Investigation of the effect of water treatment plant effluent on river quality: a case study

The influx of human sewage and effluent from most industries causes numerous pollutions in rivers, and the consequences of these pollutions may endanger human health and river ecosystems. In order to determine the effect of effluent on Karoun water quality, five sampling stations were considered. The first, third, and fifth stations were determined on the river, i.e., from Sheyban (upstream) to the Daghagheleh (downstream) treatment plant, on the other hand, the second and fourth stations were specified at the entrance of the treatment plant effluent to the river. Sampling was done monthly in four seasons from January 2020 to December 2020. Based on the values measured at the stations, the seasonal and annual quality index was calculated for each station, and then the different stations were classified based on the water quality index (WQI) system. According to the results, the annual quality index in different stations ranged from 524.79 to 648.93 (fourth group). On the other hand, comparing the results between the stations located on the river also shows that the water quality from the first to the fifth station is almost declining.