Building a (Bio)solid Partnership

Researchers find biosolids produced by cities can be an effective crop fertilizer.

With the Front Range's rapidly growing population, city and county officials are faced with many challenges. One of those challenges is disposing with municipal biosolids – residential and commercial waste. Ken Barbarick, a professor of soil sciences and researcher for the Agricultural Experiment Station, has looked for ways to use biosolids as a resource.

Barbarick started investigating the use of biosolids as an agricultural fertilizer in the early 1980s when Tom McBride, a Colorado State University Cooperative Extension agent in Adams County, was contacted by Englewood and Littleton city officials who were expanding their waste treatment facility.

"Those cities wanted to be proactive about the environment and ease the public's mind about the use of this kind of waste as a fertilizer for dryland crops," said Barbarick. "They've supported our research for 17 years. We've gathered facts on both short-term and long-term effects, and our research has found no problems with the conscientious agricultural use of biosolids."

Barbarick and colleague Ed Redente, a professor of rangeland ecosystem sciences, also have used biosolids to help restore an area in Jefferson County burned in a wildfire. The biosolids helped restart the ecosystem when added to plots replanted with native grasses. These plots recovered dramatically quicker than areas without biosolid applications.

Using biosolids as a fertilizer safely recycles waste, says Barbarick, after it has been pre-treated to kill diseases carried by humans. In Colorado, more than 80 percent of municipal biosolids go toward a beneficial use with industries such as agriculture or on disturbed lands. The national average for municipal waste recycling, says Barbarick, is more like 50 percent. The biosolids that aren't recycled back into the environment often end up in landfills.

Biosolids have proven to be an effective fertilizer; more effective, in fact, than animal manure traditionally used on crops for its nitrogen content, says Barbarick. That's because municipal biosolids are more stable than animal waste, so they break down more slowly. That allows more control of the rates of nutrients going into the soil from the waste, which helps preserve the quality of soil and the water supply from an unhealthy overload of minerals or other elements.

After application to soil, biosolids release plant nutrients such as nitrogen, phosphorus, zinc, and iron that are vital to produce a healthy crop. Biosolids must be applied to soils at an agronomic rate – a rate determined to match the nutrient needs of the crop grown. A proper application rate is essential to prevent buildup of excess nitrogen, which is mobile in soils and can leach downwards to contaminate groundwater.

The application of biosolids to soils used for crop production is governed by regulations imposed by the Colorado Department of Health and the U.S. Environmental Protection Agency. These regulations have been developed to ensure that biosolids have been treated to reduce disease-causing microbes and to minimize odor and nuisance problems after application. In addition, the biosolids are analyzed for nutrients, metals, and trace elements. The Agricultural Experiment Station's research program has monitored the uptake of nutrients and metals such as cadmium, zinc, and lead in winter wheat for the past 15 years. Properly managed biosolids application has safely improved the quality of the winter wheat crops grown.

"The use of biosolids as a fertilizer is part of a cycle," says Barbarick. "Agriculturists need nutrients for crops, the crops go to the city to be consumed, and the city's waste goes back to the land for crops. Farmers deserve credit by using their land to help cities recycle their waste and for being environmentally conscious enough to use biosolids. This is a partnership between farmers and city dwellers."