Anaerobic digestion on swine manure: Inhibition by ammonia and hydrogen sulfide

This thesis presents a laboratory study using anaerobic digestion to treat swine manure with a focus on the interaction effects of ammonia (NH 3) and hydrogen sulfide (H2S) on biogas production. A series of batch experiments were conducted by varying the temperature, pH, NH 3, and H2S concentrations. As well, continuous anaerobic digestion tests were conducted by using a completely stirred reactor system (CSTR) in three different schemes: single-stage mesophilic, single-stage thermophilic and dual-stage system with thermophilic followed by mesophilic.;Results from the batch tests showed that methane gas production will be reduced significantly if NH3 and H2S concentrations exceeded their threshold inhibitory levels of 2.0g-N/L and 100--150mg-S/L, respectively. The results show an inhibition relationship existed between NH3 and H2S on methane generation during anaerobic digestion. Temperature and pH not only affect the growth of anaerobes, but also the distribution of NH3 and H2S. Moreover, NH 3 and H2S could be accumulated in CSTR systems, leading to the failure of anaerobic process. This was particularly true at 55°C, as higher temperature increases the concentration of free NH3 and anaerobic microorganisms become more sensitive. Finally, the combined inhibition of NH3 and H2S was severe to the production of methane in anaerobic digestion.