The Affecting Factors for Optimization of Mesophilic Aceticlastic Methanogenesis

Abstract

Acontinuous-flow methane fermentation process was operated using acetate as the sole organic substrate. The phylogenetic analysis showed that 72% of the 16S rDNA clones were amliated with aceticlastic methanogens, Methanosaeta and Methanosarcina. The effects of pH, NH4+, acetic acid, propionic acid, S2-, Co2+, Ni2+, and NO3- concentrations on methanogenic activity were investigated in batch assays using the culture broth from the acetate reactor. The results showed that the patterns of specific gas evolution rate with and without pH control were different. Under the condition with pH control, the specific gas evolution rate decreased drastically when the pH was below 6.5 and over 7.5. The optimum pH was fbund to be 7 for mesophilic aceticlastic reaction. The specific gas evolution rate decreased sharply when the concentration of free NH3 exceeded 100-150mg/l; acetic acid and propionic acid did not interfere with the stability of anaerobic treatment when their concentrations were less than 3, 500mg/l and 4, 000mg/l, respectively. S2-had a toxic effect on methanogenic activity, such that the gas production rate was nearly zero at a Na2S concentration of 300mg/l; the additions of Ni2+ and Co2+ increased the gas production rate and they had almost no negative effects on methane fermentation even when their concentrations reached 10mg/l. The specific gas evolution rate also decreased sharply when the concentration of NO3- exceeded 500 mg/l which corresponded to about 110 mg-N/l.