Application of membrane separation processes on the treatment of textile effluent for water and dye reuse

Abstract

Textile industry consumes large amount of water as well as dyes and various processing chemicals during the many stages of textile processing generating substantial quantity of wastewater potentially polluting. Thus, in this context, this work aims to investigate the application of a membrane separation process applied to the treatment of textile effluent containing indigo blue, in order to generate industrial water as well as promote dye reuse. Two treatment routs was assessed. The first one consisted in microfiltration (MF), followed by membrane bioreactor (MBR) and then nanofiltration (NF). The second rout was MF followed by NF. Raw textile effluent is not biodegradable due to dye chemical complexity, however MF permeate is much more biodegradable since the molecules weight are much smaller, being readily assimilated by the microorganisms. The indigo blue dye was efficiently retained by the MF membrane (100%), which allows its recovery from the concentrate stream. The MBR resulted in COD and ammonia removal of 73% and 100%, respectively. This process already enables the water in a few textile processes, such as, floor and equipment washing. However, it is still needed a polishing step to apply this water in more noble using. NF technology was successfully applied to polish textile effluent. The best NF filtration performances were provided under a pressure of 12 bar and a cross-flow velocity of 0.63 cm s1 for both studied treatment routs. The NF performance, in terms of COD, conductivity, colour, nitrogen removal was not influenced by pH; however, higher pH values of the NF feed resulted in increased membrane fouling. High temperature and pH also reduces the NF rejection even the worst case evaluated (37.5 ºC and pH 11), NF90 is still able to attend the manufactory quality requirement. The principal cause of flux decline was determined to be concentration polarization in all studied cases, but chemical cleaning of the membrane was sufficient to regain the initial permeability. The maximum water recovery rate obtained for a single MF-NF step in the treatment of microfiltered textile effluent is 40% resulting in a total capital cost (CapEx) of the MF-NF treatment system estimated at US$ 58,362.50, and the total operational cost (OpEx) was 0.31 US$/m3 of effluent. Since both studied routs showed similar results, the MF-NF hybred system was chosen considering area requirements, energy and equipment consumption, as well as system complexity. The NF permeate meets the quality requirements for all processes within the textile industry, while the NF concentrate can be used to wash equipment, screens in the printworks, print paste containers, and floors.