Effects of Microfiltration Pretreatment and Feed pH Adjustment on Nanofiltration and Reverse Osmosis Desalination of Agricultural Drainage Water

Agricultural drainage water is a saline return flow whose reuse is constrained in intensively cultivated basins such as the Harran Plain in southeastern Türkiye. This exploratory, descriptive bench study examined microfiltration (MF) pretreatment and adjustment of the feed pH to approximately 7 on real drainage water (4.8 to 8.1 mS cm−1) with flat-sheet NF270 and XLE membranes at 8 bar. Six treatment trains, four forming a 2 × 2 factorial, were each run twice in 6 h batch concentration mode, with the two runs of each train made on separate days. XLE rejected 93 to 98% of feed conductivity and delivered 0.10 to 0.63 mS cm−1 permeate, whereas NF270 rejected 76 to 80%. The second run of every factorial cell rejected more than the first, so run order was blocked post hoc. The blocked model associates MF pretreatment with a gain of 2.0 percentage points (95% CI 0.03 to 3.97) and bounds the pH effect within two points of zero. No result reaches the 0.05 level under familywise adjustment. Normalizing flux to net driving pressure separates osmotic loss from loss of membrane permeability; one unpretreated run of eight lost permeability, an observation compatible with chance. Water recovery was not measured, and irrigation suitability was not assessed, as conductivity alone cannot establish it. These runs tested acute rejection and flux, not the scaling control that motivates acid dosing in practice; the ions that set scaling potential were not measured. The findings are preliminary and describe process configuration of these feeds rather than membrane-level mechanisms.