Forward osmosis of stored urine.
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Source separation of urine from domestic waste water provides a sustainable way of managing nutrient and water recovery from urine. This study was performed in the context of the Bill &Melinda Gates (BMFG) foundation’s Reinvent the Toilet Challenge (RTTC) which underscores the provision of low cost and sustainable sanitation solutions to poor communities. This study investigated the feasibility of applying a forward osmosis (FO) dewatering process for nutrient recovery from source separated urine under different conditions using ammonium bicarbonate as a draw solution. The diluted draw solution can be separated by moderate heating up to 60 °C using low grade heat, allowing ammonia and carbon dioxide to escape as gases from the diluted draw solution. The ease of separation from the permeate made ammonium bicarbonate the draw solution of choice. The forward osmosis process exhibited fairly high water fluxes of up to 6 L/m2.h when operated in the active layer facing feed solution (AL-FS) mode using thin film composite membrane (TFC). However, the active layer facing draw solution (AL-DS) mode had almost twice the water flux and solute flux obtained in the (AL-FS). The process also reviewed higher rejections for total nitrogen, chlorides and total phosphates and rejections for sodium and potassium were the lowest. A forward osmosis mass balance framework developed in this work as a basis for modelling was in good agreement with the experimental water flux and nutrient rejection values. Approximately 4 g of ammonium bicarbonate back diffused into the feed solution for every litre of water that permeated the membrane from the feed side towards the draw solution. Membrane fouling induced a 12 % drop in flux. Circulation of deionized water and osmotic backwashing recovered 95 % and 98 % of the fresh membrane water flux respectively.