Competition of electrogens with methanogens for hydrogen in bioanodes

摘要

Bioelectrochemical systems (BES) can provide an energy efficient way to recover nutrients from wastewaters. However, the electron donors available in wastewater are often not sufficient to recover the total amount of nutrients. This work investigates hydrogen (H-2) as an additional substrate for bioanodes. This hydrogen can be produced in the fermentation of complex organic waste or could be recycled from the cathode. Understanding how to influence the competition of electroactive microorganisms (EAM) with methanogens for H-2 gas from different sources is key to successful application of H-2 as additional electron donor in bioelectrochemical nutrient recovery. Ethanol (EtOH) was used as model compound for complex wastewaters since it is fermented into both acetate and H-2. EtOH was efficiently converted into electricity (e) by a syntrophic biofilm. Total recovered charge from 1 mM EtOH was 20% higher than for the same amount of acetate. This means that H-2 from EtOH fermentation was converted by EAM into electricity. Low EtOH concentrations (1 mM) led to higher conversion efficiencies into electricity than higher concentrations (5 and 10 mM). Thermodynamic calculations show this correlates with a higher energy gain for electrogens compared to methanogens at low H-2 concentrations. Cumulatively adding 1 mM EtOH without medium exchange (14 times in 14 days) resulted in stable conversion of H-2 to e(-) (67%-77% e(-)) rather than methane. With H-2 gas as electron donor, 68 +/- 2% H-2 was converted into e(-) with no carbon source added, and still 53 +/- 5% to e(-) when 50 mM bicarbonate was provided. These results show that under the provided conditions, electrogens can outcompete methanogens for H-2 as additional electron donor in MEC5 for nutrient recovery. (C) 2019 The Authors. Published by Elsevier Ltd.