Valorization of thermally hydrolyzed sludge with clay for sintering of ceramic tiles.

The disposal of wastewater sludge is one of the most challenging environmental problems for large cities. Wastewater sludge may be utilized as a feasible substitute for clay to sinter ceramics, given their similar mineralogical composition. However, the organics in sludge will be wasted, while their release during sintering will leave cracks in the ceramic products. In this research, after the thermal treatment for effective organic recovery, the thermally hydrolyzed sludge (THS) is incorporated with clay for the sintering of construction ceramics. The experimental results showed that a THS dosing ratio up to 40 % can be achieved for mixing with montmorillonite clay to make ceramic tiles. The sintered tiles (THS-40) had an intact shape and structure, and the tile performance was close to that made from single montmorillonite (THS-0), with water absorption of 0.4 % vs. 0.2 %, compressive strength of 136.8 vs. 140.7 MPa, and undetected heavy metal leaching. Further addition of THS would lead to a considerable deterioration of the quality of the tiles to a compressive strength of as low as 5.0 MPa for the THS only product (THS-100). Comparing with the tiles incorporated with raw sludge (RS-40), the THS-40 tiles had a more intact and denser structure with a 10 % improved compressive strength. Cristobalite, aluminum phosphate, mullite, and hematite dominated in the THS-born ceramics, which are typical components of ceramics, and the amount of hematite increased with the THS dosing ratio. Sintering at a high temperature of 1200 °C enabled efficient phase transformation from quartz to cristobalite and from muscovite to mullite, which ensured the toughness and compactness of the THS-born ceramic tiles.

Fabrication of a permeable SnO2-Sb reactive anodic filter for high-efficiency electrochemical oxidation of antibiotics in wastewater.

Electrochemical oxidation (ECO) is an appealing technology for treating emerging organic pollutants in wastewater. However, the conventional flow-by ECO process is expensive with a low energy efficiency owing to the limitations of mass transport of contaminants to the limited surface area of the anode. In this study, a novel freestanding porous and permeable SnO2-Sb anode was fabricated by one-step sintering using micrometer-sized (NH4)2CO3 grains as the pore-forming agents. This permeable SnO2-Sb anode without Ti substrate functioned as a reactive anodic filter (RAF) in an ECO cell to treat wastewater containing ciprofloxacin (CIP). Forcing the wastewater through the porous RAF depth-wise improved the mass transport and vastly enlarged the electroactive surface area. Compared with the conventional flow-by configuration, the flow-through RAF exhibited a 12-fold increase in the mass transfer rate constant (60.7 × 10-6 m s-1) and a 5-fold increase in the CIP degradation rate constant (0.077 min-1). At a cell potential of 4.0 V, more than 92% of the CIP was degraded in a single-pass operation at a filtration flux of 54 L m-2 h-1 and a short retention time of 1.7 min through the RAF. The robustness and stability of the RAF were demonstrated by its remarkable CIP degradation efficacy of 99% during 200 h of operation. The mechanism of CIP degradation was examined using probe molecules and density functional theory calculations and found to be a combined effect of direct electron transfer and oxidation by generated radicals (OH and SO4-). The great potential of RAF in flow-through ECO was further validated by its effective removal (>92%) of various organic pollutants in actual municipal wastewater at a low energy consumption of 0.33 kWh m-3. The RAF-based ECO process thus provides an advanced environmental technology for the oxidation of toxic and recalcitrant organic pollutants in wastewater treatment.

Factors and mechanisms that influence the reactivity of trivalent copper: A novel oxidant for selective degradation of antibiotics.

Trivalent copper complexes are active intermediates in aquatic redox reactions that involve copper ions or structural copper, but their reactivity and selectivity toward pollutants remain unknown. We characterized copper(III) periodate, a representative trivalent copper compound, with phenol and several antibiotics as model contaminants. The results show that Cu(III) is highly reactive to phenol degradation; near-complete degradation was achieved after 10 min at a molar ratio of 3:1 (Cu[III]: phenol). Common alcohols, including methanol and 2-propanol, showed pH-dependent reactivity for Cu(III). In contrast to aquo trivalent copper ions that react rapidly with tert-butanol, Cu(III) showed limited reactivity toward tert-butanol. A mechanistic investigation showed that the degradation was caused by direct oxidation by Cu(III) and that no hydroxyl radicals were involved. Common water components such as chloride ions did not influence the reaction, which suggests that the use of Cu(III) may help mitigate the generation of chlorinated products. As a one-electron oxidant, Cu(III) showed high reactivity to degrade electron-rich compounds; the concentrations of sulfamethazine, sulfamethoxazole, and sulfadiazine (100 µg/L) were reduced to 1.8, 7.5, and 42.5 ng/L, respectively, after 2 min of reaction with 10 µM Cu(III). These results demonstrate a novel and highly efficient oxidant for selective removal of ubiquitous micropollutants from water bodies.

Supported palladium nanoparticles as highly efficient catalysts for radical production: Support-dependent synergistic effects.

Supported metallic palladium (Pd) acts as a real catalyst for peroxymonosulfate (PMS) activation to produce highly oxidizing species. However, the species produced are surface-bound in nature, and their use for pollutant degradation requires an inert supporting material to minimize the surface scavenging effect. In this study, we synthesized Pd nanoparticles (NPs) on different supporting materials (Al2O3, TiO2, SiO2, g-C3N4, C, and TiC), and compared their reactivity toward PMS activation for the first time. Experiments with 1,4-dioxane as a target pollutant showed that Pd/SiO2 had the highest reactivity of degrading 1,4-dioxane under acidic and neutral conditions, potentially due to the active interaction between SiO2 and PMS. However, Pd/Al2O3 had the greatest value of around 107% in the conversion of PMS to radicals. The ready oxidation of methanol to formaldehyde and degradation of 1,4-dioxane suggest that the activation of PMS by all the supported Pd NPs proceeded via a radical mechanism. These findings are critical to the development of efficient composite catalysts and the scientific understanding of observing different active species produced by Pd-catalyzed PMS.

Facile and effective synthesis of adsorbent - utilization of yeast cells immobilized in sodium alginate beads for the adsorption of phosphorus in aqueous solution.

We compared the adsorption efficiency of phosphates onto Ca-alginate immobilized yeast and freely suspended yeast under different conditions of pH and temperature. The results clearly demonstrated that the adsorption efficiency onto Ca-alginate immobilized yeast was better than that of freely suspended yeast, and reached a maximum at pH 9.17 and 35 °C. Scanning electron microscopy was used to characterize the morphology of Ca-alginate immobilized yeast. Fitting the adsorption equilibrium data to existing models showed that the Freundlich isotherm model described the process better than the Langmuir model, and the process of adsorption followed pseudo-first-order kinetics. During the initial period of experiment, external diffusion was a key rate-controlling step, and intraparticle diffusion also contributed to the mass transport. The thermodynamic properties (Gibbs free energy change of -15.143 kJ/mol, enthalpy change of 274.118 kJ/mol, and entropy change of 290 J/(mol K)) indicated that the adsorption process was endothermic.