The treatment of real dyeing wastewater by the electro-Fenton process using drinking water treatment sludge as a catalyst.

This study aims to evaluate the performance of the electro-Fenton process (EFP) using drinking water treatment sludge (DWTS) for the treatment of dyeing wastewater. Effects of operating parameters including pH, electrode distance, applied voltage, operation temperature and time on the electro-Fenton-oxidation of dyeing wastewater were investigated. The decolorization and COD degradation efficiencies of 97.8% and 89.8%, respectively, were achieved indicating almost complete mineralization of organic pollutants after 90 minutes of reaction at pH 4.0, dosage of DWTS of 2.0 g, applied voltage of 20.0 V, electrode distance of 3.0 cm and ambient temperature. The morphology of the sludge and presence of Fe(OH)3 after Fenton-oxidation were investigated to understand the mechanisms involved. The degradation of COD in EFP was found to fit well the pseudo-first-order kinetic model. The thermodynamic constants of the Fenton oxidation process were also determined and showed that the Fenton-oxidation process was spontaneous and endothermic. This study provides an efficient and low-cost method for the degradation of non-biodegradable pollutants in dyeing wastewater to solve waste using waste.

Characteristics and mechanisms of cadmium adsorption onto biogenic aragonite shells-derived biosorbent: Batch and column studies.

Calcium carbonate (CaCO3)-enriched biomaterial derived from freshwater mussel shells (FMS) was used as a non-porous biosorbent to explore the characteristics and mechanisms of cadmium adsorption in aqueous solution. The adsorption mechanism was proposed by comparing the FMS properties before and after adsorption alongside various adsorption studies. The FMS biosorbent was characterized using nitrogen adsorption/desorption isotherm, X-ray diffraction, scanning electron microscopy with energy dispersive spectroscopy, Fourier-transform infrared spectroscopy, and point of zero charge. The results of batch experiments indicated that FMS possessed an excellent affinity to Cd(II) ions within solutions pH higher than 4.0. An increase in ionic strength resulted in a significant decrease in the amount of Cd(II) adsorbed onto FMS. Kinetic study demonstrated that the adsorption process quickly reached equilibrium at approximately 60 min. The FMS biosorbent exhibited the Langmuir maximum adsorption capacity as follows: 18.2 mg/g at 10 °C < 26.0 mg/g at 30 °C < 28.6 mg/g at 50 °C. The Cd(II) adsorption process was irreversible, spontaneous (-ΔG°), endothermic (+ΔH°), and more random (+ΔS°). Selective order (mmol/g) of metal cations followed as Pb2+ > Cd2+ > Cu2+ > Cr3+ > Zn2+. For column experiments, the highest Thomas adsorption capacity (7.86 mg/g) was achieved at a flow rate (9 mL/min), initial Cd(II) concentration (10 mg/L), and bed height (5 cm). The Cd(II) removal by FMS was regarded as non-activated chemisorption that occurred very rapidly (even at a low temperature) with a low magnitude of activation energy. Primary adsorption mechanism was surface precipitation. Cadmium precipitated in the primary (Cd,Ca)CO3 form with a calcite-type structure on the FMS surface. A crust of rhombohedral crystals on the substrate was observed by SEM. Freshwater mussel shells have the potential as a renewable adsorbent to remove cadmium from water.