The effect of composition on the biodegradability and toxicity

The effect of composition on the biodegradability and toxicity of drilling muds used at ologbo active onshore field, Edo State, Nigeria

The effect of composition on the biodegradability and toxicity of two muds commonly used at onshore oil fields at Ologbo, Edo State were examined. Biodegradation of drill muds by two bacterial and fungal isolates; Enterobacter aerogenes, Micrococcus sp., Aspergillus sp. and Penicillium sp. were carried in a shake flask experiment using mineral salts medium at 120 rpm for 28 days. The total viable counts were monitored and ultimate biodegradability was derived from the ratio of COD and BOD5, after every four days. Lethal effects of the drilling muds on juvenile Tilapia guineensis, Micrococcus sp. and Penicillium sp. were investigated using static renewal bioassay for 96 hr and 24 hr. The Potassium chloride (KCl) polymer water based mud (WBM) was more biodegradable than synthetic based mud (SBM). This was indicated by the highest total viable counts recorded in consortium amended with water based mud (101 �10 3 cfu/ml), and also recording the lowest chemical oxygen demand and biological oxygen demand (47 mg/l and 0.4 mg/l respectively).There were no significant differences (P > 0.05) in the degradation of the muds by the isolates. The 96 hr LC 50 of potassium chloride (KCl) polymer water based mud and synthetic based mud (SBM) were 8125 mg/l and 5800 mg/l for Tilapia guineensis respectively. The 24 hr LC50 of Potassium Chloride polymer water based mud was 200 mg/l for Micrococcus sp. and Penicillium sp. Exploration and production companies operating in Ologbo should be encouraged to put into consideration the effect composition of the drilling muds before usage.
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