WASTEWATER TREATMENT, ENERGY PRODUCTION, AND ENERGY CONSERVATION IN AN ALGAL-BACTERIAL SYSTEM

Quantitative data on the operation of an integrated photosynthetic wastewater treatment system are presented. The system was designed to treat wastewater concurrent with the production of microalgae biomass from waste nutrients and the conversion of that biomass to fuel. The proposed system involves retention of nutrients within the system to increase the biomass production potential of a given rate of nutrient inflow. The components investigated in this study were the algae growth ponds, harvesting ponds, anaerobic digesters, and algae regrowth on effluents from the anaerobic digesters.;Two 32 m('3) settling ponds were operated for the same 16-month period. The ponds were operated on a fill and draw basis to recover biomass from the growth pond effluents. The settling data collected in these ponds were augmented by 24-hour settling tests in Imhoff cones in the laboratory and by settling rate measurements in plastic cylinders in the laboratory. With some exceptions, suspended solids removals of 70 to 85% were achieved by 24-hour settling in Imhoff cones. The removal efficiency in the large settling ponds was consistently less than in the Imhoff cones. Mean settling rates were typically 10 to 30 cm/hr, but rates from 0 to 74 cm/hr were observed on isolated occasions. The dissolved BOD concentration in the settling pond effluent was generaly less than 10 mg/l. Total BOD was roughly proportional to suspended solids concentration.;The algal-bacterial solids recovered in the settling ponds were subjected to anaerobic digestion in bench scale (16 L) digesters to determine methane yield and volatile solids destruction under various conditions of temperature, feed solids concentration, and hydraulic detention time. The specific gas production obtained from the fresh algal-bacterial sludge was found to be 0.39 liters of total gas/gram of volatile matter added. At 30 days detention time a 17% reduction in gas production was observed at 25(DEGREES)C compared to 35(DEGREES)C. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of school.) UMI;Two 1080 m('2) high rate algae growth ponds were operated for 16 months at detention times of 2.0 to 8.0 days and depths of 20 to 50 cm. BOD loadings ranged from 25 to 350 kg/HA-day. The growth medium was settled municipal wastewater. The biomass production in the most productive pond averaged 38.33 g/m('2)-day during the most productive 30-day period. The measured volatile solids production in that pond was 79.3 metric tons during one calendar year (Jan. to Jan.). Peak productivity was found to be limited by the availability of carbon, even in heavily loaded ponds.