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Cathodic Electro-Fermentation (CEF) is an innovative approach to manage the spectrum of products deriving from anaerobic fermentation. Herein, mixed microbial culture fermentation using a ternary mixture containing labelled 13 C glucose and non-labelled acetate and ethanol was studied to identify the role of polarization on the metabolic pathways of glucose fermentation. CEF at an applied potential of -700 mV (vs. SHE, Standard Hydrogen Electrode) enhanced the production yield of acetate, propionate, and butyrate (0.90±0.10, 0.22±0.03, and 0.34±0.05 mol/mol; respectively) compared to control tests performed at open circuit potential (OCP) (0.54±0.09, 0.15±0.04, and 0.20±0.001 mol/mol, respectively). Results indicate that CEF affected the 13 C labelled fermented product levels and their fractional 13 C enrichments, allowing to establish metabolic pathway models. This work demonstrates that, under cathodic polarization, the abundance of both fully 13 C labelled propionate and butyrate isotopomers increased compared to control tests. The effect of CEF is mainly due to intermediates initially produced from the glucose metabolic transformation in the presence of non-labelled acetate and ethanol as external substrates. These findings represent a significant advancement in current knowledge of CEF, which offers a promising tool to control mixed cultures bioprocesses., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Polymeric materials made from renewable sources that can biodegrade in the environment are attracting considerable attention as substitutes for petroleum-based polymers in many fields, including additive manufacturing and, in particular, Fused Deposition Modelling (FDM). Among the others, poly(hydroxyalkanoates) (PHAs) hold significant potential as candidates for FDM since they meet the sustainability and biodegradability standards mentioned above. However, the most utilised PHA, consisting of the poly(hydroxybutyrate) (PHB) homopolymer, has a high degree of crystallinity and low thermal stability near the melting point. As a result, its application in FDM has not yet attained mainstream adoption. Introducing a monomer with higher excluded volume, such as hydroxyvalerate, in the PHB primary structure, as in poly(hydroxybutyrate-co-valerate) (PHBV) copolymers, reduces the degree of crystallinity and the melting temperature, hence improving the PHA printability. Blending amorphous poly(lactic acid) (PLA) with PHBV enhances further PHA printability via FDM. In this work, we investigated the printability of two blends characterised by different PLA and PHBV weight ratios (25:75 and 50:50), revealing the close connection between blend microstructures, melt rheology and 3D printability. For instance, the relaxation time associated with die swelling upon extrusion determines the diameter of the extruded filament, while the viscoelastic properties the range of extrusion speed available. Through thoroughly screening printing parameters such as deposition speed, nozzle diameter, flow percentage and deposition platform temperature, we determined the optimal printing conditions for the two PLA/PHBV blends. It turned out that the blend with a 50:50 weight ratio could be printed faster and with higher accuracy. Such a conclusion was validated by replicating with remarkable fidelity high-complexity objects, such as a patient's cancer-affected iliac crest model.

The performance of a methane-producing microbial electrolysis cell (MEC) markedly relies on the activity and resilience of its electroactive anodic biofilm. Here, the capability of an MEC anodic biofilm to recover following extended starvation periods (90 days) and to function under different applied anode potentials (i.e., +0.20 and -0.10 V, vs. Standard Hydrogen Electrode-SHE) was investigated. Cyclic voltammetry proved to be an insightful means to characterize the biofilm electrocatalytic activity and to track the dynamics of biofilm reactivation. Under all tested conditions the anodic biofilm rapidly and completely recovered from starvation in less than 144 h. However, starvation reduced the electron transfer redundancy of the biofilm causing the disappearance of redox sites operating at the more positive potentials (around 0.0 V vs. SHE) and retaining those having a formal potential lower than -0.18 V vs. SHE. This study presents compelling evidence for the resilience and efficiency of methane-producing MEC., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The research on bioplastics (both biobased and biodegradable) is steadily growing and discovering environmentally friendly substitutes for conventional plastic. This review highlights the significance of bioplastics, analyzing, for the first time, the state of the art concerning the use of agri-food waste as an alternative substrate for biopolymer generation using Haloferax mediterranei . H. mediterranei is a highly researched strain able to produce polyhydroxybutyrate (PHB) since it can grow and produce bioplastic in high-salinity environments without requiring sterilization. Extensive research has been conducted on the genes and pathways responsible for PHB production using H. mediterranei to find out how fermentation parameters can be regulated to enhance cell growth and increase PHB accumulation. This review focuses on the current advancements in utilizing food waste as a substitute for costly substrates to reduce feedstock expenses. Specifically, it examines the production of biomass and the recovery of PHB from agri-food waste. Furthermore, it emphasizes the characterization of PHB and the significance of hydroxyvalerate (HV) abundance in the formation of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymer. The downstream processing options are described, and the crucial factors associated with industrial scale-up are assessed, including substrates, bioreactors, process parameters, and bioplastic extraction and purification. Additionally, the economic implications of various options are discussed.

