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Anaerobic Process in Industrial Wastewater Treatment
Master of Technology
Under the guidance of
Dr. Athar Hussain
School of engineering
Gautam Buddha University
14EEN 001 ABHISHEK SINGH KHEVARIYA
14EEN 002 AVANEESH KUMAR
14EEN 004 NITIN YADAV
14EEN 005 SANJAY KUMAR
This is certify that the report entitled “Anaerobic Process in Industrial Wastewater
Treatment” is submitted by Abhishek Singh Khevariya, Avaneesh Kumar, Nitin
Yadav and Sanjay Kumar for the project in Master of Technology (Environmental
Engineering) submitted to Gautam Buddha University, Greater Noida.
This matter embodied in this report is original & has not been submitted earlier.
Date: 13 / 12/ 2014
Mr Athar Hussain
Inorganic Industrial Wastewater Treatment 01
Organic Industrial Wastewater Treatment 02
Sources of Industrial Wastewater Treatment 03
Anaerobic Treatment 07
Aerobic Treatment 07
Difference between Aerobic & Anaerobic Process 08
Anaerobic Fermentation 09
Aerobic Respiration 10
Fermentative Bacteria 11
Factors Affecting Anaerobic Process
pH Control 15
Retention Time 16
Feeding Strategy 16
Agitation Strategy 16
Types of Anaerobic Reactors
Anaerobic Filter Bed Reactors 17
Anaerobic Contact Process Reactors 18
Anaerobic Fluidized Bed Reactors 18
Design of Anaerobic Reactors
Design Parameters 20
Design Procedure 22
Advantages of Anaerobic Process 24
Limitations of Anaerobic Process 25
Applications in the Industries 26
The motivations for treatment of wastewater are manifold. Treatment
and reuse of wastewater conserves the supply of freshwater and this
presents clear advantages with respect to environmental protection. The
main objective of this project report was to study Anaerobic Process in
Wastewater Treatment Process.
Anaerobic Process is a biological process that can degrade waste
organic material by the concerted action of a wide range of
microorganisms in the absence of oxygen. The process consists of a
complex series of reactions that convert a wide array of polymeric
substances such as carbohydrates, proteins, and lipids, having carbon
atoms at various oxidation and/or reduction states, to one-carbon
molecules in its most oxidized state (CO
) and its most reduced state
During the last century a huge amount of industrial wastewater was discharged into
rivers, lakes and coastal areas. This resulted in serious pollution problems in the water
environment and caused negative effects to the eco-system and human’s life.
Until the mid-18th century, water pollution was essentially limited to small, localized
areas. Then came the Industrial Revolution, the development of the internal combustion
engine, and the petroleum-fuelled explosion of the chemical industry. With the rapid
development of various industries, a huge amount of fresh water is used as a raw
material, as a means of production (process water), and for cooling purposes. Many
kinds of raw material, intermediate products and wastes are brought into the water
when water passes through the industrial process. So in fact the wastewater is an
"essential by-product” of modern industry, and it plays a major role as a pollution
sources in the pollution of water environment.
There are many types of industrial wastewater based on different industries and
contaminants; each sector produces its own particular combination of pollutants.
Generally, industrial wastewater can be divided into two types: inorganic industrial
wastewater and organic industrial wastewater.
Inorganic industrial wastewater
Inorganic industrial wastewater is produced mainly in the coal and steel industry, in the
nonmetallic minerals industry, and in commercial enterprises and industries for the
surface processing of metals (iron picking works and electroplating plants).
These wastewaters contain a large proportion of suspended matter, which can be
eliminated by sedimentation, often together with chemical flocculation through the
addition of iron or aluminum salts, flocculation agents and some kinds of organic
polymers. The purification of warm and dust-laden waste gases from blast furnaces,
converters, cupola furnaces, refuse and sludge incineration plants, and aluminum works
results in wastewater containing mineral and inorganic substances in dissolved and un-
1 Anaerobic Process in Industrial Wastewater Treatment
dissolved form. Other wastewater from rolling mills contain mineral oil and require
additional installations, such as scum boards and skim-off apparatus, for the retention
and removal of mineral oils. Residues of emulsified oil remaining in the water also need
chemical flocculation. In many cases, wastewater is produced in addition to solid
substances and oils, and also contains extremely harmful solutes. These include blast-furnace
gas-washing wastewater containing cyanide, wastes from the metal processing
industry containing acids or alkaline solutions (mostly containing non-ferrous metals and
often cyanide or chromate), wastewater from eloxal works and from the waste gas
purification of aluminum works, which in both cases contain fluoride.
