Chunlong (Carl) Zhang
Permanent URI for this collectionhttps://hdl.handle.net/10657.1/2212
Dr. Zhang is a Professor of Environmental Science and Environmental Chemistry at the University of Houston-Clear Lake where he is also the Program Chair of the Environmental Science Program. Dr. Zhang's General Research Interests include Environmental sampling and analysis; Environmental chemistry; Environmental remediation; Fate, transport, and remediation of organic chemicals and heavy metals in soil, groundwater, and sediment. Some past and on-going research projects include: Sustainable remediation; Analysis of emerging contaminants (endocrine disrupting chemicals; bromate); Biodegradation of surfactants, explosives chemicals, pharmaceutical and endocrine disrupting compounds; Sorption of polycyclic aromatic hydrocarbons, explosives and endocrine disrupting compounds in soil and sediment; Effects of surfactants on air-water partition of chlorinated solvents; Zero-valent iron for the remediation of chromium contaminated soil and sediment.
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Item Studies on the Background Levels of Heavy Metals (Cu,Zn,Pb,Cd,Ni,Hg,Cr,As,Ti) in Soils along Hangzhou Section of the Grand Canal(Zhejiang Agricultural University Press,, 1984) Zhang, ChunlongItem Environmental Pollution and Biological Nitrogen Fixation: A Review(Agro-Environmental Protection, 1986) Zhang, CarlItem Effect of Trivalent and Hexavalent Forms of Chromium on Soybean Growth(Agro-Environmental Protection, 1988) Zhang, CarlItem Effect of Chromium no Growth, Physiology, Nodulation and Nitrogen Fixation of Soybean(Acta Agriculture Universitat Zhejiangensis, 1988) Zhang, CarlItem Studies in Solvent Extraction Using Polyaphrons I. Size Distribution, Stability and Flotation of Polyaphrons(Separation Science and Technology, 1996) Zhang, CarlItem Fate of TNT an TNT-Transformed Products in Mixed Aerobic Cultures(Bioremediation Journal, 1998) Zhang, CarlThe fate of 2,4,6-trinitrotoluene (TNT) and TNT transformation products in two aerobic enrichment cultures was investigated. Contaminant fate was assessed through analysis of TNT and its oxygen-stable aminated derivatives using capillary electrophoresis and by tracking the distribution of 14C-labeled products in either the dissolved, mineralized, or biomass fractions. TNT transformation products were generated by reduction with Fe(0), reduction by S2−, and transformation by Clostridium acetobutylicum and by Eichornia crassipies (water hyacinth). Enrichment cultures varied in the growth substrate and nitrogen source supplied. The dextrose-fed mixed culture (DMC) was enriched on dextrose with yeast extract providing nitrogen for growth, whereas the anthranilic acid-fed mixed culture (AMC) received anthranilic acid as its source of both energy and nitrogen. Each culture transformed TNT, but their product distributions varied. The DMC exhibited higher levels of biomass association, whereas the AMC produced higher levels of aminated nitrotoluenes and unidentified water-soluble products. Neither mineralized TNT to a significant degree. TNT disappearance was observed in all transformation systems, along with the formation of water-soluble products; however, formation of aminated nitrotoluenes was observed only in the sulfide systems. Neither aerobic culture was capable of mineralizing the TNT transformation products introduced, regardless of the transformation method used to prepare them. The distribution of products between the aqueous phase and the biomass did vary between cultures and was affected by the transformation system used.Item Nutrient and Surfactant Enhancement for the Biodegradation of Chlorinated Hdydrocarbons in the Wastewater from a Louisiana Superfund Site(Journal of Hazardous Material, 1998) Zhang, CarlSurfactant based soil washing and flushing is an emerging technology for Superfund site remediation in the United States. The presence of surfactants in the wastewater, however, poses challenging problems for subsequent biological or physical-chemical processes. The objective of this research is to evaluate the potential effects of selected surfactants on the biodegradation of chlorinated hydrocarbons in the wastewater from the Petro Processors (PPI) Superfund site north of Baton Rouge, LA. Results from this study showed