Survival and transfer of faecal indicator organisms of wastewater effluents in receiving lake waters

Abstract

Water of Lake Kallavesi, which receives wastewater effluents, is used for abstraction of drinking water, for swimming and fishing. It is also used directly for washing and drinking water, both for humans and cattle, especially in summer time. These are the reasons for the present study to follow survival and transfer of faecal indicators downstream from the wastewater treatment plant Samples were collected in winter and summer from the bottom of the lake at deep sites. At some of the sites the vertical distribution of microbes in summer was also studied. Indicators determined were faecal coliforms, enterococci, sulphite-reducing Clostridia and coliphages. The farthest point was 35km for bottom samples. All the indicators could be found in sampling sites near to the discharge point with relatively high numbers. At distant sample sites, coliphages or enterococci were the most abundant. In the winter, coliphages were found up to 18km from the discharge point. In summer, indicators survived well. The results suggest that the direct use of lake water could be considered a health risk.