Enrichment of degrading microbes and bioremediation of petrochemical contaminants in polluted soil

Soil at a site near Zibo City, China, is polluted with hydrocarbons at concentrations up to 200 g kg−1 dry soil. Samples contained 107 microbial cells g−1 dry soil, and the concentration of aerobic degradation bacteria is 107 cells g−1 dry soil. The most active species were Xanthomonas, Bacillus and Hyphomicrobium. The nitrogen and phosphorus contents of the polluted soil are typically 0.1%, and are sufficient to sustain natural or enhanced biodegradation. The BAC (Biological Activated Carbon) system was used to enrich indigenous microbes to enhance bioremediation rates in the laboratory. The BAC used the large surface area and sorption characteristics to fix bacteria and media, and effectively culture and enrich the microbes. Effluent from the BAC system contained up to 4×1011 cells ml−1, and was introduced to the contaminated soil to enhance biodegradation. The results indicated that the natural biodegradation rate of the petroleum hydrocarbons is lower than the BAC enhanced bioremediation rate, 1.7% as opposed to 42% in 32 days.