that biodegradation of a real-world waste containing a broad array of hazardous contaminants was significantly enhanced by the amendment of mineral nutrients and surfactants, especially a nonionic surfactant Witconol.Item Surfactant Screening for Soil Washing: Comparison of Foamability and Biodegradability of a Plant-Based Surfactant with Commercial Surfactants(Journal of Environmental Science and Health, 1998) Zhang, CarlBiodegradable natural surfactants obtained from plants can be an attractive alternative to synthetic surfactants in the remediation of contaminated soils. In this research, a plant-based surfactant obtained from the fruit pericarp of Sapindus mukurossi, a tree generally grown in tropical regions of Asia, is tested. A simple and economical method for the preparation of the surfactant is developed. An empirical formula for the surfactant was determined to be (C26H31O10)n. The aqueous solubilities of hexachlorobenzene (HCB) and naphthalene in the natural surfactant solutions were found to vary linearly with the concentration of the surfactant showing trends comparable to that of typical com mercial surfactants. Natural surfactant solutions were also employed for flushing HCB from one-dimensional soil columns. HCB recoveries after 12 pore volumes of flushing with 0.5 and 1% natural surfactant solutions were 20 and 100 times more than that recovered by water flooding. These promising results warrant further research to establish the usefulness of plant-based surfactants for soil washing applications.Item Kinetic Modeling of Diauxic Microibial Growth in a Plant Based Natural Surfactant from Sapindus mukorossi(Journal of Environmental Science, 1998) Zhang, CarlA plant‐based natural surfactant with potential applications in the remediation of contaminated soils was obtained from the dry fruit pericarps of Sapindus mukorossi,. Kinetics of microbial growth in the natural surfactant solution under batch aerobic conditions was shown to be dependent on the initial concentrations of the surfactant, and a typical diauxic pattern was observed at high concentrations. This unique pattern may be attributed to the two components in the surfactant solutions that are of different biodegradabilities, and to the inhibition effects of the preferential substrate at high concentrations. Based on the generalized Monod equation, a new mathematical model is proposed to account for this growth pattern. During the exponential growth period, specific growth rates (μ) were in the range of 0.0188 and 0.2574 hr, which corresponds a doubling time (tD,), of 3 to 37 hours. Parameters for the Monod model were estimated to be 1.08 hr and 11200 mg/L for μmax, and K,S,, respectively. A model similar to the logistic growth equation was used to express microbial growth at a low concentration range from 200 to 2500 mg/L, and a discrete model was developed to describe the biphasic growth curve at a high concentration of 6000 mg/L. Model parameters were estimated by a non‐linear least‐squares method. The model was in good agreement with the experimental data for the monoauxic growth at low concentrations, and diauxic growth at high concentrations of the surfactant.Item Aerobic Biodegradation Kinetics of Four Anionic and Nonionic Surfactants at Sub and Supra Critical Micelle Concentrations(Water Resarch, 1999) Zhang, CarlAerobic biodegradation of four representative commercial surfactants under a range of concentrations (i.e., sub- and supra-critical micelle concentrations, CMCs) beyond those ordinarily used in biodegradation studies was investigated. Of the four surfactants tested, sodium dodecylbenzene sulfonate (SDBS) showed no biodegradation and foam degradation. At a sub-CMC (500 mg/l), primary biodegradation, as measured by methylene blue active substances (MBAS) for an anionic surfactant sodium dodecyl sulphate (SDS) and by cobalt thiocyanate active substances (CTAS) for a nonionic surfactant Witconol, followed Monod kinetics, substrate depletion being a function of both microbial growth and substrate concentrations. However, primary biodegradation at supra-CMCs (500 for Tergitol and 2500 mg/l for SDS and Witconol) and ultimate biodegradation (mineralization) at both sub- and supra-CMCs were best described by first-order kinetics, the degradation rate being a sole function of substrate