot
= 182,793 pounds volatile matter per day
If the digestion tanks were cleaned and grit accumulation was kept to
a minimum, the maximum volatile matter loading based on 0.16 pounds per
usable cubic foot per day would be:
1,757,628 cubic feet of usable tank volume 0.16 pound volatile matter
1 usable cubic foot
= 281,220 pounds volatile matter per day
If the maximum sludge production generated at 334 million gallons per
day influent flow rate was mesophilically digested at a maximum volatile
matter loading of 0.16 pounds per cubic foot per day, and if the existing
digesters were clean of grit and grit accumulation was kept to a minimum in
the system, the maximum number of digestion tanks required (all the same
dimensions) would be:
362,022 pounds volatile matter 1 cubic foot - day 1 tank
day 0 16 pounds volatile matter x 146,469 cabic feet
= 15.4, or 16 tanks required; hydraulic flow rate governs.
M-4
-------
M.S. GALLONS OF PRIMARY AND SECONDARY SLUDGE PUMPED TO DIGESTION
If the existing digestion system was processing all the Blue Plains
sludge, the ratio of thickened secondary sludge volume to thickened primary
sludge volume would be 1.54:1. Using this ratio for allocating the 490,00
gallons gives:
Gallons
per day
192,913
297,087
490,000
Pounds
per day
118,834
103,683
222,517
Volatile Pounds
per day
84,373
66.254
150,627
Primary sludge
Secondary sludge
TOTAL
The following constraints apply to the above calculations:
o Total flow to digestion system to be no greater than 490,000
gallons per day - ok
o Minimum ratio of secondary sludge mass to total sludge mass to be
0.35
103,683 pounds secondary sludge per day ,_
222,517 pounds total sludge per day = ' " °K
o Concentration of feed solids into digestion tanks not to exceed six
percent
(222,517 pounds total sludge per day)(100) .,
(8.6 pounds per gallon) (490,000 gallons per day) ~ *"** " OK
o Concentration of solids into elutriation system from digestion
tanks to exceed 2.7 percent
From Figure 5-2, at a secondary:total mass ratio of 0.46 an
average volatile matter reduction of 53.5 percent is expected.
1(222.517 pounds of sludge per day) - 0.535(150.627 pounds volatile sludge per dap]'. 100'
(3.50 pounds per jalion)(490,000 gallons per day)
"= 3.4 percent - ok
o Sludge mass from digestion tank not to exceed 115,680 pounds per
day using the existing drum filters for dewatering and 208,234
pounds per day using the six new belt type filters for dewatering.
222,517 pounds of sludge per day - (0.535)(150,627 pounds volatile sludga per day}
= 141,932 pounds per day - not ok for current operation of drum
filters; ok for future operation with new vacuum filters.
M-5
-------
M.6. GAS PRODUCTION
M.6.1. 490,000 Gallon Per Day Sludge Processing Rate
Under the constraints imposed in developing the 490,000 gallon per day
flow rate, gas production is expected to range from 12 to 14 cubic feet per
pound of volatile matter reduced.
Volatile matter reduced:
(0.535) (150, 627) = 80,585 pounds per day
80,585 pounds 12 cubic feet „,_ no. , . - t ,
1 day - x pound - = 967'020 cubic feet per day
80,585 pounds 14 cubic feet . ,-„ inn , . , . ,
' day - X - pTSnd - = 1.128,190 cubic feet per day
Gas consumption to meet winter and summer sludge heating requirements
are:
Winter operation:
690.000 gallons 8.6 pounds (95-55)"F 24 hours 5.195.656 3TU radiation loss
day gallon * 1 day x -
600 BTU 0.8 heat efficiency factor
cubic foot of gas 1
= 510,949 cubic feet per day
Summer operation:
690.000 gallons 8.6 pounds (95-75)T t 24 hours 1,835.250 3T1' radiation loss
day gallon x 1 day x hour
600 BTU 0 8 heat efficiency factor
cubic fooc of gas 1
= 267,346 cubic feet per day
Average expected excess:
(967.Q20 + 1,128.190) cubic feet _ (510,949 + 267,346) cubic feet
2 day " 2 day
= 658,458 cubic feet per day available to be sold
M.6.2. Maximum Gallon Per Day Sludge Processing Rate
Again, gas production is expected to range from 12 to 14 cubic feet
per pound of volatile matter reduced.
