No abstract

Fly ash (FA) produced during municipal solid waste incineration contains hazardous polycyclic aromatic hydrocarbons (PAHs). Hydrothermal treatment (HT), a promising technology for the degradation of organic compounds, was applied in this study for hydrothermal detoxification of PAHs in FA. Due to different levels of Ca/(Si + Al) and Al/(Si + Al) molar ratios achieved by adjusting the SiO2 and Al2O3 added to FA, different kinds of aluminosilicate minerals were formed and different detoxification efficiencies of PAHs were observed in HT products. For aluminosilicate minerals formed at lower (0.17) and moderate (0.51) Al/(Si + Al) ratio levels, tobermorite was obtained and it enhanced with the decrease of Ca/(Si + Al) ratio levels. At higher Al/(Al + Si) ratio levels of 0.71, tobermorite cannot be synthesized completely even when the Ca/(Si + Al) ratio for FA-30-3 (1.01) was low and in the suitable range for tobermorite formation (0.67–1.20). Compared with the Ca/(Si + Al) ratio, the Al/(Si + Al) ratio not only affected the synthesis of tobermorite but also had much more significant influence on both the removal percentage of the concentration of PAHs and the removal percentage of the toxicity equivalent quality (TEQ) of PAHs. Attributing to the fact that tobermorite cannot be synthesized at higher Al/(Al + Si) ratio levels of 0.71, the weakest detoxification efficiency of PAHs was observed. When tobermorite was effectively synthesized in FA-30-1, for which both the Ca/(Al + Si) and Al/(Al + Si) ratios were in the suitable range for tobermorite formation [Ca/(Al + Si) ratio = 0.67–1.20 and Al/(Al + Si) ratio = 0–0.22], the best detoxification efficiency of PAHs was achieved. The formation of tobermorite affected by the Ca–Si–Al element proportion during the HT process has a positive effect on the detoxification of PAHs in FA. The results of regression analysis performed for investigating the relationship between the content of minerals formed and the detoxification efficiency of PAHs showed that the formation of tobermorite is helpful to promote the detoxification of PAHs but the existence of hydrocalumite reduced the detoxification. Compared with the Ca/(Si + Al) ratio, the Al/(Si + Al) ratio has more significant influence on the formation of tobermorite and hydrocalumite.

The aim of this research was to study the effect of temperature on the adhesion and disinfection activities of an Ag+-doped BiVO4 (Ag+/BiVO4) coating. Ag+/BiVO4 was prepared by a sol–gel method, and spraying was used as the deposition method of coating. X-ray diffraction patterns showed that the monoclinic scheelite phase of the samples was unchanged by annealing at 450–650 °C. Scanning electron microscopy results showed that, at high temperatures, the particles melted and formed a dense coating, and the roughness of the coating decreased after initially increasing. The adhesion and disinfection activities were evaluated by ASTM D3359-08 and disinfection experiments. The results showed that the samples modified by silver had a good disinfection activity when annealed in the range of 450–650 °C. The adhesion increased upon increasing the annealing temperature. The sample annealed at 650 °C showed the best coating adhesion and completely killed Escherichia coli, Staphylococcus aureus, Shigella, and Salmonella after 2 h of visible-light irradiation.