Adsorptive performance of activated carbon reused from household drinking water filter for hexavalent chromium-contaminated water

Powdered activated carbon blocks (PACBs) are waste products obtained from household drinking water purification systems. In this study, we demonstrate that they can be used as adsorbents for the cost-effective and environmentally benign removal of hexavalent chromium (Cr(VI)) from contaminated-water and rinse electroplating wastewater. To evaluate Cr(VI) sorption onto the PACB, studies on equilibrium, kinetics, and thermodynamics were performed using batch mode experiments. The experimental results indicated that Cr(VI) ions were efficiently adsorbed under acidic conditions (i.e., at initial pH below 3) and low initial Cr(VI) concentrations. The adsorptive behaviors of the PACB for Cr(VI) were well explained by the Langmuir isotherm, as well as pseudo-second-order kinetic models, suggesting that a Cr(VI) monolayer was adsorbed onto the PACB surface via chemisorption. The maximum adsorption capacity of Cr(VI) onto the PACB was determined to be 6.207 mg/g. The results of thermodynamic studies revealed that the adsorption process of Cr(VI) onto PACB was endothermic and non-spontaneous. Additionally, analysis of the PACB after Cr(VI) adsorption at an initial pH of 2 using scanning electron microscopy, energy dispersive spectrometry, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) revealed that the interaction between the surface oxygenic functional groups on the PACB and Cr(VI) was primarily responsible for Cr(VI) sorption via surface complexation and electrostatic interactions. Based on the result of XPS analysis, the presence of trivalent chromium on the PACB surfaces indicated that some synergistic redox reactions involving Cr(VI) could have occurred during the sorption process. Although a commercially available powdered activated carbon outperformed the PACB adsorbent with respect to Cr(VI) removal from wastewater, complete Cr(VI) adsorption could be achieved using relatively large quantities of the PACB. These findings indicate that the PACB adsorbent could be used as a cheap and efficient material for the removal of Cr(VI) from wastewater.

Performance of dissolved organic matter removal from membrane bioreactor effluent by magnetic powdered activated carbon

Magnetic powdered activated carbon (Mag-PAC) was successfully developed and applied as an adsorbent for dissolved organic matter (DOM) removal from the effluent of a membrane bioreactor (MBR) using batch experiments. The results show that a coating of iron oxide particles is consistently distributed on the surface of powdered activated carbon (PAC), resulting in a decrease in the specific surface area and in the pH at the point of zero charge, even though the particle sizes of Mag-PAC and PAC were similar. A Mag-PAC dosage of 4 g/L exhibited efficient and fast DOM adsorption with a relatively short contact time of 5 min. The iron oxide coating on the surface of PAC may play an important role in the DOM removal efficiency. Temkin isotherm and pseudo-second order kinetic models well described the DOM adsorption, suggesting that the adsorption of DOM onto Mag-PAC could be mainly governed by a chemisorption mechanism. Humic acid- and fulvic acid-like compounds and aromatic DOM with molecular weights (MWs) between 2610 Da and 3030 Da were efficiently removed by Mag-PAC, whereas aromatic DOM with an MW of 1760 Da was poorly removed. Our results demonstrate that the application of Mag-PAC for DOM adsorption is attractive and yields benefits as a posttreatment system for MBR effluent due to its efficient and fast DOM adsorption.