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Nutrient recovery systems can be impacted due to the presence of organic micropollutants (OMPs). TAN (total ammonium nitrogen, sum of ammonium and ammonia) recovery from wastewater can be achieved by combining an electrochemical system with membrane stripping. Essential components of these processes are cation-exchange membranes and a hydrophobic gas-permeable membrane. These membranes are barriers between the OMPs source (wastewater) and recovered products. Despite reports about OMPs – ion exchange membrane interactions, there is limited knowledge about the transport of OMPs in ammonium recovery systems. This work gives a first detailed description of the transport mechanism of a broad group of OMPs with varying properties during electrochemical ammonium recovery supplied with a complex matrix (digested blackwater). Even after continuous exposure to OMPs and consequent system equilibration, OMP concentrations in the effluent were often lower than in the inflow stream. The highest removal and transport towards the concentrate were found for positively charged OMPs. The presence of organic matter contributed to the adsorption and transport of OMPs. Although OMPs were transported over the CEMs, the gas permeable hydrophobic membrane for ammonia recovery retained all OMPs.

A bipolar electrodialysis (BP-ED) pilot plant including 3.15 m2 of cation exchange membrane and bipolar membrane each was operated for ammonia recovery. The pilot treated source-separated diluted urine (1 gNH4+/L). Previously found set operation parameters for lab-scale such as current density and nitrogen load did not directly influence the stack performance. However, the effluent pH was directly related to the removal efficiency of the system. 80% nitrogen removal was achieved at a set effluent pH of 4. Operating under an effluent pH control strategy was more effective to control NH4+ removal than controlling current density or nitrogen loading, as it accounts for fluctuation in wastewater availability and composition. The pilot plant removed up to 88% of the NH4+ from urine and recovered around 700 g/day (from 1 m3 of urine). This was a significant improvement compared to the pilot plant previous performance on digestate. The energy consumption was around 13 Wh/gN. The overall current efficiency was ∼40% with most losses caused by parasitic ionic shortcut currents occurring at the hydraulic manifolds of the BP-ED stack. Therefore, the energy demand can be further decreased by preventing these ionic shortcuts in the new cell designs.

Phosphorus (P) is often regarded as the primary stimulant for eutrophication, while its importance as a crucial life element is also well acknowledged. Given its future scarcity, P recycling from waste streams is suggested and practiced. Electrochemically mediated precipitation (EMP) is a robust and chemical-free process for P removal and recovery, yet it requires further developments. The first generation of the CaCO3-packed electrochemical precipitation column successfully solved the problem of H+-OH− recombination, achieving enhanced P removal efficiency with less energy consumption but suffering from low Ca-phosphate purity in recovered products. Herein, a new concept of a basket-anode electrochemical system is proposed and validated to prevent direct H+-OH− recombination and enhance product purity. The CaCO3 pellets packed basket anode alleviates the OH− depletion by CaCO3-H+ interaction and provides extra Ca2+ for enhanced P removal. The novel structure of the basket anode, by its derived acidic anode region and alkaline cathode region, completely avoids the precipitation of Ca-phosphate on the packed CaCO3 and greatly facilitates the collection of high-quality Ca-phosphate product. Our results suggest that almost 100% of the removed P was in high-purity, highly crystalline Ca-phosphate on the cathode. The recovered products contained significantly more P (13.5 wt%) than in the previous study (0.1 wt%) at similar energy consumptions (29.8 kWh/kg P). The applied current density, pellets size, and influent P concentration were critical for P removal performance, product purity, and power consumption. We further demonstrated the long-term stability of this novel system and its technical and economic feasibility in treating real stored urine. Our study provides new cell architectural designs to enhance the performance of EMP systems and may inspire innovations and developments in other electrochemical water treatment processes.

In the biotechnological gas desulfurization process, dissolved sulfide is oxidized into predominantly elemental sulfur (S8) by sulfide oxidizing bacteria (SOB) under strict oxygen limited conditions. An online measurement of the oxidation reduction potential (ORP) is used to control the O2supply to the bioreactor to maximize the selectivity for S8formation and minimize unwanted sulfate formation. While the ORP in the bioreactor is considered to be a measure of mainly sulfide and oxygen concentrations, in practice, none of these components are detectable. In this study, we investigated the sensitivity of stored charge in SOB toward ORP. Stored charge in SOB was measured in an electrochemical cell. These SOB were harvested from the bioreactor of a pilot-scale desulfurization installation. The bioreactor, in which sulfide was not detectable, was operated at different ORP setpoints (-250 to-390 mV vs Ag/AgCl). It was found that more charge was recovered from SOB when the ORP in the aerated bioreactor was lower. These measurements were used to calibrate a model to describe the ORP based on charge storage in SOB, which showed that S8formation increases and sulfate formation decreases when SOB contain more charge. This can be used to further optimize the biotechnological desulfurization process.

Metal sulfide precipitation is a viable technology for high-yield metal recovery from hydrometallurgical streams, with the potential to streamline the process design. A single-stage elemental sulfur (S0)-reducing and metal sulfide precipitating process can optimize the operational and capital costs associated with this technology, boosting the competitiveness of this technology for wider industrial application. However, limited research is available on biological sulfur reduction at high temperature and low pH, frequent conditions of hydrometallurgical process waters. Here we assessed the sulfidogenic activity of an industrial granular sludge previously shown to reduce S0 under hot (60–80 °C) and acidic conditions (pH 3.6). A 4 L gas-lift reactor was operated for 206 days and fed continuously with culture medium and copper. During the reactor operation, we explored the effect of the hydraulic retention time, copper loading rates, temperature, and H2 and CO2 flow rates on the volumetric sulfide production rates (VSPR). A maximum VSPR of 274 ± 6 mg·L−1·d−1 was reached, a 3.9-fold increase of the VSPR previously reported with this inoculum in batch operation. Interestingly, the maximum VSPR was achieved at the highest copper loading rates. At the maximum copper loading rate (509 mg·L−1·d−1), a 99.96% copper removal efficiency was observed. 16 s rRNA gene amplicon sequencing revealed an increased abundance of reads assigned to Desulfurella and Thermoanaerobacterium in periods of higher sulfidogenic activity.

The recovery of phosphorus (P) from high-strength acidic waste streams with high salinity and organic loads is challenging. Here, we addressed this challenge with a recently developed electrochemical approach and compared it with the chemical precipitation method via NaOH dosing. The electrochemical process recovers nearly 90% of P (∼820 mg/L) from cheese wastewater in 48 h at 300 mA with an energy consumption of 64.7 kWh/kg of P. With chemical precipitation, >86% of P was removed by NaOH dosing with a normalized cost of 1.34–1.80 euros/kg of P. The increase in wastewater pH caused by NaOH dosing triggered the formation of calcium phosphate sludge instead of condensed solids. However, by electrochemical precipitation, the formed calcium phosphate is attached to the electrode, allowing the subsequent collection of solids from the electrode after treatment. The collected solids are characterized as amorphous calcium phosphate (ACP) at 200 mA or a precipitation pH of ≥9. Otherwise, they are a mixture of ACP and hydroxyapatite. The products have sufficient P content (≤14%), of which up to 85% was released within 30 min in 2% citric acid and a tiny amount of heavy metals compared to phosphate rocks. This study paves the way for applying electrochemical removal and recovery of phosphorus from acidic P-rich wastewater and offers a sustainable substitute for mined phosphorus., Electrochemical phosphorus mining from high-ionic strength acidic wastewater is accomplished by electrochemically induced calcium phosphate precipitation and provides a potential phosphorus source.

