The Impact of Low Temperature on the Efficiency of Coagulation/Flocculation Process in Drinking Water Treatment

The final stage of the drinking water treatment process yields two distinct outputs: treated water and the resulting sludge. This sludge is composed of raw water impurities, coagulation and flocculation agents, and various other additives. In any volume of processed drinking water, the continuous production of sludge is not negligible, leading to a significant environmental impact. This is particularly concerning when aluminium-based agents are used, as these compounds are strongly implicated in potential detrimental health risks. This situation is significantly worsened when raw water temperature approaches zero, as the treatment process efficiency is greatly diminished. Drinking water treatment at low temperatures faces a culmination of adverse effects, including a lower rate of hydrolysis and a reduced floc size, both of which negatively impact sedimentation. An effective strategy for suppressing the high dosing of chemicals is the suitable choice of ratio between acidity and the basicity of the treated water. Simply maintaining the pH value that was optimised for higher temperatures is detrimental, leading to, among other issues, increased sludge accumulation. Therefore, attention should instead be concentrated on the pOH value. A simple algebraic relation is proposed for converting the optimised pH value for higher temperatures to an optimum value for more moderate or low-temperature conditions. The application of this method results in a reduction in the amount of chemical agents required and consequently a reduction in the volume of sludge produced.