Jeff Kuo

Effects of titanate nanotubes synthesized by a microwave hydrothermal method on photocatalytic decomposition of perfluorooctanoic acid.

Titanate nanotubes (TNTs) were used to remove perfluorooctanoic acid (PFOA) from aqueous solutions in this study. Direct photolysis of PFOA by a 254-nm UV light (400 W) was found effective to decompose PFOA without presence of photocatalysts. Shorter-chain perfluorocarboxylic acids (PFCAs) and fluoride ions were formed during photodecomposition. Addition of TNTs as photocatalysts did not greatly enhance photocatalytic decomposition of PFOA. TNTs mainly act as adsorbents to adsorb PFOA and form TNT-PFOA complexes. It suggested that sodium ions and oxygen atoms on the surfaces of TNTs play important roles in PFOA adsorption. X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) analyses indicated that ion-exchange, electrostatic interaction, and hydrophobic interaction all participated in the photocatalytic reaction of PFOA by TNTs.

Promoted degradation of perfluorooctanic acid by persulfate when adding activated carbon.

Treatment of persistent perfluorooctanoic acid (PFOA) in water using persulfate (PS) oxidation typically requires an elevated temperature or UV irradiation, which is energy-consuming. Under relatively low temperatures of 25-45°C, activated carbon (AC) activated PS oxidation of PFOA was evaluated for its potential of practical applications. With presence of AC in PS oxidation, PFOA removal efficiency at 25°C reached 682% with a high defluorination efficiency of 549% after 12h and few intermediates of short-chain perfluorinated carboxylic acids (PFCAs) were found. The removal and defluorination rates with the combined AC/PS system were approximately 12 and 19 times higher than those of the PS-only system, respectively. Activated carbon not only removes PFOA through adsorption, but also activates PS to form sulfate radicals that accelerate the decomposition and mineralization of PFOA. The activation energy for PS oxidation of PFOA was reduced from 668 to 261kJ/mol by the catalytic effect of AC, which implies a lower reaction temperature and a shorter reaction time would suffice. A 2-cycle schematic reaction mechanism was used to describe PS oxidation of PFOA with the generation of various intermediates and end-products.

Decomposition of perfluorooctanoic acid by microwaveactivated persulfate: Effects of temperature, pH, and chloride ions

Microwave-hydrothermal treatment of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water with persulfate (S2O82−) has been found effective. However, applications of this process to effectively remediate PFOA pollution require a better understanding on free-radical scavenging reactions that also take place. The objectives of this study were to investigate the effects of pH (pH = 2.5, 6.6, 8.8, and 10.5), chloride concentrations (0.01–0.15 mol·L−1), and temperature (60°C, 90°C, and 130°C) on persulfate oxidation of PFOA under microwave irradiation. Maximum PFOA degradation occurred at pH 2.5, while little or no degradation at pH 10.5. Lowering system pH resulted in an increase in PFOA degradation rate. Both high pH and chloride concentrations would result in more scavenging of sulfate free radicals and slow down PFOA degradation. When chloride concentrations were less than 0.04 mol·L−1 at 90°C and 0.06 mol·L−1 at 60°C, presence of chloride ions had insignificant impacts on PFOA degradation. However, beyond these concentration levels, PFOA degradation rates reduced significantly with an increase in chloride concentrations, especially under the higher temperature.

Enhanced sonochemical degradation of perfluorooctanoic acid by sulfate ions

This study investigated the effects of sulfate ions on the decomposition of perfluorooctanoic acid (PFOA) by ultrasonic (US) irradiation at various pHs, sulfate doses, powers and temperatures. The removal of PFOA was augmented with an increased sulfate ion concentration, with PFOA being almost completely decomposed in 90min at 25°C with a sulfate dose of 117mM. The two major mechanisms in the sulfate-assisted sonochemical system are the direct destruction of PFOA by cavitation and the indirect destruction of PFOA by sulfate free radicals. The decomposition of PFOA followed pseudo-first-order kinetics and was not influenced by pH. The reaction rate constants decreased with increases in temperature due to decreases in the surface tension of the solution.

Decomposition of perfluorooctanoic acid by ultraviolet light irradiation with Pb-modified titanium dioxide

Perfluorooctanoic acid (PFOA, C7H15COOH) is widely used in industrial and commercial applications. It has become a global concern due to its widespread occurrence in water bodies and adverse environmental impact. PFOA could not be effectively removed by the conventional UV/TiO2 system. This study synthesized Pb-modified TiO2 catalyst and used it as a catalyst with light irradiation for PFOA decomposition. It was found that the Pb-TiO2 catalyst could produce traps to capture photo-induced electrons or holes that lead to better photocatalytic efficiencies. Rate constant values for PFOA decomposition by the UV/TiO2 and UV/Pb-TiO2 systems were determined to be 0.0158 and 0.5136 h(-1), respectively. The PFOA decomposition in the UV/Pb-TiO2 system is 32.5 times faster than that in the UV/TiO2 system. The UV/Pb-TiO2 system yielded a better performance than those of the UV/Fe-TiO2 and UV/Cu-TiO2 systems. During the reaction, PFOA decomposed stepwisely into shorter-chain perfluorocarboxylic acids and F(-).

