Downstream Processing

Brewery spent grain as a biorefinery source: simultaneous volatile fatty acid production and recovery 

Researcher: Dr Juan Castilla-Archilla

 Project: The ability to utilise waste materials and biomass to produce chemical compounds not only represents a significant commercial opportunity, but also moves the world closer to uncoupling of the chemical based industry from fossil carbon. The liquid hydrolysate of the brewery spent grain during the pre-treatment step is a mix of hexose (glucose) and pentose (arabinose and xylose). The use of a partial inhibited anaerobic digestion with a mixed microbial culture ensure the complete consumption of carbohydrates with a good conversion to volatile fatty acids (VFAs). VFAs are valuable chemicals, currently obtained from fossil sources, which potential production from renewable feedstock has not yet been developed. However, VFA accumulation can alter reaction kinetics in the microbial pathways of acidogenesis and methanogenesis, resulting in unstable VFA production. The use of the liquid fraction obtained from the BSG hydrolysed resulted in a high strength liquor with easy fermentable carbohydrates for VFA production. The simultaneous production and removal of VFAs can alleviate this toxic effect at the same time that recovering them. For that, it was developed an up-flow anaerobic sludge bed reactor coupled with electrochemical cell in the recycling line. The electrochemical cell was able to recover the VFA produced at the same time that decreasing the base consumption. This allows to target VFAs as final product instead of being neglected as intermediate compounds.

Relevance and impact: Industrial and agricultural solid waste promises to be a new economical and renewable source to replace compounds from the petrochemical based industry. The use of the liquid rich in easily fermentable carbohydrates allows a higher rate VFA production. The simultaneous recovery using an electrochemical cell systems prevent any toxic effect by the accumulation of the VFA, at the same time that recover and concentrate them as a final product. 

Medium chain fatty acids production from organic wastes

Researcher: Dr Yen Nguyen

 Project: Directing mixed culture fermentation of complex feedstock towards a single and specific end product has been studied and remained challenging. Chain elongation is a carboxylate-platform bioprocess that converts short-chain carboxylates (SCCs) (e.g., acetate [C2] and n-butyrate [C4]) into a high-value medium-chain carboxylates (MCCs) (e.g., n-caprylate [C8] and n-caproate [C6]) with hydrogen gas as a side product. SCCs have become a platform for the synthesis of higher-value liquid fuels and chemicals, i.e. medium chain carboxylates (MCCs), by chain-elongation via the reverse β-oxidation pathway. However, most of studies have relied on the supplementation of external electron donors, e.g. ethanol, lactic acid, etc., for the chain elongation process. In the present study, a three-stage mixed culture fermentation will be employed for the production of SCCs and MCCs from mixed substrates of food waste (FW) and whisky spent grain (WSG). The mixed substrates are fermented into lactic acid, alcohol and SCCs in the first two stages, which are further converted into MCCs (e.g. caproic acid and caprylic acid) in the tertiary fermenter through microbial metabolism.

Relevance and impact: In our current modern society, where sustainability and climate compatibility are at the forefront, a transformation from a linear into a circular system, which based on recycling and reuse, coverts wastes into a new clean energy and material sources can solve the problem of waste treatment and disposal in an advanced and sustainable way to promote efficient economic growth with reduced environmental impacts at the same time. Resource recovery for production of low carbon biofuels and biochemical from renewable feedstocks using a biological process (anaerobic digestion) offers a more scalable, economical and eco-friendly platform by reducing greenhouse gas emissions, lowering fossil fuel combustion, and facilitating a sustainable renewable energy supply. Medium chain carboxylates (MCCs) have wide applications in various industries, e.g. ‘green’ antibiotics in agriculture, food addivitives, feedstock for the chemical industry, and a possible precursor in production of biofuels. The traditional MCCs production methods are costly and unsustainable. Anaerobic fermentation based-technologies offer a more scalable, economical and eco-friendly platform for treating organic residues and producing high value-added products, e.g. MCCs through chain elongation.

Bioplastic production using VFAs as feedstock

Researcher: Dr Tania Palmeiro Sanchez

 Project: Wastewater treatment has evolved through history. First civilizations just got rid of the residues. From the beginning of the XX century, the main objective was the treatment and management of wastes to avoid health and sanitary problems. The XXI century brings a different perspective on wastewater treatment: the use of residues as feedstock to produce value added products. The most highly praised outcome obtained from waste is methane from anaerobic waste treatment, as well as volatile fatty acids (VFAs). One of the newest value-added products that can be obtained from wastes are polyhydroxyalkanoates (PHAs), well-known due to their biodegradability and thermoplastic properties. This project focuses on the production of VFAs and PHAs under different processes and the determination of the kinetic and stoichiometric parameters of each process.

Relevance and impact: Nowadays plastics are essential for modern life and nearly 300 million tons of plastics are produced worldwide yearly. But plastics from crude oil are not sustainable because of the manufacturing process and because they can persist in the environment for hundreds of years. The progressive substitution of conventional plastics by bacterial bioplastics, i.e. PHAs, is a greener alternative.

 Application of membrane processes for recovery of Volatile fatty acids (VFAs) from anaerobic digestate

Researcher: Dr Harish Ravishankar

Project: Bio-based production of value-added products such as Volatile Fatty Acids (VFAs), lactate or alcohols through anaerobic fermentation has gained attention due to the increasing need for renewable carbon sources, e.g. dairy processed waste streams, food wastes and waste activated sludge. However, the main shortcoming of this process is separation of dissolved fermentation products from the digestate. VFA/alcohol separation through membrane processes has been widely reported. Vapour permeation through membrane contactors and pervaporation are other membrane processes that rely on the concentration/pressure difference which drive the separation of VFAs/alcohols from fermentation broth. These processes are less energy demanding as compared to electrodialysis, reverse osmosis and nanofiltration. This project examines the suitability of different hydrophobic microfiltration membranes, namely polypropylene (PP), polytetrafluoroethylene (PTFE) and polyether ether ketone (PEEK) membranes for separation of fermentation products through counter-current flow of the digestate and the extract solution (NaOH or H2O). Upon analysis of the membranes’ performance, a suitable process schematic will be designed and modelled for continuous separation of different value-added products from dark fermentation digestate.

