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Chapter: Aquaculture Engineering - Disinfection

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Chick’s law and Watson’s law - law for disinfection

Chick’s law: Inactivation of micro-organisms in a disinfection plant depends on the time that the micro-organism are exposed to the disinfectant.

Basis of disinfection


Chick’s law

Inactivation of micro-organisms in a disinfection plant depends on the time that the micro-organism are exposed to the disinfectant. This is described by Chick’s law:

 

dn / dkN

 

where:

 

dn/dt= necessary time to inactivate n micro-organisms

 

=time constant depending on disinfectant,type of micro-organism and water quality

=number of live micro-organisms t =time.

 

This differential equation can be integrated within limits to give the following equation:

 

N1= N0ekt

 

where:

 

N0=number of micro-organisms at the start

N1=number of micro-organisms after time t.

 

Watson’s law

Based on the results of Chick’s law, Watson’s law can be developed:

 


where:

 

Λ = coefficient of specific toxicity

=concentration of disinfectant

=exponent (normally around 1)

=time after start-up.

This means that the relation between the number of active and inactive micro-organisms is a product of the concentration of the disinfectant and the exposure time.

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