RESUMEN
Odorous dioxanes and dioxolanes, a class of cyclic acetals often produced as byproducts in polyester resin manufacturing, are problematic in drinking water treatment due to their low odor thresholds and resistance to conventional treatment technology. Our research focuses on the removal of ten dioxane/dioxolane compounds through oxidation and adsorption processes, exploring the key molecular properties that govern the treatmentability. We discovered that both chlorination and permanganate oxidation were largely ineffective at degrading cyclic acetals, achieving less than 20% removal even at high applicable doses. Conversely, powdered activated carbon (PAC) adsorption proved to be a more effective method, with a removal of > 90% at a PAC dosage of 10 mg/L for seven out of ten compounds. The presence of natural organic matter (NOM) reduced PAC adsorbability for all odorants, but the deterioration level substantially varied and mostly affected by structural flexibility as indicated by the number of rotatable bonds. The results of both the experimental investigation and molecular simulation corroborated the hypothesis that more rotatable bonds (from one to three here) are indicative of greater structural flexibility, which in consequence determines the susceptibility of cyclic acetals to NOM competitive adsorption. Increased structural flexibility could facilitate greater entry into silt-like micropores or achieve preferential adsorption sites with more compatible morphology against NOM competition. When pre-oxidation (chlorination and permanganate oxidation) and adsorption were applied sequentially, additional low molecular weight NOM components produced by pre-oxidation resulted in intensified NOM competition and decreased odorant adsorbability. If this combination is inevitably required for algae and odorant control, it would be beneficial to utilize a wise screen for oxidants and a reduced oxidant dose (less than 2 mg/L) to mitigate the deterioration of odorant adsorption. This study elucidates the roles of structural flexibility in influencing the treatability of dioxanes and dioxolanes, extending beyond the solely well-established effects of hydrophobicity. It also presents rational practice guidelines for the combination of pre-oxidation and adsorption in addressing odor incidents associated with dioxane and dioxolane compounds.
RESUMEN
Odor problems associated with H2S emissions often result in odor complaints from nearby residents of C&D debris landfills, especially in the early morning. As part of a field study conducted on H2S removal ability using different cover materials, daily and seasonal H2S emissions through a soil cover layer were monitored at a C&D debris landfill to investigate factors affecting H2S emissions. H2S emission rates were not a constant, but varied seasonally, with an average emission rate of 4.67×10(-6)mgm(-2)s(-1). During a the 10-month field study, as the H2S concentration increased from 140ppm to about 3500ppm underneath the cover soil in the testing cell, H2S emissions ranged from zero to a maximum emission rate of 1.24×10(-5)mgm(-2)s(-1). Continuous emission monitoring indicated that H2S emissions even changed over time throughout the day, generally increasing from morning to afternoon, and were affected by soil moisture and temperature. Laboratory experiments were also conducted to investigate the effects of H2S concentration and cover soil moisture content on H2S emissions. The results showed that increased soil moisture reduced H2S emissions by retarding H2S migration through cover soil and dissolving H2S into soil water. The field study also indicated that due to atmospheric dispersion, high H2S emissions may not cause odor problems.