Rapid formation and characterization of aerobic granules in pilot-scale sequential batch reactor for high-strength organic wastewater treatment

This work presents the first attempt in the treatment of high-strength organic wastewater at organic loading rate (OLR) up to 30 kg/m3 d in an aerobic granular sludge sequencing batch reactor. The reactor was operated for 100 days, divided into two main periods according to the applied OLR. In the first period, aerobic granules were cultivated and allowed to stabilize at an OLR of 10.2 ± 2.1 kg COD/m3 d (from the reactor start-up until day 41). In the second period (from day 42 to day 100), the applied OLR was 27.0 ± 3.5 kg COD/m3 d. Stable aerobic granules of average diameter of 1-2 mm dominated the reactor after 30 days, improving the settleability of the biomass. The COD removal efficiency was 98.4 ± 1.1% during the first 45 days of operation. However, after increasing the OLR, the COD removal efficiency decreased drastically to 64.4 ± 13.7% from days 46 to 64. Thereafter, the reactor recovered from the shock load and the removal efficiency increased to 96 ± 2.7% until the end of the 100 days. The effect of COD/N ratio was investigated for the treatment of nitrogen-deficient wastewater. It was shown that under severe nitrogen-deficient conditions (COD/N ratio > 70), the COD removal efficiency was 64.4 ± 13.7%. A COD/N ratio of 25-30 should be attained to ensure that there is no limitation in heterotrophic growth. The results from this study indicate that aerobic granulation can provide a promising high-strength organic wastewater treatment technology.