Enhanced biodegradation of petroleum hydrocarbons in polluted soil

Field investigations in the Zihe valley near Zibo City, P.R.China, indicated that soil is polluted with petroleum hydrocarbons at concentrations up to 200 g kg(-1) dry soil. Total number microbes in polluted soil reached 2.9x10(7) microbial cells g(-1) dry soil, and aerobic degrading bacteria concentrations of 10(6)-10(7) cells g(-1) dry soil in different layers of the soil. The most active specious were aerobic heterotrophic bacteria, Xanthomonas, Bacillus and Hyphomicrobium. The nitrogen and phosphorus contents of the polluted soil were typically 0.1%, and were sufficient to sustain natural or enhanced biodegradation of petroleum hydrocarbons. The BAC (Biological Activated Carbon) system was used to enrich indigenous microbes to enhance bioremediation rates in the laboratory experiments. Effluent from BAC system contained up to 10(11) cells ml(-1), and was introduced to the contaminated soil to enhance biodegradation of the petroleum hydrocarbons. The results indicated that the natural biodegradation rate of the petroleum hydrocarbons, 5% in 16 days, is lower than the enhanced bioremediation rate, 28%. The enhanced remediation rate reached 42% in 32 days. The residual petroleum hydrocarbons in the soil were almost removed in 64 days.