Agricultural effluents, industrial residues and industrial accidents contaminate the soil, surface water, air and reservoirs thereby causing a potential threat to both environment and human health. Remediation of contaminated soil is a matter of great concern. The conventional technology to get rid of these contaminants involves either chemical decomposition or high temperature incineration of chemical pollutants. This technology being complex and expensive lacks public acceptance. However, compost bioremediation technology offers an option to destroy contaminants using biological activity. This technology has proved effective in degrading soil contaminants and volatile compounds as well as can control odors.

It is the process of biological degrading of organic wastes to an innocuous state or to a level below the permissible limits recommended by regulatory authority. Bioremediation involves the use of living organisms, primarily the microorganism's viz. bacteria, fungi and actinomycetes. The microbial flora may be indigenous to the contaminated soil or can be isolated from elsewhere and brought to the contaminated site.

In situ bioremediation involves treating the contaminated material at the site, while ex situ involves the removal of the contaminated material to be treated elsewhere. Soils contaminated with diesel fuel or other petrol products, wastes from brewing, antibiotic fermentation, food processing and mineral oil may be decontaminated using this technology.

Howe does compost bring about the remediation
Compost is a source of diverse group of microorganisms. Microorganisms secrete enzymes that break down large molecules into smaller molecules thereby facilitating easy absorption into microorganisms. Intracellular decomposition occurs once the microorganism absorbs the chemical. Mineralization is the main process that occurs inside the microorganisms. The contaminants get digested, metabolized and transformed into humus and inert byproducts such as carbon dioxide; water and salts. The microbes not only degrade the pollutants but may also clean unwanted substances from air, soil and water.

Compost offers an array of ecological niche promoting metabolic diversity, coupled with high rate of metabolic activity. Complex substrates are not fully degradable by single organisms, but are degradable by a consortium of organisms, each carrying out different degradation steps. Mixed populations are required to degrade crude oils significantly.

Compost bioremediation has proved effective in degrading or altering many contaminants such as chlorinated and non chlorinate hydrocarbons, wood preserving chemicals, solvents, heavy metals, pesticides, petroleum products and explosives. In the bioremediation of xenobiotic compounds, the microbial dehalogenation is an important process as a large number of xenobiotic compounds contain halogen group in their structure. Dehalogenation also facilitates further degradation of compounds due to cleavage of carbon-halogen bond under the catalytic action of dehalogenase enzyme. Many oxygenases act as dehalogenases by actively catalyzing the dehalogenation step.

Fungi are especially good at digesting complex organic compounds that otherwise is not degraded by other organisms. Phanerochaete chrysosporium produces lignases, a group of extracellular enzymes, that include lignin peroxidase, arylmethoxy demethylase and phenol oxidase. Such enzymes are efficient in scavenging a range of hazardous polyaromatic hydrocarbons that are structurally diverse and normally considered resistant to microbial degradation. Fungi can also remove excess lignin from paper pulp.

Bacteria remove pollutant from the environment without degrading it. They take up large amount of metals and minerals to ensure adequate resources for binary fission. Only bacteria that possess the ability to produce enzymes that use petroleum as a substrate can degrade petroleum.
Many algae and bacteria produce secretions that attract metals that are toxic in high levels. The metals are removed from the food chain by being bound to the secretions. Algae are very good at absorbing nitrogen, phosphorus, sulfur and many minerals and metals from the environment.
Compost in bioremediation is applied not only as a mean of degrading toxic organic compounds but also for lessening the toxicity of heavy metal contaminants in organic residues, wastes and by products. It also stabilizes wastes for ultimate disposal by traditional manner in landfills. The iron oxides in composts can limit the bioavailability of metals. In addition, stabilized organic matter forms complexes with metals and restrict the mobility of metals and their availability for plant absorption.

Mature compost is more effective in accelerating the degradation of fumigant (1, 3 -dichloropropene) as compared to partially mature compost. Compost can also lower the concentration of pesticide to non-hazardous level in soil under crop cultivation. This may occur due to partial degradation, adsorption to compost and volatilization.

Bioremediation technology is quite safe on ecological and health aspect due to least application of chemical compounds. It is projected as an eco technology for the present century.

About Author / Additional Info:
Author: Sunita Gaind