同©大学 Tongji University m. Mechanisms of Disinfectants The five principal mechanisms that have been proposed to explain the action of disinfectants are: (1)damage to the cell wall:cell wall lysis;inhibited synthesis (2)alteration of cell permeability:detergent,loss ofselectivity (N,P) (3)alteration of the colloidal nature of the protoplasm:heat,radiation, coagulation;acid,base (4)disruption of replication of DNA or RNA:UV photons (5)inhibition of enzyme activity:O3,Cl2
Tongji University Ⅲ. Mechanisms of Disinfectants The five principal mechanisms that have been proposed to explain the action of disinfectants are: (1) damage to the cell wall: cell wall lysis; inhibited synthesis (2) alteration of cell permeability: detergent, loss of selectivity (N,P) (3) alteration of the colloidal nature of the protoplasm: heat, radiation, coagulation; acid, base (4) disruption of replication of DNA or RNA: UV photons (5) inhibition of enzyme activity: O3 , Cl2
同燎大学 Tongji University IV.Factors Influencing the Action of Disinfectants In applying the disinfectants,the following factors must be considered: (10 Contact time; (2) Concentration of the disinfectant, (3) Intensity and nature of physical agent or means, (4) Temperature, (5) Types of organisms, (6) Nature of suspending liquid
Tongji University Ⅳ. Factors Influencing the Action of Disinfectants In applying the disinfectants, the following factors must be considered: (1) Contact time; (2) Concentration of the disinfectant, (3) Intensity and nature of physical agent or means, (4) Temperature, (5) Types of organisms, (6) Nature of suspending liquid
同©大学 Tongji University Contact Time 1.Most important variable in the disinfection process. 2. For a given concentration of disinfectant,the longer the contact time,the greater the kill Fig.11-1). 3.Chick's law is: dNL=-kN: (11-1) dt Where dN/dt rate of change in the concentration of organisms with time k=inactivation rate constant,T-1 N,=number of organisms at time t
Tongji University Contact Time 1. Most important variable in the disinfection process. 2. For a given concentration of disinfectant, the longer the contact time, the greater the kill ( Fig.11-1). 3. Chick’s law is: Where dNt /dt = rate of change in the concentration of organisms with time k = inactivation rate constant, T-1 Nt = number of organisms at time t t t dN kN dt (11-1)
同©大学 Tongji University Figure 11-1 Effect of time and concentration on survival of dispersed E.coli in a batch reactor using chlorine as disinfectant at 20C 0 Increasing chlorine dose 2 3 D2>D1 Da>D2 5 6 0.1 1 10 Time,min
Tongji University Figure 11-1 Effect of time and concentration on survival of dispersed E. coli in a batch reactor using chlorine as disinfectant at 20℃