Prediction of Fenton oxidation positions in polycyclic aromatic hydrocarbons by Frontier electron density

Five recalcitrant polycyclic aromatic hydrocarbons (PAHs) in ethanol were subjected to Fenton oxidation, and following GC-MS identification of respective oxidation products, their oxidation positions were compared to those predicted by Frontier electron density. Quinone forms of oxidation products were identified in each PAH. With the exception of fluorene, oxidation positions of quinone forms of products of acenaphthylene, anthracene, benz(a)anthracene, and benzo(a)pyrene corresponded with predicted positions in which Frontier electron density was high. From these results, it appears that determining the Frontier electron density of a PAH is a promising method for predicting the Fenton oxidation position.     

Degradation of 1,4-dioxane in water with heat- and Fe2+-activated persulfate oxidation

This research investigated the 1,4-dioxane (1,4-D) degradation efficiency and rate during persulfate oxidation at different temperatures, with and without Fe²⁺ addition, also considering the effect of pH and persulfate concentration on the oxidation of 1,4-D. Degradation pathways for 1,4-D have also been proposed based on the decomposition intermediates and by-products. The results indicate that 1,4-D was completely degraded with heat-activated persulfate oxidation within 3–80 h. The kinetics of the 1,4-D degradation process fitted well to a pseudo-first-order reaction model. Temperature was identified as the most important factor influencing the 1,4-D degradation rate during the oxidation process. As the temperature increased from 40 to 60 °C, the degradation rate improved significantly. At 40 °C, the addition of Fe²⁺ also increased the 1,4-D degradation rate. Interestingly, at 50 and 60 °C, the 1,4-D degradation rate decreased slightly with the addition of Fe²⁺. This reduced degradation rate may be attributed to the rapid conversion of Fe²⁺ to Fe³⁺ and the production of an Fe(OH)₃ precipitate which limited the ultimate oxidizing capability of persulfate with Fe²⁺ under higher temperatures. Higher persulfate concentrations led to higher 1,4-D degradation rates, but pH adjustment had no significant effect on the 1,4-D degradation rate. The identification of intermediates and by-products in the aqueous and gas phases showed that acetaldehyde, acetic acid, glycolaldehyde, glycolic acid, carbon dioxide, and hydrogen ion were generated during the persulfate oxidation process. A carbon balance analysis showed that 96 and 93 % of the carbon from the 1,4-D degradation were recovered as by-products with and without Fe²⁺ addition, respectively. Overall, persulfate oxidation of 1,4-D is promising as an economical and highly efficient technology for treatment of 1,4-D-contaminated water.     

Pyrolysis of tetrabromobisphenol-A containing paper laminated printed circuit boards

Tetrabromobisphenol-A (TBBA) is the most common brominated fire retardant. In this study, a TBBA containing paper laminated printed circuit board (PCB) prepared from novolac was pyrolysed by both TGA and in a quartz glass reactor between 40 and 1,000 degrees C. The products were online detected by MS. It was found that the PCB degraded in three steps. Step one (<270 degrees C) consisted of the evolution of water and CO(2) from the paper laminate. In the second step, between 270 and 370 degrees C, the fire retardant decomposed, releasing HBr and brominated aromatics. In the third step, at temperatures above 370 degrees C, the phenol resin decomposed and char was formed. Compared to pure TBBA, which mainly produces brominated phenols, the brominated products enclosed in the char released HBr during the last degradation step as well as during the second step. Most of the bromine left the resin in the form of HBr, with about 14% of the bromine being fixed in brominated aromatics and less than 2% remaining in the residue.     

Determining storm sampling requirements for improving precision of annual load estimates of nutrients from a small forested watershed

This study sought to determine the lowest number of storm events required for adequate estimation of annual nutrient loads from a forested watershed using the regression equation between cumulative load (∑L) and cumulative stream discharge (∑Q). Hydrological surveys were conducted for 4 years, and stream water was sampled sequentially at 15-60-min intervals during 24 h in 20 events, as well as weekly in a small forested watershed. The bootstrap sampling technique was used to determine the regression (∑L-∑Q) equations of dissolved nitrogen (DN) and phosphorus (DP), particulate nitrogen (PN) and phosphorus (PP), dissolved inorganic nitrogen (DIN), and suspended solid (SS) for each dataset of ∑L and ∑Q. For dissolved nutrients (DN, DP, DIN), the coefficient of variance (CV) in 100 replicates of 4-year average annual load estimates was below 20% with datasets composed of five storm events. For particulate nutrients (PN, PP, SS), the CV exceeded 20%, even with datasets composed of more than ten storm events. The differences in the number of storm events required for precise load estimates between dissolved and particulate nutrients were attributed to the goodness of fit of the ∑L-∑Q equations. Bootstrap simulation based on flow-stratified sampling resulted in fewer storm events than the simulation based on random sampling and showed that only three storm events were required to give a CV below 20% for dissolved nutrients. These results indicate that a sampling design considering discharge levels reduces the frequency of laborious chemical analyses of water samples required throughout the year.