Industrial Wastewater Treatment: Biological Anaerobic Treatment

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Industrial Wastewater Treatment Biological
Anaerobic Treatment

• Sung S. Anaerobic short course handouts
• Speece R.E. (1996) Anaerobic Biotechnology for
  Industrial Wastewaters. Archae Press, USA

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Wastewater Treatment Options

• Aerobic treatment for soluble chemical oxygen
  demand (COD) in 50 - 40,000 mg/L range
• Anaerobic treatment for high CODs (4000 - 50,000
  traditionally). Low COD wastewater can be treated
  anaerobically under high temp., sufficient
  alkalinity and nutrient and high amounts of VFA
• Alternative processes for CODs lt 50 mg/L (e.g.,
  carbon adsorption, ion exchange) and gt 50,000
  mg/L (e.g., evaporation and incineration)

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Advantages of AD
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Waste O2 ? CO2H2O new cells
Waste ? CH4 new cells
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Advantages of AD - continued

• Ability to transform several hazardous solvents
  including
• chloroform, trichloroethylene and
  trichloroethane

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Advantages of AD - continued
11. Avoidance of foaming with surfactant
wastewaters About 70 volumes of gas are added
per volume of 2,000 mg/l wastewater in aerobic
process compared to 1.6 volumes created
anaerobically
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Advantages of AD - continued
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AD Waste Treatment and Resources Recovery
Micro-aerobic
So recovery
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Cumulative Number of AD Plants for Industrial
Applications
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Limitations of AD
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Limitations of AD continued
7. Treatment of high protein nitrogen
containing wastewater
High ammonia may cause inhibition
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Limitations of AD continued

• Insufficient inherent alkalinity generation
  potential in
• dilute or carbohydrate wastewater

Cost of alkalinity may be economically
too high for AD application

• Insufficient CH4 generation from dilute
  wastewater to
• heat to 35C optimal temperature

This is, most of the time, not a problem
for using AD in Thailand
10. Sulfide and odour generation from sulphate
rich feed stocks
11. Low kinetic rates at low temperature
Some amounts of CH4 are required to heat
up the reactor
12. High NH4 conc. required for maximum biomass
activity
Up to 40-70 mg/l is reported to be
necessary for high activity
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Comparison between Anaerobic Aerobic processes
Anaerobic Aerobic
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Anaerobic Aerobic
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Organic content in wastewater

• Organics can be subdivided into
• Carbohydrate, Protein, Lipid (Oil Fat)
• Biodegradability
• Carbohydrate gt Protein gt Lipid
• As a rule of thumb in Anaerobic Digestion
• Higher protein generates more alkalinity
• Maximum 30 of COD from Lipid
• Thermophilic digestion preferred in lipid
  digestion
• due to higher lipid solubility in higher
  temperature

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• Biodegradable COD (BCOD) Estimation
• 1. BCOD BOD5 (BODult / BOD5)
• 2. BCOD (Oil Grease) FOG 2.88
• 3. BCOD (Protein) ( TKN NH3-N) 6.29 1.50
• 4. BCOD (Carbohydrate) (1) (2) (3)

(BODult / BOD5) 1.5 2.0
Grease C8H16O C8H16O 23/2 O2 ? 8 CO2 8
H2O 2.88 g COD / g grease
Protein C16H24O5N4 (12x16 24 16x5 14x4) /
(14x4) 6.29 1.50 g COD / g protein
BODult Ultimate BOD BCOD FOG Fat, Oil
Grease TKN Total Kjeldahl Nitrogen organic-N
ammonia-N
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COD / BOD5 ratio gt Biodegradability Lower ratio
gt Higher biodegradability Typical value of raw
wastewater 1.5 2.0 Typical value of
biologically treated effluent 4 - 8 NH4-N /
TKN ratio gt Freshness Lower ratio gt Fresh
sample pH issues chemical usage, VFA
production, etc.
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Solid Matrix
TS TSS TDS

