Search

Secondary production of steel is proven to significantly decrease CO2 emissions of steelmaking, but only 40 % of steel is produced via recycling, which is made difficult by contamination of scrap resources with non-ferrous metals and non-metal debris. These contaminants include zinc, which blast furnace and electric arc systems have a low tolerance towards (0.02 wt%). In this work, clean and efficient recovery of zinc from the surface of steel substrates was investigated using a custom-made low-cost membrane-free non-flow zinc-bromine battery (ZBB) that enabled rapid and straightforward integration and removal of steel substrates. The electrical performance of the cell was characterised by charge-discharge profiles, and zinc removal and recovery onto electrodes was characterised using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Upon discharging, the cell efficiently removed99.9 wt% zinc from steel surfaces. On recharging the cell, zinc was re-electroplated onto a carbon foam electrode in an easily recoverable form and with high purity. The process was repeated over 30 cycles to demonstrate robustness. The work shows the importance of the cut-off voltage upon discharging: if less than 0.5 V, the cell co-extracted iron into the electrolyte solution, affecting cell durability and zinc purity. A two-stage process for recovering zinc from scrap steel is proposed, illustrating how ZBB technology could enable efficient and clean recovery of zinc from complex scrap steel resources in the steel industry.

A novel approach of using two stage anaerobic digestion coupled with electrodialysis technology has been investigated. This approach was used to improving bio hydrogen and methane yields from food waste while simultaneously producing a green chemical feedstock. The first digester was used for hydrogen production and the second digester was used for methane production. The first digester was combined with continuous separation of volatile fatty acids using electrodialysis. The concentrations of carbohydrates, proteins and fats in the prepared food waste were 22.7%, 5.7% and 5.2% respectively. Continuous removal of volatile fatty acids during fermentation in the hydrogen digester not only increased hydrogen yields but also increased the production rate of volatile fatty acids. As a result of continuous VFA separation, hydrogen yields increased from 17.3 mL H2/g VS fermenter to 33.68 mL H2/g VS fermenter. Methane yields also increased from 28.94 mL CH4/g VS fermenter to 43.94 mL CH4/g VS fermenter. This represents a total increase in bio-energy yields of 77.1%. COD reduced by 73% after using two stage anaerobic digestion, however, this reduction increased to 86.7% after using electrodialysis technology for separation of volatile fatty acids. Electrodialysis technology coupled with anaerobic digestion improved substrate utilization, increased bioenergy yields and looks to be promising for treating complex wastes such as food waste.

A novel method to recover VFAs from a continually-fed 100 L food waste bioreactor was developed using industrially applicable methods. The in-situ recovery of VFAs increased production rates from 4 to 35 mgvfa gvs−1 day−1 by alleviating end-product inhibition and arresting methanogenesis, and electrodialysis was able to concentrate the recovered VFAs to 4000 mg L−1. There remains considerable scope to increase the production rates and concentrations further, and the VFAs were recovered in a form that made them suitable for use as platform chemicals with minimal refining. This is the first time that continuous VFA recovery from real-world food waste has been reported at this scale with continual feeding, and represents a promising means through which to produce sustainable platform chemicals. Furthermore the production of VFAs arrests methane production in bioreactors, which is a low value product around which there is a growing concern about fugitive emissions contributing to climate change.

Methane, the final product of methanogenesis during anaerobic digestion is a low value product (0.1 $ per m3). Concerns over fugitive emissions from methane coupled with recent reduction in costs of solar and wind energy raise questions over the long-term sustainability of the anaerobic digestion process as a technology to produce renewable energy. The production of short chain volatile fatty acids (VFAs), a by-product of acetogenesis, represents a high value product. The projected VFA market demand for 2020 is 18 500 kilotons, increasing at an annual rate of 3% per year. Here, we review the business case for wastewater treatment plants (WWTPs) to produce VFAs instead of biogas. Techno-economic and sensitivity studies are conducted to understand and compare economic feasibilities. Under favourable conditions, with positive government incentives, future WWTPs could produce high purity (>98%) propionic acid at 3.8 $ per kg, 35% less than the commercial selling value (6 $ per kg).

