The final process disturbance examined was alkalization condition NaOH

The final process disturbance examined was alkalization condition. NaOH was added using the pH pump to increase the pH to 12.6 for 14 h. This process upset caused a huge difference in the production performance as the HPR decreased to only 0.7 L/L-d; however, the recovery of the process was completed in the next 4 days, reaching the original performance of 10.8 L/L-d. The biohydrogen content recorded the lowest level of 8% at the initial period, and subsequently recovered to 50% after 4 days. The γ-Secretase inhibitor IX concentration peaked to 9 g VSS/L, which could be explained as the alkali nature of the reactor causing detachment of the biofilm attached to the walls of the reactor, thus increased the VSS concentration to the high levels noted. The effluent pH dropped back to normal at 5.6 within 4 days of recovery. Interestingly, very slight changes in the VFA concentrations and proportions were noted, as less than 30% difference in the proportion of acetic acid and butyric acid was observed. The sugar utilization rate was nearly 100% during the process disturbance and recovery period.