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Abstract

Compounds present in oil sludge such as polycyclic aromatic hydrocarbons (PAHs) are known to be cytotoxic, mutagenic and potentially carcinogenic. Microorganisms including bacteria and fungi have been reported to degrade oil sludge components to innocuous compounds such as carbon dioxide, water and salts. In the present study, we isolated different bacteria with PAH-degrading capabilities from compost prepared from oil sludge and animal manures. These bacteria were isolated on a mineral base medium and mineral salt agar plates. A total of 31 morphologically distinct isolates were carefully selected from 5 different compost treatments for identification using polymerase chain reaction (PCR) of the 16S rRNA gene with specific primers (universal forward 16S-P1 PCR and reverse 16S-P2 PCR). The amplicons were sequenced and sequences were compared with the known nucleotides from the GenBank. The phylogenetic analyses of the isolates showed that they belong to 3 different clades; Firmicutes, Proteobacteria and Actinobacteria. These bacteria identified were closely related to the genera Bacillus, Arthrobacter, Staphylococcus, Brevibacterium, Variovorax, Paenibacillus, Ralstonia and Geobacillus. The results showed that Bacillus species were predominant in all composts. Based on the results of the degradation of the PAHs in the composts and results of previous studies on bacterial degradation of hydrocarbons in oil, the characteristics of these bacterial isolates suggests that they may be responsible for the breakdown of PAHs of different molecular weights in the composts. Thus, they may be potentially useful for bioremediation of oil sludge during compost bioremediation.
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Abstract

This study is aimed at measuring the effect of pig, cow, horse and poultry manures on the degradation of selected Polycyclic Aromatics Hydrocarbons present in oil sludge. Four kilograms of soil amended with 1.2 kg of oil sludge was mixed with wood chips in a ratio of 1:2 (w:v) soil mixture: wood chips. The mixture was divided into fi ve parts and four parts were separately mixed with pig, cow, horse or poultry manures in a ratio of 2:1 (w:w) and the fi fth portion was used as the control with no manure added. All experiments were incubated for 10 months at room temperature. Compost piles were turned weekly for aeration and moisture level was maintained by adding deionised water enough to prevent the compost from getting dry. Moisture level, pH, temperature, CO2 evolution and oxygen consumption were measured monthly and the ash content of the compost at the end of experimentation. Highest temperature reached was 27.5°C in all compost heaps, pH ranged from 5.5 to 7.8 and CO2 evolution was highest in poultry manure at 18.78 μg/dwt/day. Microbial growth and activities were enhanced as indicated by increase in temperature, moisture level, pH value and respiration rate in all the compost piles. Bacteria capable of utilizing PAHs were isolated, purifi ed and characterized by molecular techniques using polymerase chain reaction with specifi c universal primers and the amplicons were sequenced. Bacteria identifi ed were Bacillus, Arthrobacter and Staphylococcus species. Percentage reduction in PAHs was measured using automated soxhlet extractor with Dichloromethane and gas chromatography/mass spectrometry. Results from PAH concentration measurements showed reduction of between 77% and 99%. Co- -composting of contaminated soil with animal manures enhanced the reduction in PAHs.
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