Performance evaluation of anaerobic digestion of dairy manure in plug flow reactor and continuous stirred tank reactor

Plug flow reactor(PFR) and Continuous stirred tank reactor(CSTR) were studied to compare their performance for treating dairy manure. Three solid concentrations of dairy manure slurry of 40, 80 and 128 g/L were tested at mesophilic temperature of 35℃. The results showed that CSTR had better treatment performance of VS removal and biogas production than PFR. VS removal efficiencies in CSTR were increased by 17.4%～21.5%, 3.9%～21.5%, and 0.5%～5.3% as compared with those in PFR at 40, 80 and 128 g/L concentrations, respectively. The influent concentration of 80 g/L was believed to be the optimal one in this study in terms of gas production, in which CSTR achieved the highest gas productivity and gas yield, 9.8%～25.9% higher than those in PFR. Based on the current results, it could be concluded that mixing in CSTR could enhance the mass transfer between microorganisms and substrate, and improve the effects of organic matter removal and gas production. CSTR was recommended in the anaerobic digestion of dairy manure.