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This paper considered the toxicity assessment of some crude oil contaminated soils in Niger Delta areas. The soil samples were collected from different horizontal distances, vertical depths and contaminated soil of different ages. The heavy metals in the contaminated soils were digested and extracted using di-acid digested and DTPA extraction methods respectively. The physiochemical parameters (moisture content, pH, N, P and heavy metals (Ni, Pb and Cd) were analysed with APHA method. The heavy metals concentration was determined using atomic absorption spectrophotometer (AAS). The results show that the metals concentration decreased with the age of the contaminated soil and with increased vertical depths. However, the metals concentrations were almost constant at different horizontal distances. Similar trend was observed for the moisture content, pH, N, P and K.

The increasing growth of cassava agro-industries in Nigeria has led to the enormous generation of cassava peels waste. The feasibility of generating biogas and biofertilizer for both domestic and agricultural applications from cassava peels waste inoculated with cow dung was investigated. Fresh and stale cassava peels were used in the study. Three pretreatment chemicals such as sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)2 and ammonium chloride (NH4Cl) buffer solutions were used in pretreating the cassava peels and cow dung slurry. Six batch anaerobic biodigesters of 10-litre capacity each were used in this study for 40 days retention period. The pH, temperature, and volumes of biogas and methane produced were monitored and recorded daily. The fertilizer qualities (total solids, volatile solids, % phosphorus, % nitrogen, etc.) of the digester slurry and the digester sludge after 40 days digestion were determined using official methods of analysis of Association of Official Analytical Chemists (AOAC). The results showed that the amount of biogas generated is 2540 cm3/day. The stale cassava peels and cow dung slurry and the use of NH4Cl pretreatment chemical gave the best biogas production and methane yield of 104,961cm3 and 62.3% respectively. The digester sludge from the anaerobic digestion of cassava peels and cow dung showed and demonstrated good biofertilizer qualities.

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