Organic industrial wastewater
Organic industrial wastewater contains organic industrial waste flow from those
chemical industries and large-scale chemical works, which mainly use organic
substances for chemical reactions. The effluents contain organic substances having
various origins and properties. These can only be removed by special pretreatment of
the wastewater, followed by biological treatment. Most organic industrial wastewaters
are produced by the following industries and plants: pharmaceuticals, cosmetics,
organic dye-stuffs, glue and adhesives, soaps, synthetic detergents, pesticides and
herbicides, Tanneries and leather factories.
Industrial wastewater treatment covers the mechanisms and processes used
to treat waters that have been contaminated in some way
by anthropogenic industrial or commercial activities prior to its release into the
environment or its re-use.
2 Anaerobic Process in Industrial Wastewater Treatment
SOURCES OF INDUSTRIAL WASTEWATER
Various sources of Industrial wastewater are listed in the table below –
Iron & Steel BOD, COD, Oil, Metal, Cyanide, Phenols &
Textile & Leather BOD, Solids, Sulfates & Chromium
Pulp & Paper BOD, COD, Solids, Chlorinated Organic
Petrochemical & Refineries BOD, COD, Phenols & Chromium
Chemicals COD, Heavy Metals, Cyanide, SS
Non- Ferrous Metal Fluoride & SS
Microelectronics COD & Organic Chemicals
Mining Metal, SS, Acids & Salts
1. Iron and steel Industry: The production of iron from its ores involves
powerful reduction reactions in blast furnaces. Cooling waters are inevitably
contaminated with products especially ammonia and cyanide. Production
of coke from coal in coking plants also requires water cooling and the use of
water in by-products separation. Contamination of waste streams includes
3 Anaerobic Process in Industrial Wastewater Treatment
gasification products such as benzene, naphthalene, cyanide,
ammonia, phenols, cresols together with a range of more complex organic
compounds known collectively as polycyclic aromatic hydrocarbons (PAH).
Wastewaters include acidic rinse waters together
with waste acid. Although many plants operate acid recovery plants (particularly
those using hydrochloric acid), where the mineral acid is boiled away from the
iron salts, there remains a large volume of highly acid ferrous sulfate or ferrous
chloride to be disposed of. Many steel industry wastewaters are contaminated by
hydraulic oil, also known as soluble oil.
2. Mines and quarries: The principal waste-waters associated
with mines and quarries are slurries of rock particles in water. These arise from
rainfall washing exposed surfaces and haul roads and also from rock washing
and grading processes. Volumes of water can be very high, especially rainfall
related arising on large sites. Some specialized separation operations, such
as coal washing to separate coal from native rock using density gradients, can
produce wastewater contaminated by fine particulate hematite and surfactants.
3. Pulp and paper Industry: Effluent from the pulp and paper
industry is generally high in suspended solids and BOD. Standalone paper mills
using imported pulp may only require simple primary treatment, such
as sedimentation or dissolved air flotation. Increased BOD or chemical oxygen
demand (COD) loadings, as well as organic pollutants, may require biological
treatment such as activated sludge or up flow anaerobic sludge blanket reactors.
For mills with high inorganic loadings like salt, tertiary treatments may be
required, either general membrane treatments like ultrafiltration or reverse
osmosis or treatments to remove specific contaminants, such as nutrients.
4 Anaerobic Process in Industrial Wastewater Treatment
4. Textile Industry: Dye bath wastewater generated by textile mills is
often rated as the most polluting among all industrial sectors. The pollution load
is characterized by high color content, suspended solids, salts, nutrients and
toxic substances such as heavy metals and chlorinated organic compounds.
Many textile mills in the state currently discharge their wastewater to local
wastewater treatment plants with minimum treatment such as pH neutralization.
This process removes much of the residual dye color. Larger mills can discharge
more than 2 million gallons of wastewater of this kind per day.
5. Petrochemical Refineries: Refineries can generate a significant
amount of wastewater that has been in contact with hydrocarbons. Wastewater
can also include water rejected from boiler feed water pretreatment processes (or
generated during regenerations). Wastewater can also refer to cooling tower
blow downstream, or even once-through cooling water that leaves the refinery.
