On-Site Biodegradation of Organic Pollutants in Contaminated Soils and Groundwater

Abstract

Widespread use and improper disposal of chlorinated organic materials have resulted in contamination of soils and groundwater throughout the nation. This research focused on development of remedial technology to rehabilitate contaminated soil and groundwater. Biological treatment was chosen because it is environmentally sound and less costly than methods involving physical-chemical processes. Pentachlorophenol (PCP) was used as a model compound. A mixed microbial culture capable of utilizing PCP as a source of carbon and energy was developed from municipal wastewater treatment plant sludge. The culture was grown in a continuous flow chemostat reactor and used as the inoculum in batch and continuous flow experiments. PCP removal from contaminated groundwater and synthetic media was studied in batch tests. Complete removal and stoichiometric release of chloride ions was observed. The effects of different size sand particles on PCP biodegradation were tested to determine the rates of removal. Short and long sand columns also were tested to determine the rates of PCP removal under saturated and unsaturated flow conditions. The presence of sand particles enhanced biodegradation; small size sand particles (<25 pn) had the greatest effect. The presence of sand particles shortened the lag phase observed when the culture was inoculated into nedium containing high concentrations (-100 mg/L) of PCP. Sand columns operated in unsaturated flow conditions removed PCP more effectively than saturated flow columns. The greater effectiveness of unsaturated flow conditions appears to be due to greater availability of molecular oxygen as well as a difference in flow pattern. Enhanced adsorption of microbial cells on sand and flow of water along grain surfaces resulted in better contact between active microorganisms and PCP under unsaturated flow conditions.