Microwave-enhanced persulfate oxidation to treat mature landfill leachate.

Microwave oxidation process (MOP) was evaluated for treatment of landfill leachate. Kinetics of persulfate oxidation in MOP, effects of pH and persulfate doses on fates of derivative organic acids, and the energy cost of MOP were evaluated. The results showed that total organic carbon (TOC) removal of 79.4%, color removal of 88.4%, and UV254 removal of 77.1% were reached at MOP 550 W/85 °C within 30 min. The kinetics of oxidation by MOP followed the first-order reaction. For a given persulfate dose, the reaction rate increased with the microwave power setting (775 W>550 W>325 W>128 W) with reaction rate constants ranging from 10(-5) to 10(-2) min(-1). The adverse effects on reaction rates under higher microwave power settings and high persulfate doses are plausibly caused by excessive persulfate oxidation and self-scavenging termination of free radicals. During the MOP treatment, TOC/COD ratio dropped with time and an 86.7% reduction in TOC/COD ratio after 120 min at pH 7. Oxalic acid was the major derivative and its concentrations were higher under acidic conditions. Malic, lactic, and acetic acids were formed and soon degraded, and the solution pH has an insignificant effect on their fates. The energy cost of MOP (USD

Disinfection of Wastewater Effluent—Comparison of Alternative Technologies

6.03/m(3)) is essentially similar to that of conventional heating oxidation (CHO) (USD

Review of PSR framework and development of a DPSIR model to assess greenhouse effect in Taiwan.

6.10/m(3)).

Using pretreated waste oyster and clam shells and microwave hydrothermal treatment to recover boron from concentrated wastewater.

There is a tremendous amount of literature on and experience with wastewater disinfection alternative. However, it is difficult for wastewater professionals to sift through all of the available information, especially for relatively newer technologies. In addition, there are many factors, some of them site-specific, that influence whether a facility changes disinfection practice, and which alternative it chooses. There are few resources that provide a comprehensive discussion of decision factors with a direct comparison of the disinfection alternatives. This project developed a singular document that presents the pros and cons and costs of the various technical options for wastewater disinfection. The resulting report is intended to be utilized by wastewater professionals to help evaluate and select the appropriate technology for their application. This report presents a review of the existing literature, a survey of disinfection practice by major POTWs, and surveys of facilities with UV and ozone systems. The known advantages and disadvantages of the mature technologies (chlorine, UV, and ozone), other technologies, and combinations of multiple disinfection alternatives are summarized. The report synthesizes this information and presents a coherent method for selecting a disinfection technology, based on individual priorities and criteria. Finally, the report identifies data gaps that would benefit from additional research. This title belongs to WERF Research Report Series ISBN: 9781780403670 (eBook) ISBN: 9781843397991 (Print)

Sorption of perfluoroalkyl substances (PFASs) onto wetland soils

In dealing with the complex issues of greenhouse gas (GHG) emission and climate change mitigation, many interrelated factors such as cost, level of technology development, supply and demand of energy, structure of industry, and expenditures on research and development exist. Using indicators to monitor environmental impacts and evaluate the efficacies of policies and regulations has been practiced for a long time, and it can serve as a useful tool for decision making and for comparison between different countries. Although numerous indicators have been developed for relevant subjects, integrated approaches that consider individual changes, dynamic interaction, and multi-dimensions of indicators are scarce. This paper aimed to develop a Driving Force-Pressure-State-Impact-Response (DPSIR) framework to assess the problems. This DPSIR model is mainly related to energy consumption, environmental impacts, and policy responses. The objectives of the paper were: (1) conduct a literature review on the indicators that have been used in GHG-related studies; (2) develop a DPSIR model that incorporates GHG-related indicators and evaluate their relationships using a cause–effect chain of GHG emission; and (3) develop a calculative method that can be used to explain the dynamic correlation among the interdependent indicators. Taiwan is a significant source of global GHG emissions. A case study, using the developed framework and Taiwan’s actual data of the past two decades, was conducted. The results indicate that regulatory strategies for pollution control are inadequate in terms of ensuring environmental quality, and the nature does not have the capability to revert the impacts from the existing level of pollution.