Design and assessment of an innovative swine waste to renewable energy system

The greater reliance on concentrated animal feeding operations (CAFOs) for livestock production presents both environmental challenges and opportunities for renewable energy and resource recovery. In this article, the design, economics of construction and operation, and environmental process performance of an innovative swine waste to renewable energy management system are presented and discussed. The system was installed at a feeder-to-finish swine CAFO permitted for 8,640 head of swine. It is comprised of an in-ground 7,600 m3 anaerobic digester that receives the hog manure and generates biogas that is used on-site for renewable energy generation in a 65 kW microturbine. The effluent of the anaerobic digester is further treated biologically in a 4,200 m3 intermittently aerated basin, providing both organics removal and some nitrogen control. Water from that basin recharges and flushes the pits in the animal barns. The system has been operational for over two years and is efficiently converting swine manure to biogas. The biogas production rate typically fluctuates seasonally from 350 to 900 m3 d-1. The overall chemical oxygen demand (COD) and biochemical oxygen demand (BOD) removal are 92% and 99%, respectively, while total nitrogen removal is about 77% and total phosphorous removal is 82%. Thus far, carbon offset and Renewable Energy Certificate (REC) production have averaged 2485 offsets and 385 RECs per year when running without issue. The overall cost per 1,000 kg of steady-state live weight (SSLW) per year was estimated at 462, a value that is competitive as an environmentally superior technology. Overall, this large-scale project illustrates the significant potential of this system while simultaneously highlighting the important economic challenges of waste-to-energy bioprocesses.

Duke Scholars

Author Marc Deshusses Civil and Environmental Engineering