ABSTRACT
The quality and quantity of organic matter in raw water affects the purification processes in artificial recharge of groundwater, and thus final drinking water quality. The removal of organic matter during induced recharge of artificial groundwater was studied at two Finnish bank filtration plants (Kangasala and Nokia). Water samples from lake, observation tubes and pumping wells were taken monthly over two years. The amount of organic carbon (AOC/TOC), molecular size distribution of organic carbon and microbial activity were studied. The reduction of TOC and AOC in the Lake Vesijärvi (Kangasala) bank filtration zone was 29% and 72%, respectively. In the Lake Vihnusjärvi (Nokia) bank filtration zone the reduction in TOC content was 55%, and in AOC content 40%. The highest molecular weight fractions of organic matter were removed at the beginning of infiltration. At the end of filtration the lowest molecular weight fractions were predominant. In both study areas, the reduction in organic carbon occured mostly in the littoral region. Later, during the underground passage, no remarkable decrease in AOC content occurred, whereas the content of TOC still decreased. Results suggest that in saturated, reducing conditions only minor microbial degradation will occur. The decrease in TOC probably resulted from sorption of humic substances into soil particles.
