Dave Ta Fu Kuo

Removal Efficiency and Risk Assessment of Polycyclic Aromatic Hydrocarbons in a Typical Municipal Wastewater Treatment Facility in Guangzhou, China

The loading and removal efficiency of 16 US EPA polycyclic aromatic hydrocarbons (PAHs) were examined in an inverted A2/O wastewater treatment plant (WWTP) located in an urban area in China. The total PAH concentrations were 554.3 to 723.2 ng/L in the influent and 189.6 to 262.7 ng/L in the effluent. The removal efficiencies of ∑PAHs in the dissolved phase ranged from 63 to 69%, with the highest observed in naphthalene (80% removal). Concentration and distribution of PAHs revealed that the higher molecular weight PAHs became more concentrated with treatment in both the dissolved phase and the dewatered sludge. The sharpest reduction was observed during the pretreatment and the biological phase. Noncarcinogenic risk, carcinogenic risk, and total health risk of PAHs found in the effluent and sewage sludge were also assessed. The effluent BaP toxic equivalent quantities (TEQBaP) were above, or far above, standards in countries. The potential toxicities of PAHs in sewage effluent were approximately 10 to 15 times higher than the acceptable risk level in China. The health risk associated with the sewage sludge also exceeded international recommended levels and was mainly contributed from seven carcinogenic PAHs. Given that WWTP effluent is a major PAH contributor to surface water bodies in China and better reduction efficiencies are achievable, the present study highlights the possibility of utilizing WWTPs for restoring water quality in riverine and coastal regions heavily impacted by PAHs contamination.

Sorption and desorption kinetics of nitroglycerin and 2,4-dinitrotoluene in nitrocellulose and implications for residue-bound energetic materials

Energetic materials (EMs) bound to propellant residues can contribute to environmental risk and public health concerns. This work investigated how nitrocellulose, a common binding material in propellants, may control the release dynamics of nitroglycerin (NG) and 2,4-dinitrotoluene (2,4-DNT) from propellant residues. Batch adsorption/desorption experiments on nitrocellulose and re-interpretation on results from past leaching studies involving propellant-bound EMs were conducted. Mechanistic modeling of adsorption/desorption kinetics based on intra-particle diffusion (IPD) predicted aqueous intrinsic diffusivities (Diw) to within a factor of 2 of expected values. Furthermore, the IPD model was able to predict effective diffusivities (Deff) during the early leaching of NG from propellant residues to within a factor of 2 over a 3-log unit range. Prediction of leaching Deffs associated with fired residues was less successful probably due to the neglect of compositional and morphological heterogeneity within the residues. Close correlations were found between the early and late Deffs of residue-bound NG and between the fast- and slow-domain rate constants for both EMs, suggesting that the late leaching kinetics of bound-EMs may be empirically assessed from the early kinetics. This work illustrates that, in addition to dissolution, retarded diffusion through nitrocellulose matrix may also limit the overall release and transformation of residue-bound EMs in the field. Implications and limitations of the current study, and the steps forward are also presented.

Deriving in vivo biotransformation rate constants and metabolite parent concentration factor/stable metabolite factor from bioaccumulation and bioconcentration experiments: An illustration with worm accumulation data

Growing concern for the biological fate of organic contaminants and their metabolites and the urge to connect in vitro and in vivo toxicokinetics have prompted researchers to characterize the biotransformation behavior of organic contaminants in biota. The whole body biotransformation rate constant (kM ) is currently determined by the difference approach, which has significant methodological limitations. A new approach for determining kM from the kinetic observations of the parent contaminant and its intermediate metabolites is proposed. In this method, kM can be determined by fitting kinetic data of the parent contaminant and the metabolites to analytical equations that depict the bioaccumulation kinetics. The application of the proposed method is illustrated using worm bioaccumulation-biotransformation data collected from the literature. Furthermore, a metabolite parent concentration factor (MPCF) is also proposed to characterize the persistence of the metabolite in biota. Because both the proposed kM method and MPCF build on the existing theoretical framework for bioaccumulation, they can be readily incorporated into standard experimental bioaccumulation protocols or risk assessment procedures or frameworks. Possible limitations, implications, and future directions are elaborated. Environ Toxicol Chem 2016;35:2903-2909.

Organophosphorus flame retardants and heavy metals in municipal landfill leachate treatment system in Guangzhou, China

The occurrence, distribution and removal efficiencies of organophosphorus flame retardants (OPFRs) and metals were examined in a municipal landfill leachate treatment system in Guangzhou, China. Five OPFRs and thirty-five metals were detected in wastewater samples collected at different treatment stages. ∑OPFRs was reduced from 4807.02 ng L-1 to 103.91 ng L-1 through the treatment system, with close to 98% removed from the dissolved phase. Tris(clorisopropyl) phosphates (TCPPs) dominated through the treatment process and accounted for over 80% and 50% of ∑OPFRs at the influent and the effluent, respectively. TCPPs were most efficiently removed (98.6%) followed by tris(2-chloroethyl) phosphate (TCEP) (96.6%) and triphenyl phosphate (TPP) (88.5%). For metals, Fe, Cr, and Rb were dominant in the raw leachate, detected at 7.55, 2.82, and 4.50 mg L-1, respectively. Thirteen regulated heavy metals - including eight major pollutants (i.e., As. Cd, Cr, Cu, Hg, Ni, Pb, and Zn) - have been detected in all wastewater samples at sub-mg L-1 levels. Over 99.5% removal was achieved for Cr, Ni, and Fe, and close to 95% removal efficiency was observed for Rb. For the eight major heavy metals, over 99% removal was observed; the only exception was Cu, which was removed at 89%. It was found that microfiltration/reverse osmosis was critical for the removal of OPFRs and heavy metals while the core biological treatment played a minor role towards their removal. Remobilization of Co, Cu, Fe, Hg, Mn, Ni, Sb, and Sr from the returned sludge occurred during the second denitrification, indicating the need for additional post-biological process for effective removal of both contaminants. This study highlights the critical need to develop cheap, effective treatment technologies for contaminants-laden leachate generated from open dumps and under-designed landfills.