Reduced domestic water use

Abstract

Domestic waste water from toilets, showers, garbage grinding, and kitchens was characterized in terms of waste concentration and volume in order to formulate four representative synthetic domestic wastes. The synthetic waste formulations were used to simulate concentrated domestic wastes flowing from dwellings whose water use has been reduced by the use of water saving devices such as low flow toilets and showers. Biological treatment of wastes with Chemical Oxygen Demands (COD) of up to 1500 mg/1 using activated sludge was investigated with both bench scale batch and continuous processes. Specific items investigated as functions of waste concentration included substrate removal rates, oxygen uptake rates, aeration properties, sludge settling, sludge aeration time, and aeration tank turbulence. Substrate removal rates were not enhanced by increasing domestic waste concentrations although oxygen uptake rates did increase slightly due to possible differences in sludge yield. The minimum sludge aeration time was found to be between 12 and 16 hours per day. Increasing mixing intensity in the aeration tanks reduced sludge settling ability without significantly improving the substrate removal rate. Aeration properties of systems treating wastes at 1500 mg/1 COD were found to be inferior to those of systems treating wastes at 750 and 250 mg/1 COD. No significant differences were observed between systems treating 250 and 750 mg/I COD wastes. Results indicate that reducing the flow of water from domestic residences reduces treatment costs only so far as that afforded by the reduction in clarifier size and pumping costs.