Freezing-Induced Simultaneous Reduction of Chromate and Production of Molecular Iodine: Mechanism, Kinetics, and Practical Implications.

A new method for the concurrent treatment of Cr(VI)-contaminated wastewater and production of the useful I2 chemical was developed. The method is based on the redox reaction between Cr(VI) and I- that occurs when an aqueous wastewater solution containing Cr(VI) and I- is frozen, producing I2 and allowing for the effective removal of Cr. The redox reaction occurs primarily because of the accumulation of Cr(VI), I-, and protons in the ice grain boundaries formed during freezing (i.e., the freeze concentration effect). This effect was verified by confocal Raman spectroscopy and the experiments varying I- concentration and pH. The reduction of Cr(VI) (20 µM) was near complete after freezing at I- concentrations ≥ 100 µM, pH ≤ 3.0, and temperatures ≤ -10 °C. The freezing method (liquid cooling vs air cooling) had little effect on the final Cr(VI) reduction efficiency but had a significant effect on the Cr(VI) reduction rate. The freezing method was also tested with Cr(VI)-contaminated electroplating wastewater samples, and simultaneous Cr(VI) reduction and I2 production proceeded rapidly in a frozen solution but was not observed in an aqueous solution. Additionally, other substances in electroplating wastewater did not reduce the rate and final efficiency of Cr(VI) reduction and I2 production. Therefore, the freezing/Cr(VI)/I- system can be considered a feasible approach to water-energy nexus technology for simultaneous I2 production and Cr(VI)-contaminated wastewater treatment.

Optimizing an airborne mass-balance methodology for accurate emission rate quantification of industrial facilities: A case study of industrial facilities in South Korea.

Accurate estimation of emissions from industrial point sources is crucial in understanding the effectiveness of reduction efforts and establishing reliable emission inventories. In this study, we employ an airborne Chemical Ionization Mass Spectrometry (CIMS) instrument to quantify sulfur dioxide (SO2) emissions from prominent industrial facilities in South Korea, including power plants, a steel mill, and a petrochemical facility. Our analysis utilizes the box mass balance technique to derive SO2 emissions and associated uncertainty. We evaluate the interpolation methods between 2D kriging and 3D radial basis function. The results demonstrate that the total uncertainty of the box mass balance technique ranges from 5 % to 28 %, with an average of 20 %. Mixing ratio ground extrapolation from the lowest altitude of the airborne sampling to the ground emerges as the dominant source of uncertainty, followed by the determination of the boundary layer height. Adequate sampling at multiple altitudes is found to be essential in reducing the overall uncertainty by capturing the full extent of the plume. Furthermore, we assess the uncertainty of the single-height transect mass balance method commonly employed in previous studies. Our findings reveal an average precision of 47 % for this method, with the potential for overestimating emissions by up to 206 %. Samplings at fewer altitudes or with larger altitude gaps increase the risk of under-sampling and elevate method uncertainties. Therefore, this study provides a quantitative basis to evaluate previously airborne observational emission constraints.