The presence of pharmaceuticals in the aquatic environment is mainly due to their release from the effluents of the wastewater treatment plants (WWTPs), which are unable to completely remove them and their transformation products (TPs). Sulfonamides (SAs) are a synthetic antibacterial class used for the treatment of both human and animal infections; they have often been reported in surface water, thus contributing to the antibiotic resistance emergency. Monitoring SA TPs should be important as well because they could still exert some pharmaceutical activity; however, many TPs are still unknown since several transformation processes are possible (e. g. human and animal metabolism, WWTP activities, environmental factors etc.). In this work, three of the most used SAs, i.e., sulfamethoxazole (SMX), sulfapyridine (SPY), and sulfadiazine (SDZ), were incubated for 20 days in a batch reactor with activated sludge under controlled conditions. Then, the water sample was extracted and analyzed by ultra-high performance liquid chromatography-high resolution mass spectrometry in the data dependent acquisition (DDA) mode. Starting from the literature data, the possible transformation pathways were studied, and for each SA, a list of TPs was hypothesized and used for the identification. The raw data files were processed with Compound Discoverer, and 44 TPs (18, 13, and 13 TPs for SMX, SPY, and SDZ, respectively), including multiple TPs, were manually validated. To overcome the limitation of the DDA, the identified TPs were used in an inclusion list to analyze WWTP samples by a suspect screening approach. In this way, 4 SMX TPs and 5 SPY TPs were tentatively identified together with their parent compounds. Among these TPs, 5 of 9 were acetylated forms, in agreement with previous literature reporting that acetylation is the predominant SA transformation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The market of biobased products obtainable via fermentation processes has steadily increased over the past few years, driven by the need to create a decarbonized economy. To date, industrial fermentation (IF) employs either pure or mixed microbial cultures (MMC), whereby the type of the microbial catalysts and the used feedstock affect metabolic pathways and, in turn, the type of product(s) generated. In many cases, especially when dealing with MMC, the economic viability of IF is still hindered by factors such as the low attained product titer and selectivity, which ultimately challenge the downstream recovery and purification steps. In this context, electro-fermentation (EF) represents an innovative approach, based on the use of a polarized electrode interface to trigger changes in the rate, yield, titer or product distribution deriving from traditional fermentation processes. In principle, the electrode in EF can act as an electron acceptor (i.e., anodic electro-fermentation, AEF) or donor (i.e., cathodic electro-fermentation, CEF), or simply as a means to control the oxidation-reduction potential of the fermentation broth. However, the molecular and biochemical basis underlying EF are still largely unknown. This review provides a comprehensive overview of recent literature studies including both AEF and CEF examples using pure or mixed microbial cultures. A critical analysis of biochemical, microbiological, and engineering aspects which presently hamper the transition of the EF technology from the laboratory to the market is also presented., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The use of the halophile microorganism Haloferax mediterranei , able to synthesize poly(hydroxybutyrate-hydroxyvalerate) (PHBV), is considered as a promising tool for the industrial production of bioplastic through bioprocessing. A consistent supplementation of the growth substrate in carbohydrates and minerals is overall necessary to allow its PHBV production. In this work, wasted bread was used as substrate for bioplastic production by microbial fermentation. Instead of the consistent and expensive minerals supplement required for Hfx. mediterranei DSM1411 growth, microfiltered seawater was added to the wasted bread-derived substrate. The suitable ratio of wasted bread homogenate and seawater, corresponding to 40:60, was selected. The addition of proteases and amylase to the bread homogenate promoted the microbial growth but it did not correspond to the increase of bioplastic production by the microorganism, that reach, under the experimental conditions, 1.53 g/L. An extraction procedure of the PHBV from cells, based on repeated washing with water, followed or not by a purification through ethanol precipitation, was applied instead of the conventional extraction with chloroform. Yield of PHBV obtained using the different extraction methods were 21.6 ± 3.6 (standard extraction/purification procedure with CHCl 3 :H 2 O mixture), 24.8 ± 3.0 (water-based extraction), and 19.8 ± 3.3 mg PHAs/g of wasted bread (water-based extraction followed by ethanol purification). Slightly higher hydroxyvalerate content (12.95 vs 10.78%, w/w) was found in PHBV obtained through the water-based extraction compared to the conventional one, moreover, the former was characterized by purity of 100% (w/w). Results demonstrated the suitability of wasted bread, supplemented with seawater, to be used as substrate for bioplastic production through fermentation. Results moreover demonstrated that a solvent-free extraction, exclusively based on osmotic shock, could be used to recover the bioplastic from cells., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Montemurro, Salvatori, Alfano, Martinelli, Verni, Pontonio, Villano and Rizzello.)