Valorization of organic residual streams that produce short-chain fatty acids (SCFA) require an energetic electron donor to form more valuable elongated products. By microbial electrosynthesis such electrons donor is supplied by an electrode. Here we show that bioelectrochemical chain elongation (BCE) of SCFA was steered to high selective product formation efficiencies depending on the supplied fatty acid. n-Butyrate, n-valerate, n-caproate were in different experimental conditions formed at respectively 94.1, 95.4 and 83.4% carbon-based selectivity. The reactor microbiomes adapted to the new feeding conditions within a few days. Remarkably, propionate elongation appeared to be preferred over acetate elongation. Propionate elongation resulted in highly selective formation of the odd-chain fatty acid n-valerate; this seems contradictory to ethanol chain elongation studies in which acetate is concurrently formed leading to straight fatty acids as by products.

Biological wood oxidation (BWO) offers great potential for sustainable heat generation, and our previous work has shown that nutrient addition (especially nitrogen; N) is necessary for fast BWO. To reduce the cost and environmental impacts of chemical nutrients, human urine was chosen as a source of nutrient in this study. We investigated the factors including urine dilution ratio, the types of urine (fresh urine and synthetic urine), and urine readdition, by studying their effects on oxygen consumption and dry weight loss of the wood. After 42-day incubation, synthetic urine with five times dilution (corresponding to 1.2 ‰ N dry basis of wood) showed the best performance; it improved the oxygen consumption by 3.8 times and wood weight loss by 3.3 times than that without urine addition (analysis of variance (ANOVA), P < 0.05). At the same N level, fresh urine addition was able to enhance the BWO more efficiently than synthetic urine addition, further improving the oxygen consumption by 64% and weight loss by 47% (ANOVA, P < 0.05). During the BWO process, the decrease in wood degradation rate was possibly due to the decrease in nutrient availability. With the readdition of synthetic urine, the total oxygen consumption and weight loss after 100-day incubation increased by more than 40% compared with the group without readdition. However, readdition of only N-containing components did not increase the BWO, showing that elements (other than N) were important. To this end, we demonstrated the feasibility of human urine as a waste-based nutrient source for fast BWO and the possibility of long-term BWO operation via urine readdition.

Industrial production of phototrophic microorganisms is often hindered by low productivity due to limited light availability and therefore requires large land areas. This letter demonstrates that supply of hydrogen gas (H2) increases in phototrophic biomass productivity compared to a culture growing on light only. Experiments were performed growing Synechocystis sp. in batch bottles, with and without H2 in the headspace, which were exposed to light intensities of 70 and 100 μmol/m2/s. At 70 μmol/m2/s with H2, the average increase in biomass was 96 mg DW/L/d, whereas at 100 μmol/m2/s without H2, the average increase in biomass was 27 mg DW/L/d. Even at lower light intensity, the addition of H2 tripled the biomass yield compared to growth under light only. Photoreduction and photosynthesis occurred simultaneously, as both H2 consumption and O2 production were measured during biomass growth. Photoreduction used 1.85 mmol of H2 to produce 1.0 mmol of biomass, while photosynthesis produced 1.95 mmol of biomass. After transferring the culture to the dark, growth ceased, also in the presence of H2, showing that both light and H2 were needed for growth. A renewable H2 supply for higher biomass productivity is attractive since the combined efficiency of photovoltaics and electrolysis exceeds the photosynthetic efficiency.

Composts are commonly used as soil amendments to sustain and improve the functionality of agricultural soil. Compost has abiotic (organic matter [OM], nutrients) and biotic characteristics (microorganisms) and both can influence the soil microbiome. The abiotic and biotic characteristics of compost, in turn, depend on properties of the compost such as maturity. Few studies have investigated the relative effects of abiotic and biotic components of compost on the soil microbial community and crop growth. To bridge this gap, we used a full-factorial design with sterile and live composts that differed in maturity (fresh, intermediate, mature) that were added to sterile and live soil to investigate the separate role of abiotic and biotic characteristics of composts on the resulting soil microbial community and on wheat growth. We found that the changes in the soil microbial community were mainly due to the input of compost with the presence of microorganisms rather than due to the abiotic properties of compost. The majority of the compost-associated microorganisms (more than 70% for bacteria and 90% for fungi) were detected in the soil in the presence of native soil microorganisms. Elimination of native soil microorganisms by sterilization enhanced the prevalence and abundance of compost-associated microorganisms. Adding fresh compost increased wheat biomass production, but the positive effects of compost on plant growth were strongest when sterile composts were used. Hence, our study reports that compost-associated microorganisms are essential to modify soil microbial community but may not benefit crop growth. This highlights the importance of understanding the role of abiotic and biotic properties of composts as common soil amendments on improving the functioning of agricultural soil.

New technologies to remove organosulfur compounds from industrial sources should focus on the recovery of sulfur rather than incineration and sorption processes. The removal of organosulfur compounds using bio electrochemical systems might form a sustainable alternative. The aim of this study was to analyse ethanethiol degradation at biocathodes under anaerobic conditions. This was done by operating two cells at different loading rates for >360 days. We observed a stable removal efficiency of >70% with a maximum elimination capacity of 2.25 mM/d. Initially, ethanethiol was present in the effluent. However, over time, diethyl disulfide became the dominant organosulfur compound. Sulfate and thiosulfate were formed in small quantities in the biocathode. SEM imaging demonstrated the presence of crystalline structures with the typical bipyramid shape of elemental sulfur. The images also demonstrated the presence of a microbial community in a scattered biofilm on the electrode surface. The biocathodes from the continuous experiments were used in the batch experiments to gain more insight in the degradation kinetics. No electron donor (other than ethanethiol) was added to these serum flasks. The experiments confirmed that the oxidation of ethanethiol into diethyl disulfide was mostly biocatalytic as ethanethiol oxidation rates were much lower in the controls. Dynamic modeling indicated that ethanethiol nor diethyl disulfide were further degraded under these conditions. We hypothesize that the oxidation of ethanethiol forms the first important step in the degradation of this compound and that diethyl disulfide can be further degraded under electrochemically controlled conditions.

