Preliminary Study On The Biocidal Performance And Mechanism Of Inorganic Salts And Polyquaternary Ammonium Salts

In this dissertation,5 kinds of representative inorganic salts,such as NaCl,LiCl,CaCl₂,MgCl₂ and AlCl₃,including both mono and multivalent cations,and 4 kinds of polyquaternary ammonium salts PDMDAAC（[η]:0.86,1.30,2.30,3.11）with serial intrinsic viscosities were adopted to study the biocidal performance and the underlying mechanism.Using Escherichia coli（Chlorella）as the tested bacteria（algae）,the effects of the salt concentration,charge concentration and ionic radius of inorganic salts,and the concentration,intrinsic viscosity values of polyquaternary ammonium salts on the biocidal performance were investigated by plate counting method（chlorophyll-a determination）.The obtained results laid the foundation of the biocidal mechanism research.The experimental results are as following:For the moderately polluted water（eutrophic water）with bacteria content（chlorophyll-a content）of 10⁵cells/mL（300μg/L）,5 kinds of inorganic salts with the salt concentration of0.3².4mol/L or the charge concentration of 0.3⁴.2mol/L are added respectively.The bactericidal（algicidal）effect increases with the increase of the salt concentration,charge concentration,or cationic valence,and increases with the decrease of the ionic radius.When the salt concentration is 2.4mol/L,the maximum bactericidal rates（algicidal rates）of 24h are48.44%,56.14%,66.71%,84.38%,95.45%（33.24%,45.72%,50.22%,60.95%,75.88%）,respectively,that is,the order of bactericidal（algicidal）efficiency is NaCl<LiCl<CaCl₂<MgCl₂<AlCl₃.For the moderately polluted water（eutrophic water）with bacterial content（chlorophyll-a content）of 10⁵cells/mL（300μg/L）,4 kinds of polyquaternary ammonium salts with salt concentration of 0.04⁰.68mg/L（4⁶8mg/L）are added respectively.The bactericidal（algicidal）effect increases with the increase of the salt concentration and intrinsic viscosity.When the salt concentration is 0.68mg/L（68mg/L）,the maximum bactericidal rates（algicidal rates）of 24h are 68.89%,80%,87.89%,98.76%（51.24%,58.97%,65.30%,78.62%）,respectively,that is,the order of bactericidal（algicidal）efficiency is PDMDAAC（[η]:0.86<1.30<2.30<3.11）.The biocidal process of inorganic salts and polyquaternary ammonium salts were sdudied,and the knowladge of the underlying mechanism were obtained by the means of Zeta potential determination,IR spectrum analysis and SEM observation.The results show that:Based on the establishment of the bactericidal（algicidal）mechanism model of inorganic salts,the detailed description of the bactericidal（algicidal）action process of inorganic salts is given.Firstly,the inorganic salt cations are adsorbed on the bacteria（algae）cell surface with negative charges to cause the charge neutralization,and the apparent osmotic pressure difference of intra-and extracellular is formed simultaneously.Especially,the outer membrane substance of cell wall such as polysaccharides can be peeled off（the structure of outer layer pectin can be destroyed）,and the cell wall strongly damages because the complexation occurs between multivalent cations and functional groups on the cell surface accompanied with the flocculation.Then,the balance of intra-and extracellular osmotic pressure is largely damaged,which leads to cytoplasm leaking out and the structure of cell wall collapsing.Finally,the cellular metabolism is disabled to cause the death of the bateria（algae）cell.Based on the establishment of the bactericidal（algicidal）mechanism model of polyquaternary ammonium salts,the detailed description of the bactericidal（algicidal）action process of polyquaternary ammonium salts is given.Firstly,the polyquaternary ammonium salts are adsorbed on the bacteria（algae）cell surface with negative charge.The charge neutralization due to the polyquaternary ammonium salts and polysaccharides in the outer membrane of cell wall（galacturonic acid and other substances in the outer layer of cell wall）occurs to damage the outer membrane（outer layer pectin）barrier,and the cell wall is broken and collapsed.Then,polyquaternary ammonium salts penetrate the peptidoglycan layer（cellulose layer）and bind to the cell membrane to cause secondary damage.Finally,the cytoplasm leaks out to cause the the death of the bacteria（algae）cell.