Volatile fatty acid (VFA) rich streams from fermentation of organic residuals and wastewater are suitable feedstocks for mixed microbial culture (MMC) Polyhydroxyalkanoate (PHA) production. However, many such streams have low total VFA concentration (1-10 gCOD/L). PHA accumulation requires a flow-through bioprocess if the VFAs are not concentrated. A flow through bioprocess must balance goals of productivity (highest possible influent flow rates) with goals of substrate utilization efficiency (lowest possible effluent VFA concentration). Towards these goals, dynamics of upshift and downshift respiration kinetics for laboratory and pilot scale MMCs were evaluated. Monod kinetics described a hysteresis between the upshift and downshift responses. Substrate concentrations necessary to stimulate a given substrate uptake rate were significantly higher than the concentrations necessary to sustain the attained substrate uptake rate. A benefit of this hysteresis was explored in Monte Carlo based PHA accumulation bioprocess numerical simulations. Simulations illustrated for a potential to establish continuous flow-through PHA production bioprocesses even at a low (1 gCOD/L) influent total VFA concentration. Process biomass recirculation into an engineered higher substrate concentration mixing zone, due to the constant influent substrate flow, enabled to drive the process to maximal possible PHA production rates without sacrificing substrate utilization efficiency.

Bioelectrochemical systems are emerging technologies for the reduction in CO 2 in fuels and chemicals, in which anaerobic chemoautotrophic microorganisms such as methanogens and acetogens are typically used as biocatalysts. The anaerobic digestion digestate represents an abundant source of methanogens and acetogens microorganisms. In a mixed culture environment, methanogen's inhibition is necessary to avoid acetate consumption by the presence of acetoclastic methanogens. In this study, a methanogenesis inhibition approach based on the thermal treatment of mixed cultures was adopted and evaluated in terms of acetate production under different tests consisting of hydrogenophilic and bioelectrochemical experiments. Batch experiments were carried out under hydrogenophilic and bioelectrochemical conditions, demonstrating the effectiveness of the thermal treatment and showing a 30 times higher acetate production with respect to the raw anaerobic digestate. Moreover, a continuous flow bioelectrochemical reactor equipped with an anion exchange membrane (AEM) successfully overcomes the methanogens reactivation, allowing for a continuous acetate production. The AEM membrane guaranteed the migration of the acetate from the biological compartment and its concentration in the abiotic chamber avoiding its consumption by acetoclastic methanogenesis. The system allowed an acetate concentration of 1745 ± 30 mg/L in the abiotic chamber, nearly five times the concentration measured in the cathodic chamber.

