Kinetics of aerobic granular sludge treating low-strength synthetic wastewater at high dissolved oxygen.

Three parallel reactors (i.e. R1-R3) were operated with 340 mg-COD L-1, 42 mg-TN L-1, and 7 mg-TP L-1 at 20 ± 1°C. A mature granular sludge developed in 40 d and was stable for the 120 d experimentation period at an average food to microorganism ratio of 0.25 ± 0.08 g-COD g-VSS-1 d-1. Reactor biomass had higher inorganic content (i.e. 0.78-0.80 g-VSS g-TSS-1) than effluent biomass (i.e. 0.88-0.92 g-VSS g-TSS-1). Average granule diameter was 0.7-1.0 mm. Maximum phosphorus uptake and release rates averaged 4 ± 3 and 4 ± 2 mg-P g-VSS-1 h-1, respectively. Maximum observed nitrification rates averaged 1.9 ± 0.6 mg-N g-VSS-1 h-1. Phosphorus kinetics were similar between R1-R3 (i.e. P = 0.5309-0.6870) while nitrification kinetics varied significantly (i.e. P = 0.0002) even though conditions were the same. Effluent phosphate was on average 0.2 ± 0.4 mg-P L-1 while total inorganic nitrogen removal averaged 60 ± 10% resulting in an average effluent of 17 mg-N L-1. Aerobic granular sludge was capable of reliable nutrient removal from low-strength wastewater without volatile fatty acid source and at high dissolved oxygen concentrations.