Performance of Stainless Steel 304 Cathodes and Bicarbonate Buffer in a Microbial Electrolysis Cell Using a New Method of Gas Characterization

Open Access
Author:
Ambler, Jack
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 29, 2010
Committee Members:
  • Bruce Ernest Logan, Thesis Advisor
Keywords:
  • Microbial Electrolysis Cells
  • MEC
  • Stainless Steel
  • Bicarbonate Buffer
  • Gas Bag Method
  • GBM
  • Gas Characterization
  • Gas Measurement
Abstract:
Microbial electrolysis cells (MECs) have been shown to be efficient devices for the production of hydrogen from organics and inorganics. MECs have been studied extensively that use phosphate buffered solutions and platinum (Pt) cathodes. However, the costs associated with these materials could make scale up expensive and impractical. Several different metal catalysts have been tested in MECs to try to reduce the costs of the cathode, while other buffers have been examined in order to avoid the need for high concentrations of phosphate. In this study, MECs using a stainless steel 304 (SS304) mesh #60 cathode and a bicarbonate buffer solution were determined to perform comparably to those having a Pt cathode and using a phosphate buffer solution, in terms of hydrogen production per batch cycle, electrical energy efficiency and overall energy efficiency. MEC performance was determined using a new method to evaluate gas production called the gas bag method (GBM). The GBM produced an average error of 5.0 % for known quantities of gasses in the gas bag. The GBM does not require any additional gas flow instruments for gas measurement, which reduces the costs of monitoring MEC performance. Hydrogen production per cycle for 30 mLs of solution at 1 g/L sodium acetate was similar for different MEC conditions, with 26.6 ± 1.8 mL using a SS304 mesh cathode and bicarbonate buffer, 26.4 ± 2.8 mL using a Pt cathode and bicarbonate buffer, and 26.8 ± 2.5 mL with a Pt cathode and phosphate buffer. Electrical energy efficiency was highest with a SS304 cathode and bicarbonate buffer at 159 ± 17 %, when compared to 126 ± 14 % for a Pt cathode and bicarbonate buffer, and 134 ± 17 % for a Pt cathode and phosphate buffer. Maximum hydrogen production rates were lowest with SS304 and bicarbonate at 1.1 ± 0.3 m3 H2-m-3d-1, and Pt and bicarbonate at 1.2 ± 0.3 m3 H2-m-3d-1, compared to 1.7 ± 0.4 m3 H2-m-3d-1 with a Pt cathode and phosphate. Lower hydrogen production rates resulted in increased cycle times, which means a longer time required for treatment as well as more time for hydrogen loss due to the growth of methanogens. These results show that the GBM can be used to compare performances across different MEC setups and that SS304 mesh cathode with a bicarbonate buffer performs comparably to a platinum cathode with a phosphate buffer.