Phosphate removal such as orthophosphate, from municipal wastewater has become an environmental necessity, since the excessive phosphate ion content in municipal wastewater causes water eutrophication. According to environmental protection organization of Iran, maximum permissible concentration of residual phosphorus in treated municipal wastewater is 1 mg/L P. Almost all the phosphorus in natural water and wastewater is available in the form of phosphate. Phosphorus compounds in wastewater, after hydrolysis and biodegradation, change to solution orthophosphates. In this research, poly aluminium chloride and bentonite clay as nature coagulant were added and with low chemical cost, bentonite effect in improving poly aluminium chloride in municipal wastewater treatment, has been investigated. The research is a bench scale experimental type. Samples were collected from influent wastewater to primary and effluent of secondary clarifier and then effect of pH and dose of coagulant investigated on orthophosphate removal efficiency. The result show optimal conditions of compound of polyaluminium chloride and bentonite for removal of orthophosphate, COD, BOD and TSS in pH = 7 and optimal dose 15.55 mg/L polyaluminium chloride and 5.55 mg/L bentonite in influent wastewater to primary clarifier has been obtained 71.83, 46.1, 48.9 and 63.5 %, respectively. Under optimal condition, orthophosphate concentration was reached to 1 mg/L. So this compound coagulant, in lowest dose and consequently chemical cost decrease, was selected as suitable coagulant in removal of orthophosphate of effluent of treatment plant.
Ecosystem sustainability has been widely considered in planning of water resources in the recent years. In this study, variations of macroinvertebrates is considered as a criteria for assessing biological diversity in the downstream river in a river-reservoir system. Unlike most of the previous studies, this biological diversity index is then used in a multi-objective reservoir operation optimization model as an objective function instead of a constraint. Aboulabbas Dam in Khuzestan Province in Iran was chosen as the case study of this research. Two objectives of supplying water demand and ecological diversity were maximized for the case of Aboulabbas Dam. Based on the historical records of water quality and macroinvertebrate samples, a relationship between these two parameters was proposed. Multi Objective Particle Swarm Optimization (MOPSO) was used as the optimization algorithm and water quality variations has been modeled by linking WQRRS (Water Quality for River Reservoir Systems) model with the optimization model. Evaluation of the results in a 10-year period and comparison with single-objective optimization shows that using the proposed methodology, in addition to taking into account the water quality variations in its impacts on the river ecosystem, provides an acceptable level water supply reliability.
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