Microbial physiological biochemical activities of the low C/N shock to A²/O system and its restoration

By adding ammonium into the raw wastewater to simulate the low C/N shock, two sets of lab-scale A²/O (anaerobic-anoxic-oxic) system were constructed to investigate the physiological biochemical activities of the shock and further restoration. Results showed that oxygen uptake rate (OUR), dehydrogenases activity (DHA), adenosine triphosphate (ATP) and poly-β-hydroxybutyric acid (PHB) responsed well to the shock with a drop over 81.8%, 87.0%, 90.5% and 72.9%, respectively. Both increasing the sludge reflux ratio (R) and reducing the sludge retention time (SRT) were effective restoration measures. After the restoration the value of R, OUR barely resumed, however, DHA, ATP and PHB still had a 10% to 20% gap left, compared to those before the shock. The reduction of SRT could gradually eliminate impacts of the shock by discharging the damaged sludge. Although the A²/O system didn't well perform during the restoration period, all of the four physiological and biochemical activities of micro-organisms recovered fully in the end.