Coliforms

The unit models transport and decay of coliforms in a river.

Description

The variable representing coliforms is simply a transported substance that can decay according to first order kinetics. It does not interact with any other variable. It therefore behaves in all respects like a decaying pollutant (see DECAY).

The primary use is to model the variation of E-coli or any other bacteria.  The only parameter required to model them is their decay rate expressed in terms of a T₉₀ value. T₉₀ (in hours) is the time taken for a population to reduce to 10% of its original density.  In this respect it is different from DECAY which uses a decay rate (K) instead of T₉₀. The T₉₀ value can be varied between daytime and night-time. This allows for the increased mortality of the bacteria due to the effect of sunlight.

Equations

The decay of coliforms is simulated by a first order decay equation:

                    (1)

Where:
K = decay rate (s^-1)
C = concentration of coliforms (user defined units)

The first order decay rate constant, K (sec^-1) is obtained from T₉₀(hours) by:

                    (2)

General

The COLIFORMS module may be run independently of the other water quality modules. The COLIFORMS module simulates the transported variable name:

• Coliforms (user-defined units)