**Acknowledgements**

winery wastewater, along with some acetate supplement. COD reduction averaged 62%; however, hydrogen production was limited as the gas content was 85% methane. The system utilized a single chamber design, which resulted in methanogenesis occurring at the cathode, consuming the hydrogen. Although single chamber designs had been very efficient at the

Few years later, Heidrich et al. [67, 72] built and operated a continuous flow MEC, which had a volume of 120 L, a HRT of 1 day, and ran for a period of 12 months using raw domestic wastewater (125–4500 mgCOD·L−1) taken directly from the grit channels during pre-treatment. This was in the North East of England and the system was not heated, leading to temperatures ranging from 1 to 20°C. A low COD removal of 30% was reported; however, almost pure hydrogen (100 ± 6.4%) was produced at a rate of 0.015–0.007 LH2·L−1·d−1, with a coulombic efficiency (CE) of 41–55%. The cassette design of the electrodes that was developed in this study has seen to be versatile and scalable with its application in other pilots. The study did not reach the required energy recovery to be energy neutral and did not treat the wastewater to EU standards. Inconsistent COD balance, along with a build-up of sludge within the reactor

In Ref. [4], a similar cassette electrode design but at two different scales: 0.6 m<sup>2</sup>

anodes. It ran using settled domestic wastewater (347 mgCOD·L−1), at a real treatment site at ambient temperatures (8.6–15.6°C) for 217 days, with a HRT of 5 h. By decreasing the spacing of the cassettes and increasing the HRT from the Heidrich study, the COD removal was on average 63.5%, and the effluent reached European Urban Wastewater Treatment Directive discharge standards [73]. However, the MEC only produced 0.004 LH2·L−1·d−1 with a maximum CE of 27.7%. The problems arose from hydrogen-consuming bacteria entering the cathode compartment and scavenging hydrogen and maintaining a sterile cathode compartment were

This MEC used the primary effluent from domestic wastewater, running a 130 L MEC for a period of 5 months, at a temperature range of 18–22°C. Again this research team used the cassette style electrodes as the base for their design, with a HRT of 2 days. Hydrogen was produced at a rate of 0.032 LH2·L−1·d−1, which is the highest yet published with a purity of 95%, and consequently, high cathodic gas recovery of 82% and an energy recovery of 121% with respect to the electrical input were achieved. However, COD removal was low at around 25%. This study also treated two types of synthetic wastewater utilizing the same design and discovered that hydrogen production was in fact the highest with real wastewater out of the three carbon sources tested. Although this system is the most successful yet in terms of energy production, problems still occurred, mainly related to application of electric potential and

The term bioelectrochemical systems (BES) encompass a group of relatively novel technologies which hold a great potential for energy valorization of a wide variety of waste streams.

and 1 m2

laboratory scale, this study showed that this was not scalable.

was the cause of the poor performance.

136 Energy Systems and Environment

material deterioration.

**7. Conclusions**

shown to be vital for successful hydrogen recovery [3].

This chapter was made possible thanks to the financial support of the 'Ministerio de Economía y Competitividad' project ref.: CTQ2015-68925-R, co-financed by FEDER funds.