Once-through cooling water typically does not receive any treatment before
discharge. Cooling tower blow down water and wastewater from raw water
treating may or may not receive treatment at the wastewater treatment plant
(WWTP) before discharge. Contaminated wastewater is typically sent to either a
wastewater treatment plant that is located at the facility, or it can be pretreated
and sent to the local publicly owned treatment works or third-party treatment
facility for further treatment. Water that has not been in direct contact with
hydrocarbons or which has only minimal.
5 Anaerobic Process in Industrial Wastewater Treatment
6 Anaerobic Process in Industrial Wastewater Treatment
INDUSTRIAL WASTEWATER TREATMENT PROCESS
AEROBIC TREATMENT: Organic material decomposing with oxygen is an
"aerobic" process. When organisms that use oxygen feed upon organic matter, they
develop cell protoplasm from the nitrogen, phosphorus, some of the carbon, and other
required nutrients. Carbon serves as a source of energy for organisms and is burned up
and respired as carbon dioxide (CO2). Since carbon serves both as a source of energy
and as an element in the cell protoplasm, much more carbon than nitrogen is needed.
Generally, organisms respire about two-thirds of the carbon they consume as CO2,
while the other third is combined with nitrogen in the living cells.
In nature, the aerobic process is most common in areas
such as the forest floor, where droppings from trees and animals are converted into
relatively stable organic matter. This decomposition doesn’t smell when adequate
oxygen is present. We can try to imitate these natural systems when we plan and
maintain our landscapes. As we learn more about the biology and chemistry of
composting, we can actually hasten the decomposition process.
ANAEROBIC TREATMENT: Anaerobic process is a collection of
processes by which microorganisms break down biodegradable material in the absence
of oxygen. The process is used for industrial or domestic purposes to manage waste
and/or to produce fuels. Much of the fermentation used industrially to produce food and
drink products, as well as home fermentation, uses anaerobic digestion.
Anaerobic digestion occurs naturally in some soils and in lake and oceanic basin
sediments, where it is usually referred to as "anaerobic activity". The digestion process
begins with bacterial hydrolysis of the input materials. Insoluble organic polymers, such
as carbohydrates, are broken down to soluble derivatives that become available for
other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbon
dioxide, hydrogen, ammonia, and organic acids. These bacteria convert these resulting
7 Anaerobic Process in Industrial Wastewater Treatment
organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon
dioxide. Finally, methanogens convert these products to methane and carbon dioxide.
The methanogenic archaea populations play an indispensable role in anaerobic
Difference between Anaerobic & Aerobic Process:
Organic loading rate
-day Low loading rates:0.5-1.5 kg COD/m
High loading rates:10-40 kg COD/m
Low biomass yield:0.05-0.15 kg VSS/kg COD High biomass yield:0.35-0.45 kg VSS/kg COD
(Biomass yield is not constant but depends
on types of substrates metabolized)
(Biomass yield is fairly constant irrespective
of types of substrates metabolized)
Specific substrate utilization rate
High rate: 0.75-1.5 kg COD/kg VSS-day Low rate: 0.15-0.75 kg COD/kg VSS-day
Long start-up: 1-2 months for mesophilic Short start-up: 1-2 weeks
8 Anaerobic Process in Industrial Wastewater Treatment
Longer SRT is essential to retain the slow
growing methanogens within the reactor
SRT of 4-10 days is enough for the activated
Anaerobic treatment is a biological process carried out in the absence of O2 for the
stabilization of organic materials by conversion to CH4 and inorganic end-products such
as CO2 and NH3.
Anaerobic fermentation Anaerobic respiration
In anaerobic fermentation, there is no external electron acceptor. The product
generated during the process accepts the electrons released during the breakdown of
organic matter. Thus, organic matter acts as both electron donor and acceptor. The
process releases less energy and the major portion of the energy is still contained in the
fermentative product such as ethanol.
