Solar-Driven Microbial Photoelectrochemical System for Energy Conversion
Ever growing demand for energy and clean water for the continuous economic growth and suitable inhabitation on earth are major global problems, especially with the drastic increase of human population. Over the years, distinct strategies have been applied to address these two needs separately: the municipal wastewater is collected by local wastewater plants for purification and subsequent reuse as reclaimed water, while the energy source is mainly based on fossil fuels as coal, natural gas, and crude oil. Apparently, these two strategies are decoupled. Additionally, the use of natural gas / petroleum generates a lot of greenhouse gas and toxic chemicals, which poses a serious threat to the environment, and also leads to additional cost to treat the pollution. Therefore, it’s highly desirable to employ energy-efficient processes for wastewater treatment, and simultaneously recover the energy contained as organic matters in wastewater. This can be achieved by microbial fuel cell (MFC) technology, which is an electrochemical device that uses electrogenic bacteria as biocatalysts to decompose organic matter while simultaneously generating bioelectricity. Besides electricity, the bio-electrons generated in the microbial electrogenesis process at the anode can also be used to produce chemical fuels, such as hydrogen gas. However, microbial electrohydrogenesis process does not occur spontaneously due to the thermodynamic barrier for the conversion from protons to hydrogen gas, and therefore an electrical bias has to be supplied to supplement the energy required for the proton reduction. The requirement of external bias adds to the complexity and cost for hydrogen production, making microbial electrohydrogenesis less attractive as a cost-effective energy solution. Alternatively, the energy required to overcome the barrier can be provided by a renewable energy source such as solar light, which is a promising approach that could fundamentally address this issue. In this thesis, I will give a detailed discussion on the development of a self-sustained and highly efficient solar-driven microbial device that could simultaneously address the increasing demand of clean water and energy. I have demonstrated a hybrid device by interfacing a photoelectrochemical cell (PEC) device and an MFC device (denoted as PEC-MFC), which can generate hydrogen gas at zero external bias using biodegradable organic matter and solar light as the only energy sources. In addition to introducing the self-sustained microbial photoelectrochemical system (MPS), the efficiencies of MFC and PEC devices can be enhanced by chemical modification on anode materials of both MFC device and PEC device, separately. Moreover, based on the success of the hybrid PEC-MFC device, I have further studied the investigation of interplay between light, a hematite nanowire-arrayed photoelectrode, and Shewanella oneidensis MR-1 bacteria in a single solar-assisted MPS device. In the end, I will give a final summary and outlook on the solar-assisted MFC device for recovering energy from wastewater and simultaneously removing organic wastes.