concentrations. Parameters for the kinetic models (Ks, Y, μmax, and k) were estimated using non-linear least squares methods. Increasing surfactant concentrations from sub- to supra-CMCs significantly decreased primary biodegradation, ultimate biodegradation, and foam degradation. This decrease may be attributed to the limited bioavailability of surfactants in the micellar phase as compared to the monomeric surfactants. The results are of significance for surfactant-based remediation, since the concentrations of surfactants employed in remediation are typically much higher than CMCs, while surfactant concentrations of primary interest in biodegradation work are in the neighborhood of and below 10 mg/l, which is usually 10–100 times lower than CMCs.Item Low Aqueous Electron Donors for the Reduction of Nitroaromatics in Anaerobic Sediments(Journal of Containment Hydrology, 1999) Zhang, CarlStudies are presented investigating the ability to enhance aryl nitro-reduction processes in sediments through electron donor addition. In particular, high molecular weight (starch and guar gum) and/or low aqueous solubility electron donors (oleic acid) were studied, since they should be less prone to diffusive loss to the water column after addition to contaminated areas. For comparison, complimentary studies were conducted with water-soluble electron donors (acetate and dextrose). The ability to enhance activity was measured by methane production and reduction of either nitrobenzene or 1,3,5-trinitrobenzene to aniline or dinitroaniline. The results demonstrate that all electron donors resulted in increased methane production after a lag phase. The highest level of methane production and the shortest lag phase in uncontaminated sediment microcosms was observed in acetate-fed systems. Sorption studies of all electron donors showed that starch was partitioning the least into the water phase. In microcosms containing nitrobenzene, trinitrobenzene and acetate, methane production did not occur and nitro-reduction was not observed. Conversely, the addition of dextrose or starch yielded methane production and aryl nitro-reduction with each contaminant tested. Neither nitrobenzene nor trinitrobenzene was significantly reduced in HgCl2-killed controls. From these studies, it appears that starch may be well suited for applications of in-place, anaerobic sediment bioremediation.Item Anaerobic Biotransformation of 2,4-Dinitrotoluene and 2,6-Dinitotoluene by Clostridium acetobutylicum: A Pathway through Dihydroxylamino-Intermediates(Environmental Science and Technology, 1999) Zhang, CarlExperiments were conducted to isolate and identify the intermediates and products of 2,4-dinitrotoluene and 2,6-dinitrotoluene metabolism by Clostridium acetobutylicum. Transformation of both dinitrotoluenes initially resulted in the formation of hydroxylaminonitrotoluenes. Subsequent transformation favored the formation of dihydroxylaminotoluenes, with a limited reduction to aminonitrotoluene isomers. In cell cultures, metabolism beyond the level of dihyroxylaminotoluene was not observed. In cell extracts, where activity could be maintained for periods in excess of those in cell cultures, further transformation yielded aminohydroxylaminotoluenes and eventually diaminotoluenes. These findings further demonstrate the potential for hydroxylamines to be significant intermediates of nitroaromatic transformation under anaerobic fermentative conditions. Interestingly, the rearrangement of dihydroxylaminotoluenes was not observed, as was the case in previous studies of 2,4-dihydroxylamino-6-nitrotoluene metabolism (e.g., the dihydroxylamino metabolite of 2,4,6-trinitrotoluene transformation by C. acetobutylicum). Dihydroxylaminotoluenes were found to be quite unstable, decomposing rapidly upon exposure to oxygen, complicating the assessment of their fate in remediation processes.Item Slurry-Phase Biological Treatment of 2,4 Diitrotoluene and 2,6 Dinitrotoluene: Role of Bioaugmentation and Effects of High Dinitrotoluene Concentration(Environmental Science and Technology, 2000) Zhang, CarlA pilot-scale study was conducted to evaluate the use of aerobic slurry reactors to treat soils that were highly contaminated with 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT). Contaminated soils were obtained from