Effect of macro- and micro-nutrients addition during anaerobic mono-digestion of grass silage in leach-bed reactors

ABSTRACT

The effect of macro- (NH₄Cl) (set I) and micro-nutrients (Fe, Ni, Co and Mo) (set II) addition on chemical oxygen demand (COD) solubilisation during anaerobic mono-digestion of grass silage was investigated in two sets of leach bed reactor experiments at 35°C. Results showed that addition of NH₄Cl and micro-nutrients improved COD solubilisation by 18% (0.56 g SCOD g⁻¹ volatile solids) and 7% (0.45 g SCOD g⁻¹ VS), respectively than control. About 20–50% of the added micro-nutrients were bioavailable in the produced leachates, while the rest (50–80%) were adsorbed onto the grass silage. Results of biological methane potential assays showed that, specific methane yields of grass silage were improved by 17% (0.36 ± 0.02 m³ CH₄ kg⁻¹ VS_added) when NH₄Cl was supplemented while Fe, Ni, Co and Mo addition improved methane yields by 15% (0.33 ± 0.005 m³ CH₄ kg⁻¹ VS_added) when compared to control.

KEYWORDS:

• Leach bed reactor
• micro-nutrients
• anaerobic digestion
• grass silage
• methane

Acknowledgements

The authors gratefully acknowledge Mrs Mervi Koistinen for technical assistance in laboratory analyses.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Finnish doctoral programme in Environmental Science and Technology (EnSte) is gratefully acknowledged for funding Mrs Padma Shanthi Jagadabhi's Ph.D. studies.