M-6
-------
Volatile matter reduced:
(0.535)(319,030) = 170,681 pounds per day
170.681 pounds 12 cubic feet . ... ._, , . , ,.
- - x pound - = 2>OA8>172 cublc feet P"
170,681 pounds 14 cubic feet „ ,on _0/ , . ,
- - X pound - = 2>389>534 cublc feet
Gas consumption to meet winter and summer sludge heating requirements
(based on 18 digestion tanks) would be:
Winter operation:
1.200.062 gallons 8.6 pounds (95-5STT . 2i hours 5.272.829 BTU radiation loss
- d^ - X galloD x 1 day hour
600 BTU 0.8 beat efficiency factor
cubic feet, of gas
= 1,123,686 cubic feet per day
Summer operation:
1 200.062 gallons 8.6 pounds (95-75)°F 26 hours 3.C2S.162 BTU radiation loss
- day * gallon x 1 day hour
600 STU0.8 heat efficiency factor
cubic feet of gas 1
= 581,430 cubic feet per day
Average expected excess:
(2.048,172 + 2,389,534) cubic feet _ (1,123,686 + 581,430) cubic feet
2 day " 2 day
= 1,366,295 cubic feet per day available to be sold
M-7
-------
APPENDIX N
SECTION 6.2 SUPPORTING CALCULATIONS
N.I. DIGESTED SLUDGE VACUUM FILTER OPERATION
Each vacuum filter has 600 square feet of filtering area. Assuming a
minimum yield for this sludge, thermophilically digested, of 3.0 pounds per
hour per square foot, each filter would be able to dewater:
3.0 pounds 600 square feet 24 hours
square foot-hour filter day
= 43,200 pounds per day
As indicated elsewhere in this Appendix, if the maximum sludge produc-
tion generated at 334 million gallons per day influent flow rate was
thermophilically digested, there would be 340,050 pounds per day to de-
water. The maximum number of filters required would be:
340,050 pounds 1 filter-day
day x 43,200 pounds
= 7.9, or 8 filters required
Assuming an average cake solids of 16.5 percent, the maximum number of
wet tons to be hauled away including the polymer conditioner would be:
340,050 pounds sludge + 680 pounds polymer solids x 1 ton x 1
day day 2000 pounds 0.165
= 1,033 wet tons per day maximum
N.2. ELUTRIATION (COOLING) OPERATION
Sludge elutriation is not required, instead, the elutriation tanks
would be utilized as sludge cooling tanks. The system would still be
operated as a two-stage series, co-current, washing operation but under
different washing rates. The maximum hydraulic flow through digestion at
334 million gallon per day influent flow rate is 1,200,062 gallons per day.
The temperature of digested sludge is 122°F. Cooling water on a 1:1 flow
basis would be mixed with digested sludge before entering the elutriation
tanks. The warmest cooling water is assumed to be 60°F. In the first
stage, 1,200,062 gallons of sludge at 122°F is mixed with 600,031 gallons
of wash water at 60°F. Under these conditions, the minimum sludge dis-
charge temperature would be:
(1.200.062 gallons)(122°F) + (600,031 gallons)(60°F) _ 0
(1,200,062 + 600,031) gallons ~ J
If we assume that the sludge concentrates to 75 percent of its ori-
ginal volume, is pumped to the second stage, and blended with 600,031
gallons of wash water at 60°F, the minimum sludge temperature discharge to
dewatering would be:
N-l
-------
(1,200.062 gallons)(0.75)(101.3°F) + (600,031 gallons)(60°F) .„.
[(1,200,062)(0.75) + 600,031] gallons ~ 8^tt *
NOTE: It may be economically attractive to build a tube and tube heat
exchanger for raw sludge going to digestion and digested sludge leaving
digestion.
