Bioelectrochemistry applications for recovery and production of valuable resources from wastewater and organic waste

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The long-term objective of this work is to demonstrate sustainable conversion of unwanted wastes (wastewater sludge, food waste, and the flue gas) into valuable products (NH4+ and bioplastics). Such conversions require intensive energy consumption and other resources (e.g., organic acids for bioplastics production). To make such conversions feasible, we will research microbial electrolysis cells (MEC), bipolar membrane electrodialysis (BMED), and microbial PHA (polyhydroxyalkanoate-raw material of bioplastics) accumulation with the following short-term objectives. 1. Energy reduction in NH4+ and volatile fatty acid (VFA) separation from organic waste 2. Selective enrichment of a high-capacity PHA-accumulating microorganism 3. Sustainable H2 supply for microbial CO2 conversion into PHA BMED consists of bipolar membranes (BPMs) and ion exchange membranes (IEMs) to produce an acid and base solutions (VFA and NH4+ solutions in this work) by separating conjugate bases of VFAs (acetate, propionate) through anion exchange membranes (AEMs) and NH4+  through cation exchange membranes (CEMs). Liquid digestate (liquid wastewater separated from thermophilically pretreated wastewater sludge and food waste in this work) will be treated in BMED to produce the VFA and NH4+ solutions. To reduce electric energy consumption, BMED will be integrated in MECs where exoelectrogenic bacteria generate electric current from VFA oxidation. Ralstonia eutropha is high-capacity PHA-accumulating bacteria (80-90% of dry cells); however, there are no methods for selective enrichment of R. eutropha from a mixed culture. As a result, they are not suitable for PHA production using organics in biologically active wastewater (e.g., liquid digestate). In this work, we will utilize another unique capability of R. eutropha that can grow either heterotrophically (organic carbon as carbon source) or autotrophically (CO2 as carbon source). By alternating autotrophic and heterotrophic conditions repetitively, we hypothesize that R. eutropha can be selectively enriched from a mixed culture while other heterotrophs and autotrophs show limited growth. The VFA solution without NH4+ from BMED will be used to induce PHA accumulation during R. eutropha enrichment. We will further demonstrate autotrophic conversion of CO2 in the flue gas into PHA using the enriched R. eutropha culture. MECs will be used to supply H2, reducing the cost for PHA production. The VFA solution from BMED will provide organic substrates to exoelectrogens in the MECs and the absence of NH4+ in the VFA solution will trigger conversion of CO2 into PHA. Our research outcomes will make it feasible to utilize organic waste and the flue gas for NH4+ and PHA production at reduced costs. NH4+ recovered from organic waste can be used for land fertilizer manufacturing. PHA production from the flue gas will reduce GHG (greenhouse gas) emission as coal/natural gas power plants are responsible for ~10% of GHG emission in Canada.