Microbial desalination technology offers a promising platform for salt removal processes and for the recovery of ionic compounds. In terms of operation, systems without potential control (microbial desalination cell, MDC) and applying anode potential control (microbial electrolysis desalination cell, MEDC) can be primarily implemented. In this study, a comparative assessment of the different operational modes is carried out by using acetate-fed mixed culture MDC and MEDC reactors for NaCl removal (with 35 g L-1 initial concentration) in three-chamber setup. Desalination efficiency, kinetics, as well as the occurring electrochemical losses are evaluated. In addition, ion exchange membrane (IEM) performance and stability are addressed. It was found that MEDC mode led to faster desalination and better NaCl removal (similar to 45 %) during 24 h long batches, compared to MDC (40.3 %), thanks to the similar to 12 % higher (j = 12 +/- 5 A m(-3)) and more consistent current density generated. Severe diffusional losses occurred in both systems, leading to similar to 80 % decrease in desalination rate after 24 h of operation. In addition, IEM ionic conductivity was significantly reduced after 40 d long employment. Future research needs and directions are highlighted for system performance enhancement.

The research interest about the volatile fatty acid (VFA) formation from food or kitchen waste are significantly increasing from the last few years. Assisting the ongoing tendency, in this work, kitchen waste as low-cost carbon source was treated by acidogenic fermentation with sewage sludge digestate as inoculum for VFA production. Due to the remarkable amount of kitchen waste generated annually, investigations were made at high organic loads that simulate favourable practical needs due to the higher volumetric efficiency. Information was obtained about the pH related VFA profiles, unpretreated sludge addition, batch and fed-batch operation. Without pH control, the low pH conditions (under pH 5.5) led mostly to acetic (60.2

In this study, first, a fed-batch biogas fermenter was established using anaerobic digester sludge treating secondary sludge from a municipal wastewater treatment plant and operated for 120 days on glycerol as the sole substrate. Then, the prefiltered effluent of the anaerobic digester unit was loaded subsequently into a stirred-tank coupled with a hollow-fibre, polydimethylsiloxane (PDMS) gas-liquid membrane contactor and a dissolved methane sensor for studying the gas recovery process under continuous biogas supply, consisting of CH4 and CO2 in different proportions (70/30 CH4/CO2 vol.%; 50/50 CH4/CO2 vol.%; 30/70 CH4/CO2 vol.%.). Experiments showed that besides the actual composition of the internal biogas, the ratio (0.5-2) of sweep gas (N2) and effluent (liquid) volumetric flow rates (G/L) could be a crucial operating factor with influence on the degassing efficiency attainable by the 1 m2 PDMS membrane module. Results were compared to the performance of the same PDMS membrane module working with synthetic anaerobic digester effluents, indicating the dissolved methane recoveries observed with the synthetic effluents (>50%) considerably surpassed those with the real effluent (<20%) where the dissolved methane concentrations, at G/L of 1, were in the range of 12.4 to 17.3 mg L−1.

In this work, a novel ionogel membrane was prepared on polyethersulfone physical support from the mixture of microcrystalline cellulose and [BMIM][Cl] (1-Butyl-3-methylimidazolium chloride) ionic liquid and used in a microbial fuel cell (MFC). The ionogel membrane was characterized in terms of its morphology, mass- (substrate, oxygen) and ion transfer features and compared to Nafion 115. The membranes were deployed in acetate-fed two-chamber MFC, where the MFC equipped with the ionogel membrane showed a Coulombic efficiency and peak current density of 49.4 % and 369 mA m(-2), respectively. Through three weeks of experiments, the electrode and membrane biofouling layers were studied by 16S amplicon metagenomics and correspondence analysis. It turned out that a cellulose-degrading species, Clostridium termitidis was present with a relatively large, 23.2 % relative abundance on the surface of the ionogel membrane, which may have caused its deterioration and the consequent colonization of the cathodic compartment.

Groundwater is an important resource that can help in climate change adaptation. However, the pollution of these aquifers with nitrate is a widespread problem of growing concern. Biological denitrification using inorganic electron donors shows significant advantages in treating nitrate-polluted groundwater where organic matter presence is negligible. However, mass transfer limitations and secondary contamination seem to be the major hinderance to spread the use of these technologies. This could be solved by the use of bioelectrochemical systems (BES), which emerge as an attractive technology to solve these problems due to the reported low energy demand and high denitrification rates. However, technical and operational issues must be considered to replicate these results at full-scale. This review summarizes the biological basis of autotrophic denitrification and the key aspects of its application in bioelectrochemical systems. In addition, an estimation of the capital costs required for the implementation of a BES considering different population sizes and initial nitrate concentration in the groundwater is made.

