Pretreatment and Hybrid Processes

Nanofiltration (NF) processes have particular property profiles that lend them to removal of specific classes of compounds (divalent and heavy metal ions and low molecular weight organics). However, in some cases, NF membranes can be susceptible to scaling and fouling from the various process waters and wastewaters they are designed to treat. This chapter reviews various pretreatments for NF (e.g. species removal by coagulation or precipitation, biological treatment, or MF/UF for particulate removal). It then surveys hybrid processes that exploit NF's property profile for water production, product isolation, or wastewater treatment in areas such as metal extraction, dextrose production, seawater desalination, and olive mill wastewater treatment. In such hybrid processes, it is combined with unit operations such as ion exchange, adsorption, MF/UF, RO, electrodialysis, and thermal distillation. The advantages of some of these hybrids are highlighted.