Effect of intermittent-cycle extended-aeration treatment on the fate of carbonaceous material in pig slurry

A farm-scale treatment plant was studied during a year. Four different aeration cycles were tested in order to observe their effects on the removal of carbon material from pig slurry. The treatment plant performance was not significantly affected by a 60% reduction of aeration times, from almost 20 h per day to 12 h per day. The high removal rates observed (over 95% in terms of BOD5) appeared to be related to the low aeration rates achieved through the intermittent operation of the aerator. The removal of solid material was more variable. Percentage removals of total solids from the liquid were between 10 and 70%. The separator low performances may have been related to the highly diluted slurry produced on the farm. However, consistent results were obtained in terms of the dry matter content of the separated material A mean value of 21.3% was obtained, with a standard deviation of 3.5. The operating costs related to treatment were estimated on the basis of energy consumption. Treatment of slurry consumed from over 150 kWh/day for 19.5 h of aeration per day to about 90 kWh/day for 12 h aeration per day. Aerobic slurry treatment cost US$2.50 per pig produced.