Through this method, a cell is able to regenerate nicotinamide adenine dinucleotide
(NAD+) from the reduced form of nicotinamide adenine dinucleotide (NADH), a
molecule necessary to continue glycolysis. Anaerobic fermentation relies on enzymes to
add a phosphate group to an individual adenosine diphosphate (ADP) molecule to
produce ATP, which means it is a form of substrate-level phosphorylation. This
contrasts with oxidative phosphorylation, which uses energy from an established proton
gradient to produce ATP. There are two major types of anaerobic fermentation: ethanol
9 Anaerobic Process in Industrial Wastewater Treatment
fermentation and lactic acid fermentation. Both restore NAD+ to allow a cell to continue
generating ATP through glycolysis.
Anaerobic respiration on the other hand requires external electron acceptor. The
electron acceptors in this case could be SO4
- or CO2. These terminal acceptors
have smaller reduction potentials than O2, meaning that less energy is released per
oxidized molecule. The energy released under such a condition is higher than anaerobic
fermentation. In order for the electron transport chain to function, an exogenous final
electron acceptor must be present to allow electrons to pass through the system. In
aerobic organisms, this final electron acceptor is oxygen. Molecular oxygen is a highly
oxidizing agent and, therefore, is an excellent acceptor. Anaerobic respiration is,
therefore, in general energetically less efficient than aerobic respiration.
Anaerobic respiration is used mainly by prokaryotes that live in environments devoid of
oxygen. Many anaerobic organisms are obligate anaerobes, meaning that they can
respire only using anaerobic compounds and will die in the presence of oxygen.
10 Anaerobic Process in Industrial Wastewater Treatment
The anaerobic degradation of complex matter is carried out by a series of bacteria.
There exists a coordinated interaction among these microbes. The process may fail if
certain of these organisms are inhibited.
TYPES OF BACTERIA ON THE BASIS OF PROCESS
Fermentative bacteria: This group of bacteria is responsible for the
first stage of anaerobic digestion - hydrolysis and acidogenesis. Fermentation bacteria
are anaerobic, but use organic molecules as their final electron acceptor to produce
fermentation end-products. Streptococcus, Lactobacillus, and Bacillus, for example,
produce lactic acid, while Escherichia and Salmonella produce ethanol, lactic acid,
succinic acid, acetic acid, CO2, and H2.
Fermenting bacteria have characteristic sugar fermentation patterns, i.e., they can
metabolize some sugars but not others. For example, Neisseria meningitidis ferments
glucose and maltose, but not sucrose and lactose, while Neisseria gonorrhoea ferments
glucose, but not maltose, sucrose or lactose. Such fermentation patterns can be used to
identify and classify bacteria. The anaerobic species belonging to the family of
Streptococcaceae and Enterobacteriaceae and to the genera of Bacteroides,
Clostridium, Butyrivibrio, Eubacterium, Bifidobacterium and Lactobacillus are most
Hydrogen producing acetogenic bacteria: Acetogenic bacteria
are a specialized group of strictly anaerobic bacteria that are ubiquitous in nature.
Together with the methane‐forming archaea they constitute the last limbs in the
anaerobic food web that leads to the production of methane from polymers in the
11 Anaerobic Process in Industrial Wastewater Treatment
absence of oxygen. Acetogens are characterized by a unique pathway, the Wood–
Ljungdahl pathway of carbon dioxide reduction with the acetyl‐CoA synthase as the key
enzyme. This pathway also allows chemolitho-autotrophic growth on hydrogen and
carbon dioxide and it is the only pathway known that combines carbon dioxide fixation
with adenosine triphosphate (ATP) synthesis. Thus, it is considered the first biochemical
pathway on earth. ATP is synthesized by a chemi-osmotic mechanism with Na+ or H+ as
coupling ion, depending on the organism. In cytochrome‐free acetogens, energy is
conserved by reduction followed by dependent Na+ (or H+) translocation across the
membrane (Rnf complex). Acetogens may represent ancestors of the first bio
energetically active cells in evolution.
CH3CH2COO - CH3COO - + CO2 + H2
Homoacetogenes: The homoacetogens are much more adaptable
than methanogens because in addition to being autotrophic they can also live
as chemoheterotrophs. Clostridium aceticum and Acetobacterium woodii are the two
homoacetogenic bacteria isolated from the sludge.
In the heterotrophic growth mode they can ferment glucose and derive some ATP by
substrate level phosphorylation. In so doing they generate carbon dioxide and hydrogen
which can then be used to power the chemiosmotic mechanism which allows them to
derive some ATP also by anaerobic respiration.
The overall stoichiometry of this growth mode of homoacetogens is shown below.
