Clean green gets new life as compost

Ever wondered what happens to all that stuff you haul to the transfer station for Clean Green disposal?

All most of us see is the giant piles of grass clippings, tree and shrub prunings and weeds being pushed around by equally large front end loaders. We finish cleaning out our vehicles and leave. Just where does all that stuff go?

A few weeks ago I found myself standing on top of a 100-foot-tall, two-acre pile of crushed mint stems looking across at an even larger pile that represented Spokane’s Clean Green for this year. I was surveying the scene with Thad Schutt and Chuck Graaf of Royal Organics, the company that is contracted to take the waste and turn it into compost.

Royal Organics was started in 2004 as a way for the mint processing industry to get rid of the copious amounts of plant waste from mint oil extraction in Central Washington. The mint waste compost is used as a soil amendment in many of the region’s fruit orchards and produce farms, particularly organic operations. When Spokane’s waste became available they expanded the operation to produce several grades of compost used in everything from erosion control to more familiar garden soil amendments.

The company’s operations are located a few miles south of the Interstate 90 Vantage Bridge off State Highway 26. After delivery straight from our transfer stations, the material is immediately put through a huge shredder, ground into small pieces and deposited on a working pile where it is aerated for up to ten months to start the composting process. The pile then feeds about 50 acres of long windrowed stacks where the serious composting takes place over another six to eight months. While in the windrows, the material is turned several times to keep the composting process going. The day I was there the turning machine was stirring up great clouds of steam as it worked. Finally the finished compost is screened; coarse screenings are sold to private and public agencies for use in soil stabilization and erosion control along highways and at construction sites. The fine screenings are delivered back to half a dozen Spokane, Post Falls and Hayden, Idaho, landscape supply companies for bulk purchase. They are looking at making it available by the bag in the future.

Through the entire composting process, the compost is tested for nutrient and water content and the presence of residual chemicals or other contaminants. Temperature levels are closely monitored to make sure that the compost reaches proper temperatures that destroy weeds and break down other contaminants. As a result of this detailed quality control process, the Clean Green compost is approved by the Washington Department of Agriculture for use on certified organic farms. They are working on getting USDA National Organic Program approval.

The company’s testing process keeps the nutrient levels at about 1 percent each for nitrogen, phosphorus and potassium which allows users to use the compost as a base for custom soil mixes.