Groundwater remediation is one of the main objectives to minimize environmental impacts and health risks. Chlorinated aliphatic hydrocarbons contamination is prevalent and presents particularly challenging scenarios to manage with a single strategy. Different technologies can manage contamination sources and plumes, although they are usually energy-intensive processes. Interesting alternatives involve in-situ bioremediation strategies, which allow the chlorinated contaminant to be converted into non-toxic compounds by indigenous microbial activity. Despite several advantages offered by the bioremediation approaches, some limitations, like the relatively low reaction rates and the difficulty in the management and control of the microbial activity, can affect the effectiveness of a bioremediation approach. However, those issues can be addressed through coupling different strategies to increase the efficiency of the bioremediation strategy. This mini review describes different strategies to induce the reduction dechlorination reaction by the utilization of innovative strategies, which include the increase or the reduction of contaminant mobility as well as the use of innovative strategies of the reductive power supply. Subsequently, three future approaches for a greener and more sustainable intervention are proposed. In particular, two bio-based materials from renewable resources are intended as alternative, long-lasting electron-donor sources (e.g., polyhydroxyalkanoates from mixed microbial cultures) and a low-cost adsorbent (e.g., biochar from bio-waste). Finally, attention is drawn to novel bio-electrochemical systems that use electric current to stimulate biological reactions.

Polyhydroxyalkanoates (PHAs) production at pilot scale has been recently investigated and carried out exploiting different process configurations and organic wastes. More in detail, three pilot platforms, in Treviso (North-East of Italy), Carbonera (North-East of Italy) and Lisbon, produced PHAs by open mixed microbial cultures (MMCs) and different organic waste streams: organic fraction of municipal solid waste and sewage sludge (OFMSW-WAS), cellulosic primary sludge (CPS), and fruit waste (FW), respectively. In this context, two stabilization methods have been applied, and compared, for preserving the amount of PHA inside the cells: thermal drying and wet acidification of the biomass at the end of PHA accumulation process. Afterward, polymer has been extracted following an optimized method based on aqueous-phase inorganic reagents. Several PHA samples were then characterized to determine PHA purity, chemical composition, molecular weight, and thermal properties. The polymer contained two types of monomers, namely 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) at a relative percentage of 92.6-79.8 and 7.4-20.2 w/w, respectively, for Treviso and Lisbon plants. On the other hand, an opposite range was found for 3HB and 3HV monomers of PHA from Carbonera, which is 44.0-13.0 and 56.0-87.0 w/w, respectively. PHA extracted from wet-acidified biomass had generally higher viscosity average molecular weights ( M v ) (on average 424.8 ± 20.6 and 224.9 ± 21.9 KDa, respectively, for Treviso and Lisbon) while PHA recovered from thermally stabilized dried biomass had a three-fold lower M v ., Competing Interests: BSF was employed by company Biotrend SA. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Lorini, Martinelli, Capuani, Frison, Reis, Sommer Ferreira, Villano, Majone and Valentino.)

Electro-fermentation (EF) is an emerging and promising technology consisting in the use of a polarized electrode to control the spectrum of products deriving from anaerobic bioprocesses. Here, the effect of electrode polarization on the fermentation of glucose has been studied with two mixed microbial cultures, both in the absence and in the presence of exogenous redox mediators, to verify the viability of the proposed approach under a broader and previously unexplored range of operating conditions. In unmediated experiments, EF (with the cathode polarized at -700 mV vs. SHE, Standard Hydrogen Electrode) caused an increase in the yield of butyric acid production provided that glucose was consumed along with its own fermentation products (i.e. acetic acid and ethanol). The maximum obtained yield accounted for 0.60 mol mol -1 . Mediated experiments were performed with Neutral Red or AQDS at a concentration of 500 μM both in the absence and in the presence of the electrode polarized at -700 mV or -300 mV vs. SHE, respectively. Mediators showed a high selectivity towards the generation of n-butyric acid isomer from the condensation of acetate and ethanol, hence suggesting that they provided microbial cells with the required reducing power otherwise deriving from glucose in unmediated experiments., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Growing scientific interest in mixed microbial culture-based anaerobic biotechnologies for the production of value-added chemicals and fuels from organic waste residues requires a parallel focus on the development and implementation of