Improved anaerobic biodegradability of wheat straw, solid cattle manure and solid slaughterhouse by alkali, ultrasonic and alkali-ultrasonic pre-treatment

ABSTRACT

Wheat straw and animal wastes are important feedstock for biogas production in Europe. Yet, the high content of lignocellulosic and refractory materials causes the process to be relatively slow. Therefore, pretreatment methods have been proposed to shorten the hydrolysis phase. The present study examined the effectiveness of alkali pre-treatment (AP), ultrasonic pre-treatment (UP), and alkali-ultrasonic pre-treatment (AUP) applied on wheat straw (WS), solid fraction of cattle manure (SCM) and solid fraction of slaughterhouse waste (SSHW), by monitoring solubilisation ratio, anaerobic biodegradability and methane yield. The results indicate that the solubilisation ratio of the substrates improved regardless of the types of pre-treatment applied. Though, AP was more effective on WS and SSHW than other pre-treatments (UP and AUP), with approximately 47% and 17% extra methane, respectively. Moreover, AP of SCM caused an increased in methane production rate by 100% and minimised lag phase from 16 days to 1 day during anaerobic digestion. Based on Danish conditions, only AP of WS was economical prior to the biogas process due to high extra methane yield. A positive energy budget of 8 € t⁻¹ _VS was calculated. High-energy consumption during UP and AUP in laboratory scale hindered the positive benefits of these pre-treatments.

GRAPHICAL ABSTRACT

KEYWORDS:

• Solubilisation ratio
• Biodegradability
• Modified Gompertz
• Energy consumption
• Cost-effective

Acknowledgements

The first author expresses gratitude to Malaysian Government for the PhD scholarship. The authors wish to thank Laura Tey, Eva Romero, Laura Burgos and Eduard Muñoz at IRTA (Barcelona, Spain) for their assistance in the laboratory analysis. IRTA thanks the support of the CERCA program from the Generalitat de Catalunya.

ORCID

Belén Fernández http://orcid.org/0000-0001-6854-2349

Additional information

Funding

This work was supported by Fondation Idella [grant number 17499] and Innovation Fund Denmark [grant number NomiGas: 1305-00018B].