VS VSS
VDS
TFS FSS FDS
particulate organic
soluble organic
soluble inorganic
particulate inorganic
salts
sand, silt
T Total S Solids or Suspended D Dissolved V
Volatile F Fixed
Source Sung S. handouts
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Example Molasses
Source Sung S. handouts

• CODtotal157430mg/l
• CODfiltered132450mg/l
• VFA5690mg/l
• TS158900mg/l
• VS128000mg/l
• TSS73670mg/l
• VSS59330mg/l
• TKN500mg/l
• NH4-N100mg/l
• pH3.59

CODfiltered/CODtotal84 Low pH VS/TS80.6 Nut
rient requirement (COD/TKN) Ammonia/TKN0.2 Salt
content/ Grit removal
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ExamplePOME
Source Sung S. handouts

• CODtotal52,870mg/l
• CODfiltered25,500mg/l
• BOD533,835mg/l
• VFA11,070mg/l
• TS46,610mg/l
• VS38,680mg/l
• TSS24,920mg/l
• VSS23,125mg/l
• TKN1,080mg/l
• NH4-N100mg/l
• TP217mg/l
• FOG4,000mg/l
• pH4.1

TS TSS TDS

VS VSS
VDS
TFS FSS FDS
21,690
46,610
24,920
38,680
23,125
15,555
7,930
1,795
6,135
CODfiltered/CODtotal48 Carbohydrate
(CODeq)31 VS/TS83 VFA (CODeq)11,0701.25
13,858mg/l26 FOG (CODeq)11520mg/l
(25) CODtotal/TKN49 ? Nutrient
deficient Protein (CODeq)9369mg/l (18)
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Anaerobic Waste Treatment
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Electron acceptors O2 gt NO3- gt SO42- gt CO2
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Anaerobic Digestion
(1)
Complex Organics Carbohydrates Proteins Lipids
1. Hydrolysis
Simple Organics
(2)
Volatile Organic Acids Propionate, Butyrate, etc.
2. Acidogenesis
Acetate
H2 CO2
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(3)
3. Methanogenesis
CH4 CO2
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Biogas Content

• Methane, CH4 50 75
• Carbon Dioxide, CO2 25 50
• Nitrogen, N2 1 5
• Hydrogen Sulfide, H2S lt 1
• Hydrogen, H2 - trace

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Methane Content

• Carbon Dioxide content can be estimated by
  reactor pH
• and bicarbonate concentrations

KH Henrys Law constant
pKa1 6.33 pKa2 10.33 at 20oC

• Methane content is the balance of carbon dioxide

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Relationship between pH, bicarbonate and carbon
dioxide at 35oC and 1 atm pressure
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Theoretical methane yield per kg COD at STP
Assumption No oxygen demand could be satisfied
in an anaerobic reactor
but production of methane
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Step 3 CH4 generation rate per unit of COD
removed   From eqs. (1) and (2), we have   gt 1 g
CH4 4 g COD 1.4 L CH4   gt 4 g COD
1.4 L CH4   gt 1 g COD 1.4/4 0.35 LCH4
  or 1 Kg COD 0.35 m3 CH4
----------- (3)   Complete anaerobic
degradation of 1 Kg COD produces 0.35 m3 CH4 at
STP
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Kinetics

• Rate of reaction(s) will determine
• Process efficiency
• Effluent quality
• Reactor volume requirements (SRT HRT)
• Ultimately one or several of the rate limiting
  reactions will control the overall rate of
  conversion of organics to methane and CO2

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Monod (non-inhibitory) Kinetics