Phosphorus (P) is an essential element for the growth and reproduction of organisms. Unfortunately, the natural P cycle has been broken by the overexploitation of P ores and the associated discharge of P into water bodies, which may trigger the eutrophication of water bodies in the short term and possible P shortage soon. Consequently, technologies emerged to recover P from wastewater to mitigate pollution and exploit secondary P resources. Electrochemically induced phosphate precipitation has the merit of achieving P recovery without dosing additional chemicals via creating a localized high pH environment near the cathode. We critically reviewed the development of electrochemically induced precipitation systems toward P removal and recovery over the past ten years. We summarized and discussed the effects of pH, current density, electrode configuration, and water matrix on the performance of electrochemical systems. Next to ortho P, we identified the potential and illustrated the mechanism of electrochemical P removal and recovery from non-ortho P compounds by combined anodic or anode-mediated oxidation and cathodic reduction (precipitation). Furthermore, we assessed the economic feasibility of electrochemical methods and concluded that they are more suitable for treating acidic P-rich waste streams. Despite promising potentials and significant progress in recent years, the application of electrochemical systems toward P recovery at a larger scale requires further research and development. Future work should focus on evaluating the system's performance under long-term operation, developing an automatic process for harvesting P deposits, and performing a detailed economic and life-cycle assessment.

We investigated the effect of polysulfide formation on properties of biologically produced elemental sulfur (S8) crystals, which are produced during biological desulfurization (BD) of gas. The recent addition of an anoxic-sulfidic reactor (AnSuR) to the BD process resulted in agglomerated particles with better settleability for S8 separation. In the AnSuR, polysulfides are formed by the reaction of bisulfide (HS-) with S8 and are subsequently oxidized to S8 in a gas-lift reactor. Therefore, sulfur particles from the BD are shaped (i.e. morphology and particle size) both by formation and dissolution. We assessed the reaction of HS- with S8 particles in anoxic, abiotic experiments in a batch reactor using two S8 samples from industrial BD reactors. Under these conditions, the sulfur particle surface became coarser and more porous, and in addition the smallest particles disappeared. Agglomerates initially fell apart but were reformed at a later stage. Moreover, we found different observed polysulfide formation rates for each S8 sample, which was related to the initial morphology and size. Our findings show that particle properties can be controlled abiotically and that settleability of S8 is increased by increasing both the HS--S8 ratio and retention time.

The living soil harbors a significant number and diversity of bacteria and fungi, which are essential in sustaining soil ecosystem functions. Most studies focus on soil bacteria or fungi, ignoring potential interrelationships between kingdoms that coevolve and synergistically provide ecosystem functions. In a seven-year agricultural field, we explored the effects of organic amendments (OAs; i.e., compost and bokashi) on intra- and inter-kingdom co-occurrence networks of soil bacterial and fungal communities. We observed that OAs changed the co-occurrence patterns of bacteria and fungi. Distinct network modules were observed in the unamended and amended soils, and the physicochemical properties of the soil could partially explain the formation of these modules. We also found that compost and bokashi increased the proportion of positive correlations, and this could reduce competition among microorganisms for soil resources. Our study reveals that soil management with OAs affects relationships between bacterial and fungal subpopulations that physically co-exist, cooperate, and compete in non-random structured networks. It highlights that ecosystem functions may depend on inter-kingdom interactions shaped by different amendments and their applied dose.

Chain elongation fermentation allows for the synthesis of biobased chemicals from complex organic residue streams. To expand the product spectrum of chain elongation technology and its application range we investigated 1) how to increase selectivity towards branched chain elongation and 2) whether alternative branched carboxylates such as branched valerates can be used as electron acceptors. Elongation of isobutyrate elongation towards 4-methyl-pentanoate was achieved with a selectivity of 27% (of total products, based on carbon atoms) in a continuous system that operated under CO2 and acetate limited conditions. Increasing the CO2 load led to more in situ acetate formation that increased overall chain elongation rate but decreased the selectivity of branched chain elongation. A part of this acetate formation was related to direct ethanol oxidation that seemed to be thermodynamically coupled to hydrogenotrophic carboxylate reduction to corresponding alcohols. Several alcohols including isobutanol and n-hexanol were formed. The microbiome from the continuous reactor was also able to form small amounts of 5-methyl-hexanoate likely from 3-methyl-butanoate and ethanol as substrate in batch experiments. The highest achieved concentration of isoheptanoate was 6.4 ± 0.9 mM Carbon, or 118 ± 17 mg/L, which contributed for 7% to the total amount of products (based on carbon atoms). The formation of isoheptanoate was dependent on the isoform of branched valerate. With 3-methyl-butanoate as substrate 5-methylhexanoate was formed, whereas a racemic mixture of L/D 2-methyl-butanoate did not lead to an elongated product. When isobutyrate and isovalerate were added simultaneously as substrates there was a large preference for elongation of isobutyrate over isovalerate. Overall, this work showed that chain elongation microbiomes can be further adapted with supplement of branched-electron acceptors towards the formation of iso-caproate and iso-heptanoate as well as that longer chain alcohol formation can be stimulated.

Phosphorus (P) removal and recovery from waste streams is essential for a sustainable world. Here, we updated a previously developed abiotic electrochemical P recovery system to a bioelectrochemical system. The anode was inoculated with electroactive bacteria (electricigens) which are capable of oxidizing soluble organic substrates and releasing electrons. These electrons are then used for the reduction of water at the cathode, resulting in an increase of pH close to the cathode. Hence, phosphate can be removed with coexisting calcium ions as calcium phosphate at the surface of the cathode with a much lower energy input. Depending on the available substrate (sodium acetate) concentration, an average current density from 1.1 ± 0.1 to 6.6 ± 0.4 A/m2 was achieved. This resulted in a P removal of 20.1 ± 1.5% to 73.9 ± 3.7%, a Ca removal of 10.5 ± 0.6% to 44.3 ± 1.7% and a Mg removal of 2.7 ± 1.9% to 16.3 ± 3.0%. The specific energy consumption and the purity of the solids were limited by the relative low P concentration (0.23 mM) in the domestic wastewater. The relative abundance of calcium phosphate in the recovered product increased from 23% to 66% and the energy consumption for recovery was decreased from 224 ± 7 kWh/kg P to just 56 ± 6 kWh/kg P when treating wastewater with higher P concentration (0.76 mM). An even lower energy demand of 21 ± 2 kWh/kg P was obtained with a platinized cathode. This highlights the promising potential of bioelectrochemical P recovery from P-rich waste streams.