ZBBs have a high open circuit voltage (1.82 V), a high theoretical energy (> 400 W h-1 kg-1) and high demonstrated power densities (> 100 mW cm-2). Typically, ZBBs adopt a redox flow design involving the use of a Nafion membrane to separate aqueous zinc bromide anolyte and catholyte solutions [1]. In this study, the use of a membrane-free non-flow design was investigated for the purposes of recovering zinc from scrap and waste steel resources [2]. The rationale for this work stems from the greenhouse gas emissions produced by the iron and steel industry, which accounts for between 4-7 % of the anthropogenic CO2 emissions globally [3]. Blast furnace technology is likely to account for most stainless steel production in the coming decades, and therefore a transition to low-carbon and green steel production will require increased steel recycling rates and significantly improved waste and scrap management. To the best of our knowledge, this is the first time a zinc-bromine battery has been investigated for the recovery of materials rather than energy storage. Galvanization of steel is required to prevent rusting and degradation and involves coating the surface of steel in a protective layer of zinc. Galvanization processes account for over 50 % of global zinc consumption and by 2050 the demand for zinc will be 2.7 times greater than that of 2012 [4]. In order to enable recycling of scrap steel directly into blast furnaces, zinc is removed and recovered via mineral acid leaching. This method of recovery has a high zinc extraction efficiency but creates problematic waste streams and has poor energetic efficiency. In this work, the use of a membrane-free zinc-bromine battery has been studied for the purposes of extracting zinc from steel substrates and subsequently re-electroplating onto a conventional carbon foam electrode. The electrical performance of the cell was characterised by charge-discharge profiles and I-V curves. Zinc removal and recovery onto electrodes was characterised using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The work successfully demonstrates that ZBB technology could enable efficient and clean recovery of zinc from metal and waste substrates including scrap steel, slurries generated from basic oxygen steelmaking processes, and secondary vent dust from the primary steelmaking off gas streams. The cell studied in this work enabled dipping of zinc-containing steel substrates directly into the electrolyte solution without disassembly of the battery housing. In addition, the design involved the use of low-cost materials and reagents and potentially offers low balance-of-plant costs. The results show that zinc could be removed from steel surfaces during cell discharge with greater than 99.9 % yield. The Figure shows the extracted zinc could subsequently be re-electroplated onto a standard carbon foam electrode upon re-charging the cell. When a 0.5 V cut-off voltage was used upon discharge, the zinc was recovered selectively from the steel (see Fig. (a)); the surface elemental composition of the carbon electrode measured by EDS after charging was: carbon (26.79 wt%), oxygen (18.06 wt%), zinc (30.03 wt%) and bromine (25.11 wt%). Using a lower cut-off voltage (0.2 V) resulted in the co-extraction of iron from the substrate as well as zinc (see Fig. (b)); in this case, the elemental composition of the carbon electrode after charging was: carbon (27.53 wt%), oxygen (22.65 wt%), iron (4.72 wt%), zinc (24.44 wt%) and bromine (20.65 wt%). Provided a cut-off voltage of no less than 0.5 V was used for discharging, high purity zinc was recovered, and the cell showed good initial durability, with 30 cycles of charge-discharge demonstrated in this work. [1] S. Suresh, M. Ulaganathan, N. Venkatesan, P. Periasamy, P. Ragupathy, High performance zinc-bromine redox flow batteries: Role of various carbon felts and cell configurations. J. Energy Storage, 2018. 20: pp. 134-139. [2] S. Biswas, A. Senju, R. Mohr, T. Hodson, N. Karthikeyan, K. Knehr, A.G. Hsieh, X. Yang, B.E. Koel, D.A. Steingart, Minimal architecture zinc-bromine battery for low-cost electrochemical storage. Energy Environ. Sci., 2017. 10: pp. 114-120. [3] Iron and Steel Technology Roadmap: Towards More Sustainable Steelmaking, Energy Technology Perspectives, International Energy Agency, IEA Publications, Paris, 2020. https://www.iea.org/reports/iron-and-steel-technology-roadmap [accessed 12 April 2022]. [4] K.S. Ng, I. Head, G.C. Premier, K. Scott. E. Yu, J. Lloyd, J. Sadhukhan. A multilevel sustainability analysis of zinc recovery from wastes. Resour. Conserv. Recycl., 2016. 113: pp. 88-105. Figure. SEM images showing the carbon foam zinc electrodes after charging the cell. (a) is an electrode when a discharge cut-off voltage of 0.5 V was used, (b) is an electrode when a discharge cut-off voltage of 0.2 V was used. Figure 1

A novel combination of solids screening, centrifugation, microfiltration, pervaporation, and electrodialysis were used for the targeted and exclusive recovery of volatile fatty acids (VFAs) from an 80 L bioreactor. The bioreactor was continually–fed with grass waste, containing 40 g L–1 total solids, over three, seven–day, hydraulic retention times. A VFA solution with a concentration up to 4,500 mg L–1 was recovered. VFA yields were also increased from 707 to 875 mg of VFA per gram of volatile solids by alleviating end–product inhibition. Both these accomplishments are significant step–changes in adding value to waste, and increased substrate utilisation rates will be attractive from a waste remediation perspective.

Biogas (60%-CH4, 40%- CO2) is a potential source of renewable energy when used as energy feedstock for solid oxide fuel cells (SOFC), but releases biogenic CO2 emissions. Hybrid SOFC performance can be affected by fuel composition and reformer performance. Biohythane (58%-CH4, 35%-CO2 and 7% H2) can be a better alternative providing balance between energy and biogenic emissions. Biohythane performance is studied for a 120 kW SOFC stack using ASPEN process model and compared with other feed stocks. This work is the first to study and report on the application of biohythane in SOFC systems. Biohythane was found to produce less biogenic CO2 emissions and 6% less CO at the reformer than biogas. Comparisons show that biohythane provides better efficiencies in hybrid SOFC systems. Sensitivity studies recommends operation of stack with biohythane at Steam to Carbon Ratio (STCR) = 2.0, i = 200 mA cm−2 and UF = 0.85 respectively.

The meat and dairy industry across Europe is dependent on the production of grass. However, faced with competing pressures to reduce the environmental impact of agriculture, a potential future reduction of meat and dairy consumption in western diets, and pressure to minimize food production costs, grass could be used to produce alternative products. The biological production of polyhydroxyalkanoates (PHA) by using grass as the primary carbon source in a novel mixed culture process has been studied. A total of 30,000 t of fresh grass would yield approximately 403.65 t of dried biopolymer granules. On the basis of this early stage, non‐optimized process, the cumulative energy demand (CED) of PHA produced from waste grass and cultivated grass was found to be 248.4 MJ/kg and 271.8 MJ/kg, respectively, which is the same order of magnitude as fossil‐carbon‐based polymers. Improvements in volatile fatty acid yields, reduction in chemical and water inputs, and using residues to make other products will reduce the CED. Given the future requirement to produce polymers with little or no fossil‐carbon feedstock, an optimized version of the process could provide a viable future production option that also contributes to the long‐term sustainability of agricultural communities.

Antibiotic resistant bacteria (ARB) and their genes (ARGs) have become recognised as significant emerging environmental pollutants. ARB and ARGs in sewage sludge can be transmitted back to humans via the food chain when sludge is recycled to agricultural land, making sludge treatment key to control the release of ARB and ARGs to the environment. This study investigated the fate of antibiotic resistant Escherichia coli and a large set of antibiotic resistance genes (ARGs) during full scale anaerobic digestion (AD) of sewage sludge at two U.K. wastewater treatment plants and evaluated the impact of thermal hydrolysis (TH) pre-treatment on their abundance and diversity. Absolute abundance of 13 ARGs and the Class I integron gene intI1 was calculated using single gene quantitative (q) PCR. High through-put qPCR analysis was also used to determine the relative abundance of 370 ARGs and mobile genetic elements (MGEs). Results revealed that TH reduced the absolute abundance of all ARGs tested and intI1 by 10–12,000 fold. After subsequent AD, a rebound effect was seen in many ARGs. The fate of ARGs during AD without pre-treatment was variable. Relative abundance of most ARGs and MGEs decreased or fluctuated, with the exception of macrolide resistance genes, which were enriched at both plants, and tetracyline and glycopeptide resistance genes which were enriched in the plant employing TH. Diversity of ARGs and MGEs decreased in both plants during sludge treatment. Principal coordinates analysis revealed that ARGs are clearly distinguished according to treatment step, whereas MGEs in digested sludge cluster according to site. This study provides a comprehensive within-digestor analysis of the fate of ARGs, MGEs and antibiotic resistant E. coli and highlights the effectiveness of AD, particularly when TH is used as a pre-treatment, at reducing the abundance of most ARGs and MGEs in sludgeand preventing their release into the environment.

