Patent ID: 7291275

Claim:
A method for clarifying industrial laundry wastewater containing surfactants, fats, oil and grease (FOG), total petroleum hydrocarbon (TPH) biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), ionized metals and other contaminants while minimizing sludge, comprising the steps of: (a) adding to the wastewater a water dispersed cationic blend whose major components are effective amounts of both polydiallyldimethylammonium; chloride (pDADMAC) and aluminum chlorohydrate (ACH), the blend in a quantity of between 50 ppm and 700 ppm, to break the emulsified bond in the wastewater and produce coagulated particles having sufficient mass and cationic charge to react with an anionic polymer flocculent to be added thereafter; (b) delaying any flocculent addition by at least a predetermined time to permit the cationic blend to substantially complete the coagulation of the particles in the wastewater in step (a); (c) adding to the wastewater aqueous anionic polymer flocculent in an effective amount between about 5 ppm and 50 ppm and of sufficient molecular weight and with a charge density of at least 35% so as to react with the cationic charged coagulated particles to form flocculated waste particles of effective size to form sludge while leaving a disposable clarified water, thereby lowering the amount of sludge generated with respect to that normally generated using prior art coagulation and flocculation techniques of adding additional coagulants, flocculents, coagulant aids, flocculent aids or sludge aids, including but not limited to, poly aluminum chloride, epi-amine coagulant, bentonite clay, perlite, ferrous sulfate, ferric chloride, and diatomaceous earth; (d) separating the sludge from the clarified water; (e) passing the sludge to a plate and frame sludge press; (f) dewatering the sludge by the press, thereby forming a disposable sludge cake; and (g) disposing of the sludge cake and the clarified water.