N.3. EFFECT ON SYSTEM HEATING CAPABILITIES DUE TO INCREASE IN SLUDGE
OPERATING TEMPERATURE"
N.3.1. Heat Required for Primary Sludge Addition Only
Winter operation:
1454 gallons 8.8 pounds (122 - 55)°F
A X ^"^^^^^^^^—
MGIF** gallon 1
= 857,278 BTU's per MGIF
Summer operation:
1454 gallons 8.8 pounds (122 -
MGIF x gallon x 1
75)°F
= 601,374 BTU's per MGIF
N.3.2. Heat Required for Secondary Sludge Addition
Winter operation:
2139 gallons 8.5 pounds (122 - 60)°F
MGIF X gallon X 1
= 1,127,253 BTU's per MGIF
Summer operation:
2139 gallons 8.5 pounds (122 - 80)°F
MGIF x gallon X 1
= 763,623 BTU's per MGIF
* Assumptions and calculations are as per Appendix G except digestion
operating temperature at 122°F rather than 95°F.
** MGIF - million gallons influent flow.
N-2
-------
N.3.3. Heat Required for Conductive/Convective Losses
Roof - winter operation:
(0.23 BTU)(66,501 square feet)(122 - 0)°F _ „
- hour:squarj foot.oF - - 1,866,018 BTU per hour
Roof - summer operation:
' ° per hour
Walls - winter operation:
(0.13 BTU) (71. 154 square feet) [ (0.59) (122-0)°F + (0.4l)(122-70)°F3
hour-square foot-°F
= 863,027 BTU per hour
Walls - summer operation:
(0.13 BTU) (71. 154 square feet) [ (0.59) (122-60)°F + (0.4l)(122-70)°F]
hour-square foot-°F
= 535,576 BTU per hour
Floor - summer and winter operation:
(0.11 BTU) (90.391 square feet)(122-40)°F _ ft
hour:squar^ f00t-oF - - 815,327 BTU per hour
Sludge piping - winter operation:
(0.32 BTU) (6000 square ft)(122-0)°F + (1.6 BTU)(10,000 square ft) (122-70)°F
hour-square foot-°F hour-square foot-°F
= 234,240 + 832,000 = 1,066,240 BTU per hour
Sludge piping - summer operation:
(0.32 BTU) (6000 square ft) (122-60)°F + (1.6 BTU) (10000 square ft) (122-70)°F
hour-square foot-°F hour-square foot-°F
= 119,040 + 832,000 = 951,040 BTU per hour
N.3.4. Summary of Heat Requirements
Winter Summer
operation operation
For raw sludge addition in BTU's per MGIF
Primary sludge only 857,278 601,374
Secondary sludge only 1,127,253 763,623
TOTAL PRIMARY & SECONDARY SLUDGE 1,984,531 1,364,997
N-3
-------
Winter
operation
1,866,018
863,027
815,327
1,066,240
Summer
operation
948,304
535,576
815,327
951,040
For system heat loss in BTU's per hour
0 Roof
0 Walls
0 Floor
0 Sludge piping
TOTAL HEAT LOSSES 4,610,612 3,250,247
Based on a 334 million gallon per day (MGD) of influent flow, the
total digestion sludge heating requirements would be:
Winter operation:
(1.984,531 BTU's)(334 MGIF) + (4,610.612 BTU)(24 hours)
(MGIF) (day) (MGIF) (day)
= 7/8 x 108 BTU's per day (32.2 x 106 BTU per hour)
Summer operation:
(1.364,997 BTU's)(334 MGIF) + (3,250,247 BTU)(24 hours)
(MGIF) (day) (hour) (day)
= 5.3 x 108 BTU's per day (22.2 x 106 BTU per hour)
N.4. EFFECT ON SLUDGE PIPING DUE TO INCREASE IN SLUDGE OPERATING
TEMPERATURE
All sludge piping involved in transporting sludge from the sludge heat
exchangers to the digesters and from the digesters back to the heat ex-
changers is made of steel, located in pipe galleries protected from outside
weather conditions, and not ridgidly anchored at the ends. Any increase in
sludge operating temperature will cause a corresponding increase in pipe
expansion. Linear expansion would be of primary concern at this installa-
tion.
The additional linear expansion of the sludge piping due to increasing
the sludge temperature from the existing operating temperature to a higher
operating temperature can be calculated using the equation.
