On the importance of pH value in coagulation

Many studies have overlooked the role of pH in optimizing coagulation. Herein, the authors emphasize the importance of pH value in coagulation during the production of drinking water. We investigate the influence of pH value on the surface charges and forms of coagulants and impurities intended for removal. A methodology is suggested for optimizing key parameters for efficient coagulation - coagulant dosage and pH value. The study points out that various optimal pH ranges are required for coagulation of specific impurities and their mixtures. For natural organic matter of both humic and algogenic origin, acidic pH values are favourable for their removal through charge neutralization mechanism. Algal cells are effectively coagulated at slightly acidic to neutral pH values due to interactions with coagulant hydroxide precipitates. Inorganic particles are eliminated preferably at around neutral pH values. When mixtures of impurities are coagulated, mutual interaction between the impurities may impact dose of coagulant and also optimal pH ranges.