| Reverse electrodialysis(RED) is a novel technology which can convert the salinity gradient energy(a kind of renewable energy) into electricity. Nevertheless, the high capital costs and the need for large amounts of high concentration(HC) and low concentration(LC) solutions limit the practical application of RED. Bioelectrochemical system(BES) is a promising method for capturing the energy in wastewater as electricity or value-added products during wastewater treatment. However, electrical energy input is required for the production of value-added products. To eliminate the limitations for RED and BES, the use of ammonium bicarbonate as HC and LC solutions for RED stack was proposed in this dissertation. The RED stack utilizing ammonium bicarbonate solutions was then coupled with BES to form integrated systems. Salinity gradient energy was used to drive these integrated systems to produce value-added products(H2, H2O2 and CH4) during wastewater treatment.The effect of operating conditions and configurations on the power output of the RED stack utilizing ammonium bicarbonate solutions were studied. The concentration of LC solution and flow rate of feed solutions were optimized to be 0.02 M and 800 m L/min respectively. The optimal configuration of the RED stack contained 5 cell pairs and the S-0.2 spacer. A maximum power density of 0.85 W/m2 was achieved for the RED stack. The energy efficiency of the RED stack stabilized at about 30%. Based on the above results, a novel system for the conversion of waste heat to electricity was proposed by coupling the RED stack with a distillation column.Three integrated systems for the production of value-added products(H2, H2O2 and CH4) were successfully established by coupling the RED stack utilizing ammonium bicarbonate solutions with BES. For the hydrogen-producing integrated system, the effect of number of cell pairs on its performance was investigated, and the limitation of ammonia crossover into anolyte was eliminated. The largest hydrogen yield, energy efficiency and coulombic efficiency were obtained with 5 cell pairs. An extra LC chamber was further added between the anode chamber and the membrane stack, which decreased ammonia nitrogen losses into anolyte by 60%, increased the coulombic efficiency by 26%, and improved the hydrogen yield to a maximum of 3.5 mol H2/mol acetate.The effect of catalyst type and catalyst loading and the influence of number of cell pairs on the performance of hydrogen peroxide-producing integrated system were studied. The use of activated carbon catalyst resulted in the decomposition of produced hydrogen peroxide, which demonstrated that activated carbon couldn’t be used as catalyst in the integrated system. The optimal loading of carbon black catalyst was determined to be 17 mg/cm2. The number of cell pairs was optimized to be three based on reactor performance and a desire to minimize capital costs. A maximum hydrogen peroxide production rate of 0.99 ± 0.10 mM/h was obtained.For the methane-producing integrated system, the effect of cathode material on its performance was investigated, and electrochemical tests were carried out to explore the methanogenesis mechanism. A maximum methane yield of 0.60 ± 0.01 mol CH4/mol acetate was achieved using the stainless steel biocathode, with an overall efficiency of 60%. Electrochemical tests demonstrated that methane was generated in the integrated system via both the direct and indirect electron transfer.A model which described the relationship between the generated current and the number of cell pairs was established. This model showed that the increase rate of integrated system’s current decreased gradually with the addition of cell pairs. Thus, adding cell pairs couldn’t result in an infinite improvement of current. Additionally, the overall efficiencies of three integrated systems were compared. |
PDF Full Text Request