This paper analyzes six case studies of new water technology innovations in the last three decades and investigates the differences in timelines for moving through the various stages of water technology commercialization. The concept of two different types of innovation was explored: Crisis/Needs Driven and Value Driven. It was found that the case studies that mapped to the Crisis/Needs Driven innovation moved relatively quickly compared to Value Driven innovations and in most cases involved new entrants. New entrants refer to new companies or start-ups that have recently entered the water technology market. The case studies, which could be mapped to Value Driven innovation, had a slower rate of technology diffusion, and they involved a combination of existing companies as well as new entrants. • Practitioner points • The paper identifies two key types of innovation: Crisis/Needs Driven and Value Driven. • Legislation was observed to be a key driver for the adoption of new technology innovation in the water sector. • The Crisis/Needs driven innovations studied were observed to diffuse through the Water Technology Diffusion model at up to twice the pace of Value driven innovation. • Crisis/Needs driven innovation typically involves disruptive innovation offered by new entrants, whereas with Value driven innovation, the solutions are provided by both existing companies as well as new entrants. • It is also observed that in most cases a technology that is adopted in order to meet a crisis or need in the market is more expensive at the outset compared with incumbent solutions. • While value driven adoption has a slower cycle for adoption, it presents a lower risk as it is less dependent on external factors and timing of implementation of regulations or the occurrence of some public health related or environmental crisis.

In the biotechnological desulfurization process under haloalkaline conditions, dihydrogen sulfide (H 2 S) is removed from sour gas and oxidized to elemental sulfur (S 8 ) by sulfide-oxidizing bacteria. Besides S 8 , the byproducts sulfate (SO 4 2- ) and thiosulfate (S 2 O 3 2- ) are formed, which consume caustic and form a waste stream. The aim of this study was to increase selectivity toward S 8 by a new process line-up for biological gas desulfurization, applying two bioreactors with different substrate conditions (i.e., sulfidic and microaerophilic), instead of one (i.e., microaerophilic). A 111-day continuous test, mimicking full scale operation, demonstrated that S 8 formation was 96.6% on a molar H 2 S supply basis; selectivity for SO 4 2- and S 2 O 3 2- were 1.4 and 2.0% respectively. The selectivity for S 8 formation in a control experiment with the conventional 1-bioreactor line-up was 75.6 mol %. At start-up, the new process line-up immediately achieved lower SO 4 2- and S 2 O 3 2- formations compared to the 1-bioreactor line-up. When the microbial community adapted over time, it was observed that SO 4 2- formation further decreased. In addition, chemical formation of S 2 O 3 2- was reduced due to biologically mediated removal of sulfide from the process solution in the anaerobic bioreactor. The increased selectivity for S 8 formation will result in 90% reduction in caustic consumption and waste stream formation compared to the 1-bioreactor line-up.

BACKGROUND: The load ratio is a crucial parameter to optimize the current driven recovery of total ammonia nitrogen (TAN) from urine. The load ratio is the ratio between the current density and the TAN loading rate. It is currently not known if the load ratio concept applies to a bioelectrochemical system (BES) because the current density and TAN loading rate cannot be controlled independently. RESULTS: We found a clear increasing trend in TAN removal efficiency with respect to load ratio in the BES for both human and synthetic urine. The maximum TAN removal efficiency was 60.9% at a load ratio of 0.7, corresponding to a TAN transport rate of 119 gNm−2 day−1 at an electrical energy input of 1.9 kWh kgN−1 (synthetic urine). Low load ratios ( indicating that the current was not enough to transport all the TAN across the membrane . CONCLUSIONS: BES and ES show the same general relationship between TAN removal efficiency and load ratio. Therefore, given a stable current density, the concept of load ratio can also predict the TAN removal efficiency in BES. Higher current densities, and insights into the factors limiting current, are needed to increase the load ratio and therefore the TAN removal efficiency. &nbsp

Several industrial processes produce toxic sulfide containing streams that are often scrubbed using caustic solutions. An alternative, cost effective sulfide treatment method is bioelectrochemical sulfide removal. For the first time, a haloalkaliphilic sulfide-oxidizing microbial consortium was introduced to the anodic chamber of a microbial electrolysis cell operated at alkaline pH and with 1.0 M sodium ions. Under anode potential control, the highest sulfide removal rate was 2.16 mM/day and chemical analysis supported that the electrical current generation was from the sulfide oxidation. Biotic operation produced a maximum current density of 3625 mA/m2 compared to 210 mA/m2 while under abiotic operation. Furthermore, biotic electrical production was maintained for a longer period than for abiotic operation, potentially due to the passivation of the electrode by elemental sulfur during abiotic operation. The use of microorganisms reduced the energy input in this study compared to published electrochemical sulfide removal technologies. Sulfide-oxidizing populations dominated both the planktonic and electrode-attached communities with 16S rRNA gene sequences aligning within the genera Thioalkalivibrio, Thioalkalimicrobium, and Desulfurivibrio. The dominance of the Desulfurivibrio-like population on the anode surface offered evidence for the first haloalkaliphilic bacterium able to couple electrons from sulfide oxidation to extracellular electron transfer to the anode.

BACKGROUND: Scaling up bioelectrochemical systems for the treatment of wastewater faces challenges. Material costs, low conductivity of wastewater and clogging are issues that need a novel approach. The granular capacitive moving bed reactor can potentially solve these challenges. In this reactor, capacitive activated carbon granules are used as bioanode material. The charge storage capabilities of these capacitive granules allow for the physical separation of the charging and the discharging process and therefore a separation of the wastewater treatment and energy recovery process. RESULTS: This study investigates the performance of the granular capacitive moving bed reactor. In this reactor, activated granules were transported from the bottom to the top of the reactor using a gas lift and settled on top of the granular bed, which moved downwards through the internal discharge cell. This moving granular bed was applied to increase the contact time with the discharge anode to increase the current density. The capacitive moving bed reactor (total volume 7.7 L) produced a maximum current of 23 A m⁻² normalized to membrane area (257 A m⁻³gᵣₐₙᵤₗₑₛ). Without granules, the current was only 1.4 A m⁻²ₘₑₘbᵣₐₙₑ. The activity of the biofilm on the granules increased over time, from 436 up to 1259 A m⁻³gᵣₐₙᵤₗₑₛ. A second experiment produced similar areal current density and increase in activity over time. CONCLUSION: Whereas the produced current density is promising for further scaling up of bioanodes, the main challenges are to improve the discharge of the charged granules and growth of biofilm on the granules under shear stress. © 2019 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Sulfide oxidizing bacteria (SOB) are widely applied in industry to convert toxic H2S into elemental sulfur. Haloalkaliphilic planktonic SOB can remove sulfide from solution under anaerobic conditions (SOB are ‘charged’), and release electrons at an electrode (discharge of SOB). The effect of this electron shuttling on product formation and biomass growth is not known. Here, we study and demonstrate a continuous process in which SOB remove sulfide from solution in an anaerobic ‘uptake chamber’, and shuttle these electrons to the anode of an electrochemical cell, in the absence of dissolved sulfide. Two experiments over 31 and 41 days were performed. At a sulfide loading rate of 1.1 mmolS/day, electricity was produced continuously (3 A/m2) without dissolved sulfide in the anolyte. The main end product was sulfate (56% in experiment 1% and 78% in experiment 2), and 87% and 77% of the electrons in sulfide were recovered as electricity. It was found that the current density was dependent on the sulfide loading rate and not on the anode potential. Biological growth occurred, mainly at the anode as biofilm, in which the deltaproteobacterial genus Desulfurivibrio was dominating. Our results demonstrate a novel strategy to produce electricity from sulfide in an electrochemical system.