Short chain carboxylic acids known as volatile fatty acids (VFA) are important products of biological processes and as such, their measurement has long been of interest in animal husbandry, anaerobic digestions and other biologically mediated processes. While such measurements are widespread, a low cost and accurate sensor for online process monitoring is highly desirable, but as yet unavailable. An investigation into the suitability of Poly(3,4-ethylenedioxythiophene) (PEDOT) coated electrodes in sensing the concentrations of VFAs and their applicability as detector subsequent separation by capillary electrophoresis is presented. The electrodes were subjected to pulse amperometric operation, switching between their reduced and oxidized states to promote ion exchange between the polymer and electrolyte solutions containing the VFAs. The effects of the film thickness, properties of the analyte, the duration of the pulse and the electrolyte concentration on the current response, were studied. Linear calibration curves with high correlation coefficients (>0.998) were found within the range of concentrations 0.1–10 mM for sodium acetate, sodium propionate and sodium butyrate. Furthermore, the PEDOT electrodes were shown to be very stable and precise over at least one month and no film deterioration or loss sensitivity was in evidence. The role of the polymerization charge, the pulsation time as well as the electrophoresis detection cell configuration are discussed and guidelines to increase the analytical to background signal are given.

Research into microbial fuel cells (MFCs) has reached the point where cubic metre-scale systems and stacks are being built and tested. Apart from performance enhancement through catalysis, materials and design, an important research area for industrial applicability is stack control, which can enhance MFCs stack power output. An MFC stack is controlled using a sampled-time digital control strategy, which has the advantage of intermittent operation with consequent power saving, and when used in a hybrid series stack connectivity, can avoid voltage reversals. A MFC stack comprising four tubular MFCs was operated hydraulically in series. Each MFC was connected to an independent controller and the stack was connected electrically in series, creating a hybrid-series connectivity. The voltage of each MFC in the stack was controlled such that the overall series stack voltage generated was the algebraic sum (1.26 V) of the individual MFC voltages (0.32, 0.32, 0.32 and 0.3). The controllers were able to control the individual voltages to the point where 2.52 mA was drawn from the stack at a load of 499.9 Ω (delivering 3.18 mW). The controllers were able to reject the disturbances and perturbations caused by electrical loading, temperature and substrate concentration.

A novel eco-engineered mixed anaerobic culture was successfully demonstrated for the first time to be capable of continuous regeneration in nutrient limiting conditions. Microbial catabolism has been found to support a closed system of nutrients able to enrich a culture of lithotrophic methanogens and provide microbial cell recycling. After enrichment, the hydrogenotrophic species was the dominating methanogens while a bacterial substratum was responsible for the redistribution of nutrients. q-PCR results indicated that 7% of the total population was responsible for the direct conversion of the gases. The efficiency of H2/CO2 conversion to CH4 reached 100% at a gassing rate of above 60v/v/d. The pH of the culture media was effectively sustained at optimal levels (pH 7-8) through a buffering system created by the dissolved CO2. The novel approach can reduce the process nutrient/metal requirement and enhance the environmental and financial performance of hydrogenotrophic methanogenesis for renewable energy storage.

A tubular Microbial Fuel Cell (MFC) reactor consisting of four modules (total reactor volume of 1 l) was fed with food processing washdown water as a chemical oxygen demand (COD) removal process to decrease effluent pollution levels and discharge costs. Two different operational modes were tested: (A) Under static electrical loads with substrate circulated to and from different storage vessels and (B) employing maximum peak power point tracking (MPPT) whilst re-circulating substrate through a single storage vessel. After 7 cycles through the reactor, notionally equivalent to 28 concatenated tubular MFC modules, 84% of the soluble COD (960 mg l−1) was removed from the effluent in Mode A and 70% (800 mg l−1) in Mode B with MPPT. In the study, acetic acid was consumed first and propionic acid increased initially before depletion after 7 cycles, showing that higher carbohydrates were degraded during the effluent polishing process.

This research investigated the use of an innovative polytetrafluoroethylene (PTFE) membrane configurationcoupled to electrodialysis for the in-situ removal of Volatile Fatty Acids (VFAs) from a mixed culture bioreactor. It was shown that by stacking the PTFE membranes to increase the active membrane surface area, shortened VFArecovery times was seen. The addition of electrodialysis to the PTFE membrane stack enabled the continuousextraction of VFAs from fermentation media whilst retaining essential nutrients and organic compounds in thediluate stream. Ammonium, phosphate and nitrate remained in the diluate chamber and did not cross the PTFEmembrane stack. Up to 98% of total VFA recovery was achieved with the PTFE and electrodialysis system. Theprocess was shown to extract from a reservoir of low VFA concentration to a reservoir with a VFA concentration10 times higher. These results show that the addition of electrodialysis to PTFE provides a robust solution for thein-situ extraction of VFAs from fermentation media within bioreactors to support the demand for sustainablefuels and green chemical feedstocks.

A novel amperometric detection method based on the use of poly(3,4-ethylenedioxythiophene) (PEDOT) coated electrodes for the determination of organic and inorganic anions subsequent separation by capillary electrophoresis is presented. The analyte peak arises from the difference in the doping capability between the analytes and the buffer co-ion that affects the polymer oxidation kinetics and therefore the sampled current. A contactless conductivity detector was used simultaneously to directly compared both detection methods. LODs of 1.1, 2.6 and 4.1 µM and 2.1, 3.6 and 4.5 µM for acetate, propionate and butyrate were achieved with the PEDOT based detection method and the contactless conductivity detector respectively. Moreover, improved LODs for Cl- and NO3- and worsened LODs for SO42- and PO43- were obtained with the PEDOT based detection method which was found to perform better than the contactless conductivity detector for the determination of ions with a small effective radius. The PEDOT based detection method is very promising for its application in microfluidic devices and the development of new portable sensors for in situ analysis.

