Search

In this work, a novel zero liquid discharge technology combining of electrodialysis (ED), electrochemical catalytic oxidation (ECO), reserve osmosis (RO) and bipolar membrane electrodialysis (BMED) was developed for sustainable recovery of high-saline papermaking wastewater. The effect of membrane type, volume ratio, membrane fouling and voltage were investigated in ED process; subsequently parameter such as electrolyte conductivity was studied in ECO process. The FKB/FAB stack shows good separation performance for the salts and organics, allowing a relatively high COD rejection of 97.80%. Meanwhile, membrane fouling was investigated through a comparison between virgin and fouled membranes. To achieve a high-saline solution with low organics, a second-stage ED process was applied. The concentration factor was increased to 1.799 with a COD rejection of 96.54% at voltage of 12 V. Simultaneously, the ECO process exhibited superior COD removal of 94.99% at the electrolyte conductivity of 4 mS/cm. Through the application of BMED at Vf:Vb:Va (volume ratio of feed, base and acid solution) of 4:1:1, the final acid and base content could approach a high value of 12.30 wt% and 10.60 wt%, respectively. Therefore, this hybrid ED-ECO-RO-BMED combined process demonstrates a strongly technical applicability for sustainable resource recovery from high-saline papermaking wastewater.

In this study, an electrodialysis (ED) system which was divided into three-stage operation was designed to treat seawater concentrate. The experiment was carried using a laboratory ED-cell with an effective area of 189 cm2. Two types of monovalent selective ion-exchange membranes were investigated: CIMS/ACS and CSO/ASV. The effect of applied current density during ED process was also studied. The experimental results indicate that the separation performance for divalent ions (i.e., Ca2 +, Mg2 +) with CIMS/ACS membranes stack was superior to CSO/ASV membranes stack; furthermore, a lower current density can increase the selectivity in monovalent ions to divalent ions with either the CIMS membrane or the CSO membrane. The current efficiency and energy consumption were optimal at a current density of 4 mA/cm2 by using CIMS/ACS membranes stack as the first stage of system in this experiment. Furthermore, the desalination rate (70%) was chosen as the experimental operation endpoint of the first-stage ED operation based on the experimental results. Moreover, the latter two-stage operation was used to concentrate brine to produce coarse salt after evaporation process. Finally, the repeated batch experiments confirmed the system feasibility for treating seawater concentrate to produce coarse salt with the purity of ~ 85% under continuous operation.

Two commercial thin film composite polyamide reverse osmosis (BW-30) and nanofiltration (NF-90) membranes were studied for sorption of 2-nitrophenol and 2-chlorophenol. Adsorption kinetics and equilibrium on the surface of both membranes were studied. The rate of adsorption was adequately modeled by a linearized form of the pseudosecond-order kinetics in all cases. Adsorption isotherms obtained from equilibrium experiments were quite similar, except for the 2-nitrophenol/BW-30 system, which showed a higher maximum adsorption capacity. Experimental adsorption isotherms were compared with Freundlich and Langmuir models; the Langmuir model yields the best fit in all cases, suggesting the formation of a fouling monolayer onto the membrane surface. Organic deposition onto the membrane surface systematically increased hydrophobicity and diminished roughness. A strong graphical correlation was found between the relative flux decline and the organic concentration decrease in the feed. As expected, solute rejection was higher for the RO membrane (BW-30) than for the NF membrane (NF-90); the lowest rejection values were found for 2-nitrophenol. This was attributed to the increase of the solute concentration on the membrane surface due to organic sorption, which enhanced the driving force for diffusion through the membrane.

This study describes the influence of polyethersulfone (PES) sublayers on the performance of polyamide (PA) reverse osmosis membranes. Asymmetric polymeric sublayers were synthesized by using the DIPS technique (Diffusion Induced Phase Separation). Sublayers are optimized mainly with respect to hydrophilicity, permeability and rejection potential by adjusting synthesis procedures. Parameters that were found to have an influence are the type of solvent (DMF and NMP were used), the air humidity, processing time, and concentrations of polymer. By carefully controlling these parameters, it was possible to prepare a range of sublayers with different characteristics, in the ultrafiltration–nanofiltration area. To visualize membrane surface characteristics, both scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements were performed. In addition, titanium (TiO2) nanoparticles were assembled with polyethersulfone (PES) membranes at ultralow concentrations of nanoparticles to characterize TiO2/PES composite membranes and evaluate their permeate flux and solute rejection. Subsequently, a polyamide top layer was added by interfacial polymerization using typical reagents both in the aqueous and in the organic phase. The membrane performance was evaluated in terms of flux and salt rejection. Experimental design was performed in order to obtain the importance of some experimental variables during the polymerisation process. It was found that depending on the type of sublayer used in the procedure, a different membrane performance could be obtained.

Equilibrium adsorption experiments of phenol, 3-chlorophenol, 4-chlorophenol, and 3-nitrophenol aqueous solutions on NF90 membrane were conducted to obtain the corresponding adsorption isotherms at 25 oC. Single-compound solutions with concentration ranging from 0.1 to 8 mmol L− 1 were used. Freundlich and Langmuir models were compared to the experimental isotherms and their characteristic parameters were obtained from linear fits. In addition, the adsorptive behaviour of twelve aqueous phenolic compounds on the NF90 membrane was studied in order to investigate the relationship between adsorption and retention of selected solutes. An inverse correlation between the adsorbed amount, at the same equilibrium concentration (1 mmol L− 1), and retention was found. The influence of the molecular hydrophobicity and dipole moment of phenolic compounds on membrane adsorption, solute retention and water flux decline was also investigated.

The aim of this work is to study the concentration, temperature and pH dependences on retention for phenol and malonic acid single solutions and their mixtures. Crossflow filtration experiments were performed to measure transport of these organic compounds across a commercially available thin-film composite nanofiltration membrane (NF-90) in the temperature range 20–41°C. The influence of the feed solution pH on the rejection of phenol was verified as well. In addition, the contribution of the membrane-solute interactions on solute retention has been established.