-------
(4) Greater reliability
(a) Shock loads
(b) Industrial discharges
(5) Greater reduction of total oxygen demand
(6) Greater flexibility
New Water Quality Requirements and Standards
A - Federal Water Pollution Control Act Amendments of 1972
(1) Infiltration/Inflow control
(2) "Best practicable technology" by July 1, 1977
(Effluent limitations based on secondary treatment)
(3) "Best available technology" by July 1, 1983
(4) National goal to eliminate discharge of pollutants
B - Improved effluent quality to meet non-regulatory requirements
(1) Reduction of eutrophication
(2) Improve quality of water supply
(3) Trends toward water refuse
General Upgrading Possibilities
A - Addition of secondary treatment components to existing
primary plant
B - Common changes to existing secondary treatment facilities
8
-------
(1) Infijtration/Inflow reduction
(2) Flow equalization
(3) Chemical clarification
C - Modification of basic trickling filter plants
(1) Change from low-rate to high-rate
(2) Change from single stage to two stage
(3) Add activated sludge to high rate system
(4) Add roughing filter to high rate system
D - Modification of basic activated sludge plants
(1) Change from conventional to step-aeration
(2) Change from conventional to contact-stabilization
(3) Change from conventional to complete-mix
l
(4) Conversion to oxygen aeration
E - Other basic upgrading or polishing methods
(1) Chemical treatment
(2) Tube settlers
(3) Polishing lagoons
(4) Microscreening
(5) Media filtration
(a) Sand
(b) Dual media
(c) Multi-media
(6) Carbon adsorption (conversions to physical-chemical
treatment)
9
-------
(7) Pre- and post-aeration
(a) Diffused
(b) Mechanical
Upgrading sludge handling facilities
(1) Thickening
(2) Digestion
(3) Dewatering
Operation and maintenance
(1) Instrumentation
(2) Manpower
10
-------
Treatment Process
Approximate % Reduction
Pre-screening
Plain sedimentation
Chemical precipitation
Trickling filtration
preceded and followed
by plain sedimentation
Activated sludge
preceded and followed
by plain sedimentation
Wet burning (Extended
Aeration)
Stabilization ponds
Chlorination of effluent
of biological treatment plant
B0D5
5-10
25-40
50-85
50-95
55-95
90-95
90-95
Suspended
Solids
2-20
40-70
70-90
50-92
55-95
70-95
80-90
Coliform
Bacteria
10-20
25-75
40-80
90-95
90-98
90-98
95-98
98-99
COD
5-10
20-35
40-70
50-80
50-80
50-80
70-80
Approximate Efficiencies of Conventional
Treatment Processes
TABLE 1
11
-------
FLOW EQUALIZATION
-------
FLOW EQUALIZATION
1. Introduction
a. Flow equalization is the method of dampening or equalizing the
diurnal flow variations.
b. Achieves a constant or nearly constant flow of pollution load
to downstream treatment processes.
c. Interest in flow equalization for municipal treatment has
increased recently due to:
- Strict water quality standards
- Elimination of plant bypassing
- Increased removal efficiencies when processes are operated
at or near steady-state
2. Advantages of Flow Equalization:
a. Diurnal flow variations eliminated
b. Nearly constant flow rate provided to treatment processes
c. Distribution of shock loads of toxic materials
d. Increased reliability of treatment efficiencies
e. Optimization of process operation possible
f. Savings in Federal and/or State fines for violationof effluent
standards
3. Sizing of Equalization Basins
a. Plot hourly flow variation
b. Superimpose the inflow mass diagram of hourly fluctuations for
the typical daily wastewater flow
- Accumulate hourly flows
- Convert to equivalent volumes
c. Draw a straight line from origin to end point on inflow mass diagram
d. The slope of line A represents average pumping rate from equalization
basin to downstream units (example is 10,000 gal/hour)
I
-------
e. Draw straight lines B and D parallel to A and tangent to the inflow
mass diagram at maximum and minimum points, E and F.
f. Vertical distance between lines B and D is mLnumum required ,
equalization volume (example is 30,000 gal or approximately 12.5%
of average daily flow).
g. Additional sizing of basin should include:
- Anaerobic digester supernatant
Sludge dewatering filtrate
- Other return flows to head of plant
- These flows can create shock loads and reduce efficiency
. COD's from 10,000 - 20,000 mg/1
. Ammonia up to 1,000 mg/1
h. For the example, total equalization volume should be:
Source % Flow
Flow equalization 12.5
Digester supernatant 0.3 - 1.4
Sludge dewatering filtrate 0.5 - 1.5
Total 13.3 -15.4
i. Maximum volume to equalize typical flows depend on magnitude of
infiltration and extraneous surface water entering collection system.
- Examine plant's past flow records
- Evaluate regulatory elimination of bypassing
Consider economics to equalize extreme peaks of wet-weather flow
j. Successful operation of equalization basins should include:
- Completely mixed basins (prevents deposit)
- Use of diffused air or mechanical surface aerators (prevents
septicity)
4. Design and Costs Estimates
a. Capital cost estimates, not including land costs, contingencies,
engineering design and bonding are:
2-
-------
Plant Size
MGD
Capital Costs
$1,000*8
1
3
5
210
450
600
ENR Index 1,500
b. Costs were based on typical flow diagram and 15% of treatment
plant daily capacity.
c. Basins may be constructed as
- Shallow-lined lagoons
- Conventional circular concrete tanks
- Conventional rectangular tanks
d. Select basin dimensions to avoid interference between aerators and
to minimize fluctuations in basin water level
e. Minimum basin size of 15 to 50 feet square and minimum depth of
5 to 8 feet
f. Use compartmented basins to avoid large volumes of dead storage
- Two compartments of a four-compartment basin for diurnal flows
- All four compartments for wet-weather peaks
g. Maintain minimum water level to protect floating surface aerators
- Compartmentalization
- Low-level controls on pump and aerator
h. Suspended solids concentrations of approximately 200 mg/1 require
0.02 to 0.04 hp/1,000 gallons of maximum storage volume
i. To prevent septicity, supply oxygen to the equalized flow at
approximately 15 mg/l/hr. Mechanical aerators furnish mixing
and aeration (3-4 lbs 02/hp/hr)
j. Design considerations:
- Earthen lagoons when ground conditions and space are
satisfactory, reduces cost
- Reinforced concrete basin when lagoons are not feasible
- Anchor floating aerators to periphery of basin and permit
fluctuation with water level
3
-------
- Variable-speed centrifugal pumps
k. Two types of flow equalization basins
Flow-through
- Side-line
1. Volume requirements are identical
Flow-through type provides better mixing or mass flow dampening
Side-line type retains flow in excess of average but minimizes
Case History
a. Flow equalization utilizing side-line basin
b. Performance data for a five month period at Walled Lake-Novi plant
pumping requirements
included
WALIED LAKE NOVI WASTEWATER TREATMENT PLANT 2 I >|l
Performance Data - Walled Lake Novi
Plant
SEPT. 71
OCT. 71
NOV. 71
DEC. 71
MN. 72
MONTH
PERFORMANCE DATA
WALLED LAKE-NOVI PLANT
BOO SS BOD SS
S1.fi 91 5 6 4.1
98.8 SI 2 2 3 4
91.E S3.7 2 3 18 7
98.0 92 3 * 2 3 IS O
98.2 91.1 3 S 1.0
REMOVAL %
EFF
in mum
MLtfl BACK VISI
BAHI Sllllfif
I
Mini
imitit
Walled-Lake Novi Wastewater
Treatment Plant 2.1 mgd
-------
/ '
^ / /
m) / /
-~}-r
.^--EQUALIZATION BASIN VOLUM
30 * I 03 GALS
/-HOURLY FLO*
/ VARIATIONS
INFLOW MASS DIAGRAM
AVERAGE FLOW Id 000 GAL hi)
Figure
Equalization Requirements for a Typical Flow
5
-------
RAW
WASTEWATER
DIGESTER SUPERNATANT
AND SLUDGE DEWATERING
F ILTRATE
£
£
EQUALIZATION BASI
WITH MECHANICAL
FLOATING AERATORS
N
<*
«
r <
V
S
r
PRIMARY
TREATMENT
1
t
SECONDARY
TREATMENT
f
PUMP ING
ON
FINAL
EFFLUENT
Figure
Schematic Flow Diagram of Equalization Facilities
-------
EXPANDING PRIMARY TREATMENT FACILITIES
-------
EXPANDING PRIMARY TREATMENT FACILITIES
1. Introduction
Primary treatment facilities are rapidly becoming a thing of
the past
The 1972 Water Bill dictates a minimum of secondary treatment for
all municipal wastewater treatment operations
The local decision to make is either:
discharge into regional plant
expand existing primary facility to meet new effluent
standards
build new plant
2. Alternates to Consider for Expansion
The consultant should evaluate various treatment alternatives
and select the appropriate one to meet all objectives under
consideration
Treatment alternatives:
trickling filters
activated sludge
lagoons
I
3. Trickling Filter
The addition of trickling filter to a primary plant can increase
removal efficiencies up to 85-90% of BOD5.
5 EC OK) DA 8. Y
BXPA kJ 51 QAl
Ptf/MAZY
T M T
/
-------
Typical flow scheme
single stage
two-stage
Advantages
low initial cost
economic operation
Types
Type
Organic loading
16 BOD/1,000 cu.ft./day
Hydraulic loading
million gal/acre/day
low-rate
10 - 20
2-4
intermediate
15 - 30 *
0
11
1
high-rate
up to 90 *
10 - 30
* includes recirculation
Super-rate trickling filter using synthetic media can accommodate
hydraulic loading of 150 mgad.
Performance factors
Wastewater characteristics - vary
Filter media - rock, or synthetic
Filter depth - low-rate 5-7 ft.
- high-rate 3-6 ft.
Recirculation - 0.5 to 4.0
Hydraulic and organic loading
Ventilation
Temperature of wastewater
z
-------
4. Activated Sludge
The addition of activated sludge to an existing primary treatment
plant can increase removal efficiencies to 90-95% BOD^.
Advantage
process
Types
Conventional
most versatile and efficient biological treatment
RAW.
WASTEWATER
minion
PRIMARY
SEDIMENTATION
c-
TANK
6-8 HOURS
1 SLUDGE TO
DIGESTER
c-
riETENT I ON
i)
FINAL
CLARIFIER
ALTERNATE
FINAL
EFFLUENT
RETURN AND EXCESS SLUDGE
EXCESS SLUDGE TO
^DIGESTER OR
THICKENER
EXCESS SLUDGE
Aeration time 6-8 hrs.
Return sludge 25% - min. 15% max. 75%
BOD leadings approximately 35#/1000 ft^/day
Air requirements 700-1000 ft^/#BOD removal
High initial oxygen demand in head of aeration tank
Final clarifier subjected to high solids loading
Increase recirculation with increased BOD loading
Lack of operational stability with variations in hydraulic and
organic loadings.
Step Aeration
AERATION TANK
3-4 HOURS DETENTION TIKE
FINAL
EFFLUENT
~ EXCESS SLUDGE
PRIMARY
SEDIMENTATION
FINAL
CLARIFIER
¦~EXCESS SLUDGE
-------
Aeration time 3-4 hrs.
Return sludge 50% min. 20% max. 75%
BOD leading - approximately 50 ///1000 ft^/day
Distributes organic loading more uniformly over length of
aeration tank
Lower solids loading to final clarifiers
Air requirements - 500-700 ft-V#B0D removed
Contact Stabilization
FINAL
'effluent
SLUDGE TO
DIGESTER
RETURN
SLUDGE
EXCESS SLUDGE
-C FINAL
CLARIFIES
PA I MIRY
SEDIMENTATION
CONTACT TANK
0.5-1 0 HOURS
DETENTION
STABILIZATION TANK
2-6 HOURS
DETENTION
Aeration time:
contact tank 0.5 - 1.0 hrs.
stabilization tank 2-6 hrs.
Return sludge approximately 40%
- BOD loadings approximately 100 #/1000 ft^/day
BOD removed in short contact time by biological flocculation,
adsorption and enzyme-complexing
Air requirements - 750 ft-V#BOD Removed
Concentrated sludge is stabilized in another aeration tank
Stabilization tank offers biological buffering capacity to
handle greater shock and toxic loadings
Stabilization time is function of contact time, temperature
and strength of waste
4
-------
. Complete Mixed
RAS ( AERATION \
FINAL
»
OASILIAItU OR »{ TANA ) e
PHI BAR* EFFLUENT V 1-3 HOURS J
LLAHlr ItH
IE I URN SLOBSE
«
' * UCESS HUOGI
FINAL
EFFLUENT
- Aeration time 1-3 hrs.