Volunteer Army Ammunition Plant (VAAP; Chattanooga, TN) and Badger Army Ammunition Plant (BAAP; Baraboo, WI). Concentrations of 2,4-DNT and 2,6-DNT were 19 000 and 1380 mg/kg in VAAP soil and 8900 and 480 mg/kg in BAAP soil. Soils were homogenized and subjected to a soil washing process; the resulting soil slurry was subsequently fed to an Eimco bioreactor (70-L) operated in a draw-and-fill mode. Degradation of either isomer required augmentation with a DNT-mineralizing culture. Stable performance and essentially complete degradation of 2,4-DNT (within ∼2 days) was demonstrated for both soils at slurry concentration (sum of aqueous, sorbed, and crystalline phases) exceeding 11 000 μM. Incomplete degradation of 2,6-DNT was observed after inoculation, and low-level degradation activity could not be sustained without repeated bioaugmentation. Changing reactor operation to maintain low slurry-phase concentrations of 2,4-DNTthrough continuous feeding or by reducing the volume of soil slurry fed during draw-and-fillimproved the ability to sustain 2,6-DNT degradation activity. Complementary studies conducted in shake flasks demonstrated that the high concentrations of 2,4-DNT resulted in an inhibition of 2,6-DNT degradation. The impact of 2,4-DNT on 2,6-DNT degradation required a dual-stage approach to achieve complete treatment of both contaminants. Operating two reactors in series, where 2,4-DNT was degraded in the first reactor and 2,6-DNT was degraded in the second reactor, allowed for stable draw-and-fill operation. High nitrite concentrations resulting from 2,4-DNT degradation in the first reactor had no apparent impact on subsequent 2,6-DNT degradation.Item Toxic Effects of Hydroxylamino intermediates on Algae Selanastrum capricornutum(Bulletin of Environmental Contamination and Toxicology, 2000) Zhang, CarlThe freshwater green alga, Selenastrum capricornutum, was used to examine the toxicity of hydroxylamine intermediates of trinitrotoluene (TNT) and dinitrotoluenes (DNTs) formed during microbial transformation. Three intermediates of TNT, 2,4-DNT, and 2,6-DNT, along with the parent compounds, were used. The compound structures are tabulated. Results showed that all three intermediates of TNT were significantly less toxic than TNT, but the dihydroxylamino intermediate was as toxic as TNT at higher concentrations. For 2,4DNT, significant differences in algal toxicity were noted only for 4-hydroxylamino-2nitrotoluene and 2,4-diaminotoluene at 1.4 mg/l and 2-amino-4-nitrotoluene at 14 mg/l. For 2,6-DNT, 2-amino-6-nitrotoluene and 2-hydroxylamino-6-nitrotoluene exhibited significantly lower and higher toxicity, respectively, than the parent compound.Item Remediation of Dinitrotoluene Contaminated Soils from Former Ammunition Plants: Soil Washing Efficiency and Effective Process Monitoring in Bioslurry Reactors(Journal of Hazardous Materials, 2001) Zhang, CarlA pilot-scale bioslurry system was used to test the treatment of soils highly contaminated with 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT). The treatment scheme involved a soil-washing process followed by two sequential aerobic slurry reactors augmented with 2,4-DNT- and 2,6-DNT-mineralizing bacteria. Test soils were obtained from two former army ammunition plants, the Volunteer Army Ammunition Plant (VAAP, Chattanooga, TN) and the Badger Army Ammunition Plant (BAAP, Baraboo, WI). Soil washing was used to minimize operational problems in slurry reactors associated with large particulates. The Eimco slurry reactors were operated in a draw-and-fill mode for 3 months and were monitored for the biodegradation of 2,4-DNT and 2,6-DNT, nitrite production, NaOH consumption, and oxygen uptake rate. Results show that soil washing was very effective for the removal of sands and the recovery of soil fines containing 2,4-DNT and 2,6-DNT. Bioslurry reactors offered rapid and nearly complete degradation of both DNT isomers, but require real time monitoring to avoid long lag periods upon refeeding. Results found a significant discrepancy between the measured DNT concentrations and calculated DNT concentrations in the slurry reactors because of solids profiles in the slurry reactors and the presence of floating crystal of DNTs. Based on the actual amount of dinitrotoluene degradation, nitrite release, NaOH