Background: Biomass measurement and monitoring is a challenge in a number of biotechnology processes where fast, inexpensive, and non-contact measurement techniques would be of great benefit. Magnetic induction spectroscopy (MIS) is a novel non-destructive and contactless impedance measurement technique with many potential industrial and biomedical applications. The aim of this paper is to use computer modeling and experimental measurements to prove the suitability of the MIS system developed at the University of South Wales for controlled biomass measurements. Methods: The paper reports experimental measurements conducted on saline solutions and yeast suspensions at different concentrations to test the detection performance of the MIS system. The commercial electromagnetic simulation software CST was used to simulate the measurement outcomes with saline solutions and compare them with those of the actual measurements. We adopted two different ways for yeast suspension preparation to assess the system&rsquo, s sensitivity and accuracy. Results: For saline solutions, the simulation results agree well with the measurement results, and the MIS system was able to distinguish saline solutions at different concentrations even in the small range of 0&ndash, 1.6 g/L. For yeast suspensions, regardless of the preparation method, the MIS system can reliably distinguish yeast suspensions with lower concentrations 0&ndash, 20 g/L. The conductivity spectrum of yeast suspensions present excellent separability between different concentrations and dielectric dispersion property at concentrations higher than 100 g/L. Conclusions: The South Wales MIS system can achieve controlled yeast measurements with high sensitivity and stability, and it shows promising potential applications, with further development, for cell biology research where contactless monitoring of cellular density is of relevance.

The impact of continuous removal of volatile fatty acids on fermentative hydrogen productionfrom food waste (FW) in a Continuously Stirred Tank Reactor (CSTR) was evaluated. Two experimental phases were conducted, a control phase and one in which volatilefatty acids were removed continuously from the reactor for the first time by electrodialysis(ED). Hydrogen yields were 64.7 cm3 H2/g VS and 227.3 cm3 H2/g VS for control phase, and ED phase respectively. Continuous removal of volatile fatty acids during fermentation notonly increased H2 yields but increased the production of volatile fatty acids (a valuablechemical feedstock) from 0.14 g/g VS to 0.34 g/g VS.

An industrially applicable methodology utilising a novel combination of filtration and electrochemical separation technologies was successfully used to recover, and enhance the production of, volatile fatty acids from an 82.5 L bioreactor, continually fed with grass at 5% total solids. Volatile fatty acid yields were increased from 287 to 404 mgvfa gvs−1 and concentrated up to 4800 mg L−1 in a solution suitable for downstream conversion to platform chemicals. This work also shows that there is considerable headroom to increase further volatile fatty acid recovery rates and yields by increasing the capacity of the recovery methodology. The novel methodology developed herein could help to address some of the environmental and economic concerns that have led to the need to diversify the ways in which grass is used as a resource, and represents an alternative to petrochemicals as a carbon source for platform chemical production.

In this study, a scanning electrochemical impedance spectroscopy (EIS) technique is proposed to confirm the variation of internal resistance (Rint) including charge transfer resistance (Rct) and ohmic resistance (Rohm) under various working conditions of microbial fuel cells (MFCs). In order to establish a scanning EIS method, overall Rint of the system and Rct of anode and cathode were measured by EIS under various external resistance conditions. Using this method, it was confirmed that the Rohm and Rct of each electrode changed variably. Based on the use of scanning EIS, the rapid increase in the Rct of anode was found to be the main cause of a power-overshoot. As such, the use of scanning EIS is a methodology that can provide data to understand undesirable phenomena such as power-overshoot and voltage reversal which are generated by the typical operational characteristics of MFCs when used in scale up experiments. The use of scanning EIS should be applied as a novel measurement technique that improves on the use of the open circuit mode based EIS methods.

Recent microbial fuel cell (MFC) research frequently addresses matters associated with scale and deployability. Modularisation is often needed to reduce ohmic losses with increasing volume. Series/parallel is then often an obvious strategy to enhance power quality during operation, to make best use of generated electricity. Hence, voltage reversal resulting from power and voltage mismatch between cells become virtually unavoidable. Control MFC voltages could be used to stabilise MFC stacks. Here, nonlinear MFCs are controlled using simple gain scheduled Proportional + Integral actions. Parsimonious control may be necessary for implementation in MFC arrays, so minimising costs. Controller parameterisation used several linearised models over the dynamic operating range of the MFCs. Controller gains were then scheduled according to the operating conditions. A digital potentiometer was used to actuate the control, varying the current sourced from the MFC. The results show that the controller was able to control MFC voltages, rejecting the disturbances. It was shown that the controller was transferable between MFCs with different power performances. This study demonstrates that the control of MFCs can be achieved with relatively simple digital approaches, plausibly implementable using low cost microcontrollers, and likely to be useful in the effective deployment of MFCs in large scale arrays.

The influence of acetate and butyrate enrichment on biofilm structure for enhanced electricity and hydrogen production was investigated using bioelectrochemical systems (BES). Two reactors were enriched for 9 weeks using 20 mM L −1 acetate (AC) and butyrate (BU) in microbial fuel cell mode before transfer into MECs. Acetate and butyrate (20, 10 and 5 mM L −1 ) substrates were sequentially used as feedstocks for the AC and BU acclimated reactors. Both BU and AC reactors gave initial hydrogen production rates of 200 ± 50 cm 3 STP /L anode /day with a H 2 yield of 0.585 ± 0.085 mol mol −1 but when the substrates were switched, the BU (MEC) hydrogen production rate increased to 249 ± 3.0 cm 3 STP /L anode /day and the AC (MEC) decreased to 0 cm 3 STP /L anode /day. It was demonstrated that the amount of methane produced by MEC (BU) was 58 ± 5% lower than that produced by MEC (AC). These results show that butyrate fed BES on an equivalent molar basis, improved MEC bioanodic performance and demonstrated the potential to improve overall performance of an integrated hydrogen fermentation and BES system.

