Two towns, two solutions—one technology.

MBR/retrofit: Star, Idaho

  • Population: 2000
  • Plant size: 0.8 mgd with a peak flow of 1.2 mgd
  • Cost: $5.2 million
  • MBR/new construction: Delphos, Ohio

  • Population: 7000
  • Plant size: 3.83 mgd with a peak flow of 12 mgd
  • Cost: $32 million

Although they're half a continent apart and have never spoken, wastewater operators Hank Day and Kim Riddell solved very different treatment issues using the same technology.

Day's issue is growth. He's maintenance and operations foreman for the sewer and water district of Star, Idaho, where 20 separate housing developments are crowding his 5-acre treatment plant and have filled his three lagoons to capacity. When he joined the utility a decade ago, the city had 5 miles of sewer line. By the end of this year it will have 24.

He had to find a way to treat more wastewater in the same amount of space.

Riddell's problem is regulatory.

Just before she became water superintendent for Delphos, Ohio, in 2002, the Ohio Environmental Protection Agency ordered the city to build a facility that would bring it back into compliance with its National Pollutant Discharge Elimination System permit. Parts of the plant were a century old, its most recent upgrade was in 1982, and violations had become increasingly severe.

Day and Riddell met their respective goals with membrane bioreactors (MBR), a treatment option that many communities dismiss as cost-prohibitive. In an exclusive survey of PUBLIC WORKS readers, only 13% of respondents report using the technology.

But a perfect storm of factors—ever-tighter discharge requirements, lower membrane technology costs, and the soaring cost of reinforced concrete—is prompting operators to reconsider membranes, mainly because they increase capacity without expanding a plant's footprint and produce extremely clean water. The effluent during non-peak flows is usually better than required.

“Whatever we were going to buy, we wanted to make sure we wouldn't later have to scrap it and start all over,” says Day, whose utility borrowed $3.2 million from the Idaho Department of Environmental Quality to add a membrane bioreactor to its system. “We figured the membrane would meet any EPA guidelines coming down the pike. The output is almost drinking-water quality.”