Biogas properties and enzymatic analysis during anaerobic fermentation of Phragmites australis straw and cow dung: influence of nickel chloride supplement.
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The importance of nickel (added as NiCl2) on mesophilic anaerobic fermentation of Phragmites australis straw and cow dung was demonstrated by investigating the biogas properties, pH values, organic matter degradation [chemical oxygen demand (COD)] and enzyme activities (cellulase, protease and dehydrogenase) during the fermentation process. The results showed that Ni(2+) addition increased the cumulative biogas yields by >18 % by improving the efficiency of first peak stage and bringing forward the second peak stage. The pH values were not significantly influenced by Ni(2+) addition (p > 0.05). Biogas yields were associated with variations in COD concentrations rather than momentary concentrations. At the start-up stage of fermentation (4th day), the biogas yields increased gradually together with the increase of dehydrogenase activities at elevated Ni(2+) concentrations when cellulase and protease activities were similar in all test groups. It is suggested that Ni(2+) addition was mainly dependent on the methanogenic stage. After the start-up stage, the impact of Ni(2+) addition on biogas production was mainly dependent on its effect on cellulase activities, rather than protease or dehydrogenase activities.