Water Quality Analysis

Chlorine concentration

it is necessary to maintain at least 0.2 ppm of residual chlorine.

When the amount of chlorine is increased, it start to flavor the water and people may reject it in favor of less secure water sources.

Chlorine is consumed in the water itself and through contact with the interior wall of the pipe.

Wall coefficient

• The coefficient is found experimentally and is elusive.

• Plastic pipes have 0 wall coefficient.

• The coefficient can be measured by passing water of known concentration at constant flow rate through a long section of pipe, minimum 300 m.

Bulk coefficient

• This coefficient is measured experimentally, measuring how the chlorine coefficient in a glass container filled with water from the source change over time.

For Alem Tena water distribution system:

Assuming the bulk coefficient:

K = -0.2378 day -1

Plastic pipes have 0 wall coefficient

So first assuming the amount of chlorine added at the reservoir is 1ppm.

Steps

1. Water quality analysis can only be done in extended period simulation because we have to see the change over time. To change epanet in to extende- period mode we go to the data tab of the browser, and select options. In that menu, select times.

2. Specify what type of analysis you want to carry out Browser/option/Quality/ Parameter

3. Add the chlorine source. Click on reservoir and introduce 1 in the parameter initial quality

4. Define the chlorine consumptions, introducing the bulk cofficient in pipe properties

5. Calculate the network 6. observe the result

As it can be seen from the above image at 12 hr all of the nodes have greater than 0.8 mg/l residual chlorine level. Recommended residual chlorine is between 0.2-0.6 ppm. When the amount of chlorine is increased, it starts to flavor the water and people may reject it in favor of less secure water sources. This maximum value depends greatly on the population using the water and whether they are accustomed to chlorination or not. A maximum 0.6 ppm is advised. So the amount of residual chlorine must be reduced.

7. Change the concentration of chlorine at source to 0.5 ppm.

The chlorine concentration at source would maintain the chlorine values within the suitable range of values.

The objective of modeling chlorine is to detect points of excessive concentration that could cause refusal by consumers.

Water Age Analysis Water age – it measures how long the water stays in the network. It has two main purposes:1. To ensure contact time with chlorine: to ensure that water is drinkable it has to have had

contact with chlorine for 30 minutes.2. To avoid quality deterioration with time : when water spends a long time in pipes, the quality

deteriorate noticeably. As a general rule, plan for water to spend no more than one day in the network. (3 days recommended) It is in the furthest and most isolated areas of network where quality problems are greatest.

Steps1. To see how much time water spends in the pipes, do Browser/option/Quality/Age

The water spends between 1 – 24 hrs in the network, so the design is optimum.