(46a) An Optimization-Based Approach for Developing a Circular Economy of Swine Wastewater

Swine farming generates substantial amounts of wastewater, a trend that will continue with increasing protein demand resulting from increase in global population. Swine wastewater contains high levels of organic matter, nitrogen, and phosphorus making it particularly attractive for resource recovery. Emerging advanced anaerobic biotechnologies hold promise for recovering energy, nutrients, and other value-added chemicals from high strength wastewater streams. We have previously developed a physics-based model of an integrated anaerobic membrane bioreactor (AnMBR) treatment train. AnMBR couples anaerobic digestion with a membrane unit to decouple solids retention time from hydraulic retention time thereby enabling high carbon conversion. The treatment train also consists of nitrogen and phosphorus recovery via adsorption and coagulation/flocculation, respectively. Detailed life cycle assessment (LCA) and techno-economic assessment (TEA) of this treatment train highlighted the strong effect of plant capacity on economic feasibility and greenhouse gas (GHG) emissions. Available swine wastewater is also geographically unevenly distributed because of wide variation in capacity of swine farms across the US. A holistic systems-level approach is needed to evaluate the best strategy for swine wastewater management taking into account location and capacity of swine farms, transportation costs, treatment costs, GHG abatement potential, and value of recovered products.

This work presents a comprehensive optimization-based framework for evaluating environmentally and economically feasible strategies for swine wastewater management with a specific focus on AnMBR technology. The system is modeled as a mixed integer non-linear programming (MINLP) problem. Net profit quantified via TEA is used to represent the economic objective and life cycle GHG emissions evaluated via process-based LCA is used to represent the environmental objective. Specifically, we determine the optimal network of wastewater treatment plants for swine farms. Multiobjective optimization is also conducted to evaluate the tradeoffs between economic and environmental objectives and the resulting impact on optimal wastewater treatment network. Preliminary findings indicate that not every county needs a dedicated swine wastewater treatment plant; instead, pipeline-based routing to fewer centralized plants could be more favorable. Detailed sensitivity analysis is performed around key variables such as wastewater composition, available wastewater volume, transportation costs, to quantify their impact on optimal management options. The implications of our findings for developing circular economy solutions for animal wastewater streams will be described.