Pre-treatment

Solving the bottlenecks of sugarcane vinasse anaerobic digestion for enhanced and continuous bioenergy recovery

Researcher: Dr Lucas Fuess

Project: Efficient methane production from sugarcane vinasse, the main wastewater from ethanol production, can only be achieved by combining strategies that both remove sulfate prior to methanogenesis and maintain year-round operation of the plant by replacing vinasse with suitable substrates during the off season. To eliminate the negative effects of sulfide production in methanogenic reactors, the operation of fermentative-sulfidogenic reactors prior to methanogenesis is proposed to obtain a sulfate-free and acetate-rich fermented broth.  In turn, achieving year-round biogas production through maintaining the anaerobic plant in operation during the off season will be tested through replacing vinasse by molasses in this period in both reactors, i.e., the acidogenic and methanogenic steps

Relevance and impact: Preventing sulfide generation (in the methanogenic step) dramatically facilitates the further energetic use of biogas. The energy content of biogas is expected to increase by at least 10%, with methane proportions of at least 80%, i.e., 10 percent points higher than previous experiences. In addition, replacing fermented vinasse by fermented molasses during the off season enables the continuous application of high organic loads, leading to the continuous production of high methane flow rates and preventing the buildup of organic acids in the methanogenic bioreactor.

Biomethane from lipid-rich wastewaters through process pre-treatment

Researcher: Dr Lea Tan

Project: Anaerobic digestion (AD) has been utilized for over a century as an efficient process for treating organic waste while simultaneously producing bioenergy through different metabolic steps. However, despite the advances in AD, there is still a large bottleneck in the commercial up-scaled treatment process of diary wastewater containing high amounts of lipids or fats, oils and grease (FOG). Production of long-chain fatty acids (LCFAs) are the bottleneck in AD due to LCFA metabolic inhibition via mass transfer limitation. As such, most treatment of lipid-rich wastewater are coagulation and removal from the waste stream before employing AD. This signifies huge loss in energy recovery that can be achieved with lipid-rich WW. This project focuses on improving the biogas production from FOG through substrate pre-treatment and process manipulation. Application of different treatments to lipid-rich wastewater before (i.e. fenton and sonication) or/and during (i.e. addition of conductive material) AD can enhance the degradation and subsequent fermentation process for the generation of bioenergy and other valuable by-products from FOG.  

Relevance and impact: Lipid-rich wastewater has caused issues in AD at industrial level and current technology employed for these waste streams does not utilize the valuable energy that can be recovered from them. This project pursues to recover energy from this untapped feedstock and reduce the carbon loss. Technology learned and developed in this project can be adapted into existing AD plants, increasing the economic value of waste streams and pushing further the concept of circular economy.

Food waste bioconversion through lactic acid fermentation

Researcher: Mr Simone Pau

Project: The use of traditional plastics is, in recent decades, a source of concern due to its production, which derives from fossils fouels, that are rapidly depleted, and its disposalinvolves a high risk for various terrestrial ecosystems. This necessity led to the study of processes that use renewable sources for the production of eco-friendly materials like bioplastics. One of the most studied and industrially used bioplastics is Polylactic Acid (PLA), a biopolymer produced by the polymerization of lactic acid. The purpose of this study is to find the best operating conditions to reach high levels of biologically by-produced lactic acid in anaerobic digestion of carbohydrate food waste, and its conversion to PLA.

Relevance and impact: PLA is a thermoplastic that has excellent characterics of biodegradability and biocompatibility that make it an ideal alternative to the normal plastics. It is produced by renewable sources, such as food waste, rich in sugars and starch and is used in the packaging industry, in the biomedical industry and as a filament for 3D printing. The production of PLA integrates the need to reduce the use of conventional plastics with the necessity to find new pathways in the management and treatment of organic wastes recovering sustainable materials with a high commercial value.

