Search

The effects of algae (i.e., Chlorella vulgaris), Fe(III), humic substances, and pH on the photoreduction of Hg(II) under the irradiation of metal halide lamps (lambda>or=365 nm, 250 W) were investigated in this paper. The photoreduction rate of Hg(II) was found to increase with the increasing concentration of algae, Fe(III), and humic substances. The cooperation action of Fe(III) and humic substances accelerated the photoreduction of Hg(II). When the initial concentration of Hg(II) was in the range of 0.0-200.0 microg L(-1) with initial algae concentrations 7.0 x 10(9)cells L(-1) at pH 7.0, the initial photoreduction rate of Hg(II) could be expressed by the equation: -dC(Hg(II))/dt=0.65 x [C(Hg(II))](0.39) with a correlation coefficient of R=0.9912. The study on the photochemical process in terms of total mercury mass balance revealed that more than 40.86% of Hg(II) from the algal suspension was reduced to volatile metallic mercury. This paper discussed the photoreduction mechanism of Hg(II) in the presence of algae. This research will provide information for predicting the photoreduction of Hg(II) in the real environment. It will be helpful for understanding the photochemical transformation of Hg(II) and the formation of DGM in natural water in the presence of algae complexes. It will also be helpful for providing new methods to deal with heavy metal pollution.

The photodegradation of aniline was investigated using freshwater algae suspended in aqueous media under metal halide light (250 W). Four algal species were used: Nitzschia hantzschiana, Chlorella vulgaris, Chlamydomonas sajao and Anabaena cylindrica. Reactions were carried out under aerobic conditions. The photodegradation rate of aniline was accelerated by the algae. In the A. cylindrica suspensions, with cell density ranging from 2.5 x 10(5) cells mL(-1) to 6.5 x 10(6) cells mL(-1), the photodegradation rate of aniline was increased from 10% to 80% and rate constant k increased from 1.86 x 10(-3) min(-1) to 9.66 x 10(-3) min(-1). Reactive oxygen species were thought to be the main reason for the degradation of aniline. Hydroxyl radicals and singlet oxygen photogenerated in the algal suspensions were detected. The maximum singlet oxygen yield was 75 microM in the presence of 1.0 x 10(6) cells mL(-1)C. sajao. About 5 microM hydroxyl radicals were generated in the 4-h reaction. Oxygen played an important role in the formation of reactive oxygen species in the algal suspensions. The nature of the algae facilitating the photodegradation of aniline was also investigated.

In this thesis, the photochemical reduction of hexavalent chromium Cr(VI) in the presence of algae, Chlorella vulgaris, was investigated under the irradiation of metal halide lamps (lambda = 365 nm, 250 W). The affecting factors of photochemical reduction were studied in detail, such as exposure time, initial Cr(VI) concentration, initial algae concentration and pH. The rate of Cr(VI) photochemical reduction increased with algae concentration increasing, exposure time increasing, initial Cr(VI) concentration decreasing and the decrease of pH. When pH increased to 6, the rate of Cr(VI) photochemical reduction nearly vanished. When initial Cr(VI) concentration ranged from 0.4 to 1.0 mg L(-1) and initial algae concentration ranged from ABS(algae) (the absorbency of algae) = 0.025 to ABS(algae) = 0.180, According to the results of kinetic analyses, the kinetic equation of Cr(VI) photochemical reduction in aqueous solution with algae under 250 W metal halide lamps was V0 = kC(0)(0.1718)A(algae)(0.5235) (C0 was initial concentration of Cr(VI); A(algae) was initial concentration of algae) under the condition of pH 4.

The characterization of the Chlorella vulgaris solution was carried out using synchronous-scan spectroscopy. The range of concentration of algae and Fe(III) in aqueous solutions were 5 x 10(8)-8 x 10(9) cells l(-1) and 10-60 microM, respectively. Effective characterization method used was synchronous-scan fluorescence spectroscopy. The wavelength difference (Deltalambda) of 90 nm was maintained between excitation and emission wavelengths; 90 nm was found to be the best Deltalambda for effective characterization of Chlorella vulgaris solution with or without quencher species (e.g., Fe(III), humic acid (HA)) for the first time. The peak was observed at about EX 236.6 nm/EM 326.6 nm for synchronous-scan fluorescence spectra. The fluorescence quenching of algae in system of algae-Fe(III)-HA was studied using synchronous-scan spectroscopy for the first time. Fe(III) was clearly the effective quencher. The relationship between I0/I (quenching efficiency) and c (concentration of Fe(III) added) was a linear correlation for the algae solution with Fe(III). Also, Aldrich humic acid was found to be an effective quencher. pH effect on synchronous-scan fluorescence intensity of algal solution with Fe(III) and/or HA was evident.

The study showed that when exposed to high-pressure Hg-lamp (HPML, lambda(max) > or = 365 nm), and the concentration of Chlorella vulgaris was 4.0 x 10(10) cells x L(-1), the photodegradation rate of 17beta-estradiol could reach to 37%. When the concentration of Chlorella vulgaris was 4.2 x 10(10) cells x L(-1), the photodegradation of 1.5 x 10(-5) - 6.0 x 10(-5) mol x L(-1) 17beta-estradiol in aqueous solutions was pseudo-first order reaction. Increasing the initial concentration of 17beta-estradiol could lower its photodegradation rate. The influence of light intension and Chlorella vulgaris concentration on the photodegradation of 17beta-estradiol was also studied in this paper.