Copper recovery from distillery effluent was studied in a scalable bioelectro-chemical system with approx. 6.8 L total volume. Two control strategies based on the control of power with maximum power point tracking (MPPT) and the application of 0.5 V using an external power supply were used to investigate the resultant modified electroplating characteristics. The reactor system was constructed from two electrically separated, but hydraulically connected cells, to which the MPPT and 0.5 V control strategies were applied. Three experiments were carried out using a relatively high copper concentration i.e. 1000 mg/L followed by a lower concentration i.e. 50 mg/L, with operational run times defined to meet the treatment requirements for distillery effluents considered. Real distillery waste was introduced into the cathode to reduce ionic copper concentrations. This waste was then recirculated to the anode as a feed stock after the copper depletion step, in order to test the bioenergy self-sustainability of the system. Approx. 60–95% copper was recovered in the form of deposits depending on starting concentration. However, the recovery was low when the anode was supplied with copper depleted distillery waste. Through process control (MPPT or 0.5 V applied voltage) the amount and form of the copper recovered could be manipulated.

Volatile fatty acids are formed during microbial fermentation of organic matter and are present in a wide range of matrices, i.e., wastewater, landfill leachates, human and animal fluids, food, and environmental systems. Therefore, their quantification and speciation is important in the analysis of such natural systems. The difference in nature and complexity of the matrices has resulted in the development and publication of a great number of procedures for volatile fatty acid determination. This review gives an overview of sample preparation, separation conditions, and suitable detectors for each separation technique with a comparison of the limits of detection and the linear dynamic ranges attainable.

Real time measurement of gas production and composition were used to examine the benefits of two stage anaerobic digestion (AD) over a single stage AD, using pelletized grass as a feedstock. Controlled, parallel digestion experiments were performed in order to directly compare a two stage digestion system producing hydrogen and methane, with a single stage system producing just methane. The results indicated that as well as producing additional energy in the form of hydrogen, two stage digestion also resulted in significant increases to methane production, overall energy yields, and digester stability (as indicated by bicarbonate alkalinity and volatile fatty acid removal). Two stage AD resulted in an increase in energy yields from 10.36 MJ kg(-1) VS to 11.74 MJ kg(-1) VS, an increase of 13.4%. Using a two stage system also permitted a much shorter hydraulic retention time of 12 days whilst maintaining process stability.

Microbial fuel cells (MFCs) are bioelectrochemical systems which can degrade organic materials and are increasingly seen as potential contributors to low carbon technologies, particularly in energy recovery from and treatment of wastewaters. The theoretical maximum open circuit voltage from MFCs lies in the region of 1.1 V, but is reduced substantially by overvoltage losses. Practical use of the power requires stacking or other means to increase voltage. Series stacking of MFCs with typically encountered variability in operating conditions and performance raises the risk of cell reversal, which diminishes overall power performance. A novel strategy of MFC subsystem series connectivity along with maximum power point tracking (MPPT) generates increased power from individual MFCs whilst eliminating cell reversal. MFCs fed with lower concentrations of substrate experienced voltage reversal when connected in normal series connection with one common load, but when MFCs and loads together were connected in series, the underperforming cell is effectively bypassed and maximum power is made available. It is concluded that stack voltage may be increased and cell reversal avoided using the hybrid connectivity along with MPPT. This approach may be suitable for stacked MFC operations in the event that large scale arrays/modules are deployed in treating real wastewaters.

Methanogenesis may diminish coulombic efficiency of microbial fuel cells (MFCs), although its importance is application dependent; e.g., suppression of methanogenesis may improve MFC sensing accuracy, but may be tolerable in COD removal from wastewaters. Suppression of methanogenesis was investigated in three H-type MFCs, enriched and acclimated with acetate, propionate and butyrate substrates and subsequently operated under open and closed circuit (OC/CC) regimes. Altering the polarisation state of the electrode displaces microorganisms from the anodic biofilm and leads to observable methane inhibition. The planktonic archeal community was compared to the electrode biofilm whilst under the OC/CC regimes. Semi-quantitative DNA analyses indicate a shift in some dominant species, from the electrode to the solution, during OC operation. The effect of prolonged starvation on anodic species was also studied. The results indicate progressive inhibition of methanogenesis from OC/CC operations; and virtual cessation of methanogenesis when an MFC was starved for a significant period.

The integration of a biomethanation system within a wastewater treatment plant for conversion of CO2 and H2 to CH4 has been studied. Results indicate that the CO2 could be utilised to produce an additional 13,420 m3/day of CH4, equivalent to approximately 133,826 kWh of energy. The whole conversion process including electrolysis was found to have an energetic efficiency of 66.2%. The currently un-optimised biomethanation element of the process had a parasitic load of 19.9% of produced energy and strategies to reduce this to

In this study volatile fatty acids (VFAs), which are by-products from anaerobic fermentations, have been used as the carbon source for polyhydroxyalkanoates (PHA) production by pure culture bacteria, Cupriavidus necator. A number of factors influence the conversion efficiencies of VFAs to PHAs including the bacterial feeding regimes. When VFA was supplied as a single feed, it was found that concentrations higher than 2% v/v VFA led to substrate inhibition and only 18% acetic acid and 12% of butyric acid was converted into PHA. This resulted in less than 65% (w/w) of PHA content within the microbial cells. Hence, the single VFA feeding strategy was found to provide low conversion rates of VFA into polymer. An improved feeding strategy was found to be the use of an automatic VFA feed based on the pH control of the medium, which led to a more continuous feeding regime. The conversion of VFA to PHA was increased by almost 2-fold to 33 and 22% for acetic acid and butyric acid respectively, with up to 75% (w/w) of PHA resultant within the microbial cells.

