Determination of sorption characteristics of aluminum hydroxide sludge formed at the stage of pre-purification of water treatment plant

Abstract

An urgent task of the research is to describe the properties of the sludge formed during coagulation depending on the type of water supply source. Namely, the aim is to study the sorption capacity of the sludge for the main components removed from the water (iron compounds, organic substances, and silicic acid compounds). This indicator allows you to directly determine the effectiveness of the coagulation. When comparing the actual values of this indicator with practically obtainable values, one can say about the lack or excess of the coagulant supplied for processing. To calculate the specific sorption capacities of the sludge, the following indicators have been used: organic content, the weight concentration of silicic acid compounds in terms of SiO2 and the weight concentration of iron compounds in terms of Fe. After drying and calcining the sludge, the resulting mineral residue has been dissolved in the solution, and the content of the final components was determined. Conventional water analysis methods have been applied. For the first time, a method is proposed to determine the specific sorption capacities of aluminum hydroxide sludge for organic compounds, for iron compounds in terms of Fe, for silicic acid compounds in terms of SiO2. A classification of natural low-turbidity waters with an increased content of iron-organic compounds is proposed. Within the framework of the proposed classification of waters, the authors have obtained previously undetermined actual specific sorption capacities of the sludge. Recommendations have been given to get practical importance values of the sorption characteristics of the sludge. The proposed method to calculate the sorption capacity of aluminum hydroxide sludge and index of sorption capacity of the sludge are recommended to be used as a parameter that determines the conditions and efficiency of application of the aluminum sulfate coagulation technology. Excessive doses of the coagulant that provide a sorption capacity of the sludge greater than the recommended values, lead to an excessive consumption of both the reagent itself and purge water. Thus, some measures can be taken to bring the sorption capacity of the sludge to practically achievable values, for example, aquatic acidification.