-------
en
111
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o
to
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HI
D
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U.
u.
Ill
30
25
20
15
10 -
5 •
INFLUENT SOLUBLE BOD, mg/l
150 120 100
BIO-SURF PROCESS DESIGN CRITERIA
DOMESTIC WASTEWATER TREATMENT
Wastewater Temperature * 13*C
4—Stage Operation
60
50
40
30
20
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
HYDRAULIC LOADING, gpd/sq it
Figure 10-1. Rotating biological media for secondary treatment.
10-2
-------
The following example is an evaluation of the performance of an RBC system.
1. Define the design and operating data for the system
4-stage system; 24 shafts, 100,000 sq ft of effective surface area on
each shaft.
Effective surface area
Each stage = 600,000 sq ft
Total = 2,400,000 sq ft
Flow =3.5 mgd
BOD
Influent, total =150 rag/1
, soluble (assume 65% of total) = 98 mg/1
Effluent, total =30 mg/1
, soluble (assume 50% of total) = 15 mg/1
Temperature = 20°C
2. Determine the hydraulic loading for the RBC system
Hydraulic Loading = Total flow in gpd
Total surface area
= 3,500,000
2,400,000
= 1.46 gpd/sq ft
3. Determine the efficiency of the RBC system
% BOD removal = BODin - BODout x 100
BODin
150 - 30 x 100
150
= 80%
Process Control
The only operating variable with RBC's is the speed at which the shafts
rotate. Generally, the units are equipped with mechanical drives to rotate
the media at 1 to 3 rpm. This can be adjusted to compensate for changes in
the wastewater characteristics and flow. Other areas that should be reviewed
are sludge pumping and flow distribution. Sludge pumping schedules should be
set so that septic sludge is avoided but dilute sludge is not pumping. Inade-
quate pumping results in septic sludge. Excessive pumping results in a thin
sludge which causes inefficient dewatering performance and increases pumping
costs. Poor flow distribution between units can cause overloading on one and
a decrease in treatment efficiency.
Maintenance Considerations
The features of a good maintenance program are listed below. They should
be used in addition to the general maintenance management program presented
earlier.
10-3
-------
1.
2.
3.
4.
Spare part inventory should contain at least the following parts:
one set of each type of bearing, V-belt or chain drives for each
system, and grease seals.
Inspection each shift of the discs and appurtenant facilities to
visibly inspect the equipment for misalignment, constant rotative
speeds, any excessive vibrations.
Record flow rate per kilowatt hour is determined for the mechanical
drives. A deviation from an average value is a good indication of
efficiency and changing conditions that might require maintenance.
All non-operating equipment, such as standby electric generators
tested at least once per month.
is
5. Immersed instrumentation checked and cleaned weekly.
Records
Recommended sampling and laboratory tests are shown in Figure 10-2.
Other operating records should include:
1. Raw sewage influent flow.
2. The total energy (electricity) consumed.
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor the RBC process.
1. Analytical balance
2. Clinical centriguge with graduated tubes
3. BOD incubator
4. Drying oven
5. Oxygen analyzer or titration equipment
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware,
chemicals, miscellaneous furniture, etc. and should be referred to for any
detailed questions.
Sampling Procedures
Samples should be collected at points where the wastewater is well mixed
and homogeneous such as in the influent and effluent lines. The sample col-
lector and containers should be clean. A wide mouth sample collector of at
10-4
-------
a
a
z
a
Q
UJ
UI
UI
o
a
o
a
o
BOD
DO
COD
UJ
N
V)
Z Q
n
ALL
ALL
75
TEST
FREQUENCY |
2/W
5/W
2/W
LOCATION OF
SAMPLE
I
I
E
I
METHOD OF
SAMPLE
24C
G
24C
1 REASON
FOR TEST
H
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
SECONDARY TREATMENT
ROTATING BIOLOGICAL CONTACTOR
•INFLUENT FROM
PREVIOUS MAIN
FLOW TREATMENT
PROCESS
EFFLUENT TO]
SECONDARY J
CLARIFIER S
A. TEST FREQUENCY
H m HOUR M — MONTH
D - DAY R - RECORD CONTINUOUSLY
w- WEEK M,,- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I = INFLUENT
E = EFFLUENT
C. METHOD OF SAMPLE
24C~24 HOUR COMPOSITE
G - GRAB SAMPLE
R " RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P » PROCESS CONTROL
C =- COST CONTROL
E. FOOTNOTES:
1. THESE TESTS SHOULD ALSO BE RUN ON RECEIVING
WATER. ABOVE AND BELOW OUTFALL, ON A
PERIODIC BASIS, DEPENDING ON LOCAL CONDITIONS.
2.
FOR PLANTS DESIGNED TO CONTROL THIS
PARAMETER.
Figure 10-2
10-5
-------
least 2 inches should be used. Samples collected in the effluent channel
should be collected near the discharge point so that any isolated areas of
short circuiting do not influence the results. Where automatic samplers are
used, it is important to keep the sampler tubes clean.
Sidestreams
There are no sidestreams associated with the RBC process.
10-6
-------
Process Checklist - Rotating Biological Contactors
1.
2.
3.
What is actual plant flow
Type of RBC media
Type of RBC drive
10.
11.
12.
mgd avg.
mgd peak?
Number of units (shafts)
and surface area of each unit
Color of biomass ( ) Black
( ) Other
Odor
( ) Dark Brown ( ) Light Brown
5. Odor ( ) Septic ( ) Earthy ( ) None ( ) Other
6. Are all mechanical drives and motors operating properly? {
7. Is rotation of media uniform? ( ) Yes ( ) No
8. Is the flow distributed equally to parallel shafts? ( ) Yes
How is it distributed?
) Yes ( ) No
( ) No
9. Are the characteristics of the tank contents different in the various
units? ( ) Yes ( ) No. If yes, describe
Do mechanical equipment (mechanical drives, motors, etc.) have adequate
spare parts inventory? ( ) Yes ( ) No
Is the RBC housing adequately ventilated? ( ) Yes ( ) No
Is RBC housed in a building? ( ) Yes ( ) No, or is each unit
equipped with a cover? ( ) Yes ( ) No
How often are facilities checked? ( ) once per shift ( ) daily
( ) other
13. What is frequency of scheduled maintenance?_
14. Is the maintenance program adequate? ( ) Yes ( ) No
If no, explain
15. What is general condition of the RBC facilities? ( ) good ( ) fair
( ) poor
16. What are the most common problems the operator has had with the RBC
system?
10-7
-------
References
1. Gulp/ G.L., and Folks Helm, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
7. Benjes, H.H., Jr., Attached Growth Biological Wastewater Treatment
Estimating Performance and Construction Costs and Operating and
Maintenance Requirements, EPA Contract 68-03-2186 (January, 1977).
8. Battelle Pacific Northwest Laboratories, Evaluation of Municipal Sewage
Treatment Alternatives, Council on Environmental Quality, Contract EQC316
(February, 1974).
9. Benjes, H.H., Jr., Small Community Wastewater Treatment Facilities, U.S.
EPA Technology Transfer National Seminar on Small Wastewater Treatment
Systems (January, 1978).
10. Antonie, R.L., Fixed Biological Surfaces - Wastewater Treatment, CRC
Press, Cleveland, Ohio (1976).
10-8
-------
11. SECONDARY SEDIMENTATION
Process Description
Secondary sedimentation basins are very similar in structure to primary
sedimentation basins, but are used to remove biological solids from the waste
stream. In the case of activated sludge systems they also provide a source of
concentrated return sludge for return to the aeration basin. Secondary sedi-
mentation basins can be circular, square, or rectangular. They are equipped
with scrapers or suction type sludge removal units. The scrapers are gen-
erally used for light sludges in smaller diameter tanks (less than 50 feet)
while the suction mechanisms are installed in larger tanks. Surface skimming
is also necessary to prevent the escape of floating materials in the ef-
fluent. A radial scum arm with a blade moves the scum to the periphery of the
clarifier and deposits it in a disposal trough.
Typical Design Considerations
The design of the secondary sedimentation basins is critical to the over-
all performance of a treatment facility and is dependent upon the upstream
biplogical process. Table 11-1 summarizes loading rates for these basins.
Sedimentation basins are ordinarily sized using a surface overflow rate as
described previously in Section 5. The example given in Section 5 applies
equally to secondary sedimentation basins as to primary sedimentation basins,
however, the loading rates are different. Providing adequate surface area for
peak flows is also critical since the overall plant performance is directly
related to the sedimentation basin performance.
In the case of sedimentation following activated sludge, additional design
criteria must be considered. Because large solids concentrations limit set-
tling rates, the surface area requirement may be governed by the solids load-
ing rate; this is particularly true when the mixed liquor suspended solids
(MLSS) is greater than 2,000 to 3,000 rag/1. The criteria providing the larg-
est surface area should be used to insure adequate liquid-solids separation at
all times.
Typical Performance Evaluation
The performance of secondary wastewater treatment systems is determined by
comparing the quality of the overflow from the secondary clarifiers to that of
the incoming wastewater. Typical removals for secondary treatment facilities
are given in the previous sections dealing with biological treatment processes.
Process Control
There are different operational considerations depending on the nature of
the upstream processes. Sedimentation following trickling filters or other
attached growth processes is similar to primary sedimentation in that there is
.no solids recycle. Trickling filter humus typically has a solids concentra-
tion of 5 to 10 percent and can be pumped as described for primary sludge.
11-1
-------
TABLE 11-1. TYPICAL LOADING RATES FOR SECONDARY SEDIMENTATION BASINS
Type of treatment
Overflow rate
Average Peak
gpd/sq ft
Solids loading
Average Peak Depth
Ib solids/day/sq ft ft
Settling following
trickling filtration
Settling following
activated sludge
Settling following
oxygen-activated
sludge with primary
settling
400-600 1,000-1,200
400-800 1,000-1,200 20-30
400-800
1,000-1,200 25-35
10-12
< 50 12-15
<50 12-15
Allowable solids loadings are governed by sludge settling characteristics.
On the other hand, the controls of secondary sedimentation systems are
part of the activated slu'dge process. The secondary sedimentation basins
should not be used as a storage basin for activated sludge; the sludge should
be removed and a portion of it returned to the aeration tanks as quickly as
possible. Best return rates are often in the range of 20 to 50 percent of the
secondary inflow rate for most systems. The sludge level in each basin should
not be greater than one-quarter the total basin depth. The sludge level is
controlled by the sludge removal rate. Some of the removed solids are wasted
from the system and the remainder returned to the aeration basins. Excessive
sludge inventory in the secondary sedimentation basins can lead to loss of
sludge over the basin effluent weirs, causing high effluent solids.
Scum should be properly removed from the secondary basins. Excessive
skimming will result in too much water being carried over with the scum. If
insufficient scum is removed, it will flow around or under the baffle and
leave the tank in the effluent.
Equal flow distribution should be provided among all available secondary
settling tanks. Even with equal distribution of flow, some differences in
efficiencies may be found between two or more" units. With unequal flow, how-
ever, less SS and BOD will be removed overall.
Maintenance Considerations
The features of a good maintenance program that the inspector should note
include the items listed below. These should be used in addition to general
maintenance management consideration presented earlier.
11-2
-------
1. Scheduled inspection and maintenance of baffle boards and scraper.
2. Inspection of scum removal equipment.
3. Spare part inventory should contain the following: turntable gears
and motors for circular basins, wear shoes, sprockets, wall brackets,
chain pins and flights, shear pins, and cable for travelling bridges.
Records
Recommended sampling and laboratory tests are shown on Figure 11-1.
Other operating records are directly related to the biological treatment
process preceding secondary sedimentation. The appropriate section of this
report should be consulted for additional information.
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor secondary sedimentation. In addition, the equipment required to mon-
itor the biological process will be needed.
1. Analytical balance
2. Clinical centrifuge with graduated tubes.
3. BOD incubator
4. Drying oven
5. Imhoff Cones
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chem-
icals, miscellaneous furniture, etc. and should be referred to for any
detailed questions.
Sampling Procedures
Samples should be collected at points where the wastewater is well mixed
such as at the center of the channel of flow where velocities are high. The
sample collector and containers should be clean. A wide mouth sample collec-
tor of at least 2 inches should be used. Samples collected in the effluent
channel should be collected near the discharge point so that any isolated
areas of short circuiting do not influence the results. Where automatic
samplers are used, it is important to keep the sampler tubes clean.
Sidestrearns
The only sidestream from secondary sedimentation is the sludge pumped from
the basin. The solids from an activated sludge plant are either returned to
the aeration tank (RAS) or wasted (WAS) to the primary sedimentation tank,
thickeners, or digester. Generally, 85 to 95 percent of the settled sludge is
returned to the process. The actual amount must be determined by the plant
control considerations as discussed in Section 6. Trickling filter sludge is
11-3
-------
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Q.
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SUSPENDED
SOLIDS
BOD
SETTLEABLE
SOLIDS
TOTAL
SOLIDS
NHv-N1
ORG-N1
NOy-M1
TOTAL-P
ORTHO-P
PLOW
SLUDGE VOLUMB
LAB CENTRIFUC
TOTAL SOLIDS
ALKALINITY
pH
TURBIDITY
UJ
g
vt
Z o
a
ALL
ALL
ALL
<1
ALL
ALL
ALL
ALL
ALL
ALL
>1
p
>1
ALL
ALL
>15
TEST
FREQUENCY |
3^W
2/W
1/D
3/W
1/D
1/W
VP
VD
1/D
R
3/D
1/W
1/W
1/D
Mn
LOCATION OF
SAMPLE
I
B
E
I
E
S
E
E
E
E
E
WS
RS
S
S
1
1
E
METHOD OF
SAMPLE
24<;
24C
G
G
24C
24Q
24C
24C
24C
R
G
G
24C
G
Mn
1 REASON
FOR TEST
P
H
P
P
H
H-
9
H
H
P
P
P
P
H
P
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
SECONDARY TREATMENT
SECONDARY CLARIFIES
tiy
EFFLUENT TO
NEXT MAIN
TREATMENT
PROCESS
SLUDGE UNDERFLOW
INFLUENT FROM
SECONDARY
TREATMENT
PROCESS
RECYCLE SLUDGE
TO AERATION BASIN
(FOR ACTIVATED
SLUDGE)
A. TEST FREQUENCY
H - HOUR M - MONTH
D- DAY R - RECORD CONTINUOUSLY
W- WEEK Mn- MONITOR CONTINUOUSLY
8. LOCATION OF SAMPLE
I - INFLUENT
6 - EFFLUENT
S= SLUDGE UNDERFLOW
WS =WASTE SLUDGE
RS=RECYCLESLUDGE
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G" GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn=» MONITOR CONTINUOUSLY
0. REASON FOR TEST
H "HISTORICAL KNOWLEDGE
P -PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. TO BE RUN IF PROCESS IS DESIGNED TO
CONTROL THIS PARAMETER
Figure 11-1
11-4
-------
not recycled back to the process. Generally,"it is pumped back to the head of
the plant upstream of the primary sedimentation basins, to thickening tanks,
or directly to digesters.
Regardless of the type of secondary sludge or where it is being pumped,
pumping should be on a continuous basis. Standby units or adequate pumping
flexibility should be provided to avoid interrupted or intermittent operation.
11-5
-------
Process Checklist - Secondary Sedimentation
1.
2.
3.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
What is the total flow to the sedimentation basins
gpd peak.
What is the design flow gpd average,
gpd average,
gpd peak?
What are the dimensions of the sedimentation basin?
Is chemical addition used to improve settling? If so, what chemical(s)
are added?
, and for what reason?
gpd total,
What are the dose rate(s)
How much sludge is pumped
gpd WAS?
What is the solids concentration in the sludge?
Are there settleable solids in the effluent
Is sludge pumping
continuous
gpd RAS,
manual
mg/liter?
automatic
intermittent?
other?
How often do sludge pumps run
minutes/hour?
Frequency of maintenance inspections by plant personnel
Is maintenance program adequate? { ) Yes ( ) No
Does the influent baffle system accomplish its purpose?
Is the scum collection system operating properly? ( )
Is the sludge collection system operating properly? ( )
/year.
(i.e. exces-
No
Yes
( ) Yes ( )
Yes ( ) No
Yes ( ) No
Does the sludge collection system show any signs of mechanical failure?
( ) Yes ( ) No
Does the tank surface indicate improper sludge withdrawal?
sive floating solids, gas...) { ) Yes ( ) No
Is there an excessive accumulation of scum? ( ) Yes ( )
Does the effluent baffle system accomplish its purpose? ( )
Are the effluent weirs level? ( ) Yes ( ) No
Are the effluent weirs kept clean? ( ) Yes ( ) No
If multiple units are used, is the flow distributed evenly?
( ) Yes ( ) No
Does the unit show signs of short circuiting and/or overloads?
( ) Yes ( } No
Is there an alarm system for equipment failures or overloads?
( ) Yes ( ) No
Does the sampling program meet the recommendations? ( ) Yes ( ) No
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory equipped for the necessary analyses? ( )Yes ( ) No
What spare parts are stocked?
No
( ) No
27. What are the most common problems the operator had had with the process?
11-6
-------
References
1. Gulp, G.L., and Folks Helm, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
11-7
-------
-------
12. CHLORINATION
Process Description
The most common method of wastewater disinfection is by chlorination.
Chlorine is added to the treated effluent to destroy any bacteria, pathogens
or viruses. Other principal uses of chlorine are for odor control, and often
times for control of bulking activated sludge. Chlorine application systems
are described in Reference 1 and 2.
Typical Design Considerations
The design criteria and related performance of a chlorination system
depends upon whether the chlorine is being applied strictly for disinfection
purposes or, in the case of advanced waste treatment, for removal of nitro-
gen. Chlorine dosages vary for the two different applications.
The destruction of pathogens by chlorination is dependent upon water
temperature, pH, time of contact, degree of mixing, turbidity, presence of
interfering substances, and the concentration of chlorine available. Table
12-1 provides a general indication of chlorine dosage ranges for disinfecting
wastewater after various degrees of pretreatment.
TABLE 12-1. ESTIMATE OF CHLORINE DEMAND FOR VARIOUS WASTEWATERS
Raw fresh domestic waste
Raw septic domestic waste
Primary sedimentation effluent
Recirculated biofilter effluent
Biofilter effluent (secondary)
Trickling filter effluent
Activated sludge effluent
Sand filtered effluent
Septic tank effluent
8-15 ppra
15-30 ppm
8-15 ppm
5-8 ppm
3-8 ppm
3-10 ppm
2-8 ppra
1-5 ppm
30-45 ppm
Breakpoint chlorination is also used in advanced wastewater treatment
facilities for nitrogen removal. Chlorine is added to convert ammonia nitro-
gen to nitrogen gas. With the exception of the chlorine dosages, which may be
anywhere from 40 to 50 times greater than that required for disinfection pur-
poses only, the nitrogen removal process involves essentially the same equip-
ment. Wastewater (after secondary or tertiary treatment) enters the chlorine
contact chamber at which point chlorine is added and completely dispersed with
incoming flow. In the breakpoint chlorination process about 10 mg/1 of chlo-
rine must be added for each 1 rag/1 of ammonia nitrogen present in the waste-
water. A more highly treated wastewater requires less chlorine to reach
breakpoint. The breakpoint process can result in 99% plus percent removal of
ammonia nitrogen, reducing concentrations to less than 0.1 mg/1 (as N).
12-1
-------
Typical Performance Evaluation
To determine the adequacy of the chlorination system to accomplish dis-
infection or other objectives the evaluator should examine the chlorine con-
tact basin detention time, the chlorine residual in the basin effluent, and
the MPN count of coliform organisms after chlorination. This evaluation can
be performed very easily in the following steps:
1.
2.
Obtain design and typical operating data for the chlorination system
being studied.
Example:
Type of Effluent
Peak plant flow
Volume of chlorine contact tank, V
Chlorine dosage
Chlorine residual
Determine the contact time for the chlorine contact tank based on
peak flow.
Contact time, hrs - V in cu ft x 7.48 gal/cu ft x 24 hrs/day
Activated Sludge
5.0 mgd
13,926 cu ft
6.0 mg/1
1.0 rag/1
= (13,926)
5
Flow in gpd
(7.48) (24)
x 106
3.
=0.50 hrs or 30 min
Examine the daily disinfection log sheet for chlorine feed rates and
chlorine residual patterns. Compare calculated contact time and
measured chlorine residuals with the values for these parameters
established by the proper regulatory agency. As a general rule, if
the residual falls between 0.2 mg/1 and 1.0 mg/1 and there is 15 to
30 minutes of contact time there should be reasonable assurances of
good disinfection. In the above example the 30 minutes of contact
time with a 1.0 mg/1 of chlorine residual effluent should indicate
that the plant is meeting appropriate standards.
Process Control
In general the better the treatment plant is operated the easier it will
be to disinfect the effluent. A poorly treated effluent will contain high
levels of bacteria and higher concentrations of suspended solids which will
increase the chlorine requirement. Effective disinfection of chlorine is
dependent upon the combined effect of chlorine dosage, mixing and contact time
with the wastewater. Overall process control is accomplished by measurement
of the effluent chlorine residual. Maintenance of the proper chlorine resi-
dual is dependent upon the adequacy of the chlorination system to respond to
changes in chlorine demand.
Applying chlorine to wastewater in a well mixed system produces a much
higher degree of disinfection than when chlorine is fed without mixing, even
though the contact time and residual are adequate. Longer contact times are
more important than higher chlorine dosages or residuals in wastewater
disinfection.
12-2
-------
In breakpoint chlorination for nitrogen removal the system must be able to
respond quickly to changes in ammonia nitrogen concentration, chlorine demand,
pH, alkalinity and flow. Failure to closely match chlorine dosage to ammonia
concentration can result in incomplete nitrogen removal or chlorine over-
doses. A control system for nitrogen removal by breakpoint chlorination
should include automatic analyzers to control chlorine dosage within a narrow
range around the required values. Direct measurement of residual chlorine or
indirect measurement of pH can be used to control breakpoint chlorination.
Maintenance Considerations
The features of a good maintenance program that the inspector should look
for are:
1. Established schedules for checking all connections for chlorine gas
leaks. The piping system can be checked for chlorine leaks by using
an ammonia solution or checking for the appearance of green copper
scum around the edges of corroded metal at the joints.
2. Atmospheric chlorine leak detection equipment checked out and peri-
odically calibrated.
3. Evaporator periodically checked for corrosion.
4. Inspect chlorine gas filter at 6 months intervals.
5. Chlorine pressure reducing valve regularly inspected. Every 2 to 3
years the spring opposing the silver diaphram will suffer fatigue and
should be replaced. Every 5 years the entire assembly should be dis-
mantled and the diaphram inspected for fatigue.
6. Chlorination system regularly inspected for restrictions between the
cylinder and the chlorinator caused by impurities.
9.
10.
11.
Chlorine Institute Emergency Kit to seal off leaking cylinders.
eral units should be provided near the feed facility.
Sev-
Gas diffusion devices in the contact basins periodically inspected to
ensure that they are not clogged.
Bulk liquid chlorine storage tanks flow control valves in the dome of
the tank inspected regularly. Provisions made to hydrostatically
test the bulk liquid chlorine storage tank at 2 years intervals.
Rotameter tube and chlorine metering orifice removed from the chlori-
nator and cleaned at least once every 6 months.
Chlorine residual analyzer calibrated and maintained on a regular
basis. In order for this equipment to perform effectively it must
receive daily, weekly, and quarterly inspections.
12-3
-------
Process Checklist - Chlorination
3,
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
What is the flow to the chlorine contact basin?_
"• - mgd.peak
What are contact basin dimensions?
width/feet,
jngd avg.
length/feet,
What is contact basin detention time?_
What is applied chlorine dosage?_
depth/feet.
min. (at peak flow)
mg/1
)
mg/1
) No
chlorine cylinders
sodium hypochlorite
Ibs/pe r/day
What is normal chlorine residual in basin effluent?
Are disinfection standards being met? ( ) Yes (
What type of chlorination system is being used?(
( ) on-site sodium hypochlorite generation (
solution ( ) calcium hypochlorite solution?
What is the chlorination system design capacity?
maximum capacity? Ibs/per/day
What is the configuration of the chlorine contact basin? ( ) round
( ) rectangular ( ) other
Is contact basin adequately baffled to minimize shortcircuiting?
( ) Yes ( ) No
How is chlorine introduced into the wastewater entering contact basin?
( ) perforated diffusers ( ) injector with single entry point
( ) other *
Are mechanical mixing provisions incorporated in the chlorine contact
basin design? ( } Yes ( ) No
Is plant equipped with automatic chlorine leak detectors with alarms in
critical areas? ( ) Yes ( ) No
Is' the ventilation system for chlorine cylinders storage and chlorination
equipment rooms adequate? ( ) Yes ( ) No
How often are facilities checked? ( ) once per shift ( ) daily
( ) other
Does the treatment plant maintain an adequate spare parts inventory?
( ) Yes ( ) No
What is the frequency of scheduled maintenance? Describe "
18. Is the maintenance program adequate?
the problem?
( ) Yes ( ) No. If no, what is
) Yes { ) No
19. Are proper safety precautions used? { ) Yes ( ) No
20. Does the sampling program satisfy the recommendations? (
21. Are operating records adequate? ( ) Yes ( ) No
22. Is the laboratory equipped to perform the necessary analyses?
( ) Yes ( ) No
23. What is the general condition of the chlorination facilities?
( ) good { ) fair .( ) poor
24. What are the most common problems the operator has had with the chlorina-
tion process?
12-6
-------
References
1. Gulp, G.L., and Polks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, EPA
Report 430/9-78-001.
2. George Clifford White, Handbooks of Chlorination, Nostrand Reinhold Co.
1972.
3. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation, 1977.
4. Gulp, Gordon L., and Gulp, Russell L., Handbook of Advanced Wastewater
Treatment, Van Nostrand Reinhold, 1977.
5. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-02-0328, June 1973.
6. Rand, M.C. et al, Standards Methods for the Examination of Water and
Wastewater, American Public Health Association 14th edition, 1975.
12-7
-------
-------
13. OZONATION
Process Description
Ozone is an extremely powerful oxidizing agent which has been used princi-
pally in Europe for the disinfection of water supplies. When applied to
wastewaters, ozone will oxidize many residual organic compounds, reducing the
effluent BOD, COD, and color and adding dissolved oxygen to the final ef-
fluent. Unlike chlorine, ozone produces no residual materials which are toxic
to aquatic life in the receiving stream and adds no dissolved solids.
Ozone is produced by passing air, oxygen enriched air, or pure oxygen be-
tween two electrodes across which an alternating high voltage potential is
maintained. Figure 13-1 illustrates a basic configuration of an element com-
mon to the various types of ozone generators commercially available. This
method of ozone production is inefficient. Only about 10% of the energy sup-
plied is used to produce ozone. The remainder is lost as light, sound and
heat. Ozone gas is unstable and within a very short time period decomposes to
oxygen. The inability to store ozone requires that it must be produced at its
point of use.
There are three basic types of commercially available ozone generators:
the Otto plate, the tube and the Lowther plate. These are described in
Reference 1.
Typical Design Considerations and Performance Evaluation
The design criteria and related ozone dosages for an ozonation system de-
pends upon whether the ozone is to be applied for disinfection or as a ter-
tiary treatment process for effluent polishing. Ozone dosages and required
contact times are different for the two requirements.
A value of 200 fecal coliform/100 ml can usually be attained in secondary
effluents using an ozone dosage of about 5 mg/1. Contact times may range from
as little as 2 minutes to as much as 15 minutes. Five minutes appears to be
adequate with proper dosages and with efficient contactor design. Standards
calling for almost complete coliform removal (to 2 fecal coliform per 100 ml)
may require dosages of 15 mg/1 or more. For most cases, an ozone residual of
0.1 mg/1 for 5 minutes is adequate to disinfect waters low in organics and
free of suspended materials. The degree of pretreatment has a significant
impact upon the effectiveness of ozone for disinfection. The presence of
organic material exerts an ozone demand which can prevent maintenance of a
killing residual. Also the presence of particulate material can shield organ-
isms from the germicidal effects of ozone.
As a tertiary treatment process, ozone can reduce BOD, COD, color, turbid-
ity and odor. Ozone dosages are widely variable depending upon particular
treatment requirements. Contact times tend to be in a range similar to disin-
fection. With good mixing, a contact time of 5-10 minutes will achieve maximum
oxidation of organics. Theoretically 3 mg/1 of ozone will destroy about 1
mg/1 of COD. Experimentally, it has been observed when applying ozone to alum
coagulated and filtered secondary effluent that the COD was reduced from 36-41
13-1
-------
HEAT
DISCHARGE GAP
ELECTRODE
DIELECTRIC
03
ELECTRODE
HEAT
Figure 13-1. Basic ozonator configuration.
13-2
-------
mg/1 to 15-17 mg/1 with 63-89 mg/1 ozone. These data exhibit a COD to ozone
ratio ranging from 2.6-3.7 which corresponds reasonably to the predicted
ratio. Considering that a well treated secondary effluent has a COD range of
25-35 mg/1, a 50% reduction would require an ozone dosage ranging from 36 to
50 mg/1. For general design purposes the ozone system for polishing secondary
efflue.it to the above standards should be capable of providing ozone dosages
in excess of 50 mg/1.
The following example is for calculating ozone requirements.
Desired Dosage in contact basin
Wastewater flow
Ozone concentration (%/wt)
Peed gas
5 mg/1
10 mgd
3%
Oxygen
Determine required ozone production, Ibs/day
Ibs/day ozone = Dosage, mg/1 x flow mgd x 8.33 Ibs/gal
= 5 mg/1 x 10 mgd x 8.33 Ibs/gal
= 417 Ibs/day 03
Determine feed gas (oxygen) flow, SCFM
@ 3% O3, Ibs of 02 required per day
417 Ibs/day 03
0-03 Ibs O3/lbs 02
* 13,900 Ibs 02/day
At 70°F and 14.7 psia, 1 Ib O2 has volume of 12.08 ft3
Volume SCFM = 13,900 Ibs O? x 12.08 ft3 x 1 day x
Ib 24 hrs 60 min
1 hr
= *117 scfm oxygen flow
*Changes in temperature, pressure or feed gas oxygen concentration affect
required generator feed gas flow. Appropriate correction factors must be
applied to determine correct values. Refer to manufacturer's instruction
manuals.
Process Control
The application of ozone to a wastewater, whether it be for disinfection
or for effluent polishing, requires close control to ensure effective perform-
ance. Production of ozone which is related to the flow of water under treat-
ment and its dosage requirements may be controlled manually or automatically
by probe and relay. The automatic dosage control loop system is preferred
since it compensates for changes in flow and ozone demand to provide a preset
ozone residual. Starting up sequences are important and require establishment
of exact procedures and timing. A centralized control panel containing all
initiating controls, process performance indicators, inner locks and other
safeguards are generally incorporated in any ozone system.
13-3
-------
Maintenance Considerations
The features of a good maintenance program that the inspector should look
for are:
1. Schedules established for checking electrical and gas connections for
tightness. The piping system can be checked for ozone leaks by hold-
ing paper towels soaked in potassium iodide solution to the connec-
tors or by applying an approved leak detection material.
2. Atmospheric ozone leak detection equipment check-out and calibra-
tion. Has a specific schedule for this attention been established?
3. Ozone cells checked for accumulations of grease and dirt.
4. Gas diffusion devices in the contact basins regularly inspected to
ensure that they are performing properly. Porous diffusers may
become clogged with materials percipitated from solution requiring
acid or caustic cleaning to remove.
5. Basin covers periodically checked for gas leaks.
6. Ozone destruction devices (single pass systems) checked for effective
functioning.
7.
Instrumentation for measuring ozone concentrations of ozonator output
and the dew point analyzer on the feed gas supply periodically
calibrated.
Spare parts inventory should include: SCR rectifier and control cir-
cuit fuses, fan belt set, fan bearing, fan belt grease, fan starter,
thermal overloads, various relays for key electrical components,
replacement cell module, high temperature alarms, and spare parts for
ozone leak detection instrumentation and for other monitoring instru-
mentation. Some variation will occur with the different styles of
generators.
Records
Recommended sampling locations and laboratory tests are shown in Figure
13-2. Other operating records should include:
1. Ozone contact basin influent flow
2. Ozonizied gas flow to contact basin
3. Flow rate of off-gas from contact basin
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor the performance of the ozonation process:
13-4
-------
s
Q
UJ
t-
tn
UJ
O
O
O
t-
0.
o
OZONE
RESIDUAL
OZONE
CONCENTRATION
OZONE
CONCENTRATION
CONFORM
FECAL
COLIFORM
PH
TEMP
DO
3OD
:OD
TURBIDITY
UJ
N
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h-
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ALL
ALL
ALL
ALL
>5
ALL
ALL
ALL
ALL
=iLL
\LL
TEST
FREQUENCY
R
Mn
Mn
l^W
1/W
1/D
1/D
/W
/w
/W
/w
LOCATION OF
SAMPLE
E
°3
OG
E
E
E
E
E
E
E
I
METHOD OF
SAMPLE
R
Mn
Mn
G
G
G
G
a
G
G
G
REASON
FOR TEST
P/L
P,C
P,C
P
P
H
H
u
H
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
OZONATION
OFF GAS
03=OZONE
1
»
1
TTTT
1
<
TTTTTTT
4 OG
ttu
EFFLUENT
TO RECEIVING
WATER
•INFLUENT FROM PREVIOUS
MAIN FLOW TREATMENT
PROCESS
A. TEST FREQUENCY
H m HOUR
D - DAY
w- WEEK
M - MONTH
R - RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
O3= OZONE GAS FLOW
OG= CONTACT BASIN OFF GAS
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G- GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn=« MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. THESE TESTS SHOULD ALSO BE RUN ON RECEIVING
WATER. ABOVE AND BELOW OUTFALL, ON A
PERIODIC BASIS. DEPENDING ON LOCAL CONDITION*.
2. FOR PLANTS DESIGNED TO CONTROL THIS
PARAMETER.
Figure 13-2
13-5
-------
1. Analytical balance
2. Wet test drum meter with associated barometer and thermometer
3. Gas washing bottles (2)
4. Dewpoint meter for monitoring moisture content of feed gas
5. General laboratory glassware including volumetric flasks, graduated
cylinders, burets, beakers, pipettes, etc.
6. Tygon tubing
7. Test reagents including potassium iodide solution, sulfuric acid,
sodium thiosulfate, starch indicator solution, potassium dichromate
8. Ozone residual colormetric test kit
The EPA report entitled "Estimating Laboratory Needs for Municipal Waste-
water Treatment Facilities" provides a detailed listing of glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any
detailed questions.
Sampling Procedures
Effluent residual ozone determinations must be performed immediately
because samples can not be preserved or stored due to the instability of the
residual. Samples should be collected in a manner so as to minimize aera-
tion. There are three testing methods described in Standard Methods.
Sidestreams
The off-gas from the ozone contact basin can be considered a sidestream.
In a single pass, once-through system, the ozone in the waste gas is destroyed
by heat or chemicals, or catalyic decomposition prior to venting to atmos-
phere. In the closed loop system, the off-gas is recycled back to the ozone
generation equipment and reused.
In some applications, the introduction of ozone produces foam and scum
which collects on the contact basin and must be removed. The quantity of this
material is, however, very small and the removal requirements are minimal. The
best way of controlling of foam on contact basins is to reduce it with water
sprays.
13-6
-------
Process Checklist - Ozonation
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
What is flow through ozone contact basin
. mgd peak?
What are contact basin dimensions? length_
feet, depth feet
What is contact detention time?
What is applied ozone dosage
mgd avg?
feet, width
minutes at
mgd?
in mg/1?
What is normal ozone residual in basin effluent • mg/1?
Are disinfection standards being met? ( ) Yes ( ) No
What type of ozone generation equipment? ( ) plate style ( ) tube
style ( ) other
What is ozone generator design capacity _lbs/day, maximum
capacity Ibs/day?
Ozone generation equipment uses ( ) air, oxygen enriched air ( ) pure
oxygen ( ) as feed gas?
What type ozone contactor? ( ) gravity feed covered basin
( ) packed tower ( ) Other
Is ozonation system { ) Once through ( ) closed loop?
How is ozone introduced into contactor? { ) porous diffusers
( ) injectors ( ) turbine aerators ( ) other?
Are residual ozone determinations made with ( ) continuous analyzers or
by ( ) laboratory tests?
Is plant equipped with automatic ozone leak detectors with alarm in crit-
ical areas? ( ) Yes { ) No
Is ozone generator room adequately ventilated? ( ) Yes ( ) No
How often are facilities checked? ( ) once per shift ( ) daily
( ) other
Does the mechanical equipment have an adequate spare parts inventory?
( ) Yes ( ) No
What is the frequency of scheduled maintenance?
Describe
19. Is the maintenance program adequate? ( ) Yes ( ) No.
the problem?
If no, what is
20. Are proper safety precautions used? ( ) Yes ( ) No
21. Does the sampling program satisfy the recommendations? ( )Yes ( ) No
22. Are operating records adequate? ( )Yes ( ) No
23. Is the laboratory equipped for the necessary analyses? ( )Yes ( ) No
24. What is the general condition of the ozonation process? ( ) good
( ) fair ( ) poor
25. What are the most common problems the operator has had with the process?
13-7
-------
References
1. Gulp, G.L. and Folks Heim, N., Field Manual for Peformance Evaluation and
Troubleshooting at Municipal Wastewater Treatment Facilities, EPA Report
430/9-78-001.
2. Rosen, H.M., "Ozone Generation and It's Relationship to the Economical
Applications of Ozone and Wastewater Treatment", Chapter VI, Ozone in
Water and Wastewater Treatment, Ann Arbor Science Publishers Incorporated
1972.
3. Kinman, R.N., "Ozone and Water Disinfection" Chapter VII, Ozone in Water
and Wastewater Treatment, Ann Arbor Science Publishers Incorporated 1972.
4. Diaper, E.W.J., "Practical Aspects of Water and Wastewater Treatment by
Ozone" Chapter VII, Ozone in Water and Wastewater Treatment, Ann Arbor
Science Publishers Incorporated 1972.
5. Gulp, R.L., Wesner, G.M., and Gulp, G.C., Handbook of Advanced Wastewater
Treatment, Van Nostrand Reinhold (1978).
6. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328, June 1973.
7. Union Carbide Corporation, Linde Division, Operation and Maintenance of
the Union Carbide LG-90 Ozone Generator Tonawanda, N.Y. 1977.
8. Stopka, Karel, "Ozone Plant Improves Efficiency and Economy of Wastewater
Treatment", Water and Sewage Works, April 1978.
13-8
-------
14. FILTRATION
Process Description
The filtration process is used to remove or reduce the suspended or col-
loidal matter from a liquid stream by passing the water through a bed of
graded granular material. The granular material can be sand, gravel, coal,
garnet or similar materials. The main purpose of filtration is meet more
stringent discharge standards and improve disinfection efficiency and
reliability. Filtration is used to remove BOD, COD, turbidity, phosphorus,
virus, asbestos, heavy metals and others from secondary or tertiary effluent.
It is always used ahead of granular activated carbon contactors to protect
against fouling and improve the adsorption efficiency. Filtration is fre-
quently installed following chemical treatment processes to remove flocculant
materials not removed in the clarifiers.
Filters are classified in many ways. They can be described according to
the direction of flow through the bed, that is, downflow, upflow, biflow,
radial flow, horizontal flow, fine to coarse, or coarse to fine. They may be
classed according to the type of filter media used, such as sand, coal (or
anthracite), coal-sand, multilayered, mixed media, or diatomaceous earth.
Filters are also classed by flow rate. Slow sand filters operate at rates of
0.05-0.13 gpm/ft2, rapid sand filters operate at rates of 1-2 gpm/ft2 and
high rate filters operate at rates of 3-15 gpm/ft2. They can also be
classed by the flow characteristics of filters which can be pressure or grav-
ity flow. Filters used for wastewater treatment are predominantly downflow,
multi-media, high rate filters that can have either gravity of pressure flow
characteristics.
Because of the high loading rates currently used in filtration systems
(about 30 times the rate of slow sand filters) they capture more solids in
less time and must be cleaned more often. The filter is cleaned by reversing
the flow through the media ("backwashing"). The upward backwash rate must be
high enough that the media particles are suspended and the wastewater solids
and captured materials are washed from the bed. These backwash wastewaters
(usually less than 5% of the wastewater flow treated) are stored in an equal-
ization tank and then recycled to the wastewater treatment plant for
processing.