consumption, and oxygen uptake were close to the theoretical stoichiometric coefficients of complete DNT mineralization. Such stoichiometric relationships were not achieved if the calculation was based on the measured DNT concentrations due to the heterogeneity of DNT in the reactor. Results indicate that nitrite release, NaOH consumption, and oxygen uptake rates provide a fast assessment of 2,4-DNT degradation and microbial activity in a slurry reactor, but could not be extended to a second reactor in series where the degradation of a much lower concentration of 2,6-DNT degradation was achieved.Item Biodegradation Pathways of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX) by Clostridium acetobutylicum Cell-free Extract,(Chemosphere, 2003) Zhang, CarlHexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a military high explosive, is becoming an increasingly important pollutant in the US. The cleanup of RDX-contaminated soil and groundwater has been a serious challenge due to its recalcitrance in the environment. This study was conducted to determine the biodegradation kinetics of RDX by crude cell extract of Clostridium acetobutylicum (ATCC 824), and to examine whether this bacterium will carry out reductive transformation pathways similar to the transformation of 2,4,6-trinitrotoluene (TNT), 2,4- and 2,6-dinitrotoluenes (DNTs) we have reported previously. Batch studies on the anaerobic transformation of RDX were conducted in serum bottles with U-ring-14C-RDX. RDX and its transformation products were quantified by HPLC and qualified by LC/ MS interfaced to two soft ionization techniques--an atmospheric pressure ionization and an electron spray ionization (API-ES). Results demonstrated that C. acetobutylicum is capable of transforming RDX with H2 as the electron donor. The transformation followed a zero-order kinetics and the rates increased with increasing H2. RDX was transformed into several polar intermediates that could not be separated by reverse-phase HPLC and its molecular ions were unstable under the condition of commonly used electron impact detector. Using a polar and water immiscible solvent (ethyl acetate) and the softer MS ionization techniques, mass spectroscopy detected the presence of several RDX derivatives including mononitroso-, monohydroxylamino-, mononitrosomonohydroxylamino-, monoamino-, diamino-, and triamino-compounds. The presence of hydroxylamino compounds is analogous to the transformation of TNT and DNTs we elucidated previously.Item Soil Column Evaluation of Factors Controlling Biodegradation of DNT in the Vadose Zone(Environmental Science and Technology, 2003) Zhang, CarlHigh concentrations of 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT) are present in vadose zone soils at many facilities where explosives manufacturing has taken place. Both DNT isomers can be biodegraded under aerobic conditions, but rates of intrinsic biodegradation observed in vadose zone soils are not appreciable. Studies presented herein demonstrate that nutrient limitations control the onset of rapid 2,4-DNT biodegradation in such soils. In column studies conducted at field capacity, high levels of 2,4-DNT biodegradation were rapidly stimulated by the addition of a complete mineral medium but not by bicarbonate-buffered distilled deionized water or by phosphate-amended tap water. Biodegradation of 2,6-DNT was not observed under any conditions. Microcosm studies using a DNT-degrading culture from column effluent suggest that, after the onset of 2,4-DNT degradation, nitrite evolution will eventually control the extent of degradation achieved by two mechanisms. First, high levels of nitrite (40 mM) were found to strongly inhibit 2,4-DNT degradation. Second, nitrite production reduces the solution pH, and at pH levels below 6.0, 2,4-DNT degradation slows rapidly. Under conditions evaluated in laboratory-scale studies, 2,4-DNT biodegradation enhanced the rate of contaminant loss from the vadose zone by a factor of 10 when compared to the washout due to leaching.Item Physico-chemical Processes(Water Environment Research, 2004) Zhang, CarlZhang et al. (2004a) explored the removal of two pesticides (atrazine and simazine) from different water matrices (distilled water, tap water and river water) by nanofiltration. The researchers found that rejection of