L = (o)(L)(AT)
where
L = the change in length of the piping system being considered,
inches.
a = the coefficient of linear expansion, for steel it is
78 x 10" inches per foot per °F
N-4
-------
L = length of piping being considered, feet
A T = increase in temperature, °F
The sludge piping involved currently operates at a temperature of 90°F
to 93°F. Operating at a maximum sludge temperature of 130°F, the maximum
increased temperature, T, would be 40°F.
Maximum linear expansion would occur on the longest pipe segment. The
longest pipe segment is 400 feet long and is located on the north side of
the digestion facility where it carries heated sludge to the anaerobic
digesters.
The maximum increased linear expansion, L, is calculated to be
78 x 10"6 inches x 400 feet x 40°F
foot - °F
or 1.25 inches
Based on calculations for expansion of all other pipe segments and
best engineering judgement, the increase in temperature and the resultant
pipe expansion will not adversely effect the sludge piping involved.
N.5. EFFECT ON ANAEROBIC DIGESTION TANKS DUE TO INCREASE IN SLUDGE
OPERATING TEMPERATURE
Increasing the sludge temperature within the existing concrete diges-
tion tanks will create increased stresses on the outer face of the diges-
tion tank walls. The amount of stress developed in the concrete and the
amount of reinforcing steel required needs to be calculated and compared to
the existing situation to make sure a structural failure would not occur.
Figures N-l and N-2 show the situation that would occur on the exist-
ing structure assuming that the maximum sludge temperature is 130°F and
the coldest ambient air temperature is 0°F.
TQ - DIGESTER TEMP.
ASSUME 130°F
HORIZONTAL STEEL
REINFORCEMENT
*8 99" EF •
72
TA ' AMBIENT AIR TEMP.
ASSUME 0°F
SOIL
FIGURE N-l. Cross section of existing
anaerobic digestion tank wall.
-•— t = WALL THICKNESS
=• 21.5"
N-5
-------
V 130°F
DIGESTER
CONCRETE
WALL -
t«ZI.S
SOIL
TEMPERATURE
GRADIENT
72"
AIR
TA- 0°F
FIGURE N2. Assumed temperature gradient through digester wall and soil.
As indicated in Figures N-l and N-2, the existing tank walls are 21.5
inches thick with #8 rebar placed every 9 inches. In addition, the entire
structure is buried; the minimum soil cover on the side walls being 72
inches.
The stress in the outer concrete wall is calculated on the following
two pages.
Temperature difference through the wall, T, can be found by the fol-
lowing equations.
T = (Tn - TJ t/K
and
where:
1/K = 1/S + t/K + t./K
T. =
K =
K- =
t =
t. =
S =
1
digester temperature (°F)
ambient air temp (°F)
coefficient of conductivity for concrete
coefficient of conductivity for soil
thickness of concrete (inches)
thickness of soil (inches)
outside surface coefficient
21.5
T = (130-0)
12
= 22°F
1
6
21.5 . 72
~12~ ~~8
N-6
-------
18. T*
in Cylindrical Tank Wall* *
Tanks containing lioc liquids ire subiect co
cefflpennire stresses. Assume chat the temperature is
Ti in the inner face, T- at the oucer face, ma that the
cempenruK decreases uniformly from inner to outer
face. Ti - T, being denoted as T Fig J7 shows a seg-
ment of i tank wall in two positions, one before and
one after a uniform increase in temperature. Tie anginal
length of the are of the will has been increased, but an
increase chat is uniform throughout will not create
JUT stresses as long as the nng is supposed to be free
tod unrestrained at its edges. It is the cemperanue
differential onlv, T, which creates stresses.
Aftor
no. 37
Toe >*frr fibers being noner cend :o expand
note than the outer fibers, so if the segment is cut loose
from the adjacent portions of the wail. Point A m
Fig 38 will move to iV. 3 will move to B', and section
X ourjiOQ
rlB, which, represents the itreuless condition due to 4
uniform temperature cnange throughout, will move to
i new position A'B' Actually tne movements cram A
co A' and 3 to B' ire prevented since the circle must
remain i circle, ind irresses will be created caac ire
proportional co che horizontal distances between A3
mo A'B'
It is dear that AA' - SB' - movement due to a
temperature change of \%T or wnen > is tne coefficient
of expansion, chat
AA' • SB' » Yit X • per unit length of arc.