Typical Design Considerations
The principal criteria by which filters are sized are related to the flow
characteristics, gravity or pressure, and the type, size and depth of the
filtering media. Once these have been established, the loading, backwashing
and surface washing rates can be established. These items are briefly dis-
cussed in the following paragraphs:
Filter media designs are usually either dual media filters which consist
of 15 in. of coal (about 1.8 mm in diameter) and over 15 in. of sand (0.55 mm)
or mixed media which consists of about 16 in. of coal, 9 in. of sand, and 4
in. of garnet.
14-1
-------
The most common filtration rates used in wastewater treatment range from 3
to 6 gpm/sq ft of filter area. This range in loading rate is applicable to
both the dual media and mixed media configurations.
Backwash systems for filters usually are operated at rates in the range of
15 to 20 gpm/sq ft for 5-10 min. The backwash water is returned to the
headworks for treatment.
Typical Performance Evaluation
The filtration process is evaluated by the quality of the filtered water
measured in terms of suspended solids or turbidity. Other factors include:
Rate of headless build-up, feet/hour
Water application rate
Influent characteristics
Filtration media characteristics
Filter backwash system
Filter surface wash system
Of these factors, the most important is the quality of the influent to the
filter. When filtering secondary effluent, if the biological system always
operates well, good filter performance can be expected. However, if the bio-
logical system is frequently upset, filtration will be much more difficult.
Performance evaluation may be conducted as described below.
1. Collect the required base information.
Plant flow rate = 15 mgd
BOD in influent to filter = 20 mg/1
Suspended solids in influent to filter = 25 mg/1
BOD in filter effluent = 10 mg/1
Suspended solids in filter effluent = 3 mg/1
Filter size = 22 ft x 24 ft
Number of filters = 4
Backwash flow rate = 7920 gpm
Backwash duration = 7 min
Frequency of filter backwash = once each 12 hours
Headloss to backwash (preset condition) = 10 feet
2. Compute.the filter area and rate of filtration under normal conditions
Plant flow rate
15 mgd x 106 = 10,417 gpm
1440 min/day
Filter area = 4 x 22 x 24 = 2,112 sq ft
Filtration rate = 10,417 gpm = 4.93 gpm/sq ft
2,112 sq ft
This system is within the range of filtration rates normally used, which
is 3 to 6 gpm/ft2.
14-2
-------
3. Compute the rate of backwash and the volume used.
Rate of backwash = 7920 = 15 gpm/sq ft per filter
2112/4 filters
Flow through each filter = 15 mgd x 106
2604 gpm
4 x 1440 min/day
Volume of backwash water = 7920 gpm x 7 min/backwash x 2 day x 4 filters
= 443,520 gallons/day
Volume of water through filters = (1440 - 2 x 7). x 2604.x 4
10 6
Percent backwash water
= 14.85 mgd
0.433 x 100 = 3%
14.85
The backwash rate of 15 gpm/sq ft2 falls at the lower end of the normal
range for backwashing of 15 to 20 gpm/ft2. The backwash percentage of 3% is
within the desirable range of backwash usage of 1 to 5%.
4. Compute the percentage of BOD and suspended solids removals.
Percentage BOD removal - 20 - 10 = 50%
20
Percentage suspended solids removal = 25 - 3 = 88%
25
5. Characterize the influent water to the filter as being activated
sludge, trickling filter, chemical clarification or some other pro-
cess effluent. Using the average values developed above, compare
them to the average values expected values presented in Table 14-1.
These values are for mixed media filters and were developed using
data at several operating facilities. When treating chemically
coagulated and settled effluent, the filter effluent should be less
than 1 turbidity unit.
Process Control
The control considerations for the filtration process depend almost total-
ly on the filter aid facilities provided. These include polymer and chemical
conditioners to be added ahead of the filters. Other controls include adjust-
ment of the headloss to backwash value and the length of the backwash runs.
These are discussed in more detail in Reference 1.
Maintenance Considerations
The evaluator should study the maintenance program to determine whether
the following items are included (in addition to general maintenance manage-
ment discussed earlier).
1.
Spare parts inventory should include at least the following items:
one set of each type of bearing for pumps, grease seals, one set of
all gaskets, mechanical seals, washers or sheaves for adjusting pump
impellers, nozzles for surface wash system and underdrain system,
control solenoid and some volume of the filter media.
14-3
-------
TABLE 14-1. DESIGN CRITERIA FOR ORANGE COUNTY WATER DISTRICT
OPEN GRAVITY, MIXED MEDIA FILTER SYSTEM
Dimensions:
4 filters each
22 ft x 24 ft (plan area)
media depth = 30 in
Bed construction:
Media
Anthracite coal
Silica sand
Garnet sand
Garnet gravel
Garnet gravel
Silica gravel
Silica gravel
Silica gravel
Depth
(in)
16.5
9
4.5
1.5
1.5
2
2
2
Specific
gravity
1.6
2.6
4.0
4.0
4.0
2.6
2.6
2.6
Grain size
range (mm)
0.84-2.00
0.42-0.84
0.18-0.42
1
2.00-4.76
3.18-6.36
6.36-12.72
12.72-19.08
Surface hydraulic
loading rate:
Max operating
headless:
4.93 gpm-sq ft at 15 mgd (2604 gpm per filter)
10 ft
14-4
-------
2.
3.
4.
5.
6.
7.
Records
Daily inspection of the rotary surface washers to insure they are
free to rotate and the nozzles are not plugged? In gravity filters,
the washing operation should be monitored for any plugged orifices.
Inspection in each shift to check the calibration of the effluent
turbidimeters and any other remote recording or instrumentation.
Recorder charts on flow, headless, and turbidity meters changed
routinely and the recorder ink supply checked at each chart change-
System is monitored routinely and that the filters are not operating
out of their anticipated operating range.
.Regular readings of backwash pumping times are recorded from elapsed
time meters. These can be used for scheduling maintenance work and
also to insure that backwash cycles are correct.
Periodic performance tests run on each pumping unit to insure that it
is operating along the same pump curve as supplied at the time of
purchase of the pumping unit.
The recommended sampling and laboratory tests are shown in Figure 14-1 for
the filters. The same tests are performed on all types of filters.
Other operating records should include the following:
1.
2.
3.
4.
5.
6.
Influent flow to the filters
Backwash flow rate and duration
Surface wash flow rate and duration
Filter run time or frequency of backwash
Headless through filter as a function of time
Filter aid type and dosage
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor the filtration system.
1.
2.
3.
4.
5.
6.
Analytical balance
Clinical centrifuge with graduated tubes
BOD incubator
Drying oven
Dessicator
Turbidimeter
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for anv de-
tailed questions. y
14-5
-------
a
o
1U
-I
o
P
Q.
O
TURBIDITY
BOD
SUSPENDED
<^nT,Tpc
PLOW
pon
SUSPENDED
SOLIDS
UJ
N
t/>
t-
Z 0
n
ALL
ALL
AT.T.
ALL
AT.L
ALL
TEST
FREQUENCY |
R
1
1
R
2/W
2/W
LOCATION OF
SAMPLE
E
BW
pw
BW
I
E
I
E
METHOD OF
SAMPLE
R
G
rc
R
24C
24C
z5
3>-
< ce
uj o
ce u.
P
P'
T>,
P:
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
FILTRATION
MIXED MEDIA OR SAND TYPE
(INFLUENT FROM
PREVIOUS MAIN
FLOW TREATMENT
PROCESS
II
EFFLUENT TO
NEXT MAIN FLOW
TREATMENT PROCESS
NOTE: PRESSURE TYPE SHOWN.
GRAVITY TYPE HAVE
SIMILAR FLOW STREAMS.
BACKWASH WASTE
RECYCLE TO PLANT
INFLUENT OR
CHEMICAL TREATMENT
INFLUENT-
A. TEST FREQUENCY
H m HOUR M - MONTH
D- DAY R - RECORD CONTINUOUSLY
W- WEEK Mr.- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I - INFLUENT
E - EFFLUENT
BW = BACKWASH
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G - GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn= MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. WHEN BACKWASHING
2. FOR CONTROL OF PROCESS
RECEIVING THIS FLOW
Figure 14-1
14-6
-------
Sampling Procedures
Samples should be collected from sampling taps in the influent and ef-
fluent lines for pressure filters and from the influent distribution trough
and backwash storage well in the case of gravity filters. The sample col-
lector and containers should be clean. A wide mouth sample collector of at
least 2 inches should be used. Samples collected in the effluent lines or
storage tank should be collected near the discharge point so that any isolated
areas of short circuiting do not influence the results. Where automatic
samplers are used, it is important to keep the sampler tubes clean.
Sidestrearns
The only sidestream associated with the filtration process is the waste-
water associated with backwashing or cleaning the filters. The volume of
water is normally in the range of 1 to 5 percent of the volume of water pass-
ing through the filter, and is most frequently found to be,about 2 to 3 per-
cent of the throughput volume.
The wastewater from backwashing the filters contains suspended solids in
the range of 100 to 1000 mg/1, with an average value of about 300 mg/1. The
water may be discharged to a settling tank where the settled solids are with-
drawn and pumped to the solids handling facility and the supernatant recycled
to the treatment plant. In many cases, the backwash water is all recycled to
the treatment plant at a controlled rate from a storage tank.
14-7
-------
Process Checklist - Filtration
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
What is flow through filters
mgd min?
Type of filters ( ) gravity
and capacity of each filter
mgd avg.
mgd max.
( ) pressure, number of units
What is type of filter media? ( ) sand ( ) dual media ( ) mixed
media ( ) multi-media ( ) diatomaceous earth ( ) other
What is surface loading rate? gpm/ft2
What is backwash rate? gpm/ft2
What is surface wash rate?
Type of control system? ( )
( ) turbidity of effluent
gpm/ft2 and pressure
constant flow ( ) headless
psi
( ) time
( ) total gallons filtered ( ) other
Are all automatic valves operating correctly? ( ) Yes ( ) No
Are the valves sequencing (opening and closing in order) correctly?
( ) Yes ( ) No
Is there a coagulant aid (filtration aid) system? ( ) Yes ( ) No
If yes, what type
Is the chemical aid system operating? (
If no, explain
) Yes ( ) No
What are the dimensions of the filter?
Operation of the system is? ( ) Automatic ( ) Manual
( ) semi-automatic ( ) Other ______
Are all pumps operating? ( ) Yes ( ) No. If no, what is the
problem? ;
Does the mechanical equipment have an adequate spare parts inventory?
( ) Yes ( ) No
Is the filter building adequately ventilated? ( ) Yes ( ) No
How often are facilities checked? ( ) Once per shift ( ) Daily
( ) Other
What is frequency of scheduled maintenance?
Is the maintenance program adequate? ( ) Yes ( ) No
If no, what is problem _____________
What is the general condition of the filtration process? ( ) good
( )fair ( ) poor
What are the most common problems the operator has had with the filtration
systems?
14-8
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
7. Gulp, Gordon L., and Gulp, Russell L., New Concepts in Water Purification,
Van Nostrand Reinhold, 1974.
8. Gulp, Russell L., Wesner, G. M., and Gulp, Gordon L., Handbook of Advanced
Wastewater Treatment,-Van Nostrand Reinhold, 1978.
14-9
-------
-------
15. MICROSCREENING
Process Description
A microscreen is a mechanical filter, process used to remove suspended
solids from secondary effluent. The equipment consists of cylindrical drums
horizontally mounted in a two-compartment concrete tank. Each drum is covered
with a woven fabric which serves to trap the solids as the wastewater flows
through it. The drum is usually submerged about two-thirds underwater, with
solids being retained on the inside surface as it slowly rotates. The screen
is equipped with a backwashing unit to remove the accumulated solids. Wash-
water is collected in a hopper or trough mounted inside the screen and is re-
cycled to another process. The water used for backwashing is recycled
screened effluent, constituting about 3 to 5 percent of the total screened
flow.
Table 15-1 shows typical values for microscreen and backwash design para-
meters for solids removal from secondary effluents. Similar values would
apply to direct microscreening of good quality effluent from trickling filters
or rotating biological contactors where the microscreens replace secondary
settling tanks.
Typical Performance Evaluation
Microscreens with 23-y apertures can be expected to remove 70 to 80 per-
cent of the suspended solids in activated sludge effluent and 60 to 70 percent
of the BOD. With a larger aperture (35 y) 50 to 60 percent of the suspended
solids and 40-50 percent of the BOD would be removed. Detailed performance
factors are given in Reference 1.
Process Control
Except for drum speed there is little the operator can control with the
microscreening process. If the drum travels too fast, it will not do an ef-
fective screening job and may cause excess wear on the mechanical parts. If
it runs too slowly, the fabric will become clogged and the head between the
influent and the effluent may become so great that the fabric breaks. A
clogged screen may cause the influent to bypass the microscreen.
Maintenance Considerations
The features of a good maintenance program that the inspector should look
for are:
1.
2.
3.
Tears in screen are repaired or replaced as soon as possible.
Backwash nozzles cleaned on a regular basis.
Drum is periodically cleaned of accumulated grease and oil and algae
or slime growths.
15-1
-------
TABLE 15-1. MICROSCREEN DESIGN PARAMETERS
Item
Typical Value
Remarks
Screen mesh
Submergence
Hydraulic
Loading
Headless (HL)
through screen
Peripheral
Drum Speed
Typical Diameter
of Drum
Backwash Flow
and Pressure
20-25 microns
75 percent of height
66 percent of area
5-10 gpm/sq ft
of submerged drum
square area
3-6 in.
Range 15-60 microns
15 fpm at 3 in.(HL)
125-150 fpm at
6 in. (HL)
10 ft
2 percent of throughput
at 50 psi
5 percent of throughput
at 15 psi
Maximum under extreme condition
12-18 in. Typical designs pro-
vide for overflow weirs to
bypass part of flow when head
exceeds 6-8 in.
Speed varied to control
extreme maximum speed
150 fpm.
Use of wider drums
increases backwash
requirements.
4. Spare parts inventory should contain the following: replacement mesh
for rotating drum, gears and motors for rotating drives, backwash
nozzles, etc.
Records
Recommended sampling and laboratory tests are shown on Figure 15-1.
Other operating records should include:
1. Backwash flow rate.
2. Percent of throughput used for backwash.
15-2
-------
a
z
3
0
UJ
>
UJ
o
o
-
Z 0
< 0
s! *
ALL
ALL
ALL
ALL
ALL
ALL
TEST 1
FREQUENCY |
R
1
1
R
2/W
2/W
LOCATION OF
SAMPLE
E
BW
BW
E
E
I
E
METHOD OF
SAMPLE
R
G
G
R
24C
24C
1 REASON
FOR TEST
P
P2
P
P2
H
H
ESTIMATED UN4T PROCESS SAMPLING AND
TESTING NEEDS
M1CROSCREEN1NG
BACKWASH -.RECYCLED
MICROSCREJEN EFFLUENT
BW
INFLUENT FROM
PREVIOUS MAIN
FLOW TREAT-
MENT PROCESS
^•BACKWASH WAST.E
RECYCLE TO PLANT
INFLUENT
E
EFFLUENT TO
NEXT MAIN FLOW
TREATMENT
PROCESS
A. TEST FREQUENCY
H » HOUR M — MONTH
0- DAY R - RECORD CONTINUOUSLY
W- WEEK Mn- MONITOR CONTINUOUSLY
B. LOCATION Of SAMPLE
I = INFLUENT
E- EFFLUENT
BW =BACKWASH
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G - GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn = MONITOR CONTINUOUSLY
0. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. WHEN BACKWASHING
2. FOR CONTROL OF PROCESS
RECEIVING THIS FLOW
Figure 15-1
15-3
-------
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor the microscreening.
1. Analytical balance
2. Clinical centrifuge with graduated tubes
3. BOD incubator
4. Drying oven
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be consulted for any detailed
questions.
Sampling Procedures
Samples should be collected at points where the wastewater is well mixed
such as at the center point of the channel of flow where velocities are high.
The sample collector and containers should be clean. A wide mouth sample col-
lector of at least 2 inches should be used. Samples collected in the effluent
channels should be collected near the discharge point to insure well mixed
specimens. Where automatic samplers are used, it is important to keep the
sampler tubes clean.
Sidestreams
The backwash from microscreening constitutes about 2 to 3 percent of the
through-put and has a suspended solids concentration of 700 to 1000 mg/1. It
is ordinarily returned to the headworks of the plant and does not present any
particular operating problems. Because there is a certain amount of grease
and oil mixed in this flow, keeping the return lines clear is important to
proper plant operations.
15-4
-------
Process Checklist - Microscreens
2.
3.
4.
5.
6.
7.
8.
9,
10.
11.
12.
13,
14.
15.
What is the volume of flow to the microscreens
•. mgd peak?.
_mgd average;
Type of filter fabric
Number of microscreens
operating loading rate
Backwash rate
; mesh aperture
capacity of each unit
. • gpm/ft2.
Frequency of backwashing
Location of backwash recycle .
Are all microscreen and. backwash units operating properly?
( ) Yes ( ) No .;,..,
Does filter mesh appear to be clogged in one particular spot?
( ) Yes( ) No. Are all backwash nozzles spraying properly?( ) Yes ( )No
Is backwash collection trough adequate to collect solids and backwash
flow ( ) Yes ( ) No. If not, would adjusting it's position result in •
proper collection. ( ) Yes ( ) No. Other • , . . • .
Does backwash water flow freely to recycle point? ( ) Yes
Does filter fabric show signs of wear? ( ) Yes ( ) No.
unrepaired tears in it? ( ) .Yes { ) No
Is there a accumulation of slime or algae on filter mesh?
Grease or oil? ( ) Yes ( ) No
If multiple units are used, is flow distributed evenly?
( ) Yes ( ) No
Is all mechanical equipment operating properly? ( ) Yes
How often is facility checked? ( ) Once per shift ( )
( ) Other
Frequency of maintenance inspections by plant personnel _
Is the maintenance program adequate? ( ) Yes ( ) No
If no, explain
( ) No
Are there
( ) Yes ( ) No
( ) No
Daily
/year.
16. Does the sampling program meet the recommendations? (
17. Are operating records adequate? ( ) Yes ( ) No
18. Is the laboratory equipped for the necessary analyses?
( ) Yes ( ) No
19. What is the general condition of the microscreening facilities?
( ) Good ( ) Fair ( ) Poor
20. What spare parts are stocked?
) Yes ( ) No
21. What are the most common problems the operator has had with the filtration
systems?
15-5
-------
References
1. Gulp/ G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. CH2M-H111, Estimating Laboratory Heeds for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
3. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
4. State of Virginia O&M inspection form.
5. Hazen and Sourfer Inc., Process Design for Suspended Solids Removal, EPA
Technology Transfer (January 1975).
6. Gulp, Russell L., Wesner, G. M., and Gulp, Gordon L., Handbook of Advanced
Wastewater Treatment, Van Nostrand Reinhold, 1978.
15-6
-------
16. ACTIVATED CARBON ADSORPTION
Process Description
The activated carbon adsorption process is used to reduce the concentra-
tion of the soluble or dissolved organic matter in the wastewater. This
process is normally used in one of two treatment schemes: (1) As an advanced
wastewater treatment (AWT) process following a conventional biological treat-
ment system; or (2) in conjunction with independent physical-chemical (IPC)
treatment processes.
When used as an AWT process, the activated carbon process follows biologi-
cal treatment, or sometimes chemical coagulation and sedimentation. Filtra-
tion normally precedes the activated carbon process to protect the system from
fouling with suspended matter in the water. Biological systems can remove the
majority of organic materials, but not the more complex soluble organic mate-
rial. These organics can be removed by the activated carbon.
When the activated carbon adsorption process is used as an IPC process, it
provides the only method for organic removal. In an IPC treatment system, the
raw wastewater undergoes preliminary treatment, chemical coagulation and clar-
ification, and filtration before carbon treatment. This treatment scheme
removes a greater percentage of organics than biological secondary treatment
alone, but not as much as when used as an AWT process.
Wastewater treatment with activated carbon involves two process opera-
tions, a contact system, and a carbon regeneration system. Th« water passes
through a container filled with carbon granules or a carbon slurry. Organic
impurities are removed from the water by adsorption onto the carbon. The con-
tactors are either open concrete gravity-type systems, or steel pressure con-
tainers suitable for either upflow or downflow operation. Upflow operation
occurs when the water enters the bottom of the pressure contactor and flows
upwards through the carbon to exit at the top. Downflow is sinply the reverse
operation.
After the water has passed through the carbon beds for a period of time,
it loses its capacity to adsorb the organics and must then be regenerated.
The regeneration system is a furnace in which the carbon is placed and
heated. The regeneration process is described in detail in Section 40 of this
manual. The heat drives off the organic material that was adsorbed onto the
carbon, and "reactivates" the carbon for continued use in the treatment sys-
tem. About 5 to 10 percent of the carbon is lost during regeneration and must
be replaced with new, fresh carbon.
The activated carbon that is used for wastewater treatment is either gran-
ular or powdered.
Typical Design Considerations
Activated carbon adsorption systems are chosen based on their location in
an overall treatment system and on the estimated organic removal efficiency
16-1
-------
that is required. The type of carbon system used depends on the other treat-
ment processes and the topography of the plant site.
Sizing of the unit is based on four factors: the contact time, the hydrau-
lic loading rate, the carbon depth, and the number of contactors. Typical
contact times range from 15 to 40 min, depending on the strength of the waste-
water and the required effluent quality, and are normally selected after pilot
plant testing.
*
Hydraulic loading rates vary from 3 to 12 gpm/ft2 of cross-sectional
carbon area for upflow contactors and from 2 to 5 gpm/ft^ for downflow con-
tactors. The upflow contactors must also include an allowance for the carbon
bed expansion during operation. Typical expansion percentages for upflow
contactors are given in Figure 16-1.
The depth of the carbon contactors ranges from 10 to 30 feet. The bed
depth is normally determined from the surface area and the contact time.
The number of contactors depends on the treatment processes preceding
them. The system must produce the required effluent quality with one unit out
of operation. There should always be a minimum of two contactors.
Typical Performance Evaluation
Activated carbon contactors can' be evaluated by using plant operational
data and contactor characteristics. The following is an example of the step-
by-step procedures for evaluating the performance of an activated carbon
adsorption system:
1. Define the dimensions and design data for the carbon system.
Upflow Contactor
Pretreatment: Filtered Secondary Effluent
Column Flow Hate =» 650 gpm
. Column Diameter, D » 12 ft
Column Area, A - (Tr/^D2 - 113 sq ft
Carbon Depth - 26 ft 2 in. (312 in.)
Carbon Volume, V-A x Depth = 22,140 gal
2. Determine the contact time of the carbon column.
Contact time (min)
Volume occupied by carbon in gal
Flow rate in gpm
22,140
650
34 min
16-2
-------
80,
70
SO
1
'S
#
X
Ul
10
15
20
25
FLOW RATE, gpm/sq ft
CARBON: 12 x 40, 8 x 30
LIQUID: WATER AT 22° C
Figure l&r-l. Expansion of carbon bed at various flow rates.
16-3
-------
3. Determine the hydraulic loading rate.
Hydraulic loading rate = Flow rate in gpm
Surface area of column
- 650
113
= 5.75 gpm/sq ft
Numerous tests have shown that the efficiency of the carbon is not
affected by hydraulic loading rate (at a given contact time) for
rates in the range of 2 to 8 gpm/sq ft.
The container should be checked to see if it is large enough for the car-
bon expansion. From Figure 16-1, the expansion would be about 3% of the bed
depth.
Bed expansion
3 3 x 312 in.
100
= 10 x 312 in.
100
9.4 in. for 8 x 30 mesh
31 in. for 12 x 40 mesh
If the bed is constrained from expanding, suspended matter could be
trapped in the bed and the effectiveness of the filter will be
reduced.
Review available effluent quality data and, if needed, collect
samples from the carbon column influent and effluent, and analyze the
samples for the following:
TOG,
Soluble Organic Carbon
SS
BOD
COD
Color
Turbidity
The results should be compared to those shown in the following table.
Filtered Secondary
Description
TOC Removed, percent
Soluble Organic Carbon
Removal, %
Unfiltered Secondary
Effluent •
45 - 55
40 - 45
Effluent
50 - 60
45 - 50
Review the carbon dosage and carbon losses to see if the fall within
typical design ranges. The importance of carbon dosage is described
in the section on carbon regeneration (Section 40) and is not dis-
cussed here.
16-4
-------
Process Control
The major control variations relate to the rate of flow through the con-
tactors, the contact time, and the number of contactors in operation. These
are interrelated, because adjustment of one of these control options changes
the other two. It is important to avoid excessive contact times to prevent
excessive biological growth which fouls the bed and results in a strong odor.
This often occurs at the startup of a new plant when the flows are low. Main-
taining the contact time and rate of flow through the bed within the typical
ranges should result in efficient operation of the system.
The carbon dosage can be adjusted either upwards or downwards to optimize
treatment efficiency- The upper limit is governed by the capacity of the re-
generation system. If lower carbon doses can be used to achieve the desired
effluent quality, the operating costs for regeneration will be less.
The rate of adsorption of organics found in municipal wastewater usually
increases as the pH of the water decreases. Adsorption is very poor at pH
values above 9.0. High pH wastewaters should be neutralized before carbon
adsorption, and the influent pH should be kept fairly constant. A sudden,
upward shift in pH can lead to desorption of organics and an increase in ef-
fluent COD.
Treating water that has high turbidity will plug carbon pores and result
in the loss of carbon capacity. Thus, special attention should be given to
the control of processes upstream of the carbon columns. The adsorptive ca-
pacity and service life of the carbon can be maximized by applying to the car-
bon water that has been carefully pretreated to the highest practical clarity.
Maintenance Considerations
Proper maintenance of a facility is an important function to insuring ef-
ficient, troublefree operation. The features of a good maintenance program
are listed below. These considerations are to be used in conjunction with
general maintenance management discussed earlier.
1. Spare parts inventory should include at least one set of each type of
bearing, grease and water seals, all necessary gaskets.for replace-
ment of parts, influent and effluent strainers or underdrain systems.
2. Visual inspection each shift of the activated carbon process equip-
ment to check the equipment for misalignment, excessive noise, un-
equal loading of the contactors, excessive pressures in pressure con-
tactors.
3. Pressurized containers checked regularly to insure their integrity
against failure.
4. All non-operating equipment, such as by-pass valves, being operated
every month to test for operability.
16-5
-------
5. Saiqple lines flushed regularly to flush out material, such as carbon
fines, that may have entered the lines.
Records
«, The.recommended sampling and laboratory tests are shown in Figure 16-2 for
the activated carbon adsorption system.
Other operating records should include the following:
1. Influent flow rate
2. Carbon dosage in Ibs per million gallons.
3. The amount of COD removed per pound of carbon
4. The contact time
5. Frequency of backwashing, if also used as a filter
Laboratory Equipment
mnnir . in°lude the followin9 "«inimum equipment in order to
monitor the activated carbon adsorption system.
1. Reflux apparatus to perform COD tests
2. Colorimeter
3. Turbidimeter
TreaSenf MiS "I8""*"1* ^oratory Needs for Municipal Wastewater
uties" contains very detailed information on glassware, chemi-
furniture- etc-' and shouid b
Sampling Procedures
C0llected fr°ffl *»* influent and effluent channels of
ha tein "p"*11 aS *" Clear "•"• °r effluent channe1' w
has the combined flows. For pressure contactors, the samples are taken
'
ai cm
line. The sample container should be clean to avoid bad results if
ildof^f111 " Td' the lineS Sh°Uld be flushed regularly to avoid
build-up of solids or other deposits.
Sidestreams
h«n f 6 normallv "° »»*« sidestreams associated with an activated car-
bon contacb system. However, when the system also acts as a filter, t^ere
"^ ^^^^ with <*e backwashing cycle as described for the
Process. When the carbon has not been washed well, carbon fines
Can be f°Und in the eff luent- C"^ ^nes in the ef-
erroneous ^emical oxygen demand tests as well as greater
co"centrati0^ and higher turbidities. To avoid these prob-
Carb°n SyStemS are often Provided with the necessary piping to
fi°W thr°Ugh the C0lumns b* returning it to the the p?ant
Sldestreams "e very small and do not^dd a significant Joad
16-6
-------
s
o
a
o
COD
PH
MBAS
Ul
N
o
t-
z 5
n
ALL
ALL
AT,T.
TEST
FREQUENCY
3/W
Mn
V"
LOCATION OF
SAMPLE
I
E
I
I
J?
METHOD OF
SAMPLE
24C
Mn
?-W
REASON
FOR TEST
£
H
P
._P_
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
ACTIVATED CARBON ADSORPTION
'ACTIVATED
CARBON IN
/
f^"1 ™^>v
C, EFFLUENT TO
NEXT MAIN FLOW
TREATMENT PROCESS
V-
- SPENT CARBON TO
REGENERATION OR
FINAL DISPOSAL
INFLUENT FROM
PREVIOUS MAIN
FLOW TREATMENT
PROCESS
A. TEST FREQUENCY
H . HOUR M - MONTH
D - DAY R - RECORD CONTINUOUSLY
w- WEEK MK- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I « INFLUENT
E- EFFLUENT
C. METHOD OF SAMPLE
24C»24 HOUR COMPOSITE
G - GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P » PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. PROCESS CONTROL ON EFFLUENT
2. PROCESS CONTROL FOR SYSTEM
EQUIPMENT FOR pH ADJUSTMENT
Figure 16-2
16-7
-------
Process Checklist - Activated Carbon Adsorption
1. What is actual plant flow? mgd avg.
2. What is total flow through the carbon system?_
3. How many contactors?
4
6
7
8
9
10
mgd.
What is flow through each contactor
mgd mgd
mgd
mgd
gravity (
) series
What type of carbon system? (
( ) downflow ( ) parallel
( ) Other
What are contactor dimensions?
What is the COO removal per Ib of carbon?
What is the Ibs carbon used per million gallons?
What is contact time? min
) pressure ( ) Upflow
Ibs/lb
Ibs/MG
Does the system have pH adjustment as part of the carbon process?
( ) Yes ( ) No. If yes, what type and dose?
11. Is the flow measured through each contactor? ( ) Yes ( ) No
12. For pressure systems, are the influent pumps operating properly?
( ) Yes ( ) No. If no, what is problem?
13. If have pumps in the system, are they operating? ( } Yes ( ) No
If no, what is problem?
What are the
pumps used for?
14. Do mechanical equipment have adequate spare parts inventory? { ) Yes
( ) No. If no, what is problem?
15. Is the carbon building adequately ventilated? ( ) Yes ( ) No
16. How often are the facilities checked? ( ) once per shift ( ) daily
( ) other
17. What is frequency of scheduled maintenace?
18.
25.
20,
Is the maintenance program adequate?(
explain
) Yes ( ) No. If no,
What is the general condition of the carbon system? ( ) good
( ) fair ( ) poor
What are the most common problems the operator has had with the activated
carbon system?
16-8
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants/ Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
0
7. Gulp, Gordon L., and Gulp, Russell L., New Concepts in Water Purification,
Van Nostrand Reinhold, 1974. r
8. Gulp, Russell L., Wesner, G. M., and Gulp, Gordon L., Handbook of Advanced
Wastewater Treatment, Van Nostrand Reinhold, 1978.
9. CH2M-Hill, Process Design Manual for Carbon Adsorption, USEPA, Technology
Transfer, April 1976.
10. Shuckrow, A.M. and Gulp, G.L., "Appraisal of Powdered Activated Carbon
Processes for Municipal Wastewater Treatment," USEPA Report EPA-600/
2-77-156, September 1977.
16-9
-------
-------
17. NITRIFICATION
Process Description
Nitrification is a biological process in which specific organisms convert
ammonia-nitrogen (NH3-N) to nitrate-nitrogen (NO§-N). Nitrification
can be accomplished by a two-stage process with separate oxidation of carbon-
aceous material (BOD) and nitrogen or single-stage schemes in which both BOD
and NH3-N are removed in the same basin. All nitrification systems are
sensitive to low temperatures.
Extended aeration activated sludge systems have long aeration times (24
hours) and high solids retention times (20 to 30 days). This process is good
for maintaining a large population of nitrifying bacteria in a single treat-
ment unit.
Attached growth biological treatment systems, when properly designed and
operated can also produce nitrified effluent. A single-stage trickling filter
system designed for a very low organic loading in a warm climate can produce
nitrified effluent. Synthetic media has been found more effective than rock .
media because it provides a greater, more uniform surface area. In two-stage
trickling filter systems, the first filter is designed as a roughing filter to
remove BOD and the second is designed for nitrification. In this case, the
contact time (wetting rate) rather than the organic loading determines process
performance. Trickling filters can also be used in a two-stage system follow-
ing secondary treatment by activated sludge. The influent to the filter must
have a low BOD concentration (less than 20 rag/1) to provide effective
nitrification.
The ABP system can be designed to provide almost complete nitrification.
The tower or bio-cell is designed for BOD removal and the aeration basin for
additional BOD removal and complete ammonia conversion.
Rotating biological contactors (RBC's) are an effective means of single or
two-stage nitrification. The first series of discs in the system provides BOD
removal, while the downstream units provide nitrification.
The reader should refer to Reference 1 and other sections of this manual
to obtain more specific process information.
Typical Design Considerations
The basic design procedures for nitrification follow the same steps as for
conventional secondary treatment, but the criteria for process sizing and the
selection of equipment are different. Table 17-1 summarizes the basic design
criteria for suspended growth systems. The oxygen requirement for nitrifica-
tion is about 4.6 Ib 02/lb NH3 removed; this amount must be supplied over
and above the carbonaceous oxygen demand of about 1.4 Ib O2/lb BOD removed.
If the dissolved oxygen (DO) drops below 1 mg/1, nitrification will be re-
duced. In the activated sludge process, the degree of nitrification depends
on the sludge retention time (SRT). Nitrification normally requires an SRT of
about 10-12 days.
17-1
-------
TABLE 17-1. DESIGN PARAMETERS FOR TYPICAL
SUSPENDED GROWTH NITRIFICATION SYSTEMS
Single-stage Nitrification
Loading
F/M
SRT
Aeration time
Solids recirculation
MLSS
Ib BOD /1000 cu ft/day
Ib BODV1000 ib MLSS/day
days
hrs
%Q
mg/1
10-30
0.05-0.15
10-15
6-12
30-100
3000-6000
Extended Aeration
Loading
F/M
SRT
Aeration time
Solids recirculation
MLSS
Ib BOD /1000 cu ft/day
Ib BODg/1000 Ib MLSS/day
days
hrs
%Q
mg/1
10-15
, <0.05
> 30
16-24
100-300
2000-6000
Two-Stage Nitrification
Carbonaceous removal by high-rate activated sludge
Loading
F/M
SRT
Aeration time
Solids recirculation
MLSS
Ib BOD /1000 cu ft/day
Ib BODVlb MLSS/day
days
hrs
%Q
mg/1
Nitrogen removal by conventional plug-flow, aeration
Loading
SRT
Aeration time
Solids recirculation
MLSS
Ib NH3-N/1000 cu ft/day
days
hrs
%Q
mg/1
70-180
0.4-1.0
2-4
2-4
30-100
3000-5000
10-20
10-20
3
30-100
1000-2000
17-2
-------
Nitrification will generally not occur in trickling filters loaded at
greater than 12 Ib BOD/1000 cu ft/day. For good nitrification to occur the
loading should be less than 5 Ib BOD/1000 cu ft/day. As indicated previously
in Table 17-1, this value is the minimum loading for a low rate filter.
Plants which include recirculation generally produce a greater degree of nit-
rification. Synthetic media trickling filters tend to be more effective for
nitrification since they have a greater specific surface area on which nitri-
fying organism can grow. For two-stage trickling filters, nitrification is
limited by the contact time. Typical values for a 21.5-foot deep synthetic
media filter are given in Table 17-2.
*
TABLE 17-2. HYDRAULIC LOADING FOR TWO-STAGE NITRIFYING TRICKLING FILTER
Nitrification
performance, ?
Wetting Rate, gpm/sg ft
18°C 7°C
90
85
80
75
0.5
0.75
1.0
1.5
0.50
0.65
0.75
0.85
The design criteria for the biofilter is the same as that for the standard
ABF system; it is designed to remove only BOD and not ammonia from the waste-
water. Nitrification as well as additional BOD removal occurs in the aeration
basin. The design parameters for ABF nitrification are summarized in Table
17-3. The aeration detention time is about four times that for regular oxida-
tion and the organic loading about one-third.
The design relationship for single-stage nitrifying RBC's is given on Fig-
ure 17-1. The hydraulic loadings for various influent BOD and ammonia concen-
trations are presented. When used following secondary treatment, RBC's should
be designed according to the relationship given on Figure 17-2. The basic
curves are for a four-stage system achieving 90 to 95 percent nitrification.
Typical Performance Evaluation
Virtually any level of nitrification can be achieved with any of the proc-
esses described herein if the design parameters are selected according to the
treatment conditions. The most common cause of systems not meeting design
standards are cold weather and peak flows. These factors should be considered
when evaluating processes.
17-3
-------
TABLE 17-3.
GENERAL DESIGN PARAMETERS FOR NITRIFICATION OF
DOMESTIC WASTEWATER WITH ABF PROCESS
Parameter
Units
Typical
value
Range
Effluent criteria
5-day BOD
Suspended solids
NH3-N
Bio-cell parameters
Organic load
Media depth
BOD5 removal
Hydraulic parameters
Bio-cell recycle
Sludge recycle
Bio-cell flow
Bio-cell hydraulic
load
Aeration parameters**
Detention time*
Organic load
Ammonia load
F/M
MLVSS concentration
MLSS concentration
Carbonaceous oxygen***
Sludge production
rag/1
rag/1
rag/1
Ib BOD5/day/1000 cu ft
ft
gpra/sq ft
hr
Ib BOD5/day/1000 cu ft
Ib NH3-N/day/1000 cu ft
Ib BOD5/day/lb MLVSS
mg/1
rag/1
Ib 02/lb BOD5
Ib VS/lb BOD5 removed .
15
20
1.0
200
14
65
1.5 Q
0.5 Q
3.0 Q
3.5
3.5
25
10
0.13
3000
4000
1.4
0.45
5-30
15-30
0.5-2.5
100-350
5-22
55-85
0.5-2.0 Q
0.3-1.0 Q
2.3-4.0 Q
1.5-5.5
2.5-5.0
20-40
5.0-15.0
0.1-0.2
1500-4000
2000-5000
1.2-1.5
0.30-0.55
* Based on design average flow and secondary influent BOD5 = 150 mg/1.
** Based on aeration BOD5 loading after bio-cell removal.
*** Total oxygen utilization » carbonaceous oxygen + 4.6 Ib 02/lb NH3-N
oxidized.
17-4
-------
100
i
§
ui
x
UJ
o
o
a
<
§
90
83
80
75
70
•2501-150
r120-100-T80
INLET BO05 CONCENTRATION,
mg/l
MAXIMUM AMMONIA
NITROGEN CONCENTRA-
TION, mg/l
gpd/tq
REGION OF
UNSTABLE
NITRIFICATION
/m2/day)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
HYDRAULIC LOADING, gpd/*q ft
TEMPERATURE > 13* C
Figure 17-1. Effect of BOD concentration and hydraulic load
on nitrification in the RBC process.
17-5
-------
c
i
Ul
a
i
§
100.
95
90
85
80
75
70
85
INLET AMMONIA NITROGEN
CONCENTRATION, mg/1
1 gpd/sq It =* 41
HYDRAULIC LOADING, gpd/sq ft
RELATIVE CAPACITIES
FOR STAGED OPERATION
(80-S5S Nitrification)
No. Stage* Relative Capacity
1 0.60
2 0.80
3 0.90
4 1.00
6 1.07
Condition*
Temperature >
13* C
BODg < 20 mg/l
Figure 17-2.
Design relationships for a 4-stage RBC process
treating secondary effluent.
17-6
-------
Process Control
Because nitrifying bacteria are slow-growing and sensitive to environmen-
tal conditions, close process monitoring and specific control features must be
followed. Loss of nitrifying bacteria can mean inadequate treatment for many
months while they re-establish themselves. There are several key factors in-
fluencing the nitrification process.
The concentration of dissolved oxygen (DO) has a significant effect on the
rate of nitrification in biological wastewater treatment systems. Although
nitrification can be achieved at DO levels of 0.5 rag/1, it is at a very low
rate. The DO of the wastewater should be kept at 1 to 3 mg/1 for consistent
nitrification. Air can be supplied by additional aeration of suspended growth
systems and by increased ventilation of attached growth units.
Certain heavy metals, complex anions, and organic compounds which are
toxic to nitzifiers are listed in Table 17-4. The amounts of these substances
necessary to effect nitrifiers depend on the overall environment of a partic-
ular system. A good source control program should be established to prevent
harmful concentrations of toxic materials from entering the treatment stream.
