A multidimensional study of enzyme activity and hydrocarbon reduction for bioremediation of refinery waste by free living cyanobacteria

The continually increasing demand for fuels with the depleting resources due to expansive production generates tons of waste and effluents in the form of sludge annually across the globe. The inappropriate disposal or inadequate caution for safe elimination practices is the root cause for the deteriorating soil and water quality and the consequent dread toward the marine ecosystem as well as the terrestrial life. Remediation technique that is specific, efficient and that is safe without giving rise to new pollutant sources is the ideal solution. The present available techniques come with drawbacks of inefficiency, insufficiency, laborious, expensive, inadequate scaling, and resource dependent like requiring large span of lands or high-end instruments. The current approach brings along the solution to these shortcomings along with robust evidence. Three cyanobacterial strains cultivated for this procedure were studied morphologically, assessed on growth parameters basis, assayed for their enzyme activities, and monitored to quantify a reduced total petroleum hydrocarbon content in the cultures prior and post-treatment with the tank bottom oil sludge sourced from the Numaligarh Refinery Limited. The obtained outputs of growth parameters indicated the cyanobacteria’s survival ability toward the toxic sludge introduced into their cultures. The enzyme assays presented a diverse response of the cultures with esterase as the highest active enzyme in comparison to the rest of the enzymes. On completion of the 28-day course of incubation, the cultures exhibited a slightly reduced lipase and esterase activity and an increased polyphenol oxidase and dehydrogenase activity in comparison with the respective positive control cyanobacterial cultures. The possible reasons for the promotion and reduction of the enzyme activity were discussed in this study. In terms of the gas chromatography flame ionization detection output, the obtained chromatograms reflected significant reductions in the total petroleum hydrocarbon of the sludge post-treatment on day 28. The initial hydrocarbon chain length of C3–C22 was reduced to C4–C12 by the Nostoc spp. and the Anabaena variabilis cultures, and major peak area reduction, C3–C13, was observed in the hydrocarbon spectrum of the Nostoc muscorum culture post-treatment. The saturated and the unsaturated hydrocarbons, accessory, sulfur compounds, and polycyclic aromatic hydrocarbons (PAHs) were observed to be biodegraded from the gas chromatography-mass spectrometry data of the untreated and the Nostoc spp. treated sludge in cultivation. In sum, the obtained data direct toward the high potential of the studied cyanobacterial cultures for the efficient bioremediation of the refinery-acquired sludge.