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Wastewater Treatment
Technology Tutorial
Microbial
Degradation
Bacteria are single celled organisms, which have basic
requirements for existence and reproduce rapidly. Many
occupy unique niches and consume only certain types
of food.  Many
types of bacteria have been utilized in wastewater processing.
If certain bacterium is supplied with an environment
in which the proper pH, temperature, micro and macronutrients,
and oxygen levels are present, it can quickly and effectively
break pollutants present in wastewater down into less
harmful components.
The types of bacteria utilized in wastewater processing
can be categorized based upon their necessity or intolerance
of oxygen to survive. Those bacteria that require oxygen
to convert food into energy are called aerobic, those
that will perish in the presence of oxygen are anaerobic,
and finally facultative anaerobes may thrive in either
the presence or absence of oxygen. Typically aerobes,
which can degrade pollutants 10-100 faster than anaerobes,
are utilized most frequently. Increases in temperature
and pollutant food source have shown to increase the
rate of degradation, but if all elements necessary for
conversion of food to energy are not in balance, the
microbial degradation will be thwarted.
Recapturing Energy from Microbial
Degradation
The use of microbes to biodegrade pollutants
also offers the chance to recover some of the costs
of wastewater treatment facility operation through combustion
of biogas and the use of microbial fuel cells.
When microbes break a waste component
down, up to 60% of this waste is converted into biogas.
The biogas has a calorific value typically between 50%
and 70% of that of natural gas and can be combusted
directly in modified natural gas boilers or used to
run internal combustion engines. The energy created
through this process can then be resold to recoup the
costs of running the microbial degradation tanks.
A second process by which microbes can
both reduce pollutants and create energy is a microbial
fuel cell. In this method, bacteria attach to an anode,
and as they perform digestion, they pass electrons through
the cell to combine with hydrogen ions (protons) at
the cathode, a carbon/platinum catalyst and proton exchange
membrane. The technology still needs vast improvement
to make it useful in reducing operational costs of wastewater
facilities.
Source:
"Bacteria Power" Process Engineering,
March 24, 2004, Pg. 10.
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