Integrating an intermittent aerator in a swine wastewater treatment system for land-limited conditions
Yang, P.Y., and Zhiyu Wang
A full-scale swine (300 pigs) waste treatment system–including a solid/liquid separation unit (3m3) with solids holding tank (1.2 m3) and a liquid holding tank (20 m3), two anaerobic reactors (10 m3 each) in series, an intermittent aeration unit (20 m3), and a sluge dewatering bed (17 m2)–was used to investigate the impact of integrating an intermittent aeration unit on the overall process performance of the swine waste treatment system. The intermittent aeration unit was used for the treatment of a combination of raw liquid manure and anaerobically treated concentrated manure. Four optional ratios of aeration time to nonaeration time of 60:36, 5:1, 4:2, and 3:3 hours were investigated. At a hydraulic retention time of 3.2 days and a ratio of aeration to nonaeration of 3:3 hours, the removal efficiencies for 5-day biochemical oxygen demand (BOD5), total-nitrogen (T-N), total suspended solids (TSS), and total-phosphorus (T-P) were 98.0%, 92.4%, 95.6%, and 59.4%, respectively, for the intermittent aeration unit. Effluent concentrations of BOD5, NO–3-N, NH+4-N, and TSS were 35+12, 2.6+0.8, 36+28, and 78+13 mg/l, respectively. The impact of integrating an intermittent aeration unit in the overall swine waste treatment system, which included solid/liquid separation, anaerobic treatment, and final sedimentation/polishing units is apparent from its high treatment efficiency for BOD5 and T-N. Economic evaluation of the swine waste treatment system integrating an intermittent aeration unit was conducted based on 300, 1,000, 2,000, 3,000, and 5,000 pigs. It was found that the utilization of biogas and digesting sluge is essential for the benefit or the profit of operating this treatment system. Integrating the intermittent aeration unit in the swine waste treatment system provides reduction of energy consumption cost and reuse/disposal of treated wastewater without causing deterioration of environmental quality. The integrated system also provides the possiblity of developing a fabricated-packaged treatment plant of a central swine waste processing system for application in land-limited tropical/subtropical areas.