Design of anaerobic membrane bioreactors for the valorization of dilute organic carbon waste streams†
Aqueous waste organics are an abundant resource generated continuously by industry and human metabolism. Despite its high energy content, organic carbon is typically degraded to CO2 through energy-intensive processes due to its heterogeneity, its low concentration, and stringent requirements for effluent quality. However, valorizing waste organics alongside recovered water is critical for the viability of utilities, industry, and next generation biorefineries. To that end, we employ a quantitative sustainable design (QSD) methodology to set a research agenda for the development of anaerobic membrane bioreactors (AnMBRs) for the conversion of dilute, aqueous organic carbon into methane-rich biogas, with the simultaneous recovery of quality water. 150 unique AnMBR configurations were assembled as the landscape of possible development pathways. Each configuration was evaluated by integrating full-scale design and operation with techno-economic analysis (TEA) and life cycle assessment (LCA) in a Monte Carlo framework. Costs and environmental impacts were most sensitive to membrane configuration, membrane type, and inclusion of granular activated carbon (GAC) as physical media for membrane scouring. The least expensive designs (20th percentile) were exclusively AnMBRs with cross-flow, multi-tube membranes. Research targets were set through sensitivity analyses, prioritizing a decrease in cross-flow velocity (<0.5 m s−1), elimination of gas sparging, increase in membrane life (>10 years), decrease in upflow velocity for physical media bed expansion (<7.5 m h−1), and the development of low-cost physical media for fouling mitigation. Lastly, a subset of AnMBR designs had costs below state-of-the-art treatment (high rate activated sludge with anaerobic digestion), demonstrating the valorization of waste organics would be financially advantageous to industry and utilities.