Americans produce a lot of waste. Some of it gets thrown in the kitchen garbage can or hauled to the dump, while some of it gets flushed down the toilet or sent down the garbage disposal.
Like the stuff you throw in your garbage can, a lot of the solids in our wastewater stream eventually end up in the landfill where they emit greenhouse gasses and contribute to climate change.
However, in Grand Rapids, the city’s wastewater treatment plant takes the organic matter that comes through its sewage system and turns it into something useful: energy.
April Van Buren/Michigan Radio
Essentially, they’re turning poop into power.
The Rapid, the transit system that runs buses around Grand Rapids and its suburbs, has started converting buses over to engines that could run on compressed natural gas.
Steve Schipper, chief operating officer for the Rapid, said the move away from diesel was both environmentally and financially motivated. Natural gas produces fewer emissions and is less susceptible to huge price swings.
The Rapid has been driving on natural gas purchased from DTE for a while now. Now, some of that natural gas will be coming from the city’s sewage.
How does this work?
The Water Resource Recovery Facility is where everything that gets flushed down a Grand Rapids toilet or garbage disposal ends up.
Jared Grabinski, assistant environmental services manager at the facility, has played a big role in bringing the city’s $85 million biodigester online. A biodigester is a system that turns waste into a form of compressed natural gas.
Before the solid waste reaches the biodigesters, there is a series of processes to separate the waste they want from the waste they don’t.
“This is where the first part of the physical process of the separation for the wastewater comes,” Grabinski said, referring to the rotating screens that catch larger items that don’t belong. “We’ll strain out anything bigger than a quarter inch to our bar screens, and we will slow the velocity down enough to where sand, grit, shells, dirt, rocks will fall out of the process.”
April Van Buren/Michigan Radio
Then, the facility pumps all the wastewater that made it through those first screens into deep cement tanks outside. They then slow the velocity of the water coming through to about one foot per second.
“These passes are for grit removal. That’s where we slow the velocity enough for that heavier stuff to just drop out of suspension,” said Grabinski. “Heavier stuff, grit, sand, seashells, rocks, anything that’s big enough or small enough to get through the screens, but heavy enough to settle out.”
The rest of the water goes on to the next phase of treatment where they slow the water down again. Slow-moving bars skim any oils or scum off the surface.
“At this point, the wastewater will go to the actual meat and potatoes of the treatment process, the biological treatment,” said Grabinski.
Once they have separated all of the grit and grease, there’s a bunch of organic material mixed in with the water. That’s what they call “primary effluent.” They mix it with what’s called “return-activated sludge” to create “mixed liquor.”
“So the food and the bugs are mixed together and then they begin that treatment process all over again,” said Grabinski.
The staff ensures that the right balance of microorganisms and waste for the biodigester. They add oxygen to keep the bugs growing.
“That bubbling action provides mixing and contact between the food and the bugs, and it also gives the biology air to respirate… to make more…
Read More: Grand Rapids turns poop into power with new biodigesters