Abiological Granular Sludge Formation Benefit for Heavy Metal Wastewater Treatment Using Sulfide Precipitation

Solid–liquid separation is a fundamental and ubiquitous process in water purification. Previously, an abiological granular sludge (ABGS) formation strategy was developed to improve the solid–liquid separation in heavy metal wastewater treatment. Although this strategy can be effectively applied in hydroxide precipitation, it remains challenging to apply it to other precipitation processes and real wastewater. Here, conditions for ABGS formation in the sulfide precipitation were first optimized. The effect of pH, seed dosage, and flocculant dosage on settling velocity and metal removal was systematically investigated. The results showed that the settling velocity of ABGS reached up to 3.7 cm/s and the volume of ABGS was compressed to one fifth of the original under optimal conditions, that is, pH of 8.5, seeds dosage of 0.25 g/L, and polyacrylamide dosage of 10 mg/L. Moreover, the ABGS formed in the process was analyzed for morphology and phase composition to provide insight into the formation mechanism, involving surface nucleation and aggregation, flocculation, and rearrangement. Under the optimized conditions, real Pb–Zn smelting wastewater was treated. The settling velocity (3.4 cm/s) of ABGS formed in real wastewater was as high as that in synthetic wastewater. Therefore, the ABGS strategy is potential to be scaled up to industrial application.