Phosphorus (P) is an irreplaceable element, playing a vital role in living organisms, yet has limited earth reserves. The possibility of P recovery from wastewaters by e lectrochemically-induced ca lcium p hosphate p recipitation (ECaPP) was demonstrated previously. The current study presents a novel scalable prototype consisting of a column-shaped electrochemical reactor, a tubular stainless-steel cathode, and a Pt coated Ti anode. The adhesion of solids to the cathode, important for product recovery, was shown not to be negatively impacted by electrodes’ vertical placement. The influence of current (density), hydraulic retention time (HRT), and initial phosphate concentration in this prototype were examined under continuous flow operation. The system accomplished the highest P removal rate (1267 mg/day) at 1.5 d HRT and 800 mA in treating undiluted cheese wastewater with 48.5 kWh/kg P. Moreover, the prototype showed high stability and efficiency (> 50%) over 173 days of continuous operation without performing maintenance. After turning off the current (0 mA), the system realized a surprising P removal jump up to 97.3%, revealing the delayed diffusion of hydroxide ions by the deposition layer. The calculation of CAPEX and OPEX of ECaPP in treating 100 m3 cheese wastewater per week indicates that the ECaPP plant can realize net-positive from the 12th year. The recovered solids have relatively high P content (> 9wt%) and insignificant contamination of heavy metals. Overall, the proven suitability of the scalable prototype can pave the way towards the actual adoption of the ECaPP process.

The biotechnological gas desulfurization process under haloalkaline conditions is widely applied for removal of toxic H2S from sour gas streams. In this process H2S is biologically oxidized into elemental sulfur. Recently, the process has been extended with an anaerobic process step (dual-reactor line-up), increasing the selectivity for elemental sulfur (S8) from ~85–97% and decreasing the formation of (thio)sulfate. It was also found that biological sulfide uptake took place in the anaerobic bioreactor. In order to apply this process in industry, more insight is needed of the effect of the process conditions on the process performance. The effect of the process conditions HRT and sulfide concentration in the anaerobic bioreactor and pH on the overall product selectivities and on biological sulfide uptake in the anaerobic bioreactor were investigated. 7 experiments were performed in a pilot-scale biodesulfurization set-up. In all experiments, high selectivities (>95%) for S8 formation were obtained, except when the pH in the aerated bioreactor was increased from 8.5 to 9.1 (selectivity of 88%). Furthermore, biological sulfide uptake in the anaerobic bioreactor increased at higher sulfide concentrations and at higher pH. We hypothesize the biological sulfide uptake under anaerobic conditions is related to polysulfide formation. Our results increase the understanding how to control biological sulfide conversion in the dual-reactor biodesulfurization process.

Herein we report the findings of an integrated green process for the continuous oxidation and biomineralization of the most toxic As(III) from acidic streams using a laboratory-scale airlift bioreactor operated at thermoacidophilic conditions and fed with Fe(II) as electron donor. As(III) oxidation catalyzed by granular activated carbon (GAC), biological Fe(II) oxidation and scorodite crystallization took place simultaneously in the reactor, allowing the treatment of influent solutions containing 0.65 g·L−1 As(III). At a hydraulic retention time of 2.2 days, a stable arsenite oxidation efficiency of 99% was achieved, while the removal of total arsenic was 93%. Scorodite was yielded as the main solid product whose physical characteristics such as average size (250 µm) and the developed crystalline structure allowed the easy harvesting from the reactor and reflected the high stability by the low arsenic release of 0.4 mg.L−1 after 60 days of leaching. The analysis of the microbial composition in the reactor suspension and the precipitates indicated the dominance of thermoacidophilic archaeon of the genus Acidianus. Similarly, the attachment of microorganisms to the precipitates observed by scanning electron microscopy, suggested that the precipitation in our system was biologically mediated. The simultaneous arsenic oxidation and removal through catalyzed oxidation and biological processes provide the basis for a new and cost effective green methodology for arsenic fixation from acid As(III)-containing wastewaters.

Medium-chain carboxylates (MCC) derived from biomass biorefining are attractive biochemicals to uncouple the production of a wide array of products from the use of non-renewable sources. Biological conversion of biomass-derived lactate during secondary fermentation can be steered to produce a variety of MCC through chain elongation. We explored the effects of zero-valent iron nanoparticles (nZVI) and lactate enantiomers on substrate consumption, product formation and microbiome composition in batch lactate-based chain elongation. In abiotic tests, nZVI supported chemical hydrolysis of lactate oligomers present in concentrated lactic acid. In fermentation experiments, nZVI created favorable conditions for either chain-elongating or propionate-producing microbiomes in a dose-dependent manner. Improved lactate conversion rates and n-caproate production were promoted at 0.5–2 g nZVI⋅L–1 while propionate formation became relevant at ≥ 3.5 g nZVI⋅L–1. Even-chain carboxylates (n-butyrate) were produced when using enantiopure and racemic lactate with lactate conversion rates increased in nZVI presence (1 g⋅L–1). Consumption of hydrogen and carbon dioxide was observed late in the incubations and correlated with acetate formation or substrate conversion to elongated products in the presence of nZVI. Lactate racemization was observed during chain elongation while isomerization to D-lactate was detected during propionate formation. Clostridium luticellarii, Caproiciproducens, and Ruminococcaceae related species were associated with n-valerate and n-caproate production while propionate was likely produced through the acrylate pathway by Clostridium novyi. The enrichment of different potential n-butyrate producers (Clostridium tyrobutyricum, Lachnospiraceae, Oscillibacter, Sedimentibacter) was affected by nZVI presence and concentrations. Possible theories and mechanisms underlying the effects of nZVI on substrate conversion and microbiome composition are discussed. An outlook is provided to integrate (bio)electrochemical systems to recycle (n)ZVI and provide an alternative reducing power agent as durable control method.

Anaerobic digestion is an attractive treatment technology for concentrated waste streams. However, high ammonia concentrations cause inhibition of methanogenesis, especially when operated at elevated temperatures like (hyper-)thermophilic (55 and 70 °C) anaerobic digestion. These emerging (hyper-)thermophilic technologies are beneficial due to high conversion rates and pathogen removal, but are more susceptible for ammonia toxicity as consequence of a temperature-induced pKa shift. Determination of NH3-N (free ammonia nitrogen (FAN); toxic form) concentrations is conventionally based on an equilibrium model and the total ammonia nitrogen concentration (TAN). However, the conventional equilibrium model overestimates the FAN concentration and therefore we developed an Ionic Activity Model which takes the ionic strength and organic matter interactions into account. The difference between the two models could mainly be attributed to the high ionic strength of the waste stream, whereas interactions with organic matter had a smaller effect. Based on this Ionic Activity Model and batch experiments at hyper-thermophilic conditions, we found that acetoclastic methanogenesis was completely inhibited at FAN concentrations exceeding 588 mg/L, whereas hydrogenotrophic methanogenesis could produce methane up to 925 mg/L. During thermophilic and hyper-thermophilic black water treatment, the ionic strength and organic matter interactions resulted in NH3 concentrations below the inhibitory threshold.