µ Maximum specific growth rate
(h-1)
Ks Half saturation constant, mg/L
S (g/L as COD)
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Particulate Hydrolysis
steps
Complex Biodegradable Particulates
1
1 2 3
Lipids
Proteins and Carbohydrates
Long Chain Fatty Acids
Amino Acids and Simple Sugars
1
1
Acidogenesis
anaerobic oxidation
Volatile Acids (propionic, butyric, etc.)
fermentation
Methane Forming Acid Forming
Hydrolysis
2
2
Hydrogen
Homoacetogenesis
Acetic Acid
3
Methanogenesis
5
4
aceticlastic methanogens
hydrogen oxidizing methanogens
Methane
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Process Microbiology
The anaerobic degradation of complex organic
matters is carried out by a series of bacteria
as indicated in the figure (with numbers). There
exists a coordinated interaction among these
bacteria. The process may fail if a certain
group of these bacteria is inhibited.
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Hydrogen producing acetogenic bacteria (2)
Syntrophic association of acetogenic organisms
with methanogenic H2- consuming bacteria helps
to lower the concentration of H2 below
inhibitory level so that propionate degrading
bacteria are not suppressed by excessive H2
level. H2 partial pressure lt 10-2 (100 ppm)
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Homoacetogenes (3)
Homoacetogenesis has gained much attention in
recent years in anaerobic processes due to its
final product acetate, which is the important
precursor to methane generation. The bacteria
are, H2 and CO2 users. Clostridium aceticum and
Acetobacterium woodii are the two
homoacetogenic bacteria isolated from the
sewage sludge sample. Homoacetogenic bacteria
has a high thermodynamic efficiency as a result
there is no accumulation H2 and CO2 during growth
on multi-carbon compounds.
CO2 H2 ? CH3COOH 2H2O
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Methanogens (4 and 5)
Methanogens are unique group of microbes
classified as Archaebacteria, that are
distinguished from the true bacteria by a number
of characteristics, including the possession of
membrane lipids, absence of the basic cellular
characteristics (e.g. peptidoglycan) and
distinctive ribosomal RNA. Methanogens are
obligate anaerobes and considered as a rate
limiting species in anaerobic treatment of
wastewater. Moreover, methanogens co-exist or
compete with sulfate reducing bacteria for the
substrates in anaerobic treatment of
sulfate-laden wastewater.
 
Two classes of methanogens that metabolize
acetate to methane are

• Methanosaeta (old name Methanothrix) Rod shape,
  low Ks, high affinity

• Methanosarcina (also known as M. mazei )
  Spherical shape, high Ks,
• low affinity

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Growth kinetics of Methanosarcina and
Methanosaeta
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Essential Conditions for Anaerobic Treatment
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Staging Benefits(Plug Flow VS CSTR)

• If KS of aerobic biomass 20 mg/l and effluent
  concentration is also 20 mg/l ? aerobic biomass
  would be working at 50 of kmax
• If KS of anaerobic biomass 200 mg/l ?
  anaerobic biomass in a
• CSTR would be working at only 9
• To achieve low effluent BOD, high concentration
  of biomass is required or staging/plug flow
  configuration must be incorporated

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Example Staging to compensate for temperature
reduction

• Wastewater 0.057m3/s with COD of 2300mg/l is
  treated in AD having 20,000mgMLVSS/l at 25C
  calculate
• Volume of one-stage CSTR to produce 100mg/l
  effluent (using kinetic coefficients in Fig 3.8)
• Total volume of two stage reactor with COD of 500
  and 100mg/l in the first and second reactors

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Environmental factors

• Temperature
• Anaerobic processes like other biological
  processes strongly
• depend on temperature.
• In anaerobic system three optimal temperature
  ranges
• Psychrophilic (5 - 15oC)
• Mesophilic (30 38 ?C)
• Thermophilic (50 - 60 oC)

