Biodegradability of Unused Lubricating Engine Oils in Fresh Aquatic System
Lucky O. Odokuma & Vincent C. Wokem
Department of Microbiology
University of Port Harcourt, P.M.B. 5323, Port Harcourt, Rivers State, Nigeria
ABSTRACT
The biodegradability of four unused lubricating engine oils (Total engine oil, Tonimas engine oil, Oando engine and Lubical engine oil) was investigated in fresh aquatic system obtained from Isokpo stream of Rivers State in the Niger Delta, Nigeria. Biodegradability (mineralization) of the lubricating oil samples were monitored for a 56 – day period using the percentage ratio of Biological Oxygen Demand (BOD) to Chemical Oxygen Demand (COD). Olive oil served as a positive control while sodium azide served as a negative control. The results obtained indicated the following rate of mineralization, Total engine oil 5.3 percent, Oando engine oil 7%, Tonimas engine oil 16% and Lubicol engines oil 73%. Statistical analysis using ANOVA, showed that there was no significant difference (P=0.05) in the percentage mineralization of the engine oils. Result obtained from the viable bacterial and fungi counts, indicated higher total heterotrophic bacteria (THB) counts than total fungi (TF) counts, and higher hydrocarbon utilizing bacteria (HUB) counts than hydrocarbon utilizing, fungi (HUF) counts. Characterization and identification test reveal that a microbial consortium comprising of the following genera; Bacillus, Pseudomonas, Microcosus, Proteus, Escherichia, Enterobacter, Arthrobacter were implicated in the biodegradation process in the fresh water source. Similarly the molds encountered in the degradation process were Aspergillus, Geotricum, Cladosporium, Penicillium, Fusarium and Candida species. Changes in the physicochemical parameters during the biodegradability monitoring period included, pH, temperature, alkalinity, conductivity, biological oxygen demand, chemical oxygen demand, total organic carbon, dissolved oxygen, nitrate, sulphate, phosphate and inorganic carbon. Biodegradability result obtained indicated that the degradation of any petroleum product (engine oil) in the environment depends on interplay of many factors which includes; type of lubricating oil, microbial load/species present in the environment and physicochemical characteristics of the natural habitat. The results of this study have provided an insight into the biodegradability of some lubricating engine oils in fresh water ecosystem. Three out of the four petroleum lubricating engine oils investigated were not readily biodegradable, hence research into the production of biobased lubricating oils that are environmentally friendly, cost effective and efficient in performance like the petroleum base oils is recommended and as well as enhancing the biodegradation of these petroleum base lubricating oils that may spill into the environment.
Key Words: Biodegradability, Biodegradation, Lubricating Oil, Mineralization
