Studies On The Down-Flow Microbial Fuel Cell And The Microbial Denitrification Cell

A microbial fuel cell (MFC) is a device that uses microorganisms to convert chemical energy (such as organic acids, sugars, etc.) from biodegradable substrates to electrical energy via microbial-catalyzed redox reactions. As a renewable clean energy, it has many advantages, such as high energy conversion efficiency, mild operating conditions, and more energy output and etc. Because it can not only degrade organic matters in wastewater or sludge but also transform the electrons generated from the degradation of organic compounds by microbial metabolism into electronic current, MFC can be used for the development of new energy sources while mitigating the increasingly serious environmental pollution.In this dissertation, a new type of down-flow air-cathode MFC was constructed to treat the wastewater while producing electricity. Compared to the conventional up-flow MFC, the developed system is not only of simple configuration and easy operation but also produce higher power. In addition, a study was also conducted on microbial denitrification cell for the treatment of ammonia containing wastewater. Electrical power was produced during the removal of NH4+-N from wastewater.The main contents and results obtained are as follows:In the first section, a novel membrane-less MFC with down-flow feeding was constructed to generate electricity. Wastewater was fed directly onto the cathode which was horizontally installed in the upper part of the MFC. Oxygen could be utilized readily from the air and thus air aeration was not required. The concentration of dissolved oxygen in the influent wastewater had little effect on the power generation. A saturation-type relationship was observed between the initial COD and the power generation. The influent flow rate could affect greatly the power density. Fed by the wastewater with a COD value of 3500 mg/L at a flow rate of 4.0 mL/min, the MFC could produce a maximum power density of 37.4 mW/m2, and its applicability was further evaluated by the treatment of brewery wastewater. The developed MFC could be scaled up readily due to its simple configuration, inexpensive non-catalyzd flat graphite electrodes, easy operation and relatively high power density.In the second section, we created a novel nitrogen removal technology using the microbial denitrification cell to treat wastewater and generate electricity while removing NH4+-N from wastewater. The results showed that microbial denitrification cell could produce steady electricity while remove NH4+-N. In the start-up phase, the denitrification time decreased with the increasing of cell voltage. When the voltage increased to about 450mV, the denitrificaiton time reduced to 46h and the NH4+-N removal rate was up to 95.15%. However, with the voltage further increasing to 550mV, there was little effect on denitrifcation time and the NH4+-N removal rate slightly rose to 97.09%. The charge transfer efficiency generally remained at a high level, approximately 100±5%, and the residual NH4+-N was about 5mg/L. Increasing the cathode area could shorten the denitrifcation time, yet the pH of the cathode solution had little effect on the removal time, which indicated that the developed system had a certain anti-shock load capacity.