Adding waste iron shavings in a pilot-scale two-stage SBRs to develop aerobic granular sludge treating real wastewater

A pilot-scale two-stage SBRs added waste iron shavings was proposed and established to develop aerobic granular sludge for real wastewater treatment based on a previous lab-scale study. The results showed that aerobic granular sludge was successfully cultivated, and the treatment performance was satisfactory. The sludge volume index at 30 min (SVI30) was approximately 25.0 mL/g and the mean particle size reached approximately 0.8 mm. The mixed liquor suspended solids (MLSS) exceeded 14 g/L and 10 g/L in the two SBRs. The average removal rates of chemical oxygen demand (COD), total phosphorus (TP), ammonia nitrogen (NH4+-N), total nitrogen (TN), and suspended solids (SS) were 95.2%, 99.2%, 96.1%, 82.9%, and 95.0%, respectively. In addition, low total iron (TFe) concentrations were unlikely to impact the effluent. Two-stage SBRs can efficiently reduce the effluent SS concentration during early in the operation process, and improve the utilisation of carbon source from raw wastewater for denitrification. Overall, the coupling of iron shavings micro-electrolysis and biological processes promoted aerobic sludge granulation and pollutant removal.