Research On The Property Of Algae Removal By Photoresponsive Advanced Oxidation Processes

The frequent occurrence of harmful algal blooms result in the worse environment and seriously affect the normal life of the human. Various technologies of the algae removal have been used to control harmful algal blooms. However, some of them can not been applied widely the removal of algae for high cost-consuming second pollution. Nowadays,the development of effective method for harmful algal blooms control has become one of the most important environmental issues.In recent years, advanced oxidation processes with advantages of strong oxidizing, no secondary pollution, economic and environmental protection has widely been used for degrading a variety of organic compounds. However, there is less study on the application of advanced oxidation processes to inhibit and eliminate cyanobacteria blooms.This paper adopted two kinds of advanced oxidation processes i.e. photocatalysis and sulfate radical anion to control cyanobacterial bloom in landscape water body. It has been found that the preponderant algae species causing water bloom is Microcystis aeruginosa through the microscopic analysis of samples in landscape water system. Then this paper studied the effect of photocatalysis and sulfate radical anion on removing Microcystis aeruginosa using the removal rate of chlorophyll a or total soluble protein as the indicator for algal removal.The following innovative progresses were achieved in this work:1) Zinc titanium hydrotalcite was prepared by urea hydrolysis-homogeneous coprecipitation and then calcinated to prepare composite metal oxide. The synthesized samples were characterized by X-ray diffraction(XRD), fourier transform infrared spectroscopy(FT-IR), thermogravimetry-differential thermal analysis(TG-DTA),transmission electron microscopy(TEM) and scanning electron microscopy(SEM). The conditions for preparing zinc titanium hydrotalcite and composite metal oxide were as follows: the molar ratio of zinc to titanium was 4:1, the crystallization time was 10 h, urea content was 0.10 mol. Zinc titanium hydrotalcite was calcinated for 6 h in air atomosphere at 700℃ to obtain a photocatalyst with high photocatalytic activity.2) Zinc titanium hydrotalcite and composite metal oxide with photocatalytic activity were applied to removel Microcystis aeruginosa. The optimal Microcystis aeruginosa removal conditions were obtained through the single factor experiments and orthogonal test. The removal rate of chlorophyll a and total soluble protein Zn-Ti LDHs were 96.38%and 90.87% when the photocatalyst dosage was 20 mg, irradiation time was 3.0 h, pH was8 and adsorption time was 30 min. The variation of relative content of microcystins indicated that photocatalyst can degrade the microcystins. The photocatalysis destroyed the cell wall and cell membrane and degraded the inclusions in algae cells.3) The sulfate free radical produced from sodium persulfate activated by ferrous ion and ultraviolet light was used to degrade Microcystis aeruginosa..Through the single factor experiments and orthogonal test, the optimal algal removal conditions were determined as follows: Na2S2O8/Fe2+ ratio was 2:1, sodium persulfate concentration was20 mg/L, pH was 7. The removal rate of chlorophyll a and total soluble protein Zn-Ti LDHs were 95.34% 和 92.78%. The variation of relative content of microcystins demonstrated that sulfate free radical can also degrade the microcystins.