Disinfection temperature effects

If the third substance dissolves in both liquids (and the solubility in each of the liquids is of the same order), the mutual solubility of the liquids will be increased and an upper C.S.T. will be lowered, as is the case when succinic acid or sodium oleate is added to the phenol - water system. A 0 083 molar solution of sodium oleate lowers the C.S.T. by 56 -7° this large effect has been applied industrially in the preparation of the disinfectant sold under the name of Lysol. Mixtures of tar acids (phenol cresols) do not mix completely with water at the ordinary temperature, but the addition of a small amount of soap ( = sodium oleate) lowers the miscibility temperature so that Lysol exists as a clear liquid at the ordinary temperature. 

Disinfection. Ozone is a more effective broad-spectmm disinfectant than chlorine-based compounds (105). Ozone is very effective against bacteria because even concentrations as low as 0.01 ppm are toxic to bacteria. Whereas disinfection of bacteria by chlorine involves the diffusion of HOGl through the ceU membrane, disinfection by ozone occurs with the lysing (ie, mpture) of the ceU wall. The disinfection rate depends on the type of organism and is affected by ozone concentration, temperature (106), pH, turbidity, clumping of organisms, oxidizable substances, and the type of contactor employed (107). The presence of oxidizable substances in ordinary water can retard disinfection until the initial ozone demand is satisfied, at which point rapid disinfection is observed. 

Boiling - This involves bringing the water to its boiling point in a container over heat. The water must be maintained at this temperature 15 to 20 minutes. This will disinfect the water. Boiling water is an effective method of treatment because no important waterborne diseases are caused by heat-resisting organisms. 

It has also been demonstrated that the germicidal effectiveness of free and combined chlorine is markedly diminished with decreasing water temperature. In any situation in which the effects of lowered temperature and high pH value are combined, reduced efficiency of free chlorine and chloramines is marked. These factors directly affect the exposure time needed to achieve satisfactory disinfection. Under the most ideal conditions, the contact time needed with free available chlorine may only be on the order of a few minutes combined available chlorine under the same conditions might require hours. 

The third is the effect of temperature as typically the inactivation rate increases/decreases with temperature for gram-positive/gram-negative bacteria. The exception to this rule are coliforms. All microorganisms display, in any case, very narrow temperature ranges where photocatalytic disinfection activity reaches maximum values. ... 

Halogen a ted Hydantoins. These are stable solids with limited use as bleaches. They dissolve too slowly to use in household laundry and automatic dishwashing. l,3-Dichloro-5,5-dimethylhydantoin [118-52-5] (3) is sold with 65—75% available chlorine. It is used as a bleach in hospital and other industrial laundries and in disinfectant cleaners. Some l-bromo-3-chloro-5,5-dimethylhydantoin [6079-88-2] is also used. It is a more effective bleach and disinfectant at lower temperatures and higher alkalinities than l,3-dichloro-5,5-dimethylhydantoin because it hydrolyzes to hypobromite. 

PHENOL COEFFICIENT. In determining the effectiveness of a disinfectant using phenol as a standard of comparison, the phenol coefficient is a value obtained by dividing the highest dilution of the test disinfectant by the highest dilution of phenol that sterilizes a given culture of bacteria under standard conditions of time and temperature. 

Similar to ozonation processes, since the discovery of the germicidal effects of solar UV radiation by Downes and Blount in 1877 [13], UV radiation was first used for disinfection. The development of reaction mechanisms in photochemistry led to the discovery of the advantages of UV radiation as an oxidation technology. At room temperature, most molecules... 

A very commonly used disinfectant is ethanol-water in neutral or, preferably, in acidic conditions. Aqueous ethanol displays its best germicidal efficiency at a concentration of 60 to 70%. However, the most commonly used concentration in industry is about 20%, because higher concentrations require specific explosion-proof facilities. At 20%, ethanol has no sporicidal effect, its effect on viral inactivation is only partial and it does not destroy pyrogens (it only tends to destabilize large molecular aggregates of lipopolysaccharide molecules). For these reasons, 20% ethanol can only be considered as a bacteriostatic agent. Mixtures of ethanol with bases or acids are somewhat more sporicidal, but are not sufficient to provide sterilization at short incubation times and low temperatures. 

The effectivity of disinfectants are affected by the following factors time of contact between disinfectant and the microorganism and the intensity of the disinfectant, age of the microorganism, nature of the suspending liquid, and temperature. Each of these factors are discussed next. 

We have learned from previous chapters that equilibrium and reaction constants are affected by temperature. The length of time that a disinfection process proceeds is a function of the constants of the underlying reaction between the microorganism and the disinfectant thus, it must also be a function of temperature. The variation of the contact time to effect a given percentage kill with respect to temperature can therefore be modeled by means of the Van t Hoff equation. This equation was derived for the equilibrium constants in Chapter 11, which is reproduced next ... 

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