BIOREACTOR TREATMENT OF CONTAMINATED GROUND WATER

J.A. Puhakka Institute of Water and Environmental Engineering, Tampere University of Teachnology, P.O. Box 541, FIN-33101 Tampere, Finland

Remediation of groundwater aquifers often involves a combination of many unit processes aiming at containment of the contaminant plume and converting the harmfull chemicals into less harmfull compounds. Unit processes may be applied in situ, on-site or ex situ. Bioremediation refers to the use of biodegradative processes to oxididize or reduce the contaminants into innocuous end products. Bioreactor applications for contaminated groundwater are on-site processes and often combined with pumping arrangements for plume containment. Bioreactor treatment is a common ground water remediation process in many countries whereas in Finland only a few applications exist. One of the major environmental factors affecting the applicability of bioremediation of Finnish ground waters is their cold temperature typically ranging from 5 to 8 oC.Mechanical wood processing is an important industrial activity in Finland. Many harmful chemicals for wood preservation or impregnation have been used in large quantities by this industry. Chlorophenols are the most common wood preservatives used in Finnish sawmills. The improper handling has often resulted in releases of chlorophenols into the environment. They are very common soil contaminants and in some cases also serious contamination of the saturated subsurface has been observed. The case site presented in this paper is a small Kärkölä municipality in Southern Finland where a serious ground water contamination was observed in 1987. The heavily contamninated plume is at least 100 000 m3 containing over 3 000 kg of chlorophenols. Typical chlorophenol concentrations in the ground water range from 10 to 40 mg/l. This site was the first large-scale contamination case in Finland that received wide public attention. It also served as a stimulus for starting contaminated soil and ground water remediation research and development in the country. Our team at the Tampere University of Technology started chlorophenol remediation research in 1987. This work resulted in a full-scale, on-site, high-rate, fluidized-bed process which operates at ambient temperatures. This process has now been used over three years for pump and treat remediation of Kärkölä ground water. This pump and treat application contains the plume from spreading and has decreased the the average chlorophenol concentration to below 10 mg/l. So far, approximately 50 000 m3 of ground water has been treated with 95 to 99 % mineralization of chlorophenols. During steady-state operation, the chlorophenol concentratrion in the treated effluent remains at below 50 (g/l. The operation costs are 4 to 8 FIM/m3 of groundwater or 04 to 0.8 FIM/g of chlorophenol removed. Our on-going pilot-experimentations focus on combining an in situ bioremediation process with the existing on-site treatment in Kärkölä. This work includes fundamental studies of the microbiology and microbial ecology of the contaminated saturated subsurfaces.