Effects of acclimation methods on anaerobic fluidized bed membrane bioreactors and methanogenic microbial electrolysis cells

Open Access
Author:
Labarge, Nicole Alyse
Graduate Program:
Civil Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 12, 2016
Committee Members:
  • Bruce Ernest Logan, Thesis Advisor
Keywords:
  • AFMBR
  • MEC
  • wastewater treatment
  • COD removal
  • methane generation
  • GAC
  • activated carbon
Abstract:
Microbial electrochemical technologies (METs) can help address energy needs by recovering energy from wastewater, decreasing energy input for wastewater treatment, and generating useful fuels. Microbial fuel cells (MFCs) can be used to produce electricity from organics, but they cannot treat the wastewater to levels needed to meet discharge limits while producing power. Anaerobic fluidized bed membrane bioreactors (AFMBRs) are an energy-efficient method for treating low strength wastewater, and thus they can be used to treat MFC effluent to meet discharge standards. Methanogenic microbial electrolysis cells (MECs) generate methane by fixing carbon dioxide. The purpose of these studies was to examine the effect of different acclimation methods on the performance and microbial communities of AFMBRs and MECs. Different AFMBR startup methods were compared to determine effect of startup on reactor performance, and to assess microbial communities in AFMBRs. Similar (t-test,α = 0.05, P > 0.4) COD removal was achieved for diluted wastewater using AFMBRs acclimated to methanol (M), wastewater (W), or anaerobic digester sludge (D), with an average COD removal of 63 ± 12%. Acclimation to acetate (A) significantly increased COD removal to 84 ± 6%. Improved removal efficiency by acetate acclimation was also seen after exposing reactor M to acetate feed for a week. When reactor M was subsequently fed diluted wastewater, the COD removal increased to 70 ± 6%. Microbial communities on the GAC were significantly different (P < 0.05) from those in the influent and reactor fluid, and were distinguished by greater abundances of Geobacter, sulfur-reducing bacteria, Syntrophaceae, and Chlorobiaceae. Reactor A demonstrated the highest relative abundance of Geobacter. These studies showed that acetate was a useful substrate for acclimation of AFMBR communities to achieve improved COD removal. The cathode chamber of methanogenic MECs was inoculated with microbial communities pre-acclimated with GAC and chemical substrates to improve methane generation. Hydrogen-acclimated GAC had the highest relative abundance of Methanobacterium, which has been shown to dominate mixed-culture MEC archaeal communities. However, methane production from hydrogen-acclimated MECs was similar to communities acclimated to methanol and a VFA mix, which all averaged 23.5 ± 9.7 nmol cm–3 d–1. Startup time was also insensitive to the substrate used in pre-acclimation. Pre-acclimation of communities with GAC promoted increased methane generation compared to MECs directly inoculated with GAC and an inoculum of bog sediment (12.7 ± 4.1 nmol cm–3 d–1). Methane generation ceased after two cycles for MECs operated with bog sediment inoculum only. GAC could be a good growth support for enriching microbial communities associated with methanogenic MECs and exocellular electron transfer, as GAC communities had higher relative abundances of Methanobacterium, Geobacter, and sulfur-reducing bacteria which are known to be associated with microbial communities that develop in well-performing bioelectrochemical systems.