THE USE OF SOLUBLE ORGANIC POLYMERS IN WASTE TREATMENT

Organic polymeric flocculants have been used in water purification for several decades as coagulant aids or flee builders, after the additio n of inorganic coagulants like alum, iron salts or lime. The increased use of cationic polyelectrolytes as primary coagulants instead of ino rganic salts, which has occurred in recent times, arises from their si gnificant inherent advantages. The main ones are faster processing, a lower content of insoluble solids to handle, whether by sedimentation, filtration, flotation or in biological conversion, and a much smaller sludge volume. Polymers have often been used in chemically assisted s edimentation of sewage solids to enhance the removal of suspended matt er. The concept is applicable as well to the primary coagulation of in dustrial wastewaters where the separation may be based on flotation, a s id examples from the leather, steel, wool scouring, cosmetic, deterg ent, plastics, dyehouse, paper, food processing and brewing industries . A cationic polymer of particular charge density is optimal, and hydr ophobically modified polymers have relevance in the case of oil and gr ease removal. The burden of solids which must be floated is much reduc ed relative to systems utilising inorganic coagulants, and the dosage of chemicals overall is lower. In some cases the addition of some inor ganic coagulant is unavoidable, as in the case of highly coloured effl uents; in others, an anionic surfactant is needed to facilitate flotat ion. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd.