When chlorinating treated wastewater, which chlorine residual do we test for?

When chlorinating treated wastewater, the appropriate chlorine residual to test for is primarily free chlorine. Free chlorine refers to the amount of chlorine available to disinfect and is crucial in ensuring that harmful pathogens are effectively eliminated from the water.

While testing for chloramine and total chlorine can provide useful information, especially in systems where chloramines are used as a secondary disinfectant, it is free chlorine that is the primary focus during the disinfection process. Free chlorine is the form of chlorine that has not reacted with any contaminants in the water and is available to perform the necessary disinfection.

Total chlorine encompasses both free and combined chlorine but may not provide an accurate representation of the effectiveness of disinfection. Combined chlorine consists of chlorine that has already reacted with ammonia or organic nitrogen compounds and is less effective as a disinfectant.

Testing for residual chlorine is important as it indicates whether there is enough chlorine remaining in the system to maintain disinfection throughout the distribution system. However, the focus on specific types of chlorine residual can vary depending on treatment methods and objectives, which could lead to confusion in selecting the correct response.

In conclusion, focusing on free chlorine residual gives the best indication of disinfection potential, while testing for chloramine and total chlorines offers a broader understanding of the chlorine chemistry