Ku-Fan Chen

Control of petroleum-hydrocarbon contaminated groundwater by intrinsic and enhanced bioremediation

In the first phase of this study, the effectiveness of intrinsic bioremediation on the containment of petroleum hydrocarbons was evaluated at a gasoline spill site. Evidences of the occurrence of intrinsic bioremediation within the BTEX (benzene, toluene, ethylbenzene, and xylenes) plume included (1) decreased BTEX concentrations; (2) depletion of dissolved oxygen (DO), nitrate, and sulfate; (3) production of dissolved ferrous iron, methane, and CO2; (4) deceased pH and redox potential; and (5) increased methanogens, total heterotrophs, and total anaerobes, especially within the highly contaminated areas. In the second phase of this study, enhanced aerobic bioremediation process was applied at site to enhance the BTEX decay rates. Air was injected into the subsurface near the mid-plume area to biostimulate the naturally occurring microorganisms for BTEX biodegradation. Field results showed that enhanced bioremediation process caused the change of BTEX removal mechanisms from anaerobic biodegradation inside the plume to aerobic biodegradation. This variation could be confirmed by the following field observations inside the plume due to the enhanced aerobic bioremediation process: (1) increased in DO, CO2, redox potential, nitrate, and sulfate, (2) decreased in dissolved ferrous iron, sulfide, and methane, (3) increased total heterotrophs and decreased total anaerobes. Field results also showed that the percentage of total BTEX removal increased from 92% to 99%, and the calculated total BTEX first-order natural attenuation rates increased from 0.0092% to 0.0188% per day, respectively, after the application of enhanced bioremediation system from the spill area to the downgradient area (located approximately 300 m from the source area).

Enzymatic degradation of nitriles by Klebsiella oxytoca.

Klebsiella oxytoca, isolated from cyanide-containing wastewater, was able to utilize many nitriles as sole source of nitrogen. The major objective of this study was to explore the ability of K. oxytoca to utilize some nitriles and then further evaluate the pathways of transformation of cyanide compounds by K. oxytoca. Results from this study indicate that succinonitrile and valeronitrile were the most optimal sources of nitrogen for the growth of K. oxytoca. The biodegradation of acetonitrile proceeded with the formation of acetamide followed by acetic acid. The production of ammonia was also detected in this biodegradation experiment. Similar results were observed in the propionitrile biodegradation experiments. Collectively, this study suggests that the breakdown of acetonitrile or propionitrile by this bacterium was via a two-step enzymatic hydrolysis with amides as the intermediates and organic acids plus with ammonia as the end products.

Application of persulfate-releasing barrier to remediate MTBE and benzene contaminated groundwater.

The objective of this study was to assess the potential of using an in situ oxidation barrier system to remediate gasoline-contaminated groundwater. The passive remedial system included a persulfate-releasing barrier containing persulfate-releasing materials to release persulfate for contaminant oxidation. Bench experiments were performed to determine the components and persulfate-releasing rate of the persulfate-releasing materials. Column experiments were conducted to evaluate the effectiveness of the designed persulfate-releasing materials on the control of petroleum-hydrocarbon plume. In this study, methyl tert-butyl ether (MTBE) and benzene were used as the target compounds. The optimal persulfate releasing rate was obtained when the mass ratio of persulfate/cement/sand/water was 1/1/0.16/0.5, and the rate varied from 31 to 8 mg persulfate per day per g of material. Significant amounts of MTBE and benzene were removed through the oxidation process due to the release of persulfate, and the produced tert-butyl formate (TBF) and tert-butyl alcohol (TBA), byproducts of MTBE, were further oxidized in the system. Results suggest that the oxidation rate would be affected by the oxidant reduction potential and concentrations of ferrous iron and persulfate.

Application of polycolloid-releasing substrate to remediate trichloroethylene-contaminated groundwater: a pilot-scale study.

