Oil recovery from Algerian petroleum sludge using indigenous bacterium: an environmentally sustainable method for handling oily sludge

Abstract

One type of solid emulsified waste produced by the petroleum industry is oily sludge. Due to the high levels of hazardous substances it contains, it poses a significant risk to human health and the environment. Therefore, treatment is necessary to reduce its toxicity. Crude oil, which has a high recycling value, accounts for a significant proportion of oily sludge. This study aims to use the indigenous bacterium Enterococcus faecium NL 6 to produce a biosurfactant for use in oil recovery from sludge. This strain can produce biosurfactant using low-cost, renewable substrates such as whey, reaching an E24 of 72% and achieving a significant reduction in surface tension (27.2 mN/m). This extracellular biosurfactant was produced at a concentration of 32 mg/L and remains stable under extreme conditions of temperature, pH and salinity. Identified as rhamnolipids, the biosurfactants were able to recover 95% of the oil from oily sludge sampled from crude oil storage tanks in just a few hours (4 h). Gas chromatography has demonstrated the presence of normal alkanes in the crude oil extracted from the sludge, thereby indicating its potential for reuse as an energy source. Incorporating 5% of the recovered oil into the crude oil enhances its efficiency, resulting in a calorific value of 10,324.675 kcal/kg. Given the economic and environmental advantages of biosurfactants, the resulting rhamnolipid can be considered an effective, efficient and reliable washing agent for the recovery and treatment of oily sludge waste.