Study On Flocculation Characteristics Of Microcystis Aeruginosa

In recent years,with the development of agriculture and industry,eutrophication of water is widespread in China,which leads to a large number of surface algae blooms outbreak phenomenon.On the one hand,algae release fishy smell and earthy smell of substances,algal toxins and other toxic substances and trihalomethane precursor material.All of these affect the safety of drinking water supply directly;on the other hand,algae breed rapidly in the filter,and may plug the filter layer.For most of the algae are small and suspended,it is difficult to treat.Flocculation and sedimentation is the most popular technology in removing algae and the type and concentration of flocculants and the pretreatment methods are the important factors that affect the treatment effect and running cost.Microcystis aeruginosa,which is one of the dominant algae species in the eutrophic water body,was selected as experimental material in this study.We try to get the most suitable flocculant type,concentration and its flocculation characteristics through the beaker experiments.The aim of this study is to explore the effects of pre-oxidation on flocculation,and to select the best effects of the pre-oxidants and the use of concentration.In addition,the potential environmental risks of flocculants and pre-oxidants will be evaluated in order to provide technical support for the removal of algae in production.The main results are as follows:Aluminum chloride?AlCl₃?,polyaluminium chloride?PAC?and polyacrylamide?PAM?had good flocculation effects on Microcystis aeruginosa,they could reduce the water turbidity and chlorophyll content for more than 80%.The optimum dosage of AlCl₃ was 12.0 mg/L,PAC was 5.0 mg/L,and PAM was only 1.0 mg/L.The flocculation characteristics of the three flocculants were also different.With the increase of dosing concentration,the water turbidity and chlorophyll removal rate of AlCl₃ and PAC increased significantly,while the PAM concentration was more than 1.0 mg/L,the removal rate decreased.After stirring,flocculation of alum produced precipitation time between AlCl₃,PAC and Microcystis aeruginosa was longer for about 2 h corresponding to 15 min of PAM.Accordingly,Microcystis aeruginosa removal by PAM is a better selection.The results of pretreatment with potassium permanganate?KMnO4?,sodium hypochlorite?NaClO?and hydrogen peroxide?H₂O₂?showed that the addition of preoxidizing agent can promote the flocculation effect of flocculant,and its type,adding concentration and treatment time affected flocculant flocculation effect of Microcystis aeruginosa.The best time for H₂O₂ and NaClO was 10 min,and KMnO4 treatment was 5 min.The choice of pre-oxidant type was related to the type of flocculant.When using AlCl₃ as flocculant,the effect of pre-oxidation treatment with 2.0 mg/L NaClO on flocculation is the best.When PAC was used as flocculant,the pre-oxidation treatment with 2.0 mg/L H₂O₂ could promote the flocculation effect of Microcystis aeruginosa.When using PAM as flocculant,5.0 mg/L H₂O₂ had the best effect.The use of three flocculants had a certain negative impact on water quality.The use of AlCl₃ and PAC increased the amount of Al in the water,and the use of PAM increased the amount of dissolved organic carbon?DOC?in the body.The use of the pre-oxidizer increases these two effects,especially the use of the preoxidizer could significantly increase the DOC content,which brings the potential risk to water quality.Although the pre-oxidant in improving the flocculation efficiency has a certain effect,it still needs further testing and evaluation in the production practice.