Resource recovery and carbon valorization during wastewater treatment using electrochemical and microbial electrochemical methods

Abstract

Efficient resource recovery from waste streams and effective carbon management are challenges for developing a sustainable circular economy. This dissertation research addresses nutrients recovery and carbon valorization using electrochemical methods in two systems. The first part of the dissertation investigated nutrients (nitrogen and phosphorus) removal and recovery from wastewater using flow-electrode capacitive deionization (FCDI). Results showed FCDI can concurrently removal salts and nutrient ions from wastewater effluent and recover them as concentrate efficiently. Phosphorus removal could be further improved by operating FCDI with external electrode mixing. Furthermore, the mechanism of pH effects on phosphate transport behavior was investigated through experiments and modeling. Results showed that feed solution pH has significant impacts on phosphorus removal due to speciation of phosphate at different pH. Flow-electrode pH influences phosphate distribution in the electrolyte and carbon particles, which was caused by the discrepancy of carbon surface charge at different pH. This study provides in-depth understanding of nutrients removal and recovery in electrochemical systems and offers guidance for future applications. The second part investigated the carbon valorization in microbial electrosynthesis (MES). The crucial role of H2 evolution on volatile fatty acids (VFAs) production was identified, and high acetate titer was obtained with a hybrid cathode electrode comprising nickel foam and carbon felt. Results also reveal a shift microbial community during long-term operation, leading to issues of methanogenesis and low Faradaic efficiency (FE) for VFAs production at lower cathode potentials. In addition, the feasibility of using bioanode in MES for simultaneous food waste treatment and microbial CO2 utilization was demonstrated using a tubular MES with total volume of 6 L. Results showed that bioanode MES could deliver efficient electron recovery for food waste treatment and efficient VFAs production in the cathode. Several operational parameters were optimized, and the flow rate was found to have significant influence on cathode by affecting mass transfer. This study offers valuable insights into microbial CO2 utilization and bridges the knowledge gaps in bioanode MES, particularly for scaling up applications.