Regarding the treatment of (waste)water, electrochemical processes have various advantages over other methods. They are robust, easy to operate and flexible in case of fluctuating wastewater streams. In addition, a relatively broad spectrum of organic and inorganic impurities can be removed. This contribution provides an overview of electrochemical reactors for water, process water, and wastewater treatment, which are already in technical‐scale operation or subject of research. Some essential basics of electrochemical processes for the treatment of water are presented and examples for applications are given. This is followed by a description of the reactors.

For the improvement of microbial fuel cell (MFC) performance in real wastewater it is necessary to implement catalysts on the cathode. Potential electrochemical catalysts for the MFC have to be widely available and should be low cost materials. Graphite, MnO 2 and MoS 2 fulfill the requirements and were evaluated in this work. These materials were prepared by dispersion of MnO 2 and/or MoS 2 and graphite in a solution of celluloid using butanone as solvent. Four MFCs with an active area of 225 cm 2 were connected in series with the wastewater supply. Their individual maximum output power densities were evaluated in relation to time. The results showed that MFC without catalyst reached a power density of only 40 mW/m 2 , while the best performance of MFC with graphite plus MnO 2 coating (10:1) was higher than 100 mW/m 2 . Comparing with graphite plus MnO 2 coating, the graphite plus MoS 2 paint shows a lower power density but much higher long-term stability than graphite plus MnO 2 coating. The scaling up of MFC with catalyst on the cathode is also studied in this research. Four MFCs with dimension of 980 cm 2 were constructed and connected in series, whose anodes have two sides for enlargement of reaction surface area. Rising demand for energy and fossil fuel resources being finite, the search for new alternative sustainable energy solutions have increased tremendously.1 Hydraulic, wind and solar radiation are clean energy resources as alternatives to fossil resources to produce electricity. However, these energy sources are limited by climate and geographical factors. Comparing with the energy sources that are mentioned above, biomass is one of the important renewable carbon sources and has been recognized as a promising energy supplier in the future. The increasing demand for biofuels has encouraged researchers and politicians worldwide to find sustainable biofuel production systems in accordance with the regional conditions and needs. 2 A MFC is an innovative method to generate electricity from organic matter using exoelectrogenic bacteria.3 Furthermore MFCs have drawn increasing attention as they can generate renewable energy and purify wastewater simultaneously. 4 The main MFC-components are the electrodes, separated into the anodic-and cathodic-chamber. Electrons and protons are produced on the anode from the oxidation of organic matters using bacteria as biocatalyst. In the cathode chamber, an electron acceptor is reduced with the electrons transferred via an external circuit and the protons diffused through the solution. However, complete treatment of wastewater cannot be accomplished solely with MFCs as current production is rapidly reduced to low levels when the chemical oxygen demand of the organic matter is reduced to ∼100-200 mg/L. 6,7 Scaling up MFCs is challenging based on the need to use inexpensive and non-precious metal materials and to achieve good performance. The use of carbon fiber brushes provides a route to make low-cost anodes, [8][9][10] and several different cathodes have been construc...

The influence of process parameters on the H2O2 yield of gas diffusion electrodes (GDE) are investigated. The investigated GDEs consist of Vulcan XC72 carbon black and PTFE on gold‐plated nickel wire cloth. An electrolysis cell is used to evaluate the influence of various process parameters, such as temperature, pH value, oxygen pressure and stoichiometric factor, electrolyte flow regime, current density and separator material at steady‐state conditions. It is found that the investigated GDE enables current efficiencies greater than 90 % at up to 2 kA m−2, whereby lower electrolyte temperatures and higher pH values contribute to higher H2O2 yields above 90 % current efficiency.

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In this study, mixtures of graphite, γ-MnO 2 and MoS 2 with different weight proportions (20:1:1, 30:1:2 and 30:2:1) were used in microbial fuel cells (MFCs) and the catalysts were also subjected to ultrasonication to study its influence. The data suggest that the MFC fabricated with the catalyst prepared using graphite, γ-MnO 2 and MoS 2 in a weight proportion of 20:1:1 exhibited the highest optimal power density of 120 mW/m 2 . However, after ultrasonic treatment, the power density was significantly improved, which was 183 mW/m 2 . It can also be observed that after using ß-MnO 2 , the optimal power density of the MFC fabricated with the catalyst prepared with graphite, ß-MnO 2 and MoS 2 in a proportion of 20:1:1 higher (158 mW/m 2 ) than that of the MFC fabricated with γ-MnO 2 in the same proportion, showing that the performance of ß-MnO 2 with a whisker structure was better than that of γ-MnO 2 owing to its higher surface area, larger pore diameter and great pore volume. The long term performances of the MFCs fabricated using catalysts prepared with the different graphite, γ-MnO 2 (ß-MnO 2 ) and MoS 2 proportions decreased finally in the order of 20:1:1 (ß-MnO 2 ) > 20:1:1 (ultrasonicated γ-MnO 2 ) > 10:1 (ß-MnO 2 ) >20:1:1 (γ-MnO 2 ) > 30:2:1 (γ-MnO 2 ) >30:1:2 (γ-MnO 2 ).