A multicriteria decision-making model for the selection of conventional/hybrid coagulants in water treatment

The coagulation process is a well-known process that has been used in water treatment for many years. The coagulation process shows treatment efficiency in terms of turbidity and suspended solids removal. However, despite good results, coagulant selection is not an easy task. A coagulant can effectively remove suspended solids but, at the same time, increase conductivity; coagulants can also significantly increase chemical sludge production. The final selection of coagulants depends on the importance attributed to the parameter desired to be removed. In this study, the use of multicriteria decision-making is proposed to help select organic coagulants and hybrid coagulants, which have emerged as an alternative to inorganic coagulants in recent years due to the disadvantages of chemical coagulants and whose use and variety are increasing. Therefore, starting from the parameters determined by coagulation process results, these techniques allow weighting these parameters according to the judgments of drinking water treatment plant professionals and determining priorities among coagulants. The agreement between the obtained results and the literature shows that the analytical hierarchy process (AHP) method is a useful tool for selecting coagulants. According to the results of the AHP matrix created with four criteria and nine alternatives, it was found that hybrid coagulants with similar performance to inorganic coagulants have not yet been adopted by drinking water treatment professionals. This may have been due to the higher price of hybrid coagulants and the fact that they are not yet widely used in the drinking water industry. Key points The process of selecting a coagulant for water treatment is complex; however, hybrid coagulants have emerged as alternatives to traditional inorganic options but face challenges in adoption due to higher costs and limited use in the water industry.Because the analytical hierarchy process (AHP) allows structured decision-making in multicriteria contexts by considering both qualitative and quantitative factors, in this study, the AHP method was used to evaluate and rank the coagulants according to four criteria (technical, environmental, economic, and social).Inorganic coagulants like ferric chloride demonstrated superior performance in turbidity removal; however, hybrid coagulants showed potential for environmental sustainability due to reduced sludge production and biodegradability, making them viable alternatives for future applications.The study emphasizes the importance of the technical criterion, with the highest weight (56%) in coagulant selection, while noting that small changes in criteria weights can significantly affect rankings, highlighting the need for careful prioritization in water treatment decisions.