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CHLORINATION OF PUBLIC WATER SYSTEM: ENSURING SAFETY AND QUALITY
Chlorination is a top-of-mind issue for water operators. First used in 1908 to treat drinking water, chlorine is a key component in the water operator’s toolbox for preventing the growth of harmful bacteria. Before its widespread use, people were at risk for contracting cholera, typhoid fever, dysentery and hepatitis A, and in fact, people died by the thousands each year from these illnesses.
Chlorinating water also offers other benefits beyond its principal function of disinfecting water supplies. These include:
- Removing or minimizing unpleasant tastes and smells;
- Getting rid of bacteria that produce slime, mold and algae;
- Eliminating other chemical compounds with disagreeable tastes and which can interfere with disinfecting;
- Reducing the amount of iron and manganese in water.
In their Review of Disinfectant Practices, the U.S. Chlorine Chemistry Council and the Canadian Chlorine Coordinating Committee (2003) note: “Only chlorine-based chemicals provide ‘residual disinfectant’ levels that prevent microbial re-growth and help protect treated water throughout the distribution system.”
Over the past year, chlorine and chlorination practices have been a frequent topic for discussion in the FluksAqua Forum. The most popular questions have focused on best practices and alternatives to chlorine use.
There are several excellent manuals available online for helping water operators maintain optimal water quality and safety in their water systems. Some of these manuals focus on small water systems, while others look more specifically at water disinfection or reflect a collaborative approach between Canadian and American water operators.
UPSTREAM OR DOWNSTREAM CHLORINATION?
Let’s take a look at one of the most popular questions we received in the forum: in terms of water quality, what is better: upstream or downstream chlorination? Responders to the question were largely in favour of upstream chlorination for several reasons:
- Operators can amortize the chlorine concentration by spreading it through a storage volume (tank or reservoir);
- Operators can protect their tank from bacteriological problems with the extra chlorine in the system;
- Adding chlorine upstream allows the operator to take advantage of water contact time.
Key things to remember in using chlorine include:
- maintaining the required contact time;
- paying attention to residual chlorine concentration;
- respecting the difference between average residence time vs. actual residence time in tanks;
- making sure the structure, if buried, has waterproof flaps to minimize corrosion damage (rusting) from chlorine seepage and to reduce risks to water system personnel.
One poster, Adeline, advised: “If the operation concerns a reservoir, both systems are possible but closely monitor the water residence time in the reservoir and the dose of disinfectant. These two parameters affect the by-products, particularly THMs. Chlorination (that can be regulated) at the output of a catchment or treatment plant at the base of the pump or recirculation tank (upstream or downstream of a reservoir) is an ideal way of distributing chlorine in your network.”
ALTERNATIVES TO CHLORINE
Given the safety issues chlorine use can pose and public concerns with chemicals generally, water operators are considering alternatives as part of ongoing quality improvement initiatives. Those concerns, along with consumer dissatisfaction with the “bleachy” smell and taste of water from some systems, are driving the research for alternatives to chlorine as a water treatment chemical.
The discussion in the forum highlighted the use of ozone, bromine and persulfates as possible alternatives to chlorine. Commenters noted ozone could eliminate almost all the safety issues posed by chlorine. Poster Neil suggested using bromine, although it is more expensive than chlorine. A big plus, though, is that “water does not require as much testing and is more stable than chlorine, meaning it stays balanced for a longer period of time.”
Examining the various implications of chlorine’s use in disinfecting water offers potential for innovation. The Netherlands has avoided chlorine and identified four points to ensure water quality and safety. These are:
- Using the best water sources available;
- Using alternate disinfection methods;
- Preventing contamination and microbial growth during distribution;
- Monitoring closely for timely failure detection.
How feasible are these approaches for your water system? Would you be able to eliminate chlorine use? Join us at FluksAqua’s online Q&A forums to talk about how you deal with the issues chlorination can pose and what innovations you are considering.
In the FluksAqua forums, you can keep up with what’s new in the industry, seek support from other experienced operators, or help your colleagues with their operational issues. If you’re hearing concerns from your colleagues and the people in your communities, share them with us! Our members represent organizations and communities that contribute key indicators we can use to measure and compare the performance of water networks all over the world.