Screening Of Algal Biofilm Based On Photoplasm And Analysis Of Influencing Factors For Its Removal Effect In Cadmium Polluted Wastewater

Previous studies were focused on the effects of light intensity and photoperiod,while few studies have conducted on different light qualities(Different wavelengths of light contained in irradiated light)on microalgae growth and heavy metal removal.This paper selected Chlorella pyrenoidosa,Anabaena flos-aquae,Scenedesmus obliquus and Chlamydomonas reinhardtii as the experiment algae species.Selected algae species were cultured with Cadmium-containing wastewater to optimize cadmium removal efficiency.The algae species with best cadmium removal rate was then cultured under six different light qualities to investigate the light quality effect on the growth of microalgae,as well as the cadmium removal mechanisms.The main conclusions of this paper are listed as follows:(1)Different microalgae biofilms exhibited various tolerance level under same cadmium concentration.All selected algae biofilm except Anabaena flos-aquae biofilm demonstrated continuous growth in 10 mg/L cadmium solution.The removal rates of Cd from the biofilm of Chlorella pyrenoidosa,Scenedesmus obliquus,Anabaena flos-aquae,Chlamydomonas reinhardtii were55.19%,97.40%,94.08%and 55.30%,respectively.(2)The white-blue light was the most suitable light for the growth of Scenedesmus obliquus biofilm,with its biomass,protein content,chlorophyll a content and carotenoid content achieved 0.44 mg/L,0.30 mg/L,1.05 mg/L and1.49 mg/L,respectively,after 7-day incubation.(3)After normalization of the index data by z-score standardization method,the radar distribution index was plotted for comprehensive analysis.Results showed that the optimized algal membrane was Scenedesmus obliquus biofilm,and the light quality was white and blue.(4)Scenedesmus obliquus biofilm showed steady growth in cadmium solution at 6 mg/L,8 mg/L and 10 mg/L.Cadmium concentrations of 12 mg/L and 14 mg/L caused death effect on Scenedesmus obliquus biofilm.The toxicity of cadmium at high concentration showed lethal destruction of cell membrane.(5)Changes of each index were positively correlated when algae biofilm grew normally.When its growth was disturbed by cadmium,changes of each index were affected to different degree,leading to the change of the correlation among different indexes.However,a positive correlation was found between chlorophyll a and carotenoids under various cadmium concentration.(6)The adsorption of cadmium was consistent with pseudo second order kinetic model with a correlation ofR²=0.9996and adsorption rate at 0.0131min^-1.(7)The Alkanes,amino and carboxyl groups functional groups in the Scenedesmus obliquus biofilm changed during the adsorption and absorption of cadmium based on FT-IR results,indicating potential negative impact of cadmium on the functional groups attached to the algae surface.