TABLE 17-4. SUBSTANCES TOXIC TO NITRIFYING ORGANISMS
Organics
Inorganics
Thiourea
Ally1-thiourea
8-hydroxyquinoline
Salicyladoxine
Histidine
Amino acids
Mercaptobenzth iazole
Perchloroethylene
Tr ich lor oe thy lene
Abietec acid
Zn
octr1
CIO"1
Cu
Hg
Cr
Ni
Maintenance Considerations
Maintenance considerations for the specific facility used apply here also.
Records
Recommended sampling and laboratory tests are shown in Figure 17-3 through
17-6, depending on the basic process being examined.
17-7
-------
o
a
O
'
BOD
SUSPENDED
SOLIDS
SETTLEABILITY
pH
DO
MR INPUT1
ra3-N
3RG-N
I03-N
PLOW
HCROSOPie
ANALYSIS
XWAL SOLIDS
TOTAL
VOLATILE
SOLIDS
COD
1U
N
7
!!
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ILL
>1
>1
>5
EST
:REQUENCY
2/W
5/W
5/W
5/W
5/W
R
L/D
L/D
L/D
R
/W
3/W
£/W
2/W
.OCATION OF
AMPLE
I
E
E
P
P
B
J»
£
J»
RS
>
E
I
METHOD OF
AMPLE
24C
24C
G
G
G
R
24C
24C
24C
R
G
24C
24C
24C
i-
z£
S"
< a
UJ O
P
p
P
P
P
H
P
H
H
P
H
H
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
NITRIFICATION
2 - STAGE ACTIVATED SLUDGE
OXIDATION
NITRIFICATION
1 - STAGE ACTIVATED SLUDGE
OXIDATION-NITRIFICATION
1
'2
INFLUENT FROM PREVIOUS MAIN FLOW TltCATMENT PROCESS
EFFLUENT FROM 1ST STAGE
E = EFFLUENT TO DOWNSTREAM PROCESS
RS= RECYCLE SLUDGE
A. TEST FREQUENCY
H m HOUR M - MONTH
D-DAY R . RECORD CONTINUOUSLY
W- WEEK MK- MONITOR CONTINUOUSLY
B. LOCATION OP SAMPLE
I - INFLUENT
E » EFFLUENT
RS= RECYCLE SLUDGE
B = BLOWER
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G - GRAB SAMPLE
R - RECORD CONTINUOUSLY
MB- MONITOR CONTINUOUSLY
D« REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C • COST CONTROL
E. FOOTNOTES:
1. DIFFUSED AIR ONLY
i MAYBE RUN ON PLANT INFLUENT IF THIS
IS INITIAL UNIT PROCESS FOLLOWING
PRETREATMENT
Figure 17-3
17-8
-------
a.
o
BOD
NH,-N
ORG-N
NO~-N
W
DO
COD
PLANT SIZE 1
(MOD) 1
ALL
ALL
ALL
ALL
ALL
>5
TEST
FREQUENCY |
2/W
1/D
1/D
1/D
5/W
2/W
LOCATION OF
SAMPLE |
I
I
B
I
E
I
E
I
E
I
METHOD OF
SAMPLE
24C
24C
24C
24C
6
24C
zS
< a
Ul O
a: u.
P
P
H
H
P
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
NITRIFICATION
OXIDATION
NITRIF.
2 . STAGE TRICKLING FILTER
f1 \
h ... T
OXIDATION -
NITRIFICATION
^
^ \
J
1 M
EFFLUENT TO
SECONDARY
SEDIMENTATION
k INFLUENT FROM
PREVIOUS MAIN
FLOW PROCESS
1 - STAGE TRICKLING FILTER
A. TEST FREQUENCY
H m HOUR M - MONTH
D - DAY R - RECORD CONTINUOUSLY
W- WEEK Mn" MONITOR CONTINUOUSLY
B. LOCATION OP SAMPLE
I m INFLUENT
6 - EFFLUENT
C. METHOD OP SAMPLE
24C-24 HOUR COMPOSITE
G * GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn« MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
Figure 17-4
17-9
-------
a
o
UJ
i
a
a
o
BOD
DO
NH..-N
ORG-N
NO,-N
•
COD
PLANT SIZE 1
(MCD)
ALL
ALL
ALL
ALL
ALL
>5
TEST
FREQUENCY
2/W
5/W
1/D
1/D
1/D
/w
LOCATION OF
SAMPLE
I
I
E
I
E
I
E
I
E
I
METHOD OF
SAMPLE
24C
G
24C
24C
24C
24C
s^
2>-
< oc
UJ O
a: u.
H
H
P
H
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
NITRIFICATION
ROTATING BIOLOGICAL CONTACTOR
*• INFLUENT FROM
PREVIOUS MAIN
FLOW TREATMENT
PROCESS
EFFLUENT TO
SECONDARY
CLARIFIER
A. TEST FREQUENCY
H . HOUR M - MONTH
0 - DAY R • RECORD CONTINUOUSLY
W- WEEKS Mn- MONITOR CONTINUOUSLY
8. LOCATION OF SAMPLE
I - INFLUENT
E=• EFFLUENT
C. METHOD OP SAMPLE
24C-24 HOUR COMPOSITE
G- GRAB SAMPLE
H - RECORD CONTINUOUSLY
Mn« MONITOR CONTINUOUSLY
0. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. THESE TESTS SHOULD ALSO BE RUN ON RECEIVING
WATER, ABOVE AND BELOW OUTFALL, ON A
PERIODIC BASIS, DEPENDING ON LOCAL CONDITIONS.
3. FOR PLANTS DESIGNED TO CONTROL THIS
PARAMETER.
Figure 17-5
17-10
-------
Q
U
I
a
o
BOO
SUSPENDED
SOLIDS
SETTLEABILITY
pH
DO
PLOW
NH,-N
ORG-N
COD
TOTAL SOLIDS
TOTAL VOLATILI
SOLIDS
MICROSCOPIC
ANALYSES
PLANT SIZE
(MGO) |
ALL
ATiTi
ALL
ALL
ATTi
ALL
ALL
ALL
>5
>1
>1
ALL
TEST
FREQUENCY |
2/W
•i/W
5/W
5/W
VW
R
1/D
1/D
2/W
3/W
J/W
>/w
LOCATION OF
SAMPLE
xl
In
K
z
En
?
s»
Ilsj,
R,,*
^
^
^
E
E
*
METHOD OF
SAMPLE
24C
24n
G
G
G
R
24C
24C
24C
24C
24C
G
REASON
FOR TEST
P
J?
P
P
P ,„
P
P
H
H
H
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
NITRIFICATION
ACTIVATED BIOFILTER PROCESS
R2_
INFLUENT PROM
PREVIOUS MAIN
FLOW TREATMENT <
PROCESS— j
'' / 1—
j-L»n
I
BIO-CELL
1 + . 1
| ^ .,_., L.,^. 1 > | ^
ft! ' (<- EFFLUENT TO
~^ Ri 12 1 SECONDARY
- -WET WELL 8. AERATION BAS.N
P,, ,
PUMP STATION
RECYCLED SLUDGE
A. TEST FREQUENCY
H a HOUR M - MONTH
D- DAY R - RECORD CONTINUOUSLY
W- WEEK Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
'l « INFLUENT TO WETWELL
I2 = INFLUENT TO AERATION BASIN
E = EFFLUENT FROM AERATION BASIN
RS = RECYCLED SLUDGE
R! = BIO-CELL RECYCLE R2 = BIO-CELL RECIRCULATION
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G - GRAB SAMPLE
R " RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
Figure 17-6
17-11
-------
Other operating records should include:
1. Raw sewage influent flow.
2. Total electrical energy consumed.
3. Recirculation flows - liquid and solids.
4. MLSS and MLVSS in any aeration basins and return sludge lines.
5. The unit volume of air supplied per Ib BOD and ammonia removed by any
aeration equipment.
6. Quantity and location of lime or caustic added to buffer wastewater.
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor the activated sludge process.
1. Analytical balance
2. Clinical centrifuge with graduated tubes
3. BOD incubator
4. Drying oven
5. Oxygen analyzer or titration equipment
6. Wet chemistry equipment for monitoring ammonia conversion
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any
detailed questions.
Sampling Procedures
Samples should be collected at points in the process where the wastewater
is well mixed and homogeneous. The sample collector and containers should be
clean. A wide mouth sample collector of at least 2 inches should be used.
Samples collected in the effluent channel should be collected near the dis-
charge point so that any isolated (area's of short circuiting do not influence
the results. Where automatic samplers are used, it is important to keep the
sampler tubes clean.
Sidestreams
The sidestreams associated with nitrification are the same as those
associated with carbonaceous oxidation. There is little wasting of solids
from the nitrification step of two-stage processes and reduced wasting from
single-stage process. Refer to the secondary sedimentation section for addit-
ional information on sidestreams.
17-12
-------
Process Checklist - Suspended Growth Nitrification
. 1. What is the actual plant flow?
mgd, peak.
2. How many stages does the nitrification system have?
mgd, average;
type of aeration system (flow regime) does each have?
What
3. What type of aeration equipment does each have?
Number of units
4. What are the aeration basin(s) dimensions?
Capacity of each unit
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17,
18,
19.
20.
21.
Color ( ) Black
Other
heavy white
{ ) Black
Basin characteristics - Carbonaceous oxidations
( ) Dark Brown ( ) Light Brown ( ) Other
Odor ( ). Septic ( ) Earthy ( ) None ( )"
Foam ( ) Light, crisp ( ) Dark, thick ( )
{ ) Other
Basin characteristics - Nitrification:Color
( ) Dark Brown ( ) Light Brown ( ) Other
Odor ( ) Septic ( ) Earthy ( ) None ( )
Foam ( ) Light, crisp ( ) Dark, thick ( )
( ) Other
Are tank(s) contents mixed thoroughly? ( ) Yes ( ) No
Are all diffusers or mech. aerators operating properly? ( ) Yes ( )No
Does mixing appear excessive? ( ) Yes ( ) No
Do there appear to be dead spots in tank(s) ( ) Yes ( ) No
If yes, at what location?
Other
heavy white
Is the process operating in its design mode?
no, explain
( ) Yes ( ) No If
Are HAS pumps operating?
reason?
( ) Yes { ) No. if no, what is the
Are there flow measurement devices for the RAS and WAS systems
( ) Yes ( ) No. Are they operable? ( ) Yes ( ) No
Does the aeration basin(s) have a foam control system? ( ) Yes
Is it operable? ( ) Yes ( ) No. Is it operating?
Yes
If multiple basins for each step are operating, is the flow distributed
equally? ( ) Yes ( ) No How is it distributed
Are the characteristics of the basin contents for each step different?
( ) Yes ( ) No. If yes, describe
No
No
( ) Yes
Is there an alkaline buffer added?
it? • . Dose
Is operation of the system ( ) Manual ( )
( ) Automatic ( ) Computer controlled (
Is there an adequate spare parts inventory? (
it contain?
) No. If yes, what is
Semi-Automatic
) Other
) Yes( ) No. What does
Is the pump station housing adequately ventilated? ( ) Yes
How often are facilities checked? ( ) Once per shift ( )
{ ) Other
( ) No
Daily
22. What is frequency of scheduled maintenance?
17-13
-------
23. Is the maintenance program adequate? {
If no, explain
) Yes
( ) No
24. What is general condition of the nitrification facilities?
( ) good ( ) fair ( ) poor
25. What are the most common problems the operator has had with the nitrifica-
tion system? ^
Process Checklist - Nitrifying Trickling Filters
1. What is actual plant flow?_
2. How many stages?
mgd, average;
jngd, peak
4.
5.
What is recycle flow to each -stage?
intermittent?
What type of media is used?
What is the depth of media?
Is it
constant,
6. Number of units in each stage
feet
; Size of units
10.
11.
12.
13
Characteristics of Oxidation Tower:
Color ( ) Black ( ) Dark Brown ( ) Light Brown ( )
Odor ( ) Septic ( ) Earthy ( ) None ( ) Other
Characteristics of Nitrification Tower:
Color ( ) Black ( ) Dark Brown ( ) Light Brown ( )
Odor ( ) Septic ( ) Earthy ( ) None ( ) Other
Other
Other
Is there evidence of uneven flow distribution in each stage? ( ) Yes
( ) No. Are any nozzles clogged? ( ) Yes ( ) No
Is there evidence of filter clogging such as ponding? ( ) Yes
( ) No. Icing? ( ) Yes ( ) No Other
Is there evidence of filter flies? ( ) Yes ( . ) No. Snails
( ) Yes ( ) No. Roaches (. ) Yes ( ) No. Other
Is there grass or other vegetative material growing on the filter?
( ) Yes ( ) No Other .
Are there flow measurement devices for the recirculation flow?
( ) Yes ( ) No. Are they operable? ( ) Yes ( ) No
14. Are the recirculation pumps operating? ( ) Yes ( ) No. If no,
why? ;
15. If multiple filters are operating for each stage, is the flow distributed
equally?( ) Yes ( ) No How is it distributed?
16. Are the characteristics of the filter contents different in the various
units of each stage? ( ) Yes ( ) No. If yes, describe ,
17. Is operation of the system ( )• manual ( ) semi-automatic
( ) automatic ( ) computer controlled ( ) other
18. Is there an alkaline buffer added? ( } Yes ( ) No. If yes, what is
it? . Dose
17-14
-------
19. Does mechanical equipment (flow distributors, pumps, etc) have adequate
spare parts inventory? ( ) Yes ( ) No. What does it contain?
20. Is the pump station housing adequately ventilated?() Yes(jNo
21. How often are facilities checked? ( ) Once per shift ( ) Daily
( ) other .
22. What is frequency of scheduled maintenance?
23. Is the maintenance program adequate? ( ) Yes ( ) No. If no,
explain . .
24. What is general condition of the nitrification facilities?
( ) good ( ) fair ( ) poor
25. What are the most common problems the operator has had with the nitrifica-
tion system?
Process Checklist - Nitrifying Rotating Biological Contactors
1. What is actual plant flow?_
2. Number of stages
3. Type of RBC media
3. Type of RBC drive
ragd, average;
mgd peak?
; Number of shafts
and surface area of each unit
4. Color of biomass ( ) Black ( ) Dark Brown < ) Light Brown
( ) Other .
5. Odor ( ) Septic { ) Earthy ( ) None ( ) Other ,
6. Are all drives operating properly? ( ) Yes ( ) No. What type of
drive is used ( ) Mech. ( ) Air?
7. Is rotation of media uniform? ( ) Yes ( ) No
8. Is the flow distributed equally to parallel shafts? ( ) Yes ( ) No
How is it distributed?
9. Are the characteristics of the tank contents different in the various
units? { ) Yes ( ) No. If yes, describe '
10. Is there an alkaline buffer added? ( ) Yes ( ) No. If yes, what is
it? . Dose .
11. Does mechanical equipment (mechanical drives, motors, etc.) have an
adequate spare parts inventory? ( ) Yes ( ) No. What does it
contain?
Are the units housed in a building? ( ) Yes ( ) No, or does each
unit have a cover? ( ) Yes ( ) No
12. Is the RBC housing adequately ventilated? ( ) Yes ( ) No.
13. How often are facilities checked? ( ) once per shift ( ) daily
( ) other .
14. What is frequency of scheduled maintenance?
17-15
-------
15,
16,
17.
Is the maintenance program adequate? (
If no, explain
) Yes '( ) No
What is general condition of the nitrification facilities?
( ) good ( ) fair( ) poor
What are the most common problems the operator has had with the nitrifica-
tion system?
Process Checklist - Nitrifying ABF
1.
2.
3.
4.
5.
6.
7.
8.
What is actual plant flow?
ragd,
average;
ragd?
What is underflow recycle rate
recycle rate to the bio-cell mgd?
What type of media is used in the biocell?
What is the depth of media feet?
Number of bio-cell units
mgd, peak
What is the solids
; Size of bio-cell units
Type of aeration system (flow regime)
Type of aeration equipment -
Capacity of each unit
Number of units
Tank dimensions
( ) Light Brown ( ) Other
( ) Light Brown ( ) Other
) None ( ) Other
10.
11.
12.
13.
14.
15.
16.
17.
) None ( )
Other
(
) Yes ( ) No. Are
Color of bio-cell growth:
( ) Black ( ) Dark Brown
Color of activated sludge:
( } Black ( ) Dark Brown
Odor of bio-cell growth:
( ) Septic ( ) Earthy (
Odor of activated sludge:
( ) Septic ( ) Earthy (
Is there evidence of uneven flow distribution?
any nozzles clogged? ( ) Yes ( ) No
Is there evidence of filter clogging, such as ponding? (
Is there evidence of filter flies? { ) Yes ( )• No.
( ) No. Roaches? ( ) Yes ( ) No. Other
Is there grass or other vegetative material growing on filter? (
( ) No. Other
Are there flow measurement devices for the recirculation and return sludge
flows? ( ) Yes ( ) No. Are they operable? ( ) Yes ( ) No
Are recirculation left station and RAS pumps operating? ( ) Yes ( )
No. If no, what is the reason?
If multiple bio-cells are operating, is the flow distributed equally?
( ) Yes ( ) No How is it distributed?
) Yes
Snails?
( ) No
( ) Yes
) Yes
Are the characteristics of the bio-cells contents for each step different?
{ ) Yes ( ) No. If yes, describe
18. Are aeration tank contents mixed thoroughly? (
19. Are aerators operating properly? ( ) Yes ( )No
20. Does mixing appear excessive? { ) Yes ( ) No
) Yes ( ) No
17-16
-------
21.
22.
23.
24.
25.
26.
27.
28.
29.
Do there appear to be dead spots in the aeration tank? ( }
If yes, at what location? . _
Yes ( ) No
is the process operating in its design mode? (
no, explain
) Yes ( ) No If
Does the aeration basin have a foam control system?( ) Yes ( ) No
Is it operable? ( ) Yes ( ) No. Is it operating? ( ) Yes ( )
If multiple basins for each step are operating, is the flow distributed
equally? ( ) Yes ( ) No How is it distributed
Is there an alkaline buffer added? ( ) Yes ( ) No. If yes, what is
it? • . Dose .
Is operation of the system ( ) Manual ( ) Semi-Automatic
( ) Automatic ( ) Computer controlled ( ) Other
No
Does mechanical equipment (flow distributors, pumps, mechanical aerators,
etc) have adequate spare parts inventory? ( ) Yes ( ) No
Is the pump station housing adequately ventilated? ( ) Yes ( ) No
How often are facilities checked? ( ) Once per shift ( ) Daily
( ) Other
30. What is frequency of scheduled maintenance?
31.
32.
33.
Is the maintenance program adequate? (
If no, explain
) Yes
( ) No
What is general condition of the nitrification facilities?
( ) good ( ) fair ( ) poor
What are the most common problems the operator has had with the nitrifica-
tion system?
17-17
-------
References
1. Gulp, G.L., and Folks Helm, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al/ Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirtsf J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
7. Benjes, H.H., Jr., Attached Growth Biological Wastewater Treatment
Estimating Performance and Construction Costs and Operating and
Maintenance Requirements, EPA Contract 68-03-2186 (January, 1977).
8. Battelle Pacific Northwest Laboratories, Evaluation of Municipal Sewage
Treatment Alternatives, Council on Environmental Quality, Contract EQC316
(February, 1974).
9. Sawyer, C.N., et al, Nitrification and Denitrification Facilities;
Wastewater Treatment, EPA Technology Transfer (August 1973).
10. Gulp, Russell L., et al, Handbook of Advanced Wastewater Treatment, Van
Nostrand Reinhold Co., 1978.
11. Dunnahoe, R.G., and Hemphill, B.W., "The ABF Process, A Combined
Fixed/Suspended Growth Biological Treatment System", AWWA-FACE Conference
(September 1976).
12. Antonie, R.L., "Fixed Biological Surfaces-Wastewater Treatment," CRC
Press, 1976.
17-18
-------
18. DENITRIFICATION ;
Process Description
Denitrification is the reaction in which nitrate-nitrogen gas (N03~N)
is converted to nitrogen gas (N2>. It occurs when nitrified wastewater
comes in contact with certain microorganisms and there is no oxygen present.
If low effluent nitrogen is desirable, controlled denitrification is one way
to meet treatment standards. Unaided denitrification is a slow, process, how-
ever, it can be speeded up if an oxygen-demanding food source is added to the
wastewater. Methanol is commonly used, industrial waste which is low in
nitrogen, such as that from a brewery, can also be used.
Suspended growth denitrification requires a gently mixed, plug-flow
reactor followed by solids separation. Although a tightly fitting cover may
not be needed, the dissolved oxygen of the wastewater must be kept below 0.5
rag/1. Mixing is provided to keep solids in suspension without adding oxygen
to the reactor. In order to release the nitrogen gas and carbon dioxide pro-
duced in the denitrification reaction, short-term aeration must be provided
before final sedimentation. This also oxidizes any methanol which might re-
main in the wastewater after denitrification.
The alternative to suspended growth denitrification is an attached growth
system. Many types of media have been tested and used including plastic,
sand and activated carbon. In general, re-aeration is not required following
fixed growth denitrification, but final sedimentation or filtration is needed
to remove solids from the effluent. Depending on the mode of operation of
the denitrification system, backwashing may be required.
Typical Design Considerations
Suspended growth reactors are usually designed as plug-flow units to pre-
vent short circuiting. Submerged mechanical mixers (0.25-0.5 hp/1000 cu ft)
are usually used for mixing. Detention times range from 1 to 3 hours, de-
pending upon temperature conditions (longer detention times at lower tempera-
tures) and nitrogen concentrations. The mixed liquor volatile suspended
solids should be maintained at least 1500 to 2000 rag/1 and the sludge recycle
capacity should be 50 to 100 percent of average flow.
About 3 mg/1 of methanol usually is fed per rag/1 of nitrate-nitrogen.
Other organic materials also have been used, but cause increased sludge pro-
duction. For example, about twice as much sludge is produced when saccharose
is used instead of methanol. Low-nitrogen industrial wastes (such as brewery
wastes) have also been used when available. Automatic methanol feed systems
are recommended since the organic source must be carefully controlled.
Post-denitrification aeration should only be long enough for facultative
bacteria to be mixed with the waste flow. While they oxidize the residual
methanol, the mixing action releases the nitrogen gas and carbon dioxide
trapped in the biological floes. This can generally be accomplished in less
than one hour.
18-1
-------
The design of denitrificafcion columns depends on the configuration and
media used. Examples of process sizing include using 6 feet of uniformly
graded 2- to 4- mm sand. Filtration rates of 1.0 and 2.5 gpm/sq ft at 10°C
and 21°C, respectively, have removed 20 mg/1 N03-N from wastewater.
Mixed-media filters (coal, sand, garnet) have also been used as downflow,
packed beds for denitrification. Using a 36-inch mixed-media filter (3
inches of 0.27 mm garnet, 9 inches of 0.5 mm sand, 8 inches of 1.05 mm coal,
and 16 inches of 1.75 mm coal), almost complete denitrification is possible
at 1.5 gpm/sq ft.at a temperature of 10°c, and at 3 gpm/sq ft at a tempera-
ture of 20°c.
Typical Performance Evaluation
The overall effectiveness of nitrogen reduction by nitrification-denitri-
fication depends on the nitrification process. Since denitrification is only
effective in reducing N03-N, a high level of nitrification is important. A
good system can produce an effluent with a total nitrogen concentration of
about 2 to 3 mg/1. About half of this would be organic-N and the remainder
ammonia and nitrate-N. Data from actual operating plants is lacking since
there are no established, full-scale operations. Pilot-scale test data in-
dicate that about 90 percent nitrogen removal can be achieved on a long-term
basis.
The following example•illustrates the evaluation of typical denitrifica-
tion process performance.
Determine process characteristics
Suspended growth denitrification
Design flow, average
, peak
N03-N concentration
Influent
Effluent
MLVSS
Minimum temperature
Denitrification volume
Determine process loading
Total peak N03-N loading = Influent NO3-N concentration (mg/1) x
peak flow (mgd) x 8.34 lb/mg/1
- 20 x 15 x 8.34 « 2500 Ib/day
Denitrification tank loading = Total peak N03-N loading (Ib/day)
10 mgd
15 mgd
20 mg/1
1.5 mg/1
2000 mg/1
10°C
120,000 cu ft
Tank volume (cu ft) - 1000
= 2500 x 1000 = 21 Ib N03/1000 cu ft/day
120,000
Determine efficiency of nitrate removal for the system.
% N03-N removal = (Influent N03-N - Effluent N03-N) x 100
Influent N03-N
= 20 - 1.5 x 100 = 93%
20
18-2
-------
Process Control
As with nitrification, pH and temperature will affect the rate of denitr i
fication. Denitcification rates are much lower when the pH is below 6 0 or
above 8.0. The highest rates occur around 7.0. The denitr ification reaction
produces bicarbonate while reducing carbonic acid. This tends to neutralize
any acid produced during nitrification and reduces or eliminates the need for
chemical addition to adjust the pH of the wastewater.
Temperature has a significant affect on the rate of denitr ification.
There 1S a marked suppression of denitr ification below 15°C. To compensate
denitr ification in extremely cold climates, covered units can be
°f *• few process <=°n«*°ls available. Gen-
H < Paced according to the nitrate concen-
the nitrified effluent. If for any reason there is a process up-
set, methanol can be fed manually. However, excess methanol can result in
high effluent BOD and possible discharge violations.
Fixed bed reactors must be backwashed periodically to prevent media clog-
a~inndh n°r?aSeS in h*adloss- To prevent excessive accumulation of nitrogen
gas in the columns, a -bumping- procedure should be used after four to twelve
hours of operation. It consists of a short backwash cycle lasting ont o
effluents are
Maintenance Considerations
K~ ~v w- ^ . °f a good roaintenance program are listed below. These should
be combined with sedimentation and general maintenance management.
1. Spare parts inventory should contain at least the following parts:
one set of each^type of bearing, V-belt or chain drives for each sys-
„«*=» «,«,-,- _-,-, necegsary gasket for replacement of parts, one
ment of
2. Inspection each shift of the denitrification basin or fixed growth
column appurtenant facilities to visibly inspect the equipment.
Records
Recommended sampling and laboratory tests are shown in Figure 18-1.
18-3
-------
o
ui
a
j
a
o
PH
DO
NH3-N
ORG-N
NO.,-N
UJ
N
V?
f-
z S
a
ALL
ALL
ALL
ALL
ALL
TEST 1
FREQUENCY
5/W
5/W
1/D
1/D
1/D
•
LOCATION OF 1
SAMPLE
I
I
I
I
I
E
METHOD OF
SAMPLE
G
G
24C
24C
24C
*£
2-
< K
UJ O
cr u.
H
P
P
H
P
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
D6NITRIFICATION
INFLUENT FROM
NITRIFICATION
PROCESS-
S-,
i
R5 —
RECYCLE SLUDGE
(SUSPENDED GROWTH
PROCESSES)
^DENITRIFIED EFFLUENT
TO FINAL SEDIMENTATION
OR NEXT MAIN FLOW
TREATMENT PROCESS
A. TEST FREQUENCY
H m HOUR M - MONTH
0- DAY R - RECORD CONTINUOUSLY
W- WEEK M*- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I *= INFLUENT
E = EFFLUENT
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G " GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P * PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. THIS PROCESS MUST FOLLOW BIOLOGICAL NITRIFICATION
Figure 18-1
18-4
-------
Other operating records should include:
i». > *'
1. Raw sewage influent flow.
2. Return'sludge flows for suspended growth systems.
3. MLSS and MLVSS in the suspended growth basin and the return sludge
line.
4. Hydraulic loading and backwash rate on fixed film columns.
5. .The total energy (electricity) consumed.
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor the denitrification process.
1.
2.
3.
4.
Analytical balance
Clinical centrifuge with graduated tubes
Wet chemistry equipment for monitoring ammonia
Spectrophotometer
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any
detailed questions.
Sampling Procedures
Samples should be collected at points where the wastewater is well mixed
and homogeneous such as in the denitrification basin close to the mixing de-
vice or from the sludge lines after the sludge has been flowing for about a
minute. The sample collector and containers should be clean. A wide mouth
sample collector of at least 2 inches should be used. Samples collected in
the effluent channel should be collected near the discharge point so that any
isolated areas of short circuiting do not influence the results. Where
automatic samplers are used, sampler tubes should be kept clean.
Sidestreams
There are no significant sidestreams associated with the denitrification
processes. Settled solids not recycled within the process are generally di-
verted to the primary treatment process. The sludge quantity has been found
to be about 0.2 Ib/lb of methanol feed.
18-5
-------
Process Checklist - Denitrification
1.
2.
3.
4.
5.
6.
7.
8.
rogd avg.
What is actual plant flow
Type of denitrification system
Type of mixing equipment or media
units and capacity of each unit
What are the tank (or column) dimensions?
Are tank contents mixed thoroughly? ( )
ragd peak?
Number of
Yes (
) No
Are all mechanical mixers operating properly? ( ) Yes (
Does mixing appear excessive so as to cause oxygenation?
Do there appear' to be dead spots in tank? ( ) Yes ( )
If yes, at what location? '^
)No
( ) Yes
No
( ) NO
Is the process operating in its design mode? (
no, explain
) Yes ( ) No If
10.
11.
12.
13.
Are the column pumping systems operating? ( )
Is the backwash system operating correctly? (
How often is it used?
Is operation of the system? ( ) Manual ( )
( ) Automatic ( ) Computer controlled ( ;
Is there an adequate spare parts inventory? ( ]
What does it contain?
Yes ( ) No.
) Yes ( ) No.
Semi- Automatic
) Other
1 Yes ( ) No
14. Is the pump station housing adequately ventilated? ( ) Yes
15. How often are facilities checked? ( ) Once per shift ( )
( ) Other
16. What is frequency of scheduled maintenance?
( > No
Daily
17,
18
Is the maintenance program adequate? (
If no, explain
) Yes
( )
What is general condition of the denitrification facilities?
( ) good ( ) fair ( ) poor
20. What are the most common problems the operator has had with the system?
18-6
-------
References
1. Gulp, G.L., and Polks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
7. Parker, D.S., et al, Process Design Manual for Nitrogen Control, EPA,
Technology Transfer, (October 1975).
8. Battelle Pacific Northwest Laboratories, Evaluation of Municipal Sewage
Treatment Alternatives, Council on Environmental Quality, Contract EQC316
(February, 1974).
9. Gulp, Russell L., Wesner, G.M. and Gulp, G.L., Handbook of Advanced
Wastewater Treatment, Van Nostrand Reinhold Co., 1978.
18-7
-------
-------
19. AMMONIA STRIPPING
Process Description
Ammonia stripping is used to remove ammonia from water by passing high
volumes of air through an agitated water-gas mixture. In wastewaters, most of
the nitrogen is present in the form of ammonium ions (NH|) and must be
converted to ammonia gas (NH3) by raising the pH of the wastewater to the
range of 10.8 to 11.5. At this high pH, the nitrogen is almost totally con-
verted to the ammonia form from the ammonium form. Wastewater is pumped to
the top of a stripping tower and allowed to fall downwards through a series of
splash bars. At the same time, high volumes of air are forced upwards through
the stripping tower by a large fan. Lime is almost always used to raise the
pH since it also removes phosphorous and suspended solids.
The two types of ammonia stripping towers that are commonly used look much
like cooling towers. The towers differ in design only in the location of the
air inlet louvers. For the cross-flow tower, the air is drawn through the
sides for the total height of the packing. The counter-current tower draws
the entire air flow through the bottom of the tower. The cross-flow towers
have been found to be more susceptible to scaling problems (build-up of cal-
cium deposits) and are less efficient than the counter-current towers.
Typical Design Considerations
The major design considerations for ammonia stripping towers are pH, tem-
perature, hydraulic loading, tower packing, air flow and scale deposit control.
The pH of the water has a major effect on the efficiency of the process.
If the pH is not raised to a value at which all the ammonium ions are con-
verted to ammonia gas, ammonia removal is not complete.
As air and water temperatures decrease, it it harder to strip the ammonia
from the water. To maintain ammonia removal efficiencies at lower tempera-
tures, the air volume must be substantially increased.
The hydraulic-loading rate is expressed in terms of gallons per minute
applied to each square foot of the plan area of the tower packing. The area
is selected to allow the formation of water droplets which are needed for ef-
ficient ammonia removal. If the loading rate is too high, the efficiency is
reduced because the water does not form the droplets. The normal range of
loading rate is 1 to 3 gpra/ft2, but mostly the rates are less than 2
gpm/ft2.
The tower packing depth, material, and shape all affect the ammonia re-
moval efficiency. The greater the depth the better the performance, up to a
maximum of about 24 feet. The packing material can be either wood or plastic,
with the plastic showing more resistance to scaling. The shape refers to the
.shape of the individual members as well as how the members are placed in the
tower. Packing should be shaped to produce as many water droplets as possible
as the water cascades down through the tower.
19-1
-------
Gas transfer relationships and practice show that the percentage ammonia
removal is increased with increasing air flow, for a given tower height.
There is a practical limit on the air flow rate which is related to the pres-
sure drop across the tower packing. This maximum value is approximately 550
cfm/sq ft. Typical air requirements are about 300 cfm/gal for 90 percent
removal and 500 cfm/gal for 95 percent removal.
The scaling, or deposition of calcium carbonate, on the packing material
reduces the efficiency of the ammonia removal process. The deposits are
caused by the unstable, high pH waters flowing through the tower. To minimize
scaling, as much calcium carbonate as possible should be removed during the
chemical treatment step. Scaling can also be controlled by eliminating carbon
dioxide from the air.
Typical Performance Evaluation
The ammonia stripping process performance is judged on meeting discharge
standards. The following steps can be used to check the performance of the
stripping process.
1. Obtain the tower dimensions and operating conditions and results.
Wastewater flow to tower = 5200 gpm
pH of wastewater =10.9
Ammonia concentration in influent and effluent of wastewater = 20 and
2 mg/1, respectively.
Air temperature s 65°F
2. Check influent pH - it should be above 10.8
3. Check the tower hydraulic loading rate:
Area covered by tower packing =• 4752 sq ft
Plow to tower = 5200 gpm
Hydraulic loading - 5200 gpm » j^j. gpm/sq ft
4752 sq ft
Loadings should be less than 2 gpm/sq ft to keep water from moving
through the tower in sheets rather than in drops.
4. Check the tower packing to make sure it is not coated with calcium
carbonate.
5. Calculate the removal of ammonia in the tower and check the air
temperature:
Influent » 20 mg/1
Effluent - 2 mg/1
Removal = (20 - 2) x IQO = 90%
20
Air Temperature 3 65°P
At 65°F, 90 percent removal is good. For every °F decrease in
temperature, the efficiency will drop about 0.5%.
19-2
-------
Process Control
The control options for an ammonia stripping facility are related to the
influent pH, the rate of air flow, and the hydraulic loading rate. These
items are discussed in Reference 1.
Maintenance Considerations
Proper maintenance of a facility will ensure an efficient and trouble free
operating plant. The features of a maintenance program to insure these con-
ditions are listed below. They do not consider any other process, such as pH
adjustment, which are discussed under other process descriptions.
1. Spare parts inventory should include at least one set of each type of
bearing, grease and water seals, all necessary gaskets for replace-
ment of parts, tower packing and spray nozzles.
2. Tower and appurtenant equipment painted regularly to protect against
corrosion or weathering.
3. Scale (calcium carbonate) formation regularly cleaned off.
4. Visual examination of the stripping process each shift to check the
equipment for misalignment, excessive noise, unequal hydraulic load-
ing or damage to the tower.
5. All wastewater sampling lines flushed out regularly to insure no de-
posits are formed.
Records
The recommended sampling and laboratory tests are shown in Figure 19-1 for
the ammonia stripping process.
Other operating records should include the following:
1. Influent flow rate
2. Air flow rate
Laboratory Equipment
The laboratory should include the following list of equipment as a minimum
in order to monitor the ammonia stripping process.
1. pH meter
2. Spectophotometer or filter photometer
3. Nessler Tubes
19-3
-------
a
i
a
Ul
a
u>
1
0.
o
ORG-N
NOyN
NHyN
PH
TEMP
HARDNESS
UJ
M
t/t
t-
r S
n
ALL
ALL
ALL
ALL
ALL
ALL
TEST
FREQUENCY
1/W
1/W
1/W
3/D
3/D
1/W
LOCATION OF
SAMPLE
I
E
I
E
I
E
I
E
I
E
I
E
'
METHOD OF
SAMPLE
24C
24C
24C
G
G
24C
z%
s*-
< o:
uj o
o: u.
H
H
H
P1
H
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
NITROGEN REMOVAL
AMMONIA STRIPPING
tlNFLI
'INFLUENT FROM
PREVIOUS MAIN
FLOW TREATMEN
PROCESS
V
EFFLUENT TO
NEXT MAIN
FLOW TREATMENT
PROCESS
A. TEST FREQUENCY
H m HOUR M - MONTH
0- DAY R - RECORD CONTINUOUSLY
W- WEEK MB- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I » INFLUENT
E - EFFLUENT
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G- GRAB SAMPLE
R " RECORD CONTINUOUSLY
Mn« MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C . COST CONTROL
E. FOOTNOTES:
I. PROCESS CONTROL ON EFFLUENT
Figure 19-1
19-4
-------
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any de-
tailed questions.
Sampling Procedures
Samples should be collected from the chemical clarifier effluent channel
or the influent pumping station wet well and the effluent collection chan-
nels. Samples should be taken from the center of the channels, where the
wastewater is normally homogeneous.
Sidestreams
There are no sidestreams associated with the ammonia stripping tower
process.
19-5
-------
Process Checklist - Ammonia Stripping Tower
1.
2.
3.
4.
6.
7
8.
9
10.
11.
12.
13.
What is the actual plant flow
What is total flow through the towers
How many towers?
mgd avg
mgd
What is the flow through each tower
mgd mgd
mgd
What type of stripping tower?
( ) Other
( ) counter current ( ) cross flow
What are tower packing dimensions?
What is ammonia removal?
JType of packing_
What is ammonia removal percentage?
What is the air flow?
Ibs NH3
cfm
Does previous process have automatic pH adjustment? (
Are the influent pumps operating properly? ( ) Yes
what is problem?
(
Yes (
) No.
) Mo
If no,
Do the mechanical equipment have an adequate spare parts inventory?
( ) Yes ( ) No. If no, what is problem?
How often are the facilities checked?
( ) Daily ( ) Other
( ) Once per shift
14. What is frequency of scheduled maintenance?
15,
16.
17.
Is the maintenance program adequate? (
explain
) Yes ( ) No. If no.
What is the general condition of the ammonia stripping system?
( ) good ( ) fair ( ) poor
What are the most common problems the operator has had with the ammonia
stripping process? ° ;
19-6
-------
References'
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
7. Gulp, Gordon L., and Gulp, Russell L., New Concepts in Water Purification,
Van Nostrand Reinhold, 1974.
8. Gulp, Russell L., Wesner, G. M., and Gulp, Gordon L., Handbook of Advanced
Wastewater Treatment, Van Nostrand Reinhold, 1978.
9. Parker, D.S., et al, Process Design Manual for Nitrogen Control, USEPA,
Technology Transfer, October 1975.
19-7
-------
-------
20. CHEMICAL FEEDING AND CONDITIONING
Process Description
Many different chemicals are used for the treatment of municipal waste-
waters as listed in Table 20-1. However, many of these are for special condi-
tions and are not often used. The chemicals that are used most frequently
include lime/ aluminum sulfate (alum), ferric chloride, and sodium hydroxide
(caustic soda). Others used less frequently include ferric sulfate, ferrous
sulfate (copperas), and sodium aluminate. The selection of which chemical to
use depends on the principal purpose of the chemical addition (coagulant or
phosphorus removal), the quality of the wastewater, the type of handling and
feeding equipment available, and the chemical costs. To minimize chemical
costs and to prevent excess use, it is very important that the system include
good and reliable chemical feed equipment.
Chemical feed systems are divided into two principal categories, dry feed-
ers and solution feeders. Within each category there are several different
methods of feeding the chemical. The most widely used equipment are the
volumetric, the belt gravimetric, and loss-in-weight gravimetric feeders, all
of which are of the dry feeder type. Liquid feeders usually are metering
pumps or orifices. These metering pumps usually are positive displacement,
plunger, or diaphragm type pumps.
Lime can be added either before primary treatment or after secondary
treatment (as part of an AWT process). As a coagulant used in primary treat-
ment, lime helps to remove SS, phosphorus, heavy metals, grease and viruses.