Brewery spent grain waste as source of green chemicals

Researcher: Mr Juan Castilla-Archilla

Project: Over the last decade, sustainability has become a key consideration for society and industry. This has largely been driven by increasingenvironmental awareness and decreasing reservoirs of fossil fuels and natural resources. Industrial and agricultural solid wastes can be used as feedstock for a biomass based refining process. A good example in Ireland is the brewery sector, with solid spent grain as the most abundant side-stream. This solid waste is a low cost biomass, which can be pre-treated to break its complex structure into easy biodegradable compounds and fermented into volatile fatty acids, H2, alcohols and lactic acid. All these compounds can be recovered and used asbuilding blocks for added value materials, such as longer alcohols or biopolymers (like polylactic acid, PHB or PHA). This project aims to study two approaches for the production of fermented compounds using the brewery spent grain: 1) the simplest possible process to treat the solid waste by the simultaneous hydrolysis and acidogenesis fermentation, and 2) separate these two processes to achieve a higher control during the pre-hydrolysis step followed by the acidogenesis fermentation. In both cases, the VFAs will be recovered and the feasibility for production of PHAs will be studied.

Relevance and impact: 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. Industrial and agricultural solid waste promises to be a new economical and renewable source to replacecompounds from the petrochemical based industry.

 Anaerobic digestion of lignocellulosic material: different pretreatment methods to enhance biogas production

Researcher: Mr Armando Oliva

 Project: Anaerobic digestion is an efficient process for treating organic waste. It is used to control pollution and, at the same time, to produce renewable energy, in the form of methane and valuable products. Anaerobic digestion consists of four stages: hydrolysis, acidogenesis, acetogenesis and methanogenesis. The microorganisms responsable for the different stages need different conditions to optimize the process. Failure of this balance is the primary cause of reactor instability. Lignocellulosic materials represent a great opportunity for anaerobic digestion, as they are one of the most abundant bio-resource in the world. However, anaerobic digestion with no pretreatment is usually not so effective because of high stability of the materials to enzymatic attacks. This project aims to study the effects of chemical and biological pretreatment on three different types of lignocellulosic materials, which are cocoa bean shell, hazelnut skin and coffee roasted bean. Further, different process conditions of anaerobic digestion will be studied, such as the effects of different inocula, different process temperatures and different solid content. Finally, batch and semi-continuous reactors management will be operated.

Relevance and impact: The global economy mostly depends on fossil fuels. However, to reduce greenhouse gas emissions, a transition to a sustainable carbon-neutral bioeconomy will have to take place. Biomass seems to be the only sustainable bioresource that can provide sufficient fuels and renewable materials at the same time. Especially, lignocellulosic materials serve as a cheap and abundant feedstock for biogas production by anaerobic digestion. Further, the use of lignocellulosic materials does not create conflicts between food and energy production.

Anaerobic digestion of selenium rich waste

Researcher: Mr Mohanakrishnan Logan

 Project: Fats that are rich in lipids are produced in huge volume during several industrial processes such as dissolved air flotation. Despite the potential of these fats to serve as an excellent carbon source, their energy is seldom recovered and largely untapped. The prospects are bright for the application of these fats as feedstock for anaerobic digestion. The fate of selenium during anaerobic digestion needs to be clearly established. Therefore, the study aims to investigate the anaerobic digestion of Se supplemented fat, along with the bioreduction of selenium oxyanions. Wetland crops such as duckweed (Lemna minor) offer phytoremediation for selenium contamination. The treatment of duckweeds enriched with Se will be investigated for anaerobic digestion for the first time. Subsequently, food waste will be used as a co-digestion substrate to further improve the performance of anaerobic digestion for higher methane yield.  

Relevance and impact: Development of novel bioreactors recovers energy from waste, thereby adding new biofuels generated to Ireland’s energy mix, and in turn support the Government’s strategy for an energy self-sufficient Irish bio economy. Bioenergy production from waste streams is also aligned with the UN Sustainable Development Goals, which focus on affordable and clean energy (SDG 7), sustainable management of natural resources (SDG 12) and taking urgent action on climate change (SDG 13) for sustainable cities and communities (SDG 11).