Polymers as Coagulants for Wastewater Treatment

Coagulation is a well-known, widely used process for wastewater treatment. Various coagulants have been used over the years, such as alum for commercial, large-scale water treatment plants. But there are certain disadvantages of these materials, such as large dosages, high pH sensitivity, and residual aluminum in treated water, which raises serious health concerns. Though synthetic polymers were found to be better than metallic salts on these counts, many countries across the world have laid strict regulations on the use of synthetic polymers due to their toxic nature, non-biodegradability, and residual polymer/monomers in treated water, which cause health problems. Biopolymers, on the other hand, are safe and non-toxic in nature, easily available and have shown promising results in terms of high removal efficiency and excellent selectivity toward metals and toxic substances. But their shorter shelf life and higher dosage requirement are an offset for their wide acceptance. Modifying biopolymers by “grafting” suitable monomers to their backbone structure overcome the known problems of synthetic polymers while improving the properties of the biopolymers. This chapter briefly describes the inorganic and organic polymers used for coagulation in the wastewater treatment industry, with a main focus on the more recent technology of grafted polymers.