- BOD loading approximately 80///1000 ft^/day
- Air requirements - 600 ft^///B0D removed
Influent waste and recycled sludge are introduced
uniformly throughout aeration tank
- Operational stability for slug loads of industrial
waste
. Two-Stage
SECOND STAGE
AERATION TANA
FIRST
STAGE
AERATION
TANK
RA*
UASTEIATER.
OR PRINARY
EFFLUENT
SECOND
STAGE
CLARIFIER
FIRST
STAGE
CLARIFIER
RETURN SLUDGE
EXCESS SLUDGE
SLUDGE
EXCESS SLUOGE
Two separate activated sludge processes operating in series
- Develops two specialized microbial populations
- Competitive only when nitrification is required.
Oxygen Aeration
Utilizes pure oxygen instead of air in the activated sludge
process
-------
Lagoons
The addition of lagoons or oxidation ponds to an existing primary
plant can meet secondary treatment requirements in certain cases
80-95% waste organic matter is converted to algae
Economical treatment alternative when land is available
t Types
- High rate aerobic ponds
shallow depth 12-18 inches
intermittently mixed
aerobic bacterial oxidation and algal photosynthesis
organic loading range
60 - 200 lbs BOD^/acre/day
BODj removal 80-95%
- Facultative Ponds
deeper ponds 3-8 feet
two zones
aerobic surface zone
anaerobic bottom layer
organic loading range 15-80 lbs BOD,./acre/day
BOD5 removals 70-95%
- Anaerobic Ponds
high organic loadings 200-1000 lbs BOD^/acre/day
anaerobic condition prevails
BOD5 removals 50-80%
follow with aerobic or facultative ponds
-------
- Tertiary Ponds
polishing pond after secondary treatment (trickling
filter or activated sludge)
reduces settleable solids, BOD^, fecal organisms
and ammonia
organic loadings usually less than 15 lbs BC^/acre/day
- Aerated Lagoons
aerobic stabilization by air diffusion or mechanical
aeration
BOD5 removals 90-95%
7
-------
NEW TECHNOLOGY IN WASTEWATER TREATMENT
-------
NEW TECHNOLOGY IN WASTEWATER TREATMENT
1. Conventional Methods of Wastewater Treatment Usually Considered As
Biological Treatment
A - Activated Sludge
B - Trickling Filters
C - Oxidation Ponds
2. Major New Advances in Municipal Wastewater Treatment
A - Pure oxygen activated sludge (UNOX system developed by Union
Carbide with EPA - Other companies now marketing variations
(1) First successful full-scale demonstration at
Batavia, N. Y.
(2) Characteristics of system
(a) Utilizes covered and staged oxygenation for contact
of oxygen gas and mixed liquor
(b) High purity oxygen (over 90%) enters first stage
and flows co-currently with wastewater
(c) Slight pressure (2-4 inches water column) to maintain
control and prevent back mixing
(d) Low power requirements
(e) Mass transfer and mixing within each stage
1) Surface aerators
2) Submerged turbine rotating sparge system
(f) Good sludge settling characteristics
(g) DJuHoJved oxygen concentration maintained at
approximately 5-8 mg/1
1
-------
(3) Design criteria and considerations
(a) "Food" to biomass ratio (lbs BOD/lbs MLVSS) normally
.5 to .8
(b) 1.3 - 1.8 lbs oxygen per pound of BOD removed
(c) Mixed liquor suspended solids 6,000 - 8,000
(d) 160 - 200 lbs BOD5/IOOO cu. ft.
(4) Oxygen generation
(a) On site liquid oxygen storage
(b) On site generation
1) Pressure swing adsorption (PSA)
2) Cryogenic generation
(5) Advantages of oxygen activated sludge
(a) High MLSS concentrations
(b) Low detention periods
(c) Low quantities of excess biological sludge
(d) Improved sludge settling characteristics
(e) Reduced power requirements
(f) High dissolved oxygen levels all stages
(g) Low waste gas volume
(6) Middlesex County, N. J. Oxygen-activated sludge design
(a) 120 mgd average flow; high strength (382 mg/1 BOD^);
88% total BODj removal
(b) Total cost oxygen: $83.58 million
Annual cost: 7.39 million
Comparable Air: $104. million (comp. mix.)
Annual cost: 8.29 million
(7) Westgate Plant, Fairfax County, Va.
2
-------
OXYGEN PROCESS FlOtK SHEET
OXYGEN GAS
RET URN
SLUDGE
WASTE GAS
^ T
PUMP
OXYGEN
SOURCE &
STORAGE
FINAL
SETTLING
TANKS
RAW OR SETTLED WASTE WATER
MIXED LIQUOR
COVERED
OXYGENATION
TANKS
WITH MIXERS,
OXYGEN
COMPRESSORS
AND SPARGERS
WASTE
SLUDGE
EFFLUENT
FIGURE 1
-------
AERATION GAS RECIRCULATION
TANK COVER
COMPRESSORS
CONTROL
VALVE ¦
AGITATOR
OXYGEN
FEEDGAS
EXHAUSI
GAS
WASTE
LIQUOR
FEED
MIXED LIQUOR
EFFLUENT TO
CLARIFIER
STAGE BAFFLE
-4 - o
° "N
RECYCLE
SLUDGE "
SCHEMATIC DIAGRAM OF OXYGEN SYSTEM WITH
ROTATING SPARGER
FIGURE 2
-------
AERATION
TANK COVER
CONTROL
VALVE,
AGITATOR
OXYGEN
FEED GAS
WASTE
LIQUOR
FEED
RECYCLE
SLUDGE"
STAGE BAFFLE
. EXHAUST
GAS
MIXtD LIQUOR
¦LFFLUtNT TO
CLARIf IER
SCHEMATIC DIAGRAM OF OXYGEN SYSTEM WITH
SURFACE AERATOR
FIGURE 3
-------
SETTLING CHARACTERISTICS FOR
AIR AND OXYGEN BIOMASS
(ISR VS CONCENTRATION)
OXYGEN
BIOMASS
AIR 1
BICMASS
L, »!«*> <
##«
V" v. "* V'
V /. '-¦ -V V
V.v*' A'"'"
1000 10,000 100.000
CONCENTRATION.
mg/|
FIGURE 4
-------
FLOW DIAGRAM OF A
PSA OXYGEN GENERATING SYSTEM
30-60 PSIG
AFTER
COOLER
FEED
AIR
COOLING
WATER
PRODUCT
OXYGEN
ADSORBER
ADSORBER
ADSORBER
ADSORBER
VAPORIZER
"DRIOX"
LIQUID
OXYGEN
STORAGE
WASTE , s
NITROGEN
PRESSURE SWING ADSORPTION UNIT
FIGURE 5
7
-------
18
17
16
15
14
13
12
11
10
9
8
OXYGEN AERATION
0 20 40 60 80
PLANT SIZE MGD
FIGURE 6
8
-------
WASTEWATER TREATMENT FACILITIES, USING OXYGEN
AERATION, UNDER DESIGN, CONSTRUCTION
OR OPERATION (PARTIAL LIST)
LOCATION
Detroit, Mich.
Newtown Creek, N, Y. City
Speedway, Ind.
Louisville, Ky,
Wyandotte, Mich.
Decatur, III.
Morganton, N. C.
New Rochelle, N. Y.
Middlesex County, N. J.
Euclid, Ohio
Deer Park, Texas
Danville, Va.
Miami, Fla.
East Bay MUD, Calif.
Fayetteville, N. C.
Hollywood, Fla.
Salem, Ore.
Jacksonville, Fla.
Baltimore, Md.
Fairfax County, Va.
New Orleans, La.
Denver, Colo.
Tampa, Fla.
DESIGN FLOW (MGD)
300
20
8
105
100
18
8
11
120
22
6
21
55
120
16
36
16
10
5
12
122
73
36
FIGURE 7
9
-------
(a) Interim requirement from 50 percent to 80 percent
(b) Act removals over 90 percent
(c) Equivalent to conventional aeration with 3 times
tank volume
(8) Municipalities with oxygen systems under design, construction
or operation in figure.
B - Phosphorus Removal
(1) Technology now well established in areas with eutrophication
problems
(2) Phosphorus removal in conventional biological systems is
poor (20 - 30%)
(3) Phosphorus removal technically and economically feasible
by chemical precipitation
(a) Salts of aluminum
(b) Salts of iron
(c) Lime
(4) Chemical dosage to achieve specified degree of removal
by jar tests
(5) Chemical precipitation also upgrades performance of plant
(a) Coagulation of suspended solids
(b) Colloidal solids
(6) Chemicals for phosphorus removal can be added:
(a) Just before primary tank
(b) In secondary section (biological) with removal in
secondary clarifier
(c) In tertiary 6tage
(7) Advantages and disadvantages of Phorphorus removal in
various treatment plant components shown in figure.
(8) Lowest costs for addition in secondary - removals below
1 tng/1 are difficult
10
-------
CHEMICAL ADDITIVE
AND/OR
AND/OR
AND/OR
FLASH MIX
BIOLOGICAL
PROCESS
FINAL
Insoluble Phosphorus
Insoluble Phosphorus
Insoluble Phosphorus
TERTIARY
SECONDARY
PRIMARY
LOCATIONS FOR CHEMICAL CONTROL OF PHOSPHORUS
FIGURE 8
-------
CHEMICALS FOR PHOSPHORUS REMOVAL
Ferric Chloride FeCl^
Ferric Sulfate Fe2(S0^)^
Ferrous Chloride FeC^
Ferrous Sulfate FeSO,
4
Alum A^CSO^)^
Sodium Aluminate NaA102
Steel Mill Pickling Liquor FeC^ + FeSO^
Lime Ca(0H)2
FACTORS AFFECTING CHOICE OF CHEMICAL
FOR PHOSPHORUS REMOVAL
Influent Phosphorus Level
Wastewater Suspended Solids and Alkalinity
Chemical Cost Including Transportation
Reliability of Chemical Supply
Sludge Handling Facilities
Ultimate Sludge Disposal Methods
Compatibility with Other Treatment Processes in Plant
FIGURE 9
12
-------
WASTEWATER TREATMENT FACILITIES, WITH PHOSPHORUS
REMOVAL, UNDER DESIGN, CONSTRUCTION OR OPERATION
(PARTIAL LIST)
MORE THAN 100 MUNICIPALITIES INCLUDING:
Milwaukee, Wise,
Tampa, Fla,
South Bend, Ind,
Arlington, Va.
Petersburg, Mich,
Hatfield Twp>, Penna,
Green Bay Metro, Wise.
Flint, Mich.
Saginaw, Mich.
Fairfax Cty., Va,
Cleveland, Ohio
Alexandria, Va.
Decatur, III,
Waukegan, III,
Bowie, Md,
Detroit Metro, Mich,
Marborough, Mass.
Greater Chicago Metro
Deerfield, Mich.
Lancaster, Calif,
Rockwood, Mich.
Sparta, Mich,
Ann Arbor, Mich.
Lorain, Ohio
East Canton, Ohio
Defiance, Ohio
Mentor, Ohio
Ashtabula, Ohio
Upper Sandusky, Ohio
Ypsilanti, Mich,
Pontiac, Mich.
Kalamazoo, Mich.
Bay City, Mich,
Piscataway, Md.
Holland, Mich,
Owosso, Mich,
Seattle, Wash,
Manassas, Va,
San Antonio, Tex.
El Lago, Tex.
Xenia, Ohio
Michigan City, Ind,
Rochester, N. Y,
Racine, Wise.
FIGURE 10
13
-------
(9) Highest cost in tertiary - excellent quality low in P,
BOD, and suspended solids
(10) Basic equipment required primarily chemical and polymer
storage tanks, chemical pumps and feed lines
(11) Cost $.03 to $.06 per 1000 gallons for 80 to 95 percent
removal at normally loaded and functioning plants.
