An on-farm swine waste management system in Hawai‘i
Yang, P.Y., and C. Gan
A prototype of a swine waste treatment system for a 20- to 25-sow operation was investigated for its potential for odor control, byproduct utilization, and treated wastewater reuse. The high solid portion of the swine waste ranging from 4% to 8% total solids was treated and stabilized by the anaerobic process with a hydraulic retention time (HRT) of 32 days. The diluted liquid portion from raw and anaerobically digested swine wastewater was effectively treated by the aeration and sedimentation units with an HRT of 3 and 4 days, respectively. The overall removal efficiency of 89% to 95.4% for total chemical oxygen demand (TCOD), 82.3% to 88.5% for total Kjeldahl nitrogen and 81.2% for total-phosphorus was achieved. The treated effluent was reused for irrigation of pasture without any negative impact of odor problems. Also, it meets the requirements of the wastewater reuse criteria, R-3, issued by the Hawai‘i Department of Health. The economic analysis was conducted by calculating the net present worth. It was found that the capital cost is the major cost for the proposed treatment system. The reuse of biogas as energy and sludge as fertilizer are the key factors as to whether or not it will turn the treatment system into a profit. More than 830 pigs (or approximately 80 sows) are required to achieve the breakeven point for the application of the swine waste treatment system. Thus, a profit could be made with the application of this treatment system to more than 830 pigs if the comprehensive utilization of methane gas and stabilized sludge could be realized.