Sunday, April 18, 2010

Cleaning Mickey Mouse

It is everywhere, the “Mickey Mouse” of molecules, H2O or water. It is essential for life, animal, plant, and even bacteria. Bacteria can live in our water pipes, which can pose a risk to human health. In the article (2009) “Effect of free chlorine application on microbial quality of drinking water in chloraminated distribution systems” researchers from Chile, Massachusetts, and North Carolina developed a new method of measuring bacteria amounts in water by flow cytometry.

Water Crisis Worsens In Southern England
The old method, R2A ager, did not show scientists an accurate representation of the bacteria amounts in water. However, flow cytometry uses a dye that causes organic material (bacteria) to glow, making it easier for scientists to count the number of bacteria present in a water sample.

Bacteria eat the ammonia produced by decaying materials and release nitrate and nitrite into the water in a process called nitrification. When pregnant women drink nitrate/nitrite rich water the nitrate competes with the oxygen in the blood of the fetus, causing the child to be born with blue tinted skin. Blue baby syndrome which results from low oxygen levels in the bloodstream.

The Distribution Systems (DS) or water plants, in the research used Chloramines as their primary method of disinfection due to its ability to kill bacteria without producing high levels of harmful by-products.

The trade-off is higher nitrification levels in chloramine treated water. In an effort to reduce nitrification levels in tap water North Carolina law requires water treatment facilities that use chloraminated disinfection as its primary disinfectant to flush the system with free chlorine of hypochlorous acid one month a year in order to reduce nitrification levels.

While the free chlorine reduces nitrification levels it presents other health problem for people. The free chlorine reacts with the water to make harmful by-products like chloroform a known carcinogen, thereby preventing its widespread use.

In areas where water is in constant use like urban and suburban centers, the public doesn’t face as much risk as people in dead end sites. A “dead end site” is essentially where water sits or pools for long periods of time, like a school during summer (1).

The researchers looked at a closed community center and found that before the introduction of free chlorine into the DS the water showed high levels of nitrification. In order to move the free chlorinated water into the community center, hydrant flushing or opening up a water source in order to get water moving was used. Once the free chlorinated water reached the community center nitrification went down, but the levels of chloroform levels increased. A second hydrant flushing was needed to remove the chloroform rich water, however it was not done.

According to Dr. Detlef Knappe a researcher in the article, the flow cytometry method of calculating bacteria count will hopefully help engineers and scientists to strike a balance between bacterial and negative chemical effects.

By engineering water systems that circulate water to eliminate dead end sites or creating a balance between chemical disinfectant and bacterial amounts flow cytometry will help provide clean and safe water to the public.

For more information on the concepts in this blog please check out:

(1)Rosenfeldt EJ, Baeza C, Knappe DR. 2009. Effect of free chlorine application on microbial quality of drinking water in chloraminated distribution systems. American Water Works Association 101(10):60-70.

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