Pioneer Press:  Members of the public got a chance Saturday to peek inside the enormous building at Howard Street and McCormick Boulevard and see how employees there treat sewage water until it’s clean enough to release into the public waterways.

The Metropolitan Water Reclamation District of Greater Chicago held an open house on May 4 at the O’Brien Water Reclamation Plant in Skokie in honor of Chicago Water Week. Employees led tour groups to demonstrate how water comes into the plant and how it is treated to remove solids and bacteria before being discharged into the North Shore Channel of the Chicago River.  According to the plant’s operations manager, Lynn Kohlhaas, the process takes weeks of what nature usually does on its own and narrows it to 12 hours.

The raw sewage that arrives at the O’Brien plant at 3500 Howard St., Skokie, comes from sewers and drains across much of the northern suburbs, from about as far west as Des Plaines to Lake Michigan on the east and between the Chicago city limits on the south up to the Cook and Lake County border on the north. The plant can treat up to 500 million gallons a day.

The water the reclamation plant treats is not clean enough to drink, and most municipalities in the area get their drinking water from either the city of Chicago or the city of Evanston. Kohlhaas said the water is 99.9% clean but still not up to federal and state drinking water standards. She said if someone were to take the water and run it through an additional water disinfection, that the average person should be able to drink it.

At the O’Brien plant, water undergoes three treatment phases. In the first, wastewater passes through coarse screens to filter out large debris. Aerated grit tanks and settling tanks then filter out fats and oils from the water. About 60% to 80% of the solids are removed in that phase.

In the second step, microorganisms are introduced to eat up organic material. One tour leader described it as an “all-you-can-eat buffet” for the microorganisms.  The water is also aerated so that the microorganisms can thrive, and the water is then taken to a final settling tank where the cleaner water flows to the top, and the remaining solids settle at the bottom.

The treatment plant workers only complete the third step during the nine warmer months of the year so the water is relatively clean for people who are canoeing or fishing the North Shore Channel, on the assumption people won’t be pursuing that type of recreation during the three coldest months of the year.

Powerful ultraviolet lightbulbs are used to prevent microbes from reproducing, effectively wiping them out before the water is released into the North Shore Channel. The O’Brien plant has the largest U.V. disinfection facility for a waste water plant in the U.S.

Plant Manager Aruch Poonsapaya told Pioneer Press that the bulbs are 10 feet long, each bulb is about 1,000 watts and has a lifespan of about three years. He said the plant has 128 channels and uses 1,000 bulbs.

The first priority of the Metropolitan Water Reclamation District is to clean water, but the second priority is to mitigate flooding, said Kohlhaas. She said storm water is also sent to the plant, is treated the same as water from domestic sewers and uses its connection to the Tunnel and Reservoir Plan, also known as the Deep Tunnel, to get water out of the street and away from homeowners’ basements during heavy rain.

Daniel Thomas, an Evanston resident, attended the open house and said he had always wanted to get a tour of the facility.

“I’m an environmentalist, I want to save the earth, I want to be a good steward,” he said. “(The Metropolitan Water Reclamation District) is a good organization, they are good workers, and I think they are really sharp people.”

Chicago Water Week continues through May 11 and will include an Open House at the Stickney Water Reclamation Plant, 6001 W. Pershing Rd., Cicero.

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