Biosolids, the stabilized solids from municipal wastewater treatment meeting federal standards for land application, are an excellent source of plant nutrients. But growers need to know how to apply them, how much to use, and how they’ll perform. To fill in these blanks, WSU soil scientist Craig Cogger and colleagues at the WSU Puyallup Research and Extension Center, Northwest Biosolids Management Association, and other organizations across the country have studied the issues involved for the past 15 years.
After conducting field tests and laboratory studies on 25 types of biosolids from different sources and types of processing, Cogger and his associates found little variation in how the biosolids performed other than a faster release of nutrients in warmer climates. As a result of this research, growers now have national guidelines based on nutrient availability and maps to help them determine appropriate levels of biosolid application in their areas.
Cogger’s team also focused on nutrient availability from biosolids for growing wheat. A number of municipalities in eastern Washington now use their biosolids to fertilize their dryland wheat crops. In Douglas County alone, more than 20,000 acres were fertilized with biosolids in the last four years, and demand from growers is outstripping supply. The team is also researching applications to hard wheat varieties.
Working with the city of Tacoma and scientists at the WSU Puyallup Research and Extension Center, the team helped develop an effective biosolids-based greenhouse potting medium called Tagro Potting Mix that the city sells at local nurseries, along with a biosolids mulch.
Currently the team is evaluating locally produced biosolid formulas for use as a turf fertilizer, including high-end applications such as golf courses.
Phosphorous: From problem to profitable product
In the right proportion, phosphorous is a rich and valuable soil nutrient. But as a byproduct of nearly a quarter million Washington cows, it is a thorny environmental challenge, especially in terms of water quality.
Joe Harrison, professor and nutrient management specialist at the WSU Puyallup Research and Extension Center, is working closely with Washington dairy owners not only to find a solution to the nutrient run-off problem, but also to turn that manure into money. He is perfecting a technology that extracts the phosphorous in dairy manure and converts it into a dry, commercially saleable fertilizer. Called “struvite,” the product helps eliminate the expense of manure disposal, preserves the quality of groundwater on and around dairies, and provides dairy farmers with an extra source of income.
Harrison also is project director for the National Feed Management Education Project, which is funded with a grant from the U.S. Natural Resources Conservation Service. “The goal of the education project is to help producers adopt feed management practices that keep farms from accumulating excess nutrients and losing those nutrients to the environment,” Harrison explained. “An ideal situation would be that everything a farmer imports onto his farm in the way of feed, fertilizer, and other inputs balances with what he exports.”
For example, if 25 percent of the phosphorous a cow eats in the form of dairy cattle feed is exported in the form of milk products, the farmer still has 75 percent of that phosphorous to manage. If the farmer has enough land, the phosphorus in manure could all be used to fertilize crops. If enough land is not available, then exporting nutrients from manure should be considered. “Our primary goal is protecting water quality on and around the farm,” Harrison said.
Biodegradable food utensils
Besides his work on bioplastics, Jinwen Zhang also is trying to improve the negative impact plastic food utensils and other household items have on the environment. Using the WSU Wood Materials and Engineering Laboratory, Zhang creates composites out of natural fibers like bamboo and soy meal, which are then paired with plastic to create biodegradable products.
“Traditionally, plastic utensils have been made out of petroleum,” Zhang said, “but when we dispose of them, it is damaging to the environment. My research focuses on ways to incorporate natural wastes into products that are non-toxic when put into a landfill.”
For example, Zhang is creating a prototype that uses bamboo fiber and PHA composites— thermoplastics derived from cornstarch—that will eventually create a more durable product. “By adding the fiber, the plastic product becomes stronger, allowing for a longer service life,” Zhang said.
Zhang also has an interest in using local agriculture to assist with the development of composites. “I am working on a new proposal that would use Washington wheat and potato wastes to produce a biopolymer,” he said. “Currently, I use cornstarch as a feedstock but it would be more beneficial to the local economy if leftover potato and wheat crops were used.”