Removal of phosphorous from waste water

Claim 1

A process for removing phosphate from aqueous waste selected from the group consisting of raw sewage, an effluent from a primary or secondary sewage sedimentation process, and a food processing factory effluent containing phosphate comprising the steps of, in order, (1) precipitating soluble and colloidal phosphate in the waste by adding a sufficient amount of an inorganic coagulant containing a multivalent metal cation selected from the group consisting of aluminum, ferrous, ferric and calcium to the waste to precipitate soluble and colloidal phosphate therefrom, (2) adding to the waste after an interval of about 15 seconds to 4 minutes a sufficient amount of a cationic polyelectrolyte which is quaternary ammonium salt of a copolymer, having a molecular weight such that at 25° C the viscosity in centipose of an aqueous solution have a pH of 6.0, containing 1% by weight of the polymer and in the absence of added salts using a Brookfield Model RVT viscometer with spindle No. 3 at 20 rpm is greater than 2000, and consisting essentially of units of ##STR2## in which R 1 and R 2 may be the same or different and are selected from the group consisting of hydrogen and alkyl, R 4 is alkylene containing 1 to 8 carbon atoms and R 3 is hydrogen and in which (b) is present in an amount of 80 to 97 mole % based on (a) plus (b) to flocculate the precipitated phosphate, and (3) subjecting the waste to a liquid-solids separation process.