Anaerobic Treatment

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Anaerobic Treatment

• PreetiBala Adatiya
• Lecturer
• School of Biotechnology
• DAVV

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Anaerobic Treatment
Anaerobik Aritma Biyoteknolojisi
The use of microbes in the absence of oxygen for
the stabilization of organic material by
conversion to methane, carbon dioxide, new
biomass and inorganic products.
Anaerobic treatment is most suitable for
wastewaters with COD concentrations in the high
strength range (gt2000 mg/l)
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Anaerobic Digestion Process
Anaerobik Aritma Biyoteknolojisi
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Anaerobic Digestion Process

• Three Mechanisms Occurring
• Hydrolysis Process conversion of insoluble high
  molecular compounds (lignin, carbohydrates, fats)
  to lower molecular compounds
• Acidogenesis Process conversion of soluble
  lower molecular components of fatty acids, amino
  acids and sugars (monosaccharides) to lower
  molecular intermediate products (volatile acids,
  alcohol, ammonia, H2 and CO2)
• Methanogenesis Process conversion of volatile
  acids intermediate products to final product of
  methane and CO2

Anaerobik Aritma Biyoteknolojisi
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ANAEROBIC SLUDGE DIGESTION
Anaerobik Aritma Biyoteknolojisi

• Anaerobic digestion is one of the oldest process
  used for the stabilization of sludges. It
  involves the decomposition of organic and
  inorganic matter in the absence of molecular
  oxygen.

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Process description

• In the anaerobic digestion process, the organic
  material in mixture of primary settled and
  biological sludges is converted biologically.
  Under anaerobic conditions, to a variety of and
  products including methane (CH4) and
  carbondioxide. The process is carried out in an
  airtight reactor. Sludge, introduced continuously
  or intermittently, is retained in the reactor for
  varying periods of time. The stabilized sludge,
  withdrawn from the reactor, is reduced in organic
  and pathogen content.

Anaerobik Aritma Biyoteknolojisi
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Anaerobik Aritma Biyoteknolojisi

• The two types of commanly used anaerobic
  digesters are identified as
• Standard-rate
• High-rate

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Standard-Rate Digester

• In the standard-rate digestion process the
  contents of digesters are usually unheated and
  unmixed. Detention times for the standard-rate
  process vary from 30 to 60 days.
• They are usually carried out as a single-stage
  process. The functions of digestion, sludge
  thickening, and supernatant formation are
  carried out simultaneously. As a result of
  digestion, the sludge stratifies by forming a
  supernatant layer above the digesting sludge and
  becomes more mineralized. As a result of the
  stratification and the lack of mixing, not more
  than 50 of the volume of a standard-rate
  single-stage digester is used. Because of these
  limitations, the standard-rate process is used to
  small installations.

Anaerobik Aritma Biyoteknolojisi
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High-Rate Digester

• In the high-rate digestion process the contents
  of digesters are heated and mixed completely. The
  required detention time for high-rate digestion
  is typically 15 days or less with the exception
  of higher loading rates and improved mixing,
  there are only a few difference between the
  primary digester in a conventional two-stage
  process and a single-stage high-rate digester.

Anaerobik Aritma Biyoteknolojisi
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• Two-stage digestion frequently, a high-rate
  digester is coupled in series with a second
  digestion tank. The first tank is used for
  digestion and is heated and equipped wirh mixing
  facilities. The primary function of the second
  stage is to separate the digested solids from the
  sopernatant, however additional digestion and gas
  production may occur.

Anaerobik Aritma Biyoteknolojisi
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Process design

• An anaerobic digester is well mixed with no
  liquid solids separation. Consequently, the
  bioreactor can be treated as a continuous stirred
  tank reactor (CSTR) in wich the HRT (hydraulic
  retention time) and SRT (sludge retention time or
  sludge age) are identical, the quantity of
  methane gas can be calculate as below
• VCH4 (L/day) 0,35 (L/gas)(EQS0-1,42Px)

Anaerobik Aritma Biyoteknolojisi
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AEROBIC SLUDGE DIGESTION

• Aerobic sludge digestion may be used to treat
  only
• waste activated sludge
• Mixtures of waste activated siudge and primary
  siudge
• Activated sludge treatment plant without primary
  settling

Anaerobik Aritma Biyoteknolojisi
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Advantages
Anaerobik Aritma Biyoteknolojisi

• Volatile solids reduction is equal that obtained
  anaerobically
• Lower BOD concentrations in supernatant liquor
• Production of an odorless, humus-like,
  biologically stable end
• Operation is relativeluy easy
• Lower capital cost

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Disadvantages
Anaerobik Aritma Biyoteknolojisi

• A high power cost is associated with supplying
  the required O2
• A digested sludge is produced with poor
  mechanical dewatering characteristics
• A useful by-product such as methane is not
  recovered

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Process description
Aerobic digestion is similar to the
activated-sludge process. As the supply of
available substrate (food) is depleted, the
microorganisms begin to consume their own
protoplasm to obatin energy for cell maintenance
reactions when this occurs, the microorganisms
are ssaid to be in the endogenous phase.
Anaerobik Aritma Biyoteknolojisi
5CO2 NO3- 3H2O H
C5H7NO2 7O2
Cell tissue is oxidized aerobically to CO2 and
H2O and ammonia. The ammonia form this oxdation
is subsequently oxidized to nitrate.
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• An actuality, only about 75 to 80 percent of the
  cell can be oxidized, the remaining 20 to 25
  percent is composed of inert component.
• A pH drop can occur when ammonia is oxidized to
  nitarte if the alkalinity of the wastewater is
  insufficient, chemical addition may be required.
• Two variation of the process are commonly used
• conventional aerobic digestion (with air)
• high-purity oxygen aerobic digestion
• Aerobic digestion with air is the most commonly
  used process.

Anaerobik Aritma Biyoteknolojisi
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Process design

• Factors taht must be considered in designing
  aerobic digesters include
• Solid reduction
• Hydraulic retention time
• Oxygen requirements
• Energy requirements for mixing
• environmental condition such as pH, temperature.

Anaerobik Aritma Biyoteknolojisi