Surfactant Enhanced Bioremediation Of Typical Soils Contaminated With Organic Compounds

Surfactant enhanced bioremediation (SEBR) has been reported as a promising technique to remediate soils contaminated with hydrophobic organic compounds (HOCs). Recent studies found that surfactants can enhance desorption of HOCs from soil matrix to solution and facilitate the biodegradation of HOCs. However, the effect of surfactants on the degrading activity of native microbiota during SEBR is rarely documented. A better understanding of microbial communities in response to different surfactants is expected to provide clues about the type of microbes and functional genes for successful SEBR. In this thesis, the shifts in microbial community structure and activity during SEBR were investigated. Accordingly, efficient and economic SEBR techniques were developed for soils contaminated with polycyclic aromatic hydrocarbons (PAHs) and organchlorinated pesticides (OCPs). The main results of this thesis are summarized below:(1) Surfactants induce advantageous shifts in indigenous micro flora living in PAH-contaminated soils. The three commonly used surfactants promoted the growth of bacterial biomass (10-15 times of control) and bacteria were the dominant microbial group (including bacteria, fungi, actinomycetes and protozoa) in SEBR. Bacterial composition was modified to the proliferation of Bacillus, Pseudomonas, and Sphingomonas (2-3 times of control). The phospholipid fatty acids profiling the transmembrane fluidity were enriched and concomitant functional genes, such as 1-hydroxy-2-naphthoate dioxygenase and PAH dioxygenase large subunit significantly increased after the surfactant applications (p< 0.05). Thus, the community structure and activity of bacteria involved in the biodegradation were ameliorated by surfactants.(2) Efficient and economic techniques for remediating HOC-contaminated sites were developed and applied on PAHs/OCPs-polluted sites. In situ SEBR showed high efficiency on the PAH-contaminated sites. For instance, rhamnolipids (a biosurfactant) is efficient and ecofriendly for soil remediation.10 mg/kg rhamnolipid achieved the best biodegradation rate of 95% after 90 days. In addition, the OCP-contaminated sites were remediated by surfactant- enhanced elution combined with enhanced bioremediation. Soil was washed once by surfactant solution, and then the remaining soil was piled up. The surfactant residual in the soil stimulated the growth of microbial community by 2-3 times, promoting the degradation of remaining OCPs. Therefore, the effectiveness of surfactant use was improved by enhancing the remediation efficiency while reducing the remediation cost.