and
4.~.TX *
\fy i
In i homogeneous section, the moment ,V( re-
quired co produce an angle change * in an element of
unit length mav be written as
M - Elt
Eliminating 9 gives
.. El X T X i
m • —^———
i
The stresses in che extreme nben created bv M are
/-^X--M£XrX,
The stress distribution across the cross section
is as indicated in Fig. 38. The stresses are numerically
equal at the two faces but have opposite signs. Note
chat che equation applies to uncracked sections onlv,
and that this procedure of stress calculation is co be
considered merely as a method bv which the problem
can be approached. The variables £ and I in che equa-
tions are uncertain quantities. E mav vary from
1,300.000 up to 4,300.000 p.s.i.. and / may also varv
considerably because of deviations tram che assumption
of linear relation between stress and strain. Finally, if
che concrete cracks, M can ao longer be set equal co
Eli, nor / equal to -j X — As a result, the equation
/ - yftt is to be regarded as merely indicative rather
chan formally correct.
The value of « may be taken as 0.000006, and for
che purpose of this problem choose £ • 1.300,000 p.s.i.
Then £ X i - 9 and/ - 4.jr
The value of T a the difference between tempera-
tures in che two surfaces of che concrete which mav be
computed from che temperature of cne stored liquid
and che outside air.
HO. If
a circular Concrete Tanks Wlthouc Preacreaaing.
5420 Old Orchard Road, Statue, 111. 60076.
Portland Generic Association.
N-7
-------
M'hen (he ilow of he-ic n uniform from the inside
co the outside of che wall section in Ftp. )9. the tem-
perature difference, T - 7"i - Ti. a smaller than che
difference. T, — T.. becweea che inside liquid and che
ouoide air Standard cextbooki give
T - (T, - T.)
in which
i
4- !
/ i ^ i,
• coefficient of conductivity of stone or
jravel coocrete - U B.C. it. per hour per
sq.ft. per deg. F. per to. of chicknai
ii - coefficient of conductivity of insulating
material
i • ctuckneu of concrete in in.
'i - thickness of insulating material
; - outside surface confident • 6 B.t.u. per
hour per sq.ft. per deg. F
Assuming an anuuulated wall
6 12
Consider a "«fc with wall thickness / • 10 m.
which holds a liquid with a temperanire T, - 120 deg
F while che temperature of che ouoide air 7". - 30
deg. F Then
10
, (120 - 30^^-75 deg. F
and
/ - 4 ST - 4 5 X 75 - 37J p 1.1.
The stress of / • 373 p.s.i. is tension in che out*
side and compression in the inside face. If ue uniformly
distributed nag tension due to load in che tank is. sav,
300 p.s.i.. che combined stress will be:
Ouoide fiber: 300 -r 375 - «75 p.s.i. (tension)
Inside aber: 300 - 375 - -75 p.s.i. (compression)
In realicv, coo much significance should not be
attached to che temperature stress computed from che
equation derived. The stress equation is developed from
che strain equation. AA' - >$ Ti, based on the'assump-
tion chat stress is proportional to strain. This assump-
tion is rather inaccurate for the case under ducussioa.
The inaccuracy mav be reclined co some extent by using
i relatively low value for £<, such as £, - 1,300.000
p 1.1., whica is used in this section. An even lower
value may be iiuuned.
Ai computed in che example, a temperature
differential of 75 deg r. jives a stress at 375 p.s.i. m
che extreme fiber. This is probaoiy more than che con-
crete can cake in addition co che regular nng tension
strew without cracking on che colder surface. The
temperature stress may be reduced bv means of insu-
lation. which serves co decrease the temperature dif-
ferential. or additional horizontal reinforcement mav be
provided dose to che colder surface. A procedure will
be illustrated for determination of tempera cure steel.
Ic is not based awn a rigorous mathematical analysis
but will be helpful as a guide and as an aid to engineer-
ing judgment.
It u proposed to base che design on the moment
derived in this section. M. - EJTi/i, in which che
value of £< is taken aa 1. JOO.000 p.s.i. If / is taken for a
secaoa 1 ft. high. I equal* r*. and M is the moment
per ft. Then
M - 1,300,000 X r1 X T X O.OOOOOfi - 9rT
ui.lb. per ft. in which
f m thickness of wall in in.
r • temperature differencial in deg. F.