atrazine was always higher than the rejection of simazine and presence of NOM enhanced the adsorption of pesticides onto membrane surface. Excess fluoride in drinking water is harmful to human health. In a study, Arora et al. (2004) examined the use of reverse osmosis membrane for defluoridation of underground water samples. The results indicated that RO membranes can be successfully used for the treatment of underground water to the desired purity level, as they remove up to 95% of fluoride.Item Bacterial Energetic, Stoichometry and Kinetic Modeling of 2,4-Dinitrotoluene Biodegradation in a Batch Respirometer(Environmental Toxicology and Chemistry, 2004) Zhang, CarlA stoichiometric equation and kinetic model were developed and validated using experimental data from batch respirometer studies on the biodegradation of 2,4-dinitrotoluene (DNT). The stoichiometric equation integrates bacterial energetics and is revised from that in a previous study by including the mass balance of phosphorus (P) in the biomass. Stoichiometric results on O2 consumption, CO2 evolution, and nitrite evolution are in good agreement with respirometer data. However, the optimal P requirement is significantly higher than the stoichiometrically derived P, implying potentially limited bioavailability of P and the need for buffering capacity in the media to mitigate the adverse pH effect for optimal growth of DNT-degrading bacteria. An array of models was evaluated to fit the O2/CO2 data acquired experimentally and the DNT depletion data calculated from derived stoichiometric coefficients and cell yield. The deterministic, integrated Monod model provides the goodness of fit to the test data on DNT depletion, and the Monod model parameters (Ks, X0, mumax, and Y) were estimated by nonlinear regression. Further analyses with an equilibrium model (MINTEQ) indicate the interrelated nature of medium chemical compositions in controlling the rate and extent of DNT biodegradation. Results from the present batch respirometer study help to unravel some key factors in controlling DNT biodegradation in complex remediation systems, in particular the interactions between acidogenic DNT bacteria and various parameters, including pH and P, the latter of which could serve as a nutrient, a buffer, and a controlling factor on the bioavailable fractions of minerals (Ca, Fe, Zn, and Mo) in the medium.Item Bacterial Energetics, Stoichiometry and Kinetic Modeling of 2,4-Dinitrotoluene Biodegradation in a Batch Respirometer(Environmental Toxicology and Chemistry, 2004) Zhang, CarlA stoichiometric equation and kinetic model were developed and validated using experimental data from batch respirometer studies on the biodegradation of 2,4-dinitrotoluene (DNT). The stoichiometric equation integrates bacterial energetics and is revised from that in a previous study by including the mass balance of phosphorus (P) in the biomass. Stoichiometric results on O2 consumption, CO2 evolution, and nitrite evolution are in good agreement with respirometer data. However, the optimal P requirement is significantly higher than the stoichiometrically derived P, implying potentially limited bioavailability of P and the need for buffering capacity in the media to mitigate the adverse pH effect for optimal growth of DNT-degrading bacteria. An array of models was evaluated to fit the O2/CO2 data acquired experimentally and the DNT depletion data calculated from derived stoichiometric coefficients and cell yield. The deterministic, integrated Monod model provides the goodness of fit to the test data on DNT depletion, and the Monod model parameters (Ks, X0, mumax, and Y) were estimated by nonlinear regression. Further analyses with an equilibrium model (MINTEQ) indicate the interrelated nature of medium chemical compositions in controlling the rate and extent of DNT biodegradation. Results from the present batch respirometer study help to unravel some key factors in controlling DNT biodegradation in complex remediation systems, in particular the interactions between acidogenic DNT bacteria and various parameters, including pH and P, the latter of which could serve as a nutrient, a buffer, and a controlling factor on the bioavailable fractions of minerals (Ca, Fe, Zn, and Mo) in the medium.
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