WA ST Dept of Ecology Biosolids 9/8/2022

SSLAP – Lowell Snohomish River Road Agricultural Land ___________________________________________________________________________________ ______________________________________________________________________________________ 2 application that could leach nutrients into the water. See Appendix B for the Application Rate Worksheet for the 2021 application on the East and West fields. Prior to future applications, additional soil and biosolids sampling will be performed to adjust application rate calculations. • Metals and Organic Compounds There are trace amounts of metals and organic compounds found in most biosolids products. Some of the metals contained in biosolids are micronutrients essential for plant growth and include iron, copper, manganese, and zinc. Other nonessential elements, such as nickel, cadmium, and lead, are relatively immobile in the soil and remain in the surface soil after application. Trace organics remain in the soil where they are generally degraded by soil microorganisms. Trace organics are not readily taken up by plant roots and do not pose a sign ificant risk to the food chain. Metals and organics concentrations of the City’s biosolids for the 2021 application are presented in Appendix C. Samples were taken from the aeration pond for metals and organics. • Microorganisms Wastewater solids contain bacteria, viruses, protozoa, and helminths-all of which may be pathogenic. The treatment process reduces the concentration of these pathogens by maintaining conditions hostile to these types of organisms. The organisms that thrive under the treatment conditions out compete the potentially pathogenic organisms and digest or eat the wastewater solids. The digestion and stabilization process reduces the concentration of pathogens. Class B biosolids contain some pathogens, but levels have been reduced to protect human and environmental health when land applied. Class A biosolids are virtually free from pathogens. Pathogens remaining in Class B biosolids are exposed to sunlight, fresh air , and soil microbes. These conditions continue to reduce the risk that biosolids pose to human and environmental health. • Vector Attraction Reduction Biosolids, as the remains of stabilized putrescible material, may attract vectors such as flying or crawling insects, birds, rodents, and other small vertebrates. These vectors can spread pathogens beyond the land application site boundaries and impact the surrounding environment. To reduce the biosolids’ attractiveness to vectors, Everett stabilizes its biosolids using an anaerobic process within the treatment ponds. Everett utilizes Option 2 under 40 CFR 503.33(b)(2) regulations, ensuring that less than 17% additional volatile solids are lost during bench -scale anaerobic batch digestion for 40 days at 30° to 37° Celsius. Results of this year’s VAR testing are available in Appendix C. • Solids Content Everett mechanically dewaters biosolids with centrifuges after aeration cell harvest , and solids concentrations typically range between 28% and 40%. Average total solids concentration for 2021 is 36%.