Stinky Water

Ahhh! There’s nothing more refreshing on a hot summer day than a tall glass of cold, sparkling water. But what if that water smells like mold and tastes like dirt? The satisfied “Ahhh” can quickly turn into a disgusted “Ewwwwwwwwwww!”

Lots of places on Earth have nasty drinking water. Much is not fit to drink by humans. Drinking water in the Phoenix metropolitan area is clean. However, sometimes it has a taste and odor problem. Scientists at Arizona State University are trying to figure out how to make the water more pleasant to drink.

“We knew that there were problems with how the water in our area tastes and smells. Salt River Project has been trying to deal with this problem for years,” says Milton Sommerfeld, a plant biologist at ASU. Sommerfeld and his team decided to study stinky water in the Phoenix area. However, they had a tough time finding good information about the problem. Not much was written down.

There is a lot more information available now, thanks to Sommerfeld and his research team. In 2002, the group finished a three-year study. The work was funded by the City of Phoenix. The ASU scientists studied water samples from reservoirs such as Saguaro Lake and Bartlett Lake. They studied water from canals used to transport that water. They also studied samples from the actual water treatment plants in Phoenix.

The funky water odor comes from tiny plants called cyanobacteria. These plants live in the water.

“The cyanobacteria produce chemicals that leak into the water. These chemicals cause the water to smell musty and moldy,” explains Kirsten Hintze, a doctoral student on the research team.

The main chemical that causes problems is called MIB. Treatment plants remove some of the MIB from the water using powdered, activated carbon. However, it costs too much to remove all the MIB this way when levels are very high. Instead, the researchers decided to track the problem to its source.

“We’re trying to better understand the organisms that produce the problems. Maybe we can prevent or reduce the problem at the source,” says Hintze.

The first challenge was finding out what causes cyanobacteria to produce MIB. Not all cyanobacteria produce MIB, and the types that do don’t produce it all the time. The researchers wanted to know what causes cyanobacteria to churn out high levels of MIB.

To find out, they measured different characteristics of the water itself. They measured temperature, pH, nutrient levels, and the amount of salt in the water. The scientists already suspected that temperature affected MIB. Their main clue was that taste and odor problems usually occur in late summer and early fall. Sure enough, they were right. The hotter it gets, the more the water begins to stink and taste bad.

“We found that we don’t have problems with organisms until the temperature exceeds 22 degrees Celsius (71.6 degrees Fahrenheit),” says Sommerfeld.

The team also found that MIB production goes up when nitrogen levels in the water are high. So far, they have not found any other correlations.

Another key to tracking MIB is learning which strains of the bacteria produce the chemical. There are many types of cyanobacteria, but only some of them produce MIB. The only way to tell if a particular strain will produce MIB is to take a sample and grow it in the laboratory. Unfortunately, it’s hard to mimic lake conditions in the lab. Some bacteria simply quit producing there.

“We spent three years trying to isolate a good MIB producer from Saguaro Lake. It’s hard to replicate the exact conditions of the lake in a lab. You can mimic the temperature. You can use lake water. But it’s still a different environment,” says Sommerfeld.

Understanding cyanobacteria is helping the researchers to prevent and treat the stinky water problem. The methods they use depend on where the cyanobacteria are growing.

“MIB can be produced in the lakes, canals, or treatment plants,” says Sommerfeld. “There are large areas where these organisms can grow and produce.”

Canals
Canals may be the easiest places to combat MIB. One way to do this is to add copper to the water. Copper kills the cyanobacteria so it cannot produce MIB. Another solution is to use a special brush that scrapes the cyanobacteria off the canal walls.

Both of these techniques are very effective. But Sommerfeld says that there are 135 miles of canals winding through the Phoenix area. It would be too time-consuming and expensive to repeatedly treat and brush all of the canals. So the researchers tried to find the hot spots that produce the most MIB.

They discovered that the highest production occurs between the Squaw Peak and Deer Valley water treatment plants. Other areas also produce large amounts of MIB, sometimes. The researchers monitor the other areas and recommend places for SRP to brush or add copper.

Lakes
Not all MIB is produced in the canals. Some of it comes from the lakes that are used as reservoirs. Treating lakes is more difficult than treating canals.

“You can’t scrape the sides in the rivers and reservoirs. There are no sides. And you can’t dump in biocides—there are too many other things that could be harmed,” says Hintze.

However, the researchers made an important discovery that helps them avoid stinky water from the lakes. Cyanobacteria tend to live in the upper layers of the water. It is warmer near the top, and there is lots of light.

“Think of when you jump in a lake and go swimming,” says Sommerfeld. “On top, the water is warm, but down below, it’s cold.”

In Saguaro and Bartlett Lakes, drinking water is always pulled from the bottom of the reservoir. Lake Pleasant, however, has two outlets—one at the top and one at the bottom. Now that the scientists know the bottom water has less MIB, they can pull water from the bottom of Lake Pleasant during high MIB months. This helps reduce the amount of MIB that gets released.

Treatment Plants All of this drinking water goes through a water treatment plant before moving on to homes and businesses. Cyanobacteria can grow in treatment plants, just as it grows in lakes and canals. Plant operators kill this cyanobacteria using copper, just as they do in the canals.

However, if MIB is already in the water when it flows into the plant, copper will not have any effect. To remove existing MIB, plant operators use powdered, activated carbon (PAC). They dump the PAC in the water, where it absorbs the molecules that cause the bad taste and smell. The PAC then sinks to the bottom. The plant operators skim the clean water off the top and dispose of the dirty carbon.

During high MIB months, this option becomes very expensive. However, Sommerfeld and his team have found ways to make it more cost-effective. For example, they learned that some types of PAC work better than others.

“We evaluated the PAC used by treatment plants to find out which were most cost-effective. It saved the cities considerable money,” says Sommerfeld.

“More recently, some of the treatment plants have added activated carbon filters. The water runs through beds of carbon. We continue to explore other technologies that might help solve the problem,” he adds.

In 2002, the ASU team began taking weekly water samples during high odor months. They take samples at 10 different locations. The scientists also send out a weekly newsletter with all the data they collect. They make recommendations for how to deal with the problem. Workers at the treatment plants also contribute information.

Sommerfeld adds, “The cities of Chandler and Phoenix now have taste and odor panels.” A group of people rate water samples based on their smell and taste. It’s kind of like a wine tasting for stinky water.

All of these efforts help ensure that our water tastes good, without costing a fortune.

“I think this is one of the success stories of ASU working with cities,” says Sommerfeld. “It allowed us to apply the scientific method to a real life problem.”—Diane Boudreau