Research on catalytic denitrification by zero-valent iron (Fe0) and Pd-Ag catalyst.

This study primarily focused on how to effectively remove nitrate by catalytic denitrification through zero-valent iron (Fe0) and Pd-Ag catalyst. Response surface methodology (RSM), instead of the single factor experiments and orthogonal tests, was firstly applied to optimize the condition parameters of the catalytic process. Results indicated that RSM is accurate and feasible for the condition optimization of catalytic denitrification. Better catalytic performance (71.6% N2 Selectivity) was obtained under the following conditions: 5.1 pH, 127 min reaction time, 3.2 mass ration (Pd: Ag), and 4.2 g/L Fe0, which was higher than the previous study designed by single factor experiments and orthogonal tests, 68.1% and 68.7% of N2 Selectivity, respectively. However, under this optimal conditions, N2 selectivity showed a mild decrease (69.3%), when the real wastewater was used as influent. Further study revealed that cations (K+, Na+, Ca2+, Mg2+, and Al3+) and anions (Cl-, HCO3-, and SO42-) exist in wastewater could have distinctive influence on N2 selectivity. Finally, the reaction mechanism and kinetic model of catalytic denitrification were further studied.

Study on reaction mechanism and Langmuir-Hinshelwood kinetic model of catalytic denitrification by Fe0 and bimetallic catalyst.

The focus of this research was on the catalytic reduction of nitrate to nitrogen gas for the water conservation. Zero-valent iron (Fe0) with bimetallic catalyst that carrier supported palladium (Pd) and copper (Cu) was innovatively applied in this study. First, XPS (X-ray photoelectron spectroscopy) analyses and experiments were conducted to study the mechanism of the catalytic reduction of nitrate. In the catalytic reaction, which is regarded as a stepwise process, Fe0 was the electron provider; Pd and Cu supported on carrier played indispensable but distinct roles. The kinetics suggested that the process was better reflected by first-order kinetics of the Langmuir-Hinshelwood model. Additionally, first-order kinetics of the catalytic reaction under the effect of catalysts with different carriers (SiO2, silica gel, kaolin, diatomite, γ-Al2O3, graphene) were further studied. Pd-Cu/graphene catalyst showed higher catalytic performance compared with other catalysts.

Catalytic reduction of nitrate in secondary effluent of wastewater treatment plants by Fe(0) and Pd-Cu/γ-Al2O3.

Total nitrogen, in which NO3(-) is dominant in the effluent of most wastewater treatment plants, cannot meet the requirements of the Chinese wastewater discharge standard (<15 mg/L), making nitrate (NO3(-)) elimination attract considerable attention. In this study, reductant iron (Fe(0)) and γ-Al2O3 supported palladium-copper bimetallic catalysts (Pd-Cu/γ-Al2O3) were innovatively used for the chemical catalytic reduction of nitrate in wastewater. A series of specific operational conditions (such as mass ratio of Pd:Cu, catalyst amounts, reaction time and pH of solution) were optimized for nitrate reduction in the artificial solution, and then the selected optimal conditions were further applied for investigating the nitrate elimination of secondary effluent of a wastewater treatment plant in Beijing, China. Results indicated that a better catalytic performance (74% of nitrate removal and 62% of N2 selectivity) could be obtained under the optimal condition: 5 g/L Fe(0), 3:1 mass ratio (Pd:Cu), 4 g/L catalyst, 2 h reaction time and pH 5.1. It is noteworthy to point out that nitrogen gas (N2) predominated in the byproducts without another system to treat ammonium and nitrite. Therefore, the chemical catalytic reduction combining Fe(0) with Pd-Cu/γ-Al2O3 could be regarded as a better alternative for nitrate removal in wastewater treatment.

Experimental study on the disinfection efficiencies of a continuous-flow ultrasound/ultraviolet baffled reactor.

A self-designed continuous-flow ultrasound/ultraviolet (US/UV) baffled reactor was tested in this work, and the disinfection efficiency of secondary effluent from a wastewater treatment plant (WWTP) was investigated in terms of the different locations of ultrasonic transducers inside the reactor under similar input power densities and specific energy consumptions. Results demonstrated that the two-stage simultaneous US/UV irradiation in both chambers 2 and 3 at a flow rate of 1200 L/h performed excellent disinfection efficiency. It achieved an average feacal coliforms concentration of 201±78 colony forming unit (CFU)/L in the effluent and an average of (4.24±0.26) log10 reduction. Thereafter, 8 days of continuous operation was performed under such a condition. A total of 31 samples were taken, and all the samples were analyzed in triplicate for feacal coliforms analysis. Experimental results showed that feacal coliforms concentrations remained at about 347±174 CFU/L under the selected optimum disinfection condition, even if the influent concentrations fluctuated from 3.97×10(5) to 3.57×10(6) CFU/L. This finding implied that all effluents of continuous-flow-baffled-reactor with simultaneous US/UV disinfection could meet the requirements of the discharge standard of pollutants for municipal WWTP (GB 18918-2002) Class 1-A (1000 CFU/L) with a specific energy consumption of 0.219 kWh/m(3). Therefore, the US/UV disinfection process has great potential for practical applications.

Comparative research on phosphorus removal by pilot-scale vertical flow constructed wetlands using steel slag and modified steel slag as substrates.

This research mainly focused on the phosphorus removal performance of pilot-scale vertical flow constructed wetlands with steel slag (SS) and modified steel slag (MSS). First, bench-scale experiments were conducted to evaluate the phosphorus adsorption capacity. Results showed that the Langmuir model could better describe the adsorption characteristics of the two materials; the maximum adsorption of MSS reached 12.7 mg/g, increasing by 34% compared to SS (9.5 mg/g). Moreover, pilot-scale constructed wetlands with SS and MSS were set up outdoors. Then, the influence of hydraulic retention time (HRT) and phosphorus concentration in phosphorus removal for two wetlands were investigated. Results revealed that better performance of the two systems could be achieved with an HRT of 2 d and phosphorus concentration in the range of 3-4.5 mg/L; the system with MSS had a better removal efficiency than the one with SS in the same control operation. Finally, the study implied that MSS could be used as a promising substrate for wetlands to treat wastewater with a high phosphorus concentration. However, considering energy consumption, SS could be regarded as a better alternative for substrate when treating sewage with a low phosphorus concentration.