From major headache to boon: Biosolids are in demand

Chuck Henry

Just a decade ago disposing of biosolids, the organic material left after wastewater has been cleaned in sewage treatment plants, was a major headache surrounded by public distaste and concerns about the safety of applying the material to forest and agricultural lands.

Today the demand for biosolids as a fertilizer and soil conditioner outstrips the supply in this state, according to Chuck Henry, UW research associate professor with the College of Forest Resources. The college has been involved in biosolids research for more than 25 years and Henry is responsible for guidelines on their use to heal road beds, rehabilitate log landings and enhance tree growth in forests along I-90 near Seattle.

The biosolids are being used on some of the lands in what is called the Mountain to Sound Greenway corridor. The results are so promising that the project has the endorsement of 26 businesses and environmental groups and has won a number of national awards. Within the corridor, private citizens, government agencies and businesses are working to preserve green space around growing communities, connect open areas with trails and paths, and maintain working forests and farms. Efforts are concentrated on the I-90 corridor from the shores of Puget Sound to Cle Elum on the eastern flank of the Cascades.

Part of the effort includes buying private lands and managing them cohesively with other public lands in the corridor. A cooperative agreement involving King County, the state Department of Natural Resources and Weyerhaeuser to use biosolids in Greenway has made it possible to buy more than 2,000 acres of private forest lands in recent years. About 20 percent of King County's biosolids are applied to lands in the corridor. King County saves money because it doesn't have to haul all its biosolids — some 170,000 tons a year — to Eastern Washington for use on agricultural lands.

The UW's role in the partnership includes the guidelines developed by Henry and ongoing research. Dean David Thorud is on the Greenway's board of directors, while Henry and Professor Emeritus Dale Cole are on the group's technical advisory board.

The college has conducted research on biosolids since the early '70s, involving more than 20 faculty and numerous graduate students. Today the UW program involves undergraduate lectures and field trips, and half a dozen graduate students at work across Washington state. Faculty such as Cole, Henry, Associate Professor Rob Harrison and Associate Professor Darlene Zabowski have studied many aspects of using biosolids including the fate of nutrients, contaminants and growth response.

The biosolids produced today are very different from the watery black "sludge" of the past, according to Cole, who was among the first researchers to consider how forest lands might benefit from biosolids. Today the material has most of the heavy metals and moisture removed, looks something like peat fertilizer and has EPA's blessing as a fertilizer and soil amendment.

Biosolids can improve soil texture and nutrition dramatically depending on how they are applied, Cole says. For example, unneeded log landings (places where logs were once stockpiled) and roads are being treated with biosolids, cultivated just enough to loosen the soil and seeded with wheat. The wheat, which is not meant for harvest, slows erosion and gives other plants a crucial foothold.

Old roads and log landings with compacted soils and, sometimes, steep slopes are among the most challenging areas to apply biosolids, Henry says. Land managers want to avoid having biosolids carried by runoff along the surface of the soil and into streams. Besides the obvious desire to keep contaminants out of the water, nutrients such as phosphorus and nitrogen from biosolids can cause noxious algae blooms downriver. Part of the UW research effort is to determine what grade of slopes can benefit from being treated with biosolids and how buffers can be used to further shield waterways.

Other forest sites are ideal candidates for biosolid applications, in some ways even better than agricultural lands where much of the state's biosolids end up, Henry says. For instance, forest lands absorb runoff from rain and snow better, trees take up nutrients year-round and forest soils include a great deal of organic carbon (from decayed foliage, bark, branches and trunks) which holds nitrogen in place until plants can use it.

The response of Douglas-fir trees can be impressive, according to UW research. Biosolids can enhance growth of existing stands from 2 to 100 percent, and more than 1,000 percent for seedlings planted in soils heavily amended with biosolids. Again, the UW is conducting ongoing research on how site characteristics and the age of stands of trees relate to growth, information sought by land managers in this state and elsewhere.

On the equipment side, the UW also has been involved in helping develop and test equipment at Pack Forest, the UW's experimental forest near Puyallup. UW researchers assisted King County to combine a Swedish harvester with an American-made aerospreader. An apt description of the resulting piece of equipment could include something about "when the biosolids hit the fan": the spreader uses the blades of a fan to fling chunks of material onto the landscape. The technology is the least expensive way yet to distribute biosolids on forests. ¶

Sandra Hines, News and Information