Research On The Secretion And Release Characteristics Of Cyanobacterial Algae Organic Matter And Its Water Treatment Efficiency

Algae organic matter(AOM)is the organic matter produced in the cell or released out of the cell during the growth and metabolism of cyanobacteria,which is an important source of organic pollution and deterioration of water quality.Because of the complex components high water solubility and easy dispersion of cyanobacteria AOM,it is difficult to remove effectively in the conventional water treatment process,and it has become the main factor that affects the operation effect of the treatment process and deteriorates the treated water quality.In this study,pure microcystis aeruginosa in the laboratory culture environment and cyanobacteria in the actual water environment of Taihu Lake during the bloom outbreak were taken as the research objects,aimed at the release of extracellular organic matter(EOM)of cyanobacteria secreted outside the cell during its growth cycle and intracellular organic matter(IOM)of cyanobacteria that may be damaged due to decay or external stimulation and released inside the cell.From the aspects of organic content determination,spectral absorption characteristic analysis,molecular weight distribution,fluorescent substance component characteristic analysis,etc.,the structural characteristics of specific organic components of cyanobacteria EOM and IOM were investigated,and the pollution mechanism of cyanobacteria AOM naturally secreted into water and possibly stimulated to produce and release organic matter was explored.Through coagulation removal efficiency,Zeta potential change characteristics,floc size distribution,flocculation-combined fluorescent substance characteristics change and other indicators,the flocculation-combined characteristics and treatment efficiency of cyanobacteria EOM and IOM in coagulation process under different environments were compared and analyzed.By comparing the adsorption,binding and retention removal efficiencies of cyanobacteria EOM and IOM under different activated carbon adsorption,the change characteristics of material composition and binding group characteristics of cyanobacteria AOM before and after activated carbon adsorption,the preferential removal components and functional group binding efficiency of cyanobacteria AOM in activated carbon adsorption process were analyzed.The study found that:(1)The total output of cyanobacteria AOM increased gradually during the growth cycle Among them,the release amount of EOM in cyanobacteria is related to the metabolic rate,which continues to rise due to the rapid growth and strong metabolic activity of algae cells On the other hand,the secretion of IOM in cyanobacteria leads to the direct consumption of energy substances in algae cells due to the gradual loss of nutrients and the gradual decline of cell bodies,which shows that the synthesis of IOM decreases and gradually permeates and loses to the extracellular with the breakage of cell membrane.The SUVA value of cyanobacteria EOM is low,and the small molecular substances<3kDa account for a relatively high proportion,mainly hydrophilic humic acid,fulvic acid and small molecular amino acids with low aromaticity;The SUVA value of cyanobacteria IOM is higher,and the proportion of macromolecular substances>100kDa is relatively increased,while the proportion of small molecular substances<3kDa is decreased,mainly including aromatic protein,phenols,soluble metabolites,humic acid and fulvic acid,and the proportion of hydrophobic aromatic protein is higher.When cyanobacteria are cultured in the original ecological laboratory,the similarity between IOM and EOM synthesized and secreted by cyanobacteria is higher.However,in the complex physical Taihu Lake water environment,there are more abundant chemical components and diverse microbial community structures,resulting in more obvious heterogeneity of EOM and IOM of cyanobacteria under external stimulation.(2)The cyanobacteria EOM is more difficult to be removed by coagulation,and the dosage of coagulant required by cyanobacteria IOM is less than that of EOM,and the removal effect is better.However,the complex material composition in the actual water environment easily leads to the transformation of cyanobacteria AOM which tends to be easily separated from the water environment.The flocculation efficiency of cyanobacteria AOM is affected not only by the electric neutralization controlled by Zeta potential,but also by the content level and component distribution of the removed objects in water.The blue-green algae IOM contains more macromolecular substances which are easy to adsorb and bridge with coagulants,and can be caught and swept by nets,thus improving the coagulation efficiency EOM and IOM of cyanobacteria are not easy to form alum flowers,and their flocculation and sedimentation performance is poor.Compared with blue-green algae IOM,the floc formed by blue-green algae EOM has a wider size range and worse uniformity,which is one of the reasons for the poor coagulation removal effect of blue-green algae EOM.Coagulation process has a strong ability to remove organic substances such as protein through complexing reaction,adsorption and net capture.(3)The adsorption effect of activated carbon on cyanobacteria IOM is slightly better than that of cyanobacteria EOM,and the removal efficiency of UV254 is higher than that of DOC.The adsorption efficiency of activated carbon is related to the composition and content level of adsorbed substances.The removal effect of humic acid and fulvic acid in cyanobacteria EOM and cyanobacteria IOM by activated carbon is obviously better than that of protein,especially the hydrophilic phenolic hydroxyl,alcohol hydroxyl and carboxyl are the main active functional groups,which makes it easier for activated carbon to adsorb and remove.This paper provides an important theoretical basis and data support for the mechanism analysis,flocculation treatment and adsorption removal process of cyanobacteria AOM pollution.However,in view of the fact that the nitrogen-rich soluble protein organic products and humus substances can not be completely and effectively removed under the optimal coagulant dosage and the action of activated carbon with better adsorption effect in this study,reasonable process coordination and optimization should be carried out for the treatment process of cyanobacteria outbreak source water,and the process technology system with excellent control effect for cyanobacteria AOM organic pollution should be explored.