Fundamentals of Chemical Coagulation and Precipitation

Chemical treatment is considered as a useful tool for (a) pretreatment of harmful wastes, (b) early removal of undissolved precipitating substances, (c) reduction of load fluctuations, (d) combating bulking activated sludge, (e) polishing effluents, and (f) phosphorus removal. Chemical treatment as a rule means addition of chemicals. Such chemicals are usually inorganic (such as iron or aluminum salts) or organic (such as cationic, anionic, and non-ionic polymers). These chemicals cause precipitation and/or aggregation (i.e., coagulation and flocculation) of the suspended phase in the wastewater system under consideration. The addition of chemicals in the phase of chemical treatment changes water constituents into a form that improves removal by all liquid-solid separation processes.