Microbial electrosynthesis cells (MES) are devices with demonstrated capability to treat CO2-containing gaseous streams and alongside, generate certain valuable chemical products, particularly methane gas, carboxylic acids, alcohols, etc. Although there are many varieties of MES with their own individual characteristics, all systems have a lot in common, starting from their design and operational features to the underlying microbiological phenomena. With the support of literature publications and related numerical data, this paper reviews and analyses the most important features of MES to identify general tendencies and practical recommendations pertaining to their design (electrodes, membranes), operation (cathode potential, CO2 feeding, temperature, pH) and biocatalysts ensuring an enhanced performance. As a result, several key-issues are provided to (i) successfully implement MES setups as well as to (ii) outline the perspectives of the technology towards the further promotion and development of this CO2-refinery process.

Itaconic acid is a promising biobased organic acid that can be industrially produced in an eco-friendly way by aerobic fungal fermentation. It has many applications, e.g. in biopo-lymers, and has the potential to help replace or facilitate the green production of other similar but fossil-based chemicals. Nowadays, its production costs are still relatively high, partly due to the multistep product recovery process from the fermentation broth. In this study, a reduced number of downstream processes were evaluated to recover itaconic acid from model and real fermentation effluents. To the best of our knowledge, this is the first time the whole procedure is presented from the substrates to the solid and pure product, including fermentation, electrodialysis with bipolar membrane, evaporation and optimized crystallization. Based on the fermentation temperature and elevated pH, a synergistic effect was observed that intensified certain mass transfer mechanisms. Consequently, a sig-nificant amount of water (400 cm3) and itaconic acid (15 g) was transported into the alkaline concentrate. Moreover, novel outcomes about the condition, decolorization and process enhancements of the membrane (product recovery: 65-80 %, current efficiency: 42-76 %, product purity: 99 %) were recorded. Based on the results, our group is one step closer to the final concept of a continuously operated fermentation-electrodialysis integrated system.(c) 2022 The Authors. Published by Elsevier Ltd on behalf of Institution of Chemical Engineers. This is an open access article under the CC BY license (http://creative-commons.org/licenses/by/4.0/).

Urine is a widely available renewable source of nitrogen and phosphorous. The nitrogen in urine is present in the form of urea, which is rapidly hydrolyzed to ammonia and carbonic acid by the urease enzymes occurring in nature. In order to efficiently recover urea, the inhibition of urease must be done, usually by increasing the pH value above 11. This method, however, usually is based on external chemical dosing, limiting the sustainability of the process. In this work, the simultaneous recovery of urea and phosphorous from synthetic urine was aimed at by means of electrochemical pH modulation. Electrochemical cells were constructed and used for urea stabilization from synthetic urine by the in situ formation of OH- ions at the cathode. In addition, phosphorous precipitation with divalent cations (Ca2+, Mg2+) in the course of pH elevation was studied. Electrochemical cells equipped with commercial (Fumasep FKE) and developmental (PSEBS SU) cation exchange membranes (CEM) were used in this study to carry out urea stabilization and simultaneous P-recovery at an applied current density of 60 A m−2. The urea was successfully stabilized for a long time (more than 1 month at room temperature and nearly two months at 4 °C) at a pH of 11.5. In addition, >82% P-recovery could be achieved in the form of precipitate, which was identified as amorphous calcium magnesium phosphate (CMP) by using transmission electron microscopy (TEM).

In this study, microbial fuel cells deploying heterogeneous ion exchange membranes were assessed. The behavior of the cells as a function of the membrane applied was evaluated in terms of maximal current density, electron recovery efficiency and energy production rate (up to 427.5 mA, 47.7 % and 660 J m(-2)h(-1), respectively) at different substrate (acetate) feedings (2.15 - 8.6 mM). System performance was characterized in the light of oxygen and acetate crossovers. The effect of membranes (in relation to the oxygen mass transfer coefficient, k(O)) on the microbial diversity of anodic and membrane-surface biofilms was investigated. Based on the relative abundance of bacterial orders, the two populations could be distinguished and membranes with larger k(O) tended to promote more the air-tolerant microbes in the biofouling layer. This indicates that membrane k(O) has a direct effect on membrane foulant microbial composition, and thus, on the expected time-stability of the membrane.

