BIOREMEDIATION SYSTEMS

Description

Bioremediation enhances the ability of microorganisms to degrade organic pollutants in soil. The microorganisms use the organic pollutants as a food source, forming carbon dioxide and water as final products.

The microorganisms may be isolated from the contaminated site itself and the best pollution degraders selected or, a strain is obtained from laboratory stock. The organisms are multiplied in fermenters and applied to the contaminated land. Groundwater may be circulated through an aerated tank or air may be blown into the ground to provide oxygen for the microorganisms. Nutrients may be added if necessary.

Bioremediation may be carried out in situ to avoid excavation and transportation costs. In landfarming, the contaminated land is rotovated to intimately mix the contamination with microbes and nutrients. Alternatively, drilling and injection allows the addition of air and nutrients to points of deeper contamination. The carrier solvents of leachable pollutants such as organochlorides can be degraded in situ, leaving the high molecular weight compounds fixed to the soil substrate reducing the requirement for expensive engineering to cap or bund the site.

Excavation may be unavoidable, particularly with difficult contaminants such as PCBs where more extensive soil modifications may be required. Ex situ bioremediation is usually in a form similar to composting in which covered piles of soil are inoculated, aerated and watered in a controlled manner.

Application

Bioremediation has been used to treat land contaminated with hydrocarbons, phenols, cyanides, nitriles and halogenated hydrocarbons. Petroleum hydrocarbons may be treated using landfarming methods, whereas PCBs are tackled ex situ. Most bioremediation systems operate aerobically, but anaerobic bioremediation is used to degrade chlorinated hydrocarbons. Bioremediation can be combined with vapour extraction technology to provide a robust method for removing industrial solvents and mixtures.

Sizing

For bioremediation to be a success it is important to first understand the hydrology, geology and history of the site and the nature of the contaminants and the microorganisms. Full bioremediation of a site can take 6 months to years to complete. The bioremediation of a 2000 m3 site would require an electrical power loading of about 5 kW, made up from the groundwater pumps, aerators and compressors. Larger sites would have larger power requirements.