Sewer plant to produce fertilizer and electricity
With the local food movement going strong in Northern Nevada, could local fertilizer be the next big thing? In March, the Truckee Meadows Water Reclamation Facility will begin production of Crystal Green, a phosphorus-based plant fertilizer made from, well, the stuff that goes down the pipes when we flush our toilets. Working with a Canadian company called Ostara Nutrient Recovery Technologies, TMWRF will mine phosphorus and small amounts of nitrogen and other nutrients from Truckee Meadows wastewater, precipitating the nutrients out to form small white fertilizer pellets.
“Basically, the phosphorus pellets are one of three components you’d buy at Home Depot in a bag of fertilizer: phosphorus, nitrogen, maybe a potash or potassium-type additive,” explained Reno Public Works Department professional engineer David Kershaw.
At TMWRF, wastewater is processed by microorganisms as it travels through a complex series of tanks and digesters. Digested sludge is separated into a solid (called “cake”) and liquid (called “centrate”) via a centrifuge. The cake is then hauled off to Lockwood Landfill. The nutrient-rich centrate is where the fertilizer will come from.
“The centrate that comes off the digested sludge, the liquid part of it, it’s kind of a dark beer color,” said Kershaw. “That is really high in phosphorus and ammonia, nitrogen.”
With new equipment purchased as part of a $24.9 million program to make improvements at the facility, TMWRF will produce approximately 2,000 pounds of Crystal Green pellets per day. The pellets will then be sold back to Ostara at a fixed price, providing income for the facility and helping to reduce costs in other ways.
“There’s another current process to remove the phosphorus from the centrate,” said Kershaw. “It uses a lot of a certain chemical, so [the Ostara process] will allow us to stop using that chemical, for the most part. It’ll be a chemical cost savings there. Then, we’ll be making the product and selling the product as well. So all that goes to offset the operating costs at the treatment plant.”
Another component of the improvements at TMWRF is a new co-generation unit that will allow the facility to produce electricity by combusting methane gasses that come off the digester tanks. TMWRF had this capability in the past, but the previous system stopped working about 10 years ago. The replacement unit went online in late January, and will generate about one third of the power required to operate the plant, said Kershaw.
Although the cities of Reno and Sparks were fined in 2013 for water quality violations related to nitrogen discharges to the Truckee River, TMWRF is back in compliance. When the violation occurred, the facility was operating at 99 percent of its capacity to process nitrogen. Last year, according to Kershaw, the plant operated at about 82 percent of capacity, and should be able to handle projected growth for approximately the next 20 years—assuming no major changes occur in arriving water chemistry.
It’s all about keeping the microorganisms happy, said Kershaw. “If the bugs aren’t happy, which they weren’t at the time, they’re not as efficient. Since that time, we’ve identified the issues and implemented corrected measures.”