Environmental Engineering Reference
In-Depth Information
resulting in higher substrate removal (Mahmoud
et al.
2014
; Torres
2014
).
Similarly, the anaerobic biocathode chamber
also supports the reduction reactions which help
in the removal of pollutants and toxic compo-
nents of wastewater, especially when they act
as electron acceptors. Instead of oxygen, other
substances like nutrients, viz. nitrogen, sulphur,
and metal ions, viz. iron, manganese and chro-
mium, will act as TEAs in the case of anaerobic
biocathode. This helps in the removal of those
toxic substances from the wastewater along
with power generation (Clauwaert et al.
2007
;
Hamelers et al.
2010
; Huang et al.
2011
). Both
the anode and cathode chambers function as an-
aerobic treatment units in this case except for the
variation that the presence of electrodes in each
chamber and connected in the circuit across an
external resistance/load. Generally, the biopoten-
tial maintenance in this type of operation will be
very low due to the fact that the microbes in both
chambers follow the similar metabolic function
and compete as electron donors, instead of one
acting as acceptor. This situation will not allow
the system to carry out the induced oxidation
reactions. However, the strong reduction condi-
tions prevailing in both the chambers support the
substrate removal. When the wastewater contains
a specific pollutant or component, viz. metal ions
(Fe
2 +
, Mn
2 +
), dyes, nitrates, sulphates, etc.,
which can act as an electron acceptor, treatment
efficiency will increase along with the power
output.
On the other hand, the microaerophilic en-
vironment at cathode switches between aerobic
and anaerobic microenvironments. This has an
advantage over aerobic and anaerobic biocathode
operations, especially in wastewater treatment
sector. Some pollutants like azo dye need both
the environments for complete mineralization.
The anaerobic condition helps in splitting the azo
bond, while the aerobic condition helps in min-
eralization of dye metabolites (Venkata Mohan
et al.
2013
). The lower DO levels maintained at
cathode during this operation helps in initiating
electrochemical oxidation reactions as well as
maintaining strong reduction reactions. The sur-
vival of facultative microbes which can carry out
both metabolic functions will increase the treat-
ment efficiency (Srikanth et al.
2012
).
10.3
Merits of BES in Microbial
Electroremediation
The BES function as wastewater treatment unit
has been gaining prominence more recently due
to the higher efficiency of waste remediation
compared to conventional anaerobic treatment
process (Velvizhi and Venkata Mohan
2011
; Mo-
hanakrishna et al.
2010a
). The principle of bio-
electrochemical treatment (BET) relies on the fact
that electrochemically active microorganisms can
transfer electrons from a reduced electron donor
to an electrode and finally to an oxidized electron
acceptor generating power (Pant et al.
2013
; Ven-
kata Mohan et al.
2014b
). Coupling of bioanode
to a counterelectrode (abiotic/biotic cathode) will
have positive influence on overall wastewater
treatment efficiency along with energy recov-
ery, which has to be tapped. The possibility of
integrating diverse components, viz. biological,
physical and chemical components, during BES
operation provides an opportunity to initiate
diverse reactions such as biochemical, electro-
chemical, bioelectrochemical, physicochemical,
etc. which are cohesively termed as bioelectro-
chemical reactions.
In situ
generated biopotential
helps in the enhancement of the degradability of
different pollutants in both the anode and cathode
chambers. Formation of oxidants and reactive
species like OH
−
, O
−
, etc. is an added advantage
of BES over conventional treatment systems, es-
pecially for the treatment of complex wastewater
streams (Israilides et al.
1997
; Mohanakrishna
et al.
2010a
). Sometimes the pollutants/compo-
nents of wastewater themselves act as mediators
in electron transfer. For instance, elemental sul-
phur present in the wastewater acts as a media-
tor at anode and converts itself to sulphate which
is the easier form for degradation (Dutta et al.
2009
). Similarly, azo dyes act as mediators and
decolorize during reduction (Mu et al.
2009a
) and
estrogenic compounds get oxidized in BES sys-
tem (Kiran Kumar et al.
2012
). BES is also prov-
en for considerable reduction of toxicity, colour
Search WWH ::
Custom Search