Characteristics of aerobic granules treating phenol and ammonium at different cycle time and up flow liquid velocity

Abstract

Synthetic wastewater containing phenol (400 mg L−1), thiocyanate (SCN−) (100 mg L−1) and ammonia-nitrogen (NH4+-N) (100 mg L−1) was treated in the three aerobic granular reactors at different cycle time of 6 h (R1), 12 h (R2) and 24 h (R3) with organic loading rate (OLR) of 2.03, 1.02, and 0.51 kg COD m−3 day−1, respectively. Reactor performance was analyzed in terms of granule characteristics and organics and nitrogen removals. Granule size, biomass concentration and extracellular polymeric substances (EPS) in sludge were inversely related to cycle time. In R1, mean biomass size and volatile suspended solids (VSS) were 1334.24 ± 30.56 μm and 4.31 ± 0.40 g L−1, as compared to 97.93 ± 4.21 μm size and 2.28 ± 0.13 g L−1 VSS in R3. Sludge EPS in R1 was two-fold more than R3. The ratio of protein (PN) to polysaccharide (PS) content in sludge increased with an increase in loading. Pollutant removal performance was independent of cycle time with 94–96% removal of COD (chemical oxygen demand) and 99% removals of phenol, SCN−, and NH4+-N. In reactors R1 and R3, nitrification was complete to nitrate, and in R2, 40% of influent NH4+-N was converted to nitrite. Up flow liquid velocity of 2.5 m h−1 was appropriate for better granulation and can serve as a selection pressure for granulation.