strategies to control the distribution of products. This study examined the feasibility of an electrofermentation approach, based on the introduction of a polarized (-700 mV vs. the standard hydrogen electrode) graphite electrode in the fermentation medium, to steer the product distribution during the conversion of organic substrates (glucose, ethanol, and acetate supplied as single compounds or in mixtures) by undefined mixed microbial cultures. In batch experiments, the polarized electrode triggered a nearly 20-fold increase (relative to open circuit controls) in the yield of isobutyrate production (0.43±0.01 vs. 0.02±0.02 mol mol -1 glucose) during the anaerobic fermentation of the ternary mixture of substrates, without adversely affecting the rate of substrate bioconversion. The observed change in the fermentative metabolism was most likely triggered by the (potentiostatic) regulation of the oxidation-reduction potential of the reaction medium rather than by the electrode serving as an electron donor., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A sequencing batch reactor (SBR) is typically used for selecting mixed microbial cultures (MMC) for polyhydroxyalkanoate (PHA) production. Since many waste streams suitable as process feedstock for PHA production are nitrogen-deficient, a nutrient supply in the SBR is typically required to allow for efficient microbial growth. The scope of this study was to devise a nitrogen feeding strategy which allows controlling the nitrogen levels during the feast and famine regime of a lab-scale SBR, thereby selecting for PHA-storing microorganisms. At the beginning of the cycle the reactor was fed with a synthetic mixture of acetic and propionic acids at an overall organic load rate of 8.5gCODL -1 d -1 (i.e. 260CmmolL -1 d -1 ), whereas nitrogen (in the form of ammonium sulphate) was added either simultaneously to the carbon feed (coupled feeding strategy) or after the end of the feast phase (uncoupled feeding strategy). As a main result, PHA production was more than doubled (up to about 1300±64mgCODL -1 ) when carbon and nitrogen were separately fed and the higher PHA production also corresponded to an 82% increase in the polymer HV content (up to 20±1%, wtwt -1 ). Three SBR runs were performed with the uncoupled carbon and nitrogen feeding at different carbon to nitrogen (C/N) ratios (of 14.3, 17.9, and 22.3CmolNmol -1 , respectively) which were varied by progressively reducing the concentration of the nitrogen feeding. In spite of a comparable PHA storage yield at 14.3 and 17.9CmolNmol -1 (0.41±0.05 gCOD PHA gCOD VFA -1 and 0.38±0.05 gCOD PHA gCOD VFA -1 , respectively), the storage response of the selected MMC significantly decreased when the C/N ratio was set at the highest investigated value. Notably, an increase in this parameter also resulted in a change in the HV content in the polymer regardless the composition of the organic acids solution., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Polyhydroxyalkanoates (PHA) are biodegradable polyesters that can be produced in bioprocesses from renewable resources in contrast to fossil-based bio-recalcitrant polymers. Research efforts have been directed towards establishing technical feasibility in the use of mixed microbial cultures (MMC) for PHA production using residuals as feedstock, mainly consisting of industrial process effluent waters and wastewaters. In this context, PHA production can be integrated with waste and wastewater biological treatment, with concurrent benefits of resource recovery and sludge minimization. Over the past 15 years, much of the research on MMC PHA production has been performed at laboratory scale in three process elements as follows: (1) acidogenic fermentation to obtain a volatile fatty acid (VFA)-rich stream, (2) a dedicated biomass production yielding MMCs enriched with PHA-storing potential, and (3) a PHA accumulation step where (1) and (2) outputs are combined in a final biopolymer production bioprocess. This paper reviews the recent developments on MMC PHA production from synthetic and real wastewaters. The goals of the critical review are: a) to highlight the progress of the three-steps in MMC PHA production, and as well to recommend room for improvements, and b) to explore the ideas and developments of integration of PHA production within existing infrastructure of municipal and industrial wastewaters treatment. There has been much technical advancement of ideas and results in the MMC PHA rich biomass production. However, clear demonstration of production and recovery of the polymers within a context of product quality over an extended period of time, within an up-scalable commercially viable context of regional material supply, and with well-defined quality demands for specific intent of material use, is a hill that still needs to be climbed in order to truly spur on innovations for this field of research and development., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A pure culture of the filamentous bacterium Thiothrix, strain CT3, was aerobically cultured in a chemostat under continuous acetate