Two novel cation exchange membranes (CEM) denoted as PSEBS SU and CF22R14 were examined for two electrochemical applications and compared to a commercial membrane (Fumasep FKE). Application in microbial electrolysis cells (MEC) and an abiotic electrochemical cells (EC) were selected as low and high current density systems (~1 A m -2 and 50 A m -2 , respectively). Hydration number (λ), ion exchange capacity (IEC) and ionic conductivity (σ), as well as their alteration after 10 days were studied. λ was stable after MEC operation, however EC mode caused remarkable changes and a decrease of λ (by -8.2 ± 0.3, -13.8 ± 0.8 and -39.3 ± 8.8% for FKE, PSEBS SU and CF22R14, respectively). The decrease of IEC was significant for each membrane regardless of the operation mode. However, only MEC operation led to reversible functionality losses, whereas EC mode caused permanent decrease of IEC (87.9 ± 2.8, 85.3 ± 3.8 and 46.6 ± 4.4% re-activation efficiency for FKE, PSEBS SU and CF22R14, respectively). The EC operation resulted in more severe loss of σ for each CEM, among which PSEBS SU showed the best re-activation efficiency (74.9 ± 8.1%). In general, the membrane properties were much more impaired during EC operation due to higher current densities.

The scope of the current review is to discuss and evaluate the role of the external electrical load/resistor (EEL) on the overall behavior and functional properties of microbial fuel cells (MFCs). In this work, a comprehensive analysis is made by considering various levels of MFC architecture, such as electric and energy harvesting efficiency, anode electrode potential shifts, electro-active biofilm formation, cell metabolism and extracellular electron transfer mechanisms, as a function of the EEL and its control strategies. It is outlined that taking the regulation of EEL into account at MFC optimization is highly beneficial, and in order to support this step, in this review, a variety of guidelines are collected and analyzed.

Deriving biohydrogen from dark fermentation is a practically suitable pathway for scaling-up and envisaged mass production. However, a common issue with these systems is the incomplete conversion of feedstock as a result of which, a process effluent with notable organic strength is left behind. The main components of dark fermentation effluents are volatile fatty acids that can be utilized by integrated applications involving bioelectrochemical systems, particularly microbial fuel cells (MFCs) to generate electrical energy. In this work, MFCs deployed to treat dark fermentative H2 production effluents are assessed to take a look into the current standing of this specific research area and address what MFC design and operating features (reactor configuration, mode of operation, anode surface and reactor size) seem favorable towards improved working efficiency (e.g. power density, Coulombic efficiency, COD removal). Furthermore, promising technological implementations are outlined and suggestions, conclusions for future studies for this field are given.

In this work, a novel cation exchange membrane, PSEBS SU22 was deployed in microbial fuel cells (MFCs) to examine system efficacy in line with membrane characteristics and inoculum source. It turned out that compared to a reference membrane (Nafion), employing PSEBS SU22 resulted in higher current density and electricity generation kinetics, while the electron recoveries were similar (19-28%). These outcomes indicated more beneficial ion transfer features and lower mass transfer-related losses in the PSEBS SU22-MFCs, supported by membrane water uptake, ion exchange capacity, ionic conductivity and permselectivity. By re-activating the membranes after (bio)foulant removal, PSEBS SU22 regained nearly its initial conductivity, highlighting a salient functional stability. Although the particular inoculum showed a clear effect on the microbial composition of the membrane biofouling layers, the dominance of aerobic species was revealed in all cases. Considering all the findings, the PSEBS SU22 seems to be promising for application in MFCs.

Anaerobic degradation processes: anaerobic digestion (biogasification), biohydrogen fermentation (dark) and microbial fuel cells were applied to treat the organic fraction of a municipal solid waste. The processes were compared based on their ability of energy recovery and Chemical Oxygen Demand reduction.

Hydrophobic ionic liquids (IL) may offer a special electrolyte in the form of supported ionic liquid membranes (SILM) for microbial fuel cells (MFC) due to their advantageous mass transfer characteristics. In this work, the proton and ion transfer properties of SILMs made with IL containing imidazolium cation and [PF6]− and [NTf2]− anions were studied and compared to Nafion. It resulted that both ILs show better proton mass transfer and diffusion coefficient than Nafion. The data implied the presence of water microclusters permeating through [hmim][PF6]-SILM to assist the proton transfer. This mechanism could not be assumed in the case of [NTf2]− containing IL. Ion transport numbers of K+, Na+, and H+ showed that the IL with [PF6]− anion could be beneficial in terms of reducing ion transfer losses in MFCs. Moreover, the conductivity of [bmim][PF6]-SILM at low electrolyte concentration (such as in MFCs) was comparable to Nafion.

