Time-integrative passive sampling of volatile organic compounds (VOCs) in water can now be accomplished using a solid ceramic dosimeter. A nonporous ceramic, which excludes the permeation of water, allowing only gas-phase diffusion of VOCs into the resin inside the dosimeter, effectively captured the VOCs. The mass accumulation of 11 VOCs linearly increased with time over a wide range of aqueous-phase concentrations (16.9 to 1100 μg L), and the linearity was dependent upon the Henry's constant (H). The average diffusivity of the VOCs in the solid ceramic was 1.46 × 10 m s at 25 °C, which was 4 orders of magnitude lower than that in air (8.09 × 10 m s). This value was 60% greater than that in the water-permeable porous ceramic (0.92 × 10 m s), suggesting that its mass accumulation could be more effective than that of porous ceramic dosimeters. The mass accumulation of the VOCs in the solid ceramic dosimeter increased in the presence of salt (≥0.1 M) and with increasing temperature (4 to 40 °C) but varied only slightly with dissolved organic matter concentration. The solid ceramic dosimeter was suitable for the field testing and measurement of time-weighted average concentrations of VOC-contaminated waters.

Environmental contextWastewater contains various substances such as sulfur-containing chemicals and heavy metals including mercury ions. Several technologies have been developed to trap mercury ions; however, mercury can undergo reactions with sulfite and change to its vapour form, which easily escapes to the atmosphere. Here, we devised a model to predict the formation of vapour-phase mercury as a function of sulfite concentration, temperature and water acidity based on coal-fired power plant wastewater. AbstractThe re-emission of mercury (Hg) as a consequence of the formation and dissociation of the unstable complex HgSO3 is a problem encountered in flue gas desulfurisation treatment in coal-fired power plants. A model following a pseudo-second-order rate law for Hg2+ reduction was derived as a function of [SO32–], [H+] and temperature and fitted to experimentally obtained data to generate kinetics rate values of 0.120±0.04, 0.847±0.07, 1.35±0.4mM–1 for 40°C, 60°C and 75°C respectively. The rate of reduction of Hg2+ increases with a temperature increase but shows an inverse relationship with proton concentration. Plotting the model-fit kinetics rate constants yields ΔH=61.7±1.82 kJ mol–1, which is in good agreement with literature values for the formation of Hg0 by SO32–. The model could be used to better understand the overall Hg2+ re-emission due to SO32– happening in aquatic systems such as flue gas desulfurisation wastewaters.

a b s t r a c t. In the presence of 0.1-10 mg/L DOC, the rates varied between 0.026 and 0.1 m -2 min -1 . Modeling studies showed that the increase of pH and NaCl concentrations and the decrease of DOC levels increased surface-mediated Hg 2+ reduction rate. Higher pH seemed to increase the reduction rates and this was attributed to the enhanced adsorption of Hg 2+ to ZVI surface at higher pH. The Cl -undergoes strong complexation with Hg 2+ (i.e., HgCl + , HgCl 2 , and HgCl 3 -) and prevent the adsorption of Hg 2+ to Fe 0 surface and subsequent reduction. However, the enhanced corrosion and greater release of Fe 2+ by the pitting corrosion process in the presence of Cl -affected the overall Hg 2+ reduction far more significantly, hence, increased Hg 2+ reduction was observed in the presence of Cl -in solution. The DOC seemed not only to decrease the reactivity of Hg 2+ by rendering strong complexation but also to prevent the adsorption of Hg 2+ to the Fe 0 surfaces thus inhibiting surface reduction.