12 Anaerobic Process in Industrial Wastewater Treatment
Methanogens: Methanogens are autotrophic archebacteria that use anaerobic
respiration for ATP synthesis. Methanogens use CO2 taken up from their growth
environment as the carbon substrate for growth. They use some CO2 as the ultimate
oxidizing agent of an electron transport chain which, by a chemiosmotic mechanism,
maintains a transmembrane electrochemical ion gradient which powers ATP
production. Methanogens use this hydrogen and this process maintains a lowered
hydrogen partial pressure in the reticulo-rumen. Some of the hydrogen producing
heterotrophic microorganisms show altered patterns of metabolism because of
methanogen usage of the hydrogen they produce.
Methanogens affect the growth of some but not all hydrogen producing species of
microorganism in the reticulo-rumen. The equation shows the reduction of CO2 by H2 to
produce methane. This redox reaction sustains anaerobic respiration which allows the
production of ATP.
The methane produced by reduction of the carbon dioxide is lost from the reticulo-rumen
by eructation. It is a waste of feed carbon because the rumen does not have
methanotrophic bacteria and the host ruminant cannot utilize this gas.
13 Anaerobic Process in Industrial Wastewater Treatment
FACTORS AFFECTING ANAEROBIC PROCESS
The successful operation of anaerobic reactor depends on maintaining the
environmental factors close to the comfort of the microorganisms involved in the
process. They are as follows-
1. Temperature: Anaerobic processes like other biological processes operate
in certain temperature ranges. Mesophilic (25-450C) and thermophilic (45-650C)
anaerobic digestion are commonly applied in the field. Most full-scale anaerobic
digesters are operated at mesophilic temperature. Since wastewater and bio
solids is discharged at relatively low temperature (e.g., 18 0C), recent research
toward anaerobic treatment under psychrophilical condition becomes attractive.
For instance, microbial communities involved in digestion are sensitive to
temperature changes. The rate of anaerobic degradation of organic substrates
generally increases in the order of psychrophilic, mesophilic and thermophilic
14 Anaerobic Process in Industrial Wastewater Treatment
2. pH Control: pH is an important factor for keeping functional anaerobic
digestion. A typical pH is in the range of 6.5-7.6. The accumulation of
intermediate acids leads to pH drop during fermentation. In order to maintain
stable operation, it is necessary to add bicarbonate or carbonate as an alkalinity
buffer to neutralize volatile fatty acids and carbon dioxide.
3. Nutrients: Macronutrients are the elements that the cellular material of the
anaerobic microorganisms comprises, including hydrogen, nitrogen, oxygen,
carbon, sulfur, phosphorus, potassium, calcium, magnesium and iron. Normally,
anaerobic microorganisms require these elements presented with a
concentration around 10
M. In addition to the micronutrients, a number of other
elements, such as Ni and Co must be present in small amount, i.e. below10
15 Anaerobic Process in Industrial Wastewater Treatment
This is because that these elements are important for the growth of anaerobic
organisms. For example, Ni is necessary for activating factor F
, which is a co
factor involved in methanogenesis. But it can be inhibitory for fermentative as
well as methanogens if it is present in high concentration.
4. Toxicity: Besides ammonia and nitrate/nitrite, heavy metals, such as Zn, Cu
and Cd can be toxic to acidogenic bacteria. However, many of these elements
and compounds can be tolerated in relatively high concentration due to
absorption in inert material contained in the reactor.
5. Retention Time: For the CSTR reactors, which are the most prevailingly
used types of reactors, hydraulic and solid retention time is the same. Retention
time is an important operational parameter that is easy to operate and control.
Tremendous efforts have been put into the research of the effect of retention time
on anaerobic digestion. Biologically, only those who are doubling time are shorter
than the retention time can be kept in the reactor, so retention time is one of the
best parameter to be manipulated for separating and enriching different groups of
the microbes involved in the anaerobic process. Also, retention time determines
the time that substrates can be attacked by the enzymes in the reactor.
6. Feeding Strategy: Practically, anaerobic reactors treating sewage sludge
in wastewater treatment plants are fed semi-continuously instead of continuously.
Feeding frequency determines the ratio of food to microbe (F/M) when the
retention time and the working volume have been fixed. Normally, the ratio can
be satisfied so that there is no negative effect on the stability and on the
performance of the anaerobic reactors.