C - Nitrogen Control and Removal
(1) Nitrogen controlling nutrient in some eutorphication areas
(2) Nitrogen in sewage primarily organic-N and ammonia-N
(3) Nitrogen control prevents depletion of dissolved oxygen by
biological oxidation of ammonia-N to nitrate-N (Nitrification)
(a) Nitrogenous Oxygen Demand (NOD) can be more than one-
fourth of total oxygen demand (TOD)
(b) Ammonia-N exerts chlorine demand which reduces
disinfection efficiency
(c) Toxic to some forms of aquatic life
(4) Nitrification by altering conventional activated sludge:
increase aeration rate; contact time; sludge age; and
control pH.
(5) Stable nitrification possible by two-stage system
(a) First stage for organic carbon oxidation
(b) Second stage for nitrification
(c) Separate sedimentation and recycle in each stage
(6) Nitrification alone may not be adequate
(a) Nutrient value of nitrogen
(b) Nitrate limit on potable water supply
(7) Nitrogen can be removed from wastewater by biological
and physical-chemical methods
14
-------
(a) Biiloglcal denitrification
X) Uses methyl alcohol (methanol CH3OH) as
carbon source
2) Results in release of nitrogen gas
3) Three-stage biological system developed by
EPA research program
a) First stage: high rate, short aeration (2 hour)
for organic carbon oxidation and conversion
organic nitrogen to ammonia
b) Second stage for nitrification (about 3 hours)
c) Third stage for denitrification (methanol added)
d) Theoretical need 1.9 mg methanol per mg of
nitrate-N; actual abeut 3 mg methanol per mg
of nitrate-N
e) Alternate denitrification systems shown in
figure
(b) Breakpoint chlorination
1) Chlorine addition to wastewater produce chloramines;
additional chlorine to breakpoint results in
conversion and release of nitrogen gas
2) Dosages of breakpoint approximately 8 to 10 parts
of chlorine per part of ammonia-N
3) High chlorine in effluent can be prevented by
carbon column
A) Chlorides will be added to receiving stream
(c) Ammonia stripping
1) pH raised above 11 with lime with ammonia stripped
out with air in tower
2) Classic application at Lake Tahoe
a) About 90% ammonia removal in warm weather
b) About 400 cu. ft. of air per gallon of sewage;
lower temperature much higher volumes
15
-------
3) Tower ices and becomes inoperable in freezing
weather - use limited to warmer climates or
seasons
4) Some difficulty with calcium carbonate scaling
(d) Selective Ion Exchange
1) Use naturally occurring zeolite (clinoptilolite)
2) Clino favors exchange of ammonium ion.
3) Columns may be operated 24 to 30 hours before
regeneration
4) Regeneration by solution of lime and sodium chloride
5) Approximately 0.1 to 1.0 lbs of ammonia-N per cu.ft.
of resin
6) Removals to less than 0.5 mg/1 of ammonia-N
technically feasible
7) Clino being designed for 22.5 mgd plant in Fairfax
County, Virginia
D - Physical-Chemical Treatment
(1) Major viable alternative to conventional biological treatment
(2) P-C processes include:
(a) Chemical clarification
(b) Filtration
(c) Granular activated carbon adsorption
(3) May follow biological treatment (as Tahoe) or be "independent"
P-C without biological
(4) Typical schematic flow diagram shown in figure
(5) Chemical clarification of raw sewage
1(6
-------
IMPORTANCE OF NITROGEN
IN EFFLUENTS CAN CAUSE DO SAG IN RECEIVING WATER
NH3 IS CORROSIVE TO COPPER FITTINGS
1 NH3 REQUIRES 7 PLUS Ct2 FOR BREAKPOINT
N02 CAUSES HIGH Cl2 DEMAND
NH3 INFLUENCES Ct2 CONTACT TIME
NITROGEN COMPOUNDS ARE NUTRIENTS
N03 CAN BE HEALTH HAZARD
NH3 CAN BE TOXIC TO FISH
FIGURE 11
-------
NITRIFICATION
BOD
REMOVAL
CLAR
CLAR
SLUDGE RECYCLE 1
SLUDGE RECYCLE
WASTE
WASTE
TWO STAGE BIOLOGICAL SYSTEM REQUIRED
TO GUARANTEE COMPLETE NITRIFICATION
FIGURE 12
-------
CARBONACEOUS
BOD
NITRIFICATION
DENITRIFICATION
MODEL SYSTEM FOR NITRIFICATION AND DENITRIFICATION
FIGURE 13
-------
MODIFICATIONS OF
THE DEN ITRIFICA JION PROCESS
HIGH-RATE
ORGANIC SYNTHESIS
NITRIFICATION
1
FIGURE 14
I. OPEN TANK DENITRIFICATION
(ACTIVATED SLUDGE TYPE CULTURE)
1
II. COLUMN
t
DENITRIFICATION
(FINE MEDIA)
¦
' f
SAND FILTER
OPTIONAL
9
III. COLUMN DENITRIFICATION
(COARSE MEDIA)
-------
WASTEWATER TREATMENT FACILITIES WITH NITRIFICATION AND/OR
DFNITRIFICATIQN UNDER DESIGN, CONSTRUCTION OR OPERATION
i
(PARTIAL LIST)
LOCATION
Hobbs, N. M,
Tampa., Fla,
Washington, D, C.
Salt Creek (Chicago), III.
El Lago, Tex.
Waukegan, III.
Flint, Mich.
Central Contra Costa San. Dist.
Jackson, Mich.
Benton-St, Joseph, Mich.
Fairfax Cty., Va.
Denver, Colo.
Arlington, Va.
Wellsville, N. Y.
Princeton, N. J.
Orange County, Calif,
Alexandria, Va.
No. Shore San. Dist., III.
Madison, Wise.
FIGURE 15
21
DESIGN FLOW (MGD)
5
60
300
50
.5
30
20
1
16
13
22.5
10
30
1.5
10
15
54
60
30
-------
(a) Remove 65 to 75 percent of organic material
(b) Alum, lime, or iron salts will also remove phosphorus
(c) Includes mixing, flocculation, sedimentation
(6) Granular cartxftL adsorption is major new process
(a) Removes colloidal and dissolved organics
(b) Wastewater passes through carbon columns
1) Downflow columns at flow rates of 2 to 8 gpm/ft
better flow distribution
2) Upflow at 2-7gpa/sq.ft. - allow periodic removal
of carbon at base
3) Packed bed operation provides some filtration
but requires more frequent backwash
4) Columns can be insseries or parallel
5) Commercial granular carbon sizes 8 X 30 and 12 X 40 mesh
6) Carbon requires regeneration for reuse
a) Waste carbon hydraulically transported in
water slurry
b) Regenerated in multiple hearth furnace at
1500°F - 1700°F
c) Regeneration losses 5 to 10 percent per cycle
(7) Filteation as component inPP-6 treatment
(a) Usually mixed media type
(b) Filtration before carbon column enables use of packed beds
(c) More efficient removal of solids
(d) Filtration after upflow expanded bed columns to remove
floe flushed from carbon
(e) Polymers may be added as coagulant aids
(8) Advantages of Physical-Chemical treatment
(a) Less land area (1/2 to 1/4)
22
-------
TREATMENT COSTS FOR
PHYSICAL TREATMENT (10 MGD)
STEP
TOTAL COST"
CENTS PER
1000 GALS.
PERCENT
OF TOTAL
PLANT COST
PRELIMINARY TREATMENT
0.8
2
LIME COAGULATION & RECALCINATION
10.1
36
FILTRATION
3.6
13
ACTIVATED CARBON ADSORPTION
12.9
46
DISINFECTION
0.9
3
TOTAL PLANT COST
28.3
100
NOTE: TOTAL COST INCLUDES CAPITAL COSTS, OPERATING
AND MAINTENANCE COSTS, & AMORTIZATION
FIGURE 16
-------
BACKWASH WASTEWATERS
CHLORINE
SEWAGE
Q AVG
PEA< HOUR)
ASH
CARBON
N>
COAGULANT(S)
SLUDGE
CENTRATE
OR
FILTRATE
SCRUBBER
UNDERFLOW AND
CARBON WASH WATERS
SCRUBBER
UNDE RF LOW
OVERFLOW
(A) DESIGN FLOW BASED
PEAK HOUR PLUS Q RECYCLE
DESIGN FLOW BASED
RECYCLE
AVERAGE PLUS
ILLUSTRATIVE SCHEMATIC OF
PHYSICAL - CHEMICAL TREATMENT PLANT
SLUDGE
DEWATERING
FLOW
EQUALIZATION
POND
SEDIMENTATION
RAPID MIX
AND
FLOCCULATION
SLUDGE
THICKENING
(OPTIONAL)
COMMINUTION
AND
GRIT REMOVA
FILTRATION
INCINERATION
RECARBONATION
COAG USED)
CARBON
REGENERATION
GRANULAR
CARBON
-------
SPENT CARBON FROM
CARBON COLUMNS
SPENT CARBON DRAIN
AND FEEDTANKS
SCREW
CONVEYORS
CARBON
REGENERATION
FURNACE
MAKEUP
CARBON
CARBON
SLURRY
PUMPS
QUENCH
TANK
CARBON
SLURRY BIN
REGENERATED CARBON
DE-FINING AND
STORAGE TANKS
CARBON SLURRY
PUMPS
REGENERATED CARBON
TO CARBON COLUMNS
ILLUSTRATIVE CARBON REGENERATION SYSTEM
(FROM CULP & CIJLP)
FIGURE 18
25
-------
PHYSICAL-CHEMICAL TREATMENT PROJECTS CURRENTLY
UNDER DESIGN, CONSTRUCTION OR OPERATION (PARTIAL LIST)
LOCATION DESIGN FLOW(MGD)
Niagara Falls, N. Y. 60
South Lake Tahoe, Calif, 7.5
Rocky River, Ohio 10
Garland, Texas 30
Rosemont, Minn. ,6
Nassau County, N, Y, .5
Cortland, N. Y. 10
Orange County, Calif. 15
Cleveland, Ohio 50
Fitchburg, Mass. 15
Upper Montgomery County, Md. 20
Owosso, Mich. 6
Alexandria, Va. 54
Port Jefferson, N. Y. 5
Occoquan, Fairfax County, Va. 22.5
Colorado Springs, Colo. 2.0
Piscataway, Md, 5
Leroy, N, Y. 1.5
Leetsdale, Penna, 5
Arlington, Va, 30
FIGURE 19
26
-------
(b) Lower sensitivity to diurnal variations
(c) Not affected by toxic substances
(d) Potential for heavy metal removal
(e) Flexibility in design and operation
(f) Superior organic removal
(9) New concept of centralized regeneration for smaller
communities
E - Suspended Solids Removal
(1) Gravity sedimentation no longer adequate in many
(2) Microscreens
(a) Surface filtration devices
(b) Polish effluent for secondary biological treatment plants
(c) Rotating drums with specially woven corrosion-resistant
fabric on periphery
(d) Influent enter along axis of drum and flows radially'
outward through fabric
(e) Available with variable speed drums
(f) Nashed continuously (5 percent of throughput)
(g) Removal of 50 to 80 percent removal of biological
solids in secondary effluent
(h) Screen sizes 23 to 35 microns
(3) Deep Bed Filtration
(a) Dual or mixed media filters
(b) Tri-media (e.g. Tahoe) usually anthracite, sand
and garnet
(c) Flow rates 5 to 10 gpm/sq.ft.
27
-------
(d) Provides quality control by removal of virtually
all suspended solids and high degree removals of
turbidity and phosphorus
(4) Chemical clarification (see phosphorus removal above)
(a) Now becoming standard practice inmmany areas
(b) Provides additional BOD and suspended solids removal
28
-------
WASTEWATER TREATMENT FACILITIES, USING TERTIARY MULTI-MEDIA
FILTRATION, UNDER DESIGN, CONSTRUCTION OR OPERATION
(PARTIAL LIST)
LOCATION DESIGN FLOW (MGD)
Spring Creek, Penna, 6,5
Aurora, Colo, 1,3
Louisville, Ky. 5,4
Bensenville, III, 1,1
Walled Lake, Mich, 2,8
Bedford Hts., Ohio 9,0
Beaverton, Ore, 1,6
Warren, Mich, 50,0
Barrington, III, 2,0
Hatfield Twp., Penna,, 3,6
(Midland, Mich, 6,5
Winslow, N, J, 1,0
Upper Gwynedd, Penna, 2,7
Hammond, Ind, 1,0
So, Lake Tahoe, Calif, 7,5
San Buena Ventura, Calif, 17,4
East Lansing 20
Denver, Colo, 10
Hatfield, Penna, 3,6
Arlington, Va. 30
Stony Brook, Princeton, N. J. 10
Alexandria Sew, Auth,, Va, 54
FIGURE 20
29
-------
TYPICAL
MICROSTRAINER UNIT
DRIVE UN IT
SCREENING
FA BR I C7
¦WASH WATER
JETS
EFFLUENT WEIR
EFFLUENT CHAMBER
INFLUENT CHAMBER'
FIGURE 21
-------
SLUDGE HANDLING & DISPOSAL
-------
SLUDGE HANDLING & DISPOSAL
1, Importance
2, Current and Previous Methodology
3, Nature and Handling Characteristics
of Sludges
4, Sludge Stabilization Processes
5, Sludge Thickening and Blending
6, Sludge Dewatering
7, Thermal Processing of Sludges
8, Final Disposal
/
-------
SECTION 1 - IMPORTANCE OF SLUDGE PROCESSING AND DISPOSAL
CURRENT EPA PROGRAMS
1. Introduction
Solids removed in the processing of waters for human consumption,
industrial usage, or in the case of wastewaters, for discharge
to a receiving stream, present a disposal problem.
