The final process disturbance examined was alkalization condition NaOH

Further process disturbances, starvation and alkalization, were investigated at the HRT of 8 h. In order to keep the reactor in starvation conditions, the feeding pump was stopped for 1 day. Thus, feed was not provided to the microbes, leading to a starvation period. This is, to the best of the authors’ knowledge, the first report of starvation condition in biohydrogen fermentation. The HPR dropped down to 5.0 L/L-d during the starvation phase, but recovered to 11.6 L/L-d in 5 days after the substrate was fed again. During this gamma-Secretase inhibitor IX period, the biohydrogen content was not largely affected, ranging between 38% and 53%. The effect was studied only for a shorter period of 5 days. It may be worthy of mention that the day after starvation occurred, the issue was rectified. However, significant changes were not noted in the biomass concentration, with only slight variation between 4.68 and 4.74 g VSS/L. This could clearly explain that the amount of substrate feed in to the reactor or the remaining feed in the reactor are very important and critical factors for the better production performance. The effluent pH also showed little variation from the maintained value of 5.5. In addition, the sugar utilization rate did not change much, ranging over 99% degradation. The VFA pattern was slightly changed, which will be discussed further below.