Sustainable Nutrient Water Recovery by a Hybrid Process for Hydroponic Production

Electrodialysis of Liquid Digestate to Recover Nutrient Ions 35 30 Diluate Concentrate Current density 15 10 5 0 0 50 100 150 200 250 Operational Time (min) )mc/Sm( ytivitcudnoC lacirtcelE 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0. Current Density (mA/cm ) 2 With an electric potential being applied, charged ions continuously migrated from the diluate stream into the concentrate stream. There was a huge osmotic pressure difference between the concentrate stream and diluate stream, making them ideal draw and feed solutions, respectively, in the following FO treatment. This decline in current density during ED treatment of real anaerobic effluent was attributed to (1) continuous dilution of the feed water flowing into the diluate compartment and (2) membrane fouling and scaling. EDR: reduce membrane fouling and scaling; reduce operating time, and thus energy consumption Images of AEM and CEM before and after ED treatment The color change in membranes after operating is often due to fouling and scaling AEM: organic fouling and biofouling, caused by the accumulation of substances such as humic acids, proteins, or cells, CEM: inorganic scaling Both fouling and scaling lead to an increase in membrane resistance, resulting in higher AEM CEM energy consumption and a reduction of mass transfer FO Performance: Water Flux, Water Recovery, and Final NPK Concentration 10 8 Water flux Permeate volume 4 2 0 0 20 40 60 80 100 Operational Time (min) )HML( xulF retaW 8 7 6 5 4 3 2 1 )L( emuloV etaemreP evitalumuC Liquid digestate consisting of nutrients, – organic & microbial contaminants CEM AEM CEM AEM Stage 2: FO to extract – – – + – + – + – + + clean water + + + + – + – – + – – Concentrated waste – + – + + + + – – + – – facilitates further treatment or actions + Diluate with organic & microbial contaminants Clean water & nutrients Highly concentrated ++ nutrient solution Stage 1: ED to extract nutrients Fertigation or hydroponic irrigation The decline in water flux can be attributed to (1) continuous dilution of draw solution and thereby reduced osmotic pressure driving force across the FO membrane and (2) membrane fouling which increased the resistance to water permeation through the membrane Xue Jin Assistant Professor, Environmental Engineering Oregon State University Xue.Jin@oregonstate.edu.