Disposal of sludges from wastewater treatment will today account
for up to 50 percent of the total treatment cost.
Sludge is the settleable solids that are naturally present in
water and wastewater or that are found during treatment.
Tighter effluent criteria, increasing land scarcity and population
pressure combine to make sludge disposal more difficult and expensive.
2. Quantities and Characteristics of Sludge to be Handled
Approximate amounts of sludge produced in the treatment of wastes-
water by simple clarification, Chemical treatment and biological
processes are shown in Table.
Activated sludge process contributes large quantities of sludge
for disposal.
Sludge is a semi-liquid waste and the water content of all sludges
is high, as shown in Table.
Typical sludge masses to be handled are shown in Table.
The quantity of sludge can be calculated from wastewater analysis
and efficiency of the treatment units.
Physical-chemical treatment means new kinds of sludges, more mass
and sometimes more volume.
The sludge produced when lime is added to wastewater in the primary
or as a tertiary can be calculated from water and wastewater analysis
3. Sludge Management Alternatives
Sludge can be ultimately disposed of in dry, dewatered filter
cake, liquid or in the form of ash and combusion gases.
Steps to be followed in solving a sludge handling and disposal
problem are indicated in Figure.
2
-------
Costs of Sludge Processing and Disposal
Costs of sludge processing are a function of:
Treatment sequence
The raw sewage
Location (the surrounding neighborhood)
. Climate
Scale of operation
Regulations, etc.
Costs are sensitive to all of the above and individual author'
assumptions. If possible, get all comparisons from the same
unbiased source.
The cost of some sludge handling and disposal processes is
given in Table.
The cost of some sludge handling and disposal combinations
is given in Figure.
-------
TABLE
TYPICAL QUANTITIES OF SLUDGE PRODUCED
IN WASTEWATER TREATMENT PROCESSES
Treatment
i
Plain Sedimentation
Trickling Filter Humus
Chem, Precipitation
Activated Sludge
2,MO - 3,530
530 - 750
5,250
11,600 - 19,400
TABLE
WATER CONTENT OF SLUDGES
Percent Pounds of Water/
Treatment Moisture Pound Sludge Solids
Primary Sedimentation
95
19
Chem. Precipitation
93
13.3
Trickling Filters
Humus-Low Rate
93
13.3
Humus-High Rate
97
32 A
Activated Sludge
98
- 99
- 65.6
Well Digested Sludge
Primary Treatment
85
- 90
~ 7.0
Activated Sludge
90
- 94
- 11.5
4
-------
TABLE
SLUDGE' MASSES
Percent Percentage of
Suspended Solids lb/day/mg Volatile Materials Specific Gravity
Treatment Removal Removed Removed Suspended Solids
Plain Sedimentation 60 1,020 65 1.33
Trickling Filter Humus 30 510 45 1.52
Activated Sludge 92 1,563 65 1.33
(excess)
Imhoff Tank
Dig. 60 1,020 50 1.47
5
-------
TABLE
TOTAL COST IN CENTS PER 1,000 GALLONS OF WASTEWATER
PROCESSED FOR INDICATED SLUDGE HANDLING PROCESSES
Plant Size
Process
1 mgd
10 mgd
100 mgd
Gravity thickening of primary and
waste activated sludge
Gravity thickening of primary sludge
above
Air flotation thickening of waste
activated sludge above
Anaerobic digestion of combined
primary and waste activated sludge
Dewatering of digested sludge on
sandbeds
Dewatering thickened raw sludges
on rotary vacuum filters
1.61 0.31 0.13
1.47 0.22 0.08
2.28 1.01 0.75
6.09 2.09 1.89
2.20 1.64 NA
8.39 5.15 3.70
Multiple hearth incineration of 13.53 5.02 1.16
filter cake
-------
too
THICKEN. DIGEST, SAND BEOS
THICKEN, DIGEST, FILTER, LANDFILL
THICKEN, FILTER, INCINERATE
3 6 10 20 30 60 100
WASTEWATER FLOW (MGD)
30
THICKEH, DIGEST. SIHO BEOS
THICKEN, DIGEST, FILTER, LANDFILL
THICKEN. FILTER. INCINERATE
20
I 0
4
2
10
6
00
3
60
20
30
WASTEWATER FLOW (MGD)
TYPICAL COSTS OF SLUDGE PROCESSING
AND DISPOSAL - INCLUDING AMORTIZATION
-------
CONSIDERATIONS IN THE HANDLING
AND DISPOSAL OF SLUDGE
ULTIMATE
DISPOSAL PROGRAM
LAND DISPOSAL
a. Land spreading
b Landfill
c. Other
REUSE j
a. Animal feed supply
b. By-product recovery
c. Other
SUBSURFACE AND
OCEAN DISPOSAL
a. Brine disposaI
b. Other
COLLECTION AND TRANSPORT
a Pumping
b. Pipeline
c. RemovaI f rom cI a r t fie r
d. Other
a. Mechanical
b. Drying beds
DEWATERING
c Chemical cond.
d. Other
ATMOSPHERIC DISPOSAL
a. Drying
b. Incineration
c. Nitrogen removal
d. Other
CHARACTERIZATION
a. Source
b. Type cone .
c. Tox ic materla I
d. Others
OTHER
a. Criteria dev
b. Technology t rans.
c. Other
PREPARATION FOR DEWATERING
AND/OR DISPOSAL
a. Thickening c. Dig
b. StabiI ization d. Other
FIGURE
-------
SECTION 2 - CURRENT AND PREVIOUS METHODOLOGY
1, Project Objectives - Wastewater Treatment Plants
The way it used to be - The old climate surrounding design
and startup of wastewater treatment plants.
Partial funding for and somewhat limited role of the
A/E firm.
Divided responsibility for design of sub-systems.
Emphasis on liquid handling.
Elastic enforcement policies (habit forming).
Problems with sludge handling systems.
The wa£ it is now - The new climate. The objectives have always
been there but the new climate now makes them obtainable.
Effective, reliable processing of wastewater (both liquid
and solid fractions).
. At lowest practical cost.
Concurrent non-polluting effluent streams (liquid, solid
and gaseous).
Plants must function properly, both initially and continually.
Both liquid and solids fractions must be processed
satisfactorily.
Effluent standards are going to be enforced.
Capital, operating and maintenance costs must be essentially
on forecast.
2. Essential Ingredients (for a successful project)
- Optimum Conceptual and Detailed Designs
New standards require new processes.
New processes mean text books are a questionable source.
The importance of being contemporary in process engineering
disciplines.
*
-------
Construction as Designed
Increased A/E involvement, new C.M. methods.
Proper Operation and Maintenance
Following the Doctor's orders or he is not responsible
for the results.
Continuing Plant Service and Development
Nobcdy's perfect; even naval vessels still have a shakedown
cruise.
A vital source of process improvement and future design
information.
3. Sources - Con:eptual Design Information
Textbooks and Literature
Must be reviewed but rarely give all the answers.
Laboratory and Pilot Studies
Practically always necessary.
Supplier's Recommendations
Equipment and product firms, their own R&D engineering work.
Previous Experiences
. All too seldom available.
Visitation to Other Plants
Helpful but sometimes misleading.
Client's Wishes (existing plant results)
Depends on the client's experience and capability.
4. Special Considerations - Design Rationale
Adequacy of Available Literature
Self serving publications.
Strategic omissions.
Jo
-------
Supplier's Recommendations
Essential but must be sifted carefully.
The importance of follow-up.
Plant Data - Fact vs. Folklore
Reliability, a function of adequacy of O&M.
Defending an untenable position - mistakes die hard.
Process Engineering
Unit operations technology.
Biological process technology.
Putting the whole thing together.
Experience in other industries and in plant operations.
//
-------
SECTION 3 - NATURE AND HANDLING CHARACTERISTICS OF SLUDGES
Fundamental Point
Need - Knowledge/Insight
Nature of Sludges/Handling Characteristics
Potential Pitfall
"All generalities are inherently false, including this one."
Raw Primary Sludge
Almost universally settles, thickens, dewaters and incinerates
relatively easily.
Is usually coarse and relatively fibrous,
r Vacuum filtration and centrifugation work well at low cost.
Costs are low and efficiences good.
VACUUM FILTRATION - HAW PRIMARY SLUDGE
Solids
% Sludge Conditioner Cost Yield Cake Capture
Solids Used ($/Ton) lb/ft2/hr Solid (%) (%)
10 Cationic 1.67 10 32 90-95
Polymer
Effect of Digestion (Primary Sludge)
Anaerobic digestion, contrary to some information in the literature,
makes sludges somewhat more difficult to thicken and dewater.
But results are still good and costs low.
Shear effects on particle size and increased hydration of solids.
% Sludge Conditioner Yield Cake Solids
, Solids Cost ($/Ton) ff/hr/ft^ Solids (%) Capture (% )
12.7 2.64 7.4 28 90+
Z2,
-------
4. Activated Sludges (Conventional)
Inherently more variable
Principal source of variation
Configuration and mode of operation of activated sludge
system involved.
Also, Domestic/Industrial waste ratio and type, Nature of
Collection System can have real effect.
Structure
Generally finer in particle size.
60-90 percent cellular organic matter.
Bioflocculated to some degree, by excretion of natural
polymeric material by the micro-organisms.
Density close to density of water.
Water Content
Biomass from conventional air systems has much associated
water.
Theoretically, if the loosely held and bound surface water
disengaged, up to 29 percent solids obtained.
5. Summary - Activated Sludges
Conventional Air Aeration Systems Excess Activated Sludge requires
very careful operation to give settleable sludge.
Activated sludge is sensitive to further processing. Hydration
easily and tends to float.
6. Handling Combined Primary and Activated Sludges
Existing plants, many cases designed one of two ways.
A. Recirculate E.A.S. to head of plant - Primaries
Results Primary Solids Capture goes to pot.
Greater BOD load on secondary system.
More E.A.S. created than necessary.
/3
-------
Combined Mixed Sludge
Settles poorly in digester, another recirculation load.
When elutriated (without flocculants) sludge fractionates -
another low efficiency process and recirculation load.
B. E.A.S. mixed with Primary Sludge prior to gravity thickening
Results: Better than recirculation to primaries but:
Dirty thickener overflow.
Activated portion will not settle in digesters or
elutriation basins, so still poor.
Remedy
Combine and thicken sludges just before dewatering.
Not early in process.
7. Oxygen Activated Sludges
Biomass from oxygen process has better settling characteristics.
Clarifier performance, based on overflow rate is better with
oxygen process sludge (Watch bottom loading rates).
Recycle sludge solids are higher with oxygen activated sludge.
Sludge volume indices are improved over air aeration sludge.
Gravity thickening.
Summation - oxygen activated sludge appears to gravity thicken
more readily.
- Flotation thickening
Vacuum Filtration
Centrifugation
8. Alum Use - Primary Plant - Mixed Chemical Organic Sludge
West Windsor
With no chemical addition to primaries, ferric/lime conditioning,
high yield and low cost.
/4
-------
With alum, primary solids level drops, amount of sludge
increases, yield decreases and costs go up.
Ferric and lime may not be best conditioning system for
Alum/organic sludge.
9. Lime Use - Conventional Sludge Plant - Mixed Lime/Organic Sludge (Raw)
Newmarket
2..0 mgd, lime added just ahead of primaries.