Recovery of selenium (Se) from wastewater provides a solution for both securing Se supply and preventing Se pollution. Here, we developed a high-rate process for biological selenate reduction to elemental selenium. Distinctive from other studies, we aimed for a process with selenate as the main biological electron sink, with minimal formation of methane or sulfide. A sequencing batch reactor, fed with an influent containing 120 mgSe L−1 selenate and ethanol as electron donor and carbon source, was operated for 495 days. The high rates (419 ± 17 mgSe L−1 day−1) were recorded between day 446 and day 495 for a hydraulic retention time of 6 h. The maximum conversion efficiency of selenate amounted to 96% with a volumetric conversion rate of 444 mgSe L−1 day−1, which is 6 times higher than the rates reported in the literature thus far. At the end of the experiment, a highly enriched selenate reducing biomass had developed, with a specific activity of 856 ± 26 mgSe−1day−1gbiomass−1, which was nearly 1000-fold higher than that of the inoculum. No evidence was found for the formation of methane, sulfide, or volatile reduced selenium compounds like dimethyl-selenide or H2Se, revealing a high selectivity. Ethanol was incompletely oxidized to acetate. The produced elemental selenium partially accumulated in the reactor as pure (≥80% Se of the total mixture of biomass sludge flocs and flaky aggregates, and ~100% of the specific flaky aggregates) selenium black hexagonal needles, with cluster sizes between 20 and 200 µm. The new process may serve as the basis for a high-rate technology to remove and recover pure selenium from wastewater or process streams with high selectivity.

This article presents a novel crystal agglomeration strategy for elemental sulfur (S) produced during biological desulfurization (BD). A key element is the nucleophilic dissolution of S by sulfide (HS-) to polysulfides (S x 2-), which was enhanced by a sulfide-rich, anoxic reactor. This study demonstrates that with enhanced S x 2- formation, crystal agglomerates are formed with a uniform size (14.7 ± 3.1 μm). In contrast, with minimal S x 2- formation, particle size fluctuates markedly (5.6 ± 5.9 μm) due to the presence of agglomerates and single crystals. Microscopic analysis showed that the uniformly sized agglomerates had an irregular structure, whereas the loose particles and agglomerates were more defined and bipyramidal. The irregular agglomerates are explained by dissolution of S by (poly)sulfides, which likely changed the crystal surface structure and disrupted crystal growth. Furthermore, S from S x 2- appeared to form at least 5× faster than from HS- based on the average S x 2- chain length of x ≈ 5, thereby stimulating particle agglomeration. In addition, microscopy suggested that S crystal growth proceeded via amorphous S globules. Our findings imply that the crystallization product is controlled by the balance between dissolution and formation of S. This new insight has a strong potential to prevent poor S settleability in BD.

Cyclic voltammetry (CV) is expected to cause changes in the biocathode composition, especially when using low scan rates. A recent finding stated that CV triggered further biocatalytic activity in microbial electrosynthesis systems (MES), leading to the aim of our study: to investigate the invasiveness of CV on MES. The present study confirms that a CO2 elongation MES biocathode composition changes during and right after the CV. Oxidation peaks differ over repeated CV-cycles while metal compounds and biomass were released in the biocatholyte. After CV, the current increased temporarily for up to 20 days and the metal compounds decreased from the biocatholyte solution. Further, the sole short application of open cell voltage was shown to shortly increase the current. Evidently CV affects the studied biocathode, which complicates the use of CV as an analysis technique in MESs. However, the positive effect CV has on biocathode current density may provide methods to boost reactor performance and maintain productivity.

Electrocatalytic metals and microorganisms can be combined for CO2 conversion in microbial electrosynthesis (MES). However, a systematic investigation on the nature of interactions between metals and MES is still lacking. To investigate this nature, we integrated a copper electrocatalyst, converting CO2 to formate, with microorganisms, converting CO2 to acetate. A co-catalytic (i. e. metabolic) relationship was evident, as up to 140 mg L-1 of formate was produced solely by copper oxide, while formate was also evidently produced by copper and consumed by microorganisms producing acetate. Due to non-metabolic interactions, current density decreased by over 4 times, though acetate yield increased by 3.3 times. Despite the antimicrobial role of copper, biofilm formation was possible on a pure copper surface. Overall, we show for the first time that a CO2 -reducing copper electrocatalyst can be combined with MES under biological conditions, resulting in metabolic and non-metabolic interactions.

Thermophilic and hyper-thermophilic anaerobic digestion (AD) are promising techniques for the treatment of concentrated black water (toilet fraction of domestic wastewater collected by low flush volume toilets; BW), recovery of nutrients and simultaneous pathogen removal for safe recovery and reuse of those nutrients. This study showed that thermophilic AD (55 °C) of concentrated BW reaches the same methanisation and COD removal as mesophilic anaerobic treatment of BW (conventional vacuum toilets) and kitchen waste while applying a higher loading rate (OLR) (2.5–4.0 kgCOD/m3/day). With a retention time of 8.7 days, and an OLR of >3 kgCOD/m3/day, COD removal of 70% and a methanisation of 62% (based on CODt) was achieved during thermophilic AD. Hyper-thermophilic (70 °C) reached lower levels of methanisation (38%). Start-up time of thermophilic AD was 12 days. And during thermophilic AD, a shift from acetoclastic methanogenesis towards syntrophic acetate oxidation was observed.

Capacitive bioanodes can be used to improve current production in bioelectrochemical systems for combination of energy recovery and wastewater treatment. Here, we compared current production in fixed and moving bed capacitive bioanodes. For fixed bed bioanodes, the recovered charge was studied as a function of the discharge current collector position and the thickness of the granule bed. The most capacitive charge was recovered from the current collector closest to the membrane. Increasing bed thickness from 5 mm to 10 mm resulted in a 1.6 times higher current density per membrane area. These findings were used to improve the design of a moving bed reactor, where granules moved through a discharge cell and were recirculated using a gas lift. The moving bed produced a current of 43 A/m2, about 2 times the fixed bed current over the full charging and discharging cycles. The relatively short discharge time and long charging time of the moving bed as compared to the fixed bed bioanodes led to higher capacitive currents. The design of the discharge cell and the ratio between charge and discharge times can be further optimized to make better use of stored charge of the granular capacitive bioanodes.

