Smell that? Careful noses improve scent and taste of Mpls. water

When the Minneapolis water works sucks water out of the Mississippi River that could best be described as eau de bait shop, Lucian Osuji's nose knows.

In an era of sophisticated machinery, the human nose is still the quickest way of detecting whether both incoming and treated water meet the smell test.

For Osuji and two other chemists at the city water works in Fridley, sniffing heated flasks of water is just part of a day's work. But it can mean a big difference downstream when city residents turn on their showers.

Those water customers are complaining far less than they used to about the taste and odor of city water. That smell of success? It comes in part from a 2010 upgrade to the system that adds activated carbon to water during treatment. When the noses — backed up by computer readings — detect something afoul, the system adds sufficient quantities of carbon to neutralize the off-putting taste or smell.

That typically happens in the spring, when snowmelt scours leaves and other material on the shore into the river, and the late summer or early fall, when river flow is low.

"When the ice is breaking, you get more" earthy smells, said Osuji, who has been sniffing water for 26 years.

George Kraynick, the city's water quality manager, added, "Sometimes the river just throws us a horrible smell, sometimes like a rotten tuna."

Knowing how much carbon to add has economic as well as aesthetic ramifications for the 57 million gallons of water treated daily. The Minneapolis water works spends about $1 million annually on powdered carbon, which becomes part of a slurry that is added to water during treatment. Molecules containing the offensive smells adhere to the carbon, which settles out later in the treatment process.

The noses of water works chemists aren't the only tool available for determining how much carbon to add. The water plant added a gas chromatograph mass spectrometer several years ago. The $120,000 machine has already saved the water works $180,000 by allowing it to sometimes cut back on carbon, when conditions allow. But it takes at least an hour to get a reading from the machine, if it's properly calibrated.

"Computers are great but sometimes they fail," Kraynick said.

Osuji and co-sniffers Andy Weyer and Chris Rydell can detect an "off" odor in the 10 minutes it takes to heat a water sample to the temperature of a hot home shower. That temperature is ideal for detecting odors as the trio evaluate samples for an assortment of odors on their score sheets: musty, metallic, stale, yeast, weak tea, rotten egg.

They typically smell it once, sometimes twice a day. If they have doubts, they can assemble a panel of a half-dozen people from the plant who have the training and the olfactory sensitivity to detect concentrations of a few parts per trillion.

"Before it goes into our system deeply, we can shut the intake," Osuji said.

There are also at least 24 hours built into the treatment process, as water is filtered, treated chemically, allowed to settle and refiltered before entering reservoirs or water mains.

Some residents are more sensitive to taste and odor than others. One was Heidi Hamilton, former deputy city public works director, who lived at the other end of Minneapolis from the plant. "Heidi called us up and said, 'I'm getting something.' She was really sensitive," Kraynick said.

The smell of city water also used to be a regular topic among the roughly 2,000 members of the online Minneapolis Issues Forum. But since the improvements to the treatment system? Hardly a whiff of debate.

Steve Brandt • 612-673-4438