Ammonia transfer in forward osmosis during operation to concentrate digester centrate

In forward osmosis, water is transported from a feed solution with low osmotic potential to a draw solution with high osmotic potential. Seawater is an inexpensive draw solution if the forward osmosis plant is in the vicinity of the sea, and the seawater can be discharged without treatment, provided there is no contamination from the feed solution. Forward osmosis can be used to concentrate phosphorus from wastewater, but problems have arisen with ammonia contamination of the draw solution. It is important to understand the potential to which ammonia can contaminate the draw solution, and how to reduce it. In this study we evaluate the effect pH has on thin-film composite (TFC) (Porifera, USA) and biomimetic membranes (Aquaporin A/S, Denmark) with regards to ammonia transfer and water flux.