(286d) Integrated Anaerobic Membrane Bioreactor Platform for Resource Recovery from Swine Wastewater- Evaluation of Life Cycle Economic and Environmental Impacts

In moving towards the goal of a circular economy, traditional waste streams are being considered for their potential for resource recovery. Recovering products such as energy, clean water, and nutrients from wastewater sources contributes to minimizing the extraction of virgin resources from the environment and its associated environmental impacts. In particular, phosphorus and biologically active nitrogen are nutrients of key importance because they are obtained using non-renewable resources with high life cycle environmental impacts. Concentrated animal feeding operations (CAFOs) are sources of high strength waste streams from large numbers of closely reared animals that contain significant amounts of nitrogen, phosphorus, and organics. We considered wastewater from hog CAFOs due to the high strength and relatively consistent wastewater matrix. A combination of a conventional activated sludge (CAS) and anaerobic digestion (AD) platform is typically used to treat these waste streams. This treatment platform requires high energy input for aeration of the activated sludge, and does not include recovery of resources including volatile fatty acids (VFAs), nitrogen, and phosphorus. We present an optimization based model of a novel treatment train configuration which uses an anaerobic membrane bioreactor (AnMBR). The AnMBR system couples anaerobic digestion with membrane separation which allows for long solids retention times and high carbon conversion within the system. Existing work in this domain has focused on evaluation of individual unit processes. A holistic systems approach to evaluating the environmental and economic performance of the treatment platform is needed to guide research and development and provide quantitative comparisons of the system to traditional treatment methods.

We present an optimization-based decision-making framework for the evaluation of economic and environmental impacts of the treatment of swine wastewater in an integrated resource recovery system. A physics-based model of unit operations including an An-MBR, VFA recovery, phosphorus recovery through coagulation and flocculation, nitrogen recovery through adsorption, and a final wetland polishing step was created. Parameters in individual unit operation pieces were tuned using available data from laboratory experiments and a pilot scale system. The model allows for the evaluation of a wide problem space rather than ad-hoc combinations for treatment trains. These include different configurations of parameters in unit operations, and different choices for unit operations to achieve separation and resource recovery. Optimization for the mixed integer nonlinear programing (MINLP) problem is conducted in Pyomo using the IPOPT algorithm. Optimization was also performed using multi-objective optimization to find a range of pareto-optimal solutions balancing environmental impacts with economic potential of the system. Environmental impacts were quantified using process-based life cycle assessment (LCA). Preliminary results show that there are solutions in which the AnMBR platform is comparable in economic cost to CAS and AD treatment while also having lower environmental impacts. This is achieved by offsetting high capital costs with the value of recovered nutrient and high value-added VFA products. Detailed sensitivity analysis was performed around key variables including energy for membrane cleaning, membrane replacement frequency, ambient temperature, removal of carbonate alkalinity from the system prior to phosphorus treatment, and the composition of the swine wastewater to quantify their impact on model results. The implications of the findings and challenges for developing circular economy solutions for wastewater streams will be discussed.