Experimental Study On Treatment Of Heavy Metal Lead In Wastewater By Algae Biofilm

Algae can be used to treat heavy metal in wastewater due to its strong adsorption capacity,while algae biofilm has demonstrated great potential in heavy metal treatment with advantages in biomass accumulation and post separation process.In this paper,Chlorella pyrenoidosa,Scenedesmus obliquus,Anabaena flos-aquae and Microcystis aeruginosa were selected as experimental species to analyze the adsorption capacity of lead by algae biofilm.Major influencing factors and mechanisms of lead removal by algae biofilm were studied.Main conclusions of this paper are listed as follows:（1）In general,Scenedesmus obliquus biofilm showed adequate activity under lead stress and excellent removal efficiency.After treatment,the residual lead concentration in the 5 mg/L group was 0.62 mg/L with a removal rate of 87.66%,while in the 10 mg/L group lead concentration decreased to 0.47 mg/L with a removal rate of 95.24% over 7 days of experiment.（2）Results of single factor experiment indicated that in lead stress experiment,under lead concentration of 6 mg/L,Scenedesmus obliquus biofilm achieved highest lead removal rate at 93.94% with chlorophyll a content at 2.69mg/L.In light intensity experiment,results showed that under 2000 lux,Scenedesmus obliquus biofilm demonstrated lead removal rate of 90.38%.Also,during the biomass and p H single factor experiment,when biomass of Scenedesmus obliquus biofilm reached 0.8 g/L and p H at 7.5,the removal rate of lead can be as high as 98.38%and 96.93% respectively.Competing mechanisms with Ca²⁺ and Mg²⁺was tested during the experiment,results showed that both cations can accelerate the removal of lead by biofilms.Through orthogonal experimental analysis,it was found that the light intensity had the greatest effect on the removal of lead by Scenedesmus obliquus biofilm,followed by p H and initial lead concentration,and the influence of algal biomass is the smallest.（3）During the adsorption experiment,most of the lead can be adsorbed by Scenedesmus obliquus biofilm and reached adsorption equilibrium in the first 9 hours.The maximum concentration of lead adsorbed by Scenedesmus obliquus biofilm reached 7.32 mg/L,accounting for 93.85% of the total adsorption capacity.The adsorption process of lead by Scenedesmus obliquus biofilm was consistent with the pseudo-second-order kinetic model,with a correlation R²=0.9999 with adsorption rate of 0.0479 min^-1.The equilibrium adsorption concentration predicted by the model was 7.33 mg/L,which was similar to the actual adsorption concentration measured.Lead demonstrated negative effect on the membrane hanging ability and the cell morphology of algae.The hydroxyl,carboxyl and methylene groups in algal could be essential in the adsorption process of lead on Scenedesmus obliquus biofilm based on FT-IR results.