D2.1 - EU Project Neptune

NEPTUNE · Contract-No. 036845 Deliverable 2.1
2.2.2 Description of work undertaken
The main focus of the work was to investigate the potential of using VFA mixtures, as
present in fermented sludge hydrolysate, for current generation using microbial fuel cells.
The proposed process diagram is show in (Figure 2.2). The work has comprised of two parts:
Part One: analysis of MFC performance with synthetic influent (single and mixed VFA),
evaluating the impact of loading and anode potential on both performance (i.e. current
generation) and VFA removal;
Part Two: analysis of MFC performance with fermented sludge hydrolysate.
The work thus far has been undertaken with a granular-type frame reactor with potassium
ferricyanide as the catholyte.
Figure 2.2 Flow diagram of concept
2.2.3 Results
The work thus far with pure VFA influent streams has demonstrated that the main
constituents of fermented sludge hydrolysate can effectively be degraded using a MFC
(loading of 1.9 gCOD/L.d, 500 mg/L COD). However, large differences exist between the
VFAs, with acetate and propionate more readily used. This highlights the possible role of a
fermenter operating in tandem, producing an MFC influent with a higher concentration of the
VFAs that are more readily degradable. Further work with potentiostatic control of the MFC
reactors (i.e. no longer limited by constant resistance between the positive and negative
poles of the cell) will help identify the operational parameters necessary to achieve a high
Coulombic efficiency with the whole VFA spectrum.
Initial work with mixed synthetic influent streams, representing the typical output of a
fermenter operating with CAMBI effluent, have demonstrated the ability of the MFC
technology to produce a steady current over a reasonable time period (two weeks), with the
removal of VFAs [over 50% reduction of COD (mgCOD/L)] and achieving Coulombic
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