Anaerobic Treatment The use of microbes in the absence of oxygen for the stabilization of organic...

Anaerobic Treatment

Anaerobik Arıtma Biyoteknolojisi

Anaerobik Arıtma 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 (>2000 mg/l)

Anaerobic Digestion Process



Complex Organics

CH4 ve

CO2

Organic acids and

H2 Acid Acid

producing producing bacteriabacteria

(acidogens)(acidogens)

Methane Methane producing producing bacteriabacteria

(methanogenics)(methanogenics)

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

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.

Process description:


Anaerobik Arıtma Biyoteknolojisi 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stabilized sludge, withdrawn from the reactor,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.



The two types of commanly used

anaerobic digesters are identified as;

Standard-rate

High-rate

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.

High-Rate Digester:


Anaerobik Arıtma Biyoteknolojisi 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.



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)

Process design:



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

AEROBIC SLUDGE DIGESTION



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

Advantages:



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

Disadvantages:



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.

Process description:

C5H7NO2 +

7O2Cell tissue is oxidized aerobically to CO2 and H2O

and ammonia. The ammonia form this oxdation is

subsequently oxidized to nitrate.

5CO2 + NO3- + 3H2O + H+



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.



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.

Process design:

Anaerobic Treatment The use of microbes in the absence of oxygen for the stabilization of organic...

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