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Effect of Temperature on Anaerobic Activity
Rule of thumb Rate of a reaction doubles for
every 10 degree rise
in temperature up to optimal temp.
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pH
There exist two groups of bacteria in terms of pH
optima namely acidogens and methanogens. The
best pH range for acidogens is 5.5 6.5 and for
methanogens is 7.6 8.0. The optimal pH for
combined cultures is 6.8 - 7.2.
Low pH reduces the activity of methanogens
causing accumulation of VFA and H2. At higher
partial pressure of H2, propionic acid degrading
bacteria will be severely inhibited thereby
causing excessive accumulation of higher
molecular weight VFAs such as propionic and
butyric acids and the pH drops further. If the
situation is left uncorrected, the process may
eventually fail. This condition is known as a
SOUR or STUCK
The remedial measures Reduce the loading rates
and supplement chemicals to adjust the pH.
Chemicals such as NaHCO3, NaOH, Na2CO3, Quick
lime (CaO), Slaked lime Ca(OH)2, NH3 etc.
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Effect of pH on Anaerobic Activity
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Cont..
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Cont..
CODNP 35071 (for highly loaded system)
100071 (lightly loaded system)
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Effect of Sulfate on Methane Production
When the waste contains sulfate, part of COD is
diverted to sulfate reduction and thus total COD
available for methane production would be
reduced greatly.
Sulfide will also impose toxicity to methanogens
at Concentration of 50 to 250 mg/L as free
sulfide.
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Stoichiometry of Sulfate Reduction
8e- 8 H SO42- S2- 4H2O
2O2/ SO42- 64/96 0.67
Theoretically, 1 g of COD is needed to reduce 1.5
g of sulfate.
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Biogas Production Calculation Example
An anaerobic reactor has been employed to treat
food processing wastewater at 20oC. The flow
rate is 2 m3/day with mean COD of 7,000 mg/L.
Calculate the maximum CH4 generation rate in
m3/day. What would be the biogas generation
rate at 85 COD removal efficiency and 10 of
the removed COD is utilized for biomass
synthesis. The mean CH4 content of biogas is
75. If the wastewater contains 2.0 g/L
sulfate, theoretically how much CH4 could be
generated?
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Cont..
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Cont..
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Cont..
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•  
• COD available for CH4 generation after sulfate
  reduction
• 10.71 - 2.66 8.05 Kg/d
•  
• 1 Kg COD produces 0.35 m3 CH4 at STP
•  
• 8.05 Kg COD produces 0.35 x 8.05 2.82 m3
  CH4/d at STP
•  
• At 20?C, the CH4 gas generation 2.82 x
  (293/273)
• 3.02 m3/d

Cont..
Cont..
The CH4 generation rate when sulfate is present
3.02 m3/d
Presence of sulfate reduces methane yield from
4.02 to 3.02 m3/d (25 less)
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Anaerobic Process Design
Design based on volumetric organic loading rate
(VOLR) So . Q VOLR
--------- V VOLR
Volumetric organic loading rate (kg
COD/m3-day) So Wastewater biodegradable
COD (mg/L) Q Wastewater flow rate
(m3/day) V Bioreactor volume (m3)
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So and Q can be measured easily and are known
upfront VOLR can be selected!
Efficiency,
How do we select VOLR?
VOLR

• Conducting a pilot scale study,
• Find out removal efficiency at different VOLRs,
  and
• Select VOLR based on desired efficiency.

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Design based on hydraulic loading rate V ?H
. Q ?H . Q A ---------
H H Reactor height (m) ?H
Allowable hydraulic retention time (hr) Q
Wastewater flow rate (m3/hr) A
Surface area of the reactor (m2)
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Design Factors
Anaerobic reactor design parameters

1. Solids retention time (SRT) gt 10 days

2. Hydraulic retention time (HRT) for dilute
wastes

• Volatile solids loading rate kg VS/m3-day
• for high solid content wastes

• COD loading rate Kg COD /m3-day
• for high strength soluble wastes
• 5. Food to microorganisim ratio (F/M) lt 0.5 d-1

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Hydraulic retention time (HRT)
Hydraulic retention time (HRT) is defined
Volume V (m3) Flow
rate Q (m3/day)
HRT, days
For a given HRT, the size of reactor can be
easily determined since flow rate (Q) is known
Digester volume, V (m3) Flow rate (Q) x HRT
(?H )
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Volatile solids loading rate
The size of an anaerobic reactor can also be
determined based on volatile solids loading rate
expressed as kg VS/m3-d
For a given volatile solids loading rate, the
size of reactor can be easily determined since
influent VS (kg/day) is known
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Anaerobic Lagoon