Lime also may be used to adjust the pH of the wastewater, or for sludge con-
ditioning. Lime is never fed as a solution because of its low solubility in
water.
Aluminum sulfate may be added to wastewater for coagulation or phosphorus
removal. It may be used as the primary coagulant instead of lime, or along
with lime. Alum may be added as a filter aid to the influent of a mixed-media
filter. It may also be added at several other points in the wastewater treat-
ment process including the primary influent, rapid mix basin, or first stage
recarbonation basin. It is available in either dry or liquid form.
Polymers are used as an aid to flocculation, where a light or fine floe
settles too slowly. They are also used as filter aids. By adding the right
amount of polymer at the right point in treatment, both turdibity and phos-
phorus removal can be improved.
Like alum and lime, ferric chloride is an effective coagulant used to re-
move phosphorus and to lower suspended solids. Ferric chloride also can be
used as an oxidant to control odor problems coming from hydrogen sulfide.
Since ferric chloride is always fed as a liquid, it is normally obtained as a
liquid and unloaded pneumatically.
20-1
-------
TABLE 20-1. SOME CHEMICALS AND THEIR PRINCIPAL JCJSES IN WASTEWATER TREATMENT
Chemical
Principal use
Activated, silica,
Aluminum ammonium sulfate,
Al2(SOit) 3' (NHit ) 2SCV 12H20
Aluminum sulfate (alum) ,
Ammonia (aqua or anhydrous)
or NHi^C-H
Ammonium sulfate,
Bentonite clay
Calcium hydroxide, Ca(OH)2
(hydrated lime) and calcium
CaO (quicklime)
Carbon dioxide, C02
Chlorinated ferrous sulfate
(Chlorinated Copperas)
Ferric chloride, FeCla or
Fed 3 6H20
Ferric sulfate,
Fe2(SOt,.) 3«XH2O
Hydrochlorie acid, HC1
Nitric acid, HNO3
Phosphoric acid,
Polyelectrolytes (polymers)
Sodium aluminate, Na2M2Oit
Sodium carbonate, Na2Cos
Sodium hydroxide
(Caustic Soda) , NaOH
Sulfuric acid
Coagulation aid
Coagulation
Coagulation, phosphorus precipitation
Nutrient addition
Activation of silica
Coagulant aid, weighting agent
Coagulation, neutralization,
phosphorus precipitation
Recarbonation, neutralization
Coagulation
Coagulation, phosphorus precipitation
Coagulation, phosphorus precipitation
Neutralization, pH adjustment
Neutralization, pH adjustment,
nutrient addition
Nutrient addition
Flocculation
Coagulation, phosphorus precipitation
pH adjustment
Neutralization, pH adjustment
Neutralization, pH adjustment,
activation of silica
20-2
-------
In the biological nitrification-denitrification process, an oxygen demand
source such as methanol often is added to the wastewater in order to reduce
the nitrates quickly. Methanol may be used either in a column or in a 3-stage
reaction basin as described in the Denitrification Section of this manual
(Section 18).
Sodium hydroxide (NaOH) is a strong base used to neutralize an acidic
wastewater. Without proper neutralization, acid wastewaters can damage treat-
ment facilities and biological treatment processes. Sodium hydroxide also is
used for pH adjustment along with other chemicals used in the treatment
process.
Typical Design Considerations
The chemical feed systems are designed with four factors in mind:
• Location of chemical addition in the treatment system (whether
primary sedimentation, activated sludge, rapid mix or other),
• Purpose of chemical addition,
• Chemical dosage rates, and
• Selection of equipment suitable for chemical used and feeding rate..
The location of the chemical coagulant addition is related to the reason
for the addition. Chemicals added in the primary sedimentation basins, acti-
vated sludge aeration tanks or an advanced wastewater treatment chemical
treatment system (Section 21) are to remove phosphorus. Chemicals added to
the secondary sedimentation basin and ahead of filters are to improve removal
of suspended solids. Chemical addition in a tertiary step is generally con-
sidered to be the most reliable, although it is more expensive.
The dose rate of chemical is determined experimentally by either jar tests
or zeta potential tests. Coagulant doses typically are in the following
ranges: aluminum sulfate (alum), 75 to 250 mg/1; ferric chloride, 45 to 90
tog/1; and lime, 200 to 400 mg/1.
Typical Performance Evaluation
The chemical feed system should be evaluated for its ability to maintain
the desired feed rate per million gallons of waste. Chemical treatment pro-
cess evaluation is discussed in Section 21 of this manual.
The following illustrates calculation of lime feed rates for a plant where
lime recovery by recalcining of lime sludges is practiced:
20-3
-------
Plant flow
Total CaO dosage
Ca(OH)2
380 rag/1 CaO
Makeup lime
Recalcined lime
Makeup lime dosage
Recalcined dosage
Makeup lime dosage
95 x 8.34
791 x 100
92
860 x 15
12,900
Recalcined lime
dosage
285 x 8.34
2,377 x 100
70
3,396 x 15
50,940
illustrates
15 rogd
380 mg/1
1.32 x CaO; therefore
1.32 x 380 = 500 mg/1 Ca(OH)2
92% CaO ^
70% CaO
25% of total
75% of total
0.25 x 380 rag/1
95 mg/1 as CaO
791 Ib of CaO/mg
860 Ib makeup lime at 92% purity/ing
12,900 Ibs for 15 rag, Ib/day of makeup lime
536 Ib/hr of makeup lime (makeup lime feeder
setting)
0.75 x 380 mg/1
285 mg/1 CaO
2,377 Ib of CaO/rag
3,396'lb of recalcined lime at 70% purity/MG
50,940 lb for 15 MG (Ib/day of recalcined lime)
2,123 Ibs/hr of recalcined lime (recalcined
lime feeder setting)
the calculation of alum feed rates for a piston
The following
feed pump system:
Three alum feed pumps; two dual head and one single head.
Dual head pumps
Single head pump
Plant flow
Liquid alum
strength
Alum dosage
Alum dosage
lb/15 mgd
Ib/hr
gal/hr
One pump
(2 heads)
0-50 gpm at 100% stroke/head
0-11.5 gph at 100% stroke
= 15 mgd
= 5.4 lb dry alum/gal
= 20 mg/1
= (20 mg/1) x (8.34 Ib/gal)
= 167 Ib/mg
= (167 Ib/mg) x (15 rogd)
= 2,505 Ib/day
- 2,505 Ib/day
24 hr/day
= 104 Ib/hr
= 104 Ib/hr
5.4 Ib/gal
= 19 gal/hr
= (19 gal/hr) x 3.00
(100 gal/hr)
= 19 (use 20% stroke :setting)
20-4
-------
Process Control
Chemical feed systems can be operated either manually, semi-automatically
or fully automatically* The method of control for the feed rate can be the pH
of the waste stream, in the case of lime addition or simply a dose rate or
concentration per million gallons of waste flow. These control methods are
discussed in Reference 1.
Maintenance Consideration
Proper and regular maintenance of the chemical feed system is critical to
the efficient and trouble free operation of the system. The features of a
maintenance program that should insure these conditions are listed below.
They do not consider other processes such as recarbonation which are described
under separate sections.
1. Spare parts inventory should include at least one set of each type of
bearing, grease and water s.eals, one each of all gaskets, drive
belts, isolation pads and springs, one feed pump head.
2. Spilled material (chemicals) regularly cleaned off.
3. Visual inspection each shift of the chemical feeding equipment to
check for excessive noise, unequal loading if there is more than one
metering pump, chemical-leakage, damage to storage tanks, raw mate-
rials, mixing .tanks or metering pumps.
4. Records to determine the dose rate to the wastewater and also eval-
uate whether or not this value is changing with time. If the waste-
water characteristics remain the same, changing dosages could indi-
cate a problem with the chemical feed equipment.
5. Storage bins and conveyance systems checked regularly to insure
air-tightness.
6. Check the calibration of the pH probe each shift to insure the auto-
matic control system is operating correctly.
7. Daily inspection to check for plugged feed lines.
8,
Records
All chemical feed lines whether suction, discharge or lines conveying
solid or powered materials, flushed or blown out regularly to insure
against plugging and solids build-up.
There are no recommended sampling or laboratory tests associated specifi-
cally for the chemical feeding systems. All laboratory testing is performed
in connection with the process receiving the chemical.
20-5
-------
Operating records should include the following:
1. Dose rate for each chemical.
2. Total volume or weight used per day of each chemical.
3. Dilution water volumes.
4. Remaining volumes or weight of chemicals in storage.
Laboratory Equipment
There is no laboratory equipment required specifically for the chemical
feed system. However, good plant operation dictates that the composition and
purity of the chemicals used should be checked occasionally. Tests for the
various chemicals are described in detail in Standard Methods. Also, the EPA
report "Estimating Laboratory Needs for Municipal Wastewater Treatment Facil-
ities" contains very detailed information on glassware, chemicals, miscellane-
ous furniture, etc., and should be referred to for any detailed questions.
Sampling Procedures
Saicples are not usually taken from chemical feed systems because there are
no tests done on a regular basis. However, the dose rate and chemical concen-
tration being added to the wastewater must be checked at regular intervals.
Therefore, samples from the chemical feed lines should be taken using special
sampling taps.
Sidestreams
There are no sidestreams associated with chemical storage and feed systems.
20-6
-------
Process Checklist - Chemical Feeding and Conditioning
This chemical feeding checklist relates to the liquid phase only. For the
chemical feeds for sludge processing, refer to the individual sludge processes.
1. What are actual plant flows? mgd avg. rogd peak.
2. What chemicals are used? ( ) lime ( ) alum ( ) ferric chloride
( ) sodium hydroxide ( ) other
3. Where is chemical added?()primary se
-------
References
1. Gulp, G.L., and Polks Heira, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et alf Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, US EPA Report 430/9-74-002 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design,. Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
7. Gulp, Gordon L., and Gulp, Russell L., New Concepts in Water Purification,
Van Nostrand Reinhold, 1974.
8. Gulp, Russell L., Wesner, G. M., and Gulp, Gordon L., Handbook of Advanced
Wastewater Treatment, Van Nostrand Reinhold, 1978.
9. Black & Veatch, Process Design Manual for Phosphorus Removal, USEPA,
Technology Transfer, April 1976.
10. Hudson, H.E., Jr., and Wolfner, J.P., "Design of Mixing and Flocculation
Basins", Journal AWWA, Vol. 59, October 1967, p. 1257.
11. Evans, David R., "Mixing and Flocculation", unpublished paper.
12. Rich, Linvil G., Unit Operations of Sanitary Engineering, John Wiley &
Sons, Inc., 1961.
20-8
-------
21. RAPID'MIXING, FLOCCULATION AND CLARIFICATION
Process Description
Rapid mixing and flocculation are used in series to optimize chemical
treatment of wastewater.
Rapid mixing is done in a small tank with a mechanical mixing device.
Sometimes the mixing is done with other equipment such as baffled channels,
hydraulic jump mixers, pneumatic (compressed air) mixing, or in-line static
mixing devices. The most common type of mixing device is the rotating turbine
mixer; propellers are normally used for small volumes, such as the mixing
tanks in chemical feed systems discussed before (Section 20); and paddles are
usually used for flocculation agitation.
Turbine mixers are like a centrifugal pump without the casing. They force
the water outwards to the sides of the tank and create high turbulence and
intense fluid shear. The turbine mixer is usually located in the center of
the mixing tank and can have various shaped blades. The diameter of the
impeller is usually 30 to 50 percent of the smallest dimension of the tank.
Baffles are located vertically to the wall of the tank to eliminate vortexing.
Flocculation helps the suspended particles to stick together to make
larger clumps of particles (floes) which will settle out easily in clari-
fiers. Flocculation is done by controlled agitation or slow mixing of the
coagulated wastewater in a tank which contains mechanical agitation devices
such as rotating paddles, vertical turbines,' or vertical reciprocating mecha-
nisms. The most common type used is the rotating paddle. The paddle agitator
is sized so that the sum of the width of each paddle on a wheel equals 25 per-
cent of the water depth of the basin, or the total paddle area is less than 15
to 20 percent of the cross-sectional area of the water (depth x width). The
range of speeds at the outside edge of the paddles (peripheral speed) is 0.5
to 4 feet per second (fps). The vertical turbines operate at peripheral
speeds of 2 to 4 fps and have a zone of influence of approximately 3 times the
turbine diameter on the same plane as the turbine blades. The vertical zone
of influence is 4 to 5 times the diameter of the turbine. The flocculation of
the suspended particles is caused by the small eddy currents that are formed
at the trailing (back) edge of the paddles, turbine blades or reciprocating
caps.
Clarification is gravitational settling related to chemical processes.
Chemical clarification almost always follows the rapid mix-flocculation
steps. It is similar to sedimentation which is described in Sections 5 and 11
of this manual*.
Typical Design Considerations
The principal criteria by which the rapid mixing equipment is sized are
the velocity gradient, G, and the detention time. Once these have been
selected, the type of mixer and impeller are selected and the horsepower can
be computed. Typical values for G and the detention times are given in Table
21-1. For these values, the horsepower averages about 0.5 HP per mgd for a
turbine. The design for a 10 mgd rapid mixer is shown in Table 21-2.
21-1
-------
TABLE 21-1. VELOCITY GRADIENTS (G) FOR RAPID MIX
Application
fps/ft or sec"1
In-line, instantaneous blending
Rapid Mixing
20 sec contact time
30 sec contact time
Longer contact time
3,000 to 4,000
700 to 1,000
650 to 900
500 to 700
TABLE 21-2. TYPICAL DESIGN FOR 10 MGD RAPID MIXER
Detention time at maximum flow, in minutes
Width, in feet
Water depth, in feet
Volume, in cubic feet
Propeller diameter, in inches
Propeller capacity, in cubic feet per minute
Shaft speed, in revolutions per minute
Motor horsepower
Velocity gradient, G sec"1
1.1
11.0
8.5
1,030
38
2,060
100
5
360
The principal criteria for the design of the flocculation equipment are
also the velocity gradient, G, and the detention time. The type of mixers
used will depend- upon the wastewater and process flexibility. The floccula-
tion basin is typically divided into 2 to 4 zones, each with a different G
value. Typical G values for a 3 zoned system are 100, 60 and 20, with the
percentage volumes for the respective zones of 30%, 30% and 40%. Velocities
through the flocculation basin should range from 0.35 to 1 ft/sec. Detention
times for flocculation typically range from 20 to 40 minutes. The design cri-
teria for a 10 ragd plant flow are shown in Table 21-3. Flocculation velocity
gradients for various applications are shown in Table 21-4.
21-2
-------
TABLE 21-3. TYPICAL DESIGN FOR '10 MGD PLOCCULATOR
Detention period, in minutes
Width, in feet
Depth, in feet
Length, in feet
Volume of tank, in cubic feet
Mixing zones: 1 in cu ft
2 in cu ft
3 in cu ft
Velocity gradient, G zone 1 sec'1
zone 2 sec'1
zone 3 sec'1
45
30
10
140
41,778
12,500
12,500
16,788
100
60
20
TABLE 21-4. VELOCITY GRADIENTS (G) FOR FLOCCULATION BASINS
Application
fps/ft or sec'1
Flocculation
Tertiary wastewater
Turb/color removal - no solid recirc.
Turb/color removal - solids contact
reactors (5% - vol in suspension)
Softening - solids contact
reactors (10% - vol in suspension)
Softening - ultra high solids
contact (20% to 40% - vol in
suspension)
100* taper to 40
100* taper to 40
150* taper to 50
200* taper to 100
400* taper to 250
* Drive layout should provide for alternate speeds, allowing selective down-
ward variation from the maximum values shown.
21-3
-------
The clarifiers are sized on the basis of the overflow rate and detention
time or water depth. The overflow rate for the clarifiers is based on the
chemical coagulant used. Typical design values for clarification of a lime
treated wastewater for a 10 rogd plant flow are shown in Table 21-5.
TABLE 21-5. TYPICAL DESIGN FOR 10 MGD CLARIFIERS
Type of coagulent
Number of tanks
Overflow rate/ gpd/ft2
Detention time/ hrs
Total surface area, ft2
Diameter of tanks, ft
Depth of tank, ft
Lime
2
903
2
11,083
84
10
Typical Performance Evaluation
The rapid mix, flocculation and clarification operations are typically
considered together and are ultimately judged on the suspended solids and
phosphorus removal efficiencies. Typical removal efficiencies have been
determined and are shown in Table 21-6.
To check these operations, the following simple computations can be made.
The equations used are shown in Table 21-7. For easier solution, the power
equations have also been presented in graphical form on Figure 21-1. Table
21-8 gives correction factors.
TABLE 21-6. TYPICAL PHOSPHORUS REMOVAL EFFICIENCIES
Range in percent removals
Chemical coagulant
Lime
Lime -f ferric
Alum
Ferric chloride
Ferric chloride
Ferric sulphate
Alum
Ferric chloride
Lime
Lime + ferric
Lime + ferric
Application location
Tertiary
Tertiary
Primary sed.
Primary sed.
Secondary sed.
Aeration basin
Aeration basin
Aeration basin
Primary sed.
Primary sed.
Trickling filter eff.
w/o filtration
95 to 97
96 to 98
75 to 90
70 to 90
83
91
75-85
75-85
75-90
90-95
93.5
w/filtration
97 to 99
98 to 99
21-4
-------
TABLE 21-7. EQUATIONS USED TO EVALUATE RAPID MIX AND PLOCCULATION SYSTEMS
Energy for Mixing by Mechanical Means
Water Power » P » G^V u where
Brake Horsepower,
PH - P
550 x ED x EB
Substituting for constants;
Velocity gradient » 4589.4 P/S
Plocculator paddle area
A * 2P
CD u3
- 561.2 PH
water power, ft-lb/sec
velocity gradient,
V =s volume of tank, cu ft
u = absolute viscosity of liquid,
Ib-sec/sq ft
= 2.089 x 10~5 at 20°C
ED= drive efficiency, %/100
EB= bearing efficiency, %/100
brake horsepower, HP
A = paddle area, sq ft
P » water power, ft-lbf/sec
CD- drag coeff.
1.8
3 mass density of liquid,
Ib-sec2/ft4
° 62.4
u » relative velocity of paddles, ft/sec
= 0.75 V
v » velocity of paddle tip, fps
21-5
-------
0.01
00.1
G
1 10 100
DETENTION TIME, sec
POWER REQUIRED FOR RAPID MIXING
AT«*C
2 4 6 8 10 20 40 60 80100
DETENTION TIME, mln
POWER REQUIRED FOR FLOCCULATION
AT4»C
Figure 21-1. Power requirements for rapid mix and flocculation.
21-6
-------
TABLE 21-8. TEMPERATURE CORRECTIONS
Multiply values obtained from accompanying graphs for
Water Temp.
°C
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
4°C by temperature correction factor stated
below to determine horsepower or velocity
gradient at any other temperature
Temperature Correction Factor
hp per mgd G,
1.14
1.11
1.07
1.03
1.00
0.981
0.940
0.914
0.889
0.863
0.838
0.811
0.794
0.774
0.748
0.729
0.716
0.696
0.678
0.669
0.646
0.629
0.615
0.600
0.586
0.572
0.559
0.547
0.535
0.523
0.512
sec"1
0.937
0.948
0.966
0.985
1.00
1.02
1.03
1.05
1.06
1.08
1.09
1.11
1.12
1.14
1.16
1.17
1.18
1.20
1.21
1.22
1.24
1.26
1.28
1.29
1.31
1.32
1.34
1.35
1.37
1.39
1.40
21-7
-------
3.
Collect the required base information for the rapid mix, floccula-
tion, and clarifiers.
Plant flow rate =• 5 rogd
Phosphorus influent concentration = 10 mg/1 as P
Phosphorus effluent concentration » 0.6 mg/1 as P
Rapid mix tank dimensions = 2 tanks at 6' x 6'
Rapid mixer horsepower = 1 HP per tank
Flocculator dimensions = 2 tanks of 40' x 20'
Paddle area « 47 sq ft
Mixer horsepower s 1st stage » 2 HP, 2nd stage = 1/2 HP
Clarifier diameter = 60 ft
Number of clarifiers = 2
Depth of clarifier tank = 12 ft
Compute detention time and velocity gradient for rapid mix.
x 6' water depth
x 10' water depth
Volume =» 2x6'
Detention time =
Water horsepower
x 6' x 6'
432 cu ft
432 x 7.48 x 24 x 60 x 60
56 sec
= 2
5 ragd
x 0.8
1.6 HP
Velocity gradient, G = 4589.4 x P/V
= 4589.4 x 2/432
= 312 sec'1
Water HP/ragd « 0.32
From curve, using 0.32 and 56 sec, G = 260
Correction factor from Table 21-9 for 20°C = 1.24
G value - 1.24 x 260 - 322 sec"1
Compute detention time, velocity gradient, and check paddle area for
flocculation.
Total volume » 2 x 40' x 20'x 10'
16,000 cu ft
3 8000 cu ft per basin
Detention time = 16,000 x 7.48 x 24 x 60
5 ragd
= 34.5 rain
Assumed two flocculation stages, using half volume of each tank.
(From Table 21-7)
1st stage G » 4589.4 P/V
» 4589.4 2/4000
= 102.6 sec'1
2nd stage G = 4589.4 0.5/4000
- 51.3 sec"1
Check value from graph.
Ratio of water hp/mgd » 2 x 0.8 * 0.64
2.5
Using 0.64 and detention time of 17 rain
From graph, G
88 sec
-1
1.24
Correction factor to 20°C from Table 21-8
G = 1.24 x 88 = 109 sec"1
Check paddle area using equations from Table 21-7.
Paddle area, A = 561.2 PH
V3
3 561.2 x 2
33
» 41.5 sq ft
21-8
-------
4.
Determine overflow rate and detention time for the clarifier.
Surface area = 2 x x D2
4
= -L* _ x 60 x 60 = 5g55 ffc2
Overflow rate = 5 x lp6 = 884 gp* maintenance progr^
21-9
-------
1. Spare parts inventory should include at least one set of each type of
bearing, grease and water seals, all necessary gaskets for replace-
ment of parts, paddles and drive belts.
2. Visual inspection each shift of the rapid mix, flocculation and clar-
ification equipment to check the equipment for misalignment, exces-
sive noise, and unequal loading of each operation if there are two or
more of each.
3. Regular checking and calibration of pH control equipment for lime
systems.
4. All sample lines flushed regularly to flush out material, such as
chemical floe, that may have entered the lines.
Records
The recommended sampling and laboratory tests are shown in Figure 21-2 for
the rapid mix, flocculation, and clarification operations.
Other operating records should include the following:
1. Influent flow to rapid mix
2. Chemical type and dosage
3. Estimated rotational speeds of mixers
Laboratory Equipment
The laboratory should include the following minimum equipment to monitor
the chemical treatment system.
1. Clinical centrifuge
2. pH meter
3. Titration equipment
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains detailed information on glassware, chemicals,
miscellaneous furniture, etc., and should be referred to for any detailed
questions.
Sampling Procedures
Samples should be taken from the center of the influent and effluent chan-
nels where the wastewater is normally homogeneous and the channel velocities
are high. If there are no channels, sample from the center of the flow dis-
tribution boxes. The effectiveness of the chemical addition should be as
measured by the suspended solids concentration at the outfall from the floccu-
lation tank. Samples of the chemical sludge should be taken from special
sample taps in the pump discharge lines. The solids concentration in the
sludge should be determined and recorded.
21-10
-------
z
2
a
(9
t-
a
o
pH
pH
ALKALINITY
SUSPENDED
SOLIDS
JAR TEST
HARDNESS
TURBIDITY
SLUDGE VOLUME
LAB CENTRIFUGI
TOTAL SOLIDS
TOTAL SOLIDS
FLOW
CALCIUM-
CONTENT
CHLORIDES4
SULFATES
TOTAL-P6
6
ORTHO-P
til
N
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1-
z o
< o
5! 5
ALL
ALL
ALL
ALL
ALL
ALL
ALL
AT.T.
>1
1
ALL
ALL
ALL
ALL
ALL
ALL
TEST
FREQUENCY
Mn
1/D
2/W
1/D
1
1/W
R
3/D
1/W
3/W
R
3
1/W
1/W
3/W
3/W
LOCATION OF
SAMPLE
FE
I
CE
I
PE
FE
CE
I
I
PE
I
CE
S'
S
S
S
LS
I
PE
I
PE
I
PE
I
PE
METHOD OF
SAMPLE
Mn
G
24C
24C
24C
24C
R
G
G
G
R
G
24C
24C
24C
24C
REASON
FOR TEST
P
H
H
H
P
C
H
P
p
P
P
P
C
H
H
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
CHEMICAL TREATMENT
CHEMICAL
ADDITION
.FLASH MIX
EFFLUENT TO
NEXT MAIN FLOW
TREATMENT.
PROCESS
CLARIFIER-
• INFLUENT FROM PREVIOUS
MAIN FLOW TREATMENT
PROCESS
SLUDGE UNDERFLOW TO
CHEMICAL SLUDGE
TREATMENT PROCESSES-
NOTE) CONSIDER AS INDIVIDUAL UNIT PROCESSES
A. TEST FREQUENCY
H » HOUR M — MONTH
D-DAY R - RECORD CONTINUOUSLY
W- WEEK Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I = INFLUENT
FE= FLOCCULATION EFFLUENT
LS =LIME FROM SUPPLIER (INCLUDE W/FLASH MIX PROCESS
CE=CLARIFIER EFFLUENT TESTING)
PE= PLANT EFFLUENT S -SLUDGE UNDERFLOW
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G - GRAB SAMPLE
R « RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
O. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E-. FOOTNOTES:
1. SPOT CHECK
2. IF LIME IS USED
3. WHEN LIME IS DELIVERED BY SUPPLIER
4. IF FERRIC CHLORIDE IS USED
S. IF ALUM OR FERRIC SULFATE IS USED
6. IF PROCESS IS DESIGNED TO CONTROL THIS PARAMETER
Figure 21-2
21-11
-------
Sidestteams
The only sidestream from the chemical treatment system is the chemical
sludge or mud pumped from the clarifier. The solids concentration is impor-
tant since it effects the volume of liquid to be pumped. For example, in-
creasing the solids concentrations from 1% to 2% halves the volume of liquid
to be pumped. The amount of chemical sludge produced is entirely dependent
upon the type of chemical used as the coagulant. Typically/ the solids con-
centrations from the clarifier range between 1 and 2 percent-
21-12
-------
Process Checklist - Rapid Mix, Flocculation and Clarification
1. What is plant flow?
mgd avg.
2. What is total flow through chemical treatment system?
3. How many units are there of each operation?
mgd
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
_mgd
What is the flow through of each unit?
If flow divided equally? ( ) Yes ( ) No. If no, what is
problem?
What type of rapid mixer? ( ) turbine ( ) propeller ( ) air
( ) other
What type of flocculator? ( ) turbine ( ) paddles ( ) other
What are dimensions of rapid mix tank?
What are dimensions of flocculation tank?
What are dimensions of clarifier?
What is chemical coagulant? ( ) lime ( ) alum ( ) ferric
chloride ( ) ferric sulphate { ) other
What is chemical dose?
What are detention times? Rapid mix
rain., clarifier?
What is clarifier overflow rate?
What is volume of sludge pumped?
What are solids concentration?
mg/1
sec., flocculation
hrs.
_ gpd/ft2
_ gallons/day
percent
Are mixers operating properly? ( ) Yes ( ) No. If no, explain
18. Are sludge pumps operating? ( ) Yes ( ) No. If no, explain
19. ~~~~~~~~
20.
Is chemical feed system operating correctly? { ) Yes ( ) No. If
no, explain
Is there an automatic chemical feed control system? ( ) Yes ( ) No
If yes, what kind?
Is it operating? ( ) Yes ( ) No. If no, explain
21.
22.
Do mechanical equipment have adequate spare parts inventory? ( ) Yes
( ) No. If no, explain __________
Is the sludge pumping stations adequately ventilated and illuminated?
( ) Yes ( ) No. If no, explain
How often are the facilities checked? ( ) Once per shift
( ) daily ( ) other
23.
24. What is the frequency of scheduled maintenance?
25.
Is the maintenance program adequate? ( ) Yes ( ) No. If no,
explain _________
21-13
-------
26. What is the general condition of the chemical treatment system?
( ) good ( ) fair ( ) poor
27. What are the most common problems the operator has had with the chemical
treatment system?
21-14
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
7. Gulp, Gordon L., and Gulp, Russell L., New Concepts in Water Purification,
Van Nostrand Reinhold, 1974..
8. Gulp, Russell L., Wesner, G. M., and Gulp, Gordon L., Handbook of Advanced
Wastewater Treatment/ Van Nostrand Reinhold, 1978.
9. Gulp, Gordon L., and Hamann, Carl L., "Advanced Waste Treatment Process
Selection", Public Works, March, April, May, 1974.
. 10. Hudson, H.E., Jr., and Wolfner, J.P., "Design of Mixing and Flocculation
Basins", Journal AWWA, Vol. 59, October 1967, p. 1257.
11. Evans, David R., "Mixing and Flocculation", unpublished paper.
12. Rich, Linvil G., Unit Operations of Sanitary Engineering, John Wiley &
Sons, Inc., 1961.
21-15
-------
-------
22. RBCARBONATION
Process Description
Recarbonation is the process of lowering the pH of lime treated waste-
waters to neutral (pH = 7) conditions by the injection of carbon dioxide into
the wastewater. The process is used to prevent calcium problems on equipment
and structures that follow either lime treatment or ammonia stripping. Down-
stream processes, such as filtration, carbon adsorption, reverse osmosis and
others, operate most efficiently when the pH is at or slightly below neutral
(pH = 7).
Recarbonation can be carried out in either one or two stages. In single-
stage recarbonation, the pH of the water is reduced from a range of 10 to 11.5
down to about 7 by applying the carbon dioxide to one recarbonation basin.
This results in increased calcium hardness of the effluent.
Two-stage recarbonation uses two contact basins for treating the waste-
water with the carbon dioxide. The two basins are separated by an intermedi-
ate settling tank. In the first-stage, the pH of the wastewater is lowered to
about 9.3. At this pH, calcium carbonate is insoluble and a floe readily
forms. The wastewater then enters the settling basin in which the chemical
reactions continue and the calcium carbonate floe settles out. The effluent
from the settling tank enters the second stage recarbonation basin where car-
bon dioxide is added to further reduce the pH.
The two-stage recarbonation process is normally used when very low levels
of phosphorus are required in the final effluent. The phosphorus is adsorbed
on the calcium carbonate floe formed in the first-stage basin and removed in
the settling basin.
The usual source of carbon dioxide for recarbonation is the stack gas from
either sludge incinerators or lime recalcination furnaces. When stack gas is
not available, special carbon dioxide (CO2) generators, underwater natural
gas burners, or liquid CO2 can be used.
Typical Design Considerations
The design criteria are related to the mode of operation, the number of
stages, the basin sizes, and the carbon dioxide requirement and source.
The mode of operation affects the basin sizing if an intermediate settling
tank is included. For single-stage systems, the reaction or recarbonation
basin should have a detention time of 5 min with a minimum water depth of 8
feet. If submerged burners or liquid C02 are used the water depth should be
10 to 12 feet. The reaction basin should be followed by a basin having a de-
tention time of about 15 min to permit complete reactions. The second basin
does not need settling or sludge collection equipment.
22-1
-------
Two-stage systems require the same 5 min detention time in both the first
and second stage basins and the same criteria for water depth as for the sin-
gle stage. The intermediate settling basin requires a detention time in the
range of 30 to 40 min, and a maximum overflow rate in the range 2000 to 2400
gpd/ft2.
The amount of carbon dioxide required to reduce the pH from about 11 to 7
depends upon the alkalinity of the wastewater, lime dose and the ammonia
concentration.
The sources of carbon dioxide - stack gas, pressure generators, submerged
underwater burners and liquid carbon dioxide - are discussed in Reference 1.
Typical Performance Evaluation
The effectiveness of a recarbonation systems is based on its ability to
control and reduce the pH of the water to the desired value or range of val-
ues. If the pH is within the limits of 9.2 to 9.5 and 6.5 to 7.5 for the two-
stage system and 6.5 to 7.5 for the single-stage system, then the recarbona-
tion facility is operating correctly.
Occasionally the C02 requirement or use should be checked and compared
to the theoretical requirements.
1. Collect plant information.
Plant flow 5 mgd
pH » 11.7
Alkalinity (mg/1 as CaC03)
OHT « 380
CO2- = 120
HCO§ » 0
Ammonia * 25 (mg/1 as N)
CO2 content of stack gas = 10%
Blower capacity * 1800
Loss to atmosphere =20%
Temperature of cooled stack gas « 110 °F
2. Determine Ibs of CC>2 required to reduce pH to 7
7.4 x 380 » 2812
3.7 x 120 * 444
25.4 x 25 * 635
3891 Ib /million gallons per day
C02 requirement = 5 x 3891 = 19,455 Ib/day
Determine amount of stack gas that must be compressed to deliver
19,455 Ibs/day.
Stack gas = 19,455 x 100
10
iP-P- 3 194,550 Ib/day
22-2
-------
4.
5.
Determine volume of stack gas,
60°F (520°K)
Stack gas flow = 194,550
0.116 x 1440
in cfm, required at 14.7 psia and
1165 scfm
Convert stack gas flow to conditions at the plant site.
Temperature correction: 110 + 460 x 1165 _ 1277 cfm
Altitude correction:
1618 cfm
6. Allowance for the C02 loss to atmosphere increases the required
stack gas volume by 20%.
Stack gas volume = 1.2 x 1618 = 1941 cfm.
7. Based on these computations, the existing compressors do not have
sufficient capacity.
Process Control
Using pH measurements, control of CC>2 dosages may be determined by trial
and error. In two-stage systems, the CC>2 flow should be set to reduce the
pH in the second-stage,recarbonation basin. This flow should be split between
the two stages to get a pH of 10 in the center of the intermediate settling
basin. Once the CC>2 valves are set for a proper split, they should need
very little other adjustment for changes in total C02 flow. At average
wastewater temperatures, about 15 rain are needed for all C02 bubbles to
react completely to form calcium carbonate. This is why pH is measured at the
middle of the settling basin rather than at the-entrance.
The pH control can also be automatic. Control on the output of the com-
pressors are sometimes used, but normally, surplus stack gas is vented to
atmosphere.
Maintenance Considerations
The maintenance program should include the following items.
1. Spare parts inventory should include at least the following items:
one set of each type of bearings, grease seals, water seal rings, one
set of all gaskets, mechanical seals, nozzles for CC>2 dissolution,
and items of the control system.
2. Daily inspection of the recarbonation basins to insure that the
nozzles are not plugged.
3. Inspection each shift to check the calibration of the automatic pH
control instrumentation.
4. Daily readings of compressor motor run times recorded from elapsed
time meters. These times can be used for scheduling maintenance work
22-3
-------
5.
Records
and to insure that the motors are used evenly. Also, these run times
can be used to estimate the volume of stack gas compressed and re-
leased into the recarbonation basins.
Periodic performance tests run on the compressors to insure that they
are operating at the same capacity as they were when originally sup-
plied to the plant.
The recommended sampling and laboratory tests are shown in Figure 22-1 for
the recarbonation facilities. The same tests would be used for a single-stage
recarbonation system.
Other operating records should include the following:
1. Influent flow to the recarbonation basins
2. Calcium carbonate sludge volumes
3. Carbon dioxide useage
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor the recarbonation system.
1. Analytical balance
2. Clinical centrifuge with graduated tubes
3. Drying oven
4. Dessicator
5. pH meter
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any de-
tailed questions.
Sampling Procedures
Samples should be collected from the center of the influent and effluent
channels where the wastewater is normally homogeneous and the channel veloci-
ties are sufficiently high to avoid solids deposition. To check the effec-
tiveness of the first-stage recarbonation basin, grab samples from the center
of the settling basin should be measured for pH.
Samples of the calcium carbonate sludge should be taken from sample taps
in the pump discharge lines. The solids concentration in the sludge should be
determined.
Sidestreams
The only sidestrearas from the recarbonation process is associated with the
two-stage process. The intermediate clarifier captures calcium carbonate
22-4
-------
z
a
o
o
Q.
O
3H
TOTAL SOLIDS
LAB CENTRIFUGE
TOTAL SOLIDS
DISSOLVED
SOLIDS
ALKALINITY
AMMONIA
PLANT SIZE
(MOD)
ALL
ALL
ALL
ALL
ALL
ALL
TEST
FREQUENCY
Mn
3/D
L/W
L/W
I/O
I/O
-•
LOCATION OF
SAMPLE
PIS
P2S
s
P2S
P2S
PIS
P2S
PIS
P2S
METHOD OF 1
SAMPLE
Mn
G
24C
24C
24C
24C
REASON
FOR TEST
P
P
H
H
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
TWO STAGE RECARBONATION
.INFLUENT FROM
CHEMICAL TREATMENT
OR CMMONIA STRIPPING
/•CARBON DIOXIDE
( DIFFUSERS,(TYPICAL)
1ST STAGE
SLUDGE UNDERFLOW
TO CHEMICAL SLUDGE
TREATMENT PROCESSES
EFFLUENT TO NEXT
MAIN FLOW TREATMENT
PROCESS
A. TEST FREQUENCY
H ~ HOUR M - MONTH
D- DAY R - RECORD CONTINUOUSLY
w- WEEK MH- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
P1S= PROCESS FIRST STAGE
P2S= PROCESS SECOND STAGE
S = SLUDGE UNDERFLOW
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G - GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn» MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
Figure 22-1
22-5
-------
sludge (sometimes termed mud) and returns this to the gravity thickener and
then to the recalcination furnace where the lime (CaO) is produced. The chem-
ical sludge has a concentration in the range of 1 to 2 percent. The sludge
from this process is actually equivalent to the amount of lime added in excess
of the amount required to react with the alkalinity of the wastewater and
raise the pH to about 11.3 at the chemical clarification process.
22-6
-------
Process Checklist - Recarbonation
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
What is actual plant flow?
mgd avg.
What is total flow through recarbonation system? ' mgd
What is flow through each unit? . mgd mgd
mgd mgd
What is type of system? ( ) single-stage ( ) two-stage
What are basin dimensions? * 1st stage 2nd stage
intermediate clarifier.
What is (X>2 useage? Ibs/day
What are the concentrations of chemicals?
mg/1 C0|-;
mg/1 Off";
_mg/l HCO§;
mg/1 NH3
What type of C02 system? ( ) stack gas { ) submerged burners
( ) pressure generators ( ) liquid C02 ( ) other -
What is estimated 0)3 loss to atmosphere? . percent
What is C02 concentration in stack gas? percent
What are detention times? rain., 1st stage; min.
2nd stage;
min. clarifier
What is clarifier overflow rate?
What is volume of sludge pumped?
What is sludge concentration?
_gpd/ft2
galions/day
percent
Are sludge pumps operating? ( ) Yes ( ) No. If no, explain
16. Are C02 compressors operating? ( j Yes() No. If no, explain
17. Is C02 system working properly? {)Yes() No. If no, explain
18. Do mechanical equipment have adequate spare parts inventory? ( ) Yes
{ ) No. If no, explain
19. Are the housings associated with this system adequately ventilated?
( ) Yes ( ) No. If no, explain •
20. How often are the facilities checked? ( ) ' Once per shift
( ) daily ( ) other '
21. What is frequency of scheduled maintenance?
22. Is the maintenance program adequate? ( ) Yes ( ) No. If no,
explain :
23. Are the recarbonation basins covered? ( ) with air tight structure
( ) with open type structure ( ) no covering
24. What is the general condition of the recarbonation system? ( ) good
( ) fair ( ) poor
25. What are the most common problems the operator has had with the recarbona-
tion system? - ; .
22-7
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal' Wastewater Treatment Facilities, us EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Miorin, A.F., et al, Wastewater Treatment Plant Design, Manual of Practice
No. 8, Water Pollution Control Federation (1977).
6. State of Virginia O&M inspection form.
7. Gulp, Gordon L., and Gulp, Russell L., New Concepts in Water Purification,
Van Nostrand Reinhold, 1974.
8. Gulp, Russell L., Wesner, G. M., and Gulp, Gordon L., Handbook of Advanced
Wastewater Treatment, Van Nostrand Reinhold, 1978.
9. CH2M Hill, Process Capacity and Ammonia Removal Study. South Tahoe Public
Utility District, 1977.'
10. Haney, P.O. and Hamann, C.L., "Recarbonation and Liquid Carbon Dioxide",
Journal AWWA, Vol. 61, 1969, p. 512.
22-8
-------
23. LAND APPLICATION OP WASTEWATERS
Process Description
Land treatment systems are designed or operated for different reasons.
