Loose nanofiltration membranes with assembled antifouling surfaces of organophosphonic acid/Fe(III) for managing textile dyeing effluents

A nanofiltration and electrocatalytic membrane reactor with ozone oxidation integrated system for dyeing wastewater treatment and Na2SO4 recovery

Removal of organic pollutants while recovering Na2SO4 is crucial for the dyeing wastewater resourcefulness. In this study, nanofiltration (NF) was used for the treatment of industrial dyeing wastewater (COD=294.2 mg L-1, the concentration of Na2SO4 = 3.8 g L-1). An electrochemical membrane reactor (ECMR) was then constructed with conductive carbon membrane (CM) as cathode and graphite as anode for the organic removal from the NF concentrate with high concentration of Na2SO4 for reuse. Meanwhile, ECMR was also coupled with ozone (O3) to enhance its performance. Electron spin resonance (ESR) was employed to investigate the generation of active species during the ECMR-O3 system. The organics were analyzed by excitation-emission matrix (EEM). The results show that Na2SO4 concentration of 18.4 g L-1and purity of 92.4 % were achieved from the NF concentrate. After the NF concentrate was treated by ECMR-O3 system, the COD reduced to 48.6 mg L-1 with a removal rate of 92.7 %, which was higher than that of O3 oxidation (57.7 %) and ECMR (13.9 %) alone. It was ascribed to the electrolysis of O3 flowed through the cathodic CM, leading to more HO∙ produced. Certainly, the high concentration of Na2SO4 in the NF concentrate provided a high conductivity environment for the optimal operating of ECMR and the CM promoted the enhanced mass transfer under the diffusive conditions of O3. The NF concentrate treated could be directly reused for dyeing fabrics, making a profit of 0.25 $ m-3 and reducing a carbon emission of 46.81 %. (2.79 kg CO2 m-3). In a word, this study offers a viable approach for dyeing wastewater treatment and Na2SO4 resources recover.

Effective separation of dyes/salts by sulfonated covalent organic framework membranes based on phenolamine network conditioning

This study developed a modified polyacrylonitrile (PAN) membrane controlled by a phenol-amine network and enhanced with a sulfonated covalent organic framework (SCOF), aimed at improving the efficiency of textile wastewater treatment. Utilizing a phenol-amine network control strategy allows for precise manipulation of interfacial reactions in the synthesis of SCOF, achieving highly uniform modification on the surface of the PAN membrane. This modified membrane demonstrated high rejection of over 98% for various water-soluble dyes, including Alcian blue 8GX, Coomassie Brilliant Blue G250, methyl blue, congo red, and rose bengal, and also exhibited specific selectivity in processing salt-containing wastewater. By adjusting the deposition time of the phenol-amine and the concentration of SCOF monomers, optimal retention performance and permeate flux were achieved, effectively separating dyes and salts. This research provides a new and effective solution for treating textile wastewater, especially in separating and recovering dyes and salts, offering broad application prospects in environmental management and water resource management, and highlighting its significant practical implications.

Molecular insights into impacts of EDTMPA on membrane fouling caused by transparent exopolymer particles (TEP)

While ethylenediamine tetramethylenephosphonic acid (EDTMPA) has been emerged as a stronger chelating agent than ethylene diamine tetraacetic acid (EDTA) for fouling mitigation, and transparent exopolymer particles (TEP) is a major foulant in membrane-based water treatment process, effects of EDTMPA on TEP fouling and the underlying mechanism have been not yet studied. In this study, Flory-Huggins lattice theory was combined with density functional theory (DFT) technology to explore this subject at molecular level. Filtration experiments showed a unimodal pattern of specific filtration resistance (SFR) of TEP sample with Ca²⁺ concentration in range of 0-3 mM. For the TEP sample with the peak SFR value at 1.5 mM Ca²⁺, continuous addition of EDTMPA (from 0 to 100 mg·L^-1) resulted in a sustained decrease in SFR. Energy dispersive spectroscopy (EDS) mapping characterization showed the continuing decline of calcium content in the TEP layer with increase of EDTMPA addition, indicating that EDTMPA successfully captured Ca²⁺ from alginate‑calcium ligation (TEP), and then disintegrated the TEP structure. DFT simulation showed that Ca²⁺ preferentially coordinated with the terminal carboxyl groups of alginate chains to form a coordination configuration that is conducive to stretch the three-dimensional polymer network. Such a network corresponded to an extremely high SFR according to Flory-Huggins theory. EDTMPA addition caused disintegration of the coordination configuration of Ca²⁺ binding to terminal carboxyl groups, which further resulted in collapse and flocculation of TEP gel network structure, thus leading to a continuous SFR decrease. This work provided deep thermodynamic insights into effects of EDTMPA on TEP-associated fouling at molecular level, facilitating to better understanding and mitigation of membrane fouling.