• Suspended growth continuously/batch fed system
• Typical depth of lagoons range from 15 to 35 feet
• Lagoons can be covered to collect methane and
  reduce odors, but can also remain uncovered.
• Lagoons often used in slaughterhouse industry
  (FDL Foods, Dubuque, IA)
• 1-d detention time sufficent for 50-70 BOD
  reduction (mainly through settling of suspended
  solids)
• Typical detention times of 1 50 days
• Temperature dependent

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Ambient Temperature Covered Anaerobic Lagoon
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Ambient Temperature Covered Anaerobic Lagoon
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Plug Flow Anaerobic Digester AA Dairy, Candor, NY
TS content 11 13
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Traditional AD vs. High-Rate AD

• Adequate Mixing
• Temperature Control
• Effective Way to Retain Biomass

• Separate solids retention time (SRT) from
  hydraulic
• retention time (HRT). SRT gtgt HRT
• SRT mass of solids in system (g) / daily solids
  wasted rate (g/day)

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Anaerobic Contact Process (ACP)
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Cont..
ACP was initially developed for the treatment of
dilute wastewater such as meat packing plant
which had tendency to form a settleable flocs.
ACP is suitable for the treatment of wastewater
containing suspended solids which render the
microorganisms to attach and form settleable
flocs.
The biomass concentration in the reactor ranges
from 4-6 g/L with maximum concentration as high
as 25-30 g/L depending on settleability of
sludge. The loading rate ranges from 0.5 5 kg
COD/m3-day. The required SRT could be maintained
by controlling the recycle rate similar to
activated sludge process.
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Anaerobic Filter
biogas
effluent
media
recirculation
recirculation pump
flow distribution
influent
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Anaerobic Filter

• Anaerobic filter Young and McCarty in the
  late 1960s
• to treat dilute soluble organic wastes.
• The filter was filled with rocks similar to the
  trickling filter.
• Wastewater distributed across the bottom and the
  flow was in
• the upward direction through the bed of rocks
• Whole filter submerged completely

• Anaerobic microorganisms accumulate within voids
  of media
• (rocks or other plastic media)
• The media retain or hold the active biomass
  within the filter
• The non-attached biomass within the interstices
  forms a bigger
• flocs of granular shape due to rising gas
  bubble/liquid
• Non-attached biomass contributes significantly
  to waste treatment

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Cont..
Originally, rocks were employed as packing medium
in anaerobic filter. But due to very low void
volume (40-50), serious clogging problem was
witnessed. Now, many synthetic packing media
made up of plastics, ceramic tiles of different
configuration have been used in anaerobic
filters. The void volume in these media ranges
from 85-95 . Moreover, these media provide high
specific surface area typically 100 m2/m3 or
above which enhance biofilm growth.
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Cont..
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Multi-fed Upflow Anaerobic Filter (MUAF)
Waste is fed through several points along the
depth of filter. Such feeding strategy has
unique benefits
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Upflow Anaerobic Sludge Blanket Reactor
Effluent
biogas
Diameter 0.5 5 mm
Influent
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UASB
biogas
effluent weir
three phase separator
effluent
granule
baffles
gas bubble
floc particle
gas bubbles
flocculent sludge
granular sludge
recirculation pump
distribution baffle
influent
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original granule diameter
buoyancy force
Upflow in UASB reactor
Upflow in UASB reactor
gravitational force
gas bubbles
upflow velocity
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Upflow Anaerobic Sludge Blanket (UASB)
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Cont..
Loading rate 15-30 kg COD/m3-day
Important components of UASB

1. Influent flow distributor
2. Sludge blanket
3. Solid-liquid-gas separator
4. Effluent collector

Type of waste treatable by UASB
Alcohol, bakers yeast, bakery, brewery, candy,
canneries, chocolate, citric acid, coffee, dairy
cheese, distillery, Domestic sewage,
fermentation, fruit juice, fructose, landfill
leachate, paper pulp, pharmaceutical, potato
processing, rubber,sewage sludge liquor,
slaughter house, soft drinks, starch (barley,
corn, wheat), sugar processing, vegetable
fruit, yeast, etc.
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Important considerations in UASB operation

• Initial seeding of some well digested anaerobic
  sludge could
• be used. The seed occupies 30-50 of total
  reactor volume.
• Minimum seeding is 10 of the reactor volume.

