MICROBIAL ELECTROCHEMISTRY APPLICATIONS FOR NUTRIENT RECOVERY AND ORGANIC DETECTION IN WASTEWATER TREATMENT

Abstract

This thesis presents research work on microbial electrochemistry applications for phosphorus recovery from real wastewater and bioanode sensor development. Phosphorus is a valuable but limited resource which is essential for land fertilizers. Recovering phosphorus using microbial electrolysis cells has been emphasized in wastewater treatment research. Stainless steel mesh (SSM) cathode MECs used in this study showed insufficient phosphorus recovery (68%) because struvite crystals were smaller than the open space between mesh wires (80 µm). Besides, lack of readily biodegradable substrates in the dewatering centrate resulted in limited electric current generation (< 0.2 A/m2) and local pH condition near the cathode. Thus, the following experiments were conducted with stainless steel foil (SSF) cathodes and acetate addition to improve recovery efficiency. Under high electric current density (> 2 A/m2), a thick layer of struvite crystals was formed on the SSF cathode and the phosphorus recovery was increased to 96%. These findings prove that MECs can applied as efficient tools to recover nutrients from real wastewater. Bioanode sensors can be used for real-time and in-situ assessment of water quality. However, the sensor performances are often limited by the narrow detection range, long analysis time, and hysteresis. In order to overcome the challenges for practical applications, a new operation method consisting of three sequences (Normal Operation, Reset Step, and Test Step) was proposed and examined using MEC-based bioanode sensors. Reset Step can eliminate hysteresis effects and produce accurate linear correlations between the soluble COD (chemical oxygen demand) and electric current. The total analysis time was found to be 3 min or even less. The increased detection range (from 75 to 130 mg-COD/L) was achieved by applying a high applied voltage during Test Step. The demonstrated results indicate that MECs can be used for accurate estimation of biodegradable organics in natural or engineered water systems.