In order to treat piggery wastewater from pig farms, the piggery wastewater treatment plant that consisted of filtration bed, aeration bed, and constructed wetlands (aerobic and anaerobic beds) was constructed. The optimum conditions were investigated in piggery wastewater treatment plant. Average removal rates of pollutants were investigated in piggery wastewater treatment plant during 22 months. To obtain treatment trends of pollutants in piggery wastewater treatment plant, treatment efficiency of pollutants under different types of fraction were investigated for treating piggery wastewater. The optimum filtration time in filtration bed with water plant was 90 min, the optimum hydraulic time in aeration bed was 16 hour, the optimum piggery wastewater loading was 800 L m-2 day-1, and the optimum injection method was continuous injection.
The concentrations of COD (Chemical oxygen demand), SS (Suspended solid), T-N (Total nitrogen) and T-P (Total phosphorus) in inflow were 10,246-20,833, 10,324-28,410, 587-1,750, 7,987-7,225 and 697-895 mg L-1 in piggery wastewater treatment plant during 22 months, respectively. In piggery wastewater treatment plant during 22 months, the concentrations of pollutants in effluent were 26.4-278 mg L-1 for COD, 21.8-125 mg L-1 for SS, 31.2-165 mg L-1 for T-N, and 3.41-13.1 mg L-1 for T-P, respectively.
In piggery wastewater treatment plant, average removal rates of COD, SS and T-P on seasons were above 98, 99 and 99%, respectively. The removal efficiencies of T-N in hot season (summer and autumn) were higher than those in cold season (spring and winter).
The removal velocities of COD and T-N were rapid in 1st treatment bed, and the removal velocities of SS and T-P were rapid in 3rd treatment bed. The concentration of COD in effluent by fraction was 71.5 mg L-1 for soluble COD, 142 mg L-1 insoluble COD. The concentration of SS in effluent by existing form was 102 mg L-1 for volatile SS, 15.5 mg L-1 for fixed SS. The concentration of T-N and T-P in effluent by existing form were 12.8 mg L-1 and 3.05 mg L-1 for dissolved form, 35.0 mg L-1 and 1.93 mg L-1 for suspended form.