Encyclopedia of Environmental Science and Engineering, Volume I and II

138 BIOLOGICAL TREATMENT OF WASTEWATER

carried out may be quite different under aerobic and anaero-

bic conditions, the processes of microbial growth and energy

utilization are similar. Typical reactions in these three phases

are formulated below:

• Organic Matter Oxidation (Respiration)

C xH (^) y O z + O 2 → CO 2 + H 2 O + Energy

• Inorganic Matter Oxidation (Respiration)

NH^42 O NO^3 H O^2 2H Energy

 2 →+

• Protoplasm (Cell Material) Synthesis
  C x Hy O z + NH 3 + O 2 + Energy → C 5 H 7 NO 2 + H 2

CHOxyz

 
H NO 3 Energy

 →

C 5 H 7 NO 2 +

CO 2 + H 2 O

• Protoplasm (Cell Material) Oxidation
  C 5 H 7 NO 2 + 5O 2 → 5CO 2 + 2H 2 O + NH 3 + Energy

Therefore, bacterial respiration in living protoplasm is a

biochemical process whereby energy is made available for

endothermic life processes. Being dissimilative in nature,

respiration is an important process in wastewater treat-

ment practices. On the other hand, endogenous respira-

tion is the internal process in microorganisms that results

in auto-digestion or self-destruction of cellular material.^3

Actually, bacteria require a small amount of energy to main-

tain normal functions such as motion and enzyme activation

and this basal-energy requirement of the bacteria has been

designated as endogenous respiration. Even when nutri-

ents are available, endogenous metabolism proceeds with

the breakdown of protoplasm.^5 According to Bertalanffy’s

hypothesis,^6 the microbial growth is the result of competition

between two opposing processes: Aufban—assimilation, and

Abban—endogenous metabolism. The rate of assimilation is

proportional to the mass of protoplasm in the cell and the

surface area of the cell, whereas the endogenous metabolism

is dependent primarily on environmental conditions.

In the presence of enzymes produced by the living micro-

organisms, about 1/3 of the organic matter removed is oxi-

dized into carbon dioxide and water in order to provide energy

for synthesis of the remaining 2/3 of the organic matter into

the cell material. Metabolism and process reactions occur-

ring in typical biological wastewater treatment processes are

explained schematically by Stewart^7 as shown in Figure 3.

Thus, the basic equations for biological metabolisms are:

Organic matter metabolized

= Protoplasm synthesized 
 Energy for synthesis

and

Net protoplasm accumulation

= Protoplasm synthesized  Endogenous respiration.

“Growth Kinetics”

Irvine and Schaezler^8 have developed the following

expression for non-rate limited growth of microorganisms

in logarithmic phase:

d

d

N

t

kN 0

(1)

510 gINFLUENT

INFLUENT

BOD

5

510 g

250 g

350 g 275 g

525 g

105 g

160 g

ASSIMILATIVE

BOD 5

BOD^5

REMOVED BIOMASSFORMED

O 2

O 2

O 2

RESPIR

ATIO

N

ASSIMILATIVERESPIRATIO

N

RESP

IRAT

ION

ENDOGENOU

S

RESPIRATION

120 g

40 g

10 g

ENDOGENOUS^ RE

SPIR

ATIO

N

ACTIVE BIOMASS

INACTIVEBIOMA

SS

BIOMASS

EFFLUENT

BOD UNUSED

SYSTEM METABOLISM FOR SOLUBLE WASTES

INFLUENT

(SOLUBLEBOD BOD

AND VSS)

ASSIMILATED SYNTHESIZED

BIOMASS BIOMASS GROWTH

UNUSED BOD (SOLUBLE AND VSS)

INFLUENT NON-BIODEGRADABLE FSS AND VSS

WASTE = SOLUBLES + PARTICULATES EFFLUENT

EXCESSSLUDGE

RESPIRATION

FIGURE 3 Metabolism and process reactions.

Time

Time

Log

Growth PhaseGrowth PhaseDeclining Endogenous Phase

Mass of Microorganisms

LAG

Phase

LOG

Phase

Declining

Growth

Phase

Stationary

Phase

Increasing

Death Phase LogDeath PhaseDeath

Number of Visible Microorganisms

FIGURE 2 Growth pattern of microorganisms.

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