Feasibility of constructed wetlands for removing chlorothalonil and chlorpyrifos from aqueous mixtures.

Chlorpyrifos (an insecticide) and chlorothalonil (a fungicide) are transported in stormwater runoff and can be lethal to receiving aquatic system biota. This study determined removal rates of chlorpyrifos and chlorothalonil in simulated stormwater runoff treated in constructed wetland mesocosms. Using sentinel species, Ceriodaphnia dubia and Pimephales promelas, observed declines in toxicity of the simulated runoff after treatment were 98 and 100%, respectively. First order removal rates were 0.039/h for chlorpyrifos and 0.295/h for chlorothalonil in these experiments. Constructed wetland mesocosms were effective for decreasing concentrations of chlorpyrifos and chlorothalonil in simulated stormwater runoff, and decreasing P. promelas and C. dubia mortality resulting from these exposures. The results from this study indicate that constructed wetlands could be part of an efficient mitigation strategy for stormwater runoff containing these pesticides.

Comparative toxicity of chlorothalonil: Ceriodaphnia dubia and Pimephales promelas.

Chlorothalonil is a commonly used fungicide in rural and urban environments and can be incidentally introduced into aquatic systems through rainfall runoff or direct overspray and drift from aerial applications. Few studies have been published regarding risks to aquatic organisms exposed to chlorothalonil, so this study was performed to provide a first-order risk characterization for receiving system biota. Definitive laboratory toxicity tests were conducted with aqueous solutions of chlorothalonil and sentinel aquatic organisms (Ceriodaphnia dubia Richard and Pimephales promelas Rafinesque). P. promelas was more sensitive (7-day potency=6.1% mortality/mug/L) than C. dubia (7-day potency=0.94% mortality/mug/L) to chlorothalonil exposures. All mortality of P. promelas and C. dubia resulting from these chlorothalonil exposures occurred within the first 96h and no sublethal effects (i.e., growth or reproduction) were detected under these experimental conditions following 7-day exposures.

Decolorization of the dye, Reactive Blue 19, using ozonation, ultrasound, and ultrasound-enhanced ozonation.

Reactive dyes constitute a significant portion of colorants used in industries ranging from the textile industry to the paper industry. In most cases, the effluent streams from textile plants are highly colored, and treatment methods for dye decolorization such as chemical oxidation need to be explored. The oxidation processes investigated in this study are those of ozonation, ultrasound, and ultrasound-enhanced ozonation. The oxidation of an anthraquinone dye was studied under conditions of varying ultrasonic power, dye concentration, ozone concentration, pH, and temperature. Laboratory experiments were performed using a semibatch reactor by ozonating dye samples with and without ultrasound. Under conditions of constant ultrasonic radiation and continuous gas application, decolorization rates have been enhanced by ultrasound. The apparent first-order rate constants increased between 35 and 204% for the ultrasonic power inputs between 40 W/L and 120 W/L compared with ozonation alone. The effects of ultrasonic power input on the gas-liquid mass-transfer coefficient were also investigated and the results indicate that an increase in ultrasonic power input increases the mass-transfer coefficient. The mass-transfer coefficient increased between 89 and 93% for ozone inlet concentrations between 5.4 and 9.4 mg/L at an ultrasonic power of 120 W/L compared with ozonation alone. The reactions of the dye with ultrasound-enhanced ozone occurred through the hydroxyl radical pathway.

Comparative toxicity of chlorothalonil and chlorpyrifos: Ceriodaphnia dubia and Pimephales promelas.

This study was done to characterize responses of Ceriodaphnia dubia Richard and Pimephales promelas Rafinesque exposed to aqueous solutions of chlorothalonil (tetrachloroisophthalonitrile) and chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate). Chlorothalonil (a fungicide) and chlorpyrifos (an insecticide) are intensely used in agricultural, silvicultural, and urban settings. These pesticides may enter aquatic systems through several pathways including rainfall runoff. C. dubia and P. promelas have been used to monitor surface waters and discern the effects of pesticides that contaminate those waters. Modified static renewal exposures (7 or 10 days) with individual solutions of chlorothalonil and chlorpyrifos were used to obtain mortality data for C. dubia and P. promelas, from which potency curves were derived, as well as sublethal effects data (reproduction or growth). In these experiments P. promelas was more sensitive to chlorothalonil, and C. dubia was more sensitive to chlorpyrifos. Lower and upper thresholds (i.e., LC(0) and LC(100)) for 7-day P. promelas exposures to chlorothalonil were 14.4 and 30.8 microg/L, respectively, in contrast to the lower and upper threshold values, 103 and 210 microg/L, respectively, for C. dubia. Ten-day exposures of C. dubia to chlorpyrifos resulted in lower and upper threshold values of 0.05 and 0.09 microg/L, whereas 10-day exposures of P. promelas to chlorpyrifos yielded threshold values of 26 and 274 microg/L. The results of this study illustrated differences in species' sensitivities to chlorothalonil and chlorpyrifos as well as differences in the duration of the exposure necessary to illustrate effects that might be elicited from pesticide exposures.

Oxidation of hydrogen sulfide by flocculated Thiobaccillus denitrificans in a continuous culture.

In a continuous fermentation, significant advantages may be gained by immobilization of microbial cells. Immobilization allows cells to be retained in the fermenter or to be readily recovered and recycled. Therefore, the hydraulic retention time and the biomass retention time are decoupled. A novel cell immobilization has been developed for the immobilization of autotrophic bacteria by coculture with floc-forming heterotrophic bacteria with growth of the latter limited by the availability of organic carbon. The result is an immobilization matrix which grows along with the immobilized autotroph. We have previously demonstrated the utility of this approach by immobilizing the chemoautotroph Thiobacillus denitrificans in macroscopic floc by coculture with floc-forming heterotrophs from an activated sludge treatment facility. Floc with excellent settling characteristics were produced. These floc have now been used to remove H(2)S from a gas stream bubbled through continuous cultures. The stoichiometry and kinetics of H(2)S oxidation by immobilized T. denitrificans were comparable to that reported previously for free-cell cultures. Oxygen uptake measurements indicated the growth of both T. denitrificans and the heterotrophs although the medium contained no added organic carbon. Continuous cultures with total biomass recycle were maintained for up to four months indicating the long-term stability of the commensal relationship between the immobilized autotroph and the heterotrophs which composed the immobilization matrix. It was observed that at any given H(2)S loading the biomass concentration reached a maximum and leveled out. The ultimate biomass concentration was dependent upon the H(2)S feed rate.