Development of easily-controllable dairy-farming-wastewater purification apparatus using sphere-shaped perlite as bacteria immobilizing material

Abstract

An easy to control and stable performance aerobic biological treatment apparatus for dairy farming wastewater was developed. The apparatus consisted of aerobic reactor filled with sphere-shaped perlite particles (3-1.5mm in diameter) made from obsidian, and clarifier for separating excess sludge generated from the reactor. The reactor used for the experiment was 40cm in diameter and 200cm in height (effective volume 128L). Thirty liters (nominal volume) of perlite was filled in the reactor. Aeration was carried out from the bottom of the reactor with aeration intensity of 1∼9m³/m³·h. Wastewater discharged from dairy cow barn was fed to the reactor continuously from the bottom layer after separation of coarse suspended solids with screw-press type dehydrator. Concentration of biochemical oxygen demand (BOD) of the influent was 2231 ± 1278mg/L. Hydraulic retention time was about 0.4 ± 0.2 day (Ave. ± SD). Mixture liquid in the reactor was discharged by a tube pump continuously and fed to a clarifier. Overflow liquid from the clarifier was collected as effluent. Experiment was carried out for about 300 days without temperature control. The results suggest that to maintain effluent BOD of less than 120mg/L throughout a year, BOD volumetric load should be kept less than 0.5kg/m³·day. Influent total nitrogen concentration was 135 ± 40mg/L. Removal rate of total nitrogen was 69% in average and more than 80% when water temperature was higher than 15°C. It tended to increase slightly when aeration intensity was about 4m³/m³·h. To evaluate inhibitory effect of sanitation agents used for milking facilities on biological purification activity, laboratory experiment using mixed liquor collected from the reactor was carried out. The results suggest that chlorine disinfectant, acid rinse agent and alkaline detergent cleaner had no inhibitory effect when they were diluted after used with recommended concentrations more than 25, 5 and 25 times, respectively.