Pd/Fe bimetallic particles were synthesized by chemical deposition and used to remove absorbable organic halogens (AOX) in the activated sludge of a chemical dyestuff wastewater treatment plant. Bath experiments demonstrated that the Pd/Fe bimetallic particles could effectively remove AOX. It indicated several factors, such as Pd loading, the amount of Pd/Fe used, initial activated sludge pH, and reaction time, which could affect the removal effect. The results showed that increasing the Pd content in Pd/Fe particles, from 0.01 to 0.05 wt %, significantly increased the removal efficiency of AOX in activated sludge. The Pd/Fe particles had a much higher removal efficiency of AOX in the activated sludge than bare Fe particles. A slightly acidic condition with a Pd content of 0.05% and 10 g/L of Pd/Fe was beneficial to the process of removing AOX in activated sludge. In detail, the removal efficiency of AOX in the activated sludge could reach 50.7% after 15 days of reaction with 10 g/L of Pd/Fe (Pd loading 0.05 wt %) and at an initial pH of 6.0 during the experiments. It also showed that the control samples without Fe0and Fe/Pd additions only removed 7.9% of AOX under the same conditions. Meanwhile, the concentrations of AOX in the supernatant of activated sludge were lower than the initial AOX concentration in the supernatant during the activated sludge remediation with Pd/Fe bimetallic particles. The results indicated that the AOX removal from the activated sludge matrix might be mainly due to the Pd/Fe bimetallic particles, and not just by phase transfer.
Jinkui Zhong,Xinyue Zhou,Caiya Zhu,Yin Zhang,Jiawen He,Yuanhu Gao,Liguo Wang
2,4-dichlorophenol (2,4-DCP) is a toxic and harmful organic intermediate widely used in industrial production. Recently, the utilization of nano-zero-valent iron (NZVI) for 2,4-DCP treatment has gained significant popularity, but the deactivation and agglomeration of NZVI always appear and continue to present challenges. To address these issues, sodium carboxymethyl cellulose (CMC) and noble metal catalyst Pd are used as stabilizers to improve the removal efficiency of NZVI on 2,4-DCP. The CMC-modified nanoscale Pd/Fe bimetal (CMC-Pd/Fe) particles were prepared by the liquid phase reduction method and characterized by scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The results showed that the addition of Pd and CMC succeeded in ameliorating the aggregation of NZVI. A five-level-four-factor central composite design (CCD) of response surface methodology (RSM) was used to optimize the removal of 2,4-DCP by CMC-Pd/Fe and explored the factors influencing the removal of 2,4-DCP, including the amount of catalyst, the initial pH of the system, the time of reaction, and the initial concentration of 2,4-DCP. A statistically significant and well-fitting quadratic regression model was successfully constructed to predict 2,4-DCP removal efficiency. The high F -value of 14.35, very low p- value (<0.0001), nonsignificant Lack of Fit, and appropriate coefficient of determination of 0.9399 demonstrate a good correlation between the experimental and predicted values of the proposed model. The analyses of variance reveal catalyst amount and reaction time have a positive effect on the removal efficiency of 2,4-DCP and the CMC-Pd/Fe catalyst amount shows the most apparent significance, with PC (percent contribution) greater than 26. Conversely, pH and 2,4-DCP concentration have a negative impact on the removal process. The optimum condition is 1.10 g/L of catalyst amount, 5.63 of pH, 2.31 h of reaction time, and 20 mg/L of initial 2,4-DCP concentration. The validation results from parallel experiments showed that the average removal efficiency of 2,4-DCP reached 96.32% under the optimal conditions.
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