Aerobes and Effluents - Environmental Biotechnology: Theory and Application - page 142

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manures. The method can also be adapted to be quantitative rather than simply
indicative, allowing data to be gathered on the relative preponderance of marker
bacteria from each host group in the total population of faecal bacteria present.
Tackling diffuse pollution is invariably a more difficult, more technically demand-
ing and typically more costly challenge than addressing point source contamination.
Identifying the original character of the faecal pollution obviously establishes the
likely type of source, simplifying the job of locating the specific agricultural run-off or
sewage discharge responsible on the ground and reducing the delay before remedial
action can be implemented.
CaseStudy6.2 HydrogenfromWastewater(California,USA)
Effluents are generally viewed as problems in need of treatment and ultimately safe
disposal, rather than being seen as potentially useful resources in their own right, but
the growing success of a new approach, microbial electrolysis (ME), could change
that. Although ME - a process for producing hydrogen from wastewater - was only
invented in 2003, it has developed rapidly and now offers yields that approach 100%.
The Napa Wine Company in Oakville California recently began hosting a pio-
neering continuous-flow ME demonstration plant, developed by Professor Bruce
Logan of the Department of Environmental Engineering at Penn State University,
able to process around 1000 l/day of effluent. ME cells comprise two electrodes
immersed in a liquid - in this case winery wastewater, which arises from the wine
making process itself and a range of allied activities including washing down and
equipment cleaning. Naturally occurring electrochemically active bacteria convert
the oxidisable material in the effluent to CO 2 , protons and electrons. The electrons
transfer to the anode, flowing to the cathode along an electric circuit, while the
protons (H + ions) also migrate towards the cathode by diffusing through a cation
membrane, uniting with the electrons to form hydrogen gas. To run, the reaction
requires a small addition of external electricity, typically a voltage of less than 0.2 V,
and provides a relatively high yield of hydrogen.
The part-treated water remaining after electrolysis enters the site's pre-existing
effluent treatment facilities before being recycled for irrigation purposes, while some
of the gas produced will be used on-site in a hydrogen fuel cell, establishing the
potential to develop ME into a source of clean energy in the future.