Jihee Moon

Combined coagulation-disk filtration process as a pretreatment of ultrafiltration and reverse osmosis membrane for wastewater reclamation: an autopsy study of a pilot plant.

The effects of the combined coagulation-disk filtration (CC-DF) process on the fouling characteristics and behavior caused by interactions between effluent organic matter (EfOM) and the membrane surfaces of the ultrafiltration (UF) and reverse osmosis (RO) membranes in a pilot plant for municipal wastewater reclamation (MWR) were investigated. The feed water from secondary effluents was treated by the CC-DF process used as a pretreatment for the UF membrane to mitigate fouling formation and the permeate from the CC-DF process was further filtered by two UF membrane units in parallel arrangement and fed into four RO modules in a series connection. The CC-DF process was not sufficient to mitigate biofouling but the UF membrane was effective in mitigating biofouling on the RO membrane surfaces. Fouling of the UF and RO membranes was dominated by hydrophilic fractions of EfOM (e.g., polysaccharide-like and protein-like substances) and inorganic scaling (e.g., aluminum, calcium and silica). The desorbed UF membrane foulants included more aluminum species and hydrophobic fractions than the desorbed RO membrane foulants, which was presumably due to the residual coagulants and aluminum-humic substance complexes. The significant change in the surface chemistry of the RO membrane (a decrease in surface charge and an increase in contact angle of the fouled RO membranes) induced by the accumulation of hydrophilic EfOM onto the negatively charged RO membrane surface intensified the fouling formation of the fouled RO membrane by hydrophobic interaction between the humic substances of EfOM with relatively high hydrophobicity and the fouled RO membranes with decreased surface charge and increased contract angle.

The relationship between flux decline of NF membranes with NOM transport characteristics: convection vs. diffusion

Abstract Recent studies have shown that NF membranes can effectively remove natural organic matter (NOM). However, NOM also serves as an organic foulant to membranes, resulting in flux decline. In this study, the flux decline of NF membranes was analyzed through the transport characterization of NOM in NF membrane pores. The transport of NOM through NF membrane pores was influenced by either convection or diffusion, depending on the applied hydrodynamic operating conditions, as represented by the ratio J0/k (J0 represents the initial pure water flux, and k is the mass transfer coefficient) [1]. Different behaviors of flux decline, and flux recovery of tested membranes could be obtained: depending on which transport mechanism (either convection or diffusion) dominates during NOM filtrations. The removal (or rejection) behavior of NOMs, by NF membranes, was evaluated with respect to the ratio J0/k under a dominant transport condition, along with the performance of the flux decline effects.