Reducing nitrogen crossover in microbial reverse-electrodialysis fuel cells by using ion exchange resin

Open Access
Author:
Wallack, Maxwell James
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 20, 2015
Committee Members:
  • Bruce Ernest Logan, Thesis Advisor
  • Michael Anthony Hickner, Thesis Advisor
  • Manish Kumar, Thesis Advisor
Keywords:
  • MFC
  • MREC
  • MRC
  • electrodialysis
  • resin
  • membrane
  • nitrogen
  • ammonia
  • crossover
Abstract:
Reverse electrodialysis (RED) is a technology that uses high and low concentration salt solutions between a stack of alternating anion and cation exchange membranes to induce an electrical current. A RED stack installed between the anode and cathode of a microbial fuel cell (MFC) is called a microbial reverse electrodialysis cell (MREC). An MREC produces a greater power density than an MFC alone. When a RED stack is powered using ammonium bicarbonate salt solutions, nitrogen in the form of negatively-charged carbamate can be transferred through an anion exchange membrane (AEM) into the anode chamber. The loss of this nitrogen into the anode chamber is not sustainable or economical. Total ammonia nitrogen (TAN) concentrations in the anode chamber >500 mg/L can also prevent bacteria from efficiently utilizing acetate, reducing power production by the cell. To reduce nitrogen crossover into the anode chamber, an additional low concentration (LC) chamber and AEM were installed between the high concentration cell in the RED stack and the adjacent anode chamber, and ion exchange resin was added to increase the chamber conductivity and reduce internal resistance. With this configuration, the overall nitrogen crossover into the anode was reduced by up to 96.5% compared to a standard configuration (no additional chamber) in a 24-hour fed-batch cycle. Anode pH rose from 8.5 to 10.5, instead of decreasing as is normally observed in an MREC. Resistance due to all membranes in the stack increased from 103 Ω-cm2 to 295 Ω-cm2, and an additional 637 Ω-cm2 resistance was introduced by the solution in the low concentration chamber. When the additional LC chamber was filled (50%) with anion exchange resin, solution resistance decreased by 74% to 166 Ω-cm2. In a lab-scale MREC, it was estimated that three additional RED cell pairs would be necessary to make up for power loss due to the membrane and solution resistance introduced by the LC chamber.