Biosurfactant Produced by Indigenous Bacteria During Composting Process of Crude Oil Polluted Soil: Properties and Role

Bacterial co-metabolism in composting process has been widely used to remove hydrocarbons, aided by in-situ production of bio-based surfactants, in terms of compost humic acid-like substances and biosurfactants. The properties of compost humic acid-like substances have been shown in previous studies as potential surface tension reducers and emulsifiers for hydrocarbons. The current study aimed to analyze the properties of biosurfactant of surface tension decrease, emulsification activity, and hydrocarbon solubilization ability. Four indigenous bacteria consortia were isolated from composted materials of yard waste, rumen residue, crude oil-polluted soil, and the mixture of polluted soil with organic waste (1:1, w/w) at day 0th, 20th, 40th, and 60th. Organic waste consists of yard waste and rumen residue in the ratio of 1:1. The isolated indigenous bacteria consortia were incubated for 7 days in different media, i.e., organic waste extract, 6.00% of crude oil, and a mixture of organic waste extract with 6.00% crude oil. The results indicated that the surface tension decrease and emulsification activity of biosurfactants were 8.35–52.90 mN m-1 and 0.00–12.00%, respectively, which showed the potential as surface tension reducers with low emulsification activity. The higher hydrocarbon solubility was shown by the biosurfactant from the rumen residue (13 620 µg g-1) and the mixture (10 998 µg g-1) at day 40th, which was comparable to 1.50% of Tween 80. The biosurfactants in the current research were produced with the same materials, process, and time as compost humic acid-like substances which acts as in-situ bio-based surfactants. The respective ability to solubilize hydrocarbon might be combined and estimated to be higher than Tween 80 of 24 329 µg g-1 and 21 619 µg g-1 for rumen residue and the mixture, respectively. Therefore, it was concluded that the best composition for in-situ bio-based surfactant production to assist the degradation of hydrocarbon through composting process is polluted soil with organic waste (1:1, w/w). The solubility of hydrocarbons can be increased without synthetic surfactants addition, but through providing nutrients to maintain in-situ bio-based surfactant production with intermittent addition of organic waste every 40 days. This method is expected to be an appropriate approach in composting development as a cost-effective sustainable bioremediation technique for polluted soil.