Evaluation of Hablehroud River Water Quality Using Iran Water Quality Index for Surface Water Resources-Conventional Parameters (IRWQISC) and Response Surface Methodology

The purpose of this study is to evaluate the quality of the Hablehroud river in Semnan based on the Iran Water Quality Index for Surface Water Resources-Conventional Parameters (IRWQISC). Eleven parameters of COD, BOD5, dissolved oxygen, electrical conductivity, Fecal coliform, ammonium, nitrate, phosphate, turbidity, total hardness, and pH were monitored during four seasons from winter 2020 to autumn 2020 in three sampling stations; upstream of Bonkooh village (A), downstream of the village (B) and Deh Sarab (C). The highest value of IRWQISC was 55.6 in Station A in summer and the lowest value was 40.4 in Station B in winter. The water quality of the river in Station A in summer was therefore better than the other stations and other seasons. To investigate the effect of each parameter on the water quality index and also to investigate the interaction of the above-mentioned parameters, the experiment was designed in the three studied stations in summer by using the Design Expert software. First, the parameters that had a greater effect on the IRWQISC value were screened by the Plackett-Burman method and then the RSM-BBD method was used to analyze the data. The parameters of EC, phosphate, nitrate, turbidity, and pH had the largest contribution in the IRWQISC with respective values of 51.61%, 23.13%, 14.44%, 3.17%, and 2.38%. The coefficient of determination (R2) using the BBD method was 0.9982 which indicates that the model is valid.