7. Agitation Strategy: It is normally believed that agitation is necessary to
help the diffusion of substrate and increase their contacts with the microbes,
especially when raw sludge is intermittently fed into the reactor. Agitation
strategy can affect anaerobic digestion of sewage sludge and optimum agitation
strategy should be found. In addition, it was also found that mixing levels might
be used as an operational tool to stabilize unstable anaerobic reactor.
16 Anaerobic Process in Industrial Wastewater Treatment
TYPES OF ANAEROBIC REACTORS
There are five principal process variants which are proper in anaerobic wastewater
treatment. These are as follows:
Anaerobic Filter Reactor: The anaerobic filter is similar to a trickling filter in
that a biofilm is generated on media. The bed is fully submerged and can be operated
either upflow or down flow. As wastewater flows through the filter, particles are trapped
and organic matter is degraded by the active biomass that is attached to the surface of
the filter material.
With this technology, suspended solids and BOD removal can be as high as 90%, but is
typically between 50% and 80%. Nitrogen removal is limited and normally does not
exceed 15% in terms of total nitrogen (TN).
Anaerobic filters are usually operated in upflow mode because there is less risk that the
fixed biomass will be washed out. The water level should cover the filter media by at
least 0.3 m to guarantee an even flow regime. The hydraulic retention time (HRT) is the
most important design parameter influencing filter performance. An HRT of 12 to 36
hours is recommended. The ideal filter should have a large surface area for bacteria to
grow, with pores large enough to prevent clogging. The surface area ensures increased
contact between the organic matter and the attached biomass that effectively degrades
it. Ideally, the material should provide between 90 to 300 m2 of surface area per m3 of
occupied reactor volume. Typical filter material sizes range from 12 to 55 mm in
diameter. Materials commonly used include gravel, crushed rocks or bricks, cinder,
pumice, or specially formed plastic pieces, depending on local availability.
17 Anaerobic Process in Industrial Wastewater Treatment
Anaerobic Contact Process Reactor: This process can be considered as
an anaerobic activated sludge because sludge is recycled from a clarifier or separator to
the reactor. Since the material leaving the reactor is a gas-liquid-solid mixture, a
vacuum Degasifier is required to separate the gas and avoid floating sludge in the
clarifier. Here a set of reactors are created in series, often with recycling. This recycled
material is pumped up into the bottom of the first reactor, an upflow reactor. The upflow
anaerobic process is a large reactor which allows the waste to flow up from the bottom
and separates the waste into 3 zones. At the very top is the biogas zone where the gas
is collected. Bacteria digest waste in the lowest portion of the upflow reactor;
the bioreactor zone. In between these two stages is the clarifier zone where the which
exports the stabilized waste.
Fluidized Bed Reactor: This reactor consists of a sand bed on which the
biomass is grown. Since the sand particles are small, a very large biomass can be
developed in a small volume of reactor. In order to fluidize the bed, a high recycle is
required. In this type of reactor, a fluid (gas or liquid) is passed through a granular solid
material (usually a catalyst possibly shaped as tiny spheres) at high enough velocities to
suspend the solid and cause it to behave as though it were a fluid. This process, known
as fluidization, imparts many important advantages to the FBR. As a result, the fluidized
bed reactor is now used in many industrial applications.
Upflow Anaerobic Sludge Blanket Reactor: Under proper conditions
anaerobic sludge will develop as high density granules. These will form a sludge blanket
in the reactor. The wastewater is passed upward through the blanket. Because of its
density, a high concentration of biomass can be developed in the blanket. The UASB
reactor is a methanogenic (methane-producing) digester that evolved from the clarifier.
A similar but variant technology to UASB is the expanded granular sludge bed (EGSB)
18 Anaerobic Process in Industrial Wastewater Treatment
UASB uses an anaerobic process whilst forming a blanket of granular sludge which
suspends in the tank. Wastewater flows upwards through the blanket and is processed
(degraded) by the anaerobic microorganisms. The upward flow combined with the
settling action of gravity suspends the blanket with the aid of flocculants. The blanket
begins to reach maturity at around 3 months. Small sludge granules begin to form
whose surface area is covered in aggregations of bacteria. In the absence of any
support matrix, the flow conditions create a selective environment in which only those
microorganisms, capable of attaching to each other, survive and proliferate. Eventually
the aggregates form into dense compact biofilms referred to as "granules".