The use of Ca(OH)2 pre-treatment to improve fermentative biohydrogen yields, from wheat straw was investigated. Wheat straw was pre-treated with 7.4% (w/w) Ca(OH)2 at ambient temperature (20 °C) for 2, 5, 8, and 12 days, prior to 35 °C fermentation with sewage sludge inoculum. Biohydrogen yields were evaluated during dark fermentation and simultaneous saccharification fermentation (SSF) of total pre-treated straw material and compared to those from separated solid and hydrolysate fractions. Ca(OH)2 pre-treatment followed by SSF, exhibited a synergetic relationship. On average, 58.78 mL-H2 g-VS−1 was produced from SSF of pre-treated and filtered solids. This was accompanied by approximately a 10-fold increase in volatile fatty acid production, compared to the untreated control. By omitting pre-treatment hydrolysate liquors from SSF, H2 production increased on average by 35.8%, per VS of harvested straw. Additional inhibition studies indicated that CaCO3, formed as a result of pre-treatment pH control, could promote homoacetogenesis and reduce biohydrogen yields.

The development of a simple and low cost sensor such as a microbial fuel cell (MFC) to measure short chain volatile fatty acids (VFAs) would enable the implementation of this important bioprocess parameter. However using microbial fuel cells (MFCs) as transducers requires consistent microbial biocatalysis at the anode. This study considers carbon/conductive polymer composite electrodes as a mechanism to ensure the sensor signal has temporal stability, repeatability and a short response time to variations in concentration of acetic, propionic and butyric acid. The immobilization of bacteria by; modifying the carbon surface with functionalized poly(pyrrole) coatings, increasing and holding the total number of negatively charged bacteria on the electrode; or by using natural polymers with mediators covering the pre-acclimated microbial community to improve catalytic action and to protect them from the sample matrix was investigated. Six different natural polymers and/or electropolymers anode configurations were compared and it was found that poly(pyrrole-alkyl ammonium) accelerates start-up of MFC based sensors and provided improved stability, repeatability and recovery shorter signal response.

Titration methodologies have been used for the many years for low cost routine monitoring of full scale anaerobic digestion plants. These methodologies have been correlated to indicate the carbonate alkalinity and the volatile fatty acids (VFA) content within digesters. Two commonly used two end-point titration methods were compared using a dataset of 154 samples from energy crop and animal slurry digestates and were shown to be inaccurate in the estimation of tVFA. Using this dataset correlated with HPLC VFA analysis, two empirical bivariate linear regression equations were derived, where the validation dataset showed an absolute tVFA mean error improvement from ±3386 and ±3324 mg kg −1 tVFA to ±410 and ±286 mg kg −1 tVFA, respectively. The same equation was then applied to a food waste dataset where an absolute tVFA mean error was improved from ±3828 to ±576 mg kg −1 tVFA. The newly derived titration equations can provide greater confidence in digester performance monitoring and are tools that can improve digester management.

An optimal power flow (OPF) methodology is developed to investigate the provision of a demand hydrogen as a means to maximise wind power generation in relation to a constrained electricity network. The use of excess wind energy to generate hydrogen for use as a transport fuel is investigated. Hydrogen demand is included in the objective function of the OPF, and a techno-economic analysis is presented. We conclude that using this method to generate hydrogen increases the utilisation of wind energy and allows for a hydrogen demand to be met at or near to the point of use. The OPF algorithm that has been developed optimises the amount of wind energy utilised, as well as minimising the amount of hydrogen demand not met. The cost at which the hydrogen is produced was found to be dependent on the operating methodology, component capital investment costs, level of hydrogen demand, and storage constraint.

a b s t r a c t The pseudo-capacitive behaviour of a high surface area carbon veil electrode in a tubular microbial fuel cell (MFC) was investigated as a mechanism to enhance power quality and energy efficiency. Accumu- lated charge and energy from the anodic biofilm after prolonged open circuit times (1-120 min) were compared against equivalent periods of steady state loading (R = 100-3000 � ). A significant difference in the amount of accumulated charge with different loads was observed, resulting in 1.051 C (R = 100 � ) compared to 0.006 C (R = 3 k� ). The automated application of short open and closed circuit (0.5-10 s) cycles resulted in an increase of power/current production (closed circuit alone), but presented lower efficiency considering entire open and closed period. The cumulative charge on the carbon veil electrode with biofilm was 39,807 C m −2 at 100 � . Electrochemical Impedance Spectroscopy (EIS) showed that the Helmholtz layer presented a double layer capacitance of more than ten times the biofilm on electrode. The results indicate that the capacitive behaviour could be utilized to increase the power quality, i.e. its availability/applicability with respect to the operation of low power consuming devices. © 2014 Elsevier Ltd. All rights reserved.

Simultaneous removal of organic and zinc contamination in parallel effluent streams using a Microbial Fuel Cell (MFC) would deliver a means of reducing environmental pollution whilst also recovering energy. A Microbial Fuel Cell system has been integrated with Supported Liquid Membrane (SLM) technology to simultaneously treat organic- and heavy metal containing wastewaters. The MFC anode was fed with synthetic wastewater containing 10 mM acetate, the MFC cathode chambers were fed with 400 mg L −1 Zn 2+ and this then acted as a feed phase for SLM extraction. The MFC/SLM combination produces a synergistic effect which enhances the power performance of the MFC significantly; 0.233 mW compared to 0.094 mW in the control. It is shown that the 165 ± 7 mV difference between the MFC/SLM system and the MFC control is attributable to the lower cathode pH in the integrated system experiment, the consequent lower activation overpotential and higher oxygen reduction potential. The change in the substrate removal efficiency and Coulombic Efficiency (CE) compared to controls is small. Apart from the electrolyte conductivity, the conductivities of the bipolar and liquid membrane were also found to increase during operation. The diffusion coefficient of Zn 2+ through the liquid membrane in the MFC/SLM (4.26*10 −10 m 2 s −1 ) is comparable to the SLM control (5.41*10 −10 m 2 s −1 ). The system demonstrates that within 72 h, 93 ± 4% of the zinc ions are removed from the feed phase, hence the Zn 2+ removal rate is not significantly affected and is comparable to the SLM control (96 ± 1%), while MFC power output is significantly increased.

