The citric acid is being produced by
microorganisms during fermentation
through their metabolic citric acid cycle
(Haq et al., 2002). When microbes
concern, there are many organisms which
are producing citric acids. However,
fungus is considered to be suitable
producer of citric acid. Especially,
Aspergillus niger is utilized as much as it produces.
Citric acids can be produced by
well-developed methods in using
chemicals. However, microbial
fermentations are been used for long time
for industrial scale citric acid production.
The citric acids can also be used in
remediation aspects. Citric acids are used
as chelating agents to remove heavy
metals in soils (Sayer and Gadd, 2001).
Fungal organic acids usually consisting
one or more carboxylic groups which is
responsible for the chelating properties.
The citric acids can effectively remove
zinc, chromium and nickel from the soil
(Elliott and Shastri, 1999; Wasay et al.,
2001).