The objectives of this pilot-scale study were to (1) evaluate the effectiveness of bioremediation of trichloroethylene (TCE)-contaminated groundwater with the supplement of slow polycolloid-releasing substrate (SPRS) (contained vegetable oil, cane molasses, surfactants) under reductive dechlorinating conditions, (2) apply gene analyses to confirm the existence of TCE-dechlorinating genes, and (3) apply the real-time polymerase chain reaction (PCR) to evaluate the variations in TCE-dechlorinating bacteria (Dehalococcoides spp.). Approximately 350L of SPRS solution was supplied into an injection well (IW) and groundwater samples were collected and analyzed from IW and monitor wells periodically. Results show that the SPRS caused a rapid increase of the total organic carbon concentration (up to 5794mg/L), and reductive dechlorination of TCE was significantly enhanced. TCE dechlorination byproducts were observed and up to 99% of TCE removal (initial TCE concentration=1872μg/L) was observed after 50 days of operation. The population of Dehalococcoides spp. increased from 4.6×10(1) to 3.41×10(7)cells/L after 20 days of operation. DNA sequencing results show that there were 31 bacterial species verified, which might be related to TCE biodegradation. Results demonstrate that the microbial analysis and real-time PCR are useful tools to evaluate the effectiveness of TCE reductive dechlorination.

Nano Zerovalent Iron Particles Induce Pulmonary and Cardiovascular Toxicity in an in Vitro Human Co-culture Model

Abstract Despite promising environmental applications for nano zerovalent iron (nZVI), concerns remain about the potential accumulation and toxic effects of nZVI particles. Here, we use an alveolar-capillary co-culture model to investigate a possible link between low-level epithelial exposure to nZVI and pulmonary and cardiovascular toxicity. While nZVI was unable to pass through the epithelial barrier into the endothelium, nZVI exposure did cause oxidative and inflammatory responses in both epithelial and endothelial cells. Therefore, toxic effects induced by nZVI are not restricted to epithelial cells but can be transferred into the endothelium. Communication between A549 and EA.hy926 cells is responsible for amplification of nZVI-induced toxic responses. Decreases in transepithelial electrical resistance and zonula occludens proteins after epithelial exposure to nZVI impaired epithelial barrier integrity. Increases in oxidized α1-antitrypsin and oxidized low-density lipoprotein in the co-culture model suggest that nZVI exposure increases the risk of chronic obstructive pulmonary disease and atherosclerosis. Therefore, inhalation of nZVI has the potential to induce cardiovascular disease through oxidative and inflammatory mediators produced from the damaged lung epithelium in chronic lung diseases.

Photocatalytic degradation of Rhodamine B by microwave-assisted hydrothermal synthesized N-doped titanate nanotubes

Microwave-induced nitrogen-doped titanate nanotubes (NTNTs) were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Zeta potential analysis, specific surface area (SBET), and UV-Visible spectroscopy. TEM results indicate that NTNTs retain a tubular structure with a crystalline multiwall and have a length of several hundred nanometers after nitrogen doping. XRD findings demonstrate that the crystalline structure of NTNTs was dominated by anatase, which is favored for photocatalytic application. The Ti-O-N linkage observed in the XPS N 1s spectrum is mainly responsible for narrowing the band gap and eventually enhancing the visible light photoactivity. FT-IR results demonstrated the existence of H₃O⁺, which could be excited by photo-generated holes to form hydroxyl radicals and degrade environmental pollutants. After sintering at 350°C, the UV-Vis absorbance edges of NTNTs significantly shift to the visible-light region, which indicates N atom doping into the nanotubes. Photocatalytic degradation of Rhodamine B (RhB) via NTNTs show good efficiency, with pseudo first-order kinetic model rate constants of 3.7 × 10⁻³, 2.4 × 10⁻³ and 8.0 × 10⁻⁴ sec⁻¹ at pH3, 7, and 11, respectively.

A kinetic and mechanistic study of the degradation of 1,2-dichloroethane and methyl tert-butyl ether using alkaline-activated persulfate oxidation

In this study, alkaline-activated persulfate is used to treat groundwater that is contaminated with 1,2-dichloroethane (1,2-DCA)- and methyl tert-butyl ether (MTBE). The results show that alkaline-activated persulfate accelerates the degradation of 1,2-DCA. Vinyl chloride is produced because there is dehydrochlorination of 1,2-DCA at high pH. Although the rate of degradation of MTBE in alkaline-activated persulfate systems is decreased, there is a significant reduction in the accumulation of MTBE-degrading byproducts, tert-butyl alcohol and tert-butyl formate. Alkaline-activated persulfate degrades 1,2-DCA via the mechanisms of oxidation and dehydrochlorination, but oxidation alone contributes to the removal of MTBE. The use of low-cost basic oxygen furnace (BOF) slag increases the pH of the solution (>12) and allows the alkaline-activated persulfate reaction to proceed. No detectable heavy metals are released from the BOF slag in the persulfate system that is activated by BOF slag. The degradation of 1,2-DCA and MTBE follows the pseudo-first-order kinetics for all persulfate systems. Alkaline-activated persulfate causes a decrease in ORP because there is a high pH, which adversely affects the removal of contaminants if the contaminants do not undergo base-mediated degradation. Therefore, the performance in terms of contaminant removal must be evaluated before alkaline-activated persulfate is used for different compounds. This novel, slag-activated persulfate system is an environmentally friendly and cost-effective alternative to the remediation of groundwater.