Anaerobic bioenergy production processes including fermentative biohydrogen (BioH 2 ), anaerobic digestion (AD) and bioelectrochemical system have been investigated for converting municipal waste or various biomass feedstock to useful energy carriers. However, the performance of a microbial fuel cell (MFC) fed on the effluent from a two-stage biogas production process has not yet been investigated extensively in continuous reactor operation on complex substrates. In this study we have investigated the extent to which a microbial fuel cell (MFC) can reduce COD and recover further energy from the effluent of a two-stage biohydrogen and biomethane system. The performance of a four-module tubular MFC was determined at six different organic loadings (0.036–6.149 g sCOD L −1 d −1 ) in terms of power generation, COD removal efficiency, coulombic efficiency (CE) and energy conversion efficiency (ECE). A power density of 3.1 W m −3 was observed at the OLR = 0.572 g sCOD L −1 d −1 , which resulted in the highest CE (60%) and ECE (0.8%), but the COD removal efficiency decreased at higher organic loading rates (35.1–4.4%). The energy recovery was 92.95 J L −1 and the energy conversion efficiency, based on total influent COD was found to be 0.48–0.81% at 0.572 g sCOD L −1 d −1 . However, the energy recovery by the MFC is only reported for a four-module reactor and improved performance can be expected with an extended module count, as chemical energy remained available for further electrogenesis.

The production of polyhydroxyalkanoates (PHAs) using digestate liquor as culture media is a novel application to extend the existing uses of digestates. In this study, two micro-filtered digestates (0.22 μm) were evaluated as a source of complex culture media for the production of PHA by Cupriavidus necator as compared to a conventional media. Culture media using a mixture of micro-filtered liquors from food waste and from wheat feed digesters showed a maximum PHA accumulation of 12.29 g/l PHA, with 90% cell dry weight and a yield of 0.48 g PHA/g VFA consumed, the highest reported to date for C. necator studies. From the analysis of the starting and residual media, it was concluded that ammonia, potassium, magnesium, sulfate and phosphate provided in the digestate liquors were vital for the initial growth of C. necator whereas copper, iron and nickel may have played a significant role in PHA accumulation.

Volatile fatty acid (VFA) concentration is one of the most important parameters for monitoring bio-processes such as anaerobic digestion and microbial fuel cells. In this study the correlation between VFA concentration and current/voltage responses and electrochemical properties by using the MFC technology was evaluated. The discrimination between different species of VFA by using two methods i.e., coulombic efficiency and cyclic voltammetry was investigated. Columbic efficiency gave a slow response of greater than 20 h, particularly at concentration levels of 20 mg l −1 . By using cyclic voltammetry to measure the oxidation peak at a consistent scan rate showed linear correlation to VFA concentration and peak current produced, up to −1 ) in a rapid response time of 1–2 min. The results presented showed good correlations between the individual VFA species concentration and charge, and also current generated. A MFC based biosensor array was produced capable of measuring individual acetate, propionate and butyrate concentrations with sensitivity down to 5 mg l −1 and up to 40 mg l −1 .

Microbial fuel cells (MFCs) are bioelectrochemical devices which use micro-organisms as catalyst for electrogenesis at the anode; oxidizing biodegradable substrate to produce electrical current. MFC power output is a function of many factors; including pH, temperature, loading rate, flow rate and electrical load. The study presents a system identification approach to determine a set of linear dynamic black box models able to quantify and represent specific nonlinear characteristics of a MFC. A sandwich-type MFC was subjected to varying electrical loads of various pseudo-random and step inputs, while observing the MFC voltage. Nonlinear behaviour was inferred from assumed piecewise linearised first order dynamic responses, at different operating points. The time constants increased from 0.5 s with PRBS loading of 100–150 Ω, to 6.2 s at 950–1 kΩ; although steady state gain varied little, (0.12–0.20 mV Ω−1). This suggests that the MFC's non-linear behaviour, dependent on operating conditions, may be adequately represented by a series of linear models. System identification suggested that linear 4th order ARX models produce the best fit. However, reasonable prediction was observed using piecewise linearised first order models. The models could be used to design and optimize controllers to regulate power and/or voltage generation

In this study, dielectric spectroscopy was utilised to evaluate and define the optimum harvesting time for polyhydroxyalkanoates (PHA) production. It is essential to harvest PHA at the optimum time during fermentation for maximum yield, otherwise cells start degrading. Two carbon sources (acetic and butyric acids) were used in laboratory based experiments and a number of samples were measured ex situ for PHA production. The real-time measured capacitance in addition of identifying the cells growth phase, it correlated very well with ex situ measured PHA produced within the cells. The probe has proven to be a useful tool to assess process kinetics, to monitor real-time cell growth, PHA produced and defining the optimum harvesting time.

This study investigates the use of Hotelling's T(2) control charts as the basis of a process monitor for sewage sludge anaerobic digestion. Fourier transform near infrared spectroscopy was used to produce partial least squares regression models of volatile fatty acids, bicarbonate alkalinity and volatile solids. These were utilised in a series of principle component analysis models along with spectral data from digestate and feedstock samples to produce a pseudo steady state model, which was then used with an independent test set to evaluate the system. The system was able to identify disturbances to the digester due to a temporary alteration of the type of feedstock to the digester and separately, halving of the hydraulic retention time of the digester. It could also provide advance warning of disturbances to the digester. This technique could be used to improve the performance of sewage sludge anaerobic digesters by enabling optimisation of the process.

Changes in fermenter gas composition within a given 24h period can cause severe bias in calculations of biogas or energy yields based on just one or two measurements of gas composition per day, as is common in other studies of two-stage fermentation. To overcome this bias, real time recording of gas composition and production were used to undertake a detailed and controlled comparison of single-stage and two-stage fermentation using a real world substrate (wheat feed pellets). When a two-stage fermentation system was used, methane yields increased from 261 L kg(-1)VS using a 20 day HRT, single-stage fermentation, to 359 L kg(-1) VS using a two-stage fermentation with the same overall retention time--an increase of 37%. Additionally a hydrogen yield of 7 L kg(-1) VS was obtained when two-stage fermentation was used. The two-stage system could also be operated at a shorter, 12 day HRT and still produce higher methane yields (306 L kg(-1) VS). Both two-stage fermentation systems evaluated exhibited methane yields in excess of that predicted by a biological methane potential test (BMP) performed using the same feedstock (260 L kg(-1)VS).