Sludge volume almost triples, but centrifugation looks easy
and inexpensive.
Low polymer dose to clean up centrate.
10. Alum and Lime Sludges - Conventional Activated Sludge Plant
Windsor Little River
Normal, untreated sludge conditioning costs are abnormally
high, particularly for a sludge feed to filters.
Lime usage gave a mixed sludge (with small amount of activated
sludge content?) which dewatered well at a lower cost.
Alum lowered sludge solids concentration, decreased yield and
increased conditioner costs. Cake solids were only 16 percent
with alum use.
11. Ferric Chloride/Organic Sludge - Conventional Activated Sludge Plant
North Toronto
Use of ferric chloride for phosphorus removal.
Tested for many months.
First applied at primary basins.
Current application point = at end of aeration basin.
Chemical conditioning costs about $8/ton.
Reasonable production rate and cake solids content realized.
/&
-------
12. Lake Tahoe Solids Handling
Two sludges handled separately in this tertiary plant.
Organic sludges (from a system which recirculates activated
sludge to head of plant).
Lime sludges from tertiary type treatment.
13. Aerobically Digested Activated Sludges
Aerobic digestion is an inherently "cleaner" means of reducing
the volume of activated sludge to be dewatered and to stabilize
same for land disposal.
Plant scale work current at Several locations.
Atlanta
New 6 mgd Flint River Plant tests.
Digestion process works well.
Sludge compacts to 2-3 percent and can be dewatered via
vacuum filtration using ferric chloride.
Yield is on the lean side.
If aerobically digested sludge were mixed with thickened
primary sludge, dewatering and incineration would be more
efficient.
J 6?
-------
FIGURE
CLOSE-UP RAW PRIMARY SLUDGE FILTER CAKE
-------
FIGURE
RELEASE CHARACTERISTICS - RAW PRIMARY SLUDGE FILTERS
-------
CLARIFIERS
REMOVAL
AERATION
BASINS
Z
CLARIFIERS
ANEROBIC
DIGESTION
ELUTRIATION
WASTE WATER
SLUDGE
PROCESS LIQUIDS
FILTERS
FIGURE
SECONDARY PLANT WITH SURPLUS ACTIVATED SLUDGE TO HEAD OF WORKS
-------
GRIT
REMOVAL
r~
SLUDGE
THICKENING |"
DIGESTION
FIGURE
SECONDARY PLANT WITH SURPLUS
TO THICKENING AND DIGESTION
I \
'c
ELUTRIATION *
t
DEWATERING
WASTE WATER
SLUDGE
PROCESSING LIQUIDS
ACTIVATED SLUDGE MIXED WITH PRIMARY SLUDGE PRIOR
-------
SETTLING
CHARACTERISTICS
FOR AIR AND
OXYGEN BIOMASS
(ISR VS. CONCENTRATION
OXYGEN
BIOMASS
INITIAL SETTLING
RATE, Fl/Hr.
AIR
BIOMASS
1 1 M I I 11
1000
10,000
CONCENTRATION mg/l
100,000
TYPICAL CLARIFIER PERFORMANCE FOR AIR AND OXYGEN SLUDGES
(AT 30 % RECYCLE]
10,0001
8000
MLSS (mg/l | 6°00
4000
2000
OXYGEN SLUDGE
AIR SLUDGE
J.
200 400 600 800 1000 1200 1400 1600
OVERFLOW RATE, GPD/Fr
FIGURE
-------
TYPICAL CLARIFIER PERFORMANCE FOR AIR AND OXYGEN SLUDGES
(AT 30 % RECYCLE)
% RSS
AIR SLUDGE
OXYGEN SLUDGE
1000 1200 1400 1600
OVERFLOW RATE, GPD/FT
FBGUHi
GRAVITY THICKENING
FEED SLUDGE
TYPE
OXYGEN W.A.S.
% SOLIDS
1.7
SOLIDS
LOADING
#/Ft.2/DAY
10
UNDERFLOW
CONC.
% SOLIDS LOCATION
4.8
LOUISVILLE
AIR W.A.S.
0.9
20
1.4-2.8 CHICAGO
OXYGEN MIXED
2.3
5.6
MIDDLESEX
AIR MIXED
1.1
20
3.314.4) CHICAGO
FIGURE
22
-------
SECTION 4 - SLUDGE STABILIZATION PROCESSES
1. Anaerqbic Digestion
Describes the biological conversion of organic matter in
the absence of molecular oxygen to simple compounds.
Gas products are chiefly methane and carbon dioxide.
Process advantages include:
Anaerobic digestion is the most frequently employed process
for sludge stabilization. When digestion operates properly,
it converts raw sludge to a stable material which is
inoffensive to the senses, and which has a greatly reduced
pathogen content.
Methane generated can be used for heating and to run
generators.
Can usually obtain a 50 percent reduction in volatile solids.
Do not have to or want to maintain a high dissolved oxygen
level.
Process disadvantages include:
Control is difficult because of sensitivity of micro-organisms
to toxicity, especially from industrial effluents.
Capital costs for facility construction and heating provision
are high.
Supernatant is usually high in BOD, solids, and nutrients
requiring further treatment.
Anaerobic digestion produces changes in sludge which, on the
average, reduce the filter yield. If ferric chloride and
lime are used, chemical demand is increased. If sludge
density is increased, yield can be increased.
Design criteria for anaerobic digesters
Volume - allow 3 to 6 cubic feet per capita.
Organic loading - allow from 0.02 to 0.15 pounds of applied
solids per day per cubic foot.
Reported costs
For anaerobic digestion followed by sand bed dewatering is
approximately $25/ton dry sludge solids.
21:5
-------
For anaerobic digestion of activated sludge followed by
reclamation of farm land or a strip mine is approximately
$15 to $16/ton dry solids.
i
Some recommended techniques for treating supernatants are:
Processes for the Removal of Constituents
of Anaerobic Supernatant
Constituent Means of Removal
Suspended material Coagulation, filtration, micro-
straining
Removal with suspended material,
chemical precipitation, ion exchange
Removal with suspended material,
stripping, ion exchange
Lime addition, stripping, ion
exchange
Removal with suspended material,
stripping of volatile acids,
biological treatment, adsorption
on activated carbon
2. Aerobic Digestion
Describes the separate aeration of:
Waste primary sludge
Waste biological sludge, or
A combination of waste primary and biological sludges.
Aerobic stabilization is usually used to stabilize waste
activated sludges or the waste sludges from smaller plants
which do not have separate primary clarification.
Usually designed for a 15-20 day retention.
Biological steps include:
Oxidation of biodegradable material.
Oxidation of microbial cellular material.
Phosphorus
Nitrogen
C02
24-
-------
Process advantages include:
Relatively simple to operate.
Requires small capital expenditure compared to anaerobic
digester.
Does not generate significant odors.
Reduces pathogenic organisms to low level.
Reduces grease or hexane solubles.
produces a supernatant if clarified that is low in BOD,
solids, and total P.
Reduces sludge volatile solids.
Reduces sludge respiration rate.
Production of a highly nitrified sludge which could be
denitrified if sludge is to be placed on land.
Process disadvantages include:
. High operating cost.
Unclear design parameters at present.
Aerobically stabilized sludge has poor dewatering characteristics
on vacuum filters although a recent publication claims otherwise.
Ordinarily, this sludge is dewatered on sand beds or applied in
liquid form to cropland.
Important process parameters are:
. Air requirements.
Time of aeration.
Sludge age.
Proposed method of ultimate disposal.
. Temperature and heat dissipation.
Some designs have been
To allow for a 5-day retention, a sludge concentration of
12,000 mg/1 and to size at 1.4 cubic feet per capita, or
. To load at a rate of 0.1 to 0.2 lb VSS/lb solids/day.
2^
-------
3. Chlorine Oxidation
The Purifax process oxidizes sludge with heavy doses of chlorine.
Sludge dewaters well on sandbeds. Stability is excellent.
Purifaxed sludges present some difficulties when they must be
dewatered on vacuum filters. Chemical (or polymer) conditioning
is needed, but the low pH interferes with the action of conditioning
agents. Pilot plant tests indicate that pH must be increased to
greater than 4 to get good conditioning.
Supernatant and filtrate contain high concentrations of chloramines.
They should not be carelessly discharged.
4. Lime Treatment
Lime treatment of sludge stabilizes the sludge as long as the
pH stays high (11.0 - 11.5). Kill of pathogenic bacteria is
excellent. Sludge dewaters well on sandbeds without odor.
Sludge filtrability is improved. Caution is advised on disposal
of sludge cake to landfills to avoid thick layers. The pH could
fall to near 7 before the sludge dries out, permitting regrowth
and noxious conditions.
A key factor is the maintenance of a pH of 11.0 for a sufficiently
long time (24 hours).
-------
SECTION 5 - SLUDGE THICKENING AND BLENDING
Sludge Particles
Heterogeneous mixture of various materials ranging from the
size of colloids to the size of flocculated particles.
Type of matter can be animal, vegetable or mineral and can be
fibrous, granular or amorphous in shape.
Particles can be hydrophobic (non-water loving) or hydrophilic
(water loving). Hydrophilic particles, due to presence of polar
groups such as hydroxyl, carboxyl, or amino, have a strong
affinity for the water solvent and retain a sheath of water
around the particles which tend to resist compaction.
Surface charge of most particles such as paper fibers, bacterial
cells, clays, sands, hydrated metal oxides, and the usual material
found in wastewater is negative as shown in Figure.
Behavior of the particles is dependent on their size, surface
charge, solvation, and the temperature, pH, and ionic type and
concentration of the water. But particles can have capability
of adsorbing positive or negative charge as is also shown in
Figure.
Sludge Blending
Varieties of sludges are numerous: primary, conventional
activated, high rate activated, oxygen activated, trickling
filter humus; with or without chemical addition in any of the
above; then any of the foregoing may be raw, anaerobically
digested, chlorinated or heat treated. Just from the kinds above
mentioned results in so many possible combinations as to boggle
even a sanitary engineer's mind.
Purpose of blending is to mix any two or three sludges that
result from the various kinds of wastewater treatment to eliminate
or minimize variation, eliminate duplication of facilities, and
produce a decreased volume of sludge with a higher solids
concentration.
Important considerations:
All of the factors previously discussed under sludge particles
are obviously important in sludge blending and thickening.
It is possible that blending will result in compaction as a
result of particles interacting with each other just like
particles and chemicals as shown in Figure.
27
-------
On the other hand, it is possible that blending will result
in only a minimum of compaction such as the case of the
plant that blended primary sludge, waste activated final
effluent, and centrate from the heat treated sludge. The
resultant sludge thickened to a concentration of only
1 percent.
The question appears to be whether sludges should ;be blended
to result in thickening; or thickened and then blended for
further processing. The latter is called for in the design
of the expansion at Washington, D. C., where activated sludge
will be thickened separately by flotation and primary sludge
will be thickened in gravity thickeners, and the two sludges
will be blended enroute to vacuum filtration.
Gravity Thickening (Sedimentation)
Gravity thickening has produced results that range from good to
fair to mediocre. Sludge concentrations usually increase in
primary settling tanks using polymer for raw sewage flocculation.
Although polymer improves the efficiency of suspended solids
removal, the polymer usually increases sludge concentration.
Gravity thickening was formerly accomplished in anaerobic digesters
which produced thickened solids from the bottom and relatively
low suspended solids in the straw-colored supernatant. However,
the present mode of operation blends sludges in the digester not
only physically but mechanically. This produces sludge that
does not settle completely in the secondary digester and thus
produces a supernatant that is usually a sludge of only slightly
lower solids concentration than the digester underflow.
Flotation Thickening
Flotation is the opposite of gravity thickening - the solids are
caused to float due to attachment and entrapment of fine air^
bubbles. Usually one volume of water saturated with air at 40
psig will provide sufficient air bubbles to float the solids
in an equal volume of sludge containing suspended solids at a
concentration of 5,000 mg/1.
It should be noted that flotation with chemicals effects only
marginal increase in thickened sludge concentration, but use of
chemicals does permit a 100 percent to 300 percent increase in
solids loading and about a 10 percent incremental increase in
solids capture. The latter may be or may not be an important
consideration in a given plant regarding recycle of solids.
