Study on the influence of treated wastewater upon the water quality of Lake Togou.

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Togou Twon at situated about 30 km west of Tottori city in Tottori Prefecture determined to protect Lake Togou from water contamination and to built the sewage treatment plants which purify the wastewater from rural areas. The town authority has already constructed four plants.The results are described as follows.First, with respect to organic contamination indices BOD and COD, both plants of Miyauti and Hanami purified the influent of BOD 100-150 ppm into the effluent of 15-20 ppm, which meet the criteria of under 20 ppm. In COD respect, Hanami and Miyauti plants gave the effluents of about 20 ppm and about 10 ppm throughout the year respectively. Then, we can say that both plants show the good performance on removal of organic matter.Second, the influence of effluents upon the river water are described. Comparing the river water at lower point with that at upper point of river where the treated water is discharged into, we find out that the difference of water quality at both points is very samll. Then we can say that the influence of effluents is little.Third with regard to total nitrogen, both plants gave the effluents of about. 20 ppm which meet the criteria of under 20 ppm. The denitrification is higher in Summer and lower in Winter. Comparing the total nitrogen at lower point with that 4t upper point the difference is also as small as COD and BOD. The same result is true of tatal phosphorus.Finally, we can say that both plants are very useful to purify wastewater and to protect The lake, Lake Tozou is said to be a closed water territory. We need to make more efforts for future to protect and to improve the water quality of Lake Togou.