Membrane distillation for textile wastewater treatment using polyvinylidene fluoride cloisite 15A hollow fiber composite membranes

Abstract

To date, membrane distillation (MD) has been regarded as a potential candidate in treating textile effluents as this thermally-driven membrane process has unique advantages over pressure-driven membrane processes. However, the main challenge for the MD process to be practically used in textile industry is the difficulty of getting a membrane with desirable characteristics. In this work, polyvinylidene fluoride incorporated Cloisite 15A hollow fiber composite membranes were developed for textile wastewater treatment using direct contact membrane distillation (DCMD) system. The effects of polymer concentrations, types of additives and Cloisite 15A clay loadings on the membrane properties and its DCMD performance were investigated. Membrane made of 12 wt% PVDF was found to be the best performing membrane based on its overall separation performance in comparison to the membranes prepared with higher PVDF concentration. In terms of additive, ethylene glycol (EG) was found to be better pore former agent as compared to polyvinylpyrrolidone (PVP). The 12 wt% PVDF membrane with EG as additive was further modified by Cloisite 15A at different loadings. Results showed that the PVDF membrane incorporated with 3 wt% Cloisite 15A (PVDF-3% C15A) was the best composite membrane in terms of permeate flux (10.13 ± 0.18 kg m-2 h-1) and dye rejection (>99%). Its membrane contact angle, wetting pressure, mean pore size and surface roughness was reported to improve upon addition of 3 wt% Cloisite 15A. Besides, this membrane also exhibited the highest thermal stability, mechanical strength and overall porosity compared to other composite membranes. In view of this, PVDF-3% C15A membrane was selected for further studied using synthetic dyeing solutions containing dyes and salts. With respect to separation performance, higher rejections were able to achieve in all experimental tests, regardless of operating conditions, which indicate the potential of PVDF-3% C15A membrane in producing purified water from synthetic dyeing solutions. The membrane was further subjected to another experiment using real textile wastewater collected from a textile factory located in Kulai, Johor. The treated water was analyzed with respect to biological oxygen demand (BOD5), chemical oxygen demand (COD), total dissolved solid (TDS), color, turbidity and conductivity. Higher permeate flux (36.82 ± 1.96 kg m-2 h-1) with excellent removal efficiency (>90%) was recorded for each measured analytical parameter during textile wastewater treatment. The stability of the membrane was also assessed for up to 40-h. Results showed that a significant flux decline was observed during the longterm operation, owing to fouling resulted from cake layer formed at the outer surface of the membrane. Nevertheless, the quality of permeate could be practically maintained at not less than 72% removal for both COD and color. As a conclusion, it can be said that the in-house made PVDF-Cloisite 15A composite membrane can facilitate the development of textile wastewater treatment if several issues such as membrane fouling and pore wetting can be further addressed.