Biosurfactant enhanced biodegradation of high molecular weight polycyclic aromatic hydrocarbons in a two-stage continuous stirred tank bioreactors and biofilm tank

Abstract

Polycyclic aromatic hydrocarbons (PAHs) do not dissolve easily in water, due to their hydrophobic properties. PAHs are unavailable to most aromatic compound degrading organisms, due to these properties. In this study, a biosurfactant producing culture enhancing dissolution of PAHs was isolated, to make them bioavailable. The culture was introduced to the system to improve the dissolution of PAHs and degrade the PAHs thereafter. The aim of the study was to use a strategy with a biofilm process, subsequent to a continuous stirred tank bio-reactors (CSTRs) to successfully remove PAHs from water, with microorganisms that can degrade these pollutants. The open system could easily be controlled and set to optimum conditions, stimulating the growth of PAH degraders. The feed rate and influent concentration can be controlled and the system can easily be cleaned. Biodegradation was achieved, using optimum conditions obtained from the conducted batch studies in a CSTR process ensuring a feasible biodegradation process. Two cultures, Pseudomonas aeruginosa and microbial consortia, were used during the biosurfactant production and PAHs degradation preliminary batch studies. The biosurfactants produced, were identified as Lipopeptides and degradation results indicated great degradation of fluoranthene and triphenylene with a mixed culture consortium present in the system. 90.1% of fluoranthene and 79.6% of triphenylene was degraded after 22 d of incubation in the batch system. Degradation of fluoranthene was studied using biosurfactants and microbial consortium in a three-stage continuous flow system. Reactor 2A fluoranthene influent (60.89%) was degraded, 70.02% of Reactor 2B fluoranthene influent was degraded and 77.17% of biofilm tank fluoranthene influent was degraded. Kinetic studies were conducted, using a Monod model to describe the substrates degradation for batch systems. The highest degradation rate for fluoranthene was determined to be 0.29 h-1 and for triphenylene was 0.13 h-1 with half saturation values of 991.84 mg/L and 451 mg/L respectively, indicating that fluoranthene was degraded faster than triphenylene, when incubated for 22 d. The study demonstrated that biosurfactant production and biodegradation of fluoranthene can be achieved in an open CSTR system, as much as it can be done in a batch system. The biological remediation of PAHs in wastewater plants can be introduced and applied for wastewaters rich, with PAHs.