Hybrid coagulation–NF membrane process for brackish water treatment: Effect of antiscalant on water characteristics and membrane fouling

• Scaling could severely impair the performance of membrane desalination process.
• Antiscalants have been used to prohibit and reduce the risk of scale formation.
• Influence of antiscalant on coagulation–NF membrane process was investigated.
• Interaction between antiscalant and foulants varied according to its concentration.
• Membrane fouling tendency and water characteristic changed with antiscalant dosage.

Antiscalants have been used to inhibit the formation of scales and reduce the risk of membrane scaling. However, issues such as the increased of biofouling tendency and contradictory observations of organic fouling propensity under the influence of antiscalants have been reported by other researchers. Such observations indicate the need for thorough understanding about the interaction between antiscalants and membrane/foulants in the solution. This study investigated the influence of antiscalant on the water characteristics and the performance of hybrid coagulation–nanofiltration membrane process for brackish water treatment. It was observed that scaling was mitigated with the addition of antiscalants but membrane fouling was exacerbated at higher dosage, probably due to the changes in foulant properties induced by antiscalants. Analysis carried out on the water showed that antiscalants altered the characteristics of the foulants and formed precipitates with calcium/aluminum and iron (from coagulant) ions, which eventually deposited as foulant layer on the membrane surface. This was proven with the existence of phosphorous element on the membrane surface using SEM–EDX. The findings demonstrated how the antiscalants altered the water characteristics and provided insight into the reactivity of antiscalants present in different concentrations, which could be used to interpret the contradicting findings from other researchers.