Effects of Effluent from Sewage Treatment Plant on Periphytic Algae of Rivers.

Abstract

Effects of effluent from sewage treatment plant on periphytic algae were surveyed five times in the Rivers Tsunaki and Hirose during 1993-1994.
The River Hirose is a symbolic river flowing through Sendai City and the River Tsunaki is a branch of that. In the sewage treatment plant an ozone treatment (injection rate: 4mg/l) is used for disinfection of effluents, the sewerage flowing into the River Tsunaki.
The periphytic algae and water quality were surveyed at three stations in both rivers. At all the stations the bacillariophytes were major, especially Cymbella minuta, Navicula lanceolata and Navicula gregaria were observed at most stations.And Nistzschia palea, which needs continuously elevated concentrations of organically bound nitrogen, appeared at the down stream stadons of discharging point. On the other hand the diversity index of periphytic algal communities receiving other sewage became higher than before. This indicates that the effluent from sewage treatment plant improved the periphytic algal communities at polluted places.