Simultaneous recovery of energy and nutrients from wastewater using microbial nutrient recovery systems : a self-sustainable process

Abstract

The discharge of nutrients from wastewater can cause eutrophication in water bodies and deplete valuable nutrient resources. A strategy that treats wastewater while recovering nutrients offers a promising research and development opportunity to address water and nutrient scarcity in an efficient, eco-friendly way. Conventional treatment methods often waste nutrients and energy in wastewater and require large amounts of electricity. Recently, a microbial nutrient recovery cell (MNRC) was developed to use the energy in wastewater to treat it while simultaneously recovering nutrients. The innovation of this PhD thesis lies in developing efficient electrodes (both anodes and cathodes) through a simple and scalable functionalization method that can inspire further research. This work extensively examines key factors such as electrode material, microbial cell volume, wastewater composition, and the effect of ion exchange membranes on nutrient recovery, chemical oxygen demand (COD) reduction, and net energy production.

The primary goal of the research was to develop a highly efficient microbial nutrient recovery system that selectively recovers ammonium and phosphate from the source. Various materials including carbon cloth, carbon brush, chitosan beads, activated carbon, stainless steel, and hybrids of chitosan and activated carbon were used to construct cathodes and anodes in microbial fuel cells which were thoroughly analyzed to establish their energy output, COD reduction, and microbial community growth and characterization. The work aimed to identify high-performance anode electrode materials that demonstrate enhanced nutrient selectivity and recovery.

Due to the desired properties identified in the studies that comprise this thesis, carbonaceous materials such as graphite rods and brushes, carbon cloth, carbon felt, and activated carbon are widely used as electrodes in microbial fuel cells (MFCs) . Selected electrodes were modified to understand the effect of modification on energy production and nutrient recovery in the MNRC process. For this purpose, surface modification, heat treatment, and the formation of hybrid composites were examined. The work investigates the performance of electrodes in the MNRC system in terms of COD reduction of the waste stream up to 98%, the selectivity of valuable nutrients, concentration in the recovery compartment up to 80% of phosphate for carbon brush as anode electrode, energy production as a function of time (recovery cycles up to 10), initial nutrient concentrations of 10ppm used in wastewater. In case of hybrid anode electrode containing equal volume of activated carbon and chitosan in microbial nutrient recovery system with the total COD load of 718 mg/L, a total COD removal of up to 79% was reached after 10 operation cycles.