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) solubilization during anaerobic mono-digestion of grass silage was investigated in two sets of leach bed reactor (LBR) experiments at 35°C. Results showed that addition of NH4Cl and micro-nutrients improved COD solubilization by 18% (0.56 g SCOD g(-1) volatile solids, VS) and 7% (0.45 gSCOD 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 on to the grass silage. Results of biological methane potential (BMP) assays showed that, specific methane yields of grass silage were improved by 17% (0.36±0.02 m(3) CH4kg(-1)VSadded) when NH4Cl was supplemented while Fe, Ni, Co and Mo addition improved methane yields by 15% (0.33±0.005 m(3) CH4kg(-1)VSadded) when compared to control.