No abstract

In situ and ex situ bioremediation of oil contaminated effluent pits, sludge pits, oil spilled land and tank bottom, and effluent treatment plant (ETP) oily sludge was carried out at Ankleshwar, Mehsana, Assam and Cauvery Asset of Oil and Natural Gas Corporation Limited (ONGC), India. The types of contaminant were heavy paraffinic, asphaltic and light crude oil and emulsified oily sludge /contaminated soil. An indigenous microbial consortium was developed by assembling four species of bacteria, isolated from various oil contaminated sites of India, which could biodegrade different fractions of total petroleum hydrocarbon (TPH) of the oily waste to environment friendly end products. The said consortium was on a large scale field applied to the above oil installations and it successfully bioremediated 30,706 tonnes of different types of oily waste. In 65 case studies of different batch size of in situ and ex situ bioremediation processes, the initial TPH content varying from 69.20 to 662.70 g/kg of oily waste has been biodegraded to 5.30-16.90 g/kg of oily waste in a range of 2 to 33 months. Biodegradation rate varied in the range of 0.22-1.10 Kg TPH /day/m 2 area due to the climatic condition of the treatment zone and the type of waste treated. The bioremediated soil was non-toxic and natural vegetation was found to be grown on the same ground. Successful eco-restoration of one large effluent pit of 26,000 m 2 area was carried out by cultivation of local fish species after completion of bioremediation. Bioremediation technology has helped ONGC with the management of their hazardous oily wastes in an environment friendly manner.

Feasibility study carried out at the site prior to the full scale study showed that the introduced bacterial consortium effectively adapted to the local environment of the soil at bioremediation site. The soil samples were collected from the contaminated fields after treatment with bacterial consortium at different time intervals and analyzed by gas chromatography after extraction with hexane and toluene. At time zero (just before initiation of bioremediation), the concentration of total petroleum hydrocarbons in the soil (25-cm horizon) of plot A, B, C and D was 30.90 %, 18.80 %, 25.90 % and 29.90 % respectively, after 360 days of treatment with microbial consortia was reduced to 0.97 %, 1.0 %, 1.0 %, and 1.1 % respectively. Whereas, only 5 % degradation was observed in the control plot after 365 days (microbial consortium not applied).