Production of volatile fatty acids by anaerobic digestion of biowastes: Techno-economic and life cycle assessments.

Production of volatile fatty acids from food waste and lignocellulosic materials has potential to avoid emissions from their production from petrochemicals and provide valuable feedstocks. Techno-economic and life cycle assessments of using food waste and grass to produce volatile fatty acids through anaerobic digestion have been conducted. Uncertainty and sensitivity analysis for both assessments were done to enable a robust forecast of key-aspects of the technology deployment at industrial scale. Results show low environmental impact of volatile fatty acid with food wastes being the most beneficial feedstock with global warming potential varying from -0.21 to 0.01 CO2 eq./kg of product. Food wastes had the greatest economic benefit with a breakeven selling price of 1.11-1.94 GBP/kg (1.22-2.33 USD) of volatile fatty acids in the product solution determined through sensitivity analysis. Anaerobic digestion of wastes is therefore a promising alternative to traditional volatile fatty acid production routes, providing economic and environmental benefits.

Recovery Of Zinc from Scrap Steel Using Zinc-Bromine Battery Technology.

Secondary production of steel is known to significantly decrease the CO2 emissions of steelmaking, but only 40 % of steel is produced through recycling, which is made difficult by contamination of scrap resources with nonferrous metals and nonmetal debris. These contaminants include zinc, towards which blast furnace and electric arc systems have a low tolerance (<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 characterized by charge-discharge profiles, and zinc removal and recovery onto electrodes was characterized by using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Upon discharging, the cell efficiently removed >99.9 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 cutoff 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.

Increasing 2 -Bio- (H2 and CH4) production from food waste by combining two-stage anaerobic digestion and electrodialysis for continuous volatile fatty acids removal.

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.

Continuous recovery and enhanced yields of volatile fatty acids from a continually-fed 100 L food waste bioreactor by filtration and electrodialysis.

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.

Fate of antibiotic resistant E. coli and antibiotic resistance genes during full scale conventional and advanced anaerobic digestion of sewage sludge.

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.

Overcoming nutrient loss during volatile fatty acid recovery from fermentation media by addition of electrodialysis to a polytetrafluoroethylene membrane stack.

This research investigated the use of an innovative polytetrafluoroethylene (PTFE) membrane configuration coupled 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 VFA recovery times was seen. The addition of electrodialysis to the PTFE membrane stack enabled the continuous extraction of VFAs from fermentation media whilst retaining essential nutrients and organic compounds in the diluate stream. Ammonium, phosphate and nitrate remained in the diluate chamber and did not cross the PTFE membrane stack. Up to 98% of total VFA recovery was achieved with the PTFE and electrodialysis system. The process was shown to extract from a reservoir of low VFA concentration to a reservoir with a VFA concentration 10 times higher. These results show that the addition of electrodialysis to PTFE provides a robust solution for the in-situ extraction of VFAs from fermentation media within bioreactors to support the demand for sustainable fuels and green chemical feedstocks.

Bioelectrochemical treatment and recovery of copper from distillery waste effluents using power and voltage control strategies.

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.

Stopping Hydrogen Migration in Its Tracks: The First Successful Synthesis of Group Ten Scorpionate Complexes Based on Azaindole Scaffolds.

The first successful synthesis and characterization of group 10 complexes featuring flexible scorpionate ligands based on 7-azaindole heterocycles are reported herein. Addition of 2 equiv of either K[HB(azaindolyl)3] or Li[HB(Me)(azaindolyl)2] to [M(µ-Cl)(η,1η2-COEOMe)]2 leads to the formation of 2 equiv of the complexes [M{κ3- N,N,H-HB(azaindolyl)3}(η,1η2-COEOMe)] and [M{κ3- N,N,H-HB(Me)(azaindolyl)2}(η,1η2-COEOMe)] (where M = Pt, Pd; COEOMe = 8-methoxycyclooct-4-en-1-ide), respectively. In these reactions, the borohydride group is directed toward the metal center forming square based pyramidal complexes. In contrast to analogous complexes featuring other flexible scorpionate ligands, no hydrogen migration from boron is observed in the complexes studied. The fortuitous line widths observed in some of the 11B NMR spectra allow for a closer inspection of the B-H···metal unit in scorpionate complexes than has previously been possible.

A new sequential injection analysis-capillary electrophoresis system with amperometric detection.

A novel and fully automated sequential injection analysis manifold coupled to a capillary electrophoresis apparatus with amperometric detection, is described. The sequential injection manifold was isolated from the high voltage by inserting an air plug into the circuit. Small buffer reservoirs were used to avoid the need to pump fresh buffer to the interface during the electrophoretic separation. No decoupling device was used to mitigate the interference from the high voltage electric field, instead the potential shift induced by the separation voltage, was accounted for. The new hydrodynamic injection method presented is based on the overpressure created in the circuit when a pinch valve is closed for a predetermined time. The injection method yields RSD values of peak height and area below 2.55 and 1.82%, respectively, at different durations of valve closure (n = 5). The capillary and working electrode alignment was achieved by adapting a commercial available capillary union. When the electrode was replaced, the alignment method proved to be very reliable, yielding RSD values of peak height and area lower than 2.64 and 2.08%, respectively (n = 8). Using this system with a gold microelectrode, dopamine, and epinephrine could be quantified within the concentration range of 1-500 µM and detected at a concentration of 0.3 µM. The methods here presented could be applied for the development of new capillary electrophoresis systems with amperometric detection and/or to the design of fully automated systems for online process monitoring purposes.

