Assessment of Bacterial Deteriogens of Selected Lubricating Oils Used in Industrial Generators

Abstract

The study investigates microbial deteriogens of lubricating oils used on industrial generators. Total heterotrophic bacterial and total fungal counts were determined using the spread plate method. Bacterial isolates were screened for the utilization of lubricating oil and the rate of biodeterioration was determined by monitoring the optical density and pH of medium containing specific bacterial isolates from lubricating oil. Physico-chemical characteristics of lubricating oil were determined following standard procedures and petroleum hydrocarbon profile was determined using Gas Chromatography. Bacterial counts of used and unused samples ranged from 5.55 log cfu/ml to 7.83 log cfu/ml and from 4.64 log cfu/ml to 4.86 log cfu/ml respectively while fungal counts ranged from 6.60 log cfu/ml to 8.04 log cfu/ml and from 0 log cfu/ml to 7.32 log cfu/ml respectively. Bacterial isolates identified in the study include; Micrococcus sp, Citrobacter sp., Bacillus sp., Serratia sp., Corynebacterium sp., Staphylococcus sp., Shigella sp., while the fungal genera isolated include;  Penicillium, Aspergillus, Fusarium, Cryptosporium, Candida and Saccharomyces species. Screen test for the utilization of used and unused oil samples by bacterial isolates showed that all isolates utilized the lubricating oil. Results further revealed that there was a consistent and significant (P < 0.05) increase in optical density and a fluctuation in pH during deterioration monitoring. Petroleum hydrocarbon profile analysis after 28 days of study revealed lower concentrations of hydrocarbon components in the used oil samples compared to the unused samples, this confirm the fact that isolated organisms may have utilized the lubricating oil as a source of carbon and energy thereby affecting its quality and performance.