Investigation of cathodic O2 reduction and development of a new bioelectrochemical BOD sensor

Abstract

Microbial Fuel Cells (MFCs) have been investigated intensively during the last 20 years. Through MFCs, dissolved organic matters in wastewater can be removed and used as renewable energy for electricity production at the same time. The main impediment for increasing MFCs’ efficiency is the high overpotential of the cathodic reduction. The catalyst and material of the electrode is essential to reduce the cathodic overpotential. In this master thesis, the properties of three types of gas-diffusion cathodes were tested, 1) plain carbon paper without any catalyst coating; 2) carbon paper coated with carbon nanoparticles; and 3) carbon paper coated with platinum loaded activated carbon powder. Living bacteria in both aerobic and anaerobic culture were investigated as catalyst for the cathodes. The results showed that the performance of the plain carbon gas-diffusion cathode is much worse than the cathode coated with nanoparticles. Pt showed the best cathodic catalysis while living bacteria gave no catalysis function. Anaerobic sludge even inhibited the cathode reaction. However, the performance of cathode coated with nanoparticles was stable in the presence of both kinds of sludge, which suggested that nanoparticles are suitable catalysts for single chamber MFCs. In this project, we also investigated a single chamber MFC as a BOD sensor. BOD concentration was reflected as the total transferred charge. The response time was tested under two conditions, with 100ohm external resistance loaded and with an input voltage (1V) to accelerate the reaction. For the first condition, the response time was about 3.5 days, which is shorter than the conventional BOD measuring method, 5 to 7 days. And with an input voltage, response time was even shorter, only 1.25 days was used to obtain the BOD value.