Abstract
Safe drinking water production from compositionally variable surface sources requires treatment systems that combine effective contaminant removal with stable membrane operation. This study experimentally evaluated a hybrid treatment train consisting of slow sand or zeolite pretreatment followed by NF for surface water representative of South-East Kazakhstan. The results showed that pretreatment reduced turbidity, iron, and organic load before the membrane stage, thereby improving flux stability and decreasing fouling propensity. Among the tested pretreatment options, zeolite provided the most favorable feed conditions and extended stable membrane operation. These findings demonstrate that the practical performance of NF depends not only on membrane properties but also on effective upstream conditioning of the feed stream. Under the tested recovery conditions, the selected operating regime produced permeate of acceptable final quality, confirming that hybrid pretreatment-NF systems are a robust option for drinking-water treatment from challenging surface sources.