Project title: Pre-treatment technologies for enhanced biodegradability of sludge and lignocellulosic biomass in anaerobic digestion

Project description:
Anaerobic digestion (AD) is a process by which microorganisms transform organic materials (such as manure, crop residues and wastewater sludge) under oxygen-free conditions into biogas, nutrients and additional cell matter (Montané et al., 1998). Biogas has CH₄ and CO₂ as main components and it can be used for heat and electricity generation, as a vehicle fuel and as a substitute for natural gas (Weiß et al., 2016).

In the first step of AD, hydrolysis, microorganisms produce and excrete enzymes that breakdown and solubilize large molecular structures into smaller components (Parawira et al., 2005). Hydrolysis has been considered as a rate-limiting step of AD and its efficiency can be increased by biomass pre-treatments, which aim to change the material structure and make it more accessible for enzymatic attack.

This Ph.D project will focus on the enhancement of biogas production through the application of biological pre-treatment on biomass, such as ensiling, enzymatic and fungal aerobic pre-treatments. Enzymatic pre-treatment simply applies industrial enzymes to the biomass to increase hydrolysis efficiency. Fungal pre-treatment relies on the capability of some fungi on selectively decomposing lignin (a fraction of plants which is useless for AD). This way, cellulose and hemicellulose (plant fractions relevant for AD) get more accessible for further AD. Ensiling is based on the preservation of biomass under anaerobic conditions, using bacterial fermentation to prevent further degradation. The low pH achieved by the acids produced during bacterial fermentation inhibits the activity of other microorganisms (Teixeira Franco, Buffière, & Bayard, 2016). Due to the low pH, a slow hydrolysis takes place, which can improve biogas production (Martínez-Gutiérrez, 2018).

References:
Martínez-Gutiérrez, E. (2018). Biogas production from different lignocellulosic biomass sources: advances and perspectives. 3 Biotech, 8(5), 233. doi.org/10.1007/s13205-018-1257-4

Montané, D., Farriol, X., Salvadó, J., Jollez, P., & Chornet, E. (1998). Fractionation of wheat straw by steam-explosion pre-treatment and alkali delignification. Cellulose pulp and byproducts from hemicellulose and lignin. Journal of wood Chemistry and Technology, 18(2), 171-191. https://doi.org/10.1080/02773819809349575

Parawira, W., Murto, M., Read, J. S., & Mattiasson, B. (2005). Profile of hydrolases and biogas production during two-stage mesophilic anaerobic digestion of solid potato waste. Process Biochemistry, 40(9), 2945-2952. https://doi.org/10.1016/j.procbio.2005.01.010

Teixeira Franco, R., Buffière, P., & Bayard, R. (2016). Ensiling for biogas production: Critical parameters. A review. Biomass and Bioenergy, 94, 94–104. doi.org/10.1016/J.BIOMBIOE.2016.08.014

Weiß, S., Somitsch, W., Klymiuk, I., Trajanoski, S., & Guebitz, G. M. (2016). Comparison of biogas sludge and raw crop material as source of hydrolytic cultures for anaerobic digestion. Bioresource technology, 207, 244-251. https://doi.org/10.1016/j.biortech.2016.01.137

Supervisor: Senior Researcher Henrik Bjarne Møller