It should also be noted that the usual chemical used in flotation
was a cationic polymer. However, anionic polymer is also sometimes
effective and should not be overlooked. This was recently demon-
strated at one plant when a metal salt addition to the activated
2.8
-------
sludge was implemented for operation improvement purposes.
This changed the sludge characteristics which required use of
an anionic polymer to condition the sludge for flotation, but
it appears that there was also a decrease from 8 percett to
6 percent in the floated sludge concentration. In another
plant the sludge responded equally to either cationic or
anionic polymer conditioning, so that choice could depend in
such cases on the relative costs of the two chemicals.
Centrifugal Thickening
Centrifugal thickening is accomplished by utilizing centrifugal
force which can be developed in a centrifuge to exert the
equivalent of 2,000 times the force of gravity that was utilized
in gravity thickening previously discussed.
Considerations in Design for Thickening
Provide variable speed sludge pumps so that blending and
thickening can be continuous.
Provide for possible use of chemicals. Install chemical injection
taps into pipelines at points where sludges meet, or water and
sludge meet, and also into dilution water line upstream of where
water meets the sludge. Install tap for chemical injection
immediately downstream of the pressure reducing valve or the
water line in the case of dissolved air flotation. Piping design
should provide for good mixing of water, sludge and polymer,
and then minimum of turbulence and shear to prevent deflocculation.
-------
CHARGED PARTICLE
«0
o
N
A_
ANION POLYMER
H
H-N-C
I H
H
CATION POLYMER
FIGURE
-------
POLYMER AND PARTICLE
COLLOID
POLYMER
FIGURE
INTERACTIONS
VAN der WAAL
FLOCCULATION
7WVAA/WWW\A<
INTERPARTICLE
BRIDGING
o/v\a/vwwwaat
BRIDGING & INTRAPARTICLE
NEUTRALIZATION
lA/vwWWWW
VV/WV/WW\AV>
INTRAPARTICULAR
NEUTRALIZATION
-------
SECTION 6 - SLUDGE BEWATERING
1. Definition
Sludge dewatering in this discussion means further dewatering
of slurries to change the physical form of the sludge from
a slurry of liquid to a cake which should be a solid.' However,
some sludge filter cakes are not quite solid enough to keep
from splashing when the cakes drop from the filter media
onto a conveyor belt.
2. Purpose
Reduce volume occupied by the solids in case of disposal
of sludge cake.
Reduce water associated with the solids in case of disposal
by incinecation.
Change the physical form from liquid to solid for handling
purposes.
3. Chemical Sludge Conditioning
Very few wastewater sludges will dewater without any treatment.
Inorganic chemicals have been used for many years. The most
notable have been iron chloride, calcium oxide, iron sulfate,
alum, aluminum chloride. These chemicals are effective in
most cases, but history tells us that there have been many
failures in the past and we even see them performing poorly
in certain plants today.
The need for something better than the inorganic chemieals led
to the development of water soluble polymers for sludge
conditioning. Polymers are water soluble, high molecular
weight organic chemicals that are available in nonionic (no
formal electrical charge), anionic (negatively charged), or
cationic (positively charged). These polymers can be made in
a variety of charge densities and a variety of molecular weights.
Other additives that are sometimes used in sludge filtration
are fly ash, furnace ash, and diatomaceous earth. Even rice
hulls have been used as a sludge filtration aid as well as paper
pulp.
Considerations for design of sludge conditioning process and
equipment should include laboratory and pilot plant studies;
provide flexibility In the equipment so that a variety of
31
-------
of conditioning materials could be used; provide variable
speed agitators and conditioning tanks where plug flow can be
observed and conditioning agents can be added easily in a
variety of points along with the conditioning tank for observation;
provide for gentle open trough handling of conditioned sludges
rather than through pipelines; avoid high shear of conditioned
sludge; provide ratio control of conditioning chemical to sludge
and also ratio control of water to sludge where polymers may
be used.
4. Dewatering Equipment and Results
Vacuum Filters:
Coil filter, drum filter, and belt filter are three basic types.
Coil filter and belt filter have continuous washing of the media,
but usually not found on a drum filter. Drum and belt filters
offer opportunity to change type of media but this is not easily
done with a coil filter.
All three types have been used with sludges conditioned with
polymers as well as inorganic chemicals.
Considerations in design of vacuum filtration should take into
account the following: the conditioned sludge to the filter pan
should be distributed in more than one or two points - this is
especially important with regard to low solids concentration
sludges; the under-filter agitator should have a variable speed
drive - How can a designer possibly know in advance the optimum
speed? - make it variable and give the operator some, leeway for
adjustments and compensations; the eccentric which determines
the length of the swing of the under-filter agitator should have
provision for variability. Some filters provide no variability;
others provide limited variability; proper level control of sludge
in the filter pan should be provided so as to maintain continuous
sludge conditioning and filtration; filtrate pumps should be of
adequate capacity to accommodate as mueh as a 40 percent dilution
factor when water is used with polymers; vacuum pump capacity
should be adequate enough to maintain good vacuum even with more
porous cakes which can result with some sludges with polymer
or inorganic chemical conditioning; filter valve bridge blocks
should be provided for adjustment as necessary in the field.
Centrifuges: There are three basic types - horizontal solid
bowl with scroll, disc type with nozzles, and basket type.
The horizontal solid bowl is the most widely usdd in wastewater
sludge dewatering. This type of centrifuge can be put on the
line and left to operate with only occasional attention. The
efficiency of this type of centrifuge can be greatly increased
by use of polymers. Internal feed of polymer has been found to
reduce polymer dose and appears to be very beneficial.
3$
-------
The disc type centrifuge is like the old farm cream separator.
It is used for thickening of activated sludge but has the disad-
vantage of nozzles which seem to get plugged easily. Screening
of the sludge has been tried with some success and at least one
installation uses a disc type for thickening to 4 percent solids
in series with a horizontal bowl type which dewaters to about
20 percent solids. No polymers are used with the disc type.
The basket type has recently been evaluated and reported to be
in contention. Polymers may or may not be used with this type
machine which can be automated oven though it operates on a
batch cycle.
Sandbeds have been used for sludge dewatering for many years.
The more sophisticated type sludges of today, no doubt, have
not been dewatering as well as the digested sludges of yesteryears.
But that is because present day digested sludges are not very
dewaterable without conditioning.
Press filters, moving bed filters, rotating cylindrical screens
and capillary type dewatering devices are marketed in this country,
but no large installations are in operation as yet.
5. Polymer Preparation Equipment
Since polymers are useful and sometimes necessary for sludge
conditioning, perhaps a discussion of polymer preparation
equipment is in order.
Polymers are available as dry flakes or powders and also as
liquids.
Preparation of liquid polymers presents no problem because
they mix with water very readily.
Preparation of dry polymers is not difficult but care must be
taken when contacting the dry polymers with water. Unless
each polymer particle is quickly and thoroughly wetted, the
particles stick together to form aggregates of particles from
the size and appearance of fish eyes to slubs as large as golf
balls or even larger.
To provide means for preparing solutions of dry polymers, polymer
manufacturers have developed manual devices and automatic equip-
ment. Also chemical feed equipment manufacturers have developed
their own lines of automatic equipment to meet the needs of the
field.
S)4-
-------
Several manufacturers of automatic equipment for handling
and preparing solutions of dry polymers are listed below:
Acrison, Inc., Carlstadt, New Jersey
BIF Corporation, Providence, Rhode Island
ChemiK Corporation, Troy, Michigan
Wallace & Tiernan, Belleville, New Jersey
Several polymer manufacturers also market automatic equipment
for preparing solutions of dry polymers and these are listed
below:
Calgon Corporation, Pittsburgh, Pennsylvania
The Dow Chemical Company, Midland, Michigan
Hercules, Inc., Wilmington, Delaware
-------
SECTION 7 - THERMAL PROCESSING OF SLUDGE
1. High-Temperature and High Pressure Sludge Treatment
Two basic types - wet air oxidation and thermal conditioning
WET AIR OXIDATION
2. Process Description
Flameless combustion, burning of sludge at 450° - 550° F. and
high pressures (1,200 psig) with air injection.
Equipment - sludge grinder, heating tank, heat exchangers,
high pressure reactors, separators, expansion engine and
auxiliaries.
End products - ash and sludge liquor.
Insoluble organics converted to soluble organics CO2, H2O, ammonia,
sulfates, acetates.
At 250° C. and 83.4 percent COD reduction of sludge the oxidized
liquor shows a COD of 10,000 mg/1 + BOD is only 54 percent of COD.
The pH of the oxidized liquor is 4.8.
Summation, W.A.O. does reduce sludge volumes and produce a stable
solid residue, but the nature of the oxidized acidic liquor and
the costs of the process are of some concern.
Few installations in operation and very few in design.
THERMAL SLUDGE CONDITIONING
3. Two Similar Processes
Porteous steam injection, batch process.
Sludge storage - grinding - pre/heater - high pressure and
temperature (365° F. and 250 psi) - decanter/thickener -
dewatering - auxiliary liquor treatment - off gas deodorizer -
steam boiler.
Zimpro LP0 same as Porteous except adds air via compressors.
Farrer same as Zimpro but claims continuous operation mode.
3<£>
-------
8. Installations
Porteous
Zimpro -
Farrer -
- U.S. 1 operating and 2/3 planned (10 in U.K.)
14 built and 12 under construction.
No U.S. installations, to my knowledge.
37
-------
SLUDGE
GRINDER
120"
STEAM
HEAT EXCHANGER GROUP
ACCUMULATION
TANK
SLUDGE
STORAGE
TANK
I TRANSFER |
PUMP
HEATING
120"
CONDENSATE
-txj-
COILS
STEAM
CONDENSATE
WATER
4) JtXH
s HELIFLOW
HEAT EXCHANGER
SEPARATOR
FEED PUMP
AIR
RECEIVER
VAPORS
COMPRESSOR
^lOTOR
AIR
CONDENSER
HIGH PRESSURE PUMP
WATER AND
CONDENSATE
FIGURE
WET AIR OXIDATION SYSTEM - WHEELING, WEST VIRGINIA
-------
BOILER FOR PROCESS STEAM
STEAM
RAW SLUDGE SEtTOGE RAM PUMP
STORAGE DISINTEGRATOR
I HEAT EXCHANGER REACTION VESSEL
AUTOMATIC DISCHARGE VALVE
DECANTER
PUMP
THICK5NED
SLUDGE
RESIDUAL LIQUORS
I ED SLUDGE
VACUUM FILTER
FIGURE
FLOW DIAGRAM OF THE PORTEOUS PROCESS
-------
SLUDGE
GRINDER
AIR
AIR COMPRESSOR
TO INCINERATOR
PUMP
GROUND
SLUDGE
HOLDING
TANK
POSITIVE
DISPLACEMENT
SLUDGE PUMP
)*¦
OXIDIZED
SLUDGE
TANK
HEAT
EXCHANGER
W.M* JPn
REACTOR
EXHAUST GAS
PRESSURE
CONTROL
VALVE
VAPOR
COMBUSTION
UNIT
TREATED
BOILER
WATER
FILTER
PUMP
BOILER
FIGURE
THERMAL SLUDGE CONDITIONING AND DEWATERING
ZIMPRO LPO
-------
REACTOR
CONTROL
PANEL
BOILER
SECOND HEAT
EXCHANGER
CIRCULATING
PUMP
J LEVE
LEVELING
VESSEL
PRE-HEATER
DECANTING
AND STORAGE
TANK
AIR
COMPRESSOR
j^ixixHxici¦
AUTOMATIC
VALVES
(ONE BACK-UP)
CENTRIFUGE
THICKENER
LAND FILL
SOIL
CONDITIONING
TO FS
PUMP
GRINDER
FIGURE
FLOW SHEET FOR THE DORR-OLIVER FARRER SYSTEM
-------
SECTION 8 - FINAL DISPOSAL PROCESSES
Ultimate Disposal
Criteria to follow in selection of method.
Should be in accordance with interstate, state, and
Federal Quality Office requirements.
Should not result in any significant degradation of
surface or groundwater, air, or land surfaces.
No sludge residues, grit, ash, or other solids should be
discharged into the receiving waters or plant effluent.
Sludge disposal to ocean waters is not recommended if
toxic materials may be transmitted to the aquatic food
chain. Present indications are that ocean disposal will
be banned.
Stabilization of sludge should be considered prior to
spreading on land.
t Utlimate disposal is the final treatment process. This transforms
the sludge in some instances and places it at its final site.
