The coagulation–ultrafiltration process from pilot testing to full-scale design for the achievement of ultra-low phosphorus limit

Lake water from a Shanghai theme park faces restrictive phosphorus discharge limits (≤0.02 mg/L) that are technically challenging. Laboratory bench top and pilot plant testing were conducted. The results show that a coagulation–ultrafiltration (UF) hybrid process is able to reliably achieve the objective, while a coagulation– sand filter process cannot meet the requirement. Therefore, mature technologies such as Veolia Actiflo® and GE Zeeweed® are preferred for full-scale design. In addition, alum performs better than poly alum chloride on phosphorus removal. It was also suggested the efficiency of anion polyacrylamide for the filtered samples was reduced compared with non-filtered samples. Simultaneously, soluble PO4-P was also eliminated by UF resulting from the flocs and precipitates with greater surface area and the agglomeration of residual aluminum ions and orthophosphate. Membrane filtration helps reduce chemical dosage and 6 mg/L Al³⁺ (alum) concentration was enough to meet the requirement for the influent TP around 0.3 mg/L. Finally, several considerations were given to future scale-up design, such as treatment target of coagulation precipitation system, species of coagulant aid, flocculants, and online analyzers.