AbstractsEngineering

The author presents a "state of the art" of the use of polymers for better settling in domestic waste treatment and evaluates the published research in the field. Polymers have only recently been used to obtain better settling in domestic waste treatment. Due to the number of polymer types available and to the varying compositions of domestic waste, the multitude of possible results are confusing to the practitioner. A purpose of this paper is to organize the available information so as to aid in its understanding. The most valuable function of polymers is the flocculation of the colloidal fraction of wastewater. Thus the theories of colloids and their interactions with polymers are presented. The paper summarizes the bench scale results of five researchers in some detail and includes many of their tables and figures. Results of numerous other researchers are given in tabular form. One investigator found that 0.5 mg/1 of a cationic polymer added to raw sewage caused 61% BOD and 85% suspended solids removals by settlement. Furthermore 5 mg/1 of the same polymer caused 3.5 times faster settling of activated sludge. Several investigators successfully settled bulked activated sludge with small dosages of polymer. One researcher reported remarkable improvement in settling of wastes when bentonite clay was added in conjunction with a cationic polymer. Results with the many different specific types of polymers are tabulated and compared. Cationic polymers were more successful than the anionic or nonionic polymers, and moreover the latter were only effective when multivalent cations were present. Specifically cationic polyamines and a cationic polydiallydimethylammonium were the most effective polymers which were reported in the literature. Although polymers are used at many domestic waste treatment plants today, there is a paucity of published information giving the results. The author concludes that it would be most valuable to gather and publish this information.