Incineration
Sludge is burned and reduced to combustion gases or ash.
Multiple hearth furnaces range in capacity from 200 to
8,000 lb/hr of dried sludge and operate at 1,700° F.
a. Furnace consists of refractory lined circular steel
shell with refractory hearths, which lie one above
the other.
b. Sludge enters through flopgate and proceeds with the
help of rabble arms to move down from hearth until
ash discharges at bottom.
c. Reported total annual cost for incineration varies
between $10 and aboOt $30/ton dry solids depending on
the need for supplemental fuel, pollution control, etc.
d. Typical section of multiple hearth incinerator is
shown in Figure.
In a fluidized bed furnace, the dewatered sludge is fed into
a fluidized sanbed that is supported by air at 3.5 to 5.0 psi.
4-2.
-------
a. The sludge solids are normally first degritted.
b. Fluid bed reactor is a single chamber unit where
moisture evaporates and combustion of organics occurs
at 1,400 to 1,500° F.
c. Reported total operating costs vary between about $26
to $35/ton dry solids depending on the supplemental
fuel requirement.
d. Typical section of a fluid bed reactor is shown in
Figure.
Use of Sludge in Agriculture
Stabilized, either biologically or by some other mode, sludge
may be used as a fertilizer or soil supplement. Raw sludge
presents health and nuisance problems.
Transportation costs must be considered.
Fertilizer value is normally measured by the nitrogen,
phosphorus, and potash content.
Fertilizer Value of Undigested Biological Sludge
Nitrogen 1-5%
Phosphate 1-3%
Potash 0.1 - 0.3%
The nitrogen and phosphorus contents are generally reduced
40-50 percent by digestion.
Transportation costs can make this mode of disposal
uneconomical.
Advantages of land spreading are:
a. economy.
b. it is the final treatment process.
c. it utilizes the water, nutrients, and organic material.
d. it is nuisance-free if done right.
. Disadvantages are:
a. creation of health hazards and nuisance conditions when
done wrong.
b. possible accumulation of toxic metals.
43
-------
c. possible nitrate contamination of groundwater.
Quantity of sludge to be spread is determined by:
a. soil characteristics.
b. climate.
c. land use or intended crop.
d. type and solids content of the sludge.
Typical application rates:
a. for a corn field - 10-30 tons of solids/acre/yr.
b. for a strip mine - 1,000 tons of solids/acre/yr.
Composting
Received attention because of its applicability to organic,
industrial, agricultural as well as domestic sludges.
Degree of interest in this country as well as abroad is
dwindling for economic reasons.
Difficulty exists in finding a market for the product.
Lagooning and Landfill
Lagoons may be used for:
a. anaerobic digesters but aesthetics may rule this out.
b. as evaporation ponds.
d. as permanent lagoons or landfills - if dewatering is
incomplete a full permanent lagoon remains as a permanent
liability.
Area requirement and management are important.
Drying of Sludge Filter Cake
Sell as soil conditioner.
Sell for manufacture of commerical fertilizer.
Reported to be safe hygienically.
Process is used in Houston, Milwaukee, and Chicago.
44-
-------
Reported cost is approximately $45/ton dry solids,
for Chicago.
Figure shows equipment used in flash drying.
¦4-5'
-------
WASTE COOLING AIR
TO ATMD SPHERE [S/j
CLEAN GASES TO
ATMD SPHERE
INDUCED DRAFT FAN
BYPASS ON POWER OR
WATER STOPPAGE
NERCO-ARCO
CYCLONIC JET
SCRUBBER
OATING DAMPER
A
(
\S)
PLYASH
SLURRY
MAKEUP WATER
TO DISPOSAL
FILTER CAKE
SCREEN-
INGS &
GRIT
COMBUSTION AIR
/" RETURN
RABBLE ARM DRIVE
ASH PUMP
ASH HOPPER
COOLING AIR
FIGURE
TYPICAL SECTION OF MULTIPLE HEARTH INCINERATOR
-------
SIGHT GLASS
EXHAUST
SAND PEED
FLUIDIZED
SAND
PRESSURE TAP
ACCESS DOORS
^O'Z » J << mm * .
_ - - > ' ?<>
v' '¦ V
v" * * ~ * V U''
\x' '
a Wt * ¦ . »"S . ' w "¦«
1
1
PREHEAT BURNER
«** THERMOCOUPLE
SLUDGE INLET
FLUIDIZING AIR
"" INLET
FIGURE
TYPICAL SECTION OF A FLUID BED REACTOR (DORR-OLIVER, INC.)
*7
-------
FLASH DRYING
DEODORIZER
CYCLONE
HOT GAS
PRODUCT
SLUDGE CAKE
FIGURE
-------
UPGRADING EXISTING SECONDARY TREATMENT PLANTS
-------
UPGRADING EXISTING ACTIVATED SLUDGE PLANTS
1. Conventional Activated Sludge Process
A - Uses micro-organisms in suspension to oxidize soluble and
colloidal organics to CO2 and H2O in presence of oxygen.
(1) Wastewater commonly aerated 6 to 8 hours
(2) Return sludge normally about 25 percent
(3) BOD loadings about 35 lbs/1000 cu.ft./day
B - Common characteristics
(1) High oxygen demand at head end of aeration tank
(2) Final clarifier has high solids loading
(3) Lack of operational stability with variations in hydraulic
and organic loadings
2. Activated Sludge Modifications
A - Step aeration divides influent flow to aeration tank
1
(1) Reduces initial oxygen demand
(2) Distributes organic loading more evenly
(3) More efficient utilization of micro-organisms (loadings
to 50 lbs BOD/1000 cu.ft. per day)
(4) Normally will not use more air
B - Contact stabilization
(1) Concentrated sludge is reaerated
(2) Shorter total contact time
(3) Handles greater shock and toxic loads
(4) Majority of activated sludge is isolated from main stream
of plant
1
-------
(5) Common detention times
(a) Contact tank: 0.5 - 1.0 hrs
(b) Stabilization tank: 2-6 hrs
(6) Most beneficial when organic load is present, mainly in
colloidal state
(7) Smaller plants may require greater contact times due to
extreme flow variations
C - Completely mixed
(1) Influent waste and recycled sludge introduced uniformly
throughout aeration tank
(a) Uniform oxygen demand throughout tank
(b) Operational stability for slug loads
D - Oxygen aeration
(1) Covered aeration tank
(2) Uses pure (>90%) oxygen instead of air
(3) Oxygen can be site-generated or transported
(4) Potential advantages
(a) Reduced costs
(b) Reduced sludge
(c) Higher D.O.
(d) Reliable process control
Basic Design Parameters for Activated Sludge
A - BOD removal for specific operating conditions
(1) Influent BOD
(2) Sludge recycle
-------
(3) MLVSS
(4) Aeration detention
B - Air requirements
Typical requirements for AS modifications:
Process Cu.ft. air/lb BOD removed
Conventional 700 to 1,000
Step Aeration 500 to 700
Contact Stabilization 750
Complete Mix 600
C - Sludge production (excess)
(1) Excess sludge related to organic loading
(2) For common AS loadings (0.3 to 0.6 lb BOD/lb MLVSS/day)
excess sludge about 0.5 to 0.7 lbs VSS/lb BOD removed
(3) For 02 loadings of 0.4 to 0.8 excess sludge production
about 0.3 to 0.45 lb VSS/lb BOD removed
D - Oxygen transfer Kates
(1) Temperature
(2) Degree of turbulent mixing
(3) liquid depth in aeration tank
(4) Type of aeration device
(5) Characteristics of wastewater
E - Activated sludge return
(1) Key tool for plant operator
(2) 50% min. for conventional and step aeration
(3) 100% min. for contact stabilization and complete mix
F - Pilot studies. Range up to 5 to 10 gpm to generate design parameters
(1) Evaluate performance and characteristics under various organic
loadings (lbs BOD/dny/lb MLVSS)
-------
(a) BOD removal
(b) COD removal
(c) Oxygen consumption
(d) Concentration of biological solids
(e) Physical nature of effluent (ss, odor, color)
4. Upgrading Techniques
A - To relieve organic and hydraulic overloading. Provide higher
air rate.
(a) Mechanical
(b) Diffused
B - Conventional AS to step aeration
(1) Requires minimum capital investment for overloaded plant
(a) Modify piping
(b) Renovate air system
(c) Increase secondary clarifier capacity
(2) Upgrading overloaded 5 mgd conventional AS to 8.4 mgd step
aeration with same efficiency - $410,000
C - Conventional AS to contact stabilization
(1) Modify piping
(2) Expand sludge recycle
(3) Install new mechanical aerators
(4) Upgraded overloaded 1.2 mgd AS plant to 3.0 mgd contact
stabilization for $370,000. Effluent from 40 mg/1 BOD to
20 mg/1
-------
D - Conventional AS to completely-mixed
E - Conventional AS to oxygen aeration
(1) Precast covers for aeration tanks
(2) Baffling may be required
(3) Piping modified
(4) Oxygen generating and/or storage
(5) Reduced sludge production
F - Upgrading non-overloaded AS plant to meet higher effluent standards
(1) Additional pre-AS treatment
(a) Roughing trickling filter
(b) Chemical clarification
(2) Additional post-AS treatment
(a) 2nd stage activated sludge
(b) Polishing lagoon
(c) Multi-media filters
(d) Microstraining
(e) Activated carbon
Chemical Clarification for Solids and BOD Reduction
A - Primary clarification
(1) Increase in primary sludge dewatered (more easily dewater
and thickened)
(2) Decrease in quantity of secondary sludge
(3) Decrease in organic loading to secondary treatment units
-------
B - Secondary clarification
(1) Hydraulic overloading - rise velocity of wastewater exceeds
settling velocity of solids
(2) Organic overloading - increased solids load to secondary
clarifier
C - Chemical addition to primary clarifier
(1) For intermittent or varying flows
(2) Limited space for additional clarifiers
(3) Industrial wastes hindering biological treatment
(4) Hydraulic or organic overload
(5) Interim improvement
(6) Chemicals used
(a) Salts of iron
(b) Salts of aluminum
(c) Lime
(d) Polyelectrolyte
D - Chemical addition to secondary clarifier - less experience
(1) Same chemicals as in primary
(2) Phosphorus removal added benefit (or vice-versa)
6. Miscellaneous Upgrading Techniques
A - Correction of poor initial design
(1) Inlet and outlet design
(2) Sludge withdrawal system
(3) Lack of scum removal devices
B - Use of tube settlers
(1) Used in primary or secondary clarifiers
(2) Capture solids at high overflow rates
(3) Do little for efficient primary clarifiers
(4) Do no remove colloidal solids
6
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Effluent Polishing Techniques
A - Polishing lagoons
(1) Aerobic
a) Shallow - may have solids carryover due to algae
b) Deep - use mechanical aeration
(2) Facultative - aerobic and anaerobic zones
B - Microstraining
C - Filtration
(1) Deep bed coarse sand filters - 4 ft. depth, 1-3 mm diam
(2) Mixed media - anthracite and sand
(3) Multi-media - anthracite, sand, garnet
(4) Activated carbon
a) As "tertiary" treatment
b) Used as adsorption medium
c) Pre-filter is SS >50 mg/1
d) Requires regeneration
e) Used at Tahoe - effluent BOD 2-5 mg/1
(5) Pre-aeration: Upgrading for SS and BOD removal limited
used for reducing septicity and grease removal
(6) Post-aeration: Maintain D.O. in effluent
a) Diffused
b) Mechanical
c) Cascade
d) U-Tube
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UPGRADING A CONVENTIONAL ACTIVATED SLUDGE PROCESS
TO STEP AERATION
EXAMPLE A
AERATION TAHK
PRIMARY
EFFLUENT
5.0 KGD
SECONDARY
CLARIFlER
25S SLUDGE RECYCLE
FINAL
EFFLUENT
25S SLUDGE RECYCLE^*
EXCESS SLUDGE
TREATMENT SYSTEM BEFORE UPGRADING
CONVENTIONAL ACTIVATED SLUDGE (DIFFUSED AIR SYSTEM)
AERATION TANK
PRIMARY
EFFLUENT
8.4 MGO
ADDITIONAL
REQUIRED
CAPACITY
25% SLUDGE RECYCLE
SECONDARY
CLARIFIER
EXCESS SLUOCE
TREATMENT SYSTEM AFTER UPGRADING
STEP AERATION PROCESS
FINAL
EFFLUENT
FIGURE 1
8
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Upgrading Conventional
Activated Sludge to Step Aeration - Example A
Original
Design Overloaded Upgraded
Before Design Design
Description Overloading Condition Condition
Flow, mgd 5.0 8.4 8.4
Influent BOD, mg/1 200 200 200
Primary Treatment
Percent BOD Removal 30 30' 30
Aeration Tank
MLSS, mg/1 2,000 - 2,000
Sludge Recycle, percent 25 15 25
Air Requirement, cu.ft. air/lb. BOD removed 800 - 700
Volumetric Loading, lbs. BOD/dav/1,000 cu.ft. 35 62 62
Organic Loading, lbs. BOD/day/lb. MLSS 0.34 0.88 0.54
Detention Time in Aerator, minutes" 300 180 180
Secondary Clarifier
Overflow Rate, gpd/sq.ft. 800 1,280 800
Secondary Treatment
Percent BOD Removal 86.0 75.0 86.0
Effluent BOD, mg/1 20 35 20
* Requires modification of primary clarifier to handle increased hydraulic load to achieve 30 percent
BOD removal.
