Anaerobic digestion (AD) is a promising technology for the treatment of organic solid waste and wastewater, as it combines energy recovery with waste treatment. AD has lately gained interest for treating highly biodegradable wastes such as lignocellulosic materials, animal manure, kitchen waste and municipal sewage sludge.
Lignocellulosic residues are an abundant and an accessible worldwide renewable source (e.g. agricultural biomass such as crop residues) which contain non-edible plant material. Nevertheless, the AD process using lignocellulose requires pre-treatment as lignocellulose is insoluble in water and has a complex and rigid structure that is resistant to mechanical stress and enzyme attack.
Accordingly, a pre-treatment step is necessary due to the high level of crystallinity of cellulose, as well as the cross-linking of carbohydrates and lignin (encrusting material which serves as a protective layer, the most recalcitrant component which protects cellulose and hemicelluloses by forming tight bonds reducing the surface area available for enzyme degradation of the carbohydrate structure). Therefore, the hydrolysis of the lignocellulosic residues is the key rate-limiting step in the overall AD process .
Consequently, pre-treatment is a crucial process to make cellulose more available to the enzymes that convert the carbohydrate polymers into fermentable sugars. However, the main drawback of pre-treatment is the increased production cost associated to it (≥ 20% of the total production costs), which makes it the most expensive process step .
In view of that, this project will investigate novel pre-treatment technologies with the aim of reducing the production costs by obtaining improved yields and rates of substrate conversion into hydrogen and valuable chemicals (organic acids) via AD of lignocellulosic waste (e.g. garden waste and agricultural residues like grasses and wheat).
The promising and emerging technology that will be investigated is the microwave-assisted pre-treatment, that either used solely or combined with other pre-treatments (e.g. chemical pre-treatments: MW/alkali, MW/acid, MW /ionic liquid, MW/water), will be studied and compared with conversions obtained without pre-treatment. Results will elucidate whether there is an improvement on the biomass wastes’ digestibility due to the favoured hydrolysis, and correspondingly on the conversion yields.
The important advantage of microwave technology is that the energy, which is generated by an electromagnetic field, is delivered directly to the material to provide rapid heating throughout large volumes with reduced thermal gradients and treatment time, which could lead to considerable energy savings .
The study will be in collaboration with the Microbiology Group at the Rowett Institute who will provide specialist expertise in anaerobic carbohydrate breakdown and volatile fatty acids production.
Finally, the student will investigate the feasibility of the solid residue generated from the anaerobic digestion (digestate) to be used as a precursor (or an additive) for the production of activated carbons, which will be used for environmental applications (e.g. biogas upgrading, wastewater treatment).
Formal applications can be completed online: https://www.abdn.ac.uk/pgap/login.php
• Apply for the Degree of Doctor of Philosophy in Chemical Engineering
• State the name of the lead supervisor as the Name of Proposed Supervisor
• State ‘Leverhulme CDT in Sustainable Production of Chemicals and Materials’ as the Intended Source of Funding
• State the exact project title on the application form
 S. R. Paudel, S. P. Banjara, O. K.Choi, K. Y. Park, Y. M. Kim, J.W. Lee. Pretreatment of agricultural biomass for anaerobic digestion: Current state and challenges. Bioresource Technology, 245, Part A, (2017), pp. 1194-1205.
 F. R. Amin, H. Khalid, H. Zhang, S. u Rahman, R. Zhang, G. Liu, C. Chen. Pretreatment methods of lignocellulosic biomass for anaerobic digestion. AMB Express, 7:72, (2017).
 C. Eskicioglu, N. Terzian, K.J. Kennedy, R.L. Droste, M. Hamoda. A thermal microwave effects for enhancing digestibility of waste activated sludge. Water Research, 41 (2007), pp. 2457-2466.