Impact of thiocyanate on the reformation of aerobic granules from the disintegrated granules treating phenol-contained wastewater along with the recovery of nitritation efficiency

Abstract

The focus of the study was to evaluate the effect of thiocyanate (SCN−) addition on the reformation of the aerobic granules after its disintegration along with the pollutants degradation profile and nitritation recovery in a sequencing batch reactor (SBR). Granules were cultivated with phenol (400 mg L-1) and ammonia-nitrogen (NH4+-N) (100 mg L-1) in an SBR. After 75 days of stable reactor operation with volatile suspended solids, granule size, and extracellular polymeric substances (EPS) of 3.67 g L-1, 1202.03 ± 487.78 μm, and 78.23 mg gVSS-1, respectively, the granules started to deteriorate, and disintegration continued up to 84th day. Then reformation of disintegrated granules was observed after the gradual addition of SCN− (10−340 mg L-1). The size of granules increased to 1819.87 ± 43.44 μm along with higher EPS (101.45 ± 1.06 mg gVSS-1) and recovery of nitritation efficiency. A signification impact was observed in granule characteristics (sludge volume index and granule settling velocity of 26.31 ± 0.80 mL gTSS-1 and 57.32 ± 0.96 m h-1, respectively) because of microbial aggregation caused by sticky EPS secretion. It was found that SCN− played an important role in the granule reformulation by provoking the secretion of EPS, a very high binding capacity substance.