The area of horizontal steel at the colder face
computed as for a cracker! section is
M
"3552
For example, assume t - 15 m., T • 75 deg. F ,
and d m 13 in., which gives
This area is in addition co che tegular nng steel.
N-8
-------
The stress, f, on the concrete can be determined by the equation:
f = 4.5 T = 4.5 (22°F) = 99 psi
The maximum stress on the wall should be less than 300 psi as dictated
by common engineering practice. Since the temperature stress is only 99
psi, the concrete will not crack.
The amount of reinforcing steel required to resist the temperature
stress can be calculated from the following equation:
A = 9t2T
17,500d
where A,, = cross sectional area of steel per foot of wall - square
inches (sq. in.)
d = effective concrete thickness (21.5" - 2(3") = 15.5")
A_ = 9(21.5)2(22) = 0.34 sq. in.
17,500 (15.5)
The maximum temperature stress occurs in the outer wall face. The
amount of steel in that face is one //8 bar every 9 inches. Since a #8 bar
equals 1 inch diameter or 0.79 sq. in., there is 0.79 x 1.33 or 1.05 sq.
in. of steel in the outer face. This is more than is required to resist
the temperature stress, therefore, the wall will not crack.
N.6. DIGESTION TANK OPERATION
If the existing digestion tanks were cleaned and grit accumulation
kept to a minimum, the following hydraulic and volatile matter loading
conditions would prevail.
N.6.1. Hydraulic Residence Time
Maximum 13,147,055 gallons of capacity
894,786 gallons of sludge per day
= 14.7 days
Average 13,147,055 gallons of capacity
8 1,047,424 gallons of sludge per day
= 12.6 days
M. . 13,147,055 gallons of capacity
ninimum 1,200,062 gallons of sludge per day
= 11.0 days
N-9
-------
N.6.2. Volatile Matter Loading
M. . 276,038 pounds volatile matter per day
Minimum *—___r.-0 r-.—•=—-—- *\ *•
1,757,628 cubic feet of capacity
= 0.157 pounds volatile matter per cubic
foot per day
. 319,030 pounds volatile matter per day
age 1,757,628 cubic feet of capacity
= 0.182 pounds volatile matter per cubic
foot per day
M . 362,022 pounds volatile matter per day
1,757,628 cubic feet of capacity
= 0.206 pounds volatile matter per cubic
foot per day
N.7. GAS PRODUCTION
Gas production is expected to range from 12 to 14 cubic feet per pound
of volatile matter reduced. Volatile matter reduction is expected to be
53.5 percent (same as mesophilic system but with a shorter hydraulic deten-
tion period).
Volatile matter reduced
(0.535X319,030) = 170,681 pounds per day
170,681 pounds x 12 cubic feet „ rt/0 -,„ , . c . ,
L—-,—*- -; = 2,048.172 cubic feet per day
day pound ' ' * i
170,681 pounds x 14 cubic feet = 4 cubic
day pound ' ' v 3
Gas consumption to meet winter and summer sludge heating requirements
(based on 12 digestion tanks) would be:
Winter operation:
0
7.8 xlO BTU x 1 cubic foot gas x 1 BTU delivered
day 600 BTU 0.8 BTU utilized
= 1,625,000 cubic feet per day
N-10
-------
Summer operation:
c
5.4 xlO BTU x 1 cubic foot gas x 1 BTU delivered
day 600 BTU 0.8 BTU utilized
= 1,125,000 cubic feet per day
Average expected excess:
(2,048,172 + 2,389.534) cubic feet _ (1.625,000 + 1.125.QQQ) cubic feet
2 day 2 day .