• Provide optimum pH, and enough alkalinity.

• Supplement nutrients and trace metals if
  needed. Provide
• N P at a rate of COD NP of 40071
  (conservative estimate).

• Addition of Ca2 at 200 mg/L promotes
  granulation. Ca2 conc.
• higher than 600 mg/L may form CaCO3 crystals
  which may
• allow methanogens to adhere to and then become
  washed out
• of the system.

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Expanded Granular Sludge Bed (EGSB) Reactor
USAB EGSB (Triple Baffle Internal Settler)
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Anaerobic Sequential Batch Reactor (ASBR)
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Anaerobic Sequencing Batch Reactor (ASBR)

• Developed at Iowa State University by Dague and
  Sung
• Batch fed suspended growth system.
• ASBR relies on internal clarification for solids
  retention by allowing biomass to settle.
• Four distinct phases Feed React Settle -
  Decant
• Four phases compose one cycle.
• Cycle lengths vary from 3 to 24 hours.
• Good system for wastes with high solids.
• Studies show that intermittent mixing is as
  effective as continuous mixing
• Low F/M at end of react cycle allows low gas
  production during settle phase.
• By lowering settle time selection of better
  settling granules can occur.
• Granulation is key to system (see UASB).

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Temperature-Phased Anaerobic Digestion
(TPAD) LABORATORY SETUP
Gasmeter
Gasmeter
H2S scrubber
H2S scrubber
Thermophilic at 55oC
Mesophilic at 35oC
Feed Tank
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Temperature-Phased Anaerobic Digester (TPAD)
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Expanded Bed Reactor (EBR)

• Expanded bed reactor is an attached growth
  system with
• some suspended biomass.

• The biomass gets attached on bio-carriers such
  as sand,
• GAC, pulverized polyvinyl chloride, shredded
  tyre beads
• etc.

• The bio-carriers are expanded by the upflow
  velocity of
• influent wastewater and recirculated effluent.

• In expanded bed reactor, sufficient upflow
  velocity is
• maintained to expand the bed by 15-30.

• The expanded bed reactor has less clogging
  problem and
• better substrate diffusion within the biofilm.

• Biocarriers are partly supported by fluid flow
  and partly
• by contact with adjacent biocarriers and they
  tend to
• remain same relative position within the bed.

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Fluidized Bed Reactor (FBR)

• FBR is similar to EBR in terms of configuration.
  But FBR is
• truly fixed film reactor as suspended biomass
  is washedout
• due to high upflow velocity.

• The bed expansion is 25-300 of the settled bed
  volume
• which requires much higher upflow velocity
  (10-25 m/hr).

• The bio-carriers are supported entirely by the
  upflow
• liquid velocity and therefore able to move
  freely in the bed.

• The fluidized bed reactor is free from clogging
  problem
• short-circuiting and better substrate
  diffusion within the
• biofilm.

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Anaerobic Membrane Bioreactor (AMBR)

• Low energy consumption
• (no aeration needed)
• Low sludge production
• (1/5th of aerobic)
• Able to maintain long SRT - minimize biomass
  wash-out
• Superior effluent quality for water reuse
• Useful energy byproduct methane
• Operation at ambient temperature
• Minimum knowledge of AMBR for low strength
  wastewater

Membrane
Anaerobic bioreactor
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Best candidates of Industrial Wastewaters for
Anaerobic Treatment

• Alcohol production

• Brewery and Winery

• Sugar processing

• Starch (barley, corn, potato, wheat, tapioca and
  desizing
• waste from textile industry.

• Food processing
• Bakery plant

• Pulp and paper
• Dairy

• Slaughterhouse

• Petrochemical waste