Forward osmosis desalination of brackish groundwater: Meeting water quality requirements for fertigation by integrating nanofiltration

The concept of fertiliser drawn forward osmosis (FDFO) desalination lies in the premise that fertilisers that serve as draw solutions (DS) add value to the FDFO product water for fertigation. However, because FDFO desalination is concentration based, the process cannot continue beyond the concentration equilibrium, one of the major limitations of the forward osmosis (FO) process. This results in final FDFO product water that, unless subjected to substantial dilution with fresh water, exceeds the acceptable nutrient concentrations for direct fertigation. In this study, nanofiltration (NF) has been assessed as an integrated process to FDFO desalination, either as a pre-treatment or post-treatment, to reduce the nutrient concentrations in the final product water and thereby allow direct use of the product water for fertigation without further dilution. NF as pre-treatment or post-treatment was found effective in reducing the nutrient concentrations using brackish groundwater (BGW) sources with relatively low total dissolved solid (TDS). However, when using higher TDS BGW sources, the product water still required further dilution or post-treatment before fertigation. NF as post-treatment was found to be more advantageous both in terms of reduced nutrient concentrations in the final product water and energy consumption.