Relevance and impact: VFAs are short chain fatty acids that have wide commercial applications, i.e. pharmaceuticals, food and chemical industries. They are traditionally prepared through non-renewable petrochemical sources, that have serious impact on health and environment. Green synthesis from renewable carbon sources, e.g. dairy processed waste streams, food wastes and waste activated sludge high in organics through fermentation is a suitable alternative. However, the bottleneck of VFA separation from the fermented digestate is a stumbling block for commercial implementation of this process. Application of membranes for separation processes can considerably improve the quality and yield of VFAs produced, along with production of other fermentation products such as H2, ethanol and lactate, which in turn can improve the prospects of commercialisation of fermentation processes for production of value-added products.

Biogas clean-up by gas-solid catalysis for direct grid injection

Researcher: Mr Jewel Das

Project: A novel xerophilic moving bed reactor for treating H2S at the lowest capex (e.g. enhanced mass transfer-small reactor unit) and lowest opex (e.g. low pressure drop) will be developed. The proposed xerophilic moving bed reactor consists of a bed of inert porous solids with controlled porous size. These inert supports, e.g. Celite R-640 to which the microorganisms will attach, will have the capacity to adsorb enough water to support the bioconversions. The development of the xerophilic reactor will be based on batch experiments designed to (i) quantify the effect of water activity on H2S conversion and (ii) select a suitable inert support for biomass growth and control of the water content of the biofilm.

Relevance and impact: Biogas produced in conventional anaerobic digestion technologies can contain 2000-5000 ppmv H2S, depending on the methanogenic substrate. The high H2S concentration in raw biogas forms corrosive acids that affect the biogas fired appliances and metallic accessories associated with biogas technology. Besides, energy production from the biogas can decrease significantly due to the direct inhibitory effect of H2S in the fermentation process of anaerobic digesters. Hence, raw biogas needs to be upgraded for higher efficiency as well as for better commercialization. This research will help to generate methane reach biogas from organic wastes through bioconversion of H2S into ecologically safe end products and to inject the upgraded biogas into the power grid.

Treatment of selenium-rich wastewater in floating wetlands

Researcher: Ms Ana Maria Murillo Abril

Project: Selenium (Se) is an important element, recognized an essential nutrient for humans and animals. However, this element has bioaccumulative and toxic properties at higher than homeostatic levels. Anthropogenic activities such as mining, coal combustion, oil refinery, electronic production and agriculture generate Se-laden waters which can be a problem for aquatic life and may affect human health. Among different techniques for treating Se-rich waters, constructed floating wetlands (CFWs) are a low-cost and an eco-friendly option. CFWs consist of emergent vegetation established upon a buoyant infrastructure, floating on surface waters. The removal of Se in CFWs is the result of the combination of physical, chemical and biological processes occurring due to the interaction between water, plants and microorganisms. Parameters such as plant growth rate, plant species and the concentration of the Se in the wastewater influence the Se removal rate.

Relevance and impact: Treatment of wastewaters require large amounts of energy. CFWs are cleanup methods that employ solar energy to treat Se-rich surface waters. The Se-enriched plant biomass can be used as a slow release Se fertilizer in agriculture. In addition, CFWs provide habitat for many wetland organisms.

Benchmarking the environmental impacts of bioplastics

Researcher: Mr George Bishop

Project: The production of plastic products over the last half century is significant. Recently there has been a move toward bioplastic materials (plastics that can be made from renewable biological sources) to replace petrochemical plastics. This research will assess whether bioplastic production, use and disposal has a smaller environmental impact than petrochemical-based plastic. Petrochemical and bio-based plastic value chains will be explored to better understand how these plastics are represented in studies and benchmarked against. Improvements in the current methodology will be developed to more accurately represent the complete systems and to overcome misrepresentation of environmental efficiency of systems and products.

Relevance and impact: This project is at the forefront of life cycle assessment (LCA) application to represent plastic value chains, accounting for pollution with novel environmental footprint metrics. This PhD will better represent complete petrochemical and bio-based plastic value chains to more accurately benchmark the wider environmental intensity of the systems. The project will also explore innovative bioplastic value chains, using data mined from EU projects, industry, academia and stakeholders.

In our current modern society, where sustainability and climate compatibility are at the forefront, a transformation from a linear into a circular system, which based on recycling and reuse, coverts wastes into a new clean energy and material sources can solve the problem of waste treatment and disposal in an advanced and sustainable way to promote efficient economic growth with reduced environmental impacts at the same time. Resource recovery for production of low carbon biofuels and biochemical from renewable feedstocks using a biological process (anaerobic digestion) offers a more scalable, economical and eco-friendly platform by reducing greenhouse gas emissions, lowering fossil fuel combustion, and facilitating a sustainable renewable energy supply.

Medium chain carboxylates (MCCs) have wide applications in various industries, e.g. ‘green’ antibiotics in agriculture, food addivitives, feedstock for the chemical industry, and a possible precursor in production of biofuels. The traditional MCCs production methods are costly and unsustainable. Anaerobic fermentation based-technologies offer a more scalable, economical and eco-friendly platform for treating organic residues and producing high value-added products, e.g. MCCs through chain elongation