Current projects:

 

Anaerobic digestion of food waste for the production of chemicals

This project, which will be mainly based at the School of Engineering at University of Aberdeen, will investigate the anaerobic digestion of unavoidable food waste for the production of chemicals such as hydrogen (used as a fuel and in the chemical industry), short chain organic acids (e.g. acetic, propionic and butyric acids, used in many areas of the chemical industry) and methane (used as a fuel and as a chemical). Unavoidable food waste (e.g. peelings, skins, shells) is generated globally at a rate of many millions of tonnes per year and is an interesting feedstock for the sustainable and renewable production of chemicals. 

The project will aim to investigate the effect of the process conditions, e.g. solids residence time (SRT), hydraulic residence time (HRT), pH, temperature, on the yield and composition of the obtained products. In particular, the project will aim to identify the conditions that maximise the hydrogen yield and the concentration of the liquid phase products, in order to reduce the energy consumption in the downstream separation stages. The project will be experimental and will involve the use of lab-scale batch and continuous reactors. The reactors will be run under different conditions and will be monitored on a regular basis. The monitored parameters will be: gas production and composition, COD (Chemical Oxygen Demand), organic acids (acetic, propionic, butyric and others), VS (volatile solids), TC (total carbohydrates). 

The project will compare the treatment of feedstock without pre-treatment and after microwave-assisted pre-treatments. Microwave is an innovative technology that can potentially make the hydrolysis of the waste easier with low energy consumption. Therefore, anaerobic digestion of microwave pre-treated waste can potentially achieve higher conversion yields and/or reduced digestion times with lower capital and operating costs.

The project will also investigate how the microbial community evolves in the different operating conditions. Microbial analysis will make use of the state-of-the art techniques and facilities, e.g. community profiling by NGS based 16S RNA gene sequencing and bioinformatics, available at the University of Aberdeen’s Centre for Genome Enabled Biology and Medicine.

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High yield methane upgrading via non-thermal plasma-enhanced catalysis

In recent years, plasma-catalysis has emerged as a promising technology to improve the performance of existing catalytic processes. The use of non-thermal plasmas in particular has proven effective in enabling catalysts to operate at low temperatures for a range of reactions. In non-thermal plasmas, gas temperature can be as low as environmental, however highly energetic electrons colliding with molecules can produce a variety of species such as free radicals, excited states, ions, and other molecules that can participate in subsequent reactions. As such, there are species in the plasma, available to react on catalyst surfaces, which would typically be observed only at equilibrium systems of much higher temperature. In certain cases, even synergistic effects have been experimentally demonstrated, where the performance achieved with plasma-catalysis was higher than the sum of plasma-alone and catalysis-alone.

Focus of the research programme will be on the plasma-catalytic conversion of methane, obtained from the anaerobic digestion of organic waste, towards higher hydrocarbons, such as ethylene. To achieve this, a custom dielectric barrier discharge plasma catalytic reactor will be built, aiming at elucidating reaction pathways and identifying most promising catalytic materials for the reaction. In situ Optical Emission Spectrometry (OES) will be used to detect plasma phase reactive intermediates, providing insight on the reaction mechanism.

The studentship forms part of wider research in our School in the field of plasma-catalysis, where elaborate microkinetic models are developed considering all elementary reaction processes in the plasma phase and on the catalyst surface, linking with the information obtained via OES.

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Study of the sustainable transformation of solid feedstock into valuable chemical products

The aim of this project is to investigate the conversion of solid residuals resulting from anaerobic digestion of organic waste, which will be composed mainly of lignin and cellulose, into valuable chemicals using novel organic and enzymatic methodologies. 

One of the key areas of study will be the production of surfactants in a green and sustainable way. Approximately 70% of surfactants are currently produced from petrochemical products. The production of alkyl glycoside surfactants from carbohydrate-based feedstocks has been hampered so far by the lack of efficient enzymes for cellulose degradation, and low yields for the incorporation of long alcohol chains due to lack of solubility under enzymatic conditions.

In this project, firstly carry out preliminary studies will be carried out, including molecular modelling studies to design new solvent systems that are able to solubilise cellulose. Simplified models of the reactions will also be studied to elucidate mechanistic features so as to optimise the yields and production rates of the desired products, while minimising energy consumption and catalysts use. Finally, the optimised reaction conditions will be used to study the transformation of actual solid waste samples. 

The project will be run in a group composed of organic chemists and molecular biologists, with appropriate training in advanced organic chemistry, supramolecular chemistry, computer modelling, and in the production and use of enzymes.

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Electrochemical conversion of higher alcohols to energy and added value chemicals

Fuel cells convert chemical energy directly into electrical energy with high efficiency and, therefore, low emission of pollutants. The most common fuel employed in fuel cells is hydrogen, with a very high mass-related energy density, but a very low volume-related energy density (unless compressed at high pressure). For this reason, efforts have been made to use liquid fuels, like formic acid and alcohols. Among the latter, ethanol, glycerol and other higher alcohols have received much attention due to their high volume energy density, but also because they are produced in large quantities world-wide in fermentations and other simple biological and industrial processes. Unfortunately, their complete oxidation at low temperature (the conditions at which polymer-electrolyte membrane fuel cells (PEMFC) used in mobile applications work) is very difficult due to the necessity of breaking C-C bonds, reducing the efficiency of the process. Alternatively, oxidation to the corresponding carboxylic acid is typically easier. Many of these 3 to 5 C carboxylic acids are used as preservatives in agriculture, so a PEMFC could be used to obtain energy and carboxylic acids that could be commercialised as added value products.

In this project we will explore the oxidation of 3 to 5 C alcohols to the corresponding carboxylic acids, with the aim of understanding the mechanism of the process and developing an electrocatalyst that yields low overpotential and high selectivity.

The work will involve the use of single-crystal electrodes (in order to analyse possible structure-reactivity or structure selectivity aspects), classical electrochemical techniques, in-situ infrared spectroscopy (in order to detect intermediates and products of the reaction) and in-situ scanning tunnelling microscopy (STM).

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A risk framework to establish the ecotoxicity and fate of anaerobic digestate in soil

Currently, the environment fate of anaerobic digestate is either to landfill, for incineration or added to soil. While the soil may be perceived as a repository and the digestate as a waste there is a body of evidence to support the value of such additions to pedosphere. The digestate may offer some nutritional value (nitrogen and phosphorus) as well as a carbon source, however it could also harbour pathogens or serve to immobilise inorganic fertiliser additions. 

A key constraint in understanding the fate and impact of such amendments is the soil suitability and the plant vulnerability. Here we will systematically test the response of a suite of soils (selected by their intrinsic pH, texture and organic matter) amended with various sources of anaerobic digestate to a range of bioassays- microbial, process-level and plant based. An index has been developed at the University of Aberdeen that considers both the sensitivity and robustness of the selected bioassays. The response of these assays will permit a translation from the laboratory back to the field by considering both the beneficial soil responses and the constraints. 

Soils will be selected to reflect a broad range of landuses and environments. Such a comprehensive approach will permit an understanding of (1) which soil factors govern the response to digestate amendments, (2) which assays and which trophic level best indicate the measured response, (3) how different digestates behave in different soils and (4) how responses change with time. Having established the empirical responses the studentship will use these data to develop a risk framework mechanism for the end-user community.

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