Impact of chemical cleaning on the nanofiltration of pharmaceutically active compounds (PhACs): The role of cleaning temperature

Abstract

This study investigated the impact of chemical cleaning on the physicochemical properties of a nanofiltration membrane and its subsequent separation efficiency of inorganic salts and two pharmaceutically active compounds (PhACs), sulfamethoxazole and carbamazepine. Chemical cleaning was simulated by immersing virgin membrane samples in aqueous citric acid, sodium hydroxide (NaOH), ethylenediaminetetraacetic-acid (EDTA) and sodium dodecyl sulphate (SDS) at various temperatures for 18 h. The cleaning temperature did not exert any discernible impact on the surface charge of the NF270 membrane selected in this study. However, high cleaning temperatures were shown to either amplify or reduce the impact of chemical cleaning on several other membrane properties (including hydrophobicity, surface roughness and permeability) as well as the rejection of both inorganic salts and PhACs. The influence of chemical cleaning on the membrane surface roughness was enhanced at elevated cleaning temperatures. Similarly, at a high cleaning temperature, caustic and acidic cleaning caused a more significant increase in the membrane surface hydrophobicity than that at an ambient temperature. An increase in the cleaning temperature could also slightly amplify the decrease in the membrane permeability due to acidic cleaning. When a caustic cleaning solution (pH 11.5) was used, the membrane permeability only varied slightly with the temperature. Results obtained from Fourier transform infrared spectroscopy (FTIR) analysis suggest that chemical cleaning even at a high temperature did not permanently alter the chemical composition of the membrane active or support layer. Indeed, the effects of chemical cleaning at a high temperature on the physicochemical properties of the membrane could be attributed to the conformational changes of the membrane polymeric matrix. Chemical cleaning using citric acid, SDS or EDTA at a high temperature resulted in a considerable increase in the rejection of salts and PhACs in their neutral form. On the other hand, caustic cleaning at an elevated temperature had no discernible impact on the rejection of inorganic salts and neutral PhACs. This is because caustic cleaning and an elevated cleaning temperature cause opposing effects on the rejection of these solutes. Chemical cleaning at all temperatures investigated in this study did not affect the removal of negatively charged sulfamethoxazole.

Influence of formulated chemical cleaning reagents on the surface properties and separation efficiency of nanofiltrationmembranes

“…As a result, changes in the membrane porosity did not affect the sulfamethoxazole rejection by the NF270 membrane (Figure 7a). The results reported here regarding the impact of caustic cleaning formulations on sulfamethoxazole rejection are consistent with previous studies by Simon et al [14,34].…”

“…This is consistent with a previous study, in which cleaning reagents (i.e. NaOH, Citric acid, EDTA and SDS) at various temperatures had no impact on the bonding structure of the NF270 membrane [34]. On the other hand, Zhu and Nyström [35] reported a further aromatic peak at 1500 cm 1 after a polysulphone UF-membrane was fouled and subsequently chemically cleaned with NaOH.…”

“…pH 7) solution, functional groups at the membrane surface can be re-protonated and caustic cleaning only cause small or very minor changes in the zeta potential of the membrane surface as reported previously in section 3.1.1. However, the active skin layer immediately underneath the membrane surface can experience a hysteresis condition, similar as it was observed to happen due to elevated cleaning temperatures [34,36]. Due to this hysteresis effect, over a long time scale, the porosity of the membrane active skin layer decreases and returns to the normal value.…”

Effects of hypochlorite exposure on morphology and trace organic contaminant rejection by NF/RO membranes

“…This NF/RO filtration rig has been described in details elsewhere (Simon et al, 2013). Briefly, this set-up consisted of a stainless steel plate-and-frame membrane cell with an effective surface area of 40 cm 2 (4 cm x 10 cm), a stainless steel feed reservoir, and a high-pressure pump (Hydra-cell, Wanner Engineering…”

Membrane Fouling and Chemical Cleaning in Three Full-Scale Reverse Osmosis Plants Producing Demineralized Water

“…Contact with chemical cleaners influences membrane properties such as surface charge, porosity, or hydrophobicity and thereby may also influence operational parameters such as and salt rejection. In general, chemical cleaning at high pH may cause membrane swelling, while cleaning at low pH may cause membrane shrinking [28].…”