feeding at three different culture residence times (RT 6, 12 or 22 d) and the same volumetric organic load rate (OLR 0.12gCOD/L/d). Cells cultured at decreasing RT in the chemostat had an increasing transient response to acetate spikes in batch tests. The maximum specific acetate removal rate increased from 25 to 185mgCOD/gCOD/h, corresponding to a 1.8 to 8.1 fold higher respective steady-state rate in the chemostat. The transient response was mainly due to acetate storage in the form of poly(3-hydroxybutyrate) (PHB), whereas no growth response was observed at any RT. Interestingly, even though the storage rate also decreased as the RT increased, the storage yield increased from 0.41 to 0.50 COD/COD. This finding does not support the traditional view that storage plays a more important role as the transient response increases. The transient response of the steady-state cells was much lower than in cells cultured under periodic feeding (at 6 d RT, from 82 to 247mgCOD/gCOD/h), with the latter cells showing both storage and growth responses. On the other hand, even though steady-state cells had no growth response and their storage rate was also less, steady-state cells showed a higher storage yield than cells cultured under dynamic feeding. This suggests that in Thiothrix strain CT3, the growth response is triggered by periodic feeding, whereas the storage response is a constitutive mechanism, independent from previous acclimation to transient conditions., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The conversion of electrical current into methane (electromethanogenesis) by microbes represents one of the most promising applications of bioelectrochemical systems (BES). Electromethanogenesis provides a novel approach to waste treatment, carbon dioxide fixation and renewable energy storage into a chemically stable compound, such as methane. This has become an important area of research since it was first described, attracting different research groups worldwide. Basics of the process such as microorganisms involved and main reactions are now much better understood, and recent advances in BES configuration and electrode materials in lab-scale enhance the interest in this technology. However, there are still some gaps that need to be filled to move towards its application. Side reactions or scaling-up issues are clearly among the main challenges that need to be overcome to its further development. This review summarizes the recent advances made in the field of electromethanogenesis to address the main future challenges and opportunities of this novel process. In addition, the present fundamental knowledge is critically reviewed and some insights are provided to identify potential niche applications and help researchers to overcome current technological boundaries.

The effect of the set anode potential (between + 200 mV and - 200 mV vs. SHE, standard hydrogen electrode) on the performance and distribution of internal potential losses has been analyzed in a continuous-flow methane-producing microbial electrolysis cell (MEC).Both acetate removal rate (at the anode) and methane generation rate (at the cathode) were higher (1 gCOD/L day and 0.30 m(3)/m(3) day, respectively) when the anode potential was controlled at + 200 mV. However, both the yields of acetate conversion into current and current conversion into methane were very high (72-90%) under all the tested conditions. Moreover, the sum of internal potential losses decreased from 1.46 V to 0.69 V as the anode potential was decreased from + 200 mV to - 200 mV, with cathode overpotentials always representing the main potential losses. This was likely to be due to the high energy barrier which has to be overcome in order to activate the cathode reaction. Finally, the energy efficiency correspondingly increased reaching 120% when the anode was controlled at - 200 mV.

A methane-producing microbial electrolysis cell (MEC) was continuously fed at the anode with a synthetic solution of soluble organic compounds simulating the composition of the soluble fraction of a municipal wastewater. The MEC performance was assessed at different anode potentials in terms of chemical oxygen demand (COD) removal efficiency, methane production, and energy efficiency. As a main result, about 72-80% of the removed substrate was converted into current at the anode, and about 84-86% of the current was converted into methane at the cathode. Moreover, even though both COD removed and methane production slightly decreased as the applied anode potential decreased, the energy efficiency (i.e., the energy recovered as methane with respect to the energy input into the system) increased from 54 to 63%. Denaturing gradient gel electrophoresis (DGGE) analyses revealed a high diversity in the anodic bacterial community with the presence of both fermentative (Proteiniphilum acetatigenes and Petrimonas sulphurifila) and aerobic (Rhodococcus qingshengii) microorganisms, whereas only two microorganisms (Methanobrevibacter arboriphilus and Methanosarcina mazei), both assignable to methanogens, were observed in the cathodic community.

