Development of microbial fuel cells for the treatment of wastewater

• Main Author: Cooksey, Emily
• Other Authors: Holmes, Stuart ; Theodoropoulos, Konstantinos
• Published: University of Manchester 2018
• Subjects: 660
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.764679

The aim of this study was to develop a microbial fuel cell (MFC) wastewater treatment system with a reduced production of sludge; whilst generating electricity as a product. Addition of a graphite intercalated compound, Nyex, provided an opportunity to add an adsorbent system for removal of micropollutants and dyes. Electrochemical analysis, effluent analysis and biofilm analysis provided detail on power generation and wastewater treatment ability and understanding of the biofilm. An 800ml capacity two-chamber MFC was developed and operated using anaerobic wastewater sludge as the anodic inoculum, acetate based artificial waste water as an anolyte and buffered DI water as a catholyte. Separation was provided by a proton exchange membrane, Nafion 117. Nyex was incorporated into the base design using 6 different configurations. Of those, the system with 100g of Nyex loose around each electrode saw the best overall performance. Producing a maximum power density of 0.054W m-2 and current density of 0.35A m-2, an increase of 500% and 312%, respectively, compared to the base fuel cell after 60 days of operation. This is due to a reduction in internal resistance of 86%. Scanning electron microscopy of biofilm indicated species rapidly form links between electrode material to facilitate electron transfer. 16s rRNA gene analysis of used anodic biofilm in the base fuel cell identified two dominant species; P,putida and P.caeni, neither had been used as a pure MFC inoculum. When used as pure cultures and in binary combination all MFCs generated voltage, indicating the species are exoelectrogenic. P.putida produced a current density of 0.0179A m-2, a 258% increase on P.caeni alone, 99% increase on the binary inoculum and a 49% increase on the mixed sludge used for the same time period in the same cell setup. Its maximum power density was 0.0018W m-2; a 167% increase on P.caeni, a 157% increase on the binary inoculum and a 100% increase on the mixed sludge inoculum. COD removal saw a decrease of 62.2% for P.caeni, 61.6% for the binary inoculum, 50.8% for P.caeni, treating 400mL of feed and 34% for the mixed culture treating 1L of feed during the same time period with the same maturity. Based on the results of this study, using the Nyex fuel cell with loose Nyex on both sides generates a power density of 0.054W m-2 when treating 1L of artificial wastewater. Using this system to treat the 11 billion litres of wastewater generated in the UK everyday [1] would result in a total power output of 9.5MW per day. Assuming that the benefits of modifying the fuel cell configuration and modifying the biofilm are independent, their improvements on cell performance can be assumed to be cumulative. Therefore, taking the 0.054W m-2 from the mixed culture Nyex cell and accounting for the 100% power density improvement when using P.putida, the potential power density is 0.108W m-2. Which when applied to the 11 billion litres of wastewater being treated daily within the UK would produce a total power output of 19MW per day.