By ADAM STEWART

Staff writer

A stench like rotten eggs has been emanating from Hillsboro’s wastewater lagoon, but the city is experimenting with a plan to alleviate the odor.

Bacteria that grow in the absence of oxygen in collection lines and the lagoon produce hydrogen sulfide, the source of the rotten-egg stench, City Administrator Larry Paine said last week. Hydrogen sulfide can be lethal in high concentrations, he said.

Oxygen-using bacteria also produce an odor, but it is merely a wet, musty odor with no other risks, Paine said.

One particular series of collection lines beginning near Alco are likely to blame, he said. Wastewater spends between four and six days in the lines. During that long time in the lines, bacteria run out of oxygen, allowing the stench-producing bacteria to thrive.

A possible solution is to inject ozone — which can kill the harmful bacteria, then decay into oxygen — into the system.

Wastewater treatment plant operator Joe Alvarez is testing equipment from EnvirOzone Systems Corp. that collects air and filters out most of the gases other than oxygen, Paine said. It then converts oxygen to ozone and injects it into sewage.

Engineer Jim Kohman of Great Bend recommended testing the equipment. He worked with the city on its wastewater treatment project.

The experiment began at the wastewater treatment plant about two weeks ago. The city saw no effect from using one unit at half capacity for a week, but progress was noted after turning the unit to a higher setting.

Paine said he wants to achieve a dissolved oxygen ratio of 2.0 milligrams per liter or greater, a ratio recommended by Kohman. The city will test the ozone-injection system in three places: the treatment plant, partway along the problem line, and at the beginning of the line.

Before tests began, the dissolved oxygen level at a test point along Jade Road south of 190th Road was 0.4 milligrams per liter. After turning up the unit, the dissolved oxygen increased to 1.8 milligrams per liter.

If the experiment alleviates the stench at the treatment plant, the city might purchase up to three of the ozone-injection units, but Paine wasn’t sure what the cost was Friday. The equipment could be purchased with money left over from the wastewater treatment plant project.