Using compost to reduce oil contamination in soils

The use of mineral fertilizers as amendment for bioremediation of crude oil contaminated soils has been investigated in many situations; however, the average farmer in Niger Delta, Nigeria is unable to access mineral fertilizer for routine farming purposes due to cost. The waste stream in the Niger Delta has a high percentage of biodegradable materials that are suitable for composting. Given the abundance of biodegradable materials in the region, it should be possible to use the product as a bioremediation material. This project investigated the possibility of using waste-derived compost to treat soils contaminated with crude oil. The level of oil at 5,000 mg oil/kg soil (0.5% w/w) is the limit used in Nigerian legislation. For this study, contamination values much above this level were used ranging from 5, 7.5 and 10% (w/w) as this was found to better reflect the actual situation in the Niger Delta. The total petroleum hydrocarbons were determined using spectrophotometre. The ability of compost to improve the fertility of the soil was determined using seedling germination, chosen because of its relatively rapid response. The results from this study showed that germination of seeds without the addition of compost was adversely affected by the oil pollution. There was total inhibition to growth at initial 10% oil level suggesting that 10% oil concentration is above the trigger level for plant growth. The addition of compost diluted the contamination levels producing approximately 50% increase in overall germination observed within 5 weeks. Plants grew in soil with the least diluted content of 7.5% oil level. Soils treated with compost recorded higher biomass yields compared to those not treated with compost. This suggests that compost improved the quality of contaminated soils and sustained the yield of tomatoes seeds. The factors used for evaluating the effectiveness of treatment on soil quality included soil pH, electrical conductivity and seedling test as demonstrated by germination and growth of tomato seeds. The results were used to develop equations and charts for determining the most suitable treatment regime to be used in the field. Coming from this treatment regime, a relatively simple protocol was developed for use by local farmers to enable them to make the most effective use of compost on their own contaminated soils.