In fertilizer-drawn forward osmosis (FDFO) desalination, the final nutrient concentration (nitrogen, phosphorus, potassium (NPK)) in the product water is essential for direct fertigation and to avoid over fertilization. Our study with 11 selected fertilizers indicate that blending of two or more single fertilizers as draw solution (DS) can achieve significantly lower nutrient concentration in the FDFO product water rather than using single fertilizer alone. For example, blending KCl and NH(4)H(2)PO(4) as DS can result in 0.61/1.35/1.70 g/L of N/P/K, which is comparatively lower than using them individually as DS. The nutrient composition and concentration in the final FDFO product water can also be adjusted by selecting low nutrient fertilizers containing complementary nutrients and in different ratios to produce prescription mixtures. However, blending fertilizers generally resulted in slightly reduced bulk osmotic pressure and water flux in comparison to the sum of the osmotic pressures and water fluxes of the two individual DSs as used alone. The performance ratio or PR (ratio of actual water flux to theoretical water flux) of blended fertilizer DS was observed to be between the PR of the two fertilizer solutions tested individually. In some cases, such as urea, blending also resulted in significant reduction in N nutrient loss by reverse diffusion in presence of other fertilizer species.

No abstract

Continued efforts are made in improving the performance of the low-cost forward osmosis (FO) membrane process which utilizes naturally available osmotic pressure of the draw solution (DS) as the driving force. Selection of a suitable DS and development of a better performing membrane remained the main research focus. In this study, the performance of a hollow fiber forward osmosis (HFFO) membrane was evaluated with respect to various operating conditions such as different cross-flow directions, membrane orientation, solution properties, and solution flow rates (Reynolds number). The study observed that operating parameters significantly affect the performance of the FO process. FO comparatively showed better performance at counter-current orientation. NaCl, KCl, and NH 4 Cl were evaluated as DS carrying common anion. Properties of the anionic part of the DS were found important for flux outcome, whereas reverse solute flux (RSF) was largely influenced by the properties of DS cationic part. FO was operated at different DS and feed solution (FS) flow rates and FO outcome was assessed for varying DS and FS Reynolds number ratio. FO showed better flux outcome as Re ratio for DS and FS decreases and vice versa. Results indicated that by adjusting FO processes conditions, HFFO membrane could achieve significantly lower specific RSF and higher water flux outcome. It was observed that using 2 M NaCl as DS and deionized water as FS, HFFO successfully delivered flux of 62.9 LMH which is significantly high compared to many FO membranes reported in the literature under the active layer-DS membrane orientation mode.

The performance of recently developed polyamide thin film composite hollow fibre forward osmosis (HFFO) membrane module was assessed for the desalination of brackish groundwater (BGW) for fertigation. Four different fertilisers were used as draw solution (DS) with real BGW from the Murray-Darling Basin in Australia. Membrane charge and its electrostatic interactions with ions played a significant role in the performance of the HFFO module using fertiliser as DS. Negatively charged polyamide layer promotes sorption of multivalent cations such as Ca 2+ enhancing ion flux and membrane scaling. Inorganic scaling occurred both on active layer and inside the support layer depending on the types of fertiliser DS used resulting in severe flux decline and this study therefore underscores the importance of selecting suitable fertilisers for the fertiliser drawn forward osmosis (FDFO) process. Water flux under active layer DS membrane orientation was about twice as high as the other orientation indicating the need to further optimise the membrane support structure formation. Water flux slightly improved at higher crossflow rates due to enhanced mass transfer on the fibre lumen side. At 45% packing density, HFFO could have three times more membrane area and four times more volumetric flux output for an equivalent 8040 cellulose triacetate flat-sheet FO membrane module.

Abstract-technique to reduce excessive nutrients before putting it for any direct end use.