Question

A factory building transformers and capasitors in Masai, Johor, discovered a chemical spill from one of their drums of polychlorinated biphenols (PCBs) into the soil of their compound. You are with the team of officers from the Department of Environment (DOE). What type of bioremediation would you choose of this clean-up and why? Name and describe (in detail) this specific method you would use. answer less than 500 words.

Answer 1

Bioremediation is a process of waste removal method where microorganisms are used to degrade or remove organic waste and heavy metal from sites like soil and water. Bioremediation is advantageous because it is environment-friendly, inexpensive . Bioremediation can remove multiple wastes simultaneously. Polychlorinated biphenyls also known as PCBs and are various biphenyl based products that are widely used as a dielectric fluid, industrial coolant, and lubricants. PCBs are a contamination source of soil and water. They are stable and can persist in the environment. Bioremediation is the use of microorganisms, plants and fungus to degrade chemicals from contaminated sites, either a soil or aqueous environment.

In the process of decomposition of PCBs, microbial bioremediation is used. That is microbes are used to degrade PCBs. This process relies on multiple microorganisms' co-metabolism.

Anaerobic microorganisms dechlorinate PCBs first, and other microorganisms that are capable of doing BH pathway can break down the dechlorinated PCBs to usable intermediates like acyl-CoA or carbon dioxide.

In the process of bioremediation, first, the soil and sediment structures are tested which will determine how tightly PCBs are adhered to them and what is their affect in the absorption of PCBs into cells. Presence of organic carbon and clay content can enhance PVBs’ absorption. Moreover the soil contains necessary nutrition for the growth of microbes which can help in quick growth of degrading microbes.The local microbial population has significant impacts on the rate of degradation of PCBs, which varies with different microbial strains and their activities. If no previous exposure to PCBs is found,the process of bioremediation may take months because the microbes will need time to activates their ability for the dechlorination of PCBs and break them down.

Various microorganisms are involved in a two-stage process of degradation of PCBs, which happens in aerobic and anaerobic environments. Species of Arthrobacter,Bacillus,Microbacterium ,Pseudomonas,Rhodococcus, Corynebacterium spp etc are helpful in breaking down pcb.

The first stage of the degradation pathway is chlorination of PCB. After this process PCBs will be able to be used as electron acceptors in anaerobic respiration to store energy. PCBs are dechlorinated to a certain degree,most of the times lower than five chlorines presenting in the structure and one aromatic ring which has no chlorine. Then they can undergo the biphenyl degradation pathway or BP pathway to be degraded to accessible carbon or carbondioxide in the aerobic environment. BP pathway utilizes series of enzymes and convert biphenyl to TCA cycle intermediates which are pyruvate, Acyl-CoA and benzoate. The accumulation of PCB dechlorinating microorganisms is slow, because of which the degradation rate is slowed down. Because of this PCBs usually go through a co-metabolism pathway that involving different microorganism species to fasten the process.

In short there are four steps in the entire process:

1. The PCBs first need to be solubilized inorder to enter the cell,.

2. PCBs are dechlorinated by anaerobic bacteria, then transport the metabolites to aerobic bacteria or fungi through a biofilm.

3. The presence of PCBs metabolites leads to or trigger enzyme expression in BP pathway.

4. PCBs after being broken down to Acetyl-CoA or carbondioxide can be utilized .

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