Residuals and Biosolids Committee

The Residuals and Biosolids Committee is focused on the development of best practices for conveyance, stabilization, thickening, dewatering and storage of wastewater solids and for the beneficial reuse of biosolids, nutrients and biogas produced during the treatment process.

We provide workshops, seminars, and other opportunities to advance members' knowledge of all aspects of solids processing. We have developed a pre-conference workshop for the 2016 Annual Conference, titled “Considerations for High Performance Anaerobic Digestion (HPAD)”. We have also developed a PNCWA white paper on biosolids in conjunction with Northwest Biosolids Management Association (NBMA), focusing on considerations for the evaluation of alternatives for management of residuals from a utility perspective. 

We hold monthly committee conference calls.

News & Highlights

PNCWA Members Prepare for National Residuals and Biosolids Conference in Seattle

Agencies throughout the Pacific Northwest work hard to manage their wastewater in the most responsible way, to protect human health and the environment within a framework of state and federal regulations. Many wastewater management decisions focus on the safe handling of the residuals that are removed during treatment of wastewater.

Treatment and management of residuals is a significant challenge. Planning efforts address both the treatment applied to the residuals at the facility as well as their final destination.

There are three feasible ultimate destinations for residuals generated in municipal treatment facilities:

  • Biosolids/land application: Beneficial use of some residuals can be achieved through land application. Solids are treated to remove pathogens and vector attraction (“Class A”) or substantially reduce pathogens and vector attraction (“Class B”).The treated biosolids are then applied to land per federal and state controls. Metals concentrations in land applied biosolids are also regulated. This includes biosolids that are composted with added organic waste materials such as yard waste.

  • Landfill: Some municipal solid waste landfills in Oregon and Idaho accept municipal residuals (this practice is not allowed in Washington). The solids must be partially dewatered so that no free liquid runs off, and often the solids must be at least partially stabilized to reduce pathogens and vector attraction.

  • Incineration: Residuals are dewatered to minimize water content and then combusted at about 1500 degrees F, providing a very significant reduction in volume. The resulting product is a pathogen-free ash, which is taken to landfill.

In the Pacific Northwest, the majority of agencies have selected a biosolids/land application program. There are also a number that haul solids to a landfill, and a handful of systems in Washington run successful incineration programs.

 

 

Biosolids/land application is well-suited to the region for a number of reasons, as follows:
  • Biosolids are a valuable resource because they contain important slow-releasing nutrients for plant growth and soil fertility such as nitrogen, phosphorus, and organic matter as well as essential nutrients such as copper, iron, molybdenum, and zinc.

  • Biosolids condition soil, adding organic matter to enrich depleted soils and fibrous matter to improve the soil's ability to hold water. Fixing of carbon in the soil through this process has been found to provide significant benefits in greenhouse gas reductions.

  • There is a long standing record of safe operations ensured by a regulatory framework that guides the processing and use of biosolids as a fertilizer and soil amendment on agricultural land, forests, mines, and land reclamation sites.

PNCWA recommends the following:
  • The continued management of wastewater residuals by its member agencies to maximize land application of biosolids where appropriate. 
  • The continued monitoring of the success of existing land application programs through the current regulatory framework.

  • Ongoing evaluation and development of the regulatory framework and best management practices, as new needs and potential resource recovery options are developed. 

 

Contact Info

A photograph of Susan Hildreth

 

Susan Hildreth, Chair
King County