Ammonia Reduction Through Bioaugmentation
Wastewater treatment is one of the
earliest large-scale applications of biotechnology. It
differs from other industrial microbiological processes
in that there is little or no control over the raw
material and only moderate control over the operating
conditions, yet the process is expected to produce a
uniform finished product. The goals of the process
normally include the removal of organic pollutants and
nutrients (i.e. nitrogen) before discharge.
Removal of "nitrogenous compounds is
critical" as excessive amounts of ammonia and
nitrite/nitrate levels are detrimental to water quality.
Ammonia exerts an oxygen demand in aquatic environments;
4.7 grams of oxygen are required to oxidize one gram of
ammonia. Nitrite is toxic to marine life and can induce
methemoglobinemia (a reduction in the oxygen-carrying
capacity of the blood) in humans. These factors call for
effective removal of nitrogen from the wastewater before
it is discharged to natural water systems.
The conventional method of removing
nitrogen from wastewater starts with oxidation of
ammonia to nitrite/nitrate (nitrification) and ends with
reduction of nitrite and nitrate to nitrogen gas (denitrification).
This conventional approach to ammonia
removal only converts one form of nitrogen (ammonia) to
another (nitrite or nitrate).
Nitrogen exists in wastewater in four
different forms:
- Organic nitrogen (amino acids,
proteins, purines, pyrimidines, and nucleic acids);
- Ammonia nitrogen (NH3-N);
- Nitrite nitrogen (NO2-N);
and
- Nitrate nitrogen (NO3-N)
In an untreated wastewater sample, the
major fraction is usually ammonia nitrogen and the
organic nitrogen. These are oxidized to nitrite and then
to nitrate in the environment.
The conventional biological
nitrification, a two-step process, begins with ammonia
being converted to nitrite by Nitrosomonas bacteria,
followed by nitrite being oxidized to nitrate by
Nitrobacter bacteria. These bacterial species are
typical examples for the nitrification process. They are
autotrophic in nature and use carbon dioxide as their
cell carbon source.
Because of the sensitivity of the
process, relying on the ammonia nitrification step to
convert ammonia to nitrate using the autotrophic
bacteria has some problems.
The process requires long mean cell
retention time (MCRT) of up to a few days and hence,
huge storage requirements. The bacteria are very
sensitive to cold temperatures as well as the presence
of toxic chemicals in the system. The rate of
nitrification slows down significantly during colder
weather. Temperatures below 50º F [10ºC] can stop growth
with 86º F [30ºC] being the optimum.
Bio-Pure's specially selected
microorganisms consume a wide range of organic
substances effectively. This results in an increased
carbon uptake and consequently, an increased nutrient
uptake, so their ammonia uptake as a nitrogen source
(nutrient for growth) is higher than that for the
naturally occurring microbial population in the waste
water treatment system. They are capable of utilizing
nitrite and nitrate for respiration (denitrification) as
well as for growth as nitrogen sources.
The bacteria used in the Bio-Pure
products are heterotrophic and utilize organic carbon as
their source for food and energy. First, the organic
matter is oxidized by bacterial cells to obtain energy.
Simultaneously, organic carbon is assimilated into the
new cells using the energy produced with ammonia as a
preferred nitrogen source.
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