The system can be used as a disposal area with no surface discharge. The
loading rate may be set at the maximum for soil infiltration rates, or lowered
so that crop growth can be optimized. Overland flow systems are designed for
treatment with surface discharge. The different systems can be grouped into
three categories as follows:
• Irr igation
• Overland Plow
• Infiltration-Percolation
Irrigation systems are the most flexible. These can be used for high or
low rate application. They can be used for disposal or treatment with dis-
charge. Irrigation systems operated for crop growth can be used as high rate
disposal systems during the off-season.
Irrigation is by sprinklers or surface spreading. The sprinkler system
may be solid set with underground piping, hand movable with light-weight
piping and quick couplers, or mechanically moving such as center pivot, trav-
elling gun, or side-wheel roll. Of the mechanical systems, the center pivot
system is the most widely used for wastewater irrigation.
Surface spreading may be by ridge and furrow, border check, or controlled
flooding. These require runoff control and recycling if no surface discharge
is allowed.
Typical overall removals of pollutants by irrigation are:
BOD
COD
Suspended solids
Nitrogen
Phosphorus
Metals
Micro-organ isms
98%
80%
98%
85%
95%
95%
98%
In an overland flow system, the wastewater is sprayed over a hillside with
a 2-6% slope. It flows slowly down the hill and through the vegetation.
The primary filtering mechanism for overland flow systems is the plant
growth rather than the soil mantle. Treatment efficiencies can vary consider-
ably but the following values can be attained with a properly designed, well
run system:
BOD 92%
Suspended solids 92%
Nitrogen 70-90%
Phosphorus 40-80%
Metals 50%
23-1
-------
Application of overland flow systems is somewhat limited in that a 2-9%
slope is required and a clayey soil desirable. These same conditions are very
poor sites for irrigation systems.
In infiltration-percolation systems, the groundwater is recharged by per-
colation of wastewater (after secondary treatment) using spreading basins.
This process is strictly for disposal with no surface runoff. Wastewater
applied to the land for the purpose of disposal is also being treated by
infiltration and percolation. Removals by this system are:
BOD
Suspended solids
Nitrogen
Phosphorus
Metals
85-99%
98%
0-50%
60-95%
50-95%
Infiltration-percolation is mostly a groundwater recharge system, and does
not utilize nutrients through crop growth.
Land application systems usually include the following parts:
Preapplication treatment
Transmission to the land treatment site
Storage for the wastewater during the non-irrigation season
Distribution over the irrigated area
A system to recover the renovated water
The crop system
Typical Design Considerations and Performance Evaluation
Loading rates are highly variable depending on climate, crop grown (if
any), soil type, and system objective. Table 23-1 shows typical design cri-
teria. If crops are grown (low rate irrigation) and the soils, have a high
infiltration capacity, then high rate irrigation can. be practiced in the off
season. There are other special situations where loading rates would be ad-
justed; those shown cover the ranges to be expected.
The major concerns for operation of a land treatment system are adequate
application area, adequate storage for periods when application is not possi-
ble, and adequate equipment to apply water during available time period. These
three concerns are more critical for crop irrigation than the other systems
due to the need to harvest and replant the next crop. Therefore, the follow-
ing example calculations are set up for a crop growing system. ' -
23-2
-------
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23-3
-------
1. Application area requirement:
Given: a. Location - Minden, Nevada
b. Crop - alfalfa
c. Crop moisture requirement - 4 ft/yr^1) above natural
precipitation
d. Irrigation efficiency - 80%(2)
e. Effluent quantity - 5 mgd
Areaf acres = 5 mgd x 365 days/yr x 3.07 ac. ft./mil gal x 0.80
4 ft/yr
= 1120 acres
2. Storage requirement:
Given: a. Growing season - 180 days
Storage, mil gal - 365 - 180 daya/yr x 5 mgd
= 925 mil gal
3. Application equipment capacity:
Given: a. Maximum month - July
b. Maximum water consumption - 10 inches/month
c. Irrigation efficiency - 80%
d. Acreage under irrigation - 1120 acres
e. Percent operating time - 70% (allowance for changing
fields)
Equipment capacity, gpm s
10 in./mo x 1120 acres x 10** gal/mil gal
0.80 x 12 in/ft x 31 days/mo x 24 hr/day x 60 min/hr x 3.07 ac ft/mil gal
= 8513 gpm
Once the above values are determined, individual system limitations must
be applied to refine the above values. For example, the application area may
be adjusted if application can continue after the growing season is over. If
effluent application is continued then less area will be necessary. Also, the
system must be planned around crop planting and harvesting periods, including
crop drying prior to harvest.
Other design criteria, in addition to loading rates are related to ef-
fluent qualities and precautions necessary to prevent public health problems
or nuisance conditions from developing. These criteria are applied to the
adjunct facilities such as pretreatment, storage, and recovery of renovated
water. Pretreatment requirements vary among the states and with the intended
use of the crop grown (if any). Most areas require at least primary treatment
or secondary treatment by oxidation ponds or aerated lagoons. Some areas re-
quire higher secondary effluent quality.
(1)Ft/yr is used by irrigators meaning acre-feet/acre-year.
(2)percent of applied water available for crop use.
23-4
-------
Storage ponds may be lined depending on the soil type and proximity of
groundwater aquifers. Aeration systems should be provided. The magnitude of
the aeration requirement depends on the amount of pretreatment provided.
Storage ponds or reservoirs should be inspected as treatment ponds.
Recovery of renovated water is done by underdrains, recovery wells, and/or
tailwater return systems. Irrigation efficiency used earlier to determine
area requirements would be increased depending on the degree of renovated
water recovery. Irrigation efficiency is defined as the amount of water con-
sumed by the crop divided by the amount of water passing through the soil sur-
face. Thus, if all water passing through the root zone is recovered and
returned then more application area will be necessary.
Process Control
Operation of irrigation systems requires good crop management and proper
wastewater pretreatment. Personnel must have a working knowledge of farming
practices, and principles of wastewater treatment. Seasonal (often weekly)
changes in operation must respond to changing crop requirements for nutrients
and water; monitoring must be done to determine removal efficiencies and to
forecast buildups of toxic compounds; and the system must be continuously
watched to avoid problems of ponding, runoff, or mechanical breakdowns.
Close cooperation between the treatment system management and the farm
operation is always needed. Irrigation must be scheduled with farm operations
such as planting, tilling, spraying and harvesting, for successful operation.
Farm specialists can be helpful in setting up the management of the crops,
soil, and irrigation portions of the operation.
Proper cropping is also important for good nitrogen removal to prevent
pollution of groundwater. Nitrate nitrogen can be removed by growing and re-
moving from the area a crop which takes up nitrogen. Nitrogen removal by
crops is dependent on the length of growing season, crop type, and the avail-
ability of nitrogen.
Operation of infiltration-percolation systems is much simpler. Process
control consists of rotating areas to allow drying and access for discing
equipment. Areas should be allowed to dry out annually so the soil can be
broken up to prevent clogging.
Maintenance Considerations
Maintenance concerns mainly pumps and pipelines. A good maintenance pro-
gram should include the following:
1. Pre-startup inspection of all equipment.
2. Schedules set up to carry out manufacturers' recommendations for
maintenance of pumps, motors, valves, and sprinklers (if used).
23-5
-------
3. Lubrication program for regular oil changes, cleaning and flushing of
gear housing, removal and cleaning of oil pump strainers, checking of
oil seals for leaks.
4. Keeping maintenance records current.
5. Procedure for preparing equipment for winter shut down.
6. Farm equipment maintenance schedule.
7. Access road, dike, and/or levee maintenance program.
Records
Recommended sampling and laboratory tests are shown in Figure 23-1.
Other operating records should include:
1. Influent flow quantity (from storage)
2. Volume of water recovery from wells or drainage system
3. Frequency and duration of operation of pumps
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor land application:
1. Analytical balance
2. Blender
3. Fume hood
4. Incubator
5. Kjeldahl digesting and distilling apparatus
6. Oven
7. .pH meter
8. Pump (vacuum-pressure)
9. Spectrophotometer
10. Sterilizer
11. Titrator-araperometric
Sampling Procedures
Samples should be collected at points where the wastewater is well mixed
such as at the center of channels of flow where velocities are high. The
storage pond sampling should be done near the middle. Soil samples should be
taken at several locations so an average value may be determined and extremes
eliminated. Sample collectors and containers should be clean.
A wide mouth sample collector of at least 2 inches should be used for
wastewater samples. Where automatic samplers are used, it is important to
keep the sampler tubes clean.
23-6
-------
O
IU
a
o
OH1
BOD1
SUSPENDED
SOLIDS
NH3N2
ORG-N2
NO^-N2
TOTAL-P
ORTHO-P2
K
SOIL
CONDUCTIVITY
COLIFORM
DISSOLVED
SOLIDS
ALKALINITY
HEAVY METALS
BORON
IU
M
»
t-
Z 0
a
ATiTi
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ITEST I
FREQUENCY ]
/Tt
1/D
2/W
3/W
1/W
l/w
1/W
1/W
1/W
1/W
3
1/W
2/W
2/W
S
Q
LOCATION OF
SAMPLE 1
I
R
I
E
I
I
E
E
E
E
E
E
S
S
E
E
E
S
E
METHOD OF
SAMPLE
G
G
24C
24C
24C
24C
24C
24C
24C
R
G
24C
24C
24C
24C
1 REASON
FOR TEST
H
H
P
P
P
P
P
P
P
P
P
P
H
H
H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
LAND TREATMENT
PRETREATMENT
IRRIGATION
STORAGE
A.
TEST FREQUENCY
Q = QUARTERLY
S =SEMI ANNUAL
R = RECORD CONTINUOUSLY
Mrt= MONITOR CONTINUOUSLY
H• HOUR
D- DAY
W- WEEK
B. LOCATION OF SAMPLE
I - INFLUENT TO STORAGE POND
E = EFFLUENT FORM STORAGE POND
S=SOIL
C. METHOD OF SAMPLE
24C»24 HOUR COMPOSITE
C - GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn» MONITOR CONTINUOUSLY
0. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. THESE TESTS SHOULD ALSO BE RUN ON RECEIVING
WATER, ABOVE AND BELOW OUTFALL. ON A
PERIODIC BASIS, DEPENDING ON LOCAL CONDITIONS.
2.
FOR PLANTS DESIGNED TO CONTROL THIS
PARAMETER.
Figure 23-1
23-7
-------
Tensiometers or lysimeters are used to control application rates. Either
of these can be used with automatic controls to start or stop sprinklers for
precise control of irrigation.
Groundwater monitoring is variable depending on the local health agency
requirements. Generally speaking, pathogen bacteria, nitrates, and metals are
measured. Monitoring is accomplished by small wells located around or thor-
oughout the application site.
Sidestreams
The only sidestream with this process is recovered tailwater or pumped
drainage. This water can be discharged to surface streams if allowed or re-
cycled to the irrigation system. The volume will be 10-14% of the applied
effluent. The quality of the renovated water will lower the constituent con-
centrations except total dissolved solids. Depending on the geology of the
area certain soluble metals concentrations may increase in pumped sub-surface
drainage water.
23-8
-------
Process Checklist - Land Application
A.
B.
C.
D.
E.
P.
( ) Yes ( ) No
) Yes (' ) No
Pretreatment - see appropriate section elsewhere in this guide.
Storage
1. Is scum controlled? { ) Yes ( ) No
2. Are odors present? ( ) Yes ( ) No
3. Are levees free of excessive weed growth?
4. Are there indications of levee erosion? (
5. Are there planned programs for rodent and insect control?
{ ) Yes ( ) No
Pumping
1. Frequency of maintenance /Year
2. Is maintenance program adequate? ( ) Yes ( ) No
3. Is standby pumping provided? ( ) Yes ( ) No
Irrigation System
1. Do sprinklers clog frequently? ( ) Yes ( ) No
2. Does distribution piping allow flexibility to maintain operation in
one area while another is down? ( ) Yes ( ) No
3. Are flood irrigation levees maintained? ( ) Yes ( ) No
4. Are nuisance weed growths controlled? ( ) Yes ( ) No
5. Is there a planned procedure for off season shut down and following
season startup? ( ) Yes ( ) No
6. Do any areas appear to lack moisture? ( ) Yes ( ) No. Have
excess moisture? { ) Yes ( ) No
7. Is a rotation plan in effect for changing infiltration-percolation
cells? ( ) Yes ( ) No
Farming (If applicable)
Is farming done by agency staff and equipment?
( ) Yes ( ) No
2.
3.
4.
5.
6.
Is farming done by contract?
What are crops grown?
( ) Yes ( ) No
Are crops rotated periodically? ( ) Yes (
Are soils tested to check nutrient balances?
) No
( ) Yes
( ) No
Is fertilizer added?
How much
Overall
If so, what type
Yes ( ) No
1. Is a preventive maintenance plan in use? ( )
2. Is there a safety program? ( ) Yes ( ) No
3. Is there an emergency plan for power outages or major equipment
failure? ( ) Yes ( ) No
4. Does the sampling program meet recommendations? ( ) Yes ( )
5. Is an O&M manual available? { ) Yes { ) No
6. Is O&M manual used? ( ) Yes ( } No
7. Is laboratory properly equipped? ( ) Yes { ) No
8. What spare parts are stocked?
No
9. What are the most common problems the operator has had with the
process ?
23-9
-------
References
1. Gulp, G.L., and Polks Helm, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, us EPA
Report 430/9-78-001 (Jan. 1978). ,
2. CH2M-Hillf Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
3. Pound, C.E., et al, Costs of Wastewater Treatment by Land Application, US
EPA 430/9-75-003, June 1975.
23-10
-------
24. PLOW MEASUREMENT
Process Description
Flow measurement is necessary for good operation and control of a waste-
water treatment plant. Reasons for measuring flow of wastewater include:
1. To provide operating and performance data concerning the treatment
plant.
2. To compute costs of treatment, where such costs are based on waste-
water volume.
3. To obtain data for long term planning of treatment plant capacity
versus actual capacity used.
There are many methods of measuring flow, some for open channel flows and
others to measure flow in pipelines. The most commonly used flow measurement
devices are the propeller meter, the magnetic flow meter, the Venturi tube,
the positive displacement diaphragm meter, weirs, the Parshall flume, the
parabolic nozzle and the rotameter.
Typical Performance Evaluation
Since flow measuring devices are not for treating wastewater, this section
deals with performance in terms of accuracy of measurement. The normal accu-
racy for each meter previously described is shown below:
Type of flow meter
% Accuracy
Propeller meter
Magnetic meter
Below 3 fps
3 - 30 fps
Venturi tube
Plow tube
Positive displacement
and diaphragm meter
Weirs
Parshall flume
Kennison or parabolic nozzle
Rotameter
of actual flow rate over a range
of 7:1 for small meters and up to
12:1 for large meters
±2% of maximum scale reading
+1% of maximum scale reading
+3 to 4% of flow rate
+1% of flow rate
+1% of flow rate
4;5% of flow rate
HH5% of flow rate
+2% of flow rate over flow range of
10:1
+2% of maximum scale
24-1
-------
Maintenance Considerations
The features of a good maintenance program that the inspector should look
for are:
1. A thorough periodic inspection of the flow measuring device.
2. Floats and bubbler wells regularly checked for grease or debris build
up.
3. Weir plates regularly cleaned of foreign matter.
4. Regular schedule for calibration of the flow meter.
5. Recording devices properly maintained.
Records
Records should be kept for flows on a daily basis. Many devices produce a
continuous flow chart for plant records. Flow records should contain date,
flow/ time of reading and operator's name/ if applicable. Inspection dates
and calibration data should also be recorded.
24-2
-------
Process Checklist - Flow Measurement
1.
2.
What type of flow meter is used
What is the wastewater flow
What is the design flow
jngd?
mgd?
4. Frequency of routine inspection for proper operation
5. .......
6.
7.
8.
Frequency of maintenance inspections by plant personnel
Frequency of flow meter calibration /month?
Is maintenace program adequate? ( ) Yes ( ) No
./day?
/yr?
Are floats and bubbler wells clean and free of grease of debris?
( ) Yes ( ) No
9. Are weirs free of debris? ( ) Yes ( ) No
10. Are flow records properly kept? ( ) Yes ( ) No
11. Are sharp drops or increases in flow records accounted for?
( ) Yes ( ) No
12. Does the flow chart exhibit uniform flow? ( ) Yes ( ) No
13. Do any plant return flows discharge upstream from the meter?
( ) Yes ( ) No
14. Are recording devices properly maintained? ( ) Yes ( ) No
15. Does the meter show signs of oveload? { ) Yes ( ) No
16. Are spare parts stocked, if applicable? ( ) Yes ( ) No
17. What are the most common problems that the operator has had with the flow
meter? ; ——
24-3
-------
References
1. Gulp, G.L., and Folks Helm, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. State of Virginia O&M inspection form.
24-4
-------
25. SLUDGE PUMPING
Process Description
Sludge pumps have many uses in a municipal wastewater treatment plant.
Settled primary sludge must be moved regularly; activated sludge must be re-
turned continuously to aeration tanks, with the excess sludge wasted; scum
must be pumped to digestion tanks; and sludge must be recirculated and trans-
ferred within the plant in processes such as digestion, trickling filter oper-
ation, and final disposal. The type $f pumping station used at the plant de-
pends on the characteristics of the sludge itself.
Pumps used for handling sludges may be centrifugal, air lift and ejectors,
grinding, Archimedes screw lift, and positive displacement types.
Typical Performance Evaluation
Below is a listing of various types of sludge pumps, their capacities, and
delivered pressure. This table may be used as a general guide to evaluating
the performance of sludge pumps at a treatment plant. For a very precise
evaluation, the actual operating characteristics of the pump should be checked
against manufacturers' design data for the pump. Pumps cannot be expected to
operate beyond their designed capacity.
Type of pump
Capacity (gpm)
Delivered
pressure (psi)
Plunger pump
Rotary positive displacement
(progressing cavity pump)
Diaphragm
Sludge grinding pumps
(comminuting and pumping type)
Screw lift pump
up to 500
up to 400
up to 100
25 - 300
up to 80,000
100 - 150
up to 500
up to 100
Process Control
To be effective, sludge pumping systems must be flexible under different
plant operating conditions. The overall piping, valves, and pumping system
must be set up to allow bypassing and provide standby pumping capacity when
problems occur.
The most important control considerations are discussed in Reference 1.
25-1
-------
Maintenance Considerations
See Raw Sewage Pumping Stations and General Maintenance Management.
Records
Recommended records include:
1. Amount of sludge and scum pumped per day.
2. Frequency and duration of operation of sludge pumps.
3. Maintenance charts including date, type of work and operator.
4. Inspection records including date/ type of inspection and operator.
25-2
-------
Process Checklist - Sludge Pumping
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
What is the volume of sludge pumped
What types of sludge are pumped?
gal/day?
What is the design sludge pumping rate gal/day?
Is sludge pumping ( ) manual ( } automatic?
How often do sludge pumps run? ^
Frequency of maintenance inspections by plant personnel
Is maintenance program adequate? { ) Yes { ) No
Is there an alarm system for equipment failures or overloads?
( ) Yes ( ) No
Are operating records adequate? ( ) Yes ( ) No
What spare parts are stocked?
year?
11. What are the most common problems the operator has had with the system?
25-3
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
25-4
-------
26. CHEMICAL CONDITIONING
Process Description
The most frequently encountered conditioning practice is the use of ferric
chloride either alone or in combination with lime, although the use of poly-
mers is rapidly gaining widespread acceptance. Ferric chloride and lime are
normally used in combination, although it is not unusual for them to be ap-
plied individually. Lime alone is a fairly popular conditioner for raw pri-
mary sludge and ferric chloride alone has been used for conditioning activated
sludges. Lime treatment to a pH of 10.4 or above has the added advantage of
providing a significant degree (over 99 percent) of disinfection of the sludge
according to "Water Supply and Treatment", Bulletin 211, published by the
National Lime Association.
The popularity of polymers is primarily due to their ease in handling,
small storage space requirements, and their effectiveness. All of the inor-
ganic coagulants are difficult to handle and their corrosive nature can cause
maintenance problems in the storing, handling, and feeding systems in addition
to the safety hazards inherent in their handling. Many plants in the U.S.
have abandoned the use of inorganic coagulants in favor of polymers.
The facilities for chemical conditioning are relatively simple and consist
of equipment to store the chemical(s), feed the chemical(s) at controlled
dosages, place the chemical(s) in solution or slurry, and feed the solution to
the process.
The equipment used for storing and handling these chemicals varies with
the type of chemical used, liquid or dry form of the chemical, quantity of
chemical used, and plant size. Storage requirements vary, but typically may
be 15 to 30 days of use or 150 percent of the bulk transport capacity, which-
ever is greater.
Typical Design Considerations
Peed rates for chemical conditioning of sludges are extremely variable
depending on process used, nature of the sludge, and type of chemical. Typi-
cal range of dosages are as follows:
Raw primary + waste
activated sludge
Digested primary + waste
activated sludge
Elutriated primary + waste
activated sludge*
FeCl3,
lb/solids
40-50
80-100
40-125
Lime,
lb CaO/solids
110-300
160-370
Polymer, solids
15-20
30-40
20-30
*Elutriated sludge results from a process whereby the sludge is washed with
either fresh water or plant effluent to reduce the demand for conditioning
chemicals and to improve settling of filtering characteristics.
26-1
-------
Typical Performance Evaluation
The primary benefits of chemical conditioning of sludge are improved de-
watering and thickening characteristics and higher loading rates and more ef-
fective solids capture in subsequent unit processes. Because of vast differ-
ences in sludge characteristics, typical performance data varies widely from
plant to plant.
Process Control
If the feeders are automatically paced to flow, feed rate adjustments are
required only to compensate for varying dosage requirements. If the feeder is
not paced to flow the feed rate must be adjusted each time the plant flow rate
is changed. The lime slaker requires occasional adjustment for variations in
lime quality.
Maintenance Considerations
Proper and regular maintenance of the chemical feed system is critical to
the efficient and troublefree operation of the system. The features of a main-
tenance program that should insure these conditions are listed below.
1. Spare parts inventory should include at least one set of each type of
bearing, grease and water seals, one each of all gaskets, drive *
belts, isolation pads and springs, one feed pump head.
2. Build-up or spilling of material (chemicals) regularly cleaned off.
3. Visual inspection each shift of the chemical feeding equipment to
check for excessive noise, unequal loading if there is more than one
metering pump, chemical leakage, damage to storage tanks, raw mate-
rials, mixing tanks or metering pumps.
4. Records to determine the dose rate to the wastewater and also eval-
uate whether or not this value is changing with time. If the waste-
water characteristics remain the same, changing dosages could indi-
cate a problem with the chemical feed equipment.
5. Storage bins and conveyance systems checked regularly to insure
air-tightness.
6. Check the calibration of the pH probe each shift to insure the auto-
matic control system is operating correctly.
7. Daily inspection to check for plugged feed lines.
8. All chemical feed lines whether suction, discharge or lines conveying
solid or powered materials, flushed or blown out regularly to insure
against plugging and solids build-up.
26-2
-------
Records
The. chemical dosage required for any sludge is determined in the labora-
tory using the Buchner Funnel test, filter leaf test, or jar test. Operating
records should include:
1.
2.
3.
4.
5.
6.
Type of chemical used for conditioning.
Chemical dosage applied each day.
Type of sludge conditioned.
Sludge quantity conditioned each day.
Frequency and duration of operation of feed equipment or pumps.
Maintenance charts including date, type of work, and operator.
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor chemical sludge conditioning:
1. Analytical balance
2. Floe stirrer
3. Buchner funnel
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any
detailed questions.
Sampling Procedures
Samples used to determine the chemical dosage required for any sludge
should be collected from valves provided in the sludge transfer piping. The
sample collector and containers should be clean. A wide mouth sample col-
lector of at least 2 inches should be used.
Sidestrearns
The only sidestream from sludge conditioning is the dust associated with
the handling of bulk quantities of dry chemicals. To control dust problems,
vapor and dust collection systems are often used.
26-3
-------
Process Checklist - Chemical Conditioning
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
What is the volume of sludge conditioned
What is the design sludge volume
_gallons/day average?
gallons/day average?
What typ« of sludge is conditioned (primary, waste activated, combination,
other, etc.) ?
What type of chemical is used for conditioning (lime, ferric chloride,
combination, polymer, etc.) ?
What is the chemical dosage Ib/ton dry solids average?
or as a liquid_ ?
Are chemicals purchased dry
days?
manual?
) volumetric
or
What chemical storage volume is provided
Is chemical feed system ( ) automatic (
If dry feeders are used, are the feeders
( ) gravimetric?
Are chemical feeders automatically paced? ( ) Yes ( ) No
If lime is used, is lime purchased ( ) in bags ( ) bulk quantities?
If lime feeding is used, is a vapor and dust collection system installed?
( ) Yes ( ) No. Operating? ( ) Yes ( ) No
Does the unit show signs of inadequate mixing? ( ) Yes ( ) No
Is there an alarm system for equipment failures or overloads?
( ) Yes ( ) No
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory equipped for. the necessary analyses? ( ) Yes ( ) No
What spare parts are stocked?
18
. What are the most common problems the operator has had with the process?
26-4
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. State of Virginia O&M inspection form.
6. National Lime Association, Lime Handling, Application, and Storage,
Washington, D.C. 20016.
7. Ettlich, W.F., et al, Operations Manual - Sludge Handling and
Conditioning, US EPA Report 430/9-78-002.
26-5
-------
-------
27. THERMAL TREATMENT
Process Description
There are two basic processes for thermal treatment of sludges. One, wet
air oxidation, is the flameless oxidation of sludges at temperatures of 450 to
550°F and pressures of about 1200 psig. The other type, heat treatment, is
similar, but carried out at temperatures of 350 to 400°F and pressures of
150 to 300 psig. Wet air oxidation reduces the sludge to an ash and heat
treatment improves the dewaterability of the sludge. The lower temperature
and pressure heat treatment is more widely used than the oxidation process.
Thermal treatment systems release water that is bound within the cell
structure of the sludge and improves the dewatering and thickening character-
istics of the sludge. The oxidation process further reduces the sludge to ash
by wet incineration (oxidation). The process also provides effective disin-
fection of the sludge.
Typical Design Considerations
The most important parameter is the influent sludge flow rate (gpm). The
flow rate determines the detention time in the heat exchanger(s) which is
typically 30 to 60 minutes.
The influent solids concentration is also an important parameter. Many
plants operating in the 350-400°P range use a 3 percent sludge, however, 6
percent is more desirable because less steam is needed. An example calcula-
tion for percent solids is shown below:
Percent solids concentration = weight of dry sludge x 100
weight of wet sludge
= 0.6 Ib x 100 = 6%
10 Ib
Typical Performance Evaluation
The reduction in chemical oxygen demand (COD) of the sludge depends on the
degree of wet oxidation achieved by the process. The terms used to categorize
the degree of wet oxidation - low oxidation, intermediate oxidation, and high
oxidation - refer to the degree of reduction in the chemical oxidation demand
(COD) of the sludge. Higher temperatures are required to effect higher de-
grees of oxidation, and the higher temperatures, in turn, require the use of
correspondingly higher pressures in order to prevent flashing to steam or
burning.
The operating temperature, pressure ranges, and COD reduction for the
three oxidation categories are given below:
Oxidation category
Low
Intermediate
High
COD reduction, %
5
40
92-98
Temp.,°F
350-400
450
675
Pressure, psi
300-500
750
1,650
27-1
-------
Process Control
The extent and rate of sludge solids oxidation are determined by the re-
actor pressure and temperature. These and other process control considera-
tions are discussed in Reference 7.
Maintenance Considerations
The features of a good maintenance program for both components and system
are shown below:
1. Schedule for periodic cleaning of the heat treatment system.
2. Routine cleaning procedures available for the heat exchanger, the
reactorr and the oxidized sludge decant tank.
3. .Inspection schedule for piping to determine when a solvent wash is
necessary.
4. Instructions to the operator to indicate if cleaning is necessary be-
fore the scheduled time period. For example, the need for heat ex-
changer cleaning is indicated by an increasing temperature differen-
tial between the reactor inlet and outlet, and an increasing pressure
drop through the system.
5. Provisions for a thorough check for scale buildup inside the reactor
on an annual basis to determine if acid cleaning procedures are in-
effective.
6. Provisions for mechanical removal of the scale if acid cleaning pro-
cedures are ineffective in the reactor.
7. Annual pressure check to insure the integrity of the pressure piping
• and fittings.
Records
Recommended sampling and laboratory tests are shown in Figure 27-1.
Other operating records should include:
1. Influent sludge flow
2. Treated sludge flow
3. Frequency and duration of system operation.
4. COD of oxidized sludge decant.
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor thermal treatment:
27-2
-------
s
i
(9
_l
<
a
o
TOTAL SOLIDS
TEMPERATURE
pH
SUSPENDED
SOLIDS
BOD
FLOW
f
PLANT SIZE
(MGD)
ALL
ALL
ALL
ALL
ALL
ALL
TEST
FREQUENCY
3/D
Mn
1/D
l/D
2/W
R
a
LOCATION OF
SAMPLE
I
DU
R
D
D
D
D
METHOD OF
SAMPLE
G
Mn
G
G
G
R
REASON
FOR TEST
P
P
H
H
P1
P1
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
SOLIDS REDUCTION
THERMAL TREATMENT
(DEC,
HEAT
EXCHANGER-4
DECANT TANK-1
p
. .-REACTOR
DECANT RECYCLE
TO PLANT
INFLUENT
'
1C
STEAM
SLUDGE INFLUENT
FROM PREVIOUS
ORGANIC SLUDGE
TREATMENT PROCESS
UNDERFLOW SLUDGE
TO NEXT ORGANIC
SLUDGE TREATMENT
PROCESS
A. TEST FREQUENCY
H » HOUR M - MONTH
D. DAY R - RECORD CONTINUOUSLY
W- WEEK Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I - INFLUENT
D= DECANT
R= REACTOR (INCLUDE AS PROCESS TESTING)
DU= DECANT UNDERFLOW
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G " GRAB SAMPLE
R • RECORD CONTINUOUSLY
MB- MONITOR CONTINUOUSLY
D. REASON FOB TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. FOR CONTROL OF PROCESS RECEIVING THIS FLOW
Figure 27-1
27-3
-------
1. Analytical balance
2. pH meter
3. BOD incubator
4. Drying oven
5. COD apparatus
Sampling Procedures
The system should contain sample ports to aid in the collection process.
Before collecting the sample, the ports should be opened for several seconds
to purge the line. The sample collector and containers should be clean.
Samples collected from the decant tank should be taken near the discharge
point so that any short circuiting does not influence the results. Where
automatic samplers are used, it is important to keep the sampler tubes clean.
Sideatreams
Two sidestreams, process off-gas and recycle liquor, require careful con-
sideration when operating heat treatment systems. The system off-gas can
cause odor problems if not handled properly. Treatment may include installa-
tion of deodorizing equipment, piping gases back to diffused system or piping
gases to an existing sludge incinerator.
The recycle liquor can be very difficult to treat, offensive smelling, and
can upset plant treatment processes. Typical recycle liquor characteristics
are as follows.
Substances in
strong liquor
TSS
COD
BOD
NH3-N
Phosphorus
Color
Concentration range,
mg/1 (except as shown)
100 - 20,000
100 - 17,000
3,000 - 15,000
400 - 1,700
20 - 150
1,000 - 6,000 units
These high concentrations illustrate the potential impact that recycle of
the liquor can have on the wastewater treatment processes. It is important to
recognize the significance of the recycle load in the management of the over-
all plant operation.
27-4
-------
Process Checklist - Thermal Treatment
1.
What is the influent sludge flow
temperature
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
What is the design sludge flow
temperature
i gpm? What is the operating
°F? What is the operating pressure Ib/sq in?
gpm? What is the design
°P? What is the design pressure Ib/sq in?
_gal/day?
What is the influent sludge solids concentration
What is the volume of the treated sludge
What is the recycle liquor flow gal/day?
What is the solids concentration of the treated sludge
What is the BOD of the recycle liquor _mg/l?
What is the COD of the recycle liquor mg/1?
What is the suspended solids concentration of the recycle liquor?
How is the recycle or decant liquor treated
Does treatment of the recycle liquor upset the plant? {
How are the off-gases handled ^
) Yes ( ) No
) No
_hr/day?
Are excessive odors present from off-gases? ( ) Yes (
What is the duration and frequency of system operation
Frequency of acid wash /year
Frequency of general maintenance inspections /year?
Frequency of scale buildup inspection: Heat exchanger /year
Reactor /year, Piping • /year, Oxidized sludge
decant tank
_/year
_/year, Other component
Frequency of system pressure check to insure integrity of pressure piping
and fittings /year
Is hhe maintenance program adequate? { ) Yes ( ) No
If multiple units are used, is the flow distributed evenly?
( ) Yes ( ) No
Are proper safety precautions used for handling acid? ( )
Yes (
Electrical ( ) Yes { ) No; Exposure to gases ( ) Yes
High temperatures ( ) Yes ( ) No; High pressures ( )
Mechanical equipment ( ) Yes ( ) No
Are State and Federal safety codes followed? ( ) Yes (
Does the unit show signs of overload? ( ) Yes ( ) No
Is there an alarm system for equipment failures or overloads?
( ) Yes ( ) No
Does the sampling program meet the recommendations? {
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory equipped for the necessary analyses?
What spare parts are stocked?
Yes
) No
)
No;
( )
No;
No;
) Yes ( } No
( ) Yes ( ) No
29. What are the most common problems the operator has had with the process?
27-5
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities/ EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Culp/Wesner/Culp Operation and Maintenance Manual, Water Factory 21,
Orange County Water District, (June, 1974).
6. Gulp, R.L., et al, Effects of Thermal Treatment of Sludge on Municipal
Wastewater Treatment Costs EPA Contract 68-03-2186.
7. Ettlich, W.F., et al, Operations Manual - Sludge Handling and
Conditioning, OS EPA Report 430/9-78-002.
27-6
-------
28. GRAVITY THICKENING
Process Description
Gravity thickening is the most common sludge-concentration process used in
the United States. Gravity thickening is a sedimentation process similar to
primary and secondary sedimentation. The objective of sludge thickening is to
produce as thick a sludge as possible at minimum cost. Chemicals may be used
to aid the gravity thickening process.
Solids settle by gravity to the bottom of the basin forming a sludge
blanket with a clearer liquid (supernatant) above. The supernatant is removed
from the basin over weirs located near the top of the tank at the outside
edge. Thickening takes place as the sludge particles move to the bottom of
the tank and the water moves toward the top. As the drive unit turns the
mechanism the blanket is gently stirred, which helps compact the sludge solids
and release water from the mass. Sludge solids are scraped toward a center
well and withdrawn.
Typical Design Considerations
Gravity thickeners are designed based on surface overflow rate (hydraulic
loading) and solids loadings. The principles that apply are the same as those
used in designing sedimentation tanks. Typically, a proposed design is checked
for both overflow rate and solids loading and the final selection is based on
a thickener design that will meet both of the design considerations.
The surface overflow rate is expressed in terms of gallons per day per
square foot of surface area of the tank. The overflow rate is calculated as
shown in the following example.
1. Determine thickener shape and dimensions. The plant construction
drawings and specifications include this information.
Shape = circular
Diameter, dia =30 ft
Depth, D = 10 ft
Thickener area, A = (ir/4)dia2 » 707 sq ft
2. Determine total sludge flow influent to thickener and influent sludge
and thickened sludge solids concentrations and calculate total over-
flow volume.
Influent flow = 700,000 gallons per day (gpd)
Influent solids, % = 5
Thickened solids, % = 10
Overflow volume = Influent flow ( 1 - Influent solids )
Thickened solids
= 700, 000. ( 1 - 5/10)
- 350,000 gpd
3. Calculate surface overflow rate for thickener.
Overflow rate = flow in gal/day
surface area in sq ft
= 350,000
707
= 495 gpd/sq ft
28-1
-------
The solids loading rate is expressed in terms of pounds per day of solids
per square foot of surface area of the tank. The solids loading rate is cal-
culated as shown in the following example.
1. Thickener area = 500 sq ft
2. Determine total pounds per day of solids applied to the thickener.
Sludge flow = 30,000 gpd
Solids concentration = 1.0 percent solids
Total solids, Ib/day - 30,000 gal/day x 8.34 Ib/gal x 0.01
= 2,502 Ib/day
3. Calculate solids loading rate for thickener.
Solids loading rate = 2,502 Ib/day = 5.0 Ib/sq ft/day
500 sq ft
Current practice in the United States calls for design overflow rates of
400 to 800 gpd per square foot. The design solids loadings will vary with the
type of sludge and typical loadings are shown in Table 28-1. This table was
developed from information in "Process Design Manual for Sludge Treatment and
Disposal", EPA 625/1-74-006, October, 1974.
TABLE 28-1. GRAVITY THICKENER TYPICAL LOADINGS AND PERFORMANCE
Influent solids Typical solids Thickened sludge
concentration, loading rate, concentration,
Sludge type percent Ib/scr ft/dav percent
Raw primary
Raw primary + FeCl3
Raw primary + low lime
Raw primary + high lime
Raw primary -f WAS*
Raw primary + (WAS + FeCl3)
(Raw primary + FeCl3) + WAS
Digested primary
Digested primary + WAS
Digested primary + (WAS +
PeCl3)
WAS
Trickling filter
5.0
2.0
5.0
7.5
2.0
1.5
1.8
8.0
4.0
4.0
1.0
1.0
20-30
6
20
25
6-10
6
6
25
15
15
5-6
8-10
8.0-10
4.0
7.0
12.0
4.0
3.0
3.6
12.0
8.0
6.0
2-3
7-0
*WAS
Waste activated sludge
Typical Performance Evaluation
Expected thickener performance, in terms of thickened sludge concentra-
tion, is also given in Table 28-1. Gravity thickening should remove 90 per-
cent of the solids in the feed to the thickener as an average.
28-2
-------
Process Control
Typically the flow through the thickener is continuous and should be set
for as constant a rate as possible.
The drive mechanism normally turns continuously and contains a torque mon-
itor which will shut down the drive and sound an alarm if the drive mechanism
is overloaded.
A review of Table 28-2 will show that for many sludges the thickened
sludge is only 2 or 3 times the concentration of the influent sludge. In
order to maintain the thickener solids balance, the thickened sludge flow rate
for these cases must be 30 to 50 percent of the influent flow. In most cases
it will be advantageous to draw off thickened sludge continuously at a flow
rate approximately equal tos
Thickened sludge = Influent
flow rate, gpm flow, gpm
Influent solids, %
Thickened solids, %
It is important to maintain an adequate thickened sludge flow rate or
sludge will accumulate very rapidly in the thickener.
Maintenance Considerations
The features of a good maintenance program are the same as Sedimentation
Maintenance and as described for General Maintenance Management.
Records
Recommended sampling and laboratory tests are shown in Figure 28-1.
Other operating records should include:
1. Amount of sludge and scum pumped per day.
2. Amount of thickened sludge pumped per day.
3. Frequency and duration of operation of sludge pumps.
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor gravity thickenings
1. Analytical balance
2. Clinical centrifuge with graduated tubes
3. BOD incubator
4. Drying oven
5. Imhoff Cones
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any de-
tailed questions.
28-3
-------
O
o.
o
TOTAL SOLIDS
SUSPENDED
SOLIDS
BOD
FLOW
u
N
Z?
31
o- C.
ALL
ALL
ALL
ALL
TEST
FREQUENCY
VD
1/D
2/W
R
LOCATION OF
SAMPLE
TS
SI
SO
su
su
METHOD OF
SAMPLE
G
G
G
R
H-
2s
s^-
< 0£
UJ O
cc u.
p
c
p
P1
P1
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
SLUDGE CONCENTRATION
GRAVITY THICKENER
SUPERNATANT RECYCLE
TO PLANT
INFLUENT 7 3
SU
F SLUDGE INFLUENT
FROM PREVIOUS
SLUDGE TREATMENT
PROCESS
THICKENED SLUDGE
TO NEXT SLUDGE
TREATMENT PROCESS
A. TEST FREQUENCY
H m HOUR
0- DAY
W- WBBK
M - MONTH
R - RECORD CONTINUOUSLY
MB- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
SI =SLUDGE INFLUENT
TS = THICKENED SLUDGE
SU = SUPERNATANT
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G - GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn. MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. FOR CONTROL OF PROCESS RECEIVING THIS FLOW
Figure 28-1
28-4
-------
Sampling Procedures
Sampling should be performed as outlined under Records. These samples may
be obtained through valves provided in the respective thickener piping. If
sampling points are not provided, they should be installed to facilitiate
operation and control of the process. Samples of the supernatant can be
obtained at the overflow weir. The sample collector and containers should be
clean. A wide mouth sample collector of at least 2 inches should be used.
