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Issue 6, 2017
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An integrated microbial electrolysis-anaerobic digestion process combined with pretreatment of wastewater solids to improve hydrogen production

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Abstract

A combined anaerobic digestion (AD) and microbial electrolysis cell (MEC) system, named here as ADMEC, was investigated to evaluate the energy recovery from pretreated wastewater solids. Alkaline and thermal hydrolysis pretreatment methods increased the solubility of organic compounds present in the raw solids by 25% and 20%, respectively. The soluble phase from pretreatment was separated and used for microbial electrolysis, whereas the insoluble fraction was fed into semi-continuous digesters. The digester effluent was later utilized as a second MEC substrate. The pretreatment had variable effects on AD and MEC performance. The methane content in AD biogas was higher in pretreated groups, 78.29 ± 2.89% and 73.2 ± 1.79%, for alkaline and thermal, than the control, 50.26 ± 0.53%, but the overall biogas production rates were lower than the control, 20 and 30 mL CH4 gCOD−1 d−1 for alkaline and thermal compared to 80 mL CH4 gCOD−1 d−1. The effluent streams from thermally pretreated digesters were the best substrate for microbial electrolysis, in terms of hydrogen production and efficiency. The MECs produced 1.7 ± 0.2 L-H2 per L per day, 0.3 ± 0.1 L-H2 per L per day, and 0.29 ± 0.1 L-H2 per L per day, for thermal, alkaline, and control reactors. The productivity was lower compared to acetate and propionate controls, which yielded 5.79 ± 0.03 L-H2 per L per day and 3.49 ± 0.10 L-H2 per L per day, respectively. The pretreatment solubilized fractions were not ideal substrates for microbial electrolysis. A chemical oxygen demand (COD) mass balance showed that pretreatment shifts the electron flux away from methane and biomass sinks towards hydrogen production.

Graphical abstract: An integrated microbial electrolysis-anaerobic digestion process combined with pretreatment of wastewater solids to improve hydrogen production

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Publication details

The article was received on 15 Jun 2017, accepted on 16 Aug 2017 and first published on 17 Aug 2017


Article type: Paper
DOI: 10.1039/C7EW00189D
Citation: Environ. Sci.: Water Res. Technol., 2017,3, 1073-1085
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    An integrated microbial electrolysis-anaerobic digestion process combined with pretreatment of wastewater solids to improve hydrogen production

    J. R. Beegle and A. P. Borole, Environ. Sci.: Water Res. Technol., 2017, 3, 1073
    DOI: 10.1039/C7EW00189D

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