Nutrient recovery from concentrated municipal wastewater by forward osmosis membrane and MgCl₂ based draw solution

In this study, a forward osmosis membrane was used to concentrate municipal wastewater up to 90%. The concentrated wastewater provided a high content organic matter for subsequent anaerobic treatment. At the same time, phosphorus content was recovered via precipitation. Energy-dispersive X-ray spectroscopy was done to evaluate the recovered solid. Results showed that precipitated phosphorus constituted only 2.46% cellulose triacetate (CTA membrane) and 2.24% thin-film composite (TFC membrane) of the total recovered solid. Although these percentages account for 72% of total phosphorus in the CTA test and 56% of total phosphorus in the TFC test, recovery of unwanted precipitate (Calcite) is still the main drawback. This can be attributed to the high calcium to phosphorus molar ratio in municipal wastewater and the presence of bicarbonate, which ultimately facil-itates the formation of calcite as the dominant recovered solid. Regardless of membrane type, complete water flux recovery was achieved after chemical cleaning. It indicates that chemical cleaning can effectively recover the water flux to its virgin membrane flux for direct municipal wastewater concentration.