Increased biohydrogen yields, volatile fatty acid production and substrate utilisation rates via the electrodialysis of a continually fed sucrose fermenter.

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 0.24molH2mol-1hexose to 0.90molH2mol-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 37g of VFAs, and 30L 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.

Maximising biohydrogen yields via continuous electrochemical hydrogen removal and carbon dioxide scrubbing.

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.

The impact of inocula carryover and inoculum dilution on the methane yields in batch methane potential tests.

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.

Utilising biohydrogen to increase methane production, energy yields and process efficiency via two stage anaerobic digestion of grass.

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.

Enhanced biomethane potential from wheat straw by low temperature alkaline calcium hydroxide pre-treatment.

A factorially designed experiment to examine the effectiveness of Ca(OH)2 pre-treatment, enzyme addition and particle size, on the mesophilic (35 °C) anaerobic digestion of wheat straw was conducted. Experiments used a 48 h pre-treatment with Ca(OH)2 7.4% (w/w), addition of Accellerase®-1500, with four particle sizes of wheat straw (1.25, 2, 3 and 10mm) and three digestion time periods (5, 15 and 30 days). By combining particle size reduction and Ca(OH)2 pre-treatment, the average methane potential was increased by 315% (from 48 NmL-CH4 g-VS(-1) to 202 NmL-CH4 g-VS(-1)) after 5 days of anaerobic digestion compared to the control. Enzyme addition or Ca(OH)2 pre-treatment with 3, 2 and 1.25 mm particle sizes had 30-day batch yields of between 301 and 335 NmL-CH4 g-VS(-1). Alkali pre-treatment of 3mm straw was shown to have the most potential as a cost effective pre-treatment and achieved 290 NmL-CH4 g-VS(-1), after only 15 days of digestion.

Removal and recovery of inhibitory volatile fatty acids from mixed acid fermentations by conventional electrodialysis.

Hydrogen production during dark fermentation is inhibited by the co-production of volatile fatty acids (VFAs) such as acetic and n-butyric acid. In this study, the effectiveness of conventional electrodialysis (CED) in reducing VFA concentrations in model solutions and hydrogen fermentation broths is evaluated. This is the first time CED has been reported to remove VFAs from hydrogen fermentation broths. During 60 min of operation CED removed up to 99% of VFAs from model solutions, sucrose-fed and grass-fed hydrogen fermentation broths, containing up to 1200 mg l(-1) each of acetic acid, propionic acid, i-butyric acid, n-butyric acid, i-valeric acid, and n-valeric acid. CED's ability to remove VFAs from hydrogen fermentation broths suggests that this technology is capable of improving hydrogen yields from dark fermentation.

Inhibition of methane production in microbial fuel cells: operating strategies which select electrogens over methanogens.

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 use of NaCl addition for the improvement of polyhydroxyalkanoate production by Cupriavidus necator.

External stress factors in the form of ionic species or temperature increases have been shown to produce a stress response leading to enhanced PHA production. The effect of five different NaCl concentrations, namely 3.5, 6.5, 9, 12 and 15 g/l NaCl on PHA productivity using Cupriavidus necator has been investigated alongside a control (no added NaCl). A dielectric spectroscopy probe was used to measure PHA accumulation online in conjunction with the chemical offline analysis of PHA. The highest PHA production was obtained with the addition of 9 g/l NaCl, which yielded 30% higher PHA than the control. Increasing the addition of NaCl to 15 g/l was found to inhibit the production of PHA. NaCl addition can therefore be used as a simple, low cost, sustainable, non toxic and non reactive external stress strategy for increasing PHA productivity.

The influence of anodic helical design on fluid flow and bioelectrochemical performance.

In this study three different tubular helical anode designs are compared, for each helical design the pitch and nominal sectional area/liquid flow channel between the helicoids was varied and this produced maximum power densities of 11.63, 9.2 and 6.73Wm(-3) (small, medium and large helical flow channel cross-sections). It is found that the level of mixing and the associated shear rates present in the anodes affects both the power development and biofilm formation. The small helical flow channel carbon anode produced 40% more biofilm and this result was related to modelling data which determined a system shear rate of 237s(-1), compared to 52s(-1) and 47s(-1) for the other reactor configurations. The results from computational fluid dynamic modelling further distinguishes between convective flow conditions and supports the influence of helical structure on system performance, so establishing the importance of anodic design on the overall electrogenic biofilm activity.

Augmenting Microbial Fuel Cell power by coupling with Supported Liquid Membrane permeation for zinc recovery.

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.

Increasing polyhydroxyalkanoate (PHA) yields from Cupriavidus necator by using filtered digestate liquors.

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.