A Study on Microbial Reduction of Hexavalent Chromium in Waste water
Chromium is a chemical element with symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard and brittle metal which takes a high polish, resists tarnishing, and has a high melting point. The name of the element is derived from the Greek word chrōma, meaning color, because many chromium compounds are intensely colored.
Chromium is present in the water as a trivalent and hexavalent, trivalent chromium is considered essential micro nutrients to adjust the ratio of blood sugar and cholesterol and fatty acid metabolism but in a very small proportions. Hexavalent Chromium is a highly toxic element resulting in a quick shock then harmful affects the kidneys, liver and blood-forming members and finally as a catalyst for malignant tumors (cancer).
Chrome element is used heavily in the metal coating electricity, in the metal industry and in reducing corrosion (rust), also enters in leather tanning, paints and dyes and in the manufacture of nuclear weapons.
There are many ways been employed to remove Chromium and heavy metals from industries such as sedimentation exchange by hydroxides and sulfur derivatives and adsorption by activated carbon.
Biological removal methods and bio-absorption is a new and innovative ways to remove large amounts of chromium through the absorption of chromium or convert to trivalent Chromium (less toxic and less damageable to the environment) by adding microorganisms for wastewater.
Microorganisms multiply rapidly and can storing large amounts of heavy elements inside the cells, which can be of use biomass microorganisms whatever it is living or dead, because the cell wall of microorganisms is negatively charged so it can attract variable cationic elements, so this ability give microorganisms susceptibility to adhesion cationic metals.
Hexavalent Chromium is highly toxic due to the number of electrons Given from the bonding form Cr+6, this makes has ability to oxidizing bonds and interferes with metabolic processes and cell formation in a living cell, so the metal when it is reduced and transformed to free radicals, they are very toxic but when it turns from hexavalent to trivalent Chromium, it will be less toxicity due to lack of electrons in the Cr+3 form, which making it non-toxic and more essential to human health.
Found that Staphylococcus warneri, Pantoea vagans, and Pantoea ananatis strains “mixed with each other” have capability to remove hexavalent Chromium (Cr+6) from effluent with removal efficiency ranged from 91.5% to 58.3% (remove from 197 to 274 mg Cr+6/l) at concentration ranged between 300 – 500 mg Cr+6/l, in aerobic condition for 24hr., and it can survive and tolerate the Cr+6 until 880 mg Cr+6/l with removal efficiency 0.5%.