Fundamental chemical aspects of coagulation in drinking water treatment – Back to basics

Coagulation is a fundamental process at many drinking water treatment plants (DWTPs) worldwide. It is a long-established water treatment technology but is continuously revisited for the removal of emerging pollutants. Additionally, novel coagulants are being invented and tested. This paper summarises key chemical aspects of coagulation with important implications for current research in this field. To better explain the fundamentals of coagulation, results of coagulation of surface raw water that serves as a DWTP supply are presented. Besides the identification of optimal coagulation conditions that could be recommended for the corresponding DWTP, the results distinctly illustrate the elaborated aspects of coagulation. Those include mainly: (i) the importance of the solution pH, which usually governs the coagulation behaviour of both pollutants and coagulants and is in turn simultaneously affected by them; (ii) the need to assess different coagulants carefully, considering their complete composition and hydrochemical properties; and (iii) the significance of removing not only the target pollutant but also coagulant residuals. In general, this paper contributes to better interconnection between the known fundamentals of coagulation, its current use, and its future prospects.