The Washington State Legislature appropriated Yelm $850,000 in its 2021 supplemental capital budget for a new biosolids dryer, which is one part of the city’s plan to install a new water reclamation system in its facility by the end of the year.
Yelm’s current water reclamation facility, which uses sequence batch reactors (SBR) was built in the late 90s, and was the first of its kind in the state. With the SBR system, influent water from flushed toilets comes into the water reclamation facility and goes into giant tanks.
A natural process then takes place in the tanks. Bacteria grows and eats away the unwanted elements in the influent water and then separates from the material. That water is chlorinated and turned into reclaimed water, which is pumped out to Cochrane Memorial Park, among other places, to be purified and discharged into the aquifer for renewable use.
But once the reclaimed water is separated from the bacteria and leftover material, or sludge, those solids need to be disposed. Currently, the sludge is dumped into a gravity belt thickener (GBT), a machine that moderately dries it out.
“You have to handle the solids some way,” Colt said. “Right now, we dry them out a little bit, and then we send them out to Shelton and Shelton does the rest of it.”
With the new biosolids dryer, called a BioDryer, the sludge can be repurposed onsite.
“(The BioDryer) would prevent us from having to send the solids anywhere,” Colt said. “We can do it all here. Instead of taking that sludge out of the GBT and taking it to Shelton, we’ll take that sludge that’s left and all the (bacteria) that are left over from the process and put them through the BioDryer. The BioDryer will cook off the rest of the liquid until you get to barely any moisture in there and you have dry solids left over, which can be used as fertilizer for anything.”
The good news, Colt said, is the BioDryer can expand. Once the whole system is built, more BioDryer units can be hooked in as the city continues to grow. This first unit will handle the sludge load for the next five to 10 years.
To further upgrade its water reclamation facility, the city of Yelm has secured a $23 million loan from the Washington State Department of Ecology to build a new system to reclaim the water, called a membrane reactor (MBR), by the end of the year.
With the current SBR system, the city can handle around 1 million gallons of influent water flushed from toilets a day, with the current usage somewhere between 500,000 to 600,000 gallons. With the MBR system the facility will be able to bring in 2.4 million gallons a day.
“So we’re going to double the ability of our sewer plant,” Colt said.
The membrane used in the MBR system is like a semi-permeable surface. The liquid permeates through and leaves the sludge behind to be processed into the dry solids by the BioDryer.
“It’s like a sponge,” Colt said. “Some of (the sludge) seeps through but most of it’s caught in the membrane, and then that leftover water is turned into reclaimable water. It’s a more clean and easier process than the current batch reactor. So that’s what we’re switching to, is that MBR facility.”
Instead of chlorinating the reclaimed water, it will be put through an ultraviolet light disinfection before being sent to Cochrane Memorial Park.
Next, two of the three current SBR tanks will be converted into MBRs as well, with the third being used as a holding tank.
“We are reusing what we currently have and not having to start from scratch,” Colt said.
And, with more water rights possibly on the horizon, and new development already taking place, the city will need the new system, Colt said.
Yelm currently has about 2,700 connections to its sewer system. Right now, it can probably handle about 900 to 1,000 more connections before it gets close to a maximum load with the current facility, Colt said.
“With the MBR unit, we could easily double that, even triple that number of homes or connections and we would still be OK. We’d be under it,“ he said. “So that’s the idea of upgrading this ahead of this huge flood of development that’s happening right now. We’re just trying to get ahead of the game.”
He added that he believes city officials are correct to be ahead off the curve.
“It’s just good forethought by council and the mayor to do this ahead of needing to,” Colt said. “If we waited three years, we could be at the point where we go, ‘Hey, we can’t put any more homes in because our sewer system can’t handle any more homes.’ So it’s just really good forethought to get ahead of the game and do this now in anticipation for the growth that’s coming.”