Abstract

Contaminated soil (FAO: Lithosol) containing >380 000 mg kg^-1 total petroleum hydrocarbons (TPH) was bioremediated by composting. The soil was inoculated with sewage sludge and incubated for 19 months. The soil was mixed in a ratio of 1:1 (v/v) with wood chips. The soil-wood chips mixture was then mixed in a ratio of 4:1 with sewage sludge. Compost heaps were set up in triplicates on wood pallets covered with double layers of nylon straw sheets. Control experiments which contained the contaminated soil and wood chips but without sewage sludge were set up in triplicate. Moisture, temperature, pH, ash content, C:N ratio of the compost mixture and TPH of the soil was monitored monthly. The concentrations of selected hydrocarbons in the contaminated soil were measured monthly during the incubation period. Temperature rose to about 58°C in the sewage sludge compost within two months of incubation, while temperature in the control fluctuated between 15 and 35°C throughout the incubation period. Total petroleum hydrocarbons (TPH) was reduced by 17% in the control experiments and 99% in the sewage sludge compost at the end of the incubation period. The concentrations of most of the selected hydrocarbon components were reduced by up to 100% within the same period. Microbial activities were shown to correlate with the reduction in hydrocarbon contents of the soil.

Key words: Bioremediation, composting, PAHs, sewage sludge, soil.