Effects of ammonia nitrogen of H2 and CH4 production during anaerobic digestion of dairy cattle manure.

A number of researchers have verified the inhibitory effects of elevated H2 concentrations on various anaerobic fermentation processes. The objective of this work was to investigate the potential for using hydrogen gas production to predict upsets in anaerobic digesters operating on dairy cattle manure. In an ammonia nitrogen overload experiment, urea was added to the experimental digesters to obtain increased ammonia concentrations (600, 1,500, or 3,000 mg N/l). An increase in urea concentration resulted in an initial cessation of H2 production followed by an increase in H2 formation. Additions of 600, 1,500, or 3,000 mg N/l initially resulted in the reduction of biogas H2 concentrations. After 24 h, the H2 concentration increased in the 600 and 1,500 mg N/l digesters, but production remained inhibited in the 3,000 mg N/l digesters. Both methane and total biogas production decreased following urea addition. Volatile solids reduction also decreased during these periods. The digester effluent pH and alkalinity increased due to the increased NH4 formed with added urea. Based on these results, changes in H2 concentration could be a useful parameter for monitoring changes due to increased NH3 in dairy cattle manure anaerobic digesters.