Where automatic samplers are used, it is important to keep the sampler tubes
clean.
Sidestreams
The only sidestreara from the gravity thickening process is the thickener
supernatant. Thickener supernatant is usually returned to either the primary
or the secondary treatment process and normally causes no problem to process
operation. The respective treatment process must be sized to treat the super-
natant flow and organic loading in addition to normal plant flow.
28-5
-------
Process Checklist - Gravity Thickening
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
What type of sludges ace fed to the thickener (primacy, waste activated,
combination, etc.) ?
What is the volume of influent sludge flow
What is the design influent flow
_gal/day avg?
_gal/day avg?
What are the dimensions of the thickener ?
How much thickened sludge is pumped gal/day avg?
What is the solids concentration in the influent sludge %?
What is the solids loading rate pounds/day/sq ft?
What is the solids concentration in the thickened sludge %?
What is the settleable solids concentration in the supernatant
ml/1?
Is influent sludge feeding intermittent or continuous
Is thickened sludge pumping ( ) manual ( ) automatic?
How often do thickened sludge pumps run minutes/hour?
Frequency of maintenance inspections by plant personnel /year?
Is maintenance program adequate? ( ) Yes ( ) No
How much downtime is there days/yeac?
What is the frequency of cleaning /year?
Does the influent baffle system accomplish its purpose? (" ) Yes
) Yes (
( )
) No
) Yes ( ) No
No
) Yes ( ) No
( ) No
Is the sludge collection system operating properly? (
Does the sludge collection system show any signs of mechanical failure?
( ) Yes ( ) No
Does the tank surface indicate improper sludge withdrawal? (i.e.
excessive floating solids, gas. . .)
Does the effluent baffle system accomplish its purpose? (
Ace the effluent weirs level? ( ) Yes ( ) _ No
Are surfaces and the effluent weirs kept clean? ( ) Yes
If multiple units are used, is the flow distributed evenly?
( ) Yes ( ) No
Does the unit show signs of short circuiting and/or overloads?
( ) Yes ( ) No
Is there an alarm system for equipment failures or overloads?
( ) Yes ( ) No
Does the sampling program meet the recommendations? (
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory equipped for the necessary analyses? ( ) Yes ( )No
What spare parts are stocked?
31. What are the most common problems the operator has had with the process?
28-6
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. State of Virginia O&M inspection form.
6. Ettlich, W.F., et al, Operations Manual - Sludge Handling and
Conditioning, US EPA Report 430/9-78-002.
28-7
-------
-------
29. FLOTATION THICKENING
Process Description
Sludge thickening by flotation is a process effective for light sludges.
This process causes the sludge to float so it can be skimmed from the surface
of the thickener. Flotation is especially effective on activated sludge which
is difficult to thicken by gravity because of its low specific gravity. Air
is injected into the incoming sludge under pressure. The sludge then flows
into an open tank where, at atmospheric pressure/ much of the air comes out of
solution as minute air bubbles. These bubbles attach to sludge particles,
floating them to the surface. A sludge layer 8 to 24 inches thick forms on
the surface of the tank and can be removed by a skimming mechanism for further
processing. Flotation aids such as polymers can be used to increase perform-
ance. If polymer is used the optimal chemical dosage for the feed sludge
should be determined at the start of each shift using jar test procedures.
Typical Design Considerations
Flotation thickeners are typically designed based on solids loading, over-
flow rate, and influent solids concentration. Typical design and operating
parameters are given in Table 29-1.
The solids loading rate is expressed in terms of pounds per hour of dry
solids per square foot of surface area of the tank. The solids loading rate
is calculated in the following example.
1. Determine the surface area of flotation thickener. The plant con-
struction drawings and specifications should include this information.
Area - 168 sq ft
2. Determine total pounds per day of solids applied to the thickener.
Sludge flow = 150,000 gallons/day
Sludge concentration = 1.0 percent solids
Total solids, Ib/day = 150,000 gal x 8.34 Ib x 0.01
day gal
=» 12,510 Ib/day
3. Calculate solids loading rate for thickener.
Total solids = 12,510 Ib/day x 1 day/24 hours = 521 Ib/hour
Solids loading rate = 521 Ib/hr * 3.1 Ib/sq ft/hour
168 sq ft
Solids loading often is designed at 2 Ib/hr/sq ft. This rate is possible
using flotation aids, with or without auxiliary recycle. Many flotation
thickeners are operated at 3.0 Ib/hr/sq ft, although built-in capacities of
4.0-5.0 Ib/hr/sq ft are common and provide flexibility in operation. There
are times when flotation can be done without flotation aids, and auxiliary
recycle is used instead. Without flotation aids, loading rates are about 50
percent and solids removal may be less.
29-1
-------
TABLE 29-1. FLOTATION THICKENER OPERATION AND PERFORMANCE
Operation parameter
Range
Typical
2
1
5,000 min
0.03
Solids loading, Ib dry solids/hr/sq ft
of surface
With chemicals 2 to 5
Without chemicals 1 to 2
Influent solids concentration, mg/1 5,000 min
Air to solids ratio 0.02-0.04
Blanket thickenss, in 8-24
Retention tank pressure, psi 60-70
Recycle ration, % of influent flow 30-150
Expected Performance
Float solids concentration, %
Solids removal, %
With flotation aid
Without flotation aid
3-7
95
50-80
Typical maximum hydraulic loading or overflow rate is 0.80 gpra/sq ft at
minimum solids concentration of 5,000 mg/1. Lower solids levels or higher
hydraulic loadings result in lower efficiencies and/or float solids
concentrations.
Another operating parameter included in Table 29-1 is the air to solids
ratio. The air to solids ratio is the ratio of air feed to dry Sludge solids
feed by weight. The weight of air is 0.08 times the flow rate in standard cu
ft per rain.
Ratio 3 (0.08) (Air flow, cfml
Influent dry solids, Ib
Typical Performance Evaluation
Expected thickener performance, in terms of typical float solids concen-
tration and percent solids removal, is shown in Table 29-1.
A 4 percent minimum float solids concentration by weight is normally used
for design purposes. However, a 5-6 percent float solids concentration can be
29-2
-------
expected. Flotation without chemical aids usually results in a solids concen-
tration that is about 1 percent less than with flotation aids. Using flota-
tion, at least 95 percent of suspended solids can be removed with flotation
aids, and 50-80 percent without flotation aids.
Process Control
Typically the flow through the thickener is continuous and should be set
for as constant a rate as possible. Process controls are discussed in some
detail in References 1 and 6.
Maintenance Management
The features of a good maintenance program are:
1. Major elements been inspected semi-annually for wear corrosion, and
proper adjustment.
a) Drives and gear reducers
b) Chains and sprockets
c) Guide rails
d) Shaft bearings and bores
e) Bearing brackets
f) Baffle boards
g) Flights and skimming units
2. Mechanical check made on the following units at two hour intervals.
a) Pumps: chemical feed, recycle, reaeration, and sludge sumps
b) Air manometer operation
c) Retention tank pressure
d) Sludge pit mixers
4.
5.
Retention tank inspected on a regular basis for excessive corrosion.
Chain tension (in rectangular basins) been adjusted properly so that
there is no chattering sound.
Spare part inventory should contain the following: flights and drive
chains for rectangular basins, turntable gears and motors for circu-
lar basins, wear shoes, sprockets, wall brackets, chain pins, and
shear pins.
Records
Recommended sampling and laboratory tests are shown in Figure 29-1.
Other operating records should include:
1. Amount of recycle flow pumped per day.
2. Amount of thickened sludge pumped per day.
3. Frequency and duration of operation of sludge pumps.
4. Amount of polymer or other flotation aid fed each day.
29-3
-------
I
z
o
Ul
o
§
-------
Laboratory Equipment ..; ,
The laboratory should include the following minimum equipment in order to
monitor flotation thickening.
1. Analytical balance
2. BOD incubator
3. Drying oven
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chem-
icals, miscellaneous furniture, etc., and should be referred to for any de-
tailed questions.
Sampling Procedures
Sampling should be performed as outlined under Records. These samples may
be obtained through valves provided in the respective thickener piping. If
sampling points are not provided, they should be installed to facilitate oper-
ation and control of the process. Samples of the supernatant can be obtained
at the overflow weir.
The sample collector and containers should be clean. A wide mouth, sample
collector of at least 2- inches should be used. Samples should be analyzed
according to procedures specified in Standard Methods and, in addition, should
be visually analyzed.
5idestrearns
The only sidestream from flotation thickening process is the thickener
subnatant. A portion of the subnatant flow is recycled back to the flotation
unit, while the remainder is usually returned to either the primary or the
secondary treatment process.
29-5
-------
Process Checklist - Flotation Thickening
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
How many air flotation thickening units are there ?
What are the dimensions of the thickener(s) ?
Are the flotation tanks ( ) circular ( ) rectangular?
What type of sludge is fed to the thickener (waste activated, other bio-
logical, etc.) ___?
gal/day avg?
What is the volume of influent sludge flow
What is the design influent flow
How much thickened sludge is pumped
What is the solids concentration in the influent sludge
What is the solids loading rate Ib/hour/sq ft?
What is the air to solids ratio ?
_gal/day avg?
_gallons/day?
What is the hydraulic loading or overflow rate
What is the solids concentration in the thickened sludge
What is the suspended solids concentration in the subnatant
What is the solids removal efficiency %?
Are flotation aids used?
jgpm/sq ft?
rag/1?
( ) Yes ( ) No.
What is the average dosage of flotation aid
What type
_lb/ton dry solids
inches?
What is the thickness of the floating sludge blanket
Is influent sludge feeding ( ) intermittent ( ) continuous?
What is the effluent recycle ratio (percent of influent flow) ?
Are primary and secondary effluent readily available for auxiliary
recycle? ( ) Yes (- ) No
Is thickened sludge pumping ( ) manual ( ) automatic?
How often do thickened sludge pumps run minutes/hour?
Frequency of maintenance inspections by plant personnel /year?
Is maintenance program adequate? ( ) Yes ( ) No
How much down time is there _days/year?
What is the frequency of cleaning _/year?
Does the influent baffle system accomplish its purpose? ( ) Yes ( ) No
Is the skimmer blade sludge removal system operating properly?
( ) Yes ( ) No
Is the bottom sludge collection system operating properly?
( ) Yes ( ) No
Does the sludge collection system show any signs of mechanical failure?
( ) Yes ( ) No
Does the effluent baffle system accomplish its purpose? ( ) Yes ( ) No
Are the effluent weirs level? ( ) Yes ( ) No
Are surfaces and the effluent weirs kept clean? ( ) Yes ( ) No
If multiple units are used, is the flow distributed evenly?
( ) Yes ( ) No
Does the unit show signs of short circuiting and/or overloads?
( ) Yes ( ) No
Is there an alarm system for equipment failures or overloads?
( ) Yes ( ) No
Does the sampling program meet the recommendations? ( ) Yes ( ) No
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory equipped for the necessary analyses? ( ) Yes ( ) No
29-6
-------
40. What spare parts are stocked?
41. What are the most common problems the operator has had with the process?
29-7
-------
References
1. Gulp, G.L., and Polks Helm, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.P., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice Ho. 1,
Water Pollution Control Federation (1959).
5. State of Virginia O&M inspection form.
6. Ettlich, W.F., et al. Operations Manual - Sludge Handling and
Conditioning, US EPA Report 430/9-78-001.
7. Harrison, J.R., Goodson, J.B., and Gulp, G.L., Process Design Manual for
Sludge Treatment and Disposal. US EPA 625/1-74/006.
29-8
-------
30. ANAEROBIC DIGESTION
Process Description
EPA has published "Operations Manual - Anaerobic Sludge Digestion" (EPA
430/9-76-001) which provides very detailed information on the process and
troubleshooting. This manual should be read for more complete information
than given here. In anaerobic digestion, the organic matter in the sludge is
broken down without oxygen. In low rate digestion, one digester is used.
Fresh sludge is fed into it two or three times daily. As decomposition
occurs, three separate layers form. A scum layer is formed at the top of the
digester, and below it are supernatant and sludge layers. The sludge zone has
an actively decomposing upper layer and a relatively stabilized bottom layer.
The stabilized sludge settles at the base of the digester and supernatant is
usually returned to the plant influent. Most modern systems are "high rate"
systems utilizing one or two stages. The sludge stabilizes in the first
stage, while the second stage provides settling and thickening. In a single-
stage system, the secondary digester is replaced by some other thickening
process.
The process converts about 50 percent of the organic solids to liquid and
gas, greatly reducing the amount of sludge to be disposed. About two-thirds
of the gas produced in the process is methane. Overall the gas has a heat
value of approximately 600 BTU/standard cubic foot (scf). About 15 scf of gas
is formed per pound of volatile solids destroyed. Anaerobic digester gas has
been used in wastewater treatment plants for many years to heat digesters and
buildings and as fuel for engines that drive pumps, air blowers and electrical
generators.
Typical Design Considerations
The most important design factor is the organic loading rate, calculated
as the pounds of volatile solids fed per day per cubic foot of active digester
volume. Sample calculations are as follows:
= 8000 Ib/day
= 70 percent
= 50,000 cu ft
= 50 feet
* 8000 x .7
= 5600 Ib/day
5600 = 0.11 Ib VS/cu ft/day
1. Raw sludge feed
Volatile solids content
Original digesters volume
Diameter
2. .Amount of volatile solids
3. Original organic loading =
50,000
4. Assume the digester has a scum blanket of 5 feet and a grit layer of
3 feet. This reduces the volume of the digester:
Volume reduction = Depth x (Diameter)^ x 3.14
4
= 8 x 2500 x 3.14
4
= 15,700 cu ft
30-1
-------
Usable volume
Actual organic loading
= Original volume - volume reduction
- 50,000 - 15,700
« 34,300 cu ft
= Amount of volatile solids
Usable volume
= 5600
34,300
= 0.16 Ib VS/cu ft/day
The increase in the original organic loading of 0.11 Ib VS/cu ft/day to
0.16 Ib VS/cu ft/day due to a heavy scum layer and grit buildup may cause more
frequent upsets and make the digester harder to operate.
Another important factor is the hydraulic loading rate. This is the aver-
age time in days that the liquid stays in the digester and is related to di-
gester capacity. This is calculated as follows:
1. Determine digester volume and feed volume
Digester volume
Feed volume =
Calculate hydraulic loading
Hydraulic loading »
50,000 cu ft x 7.48 gal
cu ft
374,000 gal
19,100 gal/day
Digester volume
Feed volume
- 374,000
19,100
= 19.6 days
Typical design criteria for loading rates are as follows:
Parameter
Solids loading, Ib VS/cu ft/day
Hydraulic loading, days
Low rate digester
0.04-0.1
30-60
High rate
0.15-0.40
10-20
Typical Performance Evaluation
Digester performance is usually expressed as percent reduction in volatile
solids or as volume of digester gas produced per pound of volatile solids des-
troyed. Typical values are shown below:
Parameter
Volatile solids, reduction %
Digester gas production,
cu ft/lb VS destroyed
Performance Range
40-60%
13-18
30-2
-------
Process Control
Proper control of anaerobic sludge digestion is based on:
Food supply
Time and temperature
Mixing
pH and alkalinity
Gas production
These factors are discussed in Reference 1.
Maintenance Considerations
The features of a good maintenance program are:
1. Daily check of the sludge pumping system including motors, pumps,
packing, suction, meters and clocks.
2. Daily check of boiler and heat exchanger operation, temperature and
pressures.
3. Daily check of digesters including mixing devices, covers, and gas
collection devices.
4. Regular inspections of:
(a) gas safety devices
(b) gas piping system, compressors and scrubbers
(c) water seals
(d) manometers
(e) digester structure and heat transfer system
(f) scum blanket build-up
(g) equipment lubrication
5. Digester soundings performed semi-annually to determine volume reduc-
tion from accumulation of solids and to determined temperature
profile.
6. Safety equipment such as flame traps, vacuum breakers, waste gas
burners, condensate traps, pressure relief valves, and combustible
gas detection alarms properly maintained.
7. Instrumentation regularly inspected and calibrated.
Records
Recommended sampling and laboratory tests are shown on Figures 30-1 and
30-2.
Other operating records should include
1. Production rates of 014 and CC>2 gases
Influent sludge flow
2.
3.
4.
Grit depth
Depth of scum layer
30-3
-------
Q
tu
a
Q.
O
TEMPERATURE
PH
ALKALINITY
VOLATILE
ACIDS
TOTAL SOLIDS
•jLUXALi
W&P*
rOTAJj
fflHH1"
3 AS
3REASE
UJ
Isl
«/»
(-
Z Q
21
ALL
ALL
ALL
ALL
ALL
ALL
ALL
>5
ALL
TEST
FREQUENCY
Mn
1/D
1/D
3/W
1/W
1/W
2 A?
1/W
1/M
LOCATION OF
SAMPLE
P
P
P
P
P
P
I
G
I
P
METHOD OF
SAMPLE
Mn
G
G
G
G
G
G
G
G
i-
Z"
8»-
< a:
uj o
0£ U.
P
P
P
P
P
P
P
P
P
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
SOLIDS REDUCTION
ANAEROBIC DIGESTION - PRIMARY
1
/
r ^^^^1
^-GAS TO
STORAGE OR
BURN
INFLUENT ~~**~*~~ 1
SLUDGE V. DIGESTED SLUDGE
TO SECONDARY
DIGESTER
A. TEST FREQUENCY
H m HOUR M - MONTH
D-DAY R - RECORD CONTINUOUSLY
w-WEEK M«- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I =INFLUENT
P = PROCESS
G = GAS (INCLUDE WITH PROCESS TESTING)
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G » GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
Figure 30-1
30-4
-------
O
u
(9
ui
1
a
o
pH
TOTAL SOLIDS
TOTAL
VOLATILE
spr,ms
BOD
SUSPENDED
SOLIDS
FLOW
UJ
N
7>
t-
z o
5?
ALL
ALL
ALL
ALL
ALL
ALL
EST
=REQUENCY
Mn
2
2
1/W
1/W
R
-OCATION OF
AMPLE
s1
u
n
S
S
s
METHOD OF
AMPLE
Mn
G
a
G
G
R
*£
S1-
< a:
uj O
P
H
IT
P3
H
P3
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
SOLIDS REDUCTION
r SUPERNATANT
RECYCLE TO
PLANT -X
INFLUENT J
rs
ANAEROBIC DIGESTION -SECONDARY
-GAS HOLDER
(FOR GAS STORAGE)
•INFLUENT SLUDGE
FROM PRIMARY
DIGESTER
• SLUDGE UNDERFLOW
TO NEXT ORGANIC .
SLUDGE TREATMENT
PROCESS
A. TEST FREQUENCY
H m HOUR M - MONTH
D-DAY R - RECORD CONTINUOUSLY
W- WEEK Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
U= UNDERFLOW
S = SUPERNATANT
C. METHOD OF SAMPLE
24C- 24 HOUR COMPOSITE
G - GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn. MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. IN DIGESTER (INCLUDE WITH PROCESS TESTING)
2. WHEN SLUDGE IS DRAWN OFF
3. FOR CONTROL OF PROCESS RECEIVING THIS FLOW
Figure 30-2
30-5
-------
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor anaerobic digestion:
1. Analytical balance
2. Clinical centrifuge with graduated tubes
3. BOD incubator
4. Drying oven
5. Irahoff cones
6. Graduated cylinders
7. Burettes
8. pH meter
9. Crucibles
10. Vacuum source
11. Muffle furnace, 550°C
12. Evaporating dish
13. Bunsen burner
Sampling Procedures
Samples should be collected at- points where good mixing occurs. Sample
ports should be allowed to run for a few moments to purge the line before
sampling. Always run pH and temperature tests within 10 minutes to avoid
deterioration. The remainder of the sample should be refrigerated if the
other tests are not run immediately, when storing a sludge sample in a re-
frigerator/ it is a good idea to use a plastic wrap over the jar with a rubber
band to hold it in place. This will allow any gases that might collect in the
sample to expand without bursting the jar. The sample container should be
cleaned thoroughly before and after each use.
Sidestreams
Supernatant is returned to the head of the plant; however, this recycle
stream may greatly increase the BOD, SS, and ammonia nitrogen loading on the
plant. Table 30-1 presents typical digester supernatant quality data.
TABLE 30-1. DIGESTER SUPERNATANT QUALITY
Primary plants
(mg/1)
Trickling filters*
(mg/1)
Activated
sludge plants*
(rag/1)
Suspended solids
BOD
COD
Ammonia as NH_
Total phosphorus
200-1
500-3
1,000-5
300-
as P 50-
,000
,000
,000
400
200
500- 5
500- 5
2,000-10
400-
100-
,000
,000
,000
600
300
5,0000-15
1,000-10
3,000-30
500- 1
300- 1
,000
,000
,000
,000
,000
* Includes primary sludge.
30-6
-------
Process Checklist - Anaerobic Digesters
1. What is the type of digester?
High rate
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
Low rate
secondary tanks
What type of sludge is digested?
What type of covers are used? (
What is the digester volume
primary tank
primary and
) fixed (
) floating ( )
cu ft?
none
gal/day?
%?
What is the volume of the influent sludge
What is the design influent flow
What is the influent solids concentration
What is the volatile solids content of the influent sludge
What is the design volatile solids loading
What is the frequency and duration of the sludge feed pumping?
What is the depth of the scum blanket ft?
What is the depth of the grit layer
gal/day?
Ib/cu ft/day?
ft?
What is the active capacity of the digester
What is the actual volatile solids loading
What is the hydraulic loading days?
cu ft?
Ib/cu ft/day?
What is the gas production rate
What is the average C02 content of the gas
What is the average CH4 (methane) content of the gas_
What 'is the average reduction in volatile solids
What type of mixing .is used in the primary tank?
What are the heating provisions?
cu ft/lb VS destroyed?
What is the solids concentration of the sludge withdrawn from the
digester %?
What is the average pH of the digester ?
What is the average temperature °F?
What is the average alkalinity rag/1?
What is the average volatile acids content
mg/1?
At what point in the plant flow is the supernatant returned?
Is treatment of the supernatant provided before return to the plant?
( ) Yes ( ) No
Are there metering provisions for return of supernatant?
( ) Yes { ) No
What is the average return flow of the supernatant gal/day?
What is the average BOD of the supernatant
mg/1?
What is the average suspended solids content in the supernatant
Frequency of maintenance inspection by plant personnel for:
sludge pumping /year; digesters and mixing equipment
/year; safety devices
No
jng/1
gas collection/storage equipment
Is maintenance program adequate?
_/year ;
_/year
( ) Yes ( )
Does the unit show signs of overload?
Is there an alarm system for hazardous equipment failures?
Frequency of tank cleaning ?
Does the sampling program meet the recommendations?
Are operating records adequate?
Is the laboratory equipped for the necessary analyses?
30-7
-------
41. What spare parts are stocked?-
42<
are the most common problems the operator has had with the process?
30-8
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. State of Virginia O&M inspection form.
6. Operations Manual - Anaerobic Sludge Digestion, EPA 430/9-75-001
30-9
-------
-------
31. AEROBIC DIGESTION
Process Digestion
Aerobic digestion is the separate aeration of waste sludge in open or
closed tanks. The purpose is to further treat the sludge so it will not cause
odors or other nuisances in final disposal. Aerobic digestion also reduces
the volume of sludge solids. Aerobic digestion is used commonly for package
plants. It is equally useful for larger plants especially for waste biologi-
cal sludges.
Aerobic digestion is a completely mixed activated sludge system with
either batch or continuous flow input. The contents of the digestor are aer-
ated for a period of 12 to 22 days depending on the type of sludge. The
solids resulting from digestion are separated from the liquid. They dewater
easily and do not cause odor problems.
Typical Design Considerations
Typical design criteria for aerobic digestion are shown in Table 31-1,
which was adapted from "Process Design Manual for Sludge Treatment and Dis-
posal", EPA 625/1-74-016.
Solids Retention Time (SRT) is the average time that the solids remain in
the process. For continuous feed systems:
SRT » total mass of solids in digester
mass of solids wasted/day
For batch feed systems:
SRT
average mass of the solids in digester during batch
(mass of solids wasted from batch) (number of days in batch
As an example assume the following data:
Continuous feed:
Tank volume = 65,000 gal Solids = 2.5%
Wasting rate = 2000 gal/day Solids = 5.0%
SRT = 65,000 x 0.025 = 16.3 days
2,000 x 0.05
31-1
-------
TABLE 31-1. AEROBIC DIGESTION DESIGN PARAMETERS
Parameter
Value
Solids retention
time, days
Solids retention
time, days
Volume allowance,
cu ft/capital
VSS loading,
pcf/day
Air requirements
Diffuser system
cfm/1,000 cu ft
Diffuser system,
cfm/1,000 cu ft
Mechanical system,
hp/1,000 cu ft
10-15
15-20b
3-4
0.024-0.14
20-35a
>60b
1.0-1.25
1.0-2.0
Minimum DO, mg/1
Temperature, °C
VSS reduction, percent 35-50
Tank design
Power requirement,
BHP/10,000
Population Equivalent
8-10
Remarks
Depending on temperature/
etc.
type of sludge,
Depending on temperature,
etc.
type of sludge,
Enough to keep the solids in suspension
and maintain a DO between 1-2 mg/1.
This level is governed by mixing require-
ments* Most mechanical aerators in aero-
bic digesters require bottom mixers for
solids concentration greater than 8,000
mg/1, especially if deep tanks (>12 feet)
are used.
If sludge temperatures are lower than
15°C, additional detention time should be
provided so that digestion will occur at
the lower biological reaction rates.
Aerobic digestion tanks are open and gen-
erally require no special heat transfer
equipment or insulation. For small treat-
ment systems (0.1 mgd), the tank design
should be flexible enough so that the
digester tank can also act as a sludge
thickening unit. If thickening is to be
utilized in the aeration tank, sock type
diffusers should be used to minimize
clogging.
Excess activated sludge alone.
bPrimary and excess activated sludge, or primary sludge alone.
31-2
-------
Batch feed with sludge settling and drawoff once per week:
Sludge volume in digester at beginning of week:
Sludge volume in digester at end of week:
Solids =» 2.5%
Total of supernatant and settled sludge drawoff:
Number of days in batch = 7
Average volume of sludge in digester = 40,000
40,000 gal
65,000 gal
25,000 gal
+ 65,000 = 52,500
SRT = 52,500 x 0.025 x 7 = 15 days
25,000 x 0.025
The volatile suspended solids (VSS) loading, expressed as pounds of VSS
per cubic foot of basin volume per day, is calculated as shown in the follow-
ing example for a continuous feed digester.
Tank volume = 65,000 gal
Wasting rate = 2,000 gal/day @ solids = 5.0%
Waste activated sludge, volatile solids = 80% of TSS
Total VSS wasting rate = 2,000 gal x 8.34 Ib x 0.05 x 0.80
day gal
667 Ib VSS
day
VSS loading rate =
667
x 7.48 gal = 0.077 Ib VSS/cu ft/day
65,000 gal cu ft
Typical Performance Evaluation
With aerobic digestion a 40 to 50 percent reduction in volatile suspended .
solids content is normally obtained. The supernatant may contain as little as
10 to 30 mg/1 BOD, 10 mg/1 ammonia nitrogen, and from 50 to 100 mg/1 nitrate
nitrogen. When nitrification occurs, both pH and alkalinity are reduced.
*» ' ~
Process Control
In most plants the aerobic digester is operated as a self-regulating pro-
cess with very little process control needed. That which is needed is dis-
cussed in Reference 6.
Maintenance Considerations
The maintenance program for the aerobic digester is very similar to the
program for the activated sludge process. The features of a good maintenance
program that the inspector should look for are:
1. Air diffusers and tanks inspected at least once per year.
2. Mixing, pumping, and blower equipment inspected annually for worn
blades and impellers.
3. Air filters serviced at regular intervals.
31-3
-------
4.
Records
Digester inspected once per shift for proper operation of aeration
equipment and pumps.
Recommended sampling and laboratory tests are shown in Figure 31-1.
Other operating records should include:
1. Volume of sludge recycled to aerobic digester.
2. Frequency and duration of operation of sludge pumps.
3. Periods when a digester is not operated because of inspection and
service.
4. Days when there are problems with mixing and/or odors.
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor aerobic digestion:
1. Thermometer
2. pH meter
3. Analytical balance
4. Clinical centrifuge with graduated tubes
5. BOD incubator
6. Drying oven
7. Muffler furnace
8. Oxygen gas analyzer (optional)
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chem-
icals, miscellaneous furniture, etc., and should be referred to for any de-
tailed questions.
Sampling Procedures
Sampling should be performed as outlined under Records. These samples may
be obtained through valves provided in the digester piping. If sampling
points are not provided, it may be necessary to obtain samples directly from
the digester contents.
The sample collector and containers should be clean. A wide mouth sample
collector of at least 2 inches should be used. Samples collected in the ef-
fluent channel should be collected near the discharge point so that any iso-
lated areas of short circuiting do not influence the results. Where automatic
samplers are used, it is important to keep the sampler tubes clean.
Samples should be analyzed according to procedures specified in Standard
Methods.
31-4
-------
z
3
O
U
Ul
a
a
t-
Q.
o
TEMPERATURE
pH
TOTAL SOLIDS
TOTAL
VOLATILE
SOLIDS
DO
AIR INPUT
SETTLEABLE
SOLIDS
FLOW
PH
SUSPENDED
SOLIDS
BOD
PLOW
ALKALINITY
UJ
N
Co
1-
z a
28
ALL
ALL
ALL
1
ALL.
ALL
ALL
ALL
ALL
AT.T,
ALL
ALL
ALL
rEST
=REQUENCY
VD
1/D
2/W
2/W
3/W
R
3/W
R
2
2
2
R
/w
-OCATION OF 1
AMPLE
p
p
I
DS
I
DS
p
B
P
DS
S
s
S
S
P
METHOD OF
AMPLE
G
G
G
G
G
R
G
R
G
K
G
R
G
Z%
$>-
<
•INFLUENT
SLUDGE
AEROBIC DIGESTION
a
i) i 1 i
S
DS
'•SUPERNATANT
RECYCLE TO
PLANT INFLUENT
DIGESTED SLUDGE
TO NEXT ORGANIC
SLUDGE TREATMENT
PROCESS
A. TEST FREQUENCY
H • HOUR
0- DAY
w- WEEK
M - MONTH
R - RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I - INFLUENT
DS= DIGESTED SLUDGE
S = SUPERNATANT'
P = PROCESS
B = BLOWER {INCLUDE WITH PROCESS TESTING)
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G- GRAB SAMPLE
R • RECORD CONTINUOUSLY
• MB. MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. DIFFUSED AIR ONLY
2. WHEN DRAW OFF SUPERNATANT
3. FOR CONTROL OF PROCESS RECEIVING
THIS FLOW
Figure 31-1
31-5
-------
Sidestreams
The only sidestream from the aerobic digestion process is the super-
natant. It is returned to either the primary or the secondary treatment
process and normally causes no problem to process operation.
31-6
-------
Process Checklist - Aerobic Digestion
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
How many aerobic digestion units are there ___?
What are the dimensions of each unit ;
How many units are presently operating __?
What type of sludge is treated in the aerobic digesters (waste activated,
primary, primary + waste activated, etc.) ?
What is the volume of influent sludge flow
What is the design sludge flow
How often is sludge applied to the digester
What is the total duration of influent pumping
Is influent sludge pumping ( ) manual ( ) automatic?
What is the solids concentration in the influent sludge flow
What is the solids concentration in the aerobic digesters
_gal/day average?
gal/day average?
times.per day?
hours/day?
What type of aeration equipment is used (diffused, mechanical,
combination, etc.) j ?
If diffused aeration is used, do air diffusers require frequent cleaning?
( ) Yes ( ) No
Are the aerobic digesters ( ) open ( ) closed?
Is the aeration ( ) conventional ( ) pure oxygen?
What is the sludge retention time (SET) days?
What is the volatile suspended solids (VSS) loading lb
VSS/cu ft/day?
Is a separate sedimentation tank used or is it a batch-type
system?
See Primary Clarification or Secondary Sedimentation for a checklist for
sedimentation tanks.
What is the solids concentration of the sludge following settling
How much waste sludge is pumped gallons/day?
How often do waste sludge pumps run _
Is waste sludge pumping ( ) manual
minutes/hour?
( ) automatic?
How much sludge is recycled back to the aerobic digester
gallons/day average?
What percentage of the influent sludge flow is the recycle sludge
flow %?
Are .the contents of the tanks well mixed and relatively free of odors?
( ) Yes ( ) No
Is there a foaming problem? ( ) Yes ( ) No
What is the dissolved oxygen (DO) concentration in the aerobic digestion
units mg/1?
Are there provisions for pH adjustment by the addition of lime, sodium
hydroxide, or sodium bicarbonate? ( ) Yes ( ) No
What is the volume of supernatant flow gal/day average?
What is the BOD of the supernatant flow mg/1?
What is the suspended solids concentration of the supernatant
mg/1?
What is the nitrate nitrogen concentration of the supernatant
mg/1?
What is the ammonia nitrogen concentration of the supernatant
rag/1?
Frequency of maintenance inspections by plant personnel
/year.
31-7
-------
36,
37.
38.
39.
40.
41.
42.
43.
Is maintenance program adequate? ( ) Yes ( } No
If multiple units are used, is the flow distributed evenly?
( ) Yes ( ) No
Does the unit show signs of short circuiting and/or overloads?
( ) Yes ( ) No
Is there an alarm system for equipment failures or overloads?
( ) Yes ( } No
Does the sampling program meet the recommendations? ( ) Yes (
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory equipped for the necessary analyses? ( ) Yes
What spare parts are stocked?
) No
( ) No
44. What are the most common problems the operator has had with the process?
31-8
-------
References
1. Gulp, G.L., and Polks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution-Control Federation (1959).
\
5. Harrison, J.R., Goodson, J.B., and Gulp, G.L., Process Design Manual for
Sludge Treatment and Disposal, USEPA, 625/1-74-006.
6. Ettlich, W.F., et al, Operations Manual - Sludge Handling and
Conditioning, US EPA Report 430/9-78-002.
31-9
-------
-------
32. CENTRIFUGATION
Process Description
The centrifuge is a sedimentation device in which the solids-liquid sepa-
ration is enhanced by rotating the liquid at high speeds. Centrifuges have
been used for both sludge thickening and dewataring especially for waste acti-
vated sludge and digested sludges. Both the disc type and the solid bowl
centrifuges are well suited to thickening operations.
The solid bowl centrifuge is the most widely used type for dewatering of
sewage sludge. It consists of a rotating bowl and conveyor. Sludge enters
the rotating bowl through a stationary feed pipe ex-tending into the hallow
shaft of the rotating screw conveyor and is distributed through ports into a
pool within the rotating bowl. The helical rotating conveyor moves the sludge
solids across the bowl, up the beaching incline to outlet ports and then to a
sludge cake discharge hopper.
Water or centrate is discharged from the bowl through ports in the end
which maintain the pool in the bowl at the desired depth.
The basket centrifuge is also referred to as the imperforate bowl, knife
discharge type and is a batch dewatering unit that rotates around the vertical
axis. The sludge is charged into the basket and forms an annular ring as the
unit rotates. The liquid (centrate) is displaced over a baffle or weir at the
top of the unit. When the solids concentration reaches the desired limit the
centrifuge is stopped. A knife or skimmer displaces the cake from the verti-
cal wall and out the bottom openings.
The disc centrifuge is continuous flow variation of the basket centri-
fuge. It is prone to plugging and in some cases the sludge may have to be
screened prior to centrifugation.
Typical Design Considerations
The most commonly used loading factor for centrifuges is the sludge feed
rate. Single centrifuge capacities range from 4 gpm to about 250 gpm. Feed
rates may also be given in pounds of dry solids per hour. This is calculated
as shown on the following page.
32-1
-------
1.
2.
5.
Determine wet sludge feed rate.
Feed rate = 150 gpm
Determine solids concentration in the feed sludge.
Concentration - weight of dry sludge solids x 100%
weight of wet sludge
= 0.1 Ib x 100 = 1%
10 Ib
Calculate dry feed rate.
Dry feed rate = sludge wet feed rate x concentration
= 150 x 0.01 x 8.34 Ib x 60 min
gal hr
= 750 Ib dry solids/hr
Typical feed rates for several sizes of solid bowl centrifuges for
typical municipal waste sludges are:
Feed rate
Machine size, in Ib dry solids/hr
18 300 x 800
24 700 to 2000
36 1500 to 3500
Solids recovery is the ratio of cake solids to feed solids for equal
sampling times. It can be calculated with suspended solids and flow
data or with only suspended solids data. The centrate solids must be
corrected if chemicals are fed to the centrifuge.
Recovery » wet cake flow, Ib (cake solids, %) (100)
hr
wet feed flow, Ib
hr
(feed solids, %)
Recovery »
(cake solids, %) (feed solids, % - centrate solids, %) (100)
(feed solids, %) (cake solids, % - centrate solids, %)
Centrate solids must be corrected if chemicals are added to centri-
fuge. Because it is diluted by the extra water from the chemical and
chemical dilution water feeds. The measured centrate solids, there-
fore, are less than the actual solids would be without the added
water from the chemical feed.
correction factor «
(feed rate, gpm) + (chemical flow, gpm) + (dilution water, gpm)
feed rate, gpm
corrected centrate solids =
(measured centrate solids) (correction factor)
Typical Performance Evaluation
Expected centrifuge performance is shown in Table 32-1 for a number of
conditions. These data were developed from "Process Design Manual for Sludge
Treatment and Disposal", EPA 625/1-74-006 and actual plant data.
32-2
-------
TABLE 32-1. EXPECTED CENTRIFUGE PERFORMANCE
Sludge Cake Characteristics
Wastewater sludge type
Raw or digested primary
Raw or digested primary, plus
trickling filter humus
Raw or digested primary, plus
activated sludge
Activated sludge
Oxygen activated sludge
High-lime sludges
Lime classification
Heat treated sludge
Heat treated sludge
Solids ,
25-35
28-35
20-30
25-35
15-30
15-25
9-9
8-10
50-55
50
30-50
30-50
Solids
% recovery, %
90-95
70-90
80-95
60-75
80-95
50-65
80-85
80-85
90
75
85-90
92-99
Polymer-
addition
2-4 Ibs/ton
no
5-15 Ibs/ton
no
5-20 Ibs/ton
no
5-10 Ibs/ton
3-5 Ibs/ton
no
no
no
2-5 Ibs/ton
Typical Thickening Performance
(Based on limited plant operating experience)
Underflow Solids
Type of Centrifuge solids, Feed solids, recovery,
sludge type % % %
Polymer
requirement,
WAS
EAS (after
roughing
filter)
EAS
EAS
Disc
Disc
Basket
Solid-bowl
4-5.5
5-7
9-10
5-13
0.75-1. a
0.7
0.7
0.4-1.5
80-90
80-97
90-70
70-90
85
90
95
None
None
None
None
5
5-10
10-15
WAS * waste activated sludge
EAS * extended aeration waste sludge
32-3
-------
Process Control
There are several variables that can be controlled by the operator to af-
fect optimum centrifuge performance. These are presented in Reference 6.
Maintenance Considerations
The features of a good maintenance program include general maintenance
requirements as well as the following:
1. Conveyor belts properly checked for adjustment.
2. Spare part inventory contain the following: shear pins, main bear-
ings, seals/ conveyor bushings, thrust bearing seal, feed and dis-
charge ports.
Records
Recommended sampling and laboratory tests are shown in Figure 32-1.
Other operating records should include:
1. Frequency and duration of centrifuge operating time.
2. Quantity of sludge cake produced.
3. Influent sludge flow.
Laboratory Equipment
The laboratory should include the following equipment in order to monitor
centrifugation:
1. Analytical balance
2. Clinical centrifuge with graduated tubes
3. BOD incubator
4. Drying oven
5. Imhoff Cones
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities* contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any
detailed questions.
Sampling Procedures
Samples should be collected at the points shown under the section Rec-
ords. The sample collector and containers should be clean. A wide mouth
sample collector of at least 2 inches should be used. Where automatic
samplers are used, it is important to keep the sampler tubes clean.
Sidestreams
The centrate is usually returned to the plant influent or some other ap-
propriate point in the main treatment process. Return of centrate to flota-
tion thickeners has also proven satisfactory.