^¦Excluding sludge recycle.
TABLE I
9
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UPGRADING A CONVENTIONAL ACTIVATED SLUDGE PROCESS
TO CONTACT STABILIZATION
EXAMPLE B
AERATION TRMR
PRIMARY
EFFLUENT
1.2 MGO
y
SECONDARY
CLARIFlER
FINAL
EFFLUENT
SLUDGE RECYCLE
TREATMENT SYSTEM BEFORE UPGRADING
CONVENTIONAL ACTIVATED SLUDGE (MECHANICAL AIR SYSTEM)
RAW WASTEWATER
3.0 MGO
STABILIZATION
TANKS
rA
y//.
SECONDARY
CONTACT CLARIFIERS
TANKS
I *
I
75?, SLUDGE RECYCLE
FINAL
EFFLUENT
ADDITIONAL.REQUIRED
CAPACITY PROVIDED BY
PRIMARY CLARIFIERS
TREATMENT SYSTEM AFTER UPGRADING
CONTACT STABILIZATION PROCESS
FIGURg 2
10
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Upgrading Conventional Activated
Sludge to Contact Stabilization - Example B
Description
Flow, mgd
Influent BOD, mg/1
Primary Clarifier
Overflow Rate, gpd/sq.ft.
BOD Removal, percent
Aeration Tank
Volumetric Loading, lbs. BOD/day/1,000 cu.ft.
Sludge Recycle, percent
Detention Time, hours
Contact Basin
Stabilization Basin
Secondary Clarifier
Overflow Rate, gpd/sq.ft.
BOD Removal in Secondary Units
SS Removal in Secondary Units
Effluent BOD, mg/1
Effluent SS, mg/1
Overloaded
Design
Condition
3.0
200
1,200
20
44
4A3
960
75
75
40
30
Upgraded
Design
Condition
3.0
200
1
60z
75
4.2-
780
90
90
20
18
'Primary clarifier converted to secondary clarifier.
^Total organic loading increases due to elimination of primary treatment.
^Based on influent flow plus 15 percent sludge recycle to the total basin.
Based on influent flow plus 75 percent sludge recycle to the contact basin.
^Based on 75 percent sludge recycle to the stabilization basin.
^Reduction in OFR is achieved by converting the primary clarifier to a secondary basin.
TABLE 2
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UPGRADING CONVENTIONAL ACTIVATED SLUDGE
TO A COMPLETELY-MIXED SYSTEM
EXAMPLE C
TREATMENT SYSTEM AFTER UPGRADING TO
COMPLETELY-MIXED PROCESS
NEW
EFFLUENT
WE I Rv
N
PRIMARY
EFFLUENT
10.0 MGO
605 SLUDGE RECYCLE
AO DITI ON AL REQUIRED
CAPACITY
FINAL
EFFLUENT
*
"T"
I
1 SECONDARY CLARIFIER
EXCESS SLUDGE
TYPICAL CROSS SECTION OF UPGRADED
AERATION TANK (26)
DRIVE UNIT
w
EFFLUENT
BLADE
TURBINE
SPARGER CO-
RING
r^=QJ
INFLUENT
PIPING
FTCURK 3
.1.2
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Upgrading Conventional Activated
Sludge to a Completely-Mixed System - Example C
Original
Design Overloaded Upgraded
Before Design Design
Description Overloading Condition Condition
Flow, mgd 5.0 10.0 10.0
Influent BOD, mg/1 200 305 305
Primary Treatment
Percent BOD Removal 30 30* 30
Aeration Tank
MLSS, mg/1 2,000 2,000 3,000
Sludge Recycle, percent 25 25 60
Air Requirements, cu.ft. air/lb. BOD removed 820 - 600
Volumetric Loading, lbs. BOD/day/1,000 cu.ft. 35 107 107
Organic Loading, lbs. BOD/day/lb. MLSS 0.34 1.04 0.69
Detention Time In Aerator, minutes^ 300 150 150
Secondary Clarifier
Overflow Rate, gpd/sq.ft. 800 1,600 800
Secondary Treatment
Percent BOD Removal 86 62 91
Effluent BOD, mg/1 20 80 20
* Requires modification of primary clarifier to handle increased hydraulic load to achieve 30 percent
BOD removal.
^Excluding sludge recycle.
TABLE 3
13
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Upgrading Conventional Activated
Sludge to an Oxygen Aeration System - ExampleD
Description
Flow, mgd
Influent BOD, mg/1
Primary Treatment
Percent BOD Removal
Aeration Tank
MLSS, mg/1
Sludge Recycle, percent
Air Requirements, cu.ft. air/lb. BOD removed
Oxygen Requirements, lbs. 02/lb. BOD removed
Volumetric Loading, lbs. BOD/day/1,000 cu.ft.
Organic Loading, lbs. BOD/day/lb. MLSS
Detention Time in Aerator, minutes^
Secondary Clarifier
Overflow Rate, gpd/sq.ft. .
Secondary Treatment
Percent BOD Removal
Effluent BOD, mg/1
Original
Design Overloaded Upgraded
Before Design Design
Overloading Condition , Condition
2 6 6
200 200 200
30 301 30
2,000 2,000 4,000
25 25 50
800
1.2
35 105 105
0.34 1.02 0.51
300 100 100
800 - 800
86 64 86
20 50 20
^Requires modification of the primary clarifier to handle increased hydraulic load to achieve 30 percent
BOD removal.
Excluding sludge recycle.
TAHUi 4
*4
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Approximate Capital Costs for Upgrading
Example A: Aeration Tank Modification $160,000
Secondary Clarifier Expansion 250,000
$410,000
($120/1000 gpd incremental upgraded capacity)
Example B: Aeration Tank Modification $340,000
Clarifier Conversion 30,000
$370,000
($206/1000 gpd incremental upgarded capacity)
Example C: Aeration Tank Modifications $280,000
Secondary Clarifier Expansion 420,000
$700,000
($140/1000 gpd incremental upgraded capacity)
Example D: Aeration Tank Modifications $130,000
Oxygen Generating and
Dissolution Equipment 400,000
Secondary Clarifier Expansion 170,000
$700,000
($170/1000 gpd incremental upgraded capacity)
Costs based on ENR Index of 1500
TABLE S
15
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UPGRADING EXISTING SECONDARY TREATMENT PLANTS
Trickling Filters
Upgrade to relieve organic and/or hydraulic overloading
Upgrade to increase organic removal efficiency
Upgrade existing single stage filter
Upgrade single stage filter to a two-stage biological system
Upgrade two-stage filter to a multi-stage biological system
Add processes prior to existing trickling filter plant
Modify existing trickling filter plant
Add processes following existing trickling filter plant
Factors to consider prior to upgrading trickling filter plant
Capacity of distributor arm
Ventilation in all pipes, channels and drains
Decide whether to use direct recirculation after filter or
recirculation of clarified effluent
Evaluate secondary clarifier capacity
Performance and capacity of sludge collection and handling
facilities - upgrading usually increases sludge production
Example
Upgrading low-rate trickling filter to high rate
Original plant design
Flow - 185,000 gpd
Influent . BOD - 230 mg/1
S.S.- r2A0 mg/1
- Effluent . BOD - 30 mg/1
S.S. - 23 mg/1
Overall plant performance
BOD Removal 87%
SS Removal 89%
16
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Overloaded conditions
flow - 370,000 gpd
- influent . BOD - 210 mg/1
. S.S. - 200 mg/1
- effluent . BOD - 44 mg/1
S.S2-- 36 mg/1
- overall plant performance
BOD Removal - 79%
S.S. Removal - 82%
PRIMARY EFFLUENT
185.000 GPO
TRICKLING
FILTER
SECONDARY
* FINAL
EFFLUENT
SLUDGE
TREATMENT SYSTEM BEFORE UPGRADING
Upgrading considerations and conditions
determined recycle rate 0.5
- replaced distributor arm (hydraulic capacity)
- motorized distributor arm (hydraulic head)
- existing filter media and drains were found to be
sufficient
- constructed recirculation pumping station with variable -
speed pumping capacity regulated with flow - proportioning
pump controls
increased primary and secondary clarifier capacities
- effluent . BOD - 30 mg/1
. S.S. - 22 mg/1
- overall plant performance
BOD removal - 86%
S.S. removal - 89%
17
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EXISTING
TRICKLING
FILTER
PRIMARY EFFLUENT
370.000 GPD
NEW RECIRCULATION PUMPING STATION
EXISTING SECONDARY
CLARIFIER
»FINAL
EFFLUENT
RECIRCULATION 185.000 GPO
SLUDGE
TREATMENT SYSTEM AFTER UPGRADING
ADDITIONAL
REQUIRED
CAPACITY
- Capital costs estimated for upgrading
Trickling filter modifications $51,000
Recirculation facilities 15,000
Secondary clarifier expansion 30,000
total $ 96,000
ENR index of 1,500
- Example
Upgrading single-stage trickling filter to a two-stage
Overloaded condition
flow
influent
BOD
. S.S.
effluent . BOD
. S.S.
overall plant performance
. BOD removal 72%
. S.S. removal 75%
6 mg/1
335 mg/1
340 mg/1
99 mg/1
85 mg/1
PRIMARY
EFFLUENT
6.0 MGD
INTERHEDt ATE-RflTE
TRICKLING FILTER
SLUDGE
SECONDARY
CLARIFIER
FINAL
EFFLUENT
TREATMENT SYSTEM BEFORE UPGRADING
18
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Upgrading considerations and conditions
- decision to add a complete set of units was made
- added a high-rate trickling filter and intermediate
clarifier ahead of existing system
- added new recirculation pumping station
PRIMARY
EFFLUENT
6.0 NGD
effluent
BOD
S.S,
20 mg/1
15 mg/1
- overall plant performance
BOD removal 94%
S.S. removal 96%
RECIRCULATION 7.5 MGD
SLUDGE
FINAL
EFFLUENT
I ST. STAGE-NEW NEW
HIGH-RATE FILTER INTERMEDIATE
CLARIFIER
2ND STAGE-EXISTING EXISTING
INTERMEDIATE-RATE SECONDARY
FILTER CLARIFIER
TREATMENT SYSTEM AFTER UPGRADING
Capital costs estimated for upgrading
Trickling filter additions $ 1,000,000
Recirculation facilities 100,000
Intermediate clarifier 400,000
total $ 1,500,000
ENR index of 1,500
19
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Upgrade lagoons to relieve organic overloading and increase
organic removal
Increased pond detention time increases BOD removal
Decrease areal BOD loading
- pretreatment (primary sedimentation prior to raw
sewage pond system)
Decrease areal BOD loading and increase detention time (increase
number of ponds in system)
Use lagoon recirculation
interpond and intrapond systems
Lagoon - configuration
- full use of wetted pond area
- eliminate dead spots
- eliminate short-circuiting
location of transfer inlets and outlets important
consider wind directions for possible scum problems
Evaluate feed and withdrawal design - maybe multiple
entry and single exit
Evaluate dike construction
Consider aeration and mixing
Algae removal
- mechanical
t sedimentation pond
20
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PUMP STATION
(TYP.)
RECYCLE
INTRAPOND RECIRCULATION
RECYCLE
Ser ies
Parallel
INTERPOND RECIRCULATION
Fig. Common Pond Configurations and
Recirculation Systems.
21
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