Silverton, Mt. Angel cope with a growing amount of sludge
What to do with the poo is a question every city has to answer.
In Silverton and Mt. Angel, toilet flushes have been adding up, so their wastewater treatment facilities are filling up, too. Now city leaders are doing business with the brown stuff the rest of us would rather ignore.
Biosolids or “sludge” is the stuff left behind after the sewage treatment process has removed and treated most of the water that came with it. Cities can hold it for a while, but eventually, it has to go somewhere.
Mt. Angel’s facultative lagoon system – three lagoons and a wetland – has been storing sludge for 27 years, and engineers say it’s time to dredge it up to keep things running smoothly. Permits alone are expected cost up to $50,000, but the city’s been saving since the lagoons were built in 1992, so those funds, plus $1 million for the work, are in savings.
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“This is the first time the system will be dredged,” said City Manager Amber Mathiesen. “It was originally designed to be a 20-year plant, but Mt. Angel hasn’t grown as quickly as engineers anticipated. Now we may have five to seven more years, but that’s if no additional growth happens.”
The system is far from failing, said wastewater treatment operator John Korecki. Each month, the Environmental Protection Agency requires Mt. Angel to remove a monthly average of 85 percent of biochemical oxygen demand, or BOD, from the wastewater, and its plant is typically in the 95 percent range, he said.
But he and engineers want to stay ahead of quality problems with the water Mt. Angel releases into the Pudding River after it’s treated. The lagoon system is a natural process that uses bacteria to slowly break down material. A wetland full of duckweed, cattails and pennywort is the last step before chlorination, de-chlorination and release into the river.
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“In a system like this, you don’t any have control over it; you’re always reacting to what it’s doing.” Korecki said. “It’s usually about 30 days from the time wastewater comes in to when it’s discharged, but as the sludge level rises, then the processing time to get bacteria out of the water is reduced.”
Located northwest of town, the treatment plant appears serene, almost beautiful. It’s home to ducks, egrets, eagles and other birds. Nutria, water-loving rodents, are the most troublesome because they weaken the earthen dikes by burrowing at the water’s edge, Korecki said.
It's fulltime work, warding off pests, cleaning screens, keeping water circulating, repairing equipment and conducting tests. In an old Ford Ranger, purchased surplus from the state police, he makes daily rounds, checking water levels, opening and shutting valves, taking water samples back to the lab and more.
City leaders are fast-tracking the dredging project largely because they need to find a place to put the sludge removed from the ponds. Everyone’s hoping to find a farmer willing to apply it to his or her grass field. Many cities, including Silverton, do this, but Mt. Angel’s biosolids will include untreated and partially treated sewage because residents will be flushing, washing and bathing right up until dredging.
“The sludge product is not fully composted, fully stable,” Mathiesen said. “It’s essentially raw sewage. My understanding is that any farmer that takes this will have 24 hours to get it tilled under.”
Farmers willing to take Mt. Angel’s biosolids may also already have multi-year contracts with other cities, many of which apply treated sludge every year. Although Mt. Angel is surrounded by farmland, it’s entering the market for applicable land after a 27-year hiatus.
“We don’t know what the exact costs will be,” Mathiesen said. “But we’re prepared to take out as much sludge as we can, while staying under budget.”
The City of Silverton is lucky enough to have an agreement with a farmer who uses its sludge as fertilizer after the grass seed harvest in late August. At the city’s Schemmel Lane wastewater treatment plant, solids coming in are settled, thickened, and digested through a mechanical-chemical process, exiting as Class B biosolids, EPA-approved for application on non-food crops.
Silverton’s problem is where to store the sludge while waiting for fields to become available after grass seed harvest in late August. The City of Salem once accepted excess sludge from other cities, but two years ago, application problems of its own ended the arrangement, causing the beginnings of a crisis for Silverton.
Since then, over the long, hot summer months, the city’s treatment plant is simply full of it. Its two 350,000-gallon sludge lagoons: full. Its old circular trickling-filter tanks, converted to store sludge in 350,000-and-150,000-gallon tanks: full. Its 4-million-gallon equalization basin, meant for flood control, has even been pressed into service, storing about 250,000 gallons.
“The biosolids were literally at the lip of the lagoons, ready to overflow,” said Steve Starner, water quality supervisor. “And the equalization basin? As operators, we don’t like to use it for sludge. It’s not designed for it, but you do what you’ve got to do.”
The rest of Silverton’s treatment plant has done a pretty good job keeping up with growth, as operators parceled out tax dollars and low-interest on upgrades in 1999, 2005 and 2013. It was re-engineered for safety and efficiency, received a second digester, new boiler and new buildings, and transitioned from chlorine to ultraviolet light in water purification.
Last year, Silverton received a $139,000 trade-in credit for its 19-year-old ultraviolet reactors, which went to another county via former President Obama’s Water for the World Act and helped offset the purchase of new ones.
But during the past few summers, it’s felt a little like the whole plant was drowning in biosolids as the city waited for farm fields to become available. The term “solid” is a bit misleading, as Silverton’s biosolids actually are only 1.5 percent solid. Look anywhere at the plant, and you’ll find open tanks full of brown liquid, solids just floating in patches at the edges.
Starner was so worried he started losing sleep. But this spring, the city landed a deal with FKC Co., for a $285,600 machine designed to remove water from the sludge, turning it into 17-percent solid material. This dewatering screw-press, slated to arrive in seven months, will eject a much drier material that can be scooped and stacked, rather than pumped and sprayed on farmers’ fields. Best of all, it will take up less space.
Public Works Director Petra Schuetz reported to the council that the machine is expected to pay for itself in just four years, due to the cost-savings associated with lower trucking costs to farmers’ fields.
For his part, Starner is proud that city employees will do so much of the work to tie the new machine into the old system. An engineer’s initial estimate of $1.8 has been whittled down to $580,000, just one more kind of relief for a city that’s been feeling the strain for a while.