Screening and acclimation methods for accomplishing treatment and energy recovery from wastewater in microbial electrolysis cells

Open Access
Author:
Ullery, Mark Linden
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 22, 2014
Committee Members:
  • Bruce Ernest Logan, Thesis Advisor/Co-Advisor
Keywords:
  • Microbial Electrolysis Cells
  • Wastewater treatment
  • Bio-hydrogen production
  • Mini MECs
  • Industrial wastewater
  • Energy recovery
Abstract:
Microbial electrolysis cells (MECs) are an emerging bioelectrochemical technology that can recover energy from organic matter in wastewater. In an MEC, a biological anode populated with microbes, capable of oxidizing organic compounds and generating an electrical current, is paired with a conductive, hydrogen-evolving cathode. Wastewater composition and concentration can vary significantly between sources, which influences organic treatment, gas production, and current generation in MECs. Inexpensive, miniature MECs (5 mL) have been previously used to examine MEC performance with different industrial effluents, but they have not been compared with more widely used reactor designs. In this study, mini MECs and larger cube MECs (32 mL) were compared with industrial (IW), domestic (DW), fermentation (FE), and synthetic (AC) effluents to better understand how performance corresponds between these reactor designs. Before MEC treatment, the IW, DW, FE and AC samples contained 450-4500 mg/L of chemical oxygen demand (COD) and 230-800 mg/L of biological oxygen demand (BOD). 66-92% of COD was removed in MECs for all samples, with higher average current density observed with the AC and FE samples (2.25-6.72 A/m2), which were buffered, than the IW and DW samples (0.64-1.93 A/m2). COD removal and coulombic efficiency (CE) correlated well between mini and cube MECs. Total charge (normalized to the reactor liquid volume) and the rate of current generation were similar between mini and cube MECs fed well-buffered samples (AC and FE), but significantly different for industrial and domestic effluents (IW and DW). Mini MECs were found to suitably represent cube MEC treatment performance and are useful for screening real wastewaters for potential larger scale MEC treatment. Different acclimation procedures were also investigated with cube and mini MECs to determine the influence on current generation, organic removal, and gas recovery with fermentation effluent as substrate. Pre-acclimating MEC biofilms with domestic wastewater or acetate medium prior to treating fermentation effluent slightly improved COD removal (3-5%), compared to non-pre-acclimated reactors, but gas production and current generation were unchanged by the acclimation method. Differences in protein removal were relatively small between acclimation methods in mini MECS (<5%), with no difference measured in cube MECs. Although pre-acclimation improved treatment in both mini and cube MECs, the difference in COD treatment, current generation, and protein removal was more significant between mini and cube MECs than acclimation methods. These results suggest that acclimation method has a relatively small influence on MEC performance and acetate addition may not be necessary to develop a robust electrically active biofilm.