Effect of influent alkalinity on anaerobic sequencing batch reactor

Intermittent running was carried out in a 6 L ASBR by using glucose as substrate,and with influent COD 6700 mg·L-1.Alkalinity added into the influent was gradually lowered down,and the ratios of COD0 to alkalinity(COD0/Alk) were respectively 1.0∶1,2.0∶1,2.5∶1,3.4∶1,4.2∶1 and 4.8∶1.The aim of this work was to investigate the change of pH,volatile fatty acid(VFA),bicarbonate alkalinity(BAlk) and CO2 pressure in anaerobic sequencing batch reactor(ASBR)for treating high-strength carbohydrate wastewater,and demonstrate the efficiency and stability of ASBR process at a lower pH.The results showed that alkalinity dosage had significant influences on VFA,BAlk,CO2 pressure and pH,especially acid-production rate within the first 0.5 h of reaction periods.When COD0/Alk was 1.0∶1,the pH values were always above 7.20.There was a higher acid-production rate and partial pH below 6.5 at the ratio of 3.4∶1,which indicated that the digested-liquid became acidic.It was found that the pH values were almost maintained at less than 6.5 while the ratios were 4.2∶1 and 4.8∶1,but methanogenic process was stable.During the whole operation,the process behavior was steady with COD removal efficiency higher than 97%,which proved the feasibility of methane production with ASBR at a low pH and low alkalinity.