Complex Waste Treatment And Photocatalytic Hydrogen Production Based On The Microbial Fuel Cells

Microbial fuel cell (MFC) is a new environmental biotechnology for pollutant degradation and clean energy recovery using microbial catalysis. In the thesis, plenty works were performed focusing on the conversion of lignocellulosic biomass and urine, pollutant degradation and hydrogen production using a proposed bio-photoelectrocatalytic cell with novel photoelectrocatalysis materials based on MFC technique. Through these efforts, complex waste disposal and energy recovery were achieved by the MFC. Main contents and results are as follows:1. This study demonstrated that, using an air-cathode MFC inoculated with rumen microorganisms, electricity could be directly produced with a maximum power density of 0.405 W/m3 from Canna indica (canna), a lignocellulosic aquatic plant rich in cellulose, hemicellulose and lignin, without pre-treatment. The mechanisms of canna degradation in the MFC were elucidated through analyzing the changes of canna structure and intermediates, i.e., soluble sugars and volatile fatty acids (VFAs), in the electricity generation process. The results showed that lignin was partially removed and more cellulose exposed on the sample surface after the electricity generation in the MFC. The electron transfer in this MFC was mainly completed through electron shuttling via self-produced mediators. This work presents an attempt to understand how complex lignocelluloses like aquatic plants are decomposed in an MFC during electricity generation. It might hopefully provide a promising way to utilize lignocellulosic biomass for energy generation.2. Urine pretreatment has attracted increasing interests as it is able to relieve the nitrogen and phosphorus overloading problems of municipal wastewater treatment plants. In this study, an integrated process, which combines magnesium ammonium phosphate (MAP) precipitation with MFC process, is proposed for recovery of slow-release fertilizer and electricity from urine. In such a two-step process, both nitrogen and phosphorus are recovered through the MAP process, and organic matters in urine are converted into electricity through MFC process. With this integrated process, removal efficiencies of PO43-P of 94.6%, NH4+-N of 28.6% and chemical oxygen demand (COD) of 64.9% accompanied by a power output of 2.6 W/m3 are achieved if phosphorus recovery is maximized without dose of PO43--P in the MAP precipitation process, whereas removal efficiencies of PO43-P of 42.6%, NH4+-N of 40% and COD of 62.4% as well as power density of 0.9 W/m3 are obtained if simultaneous recovery of phosphorus and nitrogen is required through dosing 620 mg/L of PO43--P in the MAP process. This work provides a new sustainable approach for the efficient and cost-effective treatment of urine with recovery of energy and resources.3. In this study, we prepared Pd nanopaticles modified silicon nanowire (Pd/SiNW) electrode, which could be effectively used to reduce the redox potential and high overpotential of proton reduction. Then, we reported a novel bio-photoelectrochemical cell, which was consisted of the Pd/SiNW photocathode and a microbially-catalyzed bioanode. Under visible light illumination, both hydrogen and electricity were continuously produced from the cell, with a maximum power density of 0.075 W/m2 (normalized to the photocathode area) and an average hydrogen-producing rate of 37.5μmol/h. At the photocathode, the photogenerated holes (hvb+) and electrons (ecb-) are produced under illumination. The electrons coming from bioanode are captured by hvb+ of the photocathode. As a result, the recombination of photogenerated carriers is efficiently reduced. The photocatalytic efficiency and hydrogen production attributed to the reduction of protons by ecb- are greatly improved.4. A cost-effective photocathode was prepared through depositing amorphous MoS3 onto SiNW electrode which could be used in the bio-photoelectrochemical cell. The amorphous MoS3 was found to act as an efficient, robust and earth-abundant co-catalyst of SiNW to catalyze the hydrogen evoluation reaction. Under visible light illumination, both hydrogen and electricity were continuously produced from the cell, with a maximum power density of 0.062 W/m2 (normalized to the photocathode area) and an average hydrogen-producing rate of 44.9μmol/h.