Anaerobic bioprocesses such as Anaerobic digestion (AD), fermentative biohydrogen (BioH2), and Bioelectrochemical system (BES), converting municipal, agro-industrial wastes and crops to energy have attracted accelerating interest. Anaerobic digestion (AD) however, still requires optimisation of conversion efficiency from biomass to methane. Augmenting methane energy production with simultaneous BioH2 and bioelectrochemical stage(s) would increase process efficiencies while meeting post treatment effluent quality. Pre-treatment of feedstock increase bacterial accessibility to biomass, thus increasing the conversion yield to target product, but an alternative is separating the acidogenic/hydrolytic processes of AD from methanogenesis. Acidogenesis can be combined with BioH2 production, prior to methanogenesis. Depending on operating conditions and without further treatment after digestion, the methanogenic stage may discharge a digestate with significant organic strength including volatile fatty acids (VFAs). To meet wastewater discharge consents; adequate use of digestates on land; to minimise environmental impact and; enhance recovery of energy, VFAs should be low. Concatenating bioelectrochemical systems (BES) producing hydrogen and/or electricity can facilitate effluent polishing and improved energy efficiency. Various configurations of the BioH2, methanogenesis and BES are plausible, and should improve the conversion of wet biomass to energy.

Electrodialysis (ED) removed volatile fatty acids (VFAs) from a continually-fed, hydrogen-producing fermenter. Simultaneously, electrochemical removal and adsorption removed gaseous H2 and CO2, respectively. Removing VFAs via ED in this novel process increased H2 yields by a factor of 3.75 from 0.24 mol H2 mol−1hexose to 0.90 mol H2 mol−1hexose. VFA production and substrate utilisation rates were consistent with the hypothesis that end product inhibition arrests H2 production. The methodology facilitated the recovery of 37 g of VFAs, and 30 L H2 that was more than 99% pure, both of which are valuable, energy dense chemicals. Typically, short hydraulic and solid retention times, and depressed pH levels are used to suppress methanogenesis, but this limits H2 production. To produce H2 from real world, low grade biomass containing complex carbohydrates, longer hydraulic retention times (HRTs) are required. The proposed system increased H2 yields via increased substrate utilisation over longer HRTs.

The use of electrochemical hydrogen removal (EHR) together with carbon dioxide removal (CDR) was demonstrated for the first time using a continuous hydrogen producing fermenter. CDR alone was found to increase hydrogen yields from 0.07molH2molhexose to 0.72molH2molhexose. When CDR was combined with EHR, hydrogen yields increased further to 1.79molH2molhexose. The pattern of carbohydrate utilisation and volatile fatty acid (VFA) production are consistent with the hypothesis that increased yields are the result of relieving end product inhibition and inhibition of microbial hydrogen consumption. In situ removal of hydrogen and carbon dioxide as demonstrated here not only increase hydrogen yield but also produces a relatively pure product gas and unlike other approaches can be used to enhance conventional, mesophilic, CSTR type fermentation of low grade/high solids biomass.

Batch studies are used to benchmark biohydrogen potential (BHP) and biomethane potential (BMP) yields from feed substrates, digestates residues and different process configurations. This study shows that BMP yields using cellulose can be biased positively by not diluting the initial sewage sludge inoculum and the bias is independent of starting inoculum volatile solids (VS) concentration. The carryover of BHP inoculum also increased the BMP yields when using cellulose as a substrate by up to 18.8%. Furthermore it was also observed that the dilution of BMP inoculum with deionised H2O reduced methane yields from cellulose by up to 132 ± 26 N mL-CH4 g-VS−1. Therefore it is proposed that inoculum and standard substrate controls (as used in this study) should be included in methane batch methodologies, particularly when using a pre-fermentation stage such as dark fermentation.

The use of excess wind energy to generate hydrogen for use as a transport fuel is investigated using Optimal Power Flow (OPF) including a hydrogen demand, and a techno- economic analysis carried out. Using this method to generate hydrogen increases the utilisation of wind energy and allows for a hydrogen demand to be supplied at or near to the point of use. An OPF routine is developed in order to optimise the amount of wind energy utilised, as well as minimising the amount of hydrogen demand not met. The cost at which the hydrogen is produced was found to be dependent on the operating methodology, component investment costs, and level of hydrogen demand.

A fast and cost effective immobilization of electron carriers, methylene blue (MB) and neutral red (NR) by pH shift was proposed to improve bioanodic performance. The adsorption of mediators onto the carbon cloth anode was verified using cyclic voltammogram (CV) and the effect of the immobilized mediators on acclimation, power density, and acetate removal of MFCs was investigated. A peak power density of Pmax(MB) = 11.3 W/m3 was achieved over days 110 ∼ 120, as compared to Pmax(Control) = 5.4 W/m3 and Pmax(NR) = 3.1 W/m3 for the treated anode after 15 sequential fed-batch operations. The VFA removal rates however were similar for all MFC systems, ranging from 82 to 87%. It could be suggested that the increase in power density for the MB treated electrode resulted from an enhanced electron transport from exo-electrogenic bacteria. MB may also have a selective effect on the bacterial community during the start-up stage, increasing the voltage production and acetate removal from day 1 to 16. However, MFC with NR treated anode produced an initial voltage under 100 mV, with lower coulombic efficiency (CE). NR exhibited less favourable mediator molecule binding to the electrode surface, when subject to pH driven physico-chemical immobilization.

Increasing amounts of variable renewable generation are likely to enter the UK's energy systems in the near future. To accommodate this generation onto electricity networks, the concept of active network management (ANM) has become a significant area of research interest. Network connected energy storage systems (ESS) are considered here as a means to actively control the network in order to increase the amount of generation that is possible to connect to a network. ESS is one of several potential methods of ANM, but has not been widely researched in this context. In this study, the ability of the ESS to increase the amount of wind energy accepted onto a network is assessed over a range of roundtrip storage efficiencies. An analysis is then conducted to determine the cost of energy produced through the ESS for a number of scenarios. The results show that the ESS is able to increase the energy accepted onto a distribution network, with the efficiency of the ESS, energy storage capacity, windfarm size, network losses and network characteristics being important in determining the relative effectiveness of the ESS and the cost at which electricity is produced.