Influence of reverse salt flux on ammonium rejection in forward osmosis for nutrients recovery

Forward osmosis has been proposed for concentration of ammonium and phosphate for nutrient recovery, e.g. in digester centrate. However, studies have found low rejection of ammoniacal nitrogen (e.g. ammonium at neutral pH). Ammonium transfer requires transfer of other ions to ensure electroneutrality, e.g. reverse transport of a cation or co-transport of an anion. Therefore, selecting a draw solute with low reverse flux from draw to feed may enhance ammonium rejection. Accordingly, this study will investigate how transfer of ions facilitates the transfer of ammonium, and how draw solutions can be designed to ensure high ammonium rejection.