Concentrating and recycling of high-concentration printing and dyeing wastewater by a disc tube reverse osmosis-Fenton oxidation/low temperature crystallization process

Abstract

Abstract A novel three-step process consisting of disc tube reverse osmosis (DTRO), Fenton oxidation, and low temperature crystallization is described for the treatment of printing and dyeing wastewater. The DTRO step was used to further concentrate the wastewater obtained from a nanofiltration (NF) treatment. The desalinated water can be directly reused in the production process, and the COD, TOC, TDS, and SO42- concentrations of the concentrated wastewater were above 1500\xa0mg/L, 500\xa0mg/L, 150\xa0g/L, and 100\xa0g/L, respectively. The concentrated wastewater was then treated by Fenton oxidation, and the COD, TOC, and chroma removal rates in this step were over 80%, 80%, and nearly 100%, respectively. Finally, when the crystallization end point temperature was 0\xa0°C, the recovery and purity of the product were above 60% and 99%, respectively. For the small amount of Cl- contained in the crystalline mother liquor, the Cl- and SO42- in the mother liquor were separated by NF and then sent back to the DTRO step to be re-concentrated. The degradation of organic compounds in wastewater was studied by UV–Vis spectroscopy, three-dimensional fluorescence spectroscopy (3D-EEM), and total organic carbon analyzer. The crystalline products were characterized by X-ray diffraction. The results showed that this new coupling process can realize high reuse of printing and dyeing wastewater.