Minimum pH Condition for Anaerobic Sequencing Batch Reactor Containing Granulated Biomass

The objective of this article was studied the minimum pH condition at anaerobic sequencing batch reactor (ASBR) to treat high concentration carbohydrate waste water and determined the lowest demand of alkalinity. Instantaneous inflow was used in whole experiment. Using glucose as substrate, the OLR of influent was 10.0g COD / (g ldr d). Sodium bicarbonate was added into the influent to control and adjust pH value and alkalinity in the reactor, alkalinity levels were characterized by the ratio of the influent COD to the alkalinity concentration, (i.e. COD / Alk.), the value of COD / Alk were respectively 1.0: U 2.0: U 2.5: 1, 3.4: 1, 4.2: 1 and 4.8, and alkalinity dosages added into the reactor were decreased step by step in the experiment. The results showed significant effects of alkalinity levels on VFA accumulated concentrations, especially acid- production rate within the first 0.5 h of reaction periods. The maximum concentration of VFA accumulated in the reactor increased to 1626 mg/L and the minimum pH value decreased to 6.10 at higher than the 4.2:1 ratio of alkalinity level, which indicated that the digestion liquid in the reactor was acidic; alkalinity levels had influences on CO₂%, Balk and pH value too, at 4.8:1 alkalinity level, the minimum Balk value in the reactor was merely 423 mg/L, and the ratio of BA to TA was 0.4 correspondingly. Simultaneously, the pH values in whole reaction period were almost always below 6.5, which was less than the lowest limit value recommended for the continuous-flow anaerobic processes. During operation of all alkalinity levels, the behavior of process was steady with COD removal efficiency higher than 97%, and no signs of instability. The results proved feasibility at the low alkalinity levels for ASBR because of its intrinsic characteristics. The minimum alkalinity demand dose expressed by the ratio of COD/Alk was 4.8:1.