32-4
-------
2
a
o
TOTAL SOLIDS
BOO
SUSPENDED
Qnr.Tns
SETTLEABLE
SOLIDS •
FLOW
•
UJ
N
t/>
t-
z 5
< 0
Si *
ALL
ALL
ATiTi
ALL
ALL
TEST
FREQUENCY
1/D
1/W
1/D
1/H
R
LOCATION OF
SAMPLE
S
C
CE
Ci£S
CE
CE
.
1 METHOD OF 1
SAMPLE
G
G
G
G
R
REASON
FOR TEST
P
P2
P
P
P1
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
SLUDGE CONCENTRATION
CENTRIFUGATION
(1)
rr
^ CENTRATE
TO PLANT
mm
RECYCLE 1
INFLUENT J— (
*^**";
f SLUDGE FEED
1
S
»
iLUDGE CAKE
NOTE: SOLID BOWL TYPE SHOWN.
FLOW PATTERN IS SIMILAR
FOR OTHER MODELS.
A. TEST FREQUENCY
H - HOUR M - MONTH
0 m DAY R - RECORD CONTINUOUSLY
W- WEEK M«- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
S = SLUDCE FEED
C= SLUDGE CAKE
CE =CENTRATE
C. METHOD Of SAMPLE
24C-24 HOUR COMPOSITE
G " GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn« MONITOR CONTINUOUSLY
0. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1.
2.
DAILY OPERATION ASSUMED
FOR CONTROL OF PROCESS RECEIVING THIS FLOW.
Figure 32-1
32-5
-------
Process Checklist - Centrifugation
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
What is the volume of influent sludge flow
What is the design flow gal/min?
How much cake is produced ?_
gal/min?
_lb/day?
What is the solids concentration in the influent sludge? %
What type and size of centrifuges are used?
What is the solids recovery %
What is the solids concentration in the discharge cake %
Is operation of centrifuge, conveyors or sludge feed pumping ( ) manual
( ) automatic.
How often does the centrifuge run rain/hr?
Frequency of maintenance inspections by plant personnel /yr
Is maintenance program adequate? ( ) Yes ( ) No
Are metering provisions available for return of the centrate?
( ) Yes ( ) No
If multiple units are used is the influent flow distributed evenly?
( ) Yes ( ) No
For multiple units are there provisions for equalization of centrate
flows? ( ) Yes ( ) No
What are the types of conditioning chemicals fed? '"•'
What amounts of chemicals are fed Ib/day?
What are chemical feed cycle times
minutes/hr?
" ) No
) No
( ) No
Is the general housekeeping satisfactory? ( } Yes
Does the unit show signs of overloading? ( ) Yes (
Does the unit show signs of excessive wear? ( ) Yes
Is there an alarm system for equipment failures or overloads?
( ) Yes ( ) No
Does the sampling program meet the recommendations? ( ) Yes
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory equipped for the necessary analyses? ( ) Yes
What spare parts are stocked?
( ) No
( ) No
27. What are the most common problems the operator has had with the process?
32-6
-------
References
1. Gulp, G.L., and Polks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. State of Virginia OSM inspection form.
6. Harrison, J.R., Goodson, J.B., and Gulp, G.L., Process Design Manual for
Sludge Treatment and Disposal, USEPA, 625/1-74-006.
7. Ettlich, W.F., et al, Operations Manual - Sludge Handling and
Conditioning, US EPA Report 430/9-78-002.
32-7
-------
-------
33. VACUUM FILTRATION
Process Description
A vacuum filter consists of a cylindrical drum which rotates partially
submerged in a vat of sludge. The filter drum is divided into compartments by
partitions or seal strips. A vacuum is applied between the drum deck and
filter medium causing filtrate to be removed and filter cake to be retained on
the medium during the pickup and cake drying cycle. The filter medium may be
a cloth made of natural or synthetic fibers, stainless steel wire mesh or coil
springs. Dewatered sludge is ordinarily removed by a fixed scraper blade.
Typical Design Considerations
The most important loading factor is the amount of solids, on a dry basis,
applied to the filter per hour. This is called the "solids loading rate" and
is expressed in pounds of solids per square foot of vacuum filter area per
hour. This factor is calculated as shown in the following example. Typical
values are shown in Table 33-1.
1. Determine effective surface area of vacuum filter. The plant con-
struction drawings or the vacuum filter O&M manual should contain the
necessary information.
Area = 75 sq ft
2. Determine sludge flow to vacuum filter from plant records (must
include chemical's).
Sludge flow = 100,000 gal/hr
3. Determine the influent sludge concentration.
Concentration = weight of dry sludge solids x 100%
wet of wet sludge
= 1 Ib x 100 = 10%
10 Ib
4. Determine the total dry weight of sludge to the vacuum filter per
hour.
Dry weight = sludge flow x concentration - 8.34
= 100,000 x 0.1 - 12oo Ib/hr
8.34
5. Determine loading rate.
Loading rate = Dry weight
Area
= 1200 = 8 ib/sg ft/hr
150
Typical Performance Evaluation
The most common measure of performance for vacuum filters is the yield.
This is expressed in terms of pounds of dry total solids in the cake dis-
charged from the filter per square foot of effective filter area per hour.
Performance of the vacuum filtration process can vary widely depending on
the sludge type, sludge characteristics, conditioning, type of vacuum filter,
and loading rates. Typical applications are shown in Table 33-1.
33-1
-------
TABLE 33-1. VACUUM FILTRATION TYPICAL LOADINGS AND PERFORMANCE
Sludge type
Primary
Primary +• FeCl
Primary +
Low Lime
Primary +
High Lime
Feed
solids,
Design assumptions %
Thickened to 10% solids 10
polymer conditioned
85 mg/1 FeCl dose 2.5
Lime conditioning
Thickening to 2.5% solids
300 mg/1 lime dose 15
Polymer conditioned
Thickened to 15% solids
600 mg/1 lime dose 15
Polymer conditioned
Typical Performance
loading cake
rates , solids ,
psf/hr %
8-10 25-38
1.0-2.0 15-20
6 32-35
10 28-32
Primary H- WAS
Primary 4-
(WAS 4- FeCl3)
(Primary +• FeCl )
+ WAS
Waste Activated
Sludge (WAS)'
WAS •»• FeCl..
Digested primary
Digested primary
+ WAS
Digested primary
+ (WAS + Fei
Tertiary alum
Thickened to 15% solids
Thickened to 8% solids 8
Polymer conditioned
Thickened to 8% solids 8
FeCl, & lime conditioned
Thickened primary sludge ~3.5
to 2.5%
Flotation thickened WAS
to 5%
Dewater blended sludges
Thickened to 5% solids 5
Polymer conditioned
Thickened to 5% solids 5
Lime + FeCl3 conditioned
Thickened to 8-10% solids 8-10
Polymer conditioned
Thickened to 6-8% solids 6-8
Polymer conditioned
Thickened to 6-8% solids 6-8
FeCl_ + lime conditioned
Diatomaceous earth precoat 0.6-0.8
4-5
1.5
2.5-3.5
1.5-2.0
7-8
3.5-6
2.5-3
0.4
16-25
20
15-20
15
15
25-38
14-22
16-18
15-20
33-2
-------
Process Control
Control of the vacuum filter systems should be based on performance. The
performance of vacuum filters may be measured by various criteria such as the
yield, the efficiency of solids removal, and the cake characteristics. Each
of these criteria is of importance, but one or the other may be particularly
significant in a given plant. Control based on .these criteria is discussed in
Reference 7.
Maintenance Considerations
The maintenance program vacuum filters includes sludge pumping, chemical
feed systems and the filter unit itself. Maintenance items specific to the
filter unit are:
1. Daily inspection of filter media for excessive or unusual wear.
2. Daily checks and lubrication of drive units.
3. Periodic cleaning of sludge lines and conveyor belts.
4. Spare parts inventory include the following: drive mechanism parts
such as sprockets, chains, gears, motors, bearings, etc. and vacuum
mechanism parts such as hoses, fittings, pumps, gauges, etc.
Records
Recommended sampling and laboratory tests are shown in Figure 33-1.
Other records should include:
1. Influent sludge flow
2. Concentration of influent sludge and sludge cake
3. Frequency and duration of operation
Laboratory Equipment
1. Analytical balance
2. Clinical centrifuge with graduated tubes
3. BOD incubator
4. Drying oven
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any de-
tailed questions.
33-3
-------
Q.
O
TOTAL SOLIDS
BOD
SUSPENDED
SOLIDS
PLOW
Ul
N
«/»
(-
Z Q
n
ALL
AH,
ALL
ALL
TEST
FREQUENCY
1/D
?^f
1/D
R
LOCATION OF
SAMPLE
S
C
F
P
F
METHOD OF
SAMPLE
G
G.
G
R
Z"
8>-
<
-------
Sampling Procedures ,
Sang?ling should be performed as outlined under Records. These samples may
be obtained through valves provided in the respective thickener piping. If
sampling points are not provided, they should be installed to facilitate oper-
ation and control of the process. Samples of the supernatant can be obtained
at the overflow weir.
Samples should be analyzed according to procedures specified in Standard
Methods.
Sidestrearns
The only sidestream is the filtrate which is the liquid removed from the
sludge during dewatering. Filtrate is returned to a main plant treatment pro-
cess. When filtrate quality is poor, it is possible to build up a large pro-
portion of fine solids in the plant and reduce plant treatment efficiency. In
an activated sludge process, the filtrate may be returned to a flotation or
thickening process.
33-5
-------
Process Checklist-Vacuum Filtration
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
What is the volume of the influent sludge flow
What is the percent solids of the influent sludge
What is the effective area of the vacuum filter
What is the design loading rate
_gal/day avg?
sq ft?
Ib/sq ft/hr?
_rag/liter?
What is the percent solids in the discharge cake
Are there settleable solids in the filtrate
How often does vacuum filter run minutes/hour?
Frequency of maintenance inspections by plant personnel /year:
Is maintenance program adequate? ( ) Yes ( ) No
Is the vacuum system inspected regularly /year?
Frequency of maintenance inspections for chemical feed system
/year
What type of conditioning chemicals are used «
What amount of conditioning chemicals are pumped Ib/day?
Are proper safety precautions used in handling these chemicals?
( ) Yes ( ) No.
Is sludge pumping ( ) manual { ) automatic?
Is chemical feed ( ) manual ( ) automatic?
How often do sludge pumps run minutes/hour?
How often does conditioning equipment run minutes/hour?
If multiple units are used, is the flow distributed evenly?
( ) Yes ( ) No
Does the unit show signs of short circuiting and/or overloads?
( ) Yes ( ) No
Is there an alarm system for equipment failures or overloads?
( ) Yes ( ) No
Does the sampling program meet the recommendations? ( ) Yes ( ) No
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory equipped for the necessary analyses? ( ) Yes ( ) No
What spare parts are stocked? ____^__
26. What are the most common problems the operator' has had with the process?
33-6
-------
References
1. Gulp, G.L., and Folks Helm, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978)."
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June. 1973).~~~
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. State of Virginia O&M inspection form.
6. Harrison, J.R., Goodson, J.B., and Gulp, G.L., Process Design Manual for
Sludge Treatment and Disposal, USEPA, 625/1-74-006.
7. Ettlich, W.F., et al, Operations Manual - Sludge Handling and
Conditioning, US EPA Report 430/9-78-002.
33-7
-------
-------
34. PRESSURE FILTRATION
Process Description
The filter press is a batch device used to dewater sludges. There are
several types of presses available but the most common consists of vertical
plates which are held in a frame and which are pressed together between a
fixed and moving end. A cloth is mounted on the face of each individual
plate. Despite its name, the filter press does not close to squeeze or press
sludge. Instead, the press is closed and then sludge is pumped into the press
at pressures up to 225 psi and passes through feed holes in the trays along
the length of the press. Filter presses usually require a precoat material
(incinerator ash or diatomaceous earth are typically used) to aid in solids
retention on the cloth and release of the cake.
The water passes through the cloth, while the solids are retained and form
a cake on the surface of the cloth. Sludge feeding is stopped when the cavi-
ties or chambers between the trays are filled. Drainage ports are provided at
the bottom of each press chamber. The filtrate is collected in these, taken
to the end of the press, and discharged to a common drain.
The pressures which may be applied to a sludge for removal of water by
filter presses now available range from 5,000 to 20,000 times the force by
gravity. In comparison,- a solid bowl centrifuge provides forces of 700 to
3,500 times the force of gravity and a vacuum filter, 1,000 times the force of
gravity. As a result of these greater pressures, filter presses may provide
higher cake solids concentrations (30 to 50 percent solids) at reduced chemi-
cal dosage. In some cases, ash from a downstream incinerator is recycled as a
sludge conditioner.
Typical Design Considerations
Typical loading rates for pressure filtration of various sludges are shown
in Table 34-1. This data was developed from "Process Design Manual for Sludge
Treatment and Disposal," (EPA 625/1-74-006). Loading rates depend on the
length of the dewatering cycle described above.
Typical Performance Evaluation
Typical performance criteria for pressure filters are the pressing cycle
length, the solids content of the cake, and the quality of the filtrate. Per-
formance of filter press on various sludges will vary widely, but the data in
Table 34-1 are typical.
Process Control
Instrumentation is usually minimal, however, it is possible to completely
automate the operation of the filter press if desired. Pressure gauges should
be provided to monitor the feed pressures and the filtrate flow must be moni-
tored either visually or with a flow indicator. Details of process control
are given in Reference 7.
34-1
-------
TABLE 34-1. TYPICAL RESULTS PRESSURE FILTRATION
Sludge type
Primary
Primary + FeCl3
Primary + 2 stage
high lime
Primary + WAS
Primary + (WAS
PeCl3)
(Primary + FeCl3)
+ WAS
WAS
WAS -f FeCl3
Digested Primary
Digested Primary
•f WAS
Digested Primay +•
(WAS + FeCl3)
Tertiary Alum
Tertiary Low Lime
Conditioning
5% FeCl3, 10% Lime
100% Ash
10% Lime
None
5% FeCl3f 10% lime
150% Ash
5% FeCl3, 10% Lime
10% Lime
7.5% FeCl3, 15% Lime
250% Ash
5% FeCl3r 10% Lime
6% FeCl3, 30% Lime
5% FeCl3, 10% Lime
100% Ash
5% FeCl3, 10% Lime
10% Lime
None
Feed
solids, %
5
4*
7.5
8*
8*
3.5*
5*
5*
8
6-8*
6-8*
4*
8*
Typical
cycle
length, hr
2
1.5
4
1.5
2.5
2.0
3
4
2.5
2.0
3.5
2
2
1.5
3
6
1.5
% solids
filter cake
solids, %
45
50
40
50
45
50
45
40
45
50
45
40
45
50
40
35
55
* Thickening used to achieve this solids concentration
34-2
-------
Maintenance Considerations
The features of a good maintenance program are:
1. A thorough semi-annual inspection of all equipment including the
following.
a) Drive and gear reducers
b) Drive chains and sprockets
c) Closing mechanism
d). Bearing brackets
e) Electrical contacts in starters and relays
2. Filter cloths or media washed in place.
3. Rubber surfaces of the plates scraped only with soft plastic or wood
to avoid damage.
4. Spare part inventory should contain the following: drives and gear
reducers, drive chains, sprockets, closing mechanism, bearing
brackets, and electrical contacts.
Records
Recommended sampling and laboratory tests are shown in Figure 34-1.
Other operating records should include:
1. Influent sludge flow
2. Volume of sludge cake produced
3. Frequency and duration of operation
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor vacuum filtration:
1. Analytical balance
2. Clinical centrifuge with graduated tubes
3. BOD incubator
4. Drying oven
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any de-
tailed questions.
34-3
-------
o
u
8
§
0.
o
TOTAL SOLIDS
BOO
SUSPENDED
SOT.TDR
PLOW
UJ
N
M
ll
ALL
ALL
AT.T
ALL
TEST
FREQUENCY
VD
2/W
1/n
R
LOCATION OF I
SAMPLE
S
C
P
P
P
METHOD OF
SAMPLE
G
G
r:
R
REASON
FOR TEST
P
P1
p
P1
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
SLUDGE CONCENTRATION
PRESSURE FILTRATION
FILTRATE
RECYCLE TO
PLANT INFLUENT
A. TEST FREQUENCY
H * HOUR
0 • DAY
W- WEEK
M - MONTH
R - RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
S= SLUDGE FEED
C= SLUDGE CAKE
F= FILTRATE
C. METHOD OF SAMPLE
24C*24 HOUR COMPOSITE
G- GRAB SAMPLE
R - RECORD CONTINUOUSLY
MB- MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. FOR CONTROL OF PROCESS RECEIVING THIS FLOW.
Figure 34-1
34-4
-------
Sampling Procedures
Sampling should be performed as outlined under Records. These samples may
be obtained through valves provided in the respective piping or directly from
the process. If sampling points are not provided, they should be installed to
facilitate operation and control of the process.
The sample collector and container should be clean. Samples should be
analyzed according to procedures specified in Standard Methods.
Sidestreams
The only sidestream is the filtrate, which is the liquid removed from the
sludge during dewater ing. Filtrate quality should be very good (less than 100
mg/1 suspended solids) if the system is properly operated. During the early
part of the cycle, the drainage from* a large press can be in the order of
2,000 to 3,000 gallons per hour. This rate falls rapidly to about 500 gallons
per hour as the cake forms and at the end of the cycle the rate is virtually
zero. Filtrate is normally returned to the plant treatment process.
34-5
-------
Process Checklist - Pressure Filtration
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
What is the volume of the influent sludge flow
What is the percent solids of the influent sludge
What is the filter press volume
gal/day avg.
cu ft?
What is the percent solids in the discharge cake
Are there settleable solids in the filtrate
How often does pressure filter run
min/hr?
Frequency of maintenance inspections by plant personnel
Is maintenance program adequate? ( ) Yes ( ) Ho
Frequency of maintenance inspections for chemical feed system
If acid washing is provided, is a recirculating system included?
( ) Yes ( ) No
What type of conditioning chemicals are used ?
What amount of conditioning chemicals are pumped _• Ib/day?
Are proper safety precautions used in handling these chemicals?
( ) Yes ( ) No
Is sludge pumping ( ) manual ( ) automatic?
Is chemical feed ( ) manual ( ) automatic?
How often do sludge pumps run minutes/hr?
How often does conditioning equipment run minutes/hr?
If multiple units are used, is the flow distributed evenly?
( ) Yes ( ) No
Does the unit show signs of short circuiting and/or overloads?
( } Yes ( ) No
Is there an alarm system for equipment failures or overloads?
( ) Yes ( ) No
Does the sampling program meet the recommendations? ( ) Yes (
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory equipped for the necessary analyses? ( ) Yes
What spare parts are stocked?
yyr?
/yr?
) No
( ) No
25.
What are the most common problems the operator has had with the process?
34-6
-------
References
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. State of Virginia O&M inspection form.
6. Harrison, J.R., Goodson, J.B., and Gulp, G.L., Process Design Manual for
Sludge Treatment and Disposal, USEPA, 625/1-74-006.
7. Ettlich, W.F., et al. Operations Manual - Sludge Handling and
Conditioning, US EPA Report 430/9-78-002.
34-7
-------
-------
35. DRYING BEDS ;
Process Description
Drying beds are generally used for dewatering of well digested sludges.
Attempts to air dry raw sludge usually results in odor problems.
Sludge drying beds consist of perforated or open joint drainage pipe laid
within a gravel base. The gravel is covered with a layer of sand. Partitions
around and between the drying beds may be of concrete, wood or earthen embank-
ment. Drying beds are generally open to the weather but may be covered with
ventilated green-house type enclosures in wet climates.
Sand beds allow water to drain from the sludge mass through the supporting
sand to the drainage piping. As the sludge dries, cracks develop in the sur-
face allowing natural exaporation to occur from the lower layers. This speeds
the drying process.
Typical Design Considerations
The most important loading factor is the solids loading rate to the drying
bed. Solids loading rate is the weight of solids on a dry weight basis ap-
plied yearly per square foot of drying bed area. As an example, assume that
10 inches of 5 percent solids anaerobically digested sludge is applied to a
drying bed five times per year. The weight of solids will be calculated for
one square foot of bed.
Solids Loading Rate "=
dry weight of solids
year
cubic feed of sludge Ibs
square feet of bed
square feet of
drying bed
% solids
100
Number of
applications
1 x 1 x 10
12 62.4 Ibs 5 (5)
sq ft of bed ft^ ioo
13 Ibs
year-sq ft
Drying beds are usually sized based upon required square feet of bed area
per capita (or per person) served by the treatment plant. The area required
for drying beds depends on climate but typical criteria are given below for
several types of digested sludge and for whether the drying beds are open or
covered.
35-1
-------
Open beds
Covered beds
Bed sizing, sq ft/capita from WPCF, 1959:
Primary digested sludge 1.0 - 1.5
Primary and humus
digested sludge 1.25 - 1.75
Primary and activated
digested sludge 1.75 - 2.5
Primary and chemically
precipitated digested sludge 2.0 - 2.5
0.75 - 1.0
1.0 - 1.25
1.25 - 1.5
1.25 - 1.5
The population which can be adequately served by a set of existing drying
beds can be calculated, as shown in the following example.
1.
2.
Determine drying bed shape and dimensions. The plant construction
drawings and specifications include this information.
Shape = 8 rectangular beds
Dimensions, each bed = 20 ft x 40 ft
Single bed area = 20 x 40 = 800 sq ft
Total Area = 8 x 800 = 6,400 sq ft
Determine area required per capita.
Sludge type * Digested primary and waste activated
Bed type =» Open beds
Area per capita = 1.75 - 2.5 sq ft/capita
(from above summary)
Use 2.0 sq ft/capita
3.
Calculate population which can be served.
Total Bed Area, Sq ft - 6,400
3,200 persons
Area per capita, sq ft/capita
Typical Performance Evaluation
2.0
The performance of sludge drying beds is different from one location to
the next. Sludge drying bed performance is affected by weather, sludge
characteristics, system design (including depth of fill), chemical condition-
ing, and drying time. Typical performance in terms of solids loading rate and
moisture content of dried sludge are as follows for open and covered beds.
Solids Loading Rate,
Ib/yr/sq ft
Moisture content of dried
sludge, percent
Process Control
Open beds
up to 25
50 - 60
Covered beds
up to 40
50 - 60
Process control practices are described in detail in Reference 4.
35-2
-------
Maintenance Considerations
The features of a good maintenance program are:
1. Drying beds inspected every few days with particular attention given
to potential odor and insect problems.
2. Beds levelled and raked prior to each sludge application.
3. Sand depth checked regularly for losses of sand during sludge removal
from beds.
4. Makeup sand added when sand depth decreases to 3 or 4 inches.
5. Weed growth on beds controlled by use of weed killer or hand pulling.
6. Fly control by destruction of breeding and use of traps and poisons.
7. Drainage system inspected and maintained on a routine basis.
8. Sludge lines drained after use in winter to prevent freezing.
9. • If earth beds are used, grass and other vegetation cut regularly.
10. Stop logs kept well maintained to minimize leakage from vehicular
access cutouts in drying bed walls.
Records
Recommended sampling and laboratory tests are shown on Figure 35-1.
Other operating records should include:
1. Time and date sludge is applied to each drying bed.
2. Number of days before sludge is dry enough for removal.
3. Volume of sludge removed from beds.
4. Date makeup sand is required for each bed and quantity of makeup
required.
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor sludge drying beds:
1. Analytical balance
2. Clinical centrifuge with graduated tubes
3. BOD incubator
4. Drying oven
5. Imhoff Cones
35-3
-------
a
z
a
o
Ul
a
VI
I
P
a
o
TOTAL SOLIDS
TOTAL SOLIDS
BOD
o
TOTAL SOLIDS
'
Ul
N
«rt
II
ALL
ALL
AT.t.
ALL
TEST
FREQUENCY
W
W
M
M
LOCATION OF
SAMPLE
I
D
r>T-
Dr
METHOD OF
SAMPLE
G
G
r;
G
REASON
FOR TEST
H
P
p
P
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
DRYING BEDS
DEWATERED SLUDGE
TO DISPOSAL
INFLUENT
SLUDGE
DRAINAGE
WATER
A. TEST FREQUENCY
H, HOUR M- MONTH
D - DAY R - RECORD CONTINUOUSLY
W- WEEK Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
I = INFLUENT SLUDGE
D= DEWATERED SLUDGE
Dr- DRAINAGE WATER
C. METHOD OF SAMPLE
24C«24 HOUR COMPOSITE
G- GRAB SAMPLE
R - RECORD CONTINUOUSLY
MB- MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
Figure 35-1
35-4
-------
The EPA report "Estimating Laboratory Heeds for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, miscellaneous furniture, etc., and should be referred to for any de-
tailed questions.
Sampling Procedures
Samples of the influent sludge may be obtained through valves provided in
the sludge lines. Samples of the dried sludge cake can be obtained directly
from the drying bed. Samples of the drainage water should be collected from
valves in the drain lines or at the recycle pumping station. The sample col-
lector and containers should be clean. A wide mouth sample collector of at
least 2 inches should be used.
Sidestrearns
The only sidestream is the drainage water. This water is normally re-
turned to the raw sewage flow to the plant or to the plant headworks.
The flow from the drainage piping consists primarily of the initial perco-
lation of water from the sludge plus some periodic percolation after rain
storms (assuming open beds).
35-5
-------
Process Checklist-Drying Beds
1. What are the dimensions of the drying beds?
2.
3.
4.
How many separate drying bed compartments are there?
Are the sludges digested before they are applied to the drying bed?
( ) Yes ( } No
What type of sludges are applied to the drying beds (digested primary,
waste activated, combination, etc. ) _ ?
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
What is the volume of sludge flow applied to the drying beds
_ gallons/day average?
What is the design sludge flow _ _ gallons/day average?
What is the solids concentration in the sludge applied to the drying
beds? _ %
What is the solids loading rate _____ _ ^^^ Ibs/yr/sq ft?
What is the population served by the treatment plant? _
What is the drying area provided, based on sq ft/capita? _
What is the solids concentration in the de watered sludge? _
What is the typical drying time required?
Are there odor problems?
days
( ) Yes ( ) No
Are- there problems with flies or other insects? ( ) Yes ( ) No-
Are there problems with weed growth? ( ) Yes { ) No
Is there an underdrain system? ( ) Yes ( ) He-
Are there provisions for the return of drainage waters to the plant?
{ ) Yes ( ) No
What is the typical sand depth? inches
Are there any beds with sand depths less than 3 or 4 inches?
( ) Yes ( ) No
Are vehicles and equipment operated on permanent vehicle treadways or on
planks or plywood laid on top of the beds? ( ) Yes ( ) No
Are splash plates or diffusion devices in place when sludge is applied to
the beds? ( ) Yes ( ) No
Are partitions between and around the bed tight so that sludge will not
flow from one compartment to another nor outside the beds?
{ ) Yes ( ) No
35-6
-------
References'
1. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control. Federation (1976).
3. State of Virginia O&M inspection form.
4. Ettlich, W.F., et al, Operations Manual - Sludge Handling and
Conditioning, US EPA Report 430/9-78-002.
35-7
-------
-------
36. DRYING LAGOONS
Process Description
Sludge lagoons are similar to sand beds in that sludge is periodically
drawn from a digester, placed in the lagoon, removed after a period of drying,
and the cycle repeated. Drying lagoons do not have an underdrain system.
Most of the drying is by decanting supernatant liquor and by evaporation.
Plastic or rubber fabrics may be used as a bottom lining, or they may be natu-
ral earth basins. Supernatant liquor and rainwater drain off points are usu-
ally provided, with the drain off liquid returned to the plant for further
processing.
Typical Design Considerations
The loading rate to the lagoon is expressed as pounds of dry solids ap-
plied per year per cubic foot of lagoon capacity. This is calculated as
follows:
1. Determine lagoon volume. The plant construction drawings may contain
this information or it may be possible to simply measure the lagoons.
Length » 100 ft
- 25 ft
= 2 ft
- 2
» Length x Width x Depth x Number of lagoons
» 100 x 25 x 2 x 2
- 10,000 cu ft
Determine sludge flow to lagoon from plant records.
Width
Depth
Number of lagoons
Total volume
Daily flow
Yearly flow
a 150 gal/day
* Daily flow x 365 (or weekly flow x 52)
- 55,000 gal/yr
3. Determine sludge solids concentration
Concentration » Weight of dry sludge
Weight of wet sludge
- 0.5 Ib - 0.05 Ib » 0.05
10 Ib
4. Determine weight of sludge applied to lagoon per year.
Weight - yearly flow x concentration x 8.34
- 55,000 x 0.05 x 8.34
- 23,000 Ib/yr
5. Calculate solids loading rate.
Solids loading rate - Weight of sludge applied per year
Volume of lagoon
- 23,000 Ib/vr
- 10,000 cu ft
- 2.3 Ib/yr/cu ft
Typical design criteria are 2.2-2.4 Ib/yr/cu ft of lagoon capacity.
36-1
-------
Typical Performance Evaluations
Drying time for sludge applied to a depth of 15 inches or less is 3 to 5
months. This figure is highly dependent on weather conditions. The sludge is
usually dried to 40 to 60 percent solids.
Process Control
Sludge depth should not exceed 15 inches after excess supernatant has been
drawn off. Unless the lagoon is situated in an arid climate, depths of over
15 inches will require excessive drying time.
The operator should promptly remove supernatant liquor and rainwater so
that the sludge cake is exposed to oxygen in the air and can dry rapidly.
Supernatant is normally returned to the main plant treatment processes.
Sludge will generally not dewater in any reasonable period of time. Dried
sludge may be removed with a front-end loader in 3 to 5 months. When sludge
is to be used for soil conditioning, it may be stored for added drying before
use. One operational approach uses a 3-year cycle in which the lagoon is
loaded for 1 year, dries for 18 months, is cleaned, and allowed to rest for 6
months.
Maintenance Considerations
The features of a good maintenance program are:
1.
2.
3.
4.
5.
6.
Records
Broken dikes repaired as required.
Excess water from rain or snow decanted to facilitate drying.
Weeds kept to a minimum.
Lagoons checked for odor and insect problems.
Lagoons leveled and weeds removed prior to each sludge application.
Sludge application lines and valves regularly inspected and
maintained.
Sludge lines drained°to prevent breakage from freezing in winter.
Monitoring of sludge lagoons generally consists of visual inspection by
the plant operator. However, records may be kept on the sludge loading, per-
cent solids, quantity, depth, date, drying time and weather conditions. This
will provide the operator with the information necessary to determine the
optimal time of sludge removal from the lagoon by comparing sludge moisture
content with time of drying for particular climatic'conditions.
Laboratory Equipment
,The laboratory should include the following equipment as a minimum to mon-
itor sludge drying lagoons.
1. Analytical balance
2. Drying oven
36-2
-------
Sampling Procedures
Samples of the influent sludge may be obtained through valves provided in
the sludge lines or directed from the lagoon. Samples of dried sludge can be
obtained directly from the lagoon. Samples of supernatant can be collected
from valves in the draw-off lines. The sample collector and containers should
be clean. A wide mouth sample collector of at least 2 inches should be used.
Sidestrearns
The only sidestream is the supernatant or rainwater draw-off. This water
is normally returned to the raw sewage flow for further processing.
36-3
-------
Processing Checklist - Drying Lagoon
1. What are the dimensions of the lagoon
are there ?
_
What is the volume of sludge applied to the lagoons
What type of sludge is applied ?
What is the design sludge application rate
What is the solids loading rate
2.
3.
4.
5. _
6. What is the typical drying time required
7.
8.
9.
10.
How many lagoons
gal/day avg.
_
Ib/yr/cu ft?
months?
_gal/day avg.
_
What is the solids concentration in the dried sludge
Are insects a problem? ( ) Yes ( ) No
Is weed growth a problem? { ) Yes ( ) No
%?
11.
12.
13.
14.
15.
Are partitions between and around the lagoons tight so that sludge will
not flow from one compartment to another? ( ) Yes ( ) No
Are there provisions for supernatant draw-off? ( ) Yes ( ) No
Are there signs of overload? ( ) Yes ( ) No
Does the sampling program meet the recommendations? ( ) Yes ( ) No
Is the laboratory equipped for the necessary analyses? ( ) Yes ( )
What are the most common problems the operator has had with the process?
No
36-4
-------
References
1. Gulp, G.t,., and Folks Helm, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
2. Guarino, C.F., et al, Operation of Wastewater Treatment Plants, Manual of
Practice No. 11, Water Pollution Control Federation (1976).
3. CH2M-Hill, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
36-5
-------
-------
37. INCINERATION - MULTIPLE HEARTH
A multiple hearth furnace consists of a circular steel shell surrounding a
number of solid refractory hearths and a central rotating shaft to which rab-
ble arms are attached. The dewatered sludge enters at the top through a
flapgate and proceeds downward through the furnace from hearth to hearth,
moved by the rotary action of the rabble arms. The hearths are constructed of
high heat duty fire brick and special fire brick shapes. Since the furnace
may operate at temperatures up to 2,000°F, the central shaft and rabble arms
are cooled by air supplied from a blower. The hot air may be discharged to
atmosphere or returned to the bottom hearth of the furnace as preheated air
for combustion purposes.
Periodically the ash produced by incineration must be removed from the
furnace. There are two options for handling ash from the furnace. One is to
provide a storage hopper and unload dry ash to trucks. The other is to add
water and handle ash as a slurry with the slurry being pumped to a lagoon.
Typical Design Considerations
Loading rates for several types of sludge are shown in Table 37-1.
Solids/
Type of sludge %
1. Primary
2.
3.
4.
5.
6.
7.
8.
9.
Primary + FeCl.
Primary + low lime
Primary + WAS
Primary + (WAS +
FeCl3)
(Primary + Fed,
+ WAS
WAS
WAS + FeCl3
Digested primary
30
IS
35
16
20
16
16
16
30
Volatile Chemical
solids, concentration,*
% mg/1
60
47
45
69
54
53
80
50
43
N/A
20
298
N/A
20
20
N/A
20
N/A
Typical wet sludge
loading rate,**
Ib/hr/sq ft
7
6
8
6
6
6
6
6
7
.0-12.0
.0-10.0
.0-12.0
.0-10.0
.5-11.0
.0-10.0
.0-10.0
.0-10.0
.0-12.0
* Assumes no dewatering chemicals.
** Low number is applicable to small plants, high number is applicable to large
plants.
The data in this table developed from manufacturers' information.
37-1
-------
The following sample calculations are examples of process control
equations.
1. Excess Air is the amount of air required beyond the theoretical air
requirements for complete combustion. This parameter is expressed as
a percentage of the theoretical air required.
Sample calculation for excess air:
excess air = (actual air rate-theoretical rate) x 100
theoretical air rate
= (1,500 - 1,000) x 100
1,000
= 50%
2- Sludge loading rate is the weight of wet sludge fed to the reactor
per square foot of reactor bed area per hour (Ib/sq ft/hr).
Sample calculation for loading rate:
loading rate = Ib sludqe/hr 100
TT/^2
% moisture content
440
100
3.14 (20)2 20
4
- 7.01 Ib/sq ft/hr
Solids concentration is the weight of solids per unit weight of
sludge. It is calculated aa follows:
concentration = weight of dry sludge solids x 100
weight of wet sludge
= 25 x 100
120
= 20.8%
Moisture content is the amount of water per unit weight of sludge
The moisture content is expressed as a percentage of the total weight
of the wet sludge. This parameter is equal to 100 minus the percent
solids concentration or can be computed as follows:
moisture content = (weight of wet solids - weight of dry solids) x 100
weight of wet solids
= (120 - 25) x 100
120
79.2%
37-2
-------
Typical Performance Evaluation
Trie volume reduction by sludge incineration is over 90 percent when com-
pared to the volume of dewatered sludge. The ash from the incineration proc-
ess is free of pesticides, viruses and pathogens. Metals will be converted to
the less soluble oxide form or volatilized. The ash can be transported in the
dry state to appropriate landfill sites or used as a soil conditioner.
The critical sidestream treatment requirement is the flue gas treatment.
The scrubbed gases should meet the most stringent air quality requirements. A
comparison of scrubbed gas quality with Southern California Air Pollution Con-
trol District Rules is shown in Table 37-2.
TABLE 37-2. STACK SAMPLING RESULTS, MULTIPLE HEARTH INCINERATOR
WITH COMBINATION LIME-ORGANIC SOLIDS PEED
Test A Test B Test C SCAPCD rules
Combustion contaminants,
grains/SCFM at 12% CO2
Oxides of sulfur:
(as SO2), ppm
Oxides of nitrogen
(as ND2), ppm
.026 .016 .014 0.1
(Rule 473)
2.2 2.3 3.2 2000
(Rule 53)
52 65 - 300
(Rule 474)
Tests made at South Lake Tahoe Public Utility District, CA, on November 10,
1970.
Process Control
Process control furnaces can be complex. A complete discussion is given
in Reference 3.
Maintenance Management
A good preventive maintenance program will reduce breakdowns which could
be costly and dangerous for operating personnel. A good preventative mainte-
nance program is very important for an incinerator because of the large drives
and the need to minimize incinerator shutdowns. The following are the major
elements which should receive regular attention.
1. Drives and gear reducers
2. Chains and sprockets
3. Burners
4. Air blowers
5. Sludge conveying equipment
6. Ash conveying equipment
37-3
-------
7.
8.
9.
10.
11.
Records
Furnace seals
Draft controller
Temperature controllers
Any standby engine drives or generators
Scrubber
Records keeping includes the process control tests shown in Figure 37-1
and historical data. Historical data include the tons of sludge incinerated
each year/ the fuel consumed, and maintenance records. Maintenance records
are extremely important since equipment lives with multiple hearth furnaces
are accurately predictable. Knowing the last date of equipment replacement
the operator can predict the next time that furnace will need to be shut down
for equipment overhaul or replacement.
Laboratory Equipment
Testing equipment for incineration monitoring is quite simple. Most con-
tinuous monitoring is accomplished by automatic equipment which is part of the
total system. Additional equipment items include a drying oven and balance
scales to determine solids contents.
Sampling Procedures
Sampling for many parameters is automatic. Sludge volatile solids and
moisture contents o£ material fed to the incinerator require a simple drawing
off of sludge from the feed line or from the proceeding unit process (storage
or dewatering). There are no special sample preservation measures to be taken
other than capping the sample to prevent a change in moisture content.
37-4
-------
a
a
2
i
o
ui
0.
O
TEMPERATURE
TOTAL
TOTAL SOLIDS
tu
ISj
Co
l!
TEST
FREQUENCY
Mn
1/D3
1/D3
LOCATION OF
SAMPLE
A
F
P
F
P
o
a uj
0 J
I O.
-1
: */i
Mn
G
G
i-
t/i
- tu
S1-
< a
UJ O
a: u.
P
P
P
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
INCINERATION
(MULTIPLE HEARTH)
FEED •
^ ^HEARTHS
•PRODUCT
A. TEST FREQUENCY
H => HQUR M — MONTH
0- DAY R -. RECORD CONTINUOUSLY
W- WEEK Mn" MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
F = FEED
f = PRODUCT
A = FURNACE ATMOSPHERE
(AT EACH HEARTH)
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G " GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn» MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P m PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. WHEN FURNACE IS OPERATING
Figure 37-1
37-5
-------
Process Checklist - Multiple Hearth
1. Are complete records kept on the following items?
4.
5,
6.
a
b.
c.
d.
e.
f.
g.
Hearth temperatures (each shift) ( ) yes ( ) NO
Maintenance work accomplished ( ) Yes ( ) No
Schedule of upcoming maintenance ( ) Yes ( ) No
Fuel consumption (daily) ( ) yes ( ) NO
Power consumption (daily) ( ) yes ( ) No
Sludge moisture content (each shift) ( ) yes ( ) No
Sludge volatile solids content (daily) ( ) yes ( ) NO
Does operator have a planned procedure for slowly shutting down the
process? ( ) Yes ( ) NO
Is there a plan for emergency operation for:
a. Power outage? ( ) Yes ( ) NO
b. Fuel shortage? ( ) Yes ( ) NO
c. Other accidents? ( ) Yes ( ) NO
Is scum burned in the incinerator? ( ) Yes ( ) No
If scum is burned, is the feed rate regulated? ( ) Yes ( ) No
Is moisture content optimized for minimum total cost of dewatering and
fuel consumption in incinerator? ( ) yes ( ) No
37-6
-------
References
1. Standard Methods for the Examination of Water and Wastewater. American
Public Health Association, 14th Edition 1975, Washington, D.C. 20036.
2. Unterberg, W., et al, Computerized Design and Cost Estimation for Multiple
Hearth Sludge Incinerators US EPA, 17070 EBP 07/71.
