Lesson 19:

Disinfection

 

Process Control Calculations

There are several calculations that are useful in operating a chlorination system. These include chlorine feed rate, chlorine dose, and chlorine demand.

 

 

Chlorine Feed Rate

 

Here is an example using the equation above:

The chorine dose is 7.25 mg/L and the flow rate is 3.25 MGD. What is the feed rate for chlorine in pounds per day?

 

 

Chlorine Dose

 

Here is an example using the equation above:

The scale indicates that the plant has used 332 pounds of chlorine during the past twenty-four hours. The flow for the same period was 5.27 MGD. What is the dose of chlorine applied to the wastewater in milligrams/liter?

 

 

Chlorine Demand

Demand, mg/L = Dose, mg/L - Residual, mg/L

 

Here is an exaple using the equation above:

If the chlorine residual for the previous example was 1.3 mg/L, what was the chlorine demand?

Demand, mg/L = 7.6 mg/L - 1.3 mg/L

Demand, mg/L = 6.3 mg/L

 

 

 

Review

Disinfection is the act of killing the pathogenic organisms in water.  This prevents the spread of waterborne diseases.

Chlorination is the most widespread form of disinfection.  Chlorine can be added to water in various forms - chlorine gas, hypochlorites and bleaches, chloramines, and chlorine dioxide.

Use of ozone and UV light for disinfection may become more widespread in the future as a result of the many disadvantages of chlorine.  

 

Assignment

Answer the following questions and send in to you instructor. Each question is worth 25 points.

  1. The chlorine dose is 6.58 mg/L and the flow rate is 2.85 MGD. What is the feed rate for chlorine in pounds per day?

  2. The scale indicates that the plant has used 275 pounds of chlorine during the past 24 hours. The flow for the same period was 4.85 MGD. What is the dose of chlorine applied to the wastewater in mg/L?

  3. If the chlorine residual for the previous problem was 1.8, what was the chlorine demand?

  4. Complete Assignment 19 on Disinfection and Chlorination. You may do the Assignment online to get credit or print it out and send it to the instructor.

 

Quiz

Answer the questions in the Lesson 19 quiz .  When you have gotten all the answers correct, print the page and either mail or fax it to the instructor.  You may also take the quiz online and submit your grade directly into the database for grading purposes.