Co-digestion of manure with grass silage and pulp and paper mill sludge using nutrient additions

ABSTRACT

There is an increasing worldwide demand for biogas. Anaerobic co-digestion involves the treatment of different substrates with the aim of improving the production of biogas and the stability of the process. This study evaluates how methane production is affected by the co-digestion of pig and dairy manure with grass silage and pulp and paper mill sludge and assesses whether methane production is affected by factors other than nutrient deficiency, low buffering capacity, inadequate dilution, and an insufficient activity and amount of microorganism culture. Anaerobic digestion was performed in batch reactors under mesophilic conditions for 20 days. The season of grass silage and manure collection proved to be an important factor affecting methane production. Spring grass silage produced a maximum of 250 mL/VS_added and spring manure 150 mL/VS_added, whereas autumn grass silage produced at most 140 ml/VS_added and autumn manure 45 mL/VS_added. The pulp mill sludge used is comprised of both primary and secondary sludge and produced at most 50 mL/VS_added regardless of season; this substrate benefitted most from co-digestion.

KEYWORDS:

• Agricultural waste
• anaerobic digestion
• biomethane potential
• co-digestion

Acknowledgements

The authors would like to thank Professor Thomas Nilsson, Karlstad University, for valuable guidance.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Karin Granström http://orcid.org/0000-0002-0380-3533