= 843,853 cubic feet per day available to be sold
N-ll
-------
APPENDIX 0
SECTION 6.3 SUPPORTING CALCULATIONS
0.1. DIGESTED SLUDGE VACUUM FILTER OPERATION
Each vacuum filter has 600 square feet of filtering area. Assuming a
minimum yield for this sludge, mesophilically and thermophilically
digested, of 3.0 pounds per hour per square foot, each filter would be able
to dewater:
3.0 pounds 600 square feet 24 hours
square foot-hour filter day
= 43,200 pounds per day
As indicated elsewhere in this Appendix, if the maximum sludge produc-
tion generated at 334 million gallons per day influent flow rate was
mesophilically-thermophilically digested there would be 316,519 pounds per
day to dewater. The maximum number of filters required would be:
316,519 pounds 1 filter-day
day x 43,200 pounds
= 7.3, or 8 filters required
Assuming an average cake solids of 16.5 percent, the maximum number of
wet tons to be hauled away including the polymer conditioner would be:
{"316,519 pound sludge 640 pounds polymer solids'! 1 ton 1
day day J x 2000 pounds X 0.165
= 961 wet tons per day maximum
0.2. EFFECT ON SYSTEMS HEATING CAPABILITIES DUE TO DUAL HEATING SYSTEM
REQUIREMENTS
0.2.1. Mesophilic System Heat Requirements
The following calculations and numbers are derived and discussed in
Appendix G.
0-1
-------
Winter operation:
r 1,148. 161 BTU 334 MGIF •> 3,195.654 ,BTU
L * J
MGIF* 24 hours hour
= 19,174,228 BTUs per hour
Summer operation:
r 528. 627 BTU 334 MGIFi 1.835.250 BTU
L MGIF x 24 hours J hour
= 9,191,976 BTUs per hour
0.2.2. Thermophilic System Heat Requirements
Heat required for sludge both winter and summer:
1,200.062 gallons 8.64 pounds (122-95)°F 1 day
day x gallon X 1 x 24 hours
= 11,664,603 BTU per hour
Heat required for conductive/convective losses:
Roof - winter operation:
(0.23 BTU) (33.205 square feet)(122-0)°F _ ner
hour-square foot-°F - ~ 931'732 BTU Per hour
Roof - summer operation:
' «» « hour
Walls - winter operation:
(0.13 BTU)(35.577 square feet) [(0.59)(122-0)°F + (0.4l)(122-70)°F]
hour-square foot-°F
= 431,513 BTU per hour
Walls - summer operation:
(0.13 BTU)(35.577 square feet) [(0.59)(122-60)°F + (0.41) (122-70)°F]
hour-square foot-°F
= 267,788 BTU per hour
" MGIF = million gallons influent flow.
0-2
-------
Floor - summer and winter operation:
(0.11 BTU)(45,195 square feet)(122-40)°F
hour-square foot-°F
= 407,659 BTU per hour
Sludge piping heat losses in thermophilic section are minimal.
Total hourly winter heat requirements:
11.664,603 BTU
hour
1.772.186 BTU 13,436,789 BTU
hour
hour
0.3. DIGESTION TANK OPERATION
At the present time, the existing tank layout lends itself to using
digesters 1 through 8 as the mesophilic units and digesters 9 through 12 as
the thermophilic units. If all the existing digestion tanks were cleaned
and grit accumulation kept to a minimum, the following hydraulic and
volatile matter loading conditions would prevail.
0.3.1. Hydraulic Residence Time
MesoohiHc System
Olcesters 1-3
Thennopnlllc System
Olqestara 3-12
Maximum
Average
Minimum
8.768,000 gallons of capacity
.394,786 gallons of sluge per day
» 9.3 days
8.763.000 gallons of capacity
1,047,424 gallons of sluge per day
• 8.2 days
8.768.000 gallons of capacity
1,200,062 gallons of sluge per day
• 7.2 days
a.384.Oflfi gallons cf capacity
394,786 gallons of sludge per day
• 4.9 days
4.384.000 gallons of capacity
1,047,424 gallons of sludqe per day
- 4.1 days
4.384.000 gallons of capacity
1,200,062 gallons of jludqe oer day
• 3.5 days
Hydraulic residence times are too short for both a mesophilic and a
thermophilic system. If two digesters of same size were added to both
processes, the new hydraulic residence times would be:
Maximum
Average
Minimum
Mesophilic
system
10 tanks
12.2
10.5
9.1
Thermophilic
system
6 tanks
7.3
6.3
5.5
0-3
-------
0.3.2. Volatile Matter Loading
Volatile matter loading based on 10 mesophilic tanks only:
. 276,038 pounds volatile matter per day
ninimum 1,464,690 cubic feet of capacity
= 0.19 pounds volatile matter per cubic
foot per day
319,030 pounds volatile matter per day
Average 1,464,690 cubic feet of capacity
= 0.22 pounds volatile matter per
cubic foot per day
362,022 pounds volatile matter per day
tlaximum 1,464,690 cubic feet of capacity
= 0.25 pounds volatile matter per
cubic foot per day
0.4. GAS PRODUCTION
Gas production is expected to range from 12 to 14 cubic feet per pound
of volatile matter reduced. The volatile matter reduction should be a
minimum of 60 percent.