Mixed microbial culture polyhydroxyalkanoates (PHA) production has been investigated by using olive oil mill wastewater (OMW) as no-cost feedstock in a multi-stage process, also involving phenols removal and recovery. The selection of PHA-storing microorganisms occurred in a sequencing batch reactor (SBR), fed with dephenolized and fermented OMW and operated at different organic loading rates (OLR), ranging from 2.40 to 8.40gCOD/Ld. The optimal operating condition was observed at an OLR of 4.70gCOD/Ld, which showed the highest values of storage rate and yield (339±48mgCOD/gCODh and 0.56±0.05 COD/COD, respectively). The OLR applied to the SBR largely affected the performance of the PHA-accumulating reactor, which was fed through multiple pulsed additions of pretreated OMW. From an overall mass balance, involving all the stages of the process, an abatement of about 85% of the OMW initial COD (chemical oxygen demand) was estimated whereas the conversion of the influent COD into PHA was about 10% (or 22% by taking into account only the COD contained in the pretreated OMW, which is directly fed to the PHA production stages). Overall, polymer volumetric productivity (calculated from the combination of both the SBR and the accumulation reactor) accounted for 1.50gPHA/Ld., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Polyhydroxyalkanoates (PHA) production with mixed microbial cultures (MMC) has been investigated by means of a sequential process involving three different stages, consisting of a lab-scale sequencing batch reactor for MMC selection, a PHA accumulation reactor and a polymer extraction reactor. All stages were performed under continuous operation for at least 4 months to check the overall process robustness as well as the related variability of polymer composition and properties. By operating both biological stages at high organic loads (8.5 and 29.1 gCOD/Ld, respectively) with a synthetic mixture of acetic and propionic acid, it was possible to continuously produce PHA at 1.43 g/Ld with stable performance (overall, the storage yield was 0.18 COD/COD). To identify the optimal operating conditions of the extraction reactor, two digestion solutions have been tested, NaOH (1m) and NaClO (5% active Cl2). The latter resulted in the best performance both in terms of yield of polymer recovery (around 100%, w/w) and purity (more than 90% of PHA content in the residual solids, on a weight basis). In spite of the stable operating conditions and performance, a large variation was observed for the HV content, ranging between 4 and 20 (%, w/w) for daily samples after accumulation and between 9 and 13 (%, w/w) for weekly average samples after extraction and lyophilization. The molecular weight of the produced polymer ranged between 3.4 × 10(5) and 5.4 × 10(5)g/mol with a large polydispersity index. By contrast, TGA and DSC analysis showed that the thermal polymer behavior did not substantially change over time, although it was strongly affected by the extraction agent used (NaClO or NaOH)., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The present work reports on the production and characterization of polyhydroxyalkanoates (PHAs) with different valerate contents, which were synthesized from microbial mixed cultures, and the subsequent development of nanocomposites incorporating bacterial cellulose nanowhiskers (BCNW) via solution casting processing. The characterization of the pure biopolyesters showed that the properties of PHAs may be strongly modified by varying the valerate ratio in the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymer, as expected. Increasing the valerate content was seen to greatly decrease the melting temperature and enthalpy of the material, as well as its rigidity and stiffness, resulting in a more ductile behaviour. Additionally, the higher valerate PHA displayed higher permeability to water and oxygen and higher moisture sensitivity. Subsequently, BCNW were incorporated into both PHA grades, achieving a high level of dispersion for a 1 wt.-% loading, whereas some agglomeration took place for 3 wt.-% BCNW. As evidenced by DSC analyses, BCNW presented a nucleating effect on the PHA matrices. BCNW also increased the thermal stability of the polymeric matrices when properly dispersed due to strong matrix-filler interactions. Barrier properties were seen to depend on relative humidity and improved at low nanofiller loadings and low relative humidity., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The anode of a two-chamber methane-producing microbial electrolysis cell (MEC) was poised at +0.200V vs. the standard hydrogen electrode (SHE) and continuously fed (1.08gCOD/Ld) with acetate in anaerobic mineral medium. A gas mixture (carbon dioxide 30vol.