Sea salt bittern-driven forward osmosis for nutrient recovery from black water: A dual waste-to-resource innovation via the osmotic membrane process

A dual“waste-to-resource”innovation in nutrient enrichment and recovery from domestic black water using a sea salt bittern(SSB)-driven forward osmosis(FO)process is proposed and demonstrated.The performance of SSB as a“waste-to-resource”draw solution for FO was first evaluated.A synthetic SSB-driven FO provided a water flux of25.67±3.36 L/m2 h,which was 1.5-1.7 times compared with synthetic seawater,1 M NaCl,and 1M MgCL.Slightly compromised performance regarding reverse solute selectivity was observed.In compensation,the enhanced reverse diffusion of Mg+suggested superior potential in terms of recovering nutrients in the form of struvite precipitation.The nutrient enrichment was performed using both the pre-filtered influent and effluent of a domestic septic tank.Over 80%of phosphate-P recovery was achieved from both low-and high-strength black water at a feed volume reduction up to 80%^90%.With an elevated feed pH(~9),approximately 60%-85%enriched phosphate-P was able to be recovered in the form of precipitated stuvite.Whereas the enrichment performance of total Kjeldahl nitrogen(TKN)largely differed depending on the strength of black water.Improved concentration factor(i.e.,3-folds)and retention(>60%)of TKN was obtained in the high-nutrient-strength black water at a feed volume reduction of 80%,in comparison with a weak TKN enrichment observed in low-strength black water.The results suggested a good potential for nutrient recovery based on this dual“waste-to-resource”FO system with proper management of membrane cleaning.