Study on detoxification and removal mechanisms of hexavalent chromiumby
microorganisms
Abstract
Extensive industrial activities have led to an increase of the content
of chromium in the environment, which causes serious pollution to the
surrounding water, soil and atmosphere. The enrichment of chromium in
the environment through the food chain ultimately affects human health.
Therefore, the remediation of chromium pollution is crucial to
development of human society. A lot of scholars have paid attention to
bioremediation technology owing to its environmentally friendly and
low-cost. Previous reviews mostly involved pure culture of
microorganisms and rarely discussed the optimization of bioreduction
conditions. To make up for these shortcomings, we not only introduced in
detail the conditions that affect microbial reduction but also
innovatively introduced consortium which may be the cornerstone for
future treatment of complex field environments. The aim of this study is
to summary chromium toxicity, factors affecting microbial remediation,
and methods for enhancing bioremediation. However, the actual
application of bioremediation technology is still facing a major
challenge. The detoxification process inclusive of bioreduction and
biosorption. When microorganisms are exposed to Cr(Ⅵ), related genes
will be up-regulated (Chr promoter and copZ) to prevent intracellular
molecules from being destroyed. Microorganisms provide electrons to
reduce Cr(Ⅵ) through autogenous enzymes or externally addedreducing
substances. The pH, temperature, concentration, and electron donor are
the major factors affectting the bioreduction owing to their close
correlation with enzyme activity. Biosorption is mainly based on
electrostatic force, combined with chromium oxide anions through
functional groups (hydroxyl, carboxyl, amino etc.) on the cell surface.
Bioaccumulation is the active uptake of Cr(VI) by living cells, a
process that usually depends on the forms and bioavailability of Cr(VI)
and is also dependent on nutrients such as energy and carbon sources.
The combination of these exogenous additives and mixed culture
microorganisms greatly improves the tolerance and reduction efficiency
of microorganisms. In previous reports on bioremediation technology, the
main object of remediation was water bodies, and arable land is
currently facing severe heavy metal pollution, so the future microbial
remediation technology should also target the soil and atmosphere. In
response to the research deficiencies has been proposed, the following
suggestions are putforward: 1. Due to the complex actual environmental
conditions, especially the soil, it is difficult to achieve the purpose
of governance using purely cultured microorganisms. The use of mixed
culture of microorganisms can improve the adaptability to the
environment and the efficiency of treatment through the synergy between
microorganisms. 2. For the complex medium of soil, the effect of using
microorganisms alone may not be obvious. Therefore, combining plants and
microorganisms can promote the application o