Effects of UV 254 irradiation on residual chlorine and DBPs in chlorination of model organic-N precursors in swimming pools

Ultraviolet (UV) irradiation is commonly applied as a secondary disinfection process in chlorinated pools. UV-based systems have been reported to yield improvements in swimming pool water and air chemistry, but to date these observations have been largely anecdotal. The objectives of this investigation were to evaluate the effects of UV irradiation on chlorination of important organic-N precursors in swimming pools.Creatinine, L-arginine, L-histidine, glycine, and urea, which comprise the majority of the organic-N in human sweat and urine, were selected as precursors for use in conducting batch experiments to examine the time-course behavior of several DBPs and residual chlorine, with and without UV₂₅₄ irradiation. In addition, water samples from two natatoria were subjected to monochromatic UV irradiation at wavelengths of 222 nm and 254 nm to evaluate changes of liquid-phase chemistry. UV₂₅₄ irradiation promoted formation and/or decay of several chlorinated N-DBPs and also increased the rate of free chlorine consumption. UV exposure resulted in loss of inorganic chloramines (e.g., NCl₃) from solution. Dichloromethylamine (CH₃NCl₂) formation from creatinine was promoted by UV exposure, when free chlorine was present in solution; however, when free chlorine was depleted, CH₃NCl₂ photodecay was observed. Dichoroacetonitrile (CNCHCl₂) formation (from L-histidine and L-arginine) was promoted by UV₂₅₄ irradiation, as long as free chlorine was present in solution. Likewise, UV exposure was observed to amplify cyanogen chloride (CNCl) formation from chlorination of L-histidine, L-arginine, and glycine, up to the point of free chlorine depletion. The results from experiments involving UV irradiation of chlorinated swimming pool water were qualitatively consistent with the results of model experiments involving UV/chlorination of precursors in terms of the behavior of residual chlorine and DBPs measured in this study.The results indicate that UV₂₅₄ irradiation promotes several reactions that are involved in the formation and/or destruction of chlorinated N-DBPs in pool settings. Enhancement of DBP formation was consistent with a mechanism whereby a rate-limiting step in DBP formation was promoted by UV exposure. Promotion of these reactions also resulted in increases of free chlorine consumption rates.     

Formation of disinfection by-products in indoor swimming pool water: the contribution from filling water natural organic matter and swimmer body fluids

The contribution and role of different precursors in the formation of three class of disinfection by-products (DBPs) [trihalomethanes (THMs), haloacetic acids (HAAs), and halonitromethanes (HNMs)] in swimming pool waters were examined using filling waters obtained from five drinking water treatment plant (WTP) effluents and three body fluid analogs (BFAs). BFAs exerted higher chlorine demands as compared to natural organic matter (NOM) in filling waters. BFAs exhibited higher HAA formation potentials than THM formation potentials, while the opposite was observed for the filling water NOM. There was no appreciable difference in the HNM formation potentials of BFAs and filling water NOM. Different components in the BFAs tested exhibited different degree and type of DBP formation. Citric acid had significantly higher THM and HAA yields than other BFA components. The effect of temperature was greater on THM formation, whereas the effect of contact time had more impact on HAA formation. Experiments with filling waters collected from WTP effluents at three different times showed more variability in HAA than THM formation at the WTPs studied.     

Modelling spatial externalities in panel data: The Spatial Durbin model revisited*

The purpose of this paper is twofold. First, it extends the spatial Durbin model to panel data allowing for non‐spherical disturbances and proposes two alternative estimators based on ML techniques. While one of the estimators exhibits more degrees of freedom, the other is computationally less burdensome. Results from a Monte Carlo study reveal that both estimators have satisfactory small sample properties also in cases when the error structure is in effect spherical. Second, the paper demonstrates that conventional testing procedures may wrongly reject the existence of spatial externalities. In particular, it shows that the incidence of a type II error increases as the spatial weight matrix becomes denser. Este artículo tiene un doble objetivo. Primero, amplia el modelo espacial de Durbin a datos de panel, permitiendo perturbaciones no esféricas y propone dos estimadores alternativos basados en técnicas de aprendizaje automático (ML). Mientras que uno de los estimadores exhibe un mayor número de grados de libertad, el otro es menos problemático en cuanto a su cómputo. Los resultados de un estudio de Monte Carlo mostraron que ambos estimadores poseen propiedades satisfactorias en cuanto a pequeños muestreos, incluso en casos en los que la estructura del error es de hecho esférica. Segundo, el artículo demuestra que los procedimientos convencionales de ensayo podrían rechazar erróneamente la existencia de externalidades espaciales. En particular, se muestra que la incidencia en un error de tipo II aumenta a medida que la matriz ponderada espacial se vuelve más densa.