**6.2. A brief summary of the pilot scale studies undertaken in the area of BES**

The first large-scale experience with BES was an MFC build and operated by the Advanced Water Management Center at the University of Queensland [68]. The MFC consisted of 12 units with a total volume of approximately 1 m<sup>3</sup> . There is scant information about the performance of this plant, although it is known that power production was limited by the low conductivity of the wastewater and biomass proliferation on the cathode [69]. In a much recent work based on a 200 L modular MFC operated in field conditions in a municipal wastewater treatment plant, Ge and He [70] reported more than 75% COD removal rates, accompanied by a power production of 200 mW, which was enough to power part of the ancillary equipment required to operate the plant. Much more complex substrates than urban wastewater have also been used as a feedstock for pilot MFC. In [71], it is reported that a 115 L MFC was able to remove almost all of the biodegradable fraction from swine manure producing about 200–400 mW of power. Moreover, the plant, which consisted of six MFC units, also allowed to remove about 50% of the nitrogen initially present in the manure.

The first large-scale MEC had a working volume of 1000 L, was a continuous flow, and ran a hydraulic retention time (HRT) of 1 day [66]. The system ran for a period 100 days, heated to 31°C, with an average influent of 760 ± 50 mgCOD·L−1 (soluble chemical oxygen demand) 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 laboratory scale, this study showed that this was not scalable.

Perhaps the clearest niche of application of BES lays in the field of wastewater treatment where this technology could help to improve the energy efficiency of the process by converting the energy content of the organic matter present in the wastewater into either electrical energy or a fuel gas. In fact, most of the pilot scale experiences developed to date have been designed for these purposes. Moreover, operational versatility of BES might bring additional opportunities for wastewater valorization, as they also allow to recover valuable chemicals and nutrients such as ammonium or phosphorus. Here, it is important to highlight that BES can perform this at a reduced energy and economic costs compared to more conventional

or short chain fatty acids. This can potentially provide a cost-effective and environmentally

In short, BES can be seen as a group of technologies capable of valorizing a wide range of liquid to gaseous waste streams. In most cases, the operation of BES requires large amounts of electrical energy, most of which ends up stored in chemical energy (methane, hydrogen, etc.) that can be readily converted back into electrical energy when required by using well-established technologies (fuel cells, cogeneration, etc.). This feature would enable BES to operate as electrical regulation system which would bring further commercial opportunities for these

This chapter was made possible thanks to the financial support of the 'Ministerio de Economía

and Adrián Escapa1,3\*

1 Chemical and Environmental Bioprocess Engineering Group, Natural Resources Institute

3 Department of Electrical Engineering and Automatic Systems, Universidad de León,

y Competitividad' project ref.: CTQ2015-68925-R, co-financed by FEDER funds.

, Daniel David Leicester<sup>2</sup>

2 School of Civil Engineering and Geosciences, Newcastle University,

, Raúl Mateos<sup>1</sup>

\*Address all correspondence to: adrian.escapa@unileon.es

(IRENA), University of León, León, Spain

emissions into the atmosphere.


into valuable organic chemicals such as methane

Bioelectrochemical Systems for Energy Valorization of Waste Streams

http://dx.doi.org/10.5772/intechopen.74039

137

, Elizabeth Susan Heidrich2

,

technologies used in fertilizers industries.

might provide a means for converting CO2

friendly method for limiting CO2

Gaseous CO<sup>2</sup>

technologies.

**Acknowledgements**

**Author details**

María Isabel San-Martín<sup>1</sup>

Newcastle upon Tyne, UK

León, Spain

Raúl Marcos Alonso1

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 was the cause of the poor performance.

In Ref. [4], a similar cassette electrode design but at two different scales: 0.6 m<sup>2</sup> and 1 m2 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 shown to be vital for successful hydrogen recovery [3].

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 material deterioration.
