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Pharmaceuticals and Personal Care Products in the Canadian Environment: Research and Policy Directions

5.4 Biosolids Management and Agricultural Best Management Practices (BMPs)

Sludge consists of the solid portion of municipal wastewater plus the solids generated during wastewater treatment. This sludge is stabilized and reduced in volume through aerobic or anaerobic digestion producing biosolids. Biosolids at the plant can be treated according to different standards, depending on the end use. Jones-Lepp and Stevens (2007) provide an overview of pathogens- and pollutant-based regulatory standards currently in place in the US and EU. In Canada, biosolids are generally applied to agricultural land if they meet provincial regulations for heavy metals content. Biosolids which do not meet land application requirements can be disposed of in landfills, or incinerated. Land application is the preferred method of biosolids from the perspective of recycling nutrients and organic matter back into the soil for crop production.

Agricultural runoff via tile drain | Photo: Ed ToppSorptive PPCPs will partition from the aqueous phase into solids during wastewater treatment, and land application of biosolids may be a more important route of environmental exposure than sewage outflows. (Kinney et al. 2006; Jones-Lepp & Stevens 2007; NAS 2002). Generally, knowledge is still limited on the fate and transport of PPCPs in land application and studies have detected only very low levels of PPCPs in the runoff from agricultural fields (WERF, 2005; Xia et al. 2005). Biosolids better management practices (BMPs) are intended to minimize the transport of biosolids components including PPCPs from the point of application to adjacent water. Current research is investigating the effectiveness of surface versus injection applications; buffer zones between application areas and watercourses; and application before or after rain events.

Other considerations in land application of biosolids include the potential effects of PPCPs on soil organisms; uptake by crops; and the dissipation kinetics and pathways in soil. Research on management options for land applied biosolids falls into two categories: 1. improved treatment of sludge prior to its application; and 2. use of BMPs during their application on land. Work on BMPs indicates that the greatest exposure risk is at or shortly after the time of biosolids application (see Topp summary in this proceedings). The risk of transportation through runoff or leaching is greatest before PPCPs residuals can bind to soil particles. Mixing the biosolids with soil at application could reduce the risk of runoff.