Many new water technologies are referred to as being disruptive. The term disruptive innovation is overused to the point that it has lost much of its meaning. There is no clear framework to quantify or measure the impact of new water technologies. This paper proposes a series of different metrics as an objective means to quantify the market impact of technologies based on empirical data, and assesses their practicality in application. Three different levels of market impact are defined, the lowest being Level 3 and the highest Level 1. Selected metrics are applied to empirical data for 11 different water technologies to test the framework. It was found that the average time required to reach Level 1 impact, from the first installation, was 21 years, while it was possible to move from Level 2 to Level 1 in 10 years. The presence of two to three competitors in the market has a synergistic effect and can accelerate overall adoption of a technology class. The fragmented nature of the water sector has been observed to act as a buffer against disruption. The metrics, which have been found to be useful in evaluating the impact of water technologies, are the total number countries in which the technology is adopted, the total number of units that have been deployed and the annual market value the technology achieved. It has also been observed that certain innovation typologies and innovation drivers are associated with high levels of market impact while other combinations are associated with zombie technologies.

Regions with intensive agriculture often encounter environmental problems caused by nutrient excess of agro-food-waste systems that have become increasingly linear over previous decades. In this study, nitrogen (N), phosphorus (P), potassium (K) and carbon (C) flows in the whole agro-food-waste system of district Cleves in Germany were quantified simultaneously using substance flow analysis. Moreover, nutrient use inefficiency hotspots were identified to establish options to improve nutrient self-sufficiency as a first step towards nutrient circularity. Data on mass flows and nutrient contents was acquired for the year 2016 from stakeholders, statistical databases, literature and modelling. Organic C was included for flows with potential as organic fertilizer. Results show that animal production drives the nutrient flows in the export-oriented district, with feed import, manure application and losses from housing and manure storage accounting for 40, 45 and 60% of all N, P and K flows, respectively. In particular agriculture is responsible for N losses, with 150 kg N lost ha−1 agricultural land. Crop production surplus and with that soil accumulation of P and K are 515 t and 4100 t respectively. Stoichiometry of N:P:K:C in the different organic materials does not allow direct application and meeting crop requirements without exceeding demand of especially P. Processing of biomass is therefore required. Based on mass, especially manure holds potential for processing into bio-based fertilizers. To improve nutrient cycling and soil C conservation, being an important element for a sustainable agricultural sector, local balances between crop and animal production need to be considered.

Nitrogen (N) is an essential nutrient for plants and plays an important role in agriculture. However, the cycle between nitrogen input into agriculture and the nitrogen content in wastewater has been broken. Recently, nitrogen recovery from wastewater was demonstrated using an electrochemical system (ES) combined with a gas permeable membrane. Once concentrated, the ammonia is recovered into an acid, producing either ammonium sulfate (AS) or ammonium nitrate (AN). The ES was operated at different conditions while guaranteeing a certain nutrient removal and producing a concentrated fertilizer. An ammonium nitrate with 25.5 gN/L and an ammonium sulfate with 21.5 gN/L were recovered. To evaluate the performance of these nitrogen fertilizers, 5 treatments were applied to two crops, spinach and radish. The treatments were (1) AS recovered with the ES, 2) commercial AS, 3) AN recovered with the ES, 4) commercial AN, and 5) no addition (control). Between fertilized treatments, a significant difference was observed for fresh biomass of spinach leaf (consumable part of the crop) between recovered and commercial fertilizers. Effective fertilization was confirmed by a significantly higher fresh biomass in fertilized crops, both radish and spinach, compared to control. After harvest, soil pH was above 5.0 for both commercial and recovered fertilizers, despite the low pH of the recovered fertilizers (pH 1.8 - 2.4). This work demonstrates that fertilizers recovered by electrochemical systems can be used to improve crop growth and are a feasible alternative to commercial fertilizers.

Electrochemical systems for total ammonium nitrogen (TAN) recovery are a promising alternative compared with conventional nitrogen-removal technologies. To make them competitive, we propose a new minimal stackable configuration using cell pairs with only bipolar membranes and cation-exchange membranes. The tested bipolar electrodialysis (BP-ED) stack included six cell pairs of feed and concentrate compartments. Critical operational parameters, such as current density and the ratio between applied current to nitrogen loading (load ratio), were varied to investigate the performance of the system using synthetic wastewater with a high nitrogen content as an influent (NH4+ ≈ 1.75 g L–1). High TAN removal (>70%) was achieved for a load ratio higher than 1. At current densities of 150 A m–2 and a load ratio of 1.2, a TAN transport rate of 1145.1±14.1 gN m–2 d–1 and a TAN-removal efficiency of 80% were observed. As the TAN removal was almost constant at different current densities, the BP-ED stack performed at a high TAN transport rate (819.1 gN m–2 d–1) while consuming the lowest energy (18.3 kJ gN–1) at a load ratio of 1.2 and 100 A m–2. The TAN transport rate, TAN removal, and energy input achieved by the minimal BP-ED stack demonstrated a promising new cell configuration for upscaling., A minimal bipolar electrodialysis configuration removed 80% ammonium at low energy consumption, allowing further upscaling while decreasing the material footprint.

The plant-microbial fuel cell (Plant-MFC) is an attraction while it produces electricity with living plants. This technology has a great potential to be further applied as new small or large-scale electricity source while servicing people and the environment. The objective of this chapter is to provide a constructive explanatory overview of the Plant-MFC and its innovative environmental technological applications. A summary is generated on research breakthroughs that lead to various emerging applications. Since the development of the first Plant-MFCs in 2008, research led to further understanding of the working principles and the various new applications. The Plant-MFC is suited to power sensors or act as a sensor by itself. The technology is integrated in various systems, including green electricity roofs, constructed wetlands, rice paddy fields, tables and road-lighting applications. The electricity is used for numerous demonstrations such as to power cell phones or even radios. Electricity generation is combined with a unique combination of microbial, geochemical, electrochemical and plant processes that allow new applications providing various services. Services include methane emission reduction, water treatment, plant growth, food production, nature preservation, agriculture monitoring, green electricity experience, education, nutrient recovery, social awareness, pollutant removal, etc.. Valorization of these services is done by companies and designers in collaboration with several researchers and stakeholders. The plant-microbial fuel cell (Plant-MFC) is an attraction while it produces electricity with living plants. This chapter aims to provide a constructive explanatory overview of the Plant-MFC and its innovative environmental technological applications. A summary is generated on research breakthroughs that lead to various emerging applications. The electricity is used for numerous demonstrations such as to power cell phones or even radios. The Plant-MFC consists of two electrodes that are connected by an electrical circuit and submerged in an electrolyte or saturated soil. Plant-MFCs have been applied for the purpose of environmental remediation in multiple systems. Plant-MFCs can also be of added value to natural wetlands. Most natural wetlands are protected areas and not automatically unsuited to agricultural practices or the construction of buildings and infrastructures. Telemetry is the process of remote data collection and transmission.

