Treatment of membrane concentrates: phosphate removal and reduction of scaling potential

The widespread application of nanofiltration (NF) and reverse osmosis (RO) membranes in wastewater reuse inevitably generates a concentrate stream. Due to high concentrations of phosphate and salts, disposal of membrane concentrates is a problem which seriously constrains the application of this technology, especially in inland applications. There is a need for technologies which facilitate an affordable and environmentally-safe disposal of membrane concentrates. The objectives of this study are to investigate appropriate treatment techniques to (1) increase the recovery of the membrane filtration thus minimising the volume of the concentrate stream, and (2) increase the concentrate quality to enable discharge into surface water bodies. The results show that both adsorption onto granular ferric hydroxide (GFH) and chemical precipitation are generally effective for phosphate removal from NF concentrates. Chemical precipitation by dosing of sodium hydroxide solution is rapid and removes more than 90% of phosphate and calcium ions. By the removal of calcium ions, chemical precipitation can significantly reduce the scaling potential of NF and RO concentrates. This may allow higher recoveries in the NF/RO process.