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Abstract Heavy metals (HMs) are highly toxic water pollutants abundant in industrial wastewater. Herein, a bis[3-(trimethoxysilyl)propyl]amine (BTMSPA) cross-linked multiwalled carbon nanotube (MWCNT) nanomaterial (CQACNT) was synthesized by silanization of MWCNT-OH followed by grafting of positively charged quaternary ammonium groups (glycidyl trimethyl ammonium chloride (GTMAC)) by an epoxide ring-opening reaction. The composite membranes were prepared by the incorporation of CQACNT into the poly(ether sulfone) (PES) polymer matrix. The CQACNT-6 composite membrane exhibited a 3.5-fold increase in pure water permeability (PWP; 312.8 L m−2 h−1 bar−1) as compared to the pristine PES (CQACNT-0) membrane (89.6 L m−2 h−1 bar−1). Moreover, the CQACNT-6 composite membrane showed high HM removal rates (Pb: 89.53%; Ni: 90.42%; Cu: 91.43%; Zn: 91.86%) as compared to the CQACNT-0 membrane (Pb: 39.73%; Ni: 40.32%; Cu: 42.52%; and Zn: 43.91%). After 9 treatment cycles, the CQACNT-6 membrane retained up to 87%, and 94% of its initial PWP and initial Cu2+ rejection, respectively, compared to only 58%, and 54%, respectively for pristine CQACNT-0. The positively charged quaternary ammonium groups enhanced the surface features of PES and MWCNTS, resulting in competitive HM removal rates due to the electrostatic repulsion between the HM and the porous membranes, as well as high PWP.

In the light of the spread of treated wastewater use for irrigation, trace heavy metals pose a great risk to humans and aquatic life. An integrated electrochemical-adsorption (i.e. EC-AD) hybrid system was investigated for the removal of iron (Fe), zinc (Zn), and copper (Cu) traces from synthetic wastewater mimicking industrial wastewater. Slag, a by-product produced in steel industries, was utilized as the adsorbent. The performance of the EC-AD hybrid system was evaluated at mass to wastewater volume ratio (i.e. M/V) ranging from 0.01 to 0.07 g/mL, current density (CD) ranging between 5 and 15 A/m2 and treatment time ranging between 60 and 120 minutes. Furthermore, process kinetics (pseudo-first-order, pseudo-second-order, Elovich, adsorption kinetic models, and Weber-Morris intraparticle diffusion), and adsorption isotherms (Langmuir and Freundlich) were investigated to provide adsorption mechanisms that reflect the interaction between EC and AD processes in the hybrid system. The results indicated that Freundlich isotherm was able to fit the linearized data points compared to Langmuir with Fe and Zn. In addition, kinetic models suggested chemisorption as the predominant removal mechanism of Fe, Zn, and Cu using slag for the EC-AD system. Results showed that the use of EC-AD significantly enhanced the removal efficiency of heavy metal traces from wastewater, reaching 99%.

The discharge of large volumes of oily wastewaters without sufficient treatment poses a huge risk on the environment. The main objective of this study was to investigate the capability of electro-coagulation/flotation (ECF) process for the removal of oil from industrial oily wastewater via different electrodes' configuration. These included anode-cathode-anode-cathode (ACAC), anode-cathode-cathode-anode (ACCA), and cathode-anode-anode-cathode (CAAC) electrode configurations. The impact of other operational conditions such as treatment time (30, 60, and 90 min), current density (50, 100 and 200 A/m2), and initial pH (4, 7, 10) was also investigated. Results showed that the up to 30.3% increase in oil removal can be achieved by optimizing the treatment time in the ACCA configuration. Similarly, it was found that operating at higher CD higher than 100 A/m2 resulted in a minor increase in oil removal in the same configuration. Optimal oil removal efficiency of 82% was achieved when the ECF system operated at a current density 100 A/m2, a treatment time of 90 min, an initial wastewater pH of 7, and using ACAC electrodes' configuration. An operational electrical energy consumption of 3.4 kWh/m3 and a treatment cost of USD 0.26/m3 were also reported for this configuration. It was concluded that oil removal using ECF process are very sensitive to changes in the electrode configuration, and an optimum configuration can be chosen by considering the time and cost of treatment.