Phosphorus removal and recovery from waste streams are crucial to prevent eutrophication and sustain fertilizer production. As has been shown in our previous papers, electrochemical treatment has the potential to achieve this goal. However, the adoption of electrochemical approach is limited by its high energy consumption. Here, we investigate the possibility of electrochemical phosphorus removal at extremely low current density using graphite felt as the cathode. We found a current density as low as 0.04 A/m2 can enhance the removal of phosphate in our electrochemical system. The removal of phosphate at extremely low current density resulted from electrochemical induced calcium phosphate precipitation and not by electrochemical adsorption. Electrochemical treatment of real domestic wastewater at 0.2 A/m2 almost eliminates the precipitation of Mg(OH)2 and limits the formation of CaCO3. The recovered precipitates are dominated by calcium phosphate (59%), followed by 35% CaCO3 and 6% Mg(OH)2. The specific energy consumption of this newly electrochemical system is between 4.4 and 26.4 kW h/kg P, which is 2 orders of magnitude lower than our previous system (110–2238 kW h/kg P). Key factors for this improvement prove to be enlarged precipitation area and hydroxide flux retardation by graphite felt. Practically, our study offers a potential way to reduce the energy consumption in electrochemical removal of phosphate by using a graphite felt cathode and at a current density below 0.2 A/m2. Fundamentally, our study contributes to the understanding of adsorption and precipitation in electrochemical removal of phosphate at an extremely low current density and with carbon-based electrodes.

Biomass fermentation technologies offer alternative methods to produce platform chemicals that currently originate from fossil sources. This research showed that an enriched microbiome was capable to produce iso-butyric acid via methanol based chain elongation of acetate. A long term continuous reactor experiment showed that the selectivity for isobutyrate (i-C4) and/or n-butyrate (n-C4) could be reversibly adjusted by changing the reactor pH. A reactor pH of 6.75 led to formation of (carbon per total carbon of products) of 0.78 n-C4 and 0.024 i-C4, whereas a reactor pH of 5.2 led to a selectivity of 0.25 n-C4 and 0.63 i-C4 . This shift in product spectrum was also represented by a shift in microbial composition. The results suggest that an Eubacterium genus is responsible for the formation of n-C4, whereas a Clostridium luticellarii strain is responsible for the formation of a mixture of i-C4 and n¬¬-C4. The formation of n and i-C4 at a low pH was observed to be coupled according to the thermodynamics of isomerization. At a reactor pH of 5.5 and 5.2 the product ratio of i-C4:n-C4 approached the ratio of 0.684 i-C4 : 0.316 n-C4, which is the theoretical ratio that would be achieved when i-C4 and n-C4 would be formed at amounts determined by the equilibrium of isomerization. Various batch experiments at pH 5.5 and 5.2 confirmed that addition of either n-C4 or i-C4 at the start of the batch would immediately lead to the formation of the other butyrate component. Moreover, batch experiments performed at pH 6.5 immediately produced mainly n-C4 and led to the development of a completely different microbiome. The imposed pH as a strong selective pressure can immediately facilitate changes in product selectivities for n-C4 and i-C4 during methanol based chain elongation of acetate.

Large-scale implementation of (plant) microbial fuel cells is greatly limited by high electrode costs. In this work, the potential of exploiting electrochemically active self-assembled biofilms in fabricating three-dimensional bioelectrodes for (plant) microbial fuel cells with minimum use of electrode materials was studied. Three-dimensional robust bioanodes were successfully developed with inexpensive polyurethane foams (PU) and activated carbon (AC). The PU/AC electrode bases were fabricated via a water-based sorption of AC particles on the surface of the PU cubes. The electrical current was enhanced by growth of bacteria on the PU/AC bioanode while sole current collectors produced minor current. Growth and electrochemical activity of the biofilm were shown with SEM imaging and DNA sequencing of the microbial community. The electric conductivity of the PU/AC electrode enhanced over time during bioanode development. The maximum current and power density of an acetate fed MFC reached 3 mA·m−2 projected surface area of anode compartment and 22 mW·m−3 anode compartment. The field test of the Plant-MFC reached a maximum performance of 0.9 mW·m−2 plant growth area (PGA) at a current density of 5.6 mA·m−2 PGA. A paddy field test showed that the PU/AC electrode was suitable as an anode material in combination with a graphite felt cathode. Finally, this study offers insights on the role of electrochemically active biofilms as natural enhancers of the conductivity of electrodes and as transformers of inert low-cost electrode materials into living electron acceptors.

The world faces urgent, multi-faceted problems in terms of water; water supply crises have been identified as one of the top five global risks to society in each of the last seven years according to the World Economic Forum. Existing technologies and policies are not adequate for tackling these problems; innovation is urgently required. However, innovation adoption in the water sector is a slow process compared with other industries; the water sector itself is necessarily conservative, and regulation-bound. It is also fragmented, with the US for example having over 161 thousand public water supply utilities. Only a fraction of research efforts yield a marketable product or device. At the same time, innovation in the water sector is of increasing interest to venture capital investors. This paper addresses a problem which is hampering the meeting of these growing interests and needs; the dynamics of water innovation are under-researched, and there is a lack of clear, agreed terminology. As an example, the phrase “disruptive innovation” has drifted significantly away from its originally-intended academic meaning. The authors critically review two theories of innovation: Disruptive Innovation Theory, and Innovation Diffusion Theory (IDT). While important, Disruptive Innovation Theory is found to have limited applicability to water – for example, there are limited opportunities for lower-end innovation which competes on price in a regulated market like water, and there is also limited opportunity to be market-creating. Although the question arises: is there a market-creating equivalent of the Ford production line that would unlock solutions to water problems in developing countries? Innovation Diffusion Theory is found to be more applicable to water, with some important caveats. In conclusion, this paper proposes a practical framework, with industry examples, for studying water technology innovation. Such a framework could provide a common shared basis to support further research into this topic, including the question: can the disruptive potential of an innovation be predicted?

Carbon dioxide (CO2) can be converted to valuable products using different catalysts, including metal or biological catalysts (e. g. microorganisms). Some products formed by metal electrocatalysts can be further utilized by microorganisms, and therefore catalytic cooperation can be envisioned. To prevent cumbersome separations, it is beneficial when both catalyst work under the same conditions, or at least in the same reaction medium. Here, we will show that a formate-producing copper electrocatalyst can function in a biological medium. Furthermore, we will show that the effluent of the copper-containing reactor can be used without purification as the sole medium for a bio-reactor, inoculated with a mixed culture of microorganisms. In that second reactor, formate, H2 and CO2 are consumed by the microorganisms, forming acetate and methane. Compared to simple buffer electrolyte, catalytic activity of copper was improved in the presence of microbial growth medium, likely due to EDTA (Ethylenediaminetetraacetic acid) present in the latter.