The Effects of Carryover on Electricity Production and Cellulose Degradation in Microbial Fuel Cells
Open Access
- Author:
- Terrill, Jennine Barbara
- Graduate Program:
- Environmental Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 27, 2008
- Committee Members:
- John Michael Regan, Thesis Advisor/Co-Advisor
- Keywords:
- Cellulose
Microbial Fuel Cell
Bioenergy
MFC - Abstract:
- Due to environmental concerns associated with fossil fuel mitigation and political volatility of oil-producing countries, and more recently with the advent of rising fuel costs, biomass energy sources have become of great interest. One of the newest ways in which to harness the energy in biomass is through the use of a microbial fuel cell (MFC). MFCs are a new technology with promising application in the field of wastewater treatment amongst many others. MFC research has focused primarily on the treatment of easily degradable soluble carbon sources, but biomass is known for its recalcitrance, and MFC treatment of particulate substrates should be explored more in depth for the best method of treatment. In previous testing of cellulose conversion to electricity in an MFC, hydrolytic and fermentative bacteria have been found to predominately reside near the suspended cellulose that they are degrading, and not on the anode of the MFC. Therefore, one of the methods to keep those organisms within a batch-fed system would be to carry over some of the substrate from the previous cycle into the next. In this study, air-cathode single-chamber bottle MFCs were used to evaluate the ability of both sludge and binary (Geobacter sulfurreducens and Clostridium cellulolyticum) inocula to degrade cellulose, remove COD, and generate power, comparing for each inoculum a system that had carryover from the previous cycle and a system with no carryover. The sludge-inoculated MFCs proved to be superior in the generation of maximum power (41.4 mW/m2 and 39.0 mW/m2 without and with carryover, respectively) to the binary-inoculated MFCs (19.4 mW/m2 and 13.7 mW/m2 without and with carryover, respectively). Higher transient values were seen in the earlier cycles (62 mW/m2 and 44 mW/m2 for sludge-inoculated MFCs without and with carryover, respectively and 28 mW/m2 and 19 mW/m2 for binary MFCs without and with carryover, respectively), but the performance generally appeared to be more stable at the later cycles. Gas composition for the sludge MFCs was monitored and methane was discovered in the headspace of only the system with carryover. For both inocula, the MFCs with carryover demonstrated the highest removal of cellulose (95% for the sludge-inoculated MFC and 90% for the binary MFC). Although carryover did promote higher fermentation rates, this operational strategy also created a system with acidity issues, needing the pH adjusted almost every other day to obtain pH > 6. The highest coulombic efficiency (CE) was observed in the binary MFC with no carryover (11.4%). The rest of the MFCs had CEs of ~ 3%. Acetate was found in abundance in the binary MFC with carryover both before (1.7 mM) and after (10.1 mM) the analyzed run, but not in any other MFCs. This residual acetate concentration suggests that the G. sulfurreducens population was not able to keep up with the fermenters. Real-time PCR with samples from the binary reactors showed that carryover was effective at retaining many more fermentative organisms than the MFC without carryover, showing an accumulation over time of these fermenters in the binary MFC with carryover. Although there appeared to be a trade-off between power density and cellulose conversion in the binary reactors, this trend was less evident in the sludge-inoculated reactors.