Sludge Densification and Low DO BNR: Anaerobic Selectors are the Key!

Intensification of wastewater treatment aims to create higher treatment capacity while reducing energy demand. Low dissolved oxygen (DO) operation can reduce energy costs, but there are concerns about process performance, particularly sludge settleability. Three phases of experimentation were completed on two bench-scale treatment configurations to compare sludge settleability and microbial kinetic rates: 1. High DO, 2. Low DO and 3. Low DO, with an extended anaerobic HRT. Excellent sludge settleability was obtained in the A/O configuration (average SVI 83 ± 5 mL/g) at low DO concentrations of 0.3 – 0.6 mg/L. Whereas, an A2 /O configuration experienced filament growth and sludge bulking. When the HRT was increased to 1.5 hour anaerobic HRT and 0.5 hour anoxic HRT, the A2 /O train was able to achieve good sludge settleability (average SVI 101 ± 7 mL/g).