Environmental Engineering Reference
In-Depth Information
Several hurdles remain in commercialization of the MFC technology, such as cost
of construction materials, scale-up issues, and ability to harness low voltage out-
put. The key to being able to commercialize this technology depends on improving
designs of the MFCs to achieve power densities in the range 400 to 1000 W/m
3
.
Recent improvements in MFC designs have shown power densities approach-
ing these goals [12, 21, 22]. Investigations into the effect of the exoelectrogenic
microorganisms and the microbial enrichment processes in influencing the MFC
performance have also shown potential in improving power densities [12, 23, 24].
Potential for production of hydrogen instead of electricity from food industry
wastewaters also exists [25-28]. A modification of the MFC process, termed as
microbial electrolysis cell (MEC) process, involves application of additional voltage
(0.3 V minimum) and use of a hydrogen-producing catalyst within an anaero-
bic cathode chamber resulting in hydrogen production instead of electricity [29].
Hydrogen production has been demonstrated from sugars and organic acids [30]
and has been proposed as a method for energy production from renewable resources
[31-33]. Hydrogen, which is a higher value product, offers a distinct economic
advantage over electricity as the primary product of the bioelectrochemical process,
since it helps compensate the high capital costs in implementing this technology
[30, 34].
A second aspect of the cleanup of food industry wastewater streams is the possi-
bility of water reuse and recycle. The quality of water has to approach drinking water
levels in order to consider its reuse; however, recycle of the water to other operations
within the industry may be possible. Several wastewater streams in the food indus-
try contain quite low levels of organic carbon. The MFC technology may have an
advantage for these streams over anaerobic digestion due to its potential to remove
contaminants to very low levels and the ability to process the water at high flow
rates using biofilm-based catalysts [12]. Currently, water reuse in the food industry
is limited due to legislative constraints and hygiene concerns. Increase in energy
costs and scarcity of the water resource in some locations has prompted rethinking
of the water use practices [35]. The regulatory, technological, monitoring, verifica-
tion and ethical aspects associated with microbiologically safe reuse of water need
to be considered for any technology that is considered for the wastewater treatment.
An alternative set of guidelines and regulations have been recently developed for
use of water other than potable water for application in the food industry [36].
In this work, we assess the potential for electricity and hydrogen production
from food industry wastewaters and discuss the potential application of this tech-
nology as the need and prospects for energy production from waste and renewable
resources increase. The niche of this technology is evaluated for treatment of low
BOD wastewaters. Energy production from high BOD wastewaters is also evalu-
ated. As a case study, we investigate electricity production fromwastewater obtained
from a local milk dairy plant (Mayfield, Athens, TN). The objective of this experi-
mental study was to test electricity production from the wastewater and to determine
the maximum power density possible using an air-cathode MFC. The need for
pretreatment/amendments into the raw wastewater was examined to identify poten-
tial limitations. The results from this study, along with reported literature values,
