Interactions between sludge conditioning, vacuum filtration, and incineration

A laboratory study of sludge disposal at the Metropolitan Wastewater Treatment Plant demonstrates that the total cost for fuel and chemicals is affected greatly by the type and dose of conditioner and the operational variables of vacuum filtration. Laboratory analyses employing specific resistance, capillary suction time, and filter leaf measurements show that (1) the predominantly waste activated sludge processed at the treatment plant requires at least 5 percent ferric chloride and 15 percent lime; (2) ferric sulfate and lime are not nearly as effective as ferric chloride and lime; (3) sludge solids yields increase with an increase of ferric chloride dose from 5 to 8 percent with a concomitant lime increase from 15 to 24 percent; and (4) the total solids content of the cake increases with an increase in the ferric chloride dose from 5 to 10 percent with a concomitant lime increase from 15 to 30 percent. Thus, polyelectrolyte conditioners have an inherent advantage over inorganic and inert conditioners (sludge ash).