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.

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An alum coagulation treatment facility employing mixing, flocculating, and settling units, designed by criteria commonly used in the design of water treatment facilities, was operated to determine whether or not it could effectively remove algae and other suspended matter from raw sewage stabilization lagoon effluent. Algal sludge produced by the treatment facility was investigated: (1) to evaluate its potential as a soil conditioner; (2) to determine whether a stabilization lagoon could be used for algal sludge disposal; and (3) to determine whether or not sludge recirculation would reflect a chemical savings. The experimental lagoons and treatment facility, owned by Sanitary District No. 1 of Pima County, Arizona, were located near Tucson, Arizona. It was found, in a field study, that mixing, flocculating, and settling units commonly used for water treatment were efficient in clarifying lagoon effluent and produced a water with the appearance of tap water. Active photosynthesizing algae, producing high oxygen concentrations in lagoon effluent, caused flotation of alum coagulated algal sludge; however, by selecting lagoon effluent low in dissolved oxygen content, algal sludge flotation in the treatment facility was prevented. Algal sludge with Less than one percent total solids was readily dewatered in three days by sand bed drying. Resuspension of air dried algal sludge resulted in a maximum moisture uptake of 50 percent of the final wet weight. Dry algal sludge contained 47 to 61 percent volatile solids, 1.6 to 5.2 percent total phosphorus, and 3.6 to 4.9 percent organic nitrogen. No significant amount of ammonia nitrogen or nitrite-nitrate nitrogen was present in the sludge. The composition and characteristics of dry algal sludge indicate applicability as an aid to soil conditioning. For three months the characteristics of a lagoon used for algal sludge disposal were compared with a control lagoon operated in parallel; it was found that the returned algal sludge was not detrimental to the stabilization process. Acid treated and non-acid treated algal sludge produced from completely treated lagoon effluent had a clarifying value when reused with alum to coagulate effluent, but neither acid treated nor nonacid treated sludge produced from partly treated effluent caused additional clarification when returned with the same coagulant dose that initially produced the sludge. None of the different types of return sludge investigated had a clarifying value when returned under operating conditions necessary to obtain a coagulant savings.

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