3. Ettlich, W.F. et al, Operations Manual Sludge Handling and Conditioning,
U.S. EPA, Office of Water Program Operations, Washington, D.C.,
430/9-78-002, February 1978.
37-7
-------
-------
38. INCINERATION - FLUIDIZED BED
The fluidized bed incinerator is a vertical cylindrical vessel with a
grid in the lower section to support a sand 6ed. Dewatered sludge is injected
above the grid and combustion air flows upward to fluidize the mixture of hot
sand and sludge. Supplemental fuel can be supplied by burners above or below
the grid. In essence, the reactor is a single chamber unit were both moisture
evaporation and combustion occur. Ash is carried out the top with combustion
exhaust and is removed by air pollution control devices. A fluidized bed in-
cinerator does not need to be operated continuously since the sand bed stores
heat, thus reducing furnace reheating requirements.
Typical Design Considerations
Typical loading rates for various types of sludge are shown on Table
38-1. The loading rates are a function of the moisture content of the feed
sludge.
TABLE 38-1 LOADING RATES
Solids,
Type of sludge %
1.
2.
3.
4.
5.
6.
7.
8.
9.
Pr imary
Primary + FeCl_
Primary + low lime
Primary + WAS
Primary + (WAS +
PeCl3)
(Primary + FeCl
+ WAS
WAS
WAS + FeCl-
Digested primary
30
16
35
16
20
16
16
16
30
Volatile
solids,
%
60
47
45
69
54
53
80
50
43
Chemical
concentration,*
mg/1
N/A
20
298
N/A
20
20
N/A
20
N/A
Wet sludge
loading rate,
Ib/hr/sq ft
14
6.8
18
6.8
8.4
6.8
6.8
6.8
14
* Assumes no dewatering chemicals.
38-1
-------
The following are sample design calculations.
1.
3.
Excess air is the amount of air required beyond the theoretical air
requirements for complete combustion. This parameter is expressed as
a percentage of the theoretical air required.
Sample calculation for excess air: Assume 1,200 SCFM actual, and
1,000 SCFM theoretical
Excess air
(actual air rate-theoretical rate) x
theoretical air rate
(1,200 - 1,000) x 100 =
100
20%
1,000
Sludge loading rate is the weight of wet sludge fed to the reactor
per square foot of reactor bed area per hour (Ib/sq ftAr).
Sample loading rate: Assume 20 foot diameter reactor, 20 percent feed
sludge moisture content and 440 pounds dry sludge per hour
Loading rate = (Ib dry sludge/hr) (100)
(% moisture content) (area)
- 440 x 100
20% x 3.14 (20)2
4.
- 7.01 Ib/sq ft/hr
Solids concentration is the weight of solids per unit weight of
sludge. It is calculated as follows:
Assume 120 Ib wet sludge with 25 Ib of dry solids.
Concentration = weight of dry sludge solids- x 100
weight of wet sludge
- 25 x 100
120
- 20.8%
Moisture content is the amount of water per unit weight of sludge.
The moisture content is expressed as a percentage of the total weight
of the wet sludge. This parameter is equal to 100 minus the percent
solids concentration or can be computed as follows:
Same assumptions as paragraph 3.
moisture content = (weight of wet solids)-(weight of dry solids x 100
weight of wet solids
= (120 - 25) x 100
120
79.2%
38-2
-------
Performance
The measure of furnace performance is the stack gas quality. The gas
quality is measured in terms of particulates, metals, gaseous pollutants, and
organic compounds. The scrubber is designed to remove particulates with the
ash. Most metals appear as oxides in the particulates removed by the scrub-
ber. Lead and mercury vaporize and will appear in the stack gas. Carbon
monoxide in the stack gas is a sign of improper design or operation.
Process Control
The fluid bed furnace is furnished with a semi-automatic process control
system and a mechanical/electrical protection system, which free the operator
from continuous supervision. The process is maintained in balance at the re-
quired excess air and operating temperatures by normal adjustments in air rate
and sludge feed rate, and automatic control of auxiliary fuel rate. The proc-
ess parameters and physical conditions are kept in check by means of a multi-
point alarm system which warns the operator of impending imbalances in the
process or mechanical equipment.
A variety of process controls are described in Reference 4.
Maintenance Considerations
Sand from the reactor bed is gradually lost through the exhuast as indi-
vidual sand particles are gradually worn into finer and finer particles. When
it has been determined that the bed level is getting low, proceed as follows:
1. Bed temperature should be at least 1,400°F before any sand is added
to the reactor bed. This is to avoid cooling the bed below
1,150°P, and being forced to light the preheat burner.
Be sure that the fluidizing blower is completely stopped.
3.
4.
Remove the blind flange on the sand feed nozzle.
chute.
Attach sand feed
Add sand in 10 bag batches. If more than 10-100 Ib bags are re-
quired, replace the blind flange on the same feed nozzle and reheat
the bed to 1,400°F before adding second 10 bag batch.
There may be slight leakage of sand down into the windbox. About once a
month (when the reactor is not operating), open the windbox manhole and rake
out any accumulation.
Occasionally a carbon deposit may form near the tip of the fuel burner.
If this happens, fuel flow to the bed will be restricted. When the reactor is
shutdown, clean the burner. If available, a slight flow of compressed air
will aid inserting the gun back in the bed.
38-3
-------
From time to time, check that the nut on the packing gland is just tight
enough to prevent loss of cooling air.
At times this pressure tap pipe may become partially plugged. Refer to
manufacturer's manual for cleaning instructions.
Keep gasketed surfaces on the reactor tight to avoid a fly ash nuisance.
Records
Records keeping includes the process control tests as well as historical
data and maintenance records.
The analyses required for furnace monitoring and their frequency are shown
on Table 38-2 for each monitoring point identified on Figure 38-1.
TABLE 38-2. MONITORING
Monitoring point
Analysis
Frequency
1
2
3
3
4
5
5
5
5
5
5
5
5
6
6
7
7
Solids content
Solids content
Solids content
Volatile solids
Fuel quantity
Oxygen content
Particulate concentration
Carbon monoxide
Lead
Mercury
Hydrogen chloride
Sulfur dioxide
Oxides of nitrogen
BOD5
Suspended solids
Metals content
Moisture content
Weekly
Weekly
Weekly
Weekly
Continuous
Continuous
Weekly
Monthly
Semiannual
Semiannual
Semiannual
Semiannual
Semiannual
Weekly
Weekly
Semiannual*
Weekly
* If ash used for soil conditioner.
Laboratory Equipment
Testing equipment for incineration monitoring is quite simple. Most con-
tinuous monitoring is accomplished by automatic equipment which is part of the
total system. Additional equipment items include a drying oven and balance
scales to determine solids contents.
38-4
-------
t-l
•H
CT>
C
N
•H
•a
•H
3
,-1
u
0)
0
1— (
CQ
0)
•fi
I
T)
0)
1
i-H
U
C
o
(fl
+J
c
•H
a
s
•H
C
-------
Sampling Procedures
Sampling for many parameters is automatic. Sludge volatile solids and
moisture contents of material fed to the incinerator require a simple drawing
off of sludge from the feed line or from the preceeding unit process (storage
or dewatering). There are no special sample preservation measures to be taken
other than capping the sample to prevent a change in moisture content.
38-6
-------
Process Checklist - Multiple Hearth and Fluidized Bed Furnaces
1. Are complete records kept on the following items?
a. Temperature (each shift) ( ) Yes
b. Maintenance work accomplished ( )
c. Schedule of upcoming maintenance (
d. Fuel consumption (daily) ( ) Yes
e. Power consumption (daily) ( ) Yes
f. Sludge moisture content (each shift)
g. Sludge volatile solids content (daily)
2. Does operator have a planned procedure for slowly shutting down the
process? ( ) Yes ( ) No
3. Is there a plan for emergency operation for:
a. Power outage? ( ) Yes ( ) No
b. Fuel shortage? ( ) Yes ( ) No
c. Other accidents? ( ) Yes ( ) No
Is scum burned in the incinerator? ( ) Yes ( ) No
If scum is burned/ is the feed rate regulated? ( ) Yes ( ) No
( ) No
Yes ( ) No
) Yes ( ) No
( ) No
( ) No
( ) Yes ( )
) ( ) Yes (
No
) No
4.
5.
6.
Is moisture content optimized for minimum total cost of dewatering and
fuel consumption in incinerator? ( ) Yes ( ) No
38-7
-------
References
1. Standard Methods for the Examination of Water and Wastewater. American
Public Health Association, 14th Edition, 1975, Washington, D.C.
2. Dorr-Oliver FS Disposal System Operating Instructions.
3. Copeland Systems Operating Instructions.
4. Ettlich, W.F. et al, Operations Manual Sludge Handling and Conditioning,
U.S. EPA, Office of Water Program Operations, Washington, D.C.,
430/9-78-002, February 1978.
38-8
-------
39. LIME RECALCINING
Process Description
Lime often is used as a coagulant either as a tertiary step or ahead of
the primary clarifier for removal of phosphorus from wastewaters. In recal-
cining, the dewatered calcium-containing sludge is heated to about 1,850°F.
This drives off water and carbon dioxide leaving calcium oxide (or quicklime).
In municipal wastewater treatment, multiple hearth furnaces have been used
for recalcining. Although fluidized bed furnaces have been used for industri-
al and water treatment purposes, these furnaces have not been used for munici-
pal wastewater recalcining. Prior to the recalcining step centrifuges can be
used to separate the phophate-rich lime from the inert solids also removed by
the lime.
The recalcined lime usually is discharged into a hammermi11 to break up
any lumps that have formed in the furnace. The material is forced against a
grinding plate by the rotating hammers. The lumps are broken up until they
are small enough to fit through the openings in a metal screen. The material
then goes to a thermal disc cooler. When cool, the reclacined lime is stored
and mixed with fresh lime before reuse.
Typical Design Considerations
The capacity of a lime recalcining multiple hearth furnace depends on
solids loading per unit of hearth surface area. Sizing also depends on the
nature of the sludge cake, including moisture, volatile solids, inerts con-
tent, and heat value. A loading rate of 7 to 12 Ib wet sludge/hr/sq ft of
hearth is common. The feed sludge should have a moisture content of less than
50 percent.
Typical Performance Evaluation
Proper operation of the recalcining furnace .should produce a recalcined
lime which will meet the AWWA standard for quicklime (CaO). Typically, the
lime should have a CaO content of at least 60 to 70 percent and should slake
readily in standard slakers. Typical loading rates are about 1 Ib dry solids <
per square foot of furnace hearth area.
Process Control
There.are two important characteristics of the recalcined lime which must
be controlled.
1. Activity, and
2. Slaking characteristics
Recalcined lime must be classified according to the AWWA Standard for
quicklime (CaO) and hydrated lime (Ca(OH)2) (AWWA B202-65):
39-1
-------
High-reactive,
soft burned lime
Med ium-reac tive,
medium burned lime
Low-reactive,
hard burned lime
Time for 40° rise
in temp., (min)
3 or less
3-6
More than 6
Time for complete
reaction (min)
10
20
More than 20
It is possible to produce quicklime with the same CaO content, but with
very different slaking properties.
The most important variables in the operation of the recalcining furnace
are temperature and feed rate. These are addressed in detail in Reference 1.
The rabble arm rate in a multiple hearth furnace has little effect on recal-
cined lime if it is within 1.5 to 2 rpra:
Maintenance Considerations
The features of a good maintenance program are:
1. Burner controls been checked and calibrated within a year.
2. Temperature controllers maintain the hearth temperatures near set
point.
3. Refractory should be inspected on a regular basis.
4. Area housekeeping around the furnace or where there are spills of
lime or buildups of lime dust.
5. Interior of the scrubber been inspected within a year.
6. Check sand level in the upper shaft seal.
Records
Recommended sampling and laboratory tests are shown in Figure 39-1.
Operating records should also include:
1. A method for determining the feed rate to the furnace.
2. Quantity of lime tecovered.
Laboratory Equipment
The laboratory equipment should include the following minimum equipment:
1. Furnace oxygen analyzer
2. Equipment and procedures for analyzing CaO content
39-2
-------
o
a
o
TEMPERATURE
CALCIUM
CONTENT (CaO)
MOISTURE
CONTENT
UJ
(si
*/>
z S
1*
ALL
ALL
ALL
TEST
FREQUENCY
Mri1
21
1/W
LOCATION OF
SAMPLE
A
P
F
METHOD OF
SAMPLE
Mn
G
G
1 REASON
FOR TEST
P
P
C
P
'
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
RECALCINATION
{MULTIPLE HEARTH)
FEED
HEARTHS
PRODUCT
A. TEST FREQUENCY
H m HOUR M — MONTH
D-DAY R - RECORD CONTINUOUSLY
W- WEEK Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
F = FEED
P = PRODUCT
A = FURNACE ATMOSPHERE
(AT EACH HEARTH)
C. METHOD OF SAMPLE
24C-Z4 HOUR COMPOSITE
G - CRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn» MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P m PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. WHEN FURNACE IS OPERATING
2. SPOT CHECK
Figure 39-1.
39-3
-------
3. Drying oven
4. Analytical balance
5. Normal glassware and accessories
The EPA report "Estimating Laboratory Needs for Municipal Wastewater
Treatment Facilities" contains very detailed information on glassware, chemi-
cals, and miscellaneous furniture and should be referred to for any detailed
questions.
Sampling Procedures
Samples should be taken at times and locations where representative
samples can be obtained. Samples of hot materials should be handled carefully
and should be stored in metal containers.
Sidestrearns
The major sidestream is the scrubber water which can be returned to the
liquid treatment process or to sludge thickeners.
39-4
-------
Process Checklist - Lime Recalcining.
1.
2.
3.
4.
5.
6.
7.
8.
10.
11.
12.
13.
14.
15.
16.
What is required lime dosage in the liquid process
average?
What is average flow through lime treatment
_lb/mg
rag/day?
Calculate approximate average lime recalciner feed rate, item 1 x item 2
Ib/day
Ib/day?
" -Ib/hr.
What is rated capacity of furnace,
Check feed rate at the current setting,
Is the recalcined lime CaO content checked as a regular process
control parameter? ( ) Yes ( ) No
Is feed sludge moisture content checked on a regular basis?
( ) Yes ( ) No ;
Is there a method to selectively waste approximately 25% of the lighter
fractions of the feed sludge in order to control inerts?
( ) Yes ( ) No
Are hearth temperatures logged and are they adequately controlled?
( ) Yes ( ) No
Is the lime grinder and cooler in operation?( ) Yes ( ) No
Is the maintenance program adequate? ( ) Yes ( ) No
Have the burners been calibrated within a year? ( ) Yes ( ) No
Are the alarms and shutdowns adequate? ( ) Yes ( ) No
Are they checked regularly? ( ) Yes ( ) No
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory and operational office equipped for the necessary
analyses? ( ) Yes ( ) No
What spare parts are stocked?
17. What are the most common problems the operator has had with the process?
39-5
-------
References
1. Gulp, G.L. and Polks Heim, N., Field Manual for Performance Evaluation and
Troubleshooting at Municipal Wastewater Treatment Facilities, EPA
430/9-78-001.~
2. Gulp, Russell It., and Gulp, Gordon L., Advanced Wastewater Treatment, Van
Nostrand Reinhold Co., 1971.
3. CH2M-H111, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Culp/Wesner/Culp, Operation and Maintenance Manual, Water Factory 21,
Orange County water District", (June, 1974).
6. CH2M-Hill, Operation and Maintenance Manual for Wastewater Reclamation
Facility, South Tahoe PUD, (1976).
7. Gulp, R.L., et al, Advanced Wastewater Treatment as Practiced at South
Tahoe, U.S. Environmental Protection Agency, Project 17010 ELQ (WPRD
52-01-67), August, 1971.
39-6
-------
40. GRANULAR CARBON REGENERATION
Process Description
Granular activated carbon removes detergents, insecticides, herbicides,
and various organic substances which contribute to the taste, odor and color
of the wastewater. The carbon eventually becomes saturated and loses its
ability to further adsorb organic materials. The carbon nearest to the inlet
of the contactor becomes saturated or exhausted first.
The purpose of the regeneration process is to restore the adsorptive
capacity of the granular carbon. Regeneration is accomplished by heating the
carbon to temperatures in excess of 1,500°F. The heat vaporizes and drives
off the adsorbed impurities restoring the carbon essentially to its original
activity. Regeneration is carried out most effectively in multiple hearth
furnaces.
The carbon is dewatered prior to feed to the furnace and the hot regen-
erated carbon cooled in a quench tank upon discharge from the furnace. The
regenerated carbon is then washed to remove fines.
Typical Design Considerations
Experience has shown that carbon dewatering can be accomplished by gravity
in about 1 hour with properly designed dewatering bins. The dewatered carbon
should have a moisture-content of 40 to 45 percent. The dewatering bin should
be sized for a reasonable quantity of carbon, typically, a days feed to the
furnace.
Typically, furnace loadings are based on the hearth area, with an average
being 50 to 70 Ibs per day of carbon per square foot of total hearth for a 6
hearth furnace. A 6-hearth, 54-inch inside diameter furnace is rated for
approximately 6,000 Ib of carbon per day. A regeneration furnace can be oper-
ated over a wide range of carbon feed, and can be turned down by a ratio of
6:1, however it is usually better to operate at a constant rate if possible.
Typical Performance Evaluation
The performance of the carbon regeneration process is best determined by
apparent density (AD) tests of the regenerated carbon. The AD of new carbon
is about 0.48. As carbon becomes saturated with adsorbed organics, the AD
increases to over 0.50. If properly regenerated, the AD will return to 0.48.
If the AD is greater than 0.49, the carbon is not being heated enough to
volatilize a sufficient quantity of organic material; conversely if the AD is
less than 0.48, the carbon is being overheated and burned in the furnace.
Process Control
The regeneration process consists of several steps as the carbon passes
through the furnace.
40-1
-------
1. Drying
2. Decomposition or pyrolyzing of the adsorbed organic matter.
3. Gasification of the organics and reactivation of the carbon pore
structure.
These and other process considerations are discussed in Reference 1.
Maintenance Considerations
The features of a good maintenance program that the inspector should look
for are:
1.
2.
3.
4.
5.
6.
7.
Records
Burner controls checked and calibrated within a year.
Temperature controllers maintain the hearth temperatures near set
point.
Refractory appears in good condition.
Dewatering screens cleaned regularly.
Area around the furnace cleaned.
Interior of the scrubber been inspected within a year.
Sand level in the upper shaft seal.
Recommended sampling and laboratory tests are shown in Figure 40-1.
(Derating records should also include:
1. A written log of carbon movements and regeneration scheduling.
2. A method to determine the carbon feed rate to the furnace.
3. A method to determine carbon losses and make-up carbon additions.
Laboratory Equipment
The laboratory equipment should include the following minimum equipment:
1. Graduated cylinder, drying over, balance, and shaker for running
apparent density test.
2. Carbon grinder and other equipment for iodine number test.
3. Furnace oxygen analyzer.
Sampling Procedures
Samples should be taken to assure that they are representative. Most of
the carbon sampling involves dipping out scoups of the material. Hot carbon
should be handled with care to avoid injury and should be stored in metal
containers.
Sidestreams
Sidestream flows consist of carbon transport water, dewatering tank drain-
age, defining water, quench tank overflow, and scrubber water. These side-
stream flows are a very small percent of the liquid process flow and may be
returned to the primary or secondary treatment process.
40-2
-------
a
s
>
8
(9
t-
a
o
TEMPERATURE
OXYGEN
CONTENT
PERCENT ASH
APPARENT
DENSITY
IODINE
NUMBER
APPARENT
DENSITY
PLANT SIZE 1
(MGD) 1
ALL
ALL
ALL
ALL
ALL
ALL
ITEST
FREQUENCY |
Mn1
1/D1
1/D1
1/H1
1/D
VP1
1 LOCATION OF
SAMPLE |
A
A
P
P
F
P
F
METHOD OF
SAMPLE
Mn
G
G
G
G
G
1 REASON
FOR TEST 1
P
P
P
P
; H
H
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
CARBON REGENERATION
(MULTIPLE HEARTH)
FEED
HEARTHS,
PRODUCT
A. TEST FREQUENCY
H - HOUR M - MONTH
0 - DAY R - RECORD CONTINUOUSLY
W-~WEEK MB- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
F =FEED
P =PRODUCT
A = FURNACE ATMOSPHERE
(AT EACH HEARTH)
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G - GRAB SAMPLE
R " RECORD CONTINUOUSLY
Mn« MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. WHEN FURNACE IS OPERATING
2. SPOT CHECK
Figure 40-1
40-3
-------
Process Checklist - Granular Carbon Regeneration
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
_lb/mg
What is required carbon dosage in the liquid process
average?
What is average flow through carbon rag/day?
Calculate approximate average carbon regeneration rate, item 1 x item 2
Ib/day
Ib/day?
Ib/hr.
What is rated regeneration capacity of furnace,
Check feed screw rate at the current setting,
Is carbon moved on a regular schedule?
( ) Yes ( ) No
Is carbon dewatering checked before carbon is fed to furnace?
( ) Yes ( ) No
Are process control tests (AD's) run during regeneration?
( } Yes ( ) No
Are hearth temperatures logged and are they adequately controlled?
( ) Yes ( ) No
Is the regenerated carbon washed to remove fines prior to use?
( ) Yes ( ) No
Is the maintenance program adequate? ( ) Yes ( ) No
Have the burners been calibrated within a year? ( ) Yes ( } No
Are the alarms and shutdowns adequate? ( ) Yes ( ) No
Are they checked regularly? ( ) Yes ( ) No
Are operating records adequate? ( ) Yes ( ) No
Is the laboratory and operational office equipped for the necessary
analyses? ( ) Yes ( ) No
What spare parts are stocked?
17. What are the most common problems the operator has had with the process?
40-4
-------
References
1. Gulp, G.L. and Polks Heim, N., Field Manual for Performance Evaluation and
Troubleshooting at Municipal Wastewater Treatment Facilities, EPA
430/9-78-001.
2. Gulp, Russell L., and Gulp, Gordon L., Advanced Wastewater Treatment, Van
Nostrand Reinhold Co., 1971.
3. CH2M-H111, Estimating Laboratory Needs for Municipal Wastewater Treatment
Facilities, EPA Contract 68-01-0328 (June, 1973).
4. Wirts, J.J., et al, Safety in Wastewater Works, Manual of Practice No. 1,
Water Pollution Control Federation (1959).
5. Culp/Wesner/Culp, Operation and Maintenance Manual, Water Factory 21,
Orange County water District", (June, 1974).
6. CH2M-Hill, Operation and Maintenance Manual for Wastewater Reclamation
Facility, South Tahoe PUP, (1976).
7. Gulp, R.L., et al, Advanced Wastewater Treatment as Practiced at South
Tahoe, U.S. Environmental Protection Agency, Project 17010 ELQ (WPRD
52-01-67), August, 1971.
40-5
-------
-------
41. LAND APPLICATION OF SLUDGES
Sludge can be applied to land areas for disposal purposes, crop growing,
or to reclaim spoiled land. Application for disposal purposes is identical in
concept to a landfill except only the top 1-2 feet of soil are used. Sludge
application can be used for providing nutrients and organic matter to crop
lands. These systems require careful controls to insure that crop nutrient
requirements are met and that no harmful elements such as cadmium are applied
in excessive amounts. Reclamation of spoiled land, such as strip mined areas,
is a special case similar in scope to application to farm lands. Due to the
specialized nature, reclamation will not be discussed. The review procedures
would be very similar to those procedures used for crop use but loading rates
and use of other materials would be different.
Sludge can be applied as a liquid, dewatered cake, dried matter, or ash.
For use with this section, the definitions of these forms are as follows:
Form
Liquid
Dewatered cake
Dried Matter
Ash
Solids Concentration
0-10%
10-40%
90-98%
100%
Application methods vary with site characteristics, use of site and form
of the sludge.
Typical Design Considerations, Evaluation, and Control
The loading rate or application rate is a function of the sludge and soil
characteristics and crop nutrient requirements. Sludge and soil characteris-
tics and crop requirements vary widely.
The sludge application rate is primarily based on the sludge nitrogen con-
tent and the nitrogen requirements of the crop. Nitrogen in sludge is avail-
able for immediate plant use in the ammonium (NH$) or nitrate (NO§)
forms. The availability of organic nitrogen to the crop depends on the miner-
alization rate which can be determined after several years of operation.
The heavy metal application rate must also be checked so that recommended
maximum are not exceeded.
The procedure for determining the application rate is described in Refer-
ence 3. To simplify this Table 41-1 is presented. This table shows applica-
tion rates for various crops based on the nitrogen requirements, and assuming
70 Ib organic nitrogen/ton of sludge, with a mineralization rate of 15-10-5,
and an ammonium nitrogen content of 30 Ib/ton of sludge.
The monitoring program consists of the analyses shown in Figure 41-1.
Sampling and monitoring must be performed by qualified personnel or outside
laboratories.
41-1
-------
Crop
Alfalfa
Orchard grass
Corn (grain)
(stover)
Sorghum (grain)
(stover)
Corn silage
Oats (grain)
(straw)
Soybeans (grain)
(straw)
Wheat (grain)
(straw)
Barley (grain)
(straw)
Yield,
per acre
8
6
6
180
8,000
8,000
32
100
60
7,000
80
6,000
100
tons
tons
tons
bu
Ib
Ib
tons
bu
bu
Ib
bu
Ib
bu
Application yr
1
9.1
7.4
4.2
1.7
3.0
3.2
5.9
2.0
0
6
2
3
1
2
1
.86
.0
.1
.6
.0
.7
.0
234
Tons/acre of sludae
7.8
6.3
3.6
1.5
2.5
2.7
5.0
1.7
0
5
1
3
0
2
0
.74
.1
.8
.0
.89
.3
.84
7.4
6.0
3.4
1.4
2.4
2.6
4.8
1
0
4
1
2
0
0
.6
.70
.8
.7
.9
.84
.2
.80
7.0
5.6
3.2
1.3
2.2
2.4
4-5
1
0
4
1
0
0
2
.66
.6
.6
.7
.79
.1
.75
5
6.6
5.4
3.0
1.2
2.1
2.3
4.3
1.4
0.62
4.3
1 5
2.6
0.75
2.0
0.71
Sensory observations can detect many problems before environmental mon-
itoring tests. When injecting sludge, the application rate should be such
that sludge does not surface. If sludge surfaces, the injector speed should
be increased or the sludge flow decreased so that the quantity injected per
unit area decreases. If the injector travel speed is excessive, soil may be
thrown away from the shank creating an open trench;
If the sludge is spread on the surface, the rate should be low enough to
prevent the excessive ponding or runoff. Excessive ponding is when the liquid
is still above the surface several hours after application. Either excessive
ponding or runoff indicates excessive application rates for the soil. This
will vary widely from soil to soil.
Maintenance Considerations
Maintenance requirements are mainly cleaning and equipment service. The
cleaning operation include daily flushing of the injectors (if used) and
periodic flushing of the tanks. Truck, tractor, and equipment preventative
maintenance schedules will be specified in manufacturer's data.
Records
t0 the n°rmal rec°rd kept for *°nitoring and process con-
where L Trat°^S) mUSt keep a dail* log OE site maP record *>
Where, when, and how much sludge has been applied.
41-2
-------
r
•
a
o
UJ
u>
8
>
_i
o
a.
o
ros
COD
TKN
NH3-N
NO -N
P
FECAL
COLIFORM
FECAL
STREP
SALMONELLA
CYSTS
pH
Cl
AJjKATvTNTTY
1 'F&lB;
METALS NlJ
\Ha
1
3
PKN
k-»
[
r
s.
PLANT SIZE 1
(MOD) j
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
ALL
SJ,L_
ALL
ALL
ATrT(
ALL
ALL
ALL
ALL
ALL
\LKALINITY |ALL
TEST 1
FREQUENCY j
w
w
w
w
w
w
M
M
M
M
D
M
W
M
M
W
M
A
A
A
A
A
[LOCATION OF
SAMPLE
SI
SI
SI
SI
SI
SI
SI
SI
SI
SI
SI
SI
R1
SI
SI
si
SI
So
So
So
So
So
[METHOD OF
SAMPLE
G
G
G
G
G
G
G
G
G
G
G
G
. G
G
G
G
G
G
G
G
G
G
H
Z%
S'1-
< o:
uj O
a u.
P
P
P
P
P
H
P
P
P
P
P
' P
c
P
P
P,,
P
P
P
P
P
P
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
LAND APPLICATION OF SLUDGES
A. TEST FREQUENCY
H m HOUR M - MONTH
0 - DAY R - RECORD CONTINUOUSLY
W. WEEK Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
SL =SLUDGE BEING APPLIED
SO =SOIL
M =MONITORING WELLS OR
NEARBY BY STREAMS
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
a - GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn- MONITOR CONTINUOUSLY
0. REASON FOR TEST
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
Figure 41-1
41-3
-------
SUGGESTED MINIUUM
_J
o
§
CONTROL EXCH.
CAPACITY
SALMONELLA
CYSTS
CHLORIDE
B
jpH
ICOLIFORM
FECAL •
COLIFORM
>JO,-N
ros
uj
N
V)
|s
2a
ALL
ALL
AT.T
ALL
ALL
ALL
ALL
ALL
ALL
ALL
>
u.
7.
u
_§
,/! 1U
iu a
1- U.
A
A
A
A
A
M
M
M
M
M
LOCATION OF
SAUPI f
So
So
So
So
So
So
M
M
M
M
METHOD OF
SAMPLE
G
G
a
G
G
G
24C
24C
24C
G
REASON
FOR TEST
P
H
P
P
P
P
P
P
P
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
LAND APPLICATION OF SLUDGES
«
A. TEST FREQUENCY
H m HOUR M - MONTH
D-DAY R - RECORD CONTINUOUSLY
W- WEEK Mn» MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
SL= SLUDGE BEING APPLIED
S0= SOIL
M = MONITORING WELLS OR
NEARBY BY STREAMS
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
G - GRAB SAMPLE
R " RECORD CONTINUOUSLY
Mn» MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
Figure 41-1 (cont'd)
41-4
-------
Laboratory Equipment
The laboratory should include the following minimum equipment in order to
monitor land application:
1. Analytical balance
2. Blender
3. Fume hood
4. Incubator
5. Kjeldahl digesting and distilling apparatus
6. Oven
7. pH meter
8. Pump (vacuum-pressure)
9. Spectrophotoraeter
10. Sterilizer
11. Titrator-araperometric
Sampling Procedures
Sampling should be done on representative sludge and soil. Sludge that
has been in storage for overnight should not be sampled for nitrogen forms or
pH. "Fresh" sludge should be used for samples to set loading rates.
Similarity, soil samples should be taken from areas of the field that pre-
dominate. In other words if a field consists mainly of a clay-loam with an
isolated area of sand, then the samples should be taken from the loam areas
and not in the sandy area. This does not mean the sandy area should be
ignored but rather that the overall loading rates should be based on results
from samples taken in the loam soil.
Sidestrearns
With a properly operated and maintained land application system there
should be no sidestreams. The land application system should b« designed such
that accidental spills will be contained and sludge will not enter surface
water.
41-5
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Process Checklist - Land Application
A. General
1. Is sludge application for disposal only, crop utilization, or recla-
mation of spoiled area? (circle one)
2. Does site visit reveal any areas of runoff or ponding?
( ) Yes ( ) No
3. Is emergency storage provided? ( ) yes ( ) NO
* Are field records in order? ( ) Yes ( ) No
Is a preventive maintenance plan in use? ( ) Yes ( ) No
Is there an emergency plan for power outages or maior equipment
failures? ( ) Yes ( ) NO
Does the sampling program meet recommendations? (
Is an O&M manual available? ( ) Yes ( ) No
Is OSM manual used? ( ) Yes ( ) No
Is laboratory properly equipped? ( ) Yes ( )
What spare parts are stocked?
5,
6.
7.
8.
9,
10.
11.
) Yes ( ) NO
No
12.
What are the most common problems the operator has had with the
process?
B. Farming (if applicable)
1. la farming done by agency staff and equipment? (
2. Is farming done by contract? ( ) yes ( ) No
What crops are grown? _^^_____^
Are crops rotated?
) Yes ( ) NO
3.
4.
5.
( ) Yes ( )
NO "
and are
41-6
-------
References
3.
Research Publication 235, Clumbus,
nnirti. tTF '- -i. np>r,M«n, M.nual Sludge Haling and Conditioning.,
U.S. EPA, Office of Water Program Operations, Washington, D.t. ,
430/9-78-002, February 1978. -
41-7
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-------
42. LANDFILL
Process Description
Burying sludge to minimize nuisance conditions or public health problems
is called landfill. Sludge is buried in layers which are covered with fill
material excavated at the site. Landfills must be located where nearby wells
or groundwater supplies will not be contaminated by leachate from the fill
operation. Sludge landfills are generally separate from refuse landfills.
Typical Design Considerations
Loading rates for landfill operations and soil layer depths for a typical
site are given in Table 42-1.
TABLE 42-1. DESIGN CRITERIA
Trench width
Bottom
Top
Trench length
Sludge layer
Intermediate fill layer
Top fill cover
Distance between
trenches
Distance from property
line
Distance from
drainage ditch
12 ft
28 ft
50 ft
2 ft
1 ft
3-5 ft
15 ft
150 ft
30 ft
The depths are required for safety (to prevent contamination of adjacent
areas and to prevent cell or trench cave-ins) and for ease of operations with
conventional excavation equipment. Variations deppend on special site
characteristics.
Typical Performance Evaluation
Performance of a, landfill is measured as a function of disposal without
harming the surrounding environment or producing nuisances.
A landfill system can be operated such that no odors or vector habitats
are produced. There should be no runoff or change in natural drainage.
Leachate is controlled by not trenching to an elevation less than 15 to 20
feet above the impervious layer. Leachate quantity can be minimized by pump-
ing excess from the trench to a tanker truck. Unlike most other processes,
this one either succeeds or fails with little margin for partial failure.
42-1
-------
Successful operation of a landfill system is measured by monitoring wells and
nearby surface streams and by sensory observations.
There should be several monitoring wells located just inside the site
boundaries. Well depths are variable. The wells should consist of a 6-inch
pipes fitted with a threaded cap on top and a well screen at the bottom (or
SkS^fS'a/flTi'i1?!11!*1? n°rmally placed in 16-inch borings, which are
packed with 3/5 to 1-1/2-inch gravel. Sampling can be accomplished through
hn^ °13 P°rtable PufflP and a 20-foot, 4-inch pipe with a foot valve at the
bottom. These wells and domestic wells within 1/4 mile of the landfill should
be sampled prior to startup of the landfill.
Table 42-2 shows a list of constituents to be included in the well
monitoring.
TABLE 42-2.
WELL ANALYSIS
Boron
Cadmium
Copper
Iron
Lead
Mercury
Zinc
TDS
PH
Chloride
Phosphorus
N02-N03
Total coliforra
Fecal coliform
Fecal streptococcus
The drainage ditch should be monitored during flow periods. The ditch
^ ShOUid ^ 3t the tW° P°intS Where the ditch crosses toe
if *r < difference between «» upstream and downstream locations win show
if there is an increase due to the landfill operation.
Table 42-3 shows the tests to be done on the drainage ditch flows.
TABLE 42-3. DRAINAGE DITCH ANALYSTS
Fecal coliform
Coliform
Suspended solids
BOD
Phosphorus
pH
42-2
-------
The monitoring wells are sampled monthly. The drainage ditch is sampled
when rainfall occurs but no more than once per week. The domestic wells are
sampled quarterly.
Process Control
Landfill controls consist of surface runoff management to prevent runoff
from passing through the fill site. The process is controlled by varying the
layers of sludge and/or fill material. If the moisture content of the sludge
increases then smaller layers of sludge would be placed in the trench.
Maintenance Considerations
Vehicle maintenance should include preventative maintenance in accordance
with manufacturer's guidelines and daily inspection.
Daily inspection should include the following:
Fuel level
Oil level
Battery
Tires (or tracks)
Hydraulic systems (where applicable)
Grease crane and crawler
Turn signals and brake lights on trucks
Completed landfill areas should be seeded and observed to insure that
grass distribution is adequate and that there are no exposed soil areas.
Records
Records for this process consist of laboratory analyses records of mon-
itoring wells and nearby drainage areas, notation of visual or sensory obser-
vations, weather records, and maps showing areas filled and dates of filling.
Sampling locations and frequencies are shown on Figure 42-1.
Laboratory Equipment
The following laboratory equipment items are required for monitoring a
landfill operation:
1. Analytical balance
2. Blender
3. Fume hood
4. Incubator
5. Kjeldahl digesting and distilling apparatus
6. Oven
7. pH meter
8. Pump (vacuum-pressure)
42-3
-------
a
o
ui
(9
5?
I
BORON
CADMIUM
COPPER
IRON
LEAD
MERCURY
ZINC
IDS
pH
CHLORTDR
PHOSPHORUS
»,-*>,
TOTAL
COLIFORM
FECAL
COLIFORM
PECAL
STRRPTornrpTT.c;
SUSPENDED
SOLIDS
BOD
SH,
UJ
N
w»
^1
OL i
ALL
ALL
ALT
ALL
ATT.
ALL
ALL
ALL
ALL
ftliTi
ALL
ALL
ALL
ALL
TiTi
ALL
\LL
\LL
TEST
FREQUENCY
S
S
S
S
S
S
S
S
M
M
M,A
M,A
Mrfl
M,A
M,A
S
A
A
A
LOCATION OF
SAMPLE
W
W
W
W
W
W
W
W
W,D
W
W,D
W,D
W.D
W,D
W.D
D
D
D
METHOD OF
SAMPLE
REASON
FOR TEST
ESTIMATED UNIT PROCESS SAMPLING AND
TESTING NEEDS
LANDFILL
DRAINAGE
DITCH
W]
A. TEST FREQUENCY
S= SEMI-ANNUAL M - MONTH
A= AS REQUIRED- R - RECORD CONTINUOUSLY
AFTER RAINFALL Mn- MONITOR CONTINUOUSLY
B. LOCATION OF SAMPLE
W= WELL( (w))
D= DITCH V^
C. METHOD OF SAMPLE
24C-24 HOUR COMPOSITE
C- GRAB SAMPLE
R - RECORD CONTINUOUSLY
Mn. MONITOR CONTINUOUSLY
D. REASON FOR TEST
H - HISTORICAL KNOWLEDGE
P - PROCESS CONTROL
C - COST CONTROL
E. FOOTNOTES:
1. THESE TESTS SHOULD ALSO BE RUN ON RECEIVING
WATER, ABOVE AND BELOW OUTFALL. ON A
PERIODIC BASIS. DEPENDING ON LOCAL CONDITIONS.
2. FOR PLANTS DESIGNED TO CONTROL THIS
PARAMETER.
Figure 42-1
42-4
-------
9. Spec tropho borne ter
10. Sterilizer
11. Titrator-araperometric
Sidestreams
The sidestream from a landfill operation is the leachate. There is very
little that can be done to control leachate from a landfill operation. Gen-
erally, leachate is controlled by selecting a site with no underlying ground-
water or with an impermeable soil layer between the fill bottom and ground-
water. Under certain conditions liners or clay soil layers are allowed to
hold moisture and minimize leachate movement.
42-5
-------
Process Checklist- - Landfill
2,
3,
4.
5,
6.
7.
8.
9.
storage available for periods of rainy weather
. Yes ( ) No
Are trenches dug in advance of fill operation? ( } Yes (
Do operators maintain safe distance from edge of trench? (
Are trenches covered each night at end of shift? ( ) Yes
Are odors present? ( ) Yes ( ) No
Are flies present? { ) Yes ( ) No
Are rodents a problem? ( ) Yes ( ) NO
Are filled areas revegetated? ( ) yes ( ) NO
Is there a scheduled maintenance plan? ( ) Yes ( ) No
(2 weeks or
) No
Yes
( ) No
( ) No
10. Are maintenance records current?
( )
( ) NO
42-6
-------
References
1. Lukasik, G.D., and Cormack, J.W., "Development and Operation of a Sanitary
Landfill for Sludge Disposal", paper presented at EPA 208 Seminar, Beston,
Virginia, March 16, 1977.
2. Standard Methods for the Examination of Water and Wastewater. American
Public Health Association, 14th Edition, 1975, Washington, D.C.
3. Gulp, G.L., and Folks Heim, N., Field Manual for Performance Evaluation
and Troubleshooting at Municipal Wastewater Treatment Facilities, US EPA
Report 430/9-78-001 (Jan. 1978).
•»U.S. GOVERNMENT PRINTING OFFICE: 1979-292-127
42-7
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