Enhanced bioelectricity generation and azo dye treatment in a reversible photo-bioelectrochemical cell by using novel anthraquinone-2,6-disulfonate (AQDS)/MnOx-doped polypyrrole film electrodes.

A novel anthraquinone-2,6-disulfonate/MnOx-doped polypyrrole film (AQDS/Mn/PPy) electrode was prepared by one-step electropolymerization method and was used to improve performance of a reversible photo-bioelectrochemical cell (RPBEC). The RPBEC was operated in polarity reversion depended on dark/light reaction of alga Chlorella vulgaris by which sequential decolorization of azo dye and mineralization of decolorization products coupled with bioelectricity generation can be achieved. The results showed that formation of uniform AQDS/Mn/PPy film significantly enhanced electroactive surface area and electrocatalytic activity of carbon electrode. The RPBEC with AQDS/Mn/PPy electrodes demonstrated 77% increases in maximum power and 73% increases in Congo red decolorization rate before polarity reversion, and 198% increases in maximum power and 138% increases in decolorization products mineralization rate after polarity reversion, respectively, compared to the RPBEC with bare electrode. This was resulted from simultaneous dynamics improvement in half-reaction rate of anode and photo-biocathode due to enhanced electron transfer and algal-bacterial biofilm formation.

The phytoattenuation of the soil metal contamination: the effects of plant growth relgualtors (GA3 and IAA) by employing wetland macrophyte vetiver and energy plant sunflower

Abstract The phytoattenuation, a novel green remediation concept, has been successfully demonstrated while employing vetiver and biostimulator (gibberellic acid GA3 and indol-3-acetic acid IAA) to gradually mitigate the soil Cu levels. The effectiveness of stimulator GA3 and IAA was in the descending sequence GA3 > IAA. Biostimulator has been demonstrated plant growth enhancement and been employed for agricultural operation. The on-site tests demonstrated Cu levels were gradually deceasing during four months monitoring time periods. The soil metal level reduction achieved a satisfactory level which complied with local environmental standards. After more rounds of planting and harvesting, the soil metal concentration expected to be further dropped while on-site operation was executed. Green remediation concepts such as the phytoattenuation need to be taken as serious concern while the Earth has faced recent unprecedented damage Japan tsunami, Green house effect, unpredicted weather fluctuation worldwide, a...

Evaluation of the effects of nanoscale zero-valent iron (nZVI) dispersants on intrinsic biodegradation of trichloroethylene (TCE)

In this study, the biodegradability of nanoscale zero-valent iron (nZVI) dispersants and their effects on the intrinsic biodegradation of trichloroethylene (TCE) were evaluated. Results of a microcosm study show that the biodegradability of three dispersants followed the sequence of: polyvinyl alcohol-co-vinyl acetate-co-itaconic acid (PV3A) > polyoxyethylene (20) sorbitan monolaurate (Tween 20) > polyacrylic acid (PAA) under aerobic conditions, and PV3A > Tween 20 > PAA under anaerobic conditions. Natural biodegradation of TCE was observed under both aerobic and anaerobic conditions. No significant effects were observed on the intrinsic biodegradation of TCE under aerobic conditions with the presence of the dispersants. The addition of PAA seemed to have a slightly adverse impact on anaerobic TCE biodegradation. Higher accumulation of the byproducts of anaerobic TCE biodegradation was detected with the addition of PV3A and Tween 20. The diversity of the microbial community was enhanced under aerobic conditions with the presence of more biodegradable PV3A and Tween 20. The results of this study indicate that it is necessary to select an appropriate dispersant for nZVI to prevent a residual of the dispersant in the subsurface. Additionally, the effects of the dispersant on TCE biodegradation and the accumulation of TCE biodegrading byproducts should also be considered.