% in N(2)) was continuously added to the cathode for both pH control and carbonate supply. At the anode, 94% of the influent acetate was removed, mostly through anaerobic oxidation (91% coulombic efficiency); the resulting electric current was mainly recovered as methane (79% cathode capture efficiency). Low biomass growth was observed at the anode and ammonium was transferred through the cationic membrane and concentrated at the cathode. These findings suggest that the MEC can be used for the treatment of low-strength wastewater, with good energy efficiency and low sludge production., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Microbial biocathodes allow converting and storing electricity produced from renewable sources in chemical fuels (e.g., H(2) ) and are, therefore, attracting considerable attention as alternative catalysts to more expensive and less available noble metals (notably Pt). Microbial biocathodes for H(2) production rely on the ability of hydrogenase-possessing microorganisms to catalyze proton reduction, with a solid electrode serving as direct electron donor. This study provides new chemical and electrochemical data on the bioelectrocatalytic activity of Desulfovibrio species. A combination of chronoamperometry, cyclic voltammetry, and impedance spectroscopy tests were used to assess the performance of the H(2) -producing microbial biocathode and to shed light on the involved electron transfer mechanisms. Cells attached onto a graphite electrode were found to catalyze H(2) production for cathode potentials more reducing than -900 mV vs. standard hydrogen electrode. The highest obtained H(2) production was 8 mmol L(-1) per day, with a Coulombic efficiency close to 100 %. The electrochemical performance of the biocathode changed over time probably due to the occurrence of enzyme activation processes induced by extended electrode polarization. Remarkably, H(2) (at least up to 20 % v/v) was not found to significantly inhibit its own production., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hydrogenophilic dechlorinating bacteria were shown to catalyze H(2) production by proton reduction, with electrodes serving as electron donors, either in the presence or in the absence of a redox mediator. In the presence of methyl viologen, Desulfitobacterium- and Dehalococcoides-enriched cultures produced H(2) at rates as high as 12.4 μeq/mgVSS (volatile suspended solids)/d, with the cathode set at -450 mV vs. the standard hydrogen electrode (SHE), hence very close to the reversible H(+)/H(2) potential value of -414 mV at pH 7. Notably, the Desulfitobacterium-enriched culture was capable of catalyzing H(2) production without mediators at cathode potentials lower than -700 mV. At -750 mV, the H(2) production rate with Desulfitobacterium spp. was 13.5 μeq/mgVSS/d (or 16 μeq/cm(2)/d), nearly four times higher than that of the abiotic controls. Overall, this study suggests the possibility of employing dechlorinating bacteria as hydrogen catalysts in new energy technologies such as microbial electrolysis cells., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

This review illuminates extracellular electron transfer mechanisms that may be involved in microbial bioelectrochemical systems with biocathodes. Microbially-catalyzed cathodes are evolving for new bioprocessing applications for waste(water) treatment, carbon dioxide fixation, chemical product formation, or bioremediation. Extracellular electron transfer processes in biological anodes, were the electrode serves as electron acceptor, have been widely studied. However, for biological cathodes the question remains: what are the biochemical mechanisms for the extracellular electron transfer from a cathode (electron donor) to a microorganism? This question was approached by not only analysing the literature on biocathodes, but also by investigating known extracellular microbial oxidation reactions in environmental processes. Here, it is predicted that in direct electron transfer reactions, c-type cytochromes often together with hydrogenases play a critical role and that, in mediated electron transfer reactions, natural redox mediators, such as PQQ, will be involved in the bioelectrochemical reaction. These mechanisms are very similar to processes at the bioanode, but the components operate at different redox potentials. The biocatalyzed cathode reactions, thereby, are not necessarily energy conserving for the microorganism., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

This study describes the performance of a microbial biocathode, based on a hydrogenophilic methanogenic culture, capable of reducing carbon dioxide to methane, at high rates (up to 0.055 + or - 0.002 mmol d(-1) mgVSS(-1)) and electron capture efficiencies (over 80%). Methane was produced, at potentials more negative than -650 mV vs. SHE, both via abiotically produced hydrogen gas (i.e., via hydrogenophilic methanogenesis) and via direct extracellular electron transfer. The relative contribution of these two mechanisms was highly dependent on the set cathode potential. Both cyclic voltammetry tests and batch potentiostatic experiments indicated that the capacity for extracellular electron transfer was a constitutive trait of the hydrogenophilic methanogenic culture. In principle, both electrons and carbon dioxide required for methane production could be obtained from a bioanode carrying out the oxidation of waste organic substrates., (Copyright 2009 Elsevier Ltd. All rights reserved.)