Biodegradation of gasoline and BTEX in a microaerophilic biobarrier

Continuous bioremediation of gasoline-contaminated water in a packed-bed biobarrier system under oxygen-limited conditions is discussed. This study was part of an extensive effort to develop an alternative technology for the in situ bioremediation of hydrocarbons where there is a limited supply of oxygen. Protruded stainless steel pieces and granulated peat moss were used as packing material to support microbial growth in two biobarriers. The inoculum was an enrichment culture of an indigenous microbial population from a soil sample. The biobarriers' inlet gasoline concentrations and the linear liquid velocities were similar to those commonly found at in situ conditions. Gasoline removal efficiencies ranged from 94% to 99.9% in the stainless steel-packed biobarrier, and from 86.6% to 99.6% in the peat moss-packed biobarrier. Effluent gasoline concentrations below 0.03 mg/l were obtained at gasoline loading rates less than 27.5 mg/l.d in the stainless steel-packed biobarrier. The remaining fraction of gasoline in the effluent consisted mainly of three aliphatic compounds and not the aromatic compounds. Both biobarrier packings supported near complete removal of the most soluble aromatic hydrocarbons of gasoline (BTEX) under all the conditions examined. The consumption of sulfate and the presence of sulfate-reducing microorganisms suggested the presence of anaerobic metabolism during the degradation of gasoline. Up to 92% gasoline was removed during the first 3 cm of the biobarriers' length.