Two stage bioethanol refining with multi litre stacked microbial fuel cell and microbial electrolysis cell.

Ethanol, electricity, hydrogen and methane were produced in a two stage bioethanol refinery setup based on a 10L microbial fuel cell (MFC) and a 33L microbial electrolysis cell (MEC). The MFC was a triple stack for ethanol and electricity co-generation. The stack configuration produced more ethanol with faster glucose consumption the higher the stack potential. Under electrolytic conditions ethanol productivity outperformed standard conditions and reached 96.3% of the theoretically best case. At lower external loads currents and working potentials oscillated in a self-synchronized manner over all three MFC units in the stack. In the second refining stage, fermentation waste was converted into methane, using the scale up MEC stack. The bioelectric methanisation reached 91% efficiency at room temperature with an applied voltage of 1.5V using nickel cathodes. The two stage bioethanol refining process employing bioelectrochemical reactors produces more energy vectors than is possible with today's ethanol distilleries.

Scale-up of phosphate remobilization from sewage sludge in a microbial fuel cell.

Phosphate remobilization from digested sewage sludge containing iron phosphate was scaled-up in a microbial fuel cell (MFC). A 3litre triple chambered MFC was constructed. This reactor was operated as a microbial fuel cell and later as a microbial electrolysis cell to accelerate cathodic phosphate remobilization. Applying an additional voltage and exceeding native MFC power accelerated chemical base formation and the related phosphate remobilization rate. The electrolysis approach was extended using a platinum-RVC cathode. The pH rose to 12.6 and phosphate was recovered by 67% in 26h. This was significantly faster than using microbial fuel cell conditions. Shrinking core modelling particle fluid kinetics showed that the reaction resistance has to move inside the sewage sludge particle for considerable rate enhancement. Remobilized phosphate was subsequently precipitated as struvite and inductively coupled plasma mass spectrometry indicated low levels of cadmium, lead, and other metals as required by law for recycling fertilizers.

Microbial electrolysis cell accelerates phosphate remobilisation from iron phosphate contained in sewage sludge.

Phosphate was remobilised from iron phosphate contained in digested sewage sludge using a bio-electric cell. A significant acceleration above former results was caused by strongly basic catholytes. For these experiments a dual chambered microbial electrolysis cell with a small cathode (40 mL) and an 80 times larger anode (2.5 L) was equipped with a platinum sputtered reticulated vitreous carbon cathode. Various applied voltages (0.2-6.0 V) generated moderate to strongly basic catholytes using artificial waste water with pH close to neutral. Phosphate from iron phosphate contained in digested sewage sludge was remobilised most effectively at pH ∼13 with up to 95% yield. Beside minor electrochemical reduction, hydroxyl substitution was the dominating remobilisation mechanism. Particle-fluid kinetics using the "shrinking core" model allowed us to determine the reaction controlling step. Reaction rates changed with temperature (15-40 °C) and an activation energy of Ea = 55 kJ mol(-1) was found. These analyses indicated chemical and physical reaction control, which is of interest for future scale-up work. Phosphate remobilisation rates increased significantly, yields doubled and recovered PO4(3-) concentrations increased four times using a task specific bio-electric system. The result is a sustainable process for decentralized phosphate mining and a green chemical base generator useful also for many other sustainable processing needs.

Probing electron transfer with Escherichia coli: a method to examine exoelectronics in microbial fuel cell type systems.

Escherichia coli require mediators or composite anodes for substantial outward electron transfer, >8A/m(2). To what extent non-mediated direct electron transfer from the outer cell envelope to the anode occurs with E. coli is a debated issue. To this end, the redox behaviour of non-exoelectrogenic E. coli K12 was investigated using a bi-cathodic microbial fuel cell. The electromotive force caused by E. coli biofilms mounted 0.2-0.3 V above the value with the surrounding medium. Surprisingly, biofilms that started forming at different times synchronised their EMF even when physically separated. Non-mediated electron transfer from E. coli biofilms increased above background currents passing through the cultivation medium. In some instances, currents were rather high because of a sudden discharge of the medium constituents. Mediated conditions provided similar but more pronounced effects. The combined step-by-step method used allowed a systematic analysis of exoelectronics as encountered in microbial fuel cells.

Microbial fuel cell enables phosphate recovery from digested sewage sludge as struvite.

Orthophosphate was mobilized from iron phosphate (FePO(4)) contained in digested sewage sludge by microbial fuel cell power. FePO(4) was reduced through electrons and protons obtained from metabolic activity of Escherichia coli. The process yielded up to 82% or 600 mg/l. Optical emission spectroscopy was used for phosphate dosage. (31)P NMR showed a singlet at δ(p)=3.72 ppm indicating that orthophosphate (H(3)PO(4), HPO(4)(-), HPO(4)(2-) and PO(4)(3-)) was recovered. The phosphate containing supernatant solution was reacted with stoichiometric amounts of MgCl(2) and NH(4)OH to precipitate struvite (MgNH(4)PO(4)·6H(2)O). The crystalline fertilizer was analyzed by scanning electron microscopy comprising elemental analysis, revealing a composition accuracy of ∼ 90% and the absence of any toxic metals such as As, Cd, Pb, or Cr. The phosphate extraction is also a means to reduce the volume of digested sewage sludge while increasing the heat of combustion. This study represents a concept for sustainable decentralized phosphate recycling.