Download anaerobic treatment(Mrs. Preetibala)

Anaerobic Treatment
PreetiBala Adatiya
Lecturer
School of Biotechnology
DAVV
Anaerobik Arıtma Biyoteknolojisi
Anaerobic Treatment
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 (>2000
mg/l)
Anaerobik Arıtma Biyoteknolojisi
Anaerobic Digestion Process
Complex
Organics
Acid producing
bacteria
(acidogens)
Organic acids
and
H2
CH4 ve CO2
Methane producing
bacteria
(methanogenics)
Anaerobic Digestion Process
Anaerobik Arıtma Biyoteknolojisi
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 Arıtma Biyoteknolojisi
ANAEROBIC SLUDGE
DIGESTION
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.
Anaerobik Arıtma Biyoteknolojisi
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 The stabilized sludge, withdrawn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 Arıtma Biyoteknolojisi
The two types of commanly used anaerobic
digesters are identified as;
 Standard-rate
 High-rate
Anaerobik Arıtma Biyoteknolojisi
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 Arıtma Biyoteknolojisi
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 Arıtma Biyoteknolojisi
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.
Process design:
Anaerobik Arıtma Biyoteknolojisi
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)*(E*Q*S0-1,42*Px)
Anaerobik Arıtma Biyoteknolojisi
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 Arıtma Biyoteknolojisi
Advantages:
 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
Anaerobik Arıtma Biyoteknolojisi
Disadvantages:
 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
Process description:
Anaerobik Arıtma Biyoteknolojisi
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.
C5H7NO2 + 7O2
5CO2 + NO3- + 3H2O + H+
Cell tissue is oxidized aerobically to CO2 and H2O and ammonia.
The ammonia form this oxdation is subsequently oxidized to
nitrate.
Anaerobik Arıtma Biyoteknolojisi
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.
Process design:
Anaerobik Arıtma Biyoteknolojisi
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.