Schematic diagrams of anaerobic wastewater treatment processes: (a) anaerobic filter reactor; (b)
anaerobic contact reactor; (c) fluidized-bed reactor; (d) upflow anaerobic sludge blanket (UASB).
19 Anaerobic Process in Industrial Wastewater Treatment
DESIGN OF ANAEROBIC REACTORS
Conditions for efficient anaerobic treatment –
• Avoid excessive air/O
• No toxic/inhibitory compounds present in the influent
• Maintain pH between 6.8 –7.2
• Sufficient alkalinity present (mainly bicarbonates)
• Low volatile fatty acids (VFAs)
• Temperature around mesophilic range (30-38
• Enough nutrients (N & P) and trace metals especially, Fe, Co, Ni, etc.
COD - N: P = 350:7:1 (for highly loaded system) 1000:7:1 (lightly loaded system)
• SRT/HRT >>1 (use high rate anaerobic reactors)
Width to diameter ratio of reactor =2-6(usually)
Height of reactor =2-12 m(usually)
Hydraulic retention time =20-30 d(for domestic wastewater)
Volumetric loading =0.2-0.8 kg COD/m3 –d
Specific area for the media =100 m2/m3 of volume
20 Anaerobic Process in Industrial Wastewater Treatment
Fluidized Bed Reactor:
Up –flow velocity =2.0 m/h
Specific area of media =10000 m2/m3 of media volume
Void space =50%
Organic loading =4-5 kg COD/m3-d
Anaerobic Contact Process:
Up-flow velocity =15-20 m/h
Rector depth =3-6 m
Volumetric loading =10-30 kg COD/m3.d
Reactor biomass =15000-20000 mg MLVSS/L
HRT =3-6 h
Up-flow velocity =0.5-0.9 m/h
Volumetric loading =6-20 kg COD/m3.d
HRT =6-48 hr
MLSS concentration (i) at the bottom of reactor =100000-150000 mg/l
(ii) at the top of reactor =5000-4000 mg/l
Reactor depth = 3-5 m (for domestic water)
Biomass production =0.2-0.5 m3/kg of COD removed
21 Anaerobic Process in Industrial Wastewater Treatment
a) Design based on volumetric organic loading rate (VOLR)
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)
b) Design based on hydraulic loading rate
H : Reactor height (m)
a : Allowable hydraulic retention time (hr)
Q : Wastewater flow rate (m3/h)
A : Surface area of the reactor (m2)
22 Anaerobic Process in Industrial Wastewater Treatment
23 Anaerobic Process in Industrial Wastewater Treatment
ADVANTAGES OF ANAEROBIC PROCESS
• Less energy requirement as no aeration is needed.
• Energy generation in the form of methane gas.
• Less biomass (sludge) generation.
• Less nutrients (N & P) required.
• Application of higher organic loading rate.
• Space saving.
• Ability to transform several hazardous solvents.
24 Anaerobic Process in Industrial Wastewater Treatment
LIMITATIONS OF ANAEROBIC PROCESS
• Long start-up time.
• Long recovery time.
• Specific nutrients/trace metal requirements.
• More susceptible to changes in environmental conditions.
• Effluent quality of treated wastewater.
• Treatment of high protein & nitrogen containing
25 Anaerobic Process in Industrial Wastewater Treatment
APPLICATIONS OF ANAEROBIC PROCESS
• Alcohol production
• Brewery and Winery
• Sugar processing
• Starch (barley, corn, potato, wheat, tapioca)
• Waste from textile industry.
• Food processing
• Bakery plant
• Pulp and paper
• Petrochemical waste
26 Anaerobic Process in Industrial Wastewater Treatment
Metcalf and Eddy, 1981. Wastewater Engineering:
Collection and pumping of Wastewater. McGraw Hill
Inc., New York.
Research Paper- Anaerobic Treatment of Industrial
Effluents, by Mustafa Evren Ersahin, Istanbul
Technical University, Turkey.
Research Paper- ANAEROBIC DIGESTION
TECHNOLOGY FOR INDUSTRIAL WASTEWATER
TREATMENT by Medhat M. A. Saleh and Usama F.
Mahmood, El Azhar Univ., Egypt.
27 Anaerobic Process in Industrial Wastewater Treatment