In this work, two commercialized anion-exchange membranes (AEMs), AMI-7001 and AF49R27, were applied in microbial electrolysis cells (MECs) and compared with a novel AEM (PSEBS CM DBC, functionalized with 1,4-diazabicyclo[2.2.2]octane) to produce biohydrogen. The evaluation regarding the effect of using different AEMs was carried out using simple (acetate) and complex (mixture of acetate, butyrate and propionate to mimic dark fermentation effluent) substrates. The MECs equipped with various AEMs were assessed based on their electrochemical efficiencies, H2 generation capacities and the composition of anodic biofilm communities. pH imbalances, ionic losses and cathodic overpotentials were taken into consideration together with changes to substantial AEM properties (particularly ion-exchange capacity, ionic conductivity, area- and specific resistances) before and after AEMs were applied in the process to describe their potential impact on the behavior of MECs. It was concluded that the MECs which employed the PSEBS CM DBC membrane provided the highest H2 yield and lowest internal losses compared to the two other separators. Therefore, it has the potential to improve MECs.

The performance and behavior of microbial fuel cells (MFCs) are influenced by among others the external load (R-ext). In this study, the anode-surface biofilm formation in MFCs operated under different R-ext selection/tracking-strategies was assessed. MFCs were characterized by electrochemical (voltage/current generation, polarization tests, EIS), molecular biological (microbial consortium analysis) and bioinformatics (principal component analysis) tools. The results indicated that the MFC with dynamic R-ext adjustment (as a function of the actual MFC internal resistance) achieved notably higher performance but relatively lower operational stability, mainly due to the acidification of the biofilm. The opposite (lower performance, increased stability) could be observed with the static (low or high) R-ext application (or OCV) strategies, where adaptive microbial processes were assumed. These possible adaptation phenomena were outlined by a theoretical framework and the significant impact of R-ext on the anode colonization process and energy recovery with MFCs was concluded.

This work characterizes and comparatively assess two cation exchange membranes (PSEBS SU22 and CF22 R14) and one bipolar membrane (FBM) in microbial electrolysis cells (MEC), fed either by acetate or the mixture of volatile fatty acids as substrates. The PSEBS SU22 is a new, patent-pending material, while the CF22 R14 and FBM are developmental and commercialized products. Based on the various MEC performance measures, membranes were ranked by the EXPROM-2 method to reveal which of the polymeric membranes could be more beneficial from a complex, H-2 production efficiency viewpoint. It turned out that the substrate-type influenced the application potential of the membranes. Still, in total, the PSEBS SU22 was found competitive with the other alternative materials. The evaluation of MEC was also supported by analyzing anodic biofilms following electroactive bacteria's development over time.

In this work, two polymeric membrane separators (a proton exchange membrane (PEM), Nafion, and an anion-exchange membrane (AEM), 1,4-diazabicyclo[2.2.2]octane (DABCO)-functionalized PSEBS) deployed in microbial fuel cells (MFCs) are comparatively assessed. The performances of MFCs according to membrane type were evaluated by biological and electrochemical techniques, employing metagenomics, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). It was found that the anodic biofilms of MFCs, irrespective of the type of membrane, were dominated by Geobacter sulfurreducens (37 and 50% for AEM-MFC and PEM-MFC, respectively), a well-known electrochemically active species. Furthermore, the AEM-MFC reflected a significantly lower internal resistance (145 Omega) compared to PEM-MFC (339 Omega) and produced higher maximal current densities and energy yields at all substrate (acetate) concentrations, as follows: 400 vs. 285 mA m(-2) (5 mM acetate); 360 vs. 320 mA m(-2) (10 mM acetate), 305 vs. 235 mA m(-2) (15 mM acetate) and 238 vs.132 kJ m(-2) g(COD) (5 mM acetate), 161 vs. 128 kJ m(-2) g(COD) (10 mM acetate), 114 vs. 59 kJ m(-2) g(COD) (15 mM acetate) respectively. The CV measurements implied diffusion limitations in the MFCs, which were supported by EIS. In addition, the PEM and AEM characterizations revealed that in both cases, the ion exchange capacity, ionic conductivity and oxygen mass transport features were altered considerably over the 39 days during which the MFCs operated.