Evaluation of Natural and Chemical Coagulants Performance in Treatment of Municipal Wastewater of Behshahr City

Municipal wastewater is one of the largest volumes of wastewater which contains various organic compounds from proteins and fats to carbohydrates and nucleic acids. Municipal wastewater of Behshahr city (Mazandaran, Iran) was evaluated using aluminum sulfate and iron chloride as chemical coagulants and pectin and sodium alginate as natural ones. Biological oxygen demand was investigated at different temperatures and coagulant concentrations. The fraction of full factorial statistical method and Qualitek-۴ software were applied for designing experiments and analyzing the results to determine the optimal conditions for achieving the highest reduction in wastewater organic load and biological oxygen demand. In the case of biological oxygen demand, the optimal condition was achieved at ۲۵°C, using ۱, ۰.۰۲, ۱.۵ and ۱ g/L of aluminum sulfate, sodium alginate, iron chloride and pectin, respectively. Under the optimal condition, the percentage of biological oxygen demand reduction was equal to ۳۴.۵%. Maximum BOD removal of ۴۰.۹% was obtained at ۲۵°C using aluminum sulfate, sodium alginate, iron chloride, and pectin at concentrations of ۰.۶, ۰.۰۲, ۱.۵, and ۶ g/L, respectively. The contribution of aluminum sulfate, sodium alginate, iron chloride, and pectin concentration in biological oxygen demand removal of the studied wastewater was ۳.۸%, ۲۲.۴%, ۱۶.۳%, and ۱۴.۴%, respectively. Coagulation temperature and aluminum sulfate concentration with approximately ۴۲.۷% and ۳.۸% contribution values were determined as the most and the least effective factors in biological oxygen demand reduction.

Keywords:

Biological oxygen demand , Coagulation , Municipal wastewater , Taguchi approach