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

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.