Volatile matter reduced:
(0.60)(319,030) = 191,418 pounds per day
191,418 pounds 12 cubic feet = fi cubi{. d
day pound ' ' r
191,418 pounds 14 cubic feet ^ic f^ d
day pound
Gas consumption to meet winter and summer sludge heating requirements
(based on 16 digestion tanks) would be:
Winter operation:
7.9 x 10 BTU x 1 cubic foot gas x 1 BTU delivered
day 600 BTU 0.8 BTU utilized
= 1,645,833 cubic feet per day
0-4
-------
Summer operation:
5.3 x 108 BTU x 1 cubic foot gas x 1 BTU delivered
day 600 BTU 0.8 BTU utilized
= 1,104,167 cubic feet per day
Average expected excess:
(2,297.016 + 2,679,852) cubic feet (1.654.833 + 1.104,167) cubic feet
2 day 2 day
= 1,108,934 cubic feet per day available to be sold.
0-5
-------
APPENDIX P
THERMOPHILIC DIGESTION REFERENCES FOR SECTION 2.2 AND 6.2
1. Rimkus, R.R., J.M. Ryan and E.J. Cook, "Full Scale Thermophilic Diges-
tion at the West-Southwest Sewage Treatment Works," Paper
presented at the Annual Water Pollution Control Federation
Conference, Las Vegas, October, 1980.
2. Smart, J. and B.I. Boyko, Full Scale Studies on the Thermophilic
Anaerobic Digestion Process, Report No. 59, Ontario Ministry of
the Environment, Toronto (1977).
3. Popova, N.M. and O.T. Bolotina, "The Present State of Purification of
Town Sewage and the Trend in Research Work in the City of
Moscow," Advances in Water Pollution Research, Vol. 2 (W.W.
Eckenfelder, ed.). MacMillan Co., New York (1964).
4. Garber, W.F., "Plant Scale Studies of Thermophilic Digestion at Los
Angeles," Sewage and Industrial Wastes, 26, 1202-1216 (1954).
5. Garber, W.F., G.T. Ohara, J.E. Colbaugh and S.K. Raksit, "Thermophilic
Digestion at the Hyperion Treatment Plant," Journal Water
Pollution Control Federation. 47, 950-961 (1975).
6. Garber, W.F., "Certain Aspects of Anaerobic Digestion of Wastewater
Solids in the Thermophilic Range at the Hyperion Treatment
Plant," Progress in Water Technology, 8, No. 6, 401-406 (1977).
7. Buhr, H.O. and J.F. Andrews, "Review Paper: The Thermophilic
Anaerobic Digestion Process," Water Research, 11, 129-143 (1977).
8. Puntenney, J.L., Personal communication, January, 1981.
9. Garber, W.F., "Thirty Years of Experience with Thermophilic Anaerobic
Digestion at the Hyperion Treatment Plant in Los Angeles,
California," Unpublished manuscript.
10. Garber, W.F., G.T. Ohara, S.K. Raksit and D.R. Olson, "Studies of
Dewatering Anaerobically Digested Wastewater Solids at the
Hyperion Treatment Plant," Progress in Water Technology, 8, No.
6, 371-378 (1977).
11. Stern, G. and J.B. Farrell, "Sludge Disinfection Techniques," Proceed-
ings National Conference on Composting of Municipal Residues and
Sludges, Information Transfer, Inc., Maryland (1977).
12. Karr, P.R., Personal communication, December, 1980.
13. Heukelekian, H. and A. J. Kaplovsky, "Effect of Change of Temperature
on Thermophilic Digestion," Sewage Works Journal, 20, 806-816
(1948).
P-l
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