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Biosolids recycling in Oregon EC 1471 Reprinted February 2002 Do you want to print a copy? We recommend downloading the print version (5.9 MB). First download the free Adobe Reader, if you don't already have it. What are biosolids? Biosolids are a beneficial byproduct of domestic wastewater treatment facilities. They're made up mostly of nutrient-rich organic materials. But that's only part of the story. To plants and earthworms, biosolids are food. To soil, they are physical conditioners. To people, they are a valuable resource that can be recycled. How do all these good things come from my wastewater? The road from wastewater to biosolids is a long one. The first thing that happens when wastewater enters a treatment facility is screening. This removes undesirable objects such as plastics, rags, rocks, and stringy matter, which are landfilled. After that, the wastewater usually goes through two stages of treatment. During the first treatment, materials called raw primary solids settle out of the wastewater by gravity. The wastewater then moves on to a second treatment, where tiny organisms called microbes feed on organic materials in the wastewater. After they're done, we're left with clean water and a mixture of organic materials and microbial remains known as raw secondary solids. Biosolids composting facility--Forest Grove. From raw solids to biosolids The work is far from over, though. The raw solids from both stages must be processed further to produce biosolids. Processing kills disease-causing organisms such as bacteria and viruses, and reduces odors. A variety of chemical, physical, and biological processes are used to process raw solids. Common processes include anaerobic digestion, aerobic digestion, composting, heat treatment, lime treatment, and air-drying Dewatered solids application--near Hermiston.   Despite their name, not all biosolids are solid. Depending on how they're processed, the water content varies from more than 98 percent (liquid) to less than 20 percent (air-dried). What are biosolids good for? After all this processing, biosolids are ready to go to work. Some beneficiaries are: Soil. Biosolids improve soils by providing organic matter, which improves the "tilth" or physical condition of the soil. Good soil tilth means that soils are easy to dig in and work up, easy for seedlings to emerge from, and easy for plant roots to move through. Plants. Healthy soil means healthy plants. For instance, biosolids increase the number and size of air spaces in the soil and enhance its ability to hold together. This provides a better balance of water and air in the soil for plant growth. Better still, biosolids contain plant nutrients, such as nitrogen, phosphorus, and sulfur, in organic and inorganic forms. The inorganic forms are immediately available to plants. Nutrients in the organic form are released slowly as the biosolids decompose in the soil. These nutrients contribute to long-term improvements in soil fertility. Tryon Creek Wastewater Treatment Facility--Lake Oswego. The amount of biosolids applied generally is based on how much nitrogen the crop needs. On some soils (primarily in eastern Oregon), the micronutrients supplied by biosolids (zinc, copper, manganese) improve crop yields. Earthworms and their friends. Organic matter also provides food for soil organisms, such as earthworms, that keep soil healthy. Streams and lakes. Better soil structure makes it easier for water to enter and stay in the soil, which reduces runoff and soil erosion. This helps keep sediment from clogging water bodies, making them better places for fish to live. How are biosolids used? Liquid biosolids application--Salem. Biosolids are applied to a wide range of crops; for example, grass (for livestock feed or seed production), field nursery crops, and cereal crops. Biosolids also are used to reclaim mining sites and establish vegetative cover on closed solid waste landfills. Liquid biosolids generally are applied via sprinkler or spreader trucks. Solid products usually are applied with manure spreaders. Composts are blended into topsoil mixes or applied as a mulch. Are they safe? To be called biosolids, raw solids must be processed to meet U.S. Environmental Protection Agency (EPA) standards. Trace element concentrations must be lower than EPA standards for arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc. Biosolids trace element concentration standards are based on more than 20 years of university research, and have a large margin of safety. The Oregon Department of Environmental Quality (DEQ) has a long history of working with wastewater treatment facilities and land application of biosolids. A DEQ-approved biosolids management plan is required for each wastewater treatment facility. DEQ issues a site authorization letter to the wastewater treatment facility for each application site. This letter prescribes appropriate management practices to protect public health and the environment, including: Physical and chemical properties of biosolids Site characteristics and soil conditions Protection of ground and surface water and wells Crop rotations or vegetation Application rate and method Timing of application Monitoring Access and use restrictions Nonapplication areas (buffers) near homes, highways, and other public areas Landscaping with biosolids compost-- Eugene. Biosolids in the backyard Some treatment plants produce composted biosolids products that are suitable for use by landscape contractors and the public. These products must meet the most stringent EPA standards for trace element content and must be processed to eliminate viruses, bacteria, and other disease-causing organisms. These products are called "Exceptional Quality Biosolids." Site permits from the DEQ are not required for recycling of these products. To learn more about biosolids recycling Contact your local wastewater treatment facility or: Oregon Association of Clean Water Agencies Oregon Department of Environmental Quality Oregon State University Financial support for this publication was provided by the Oregon Association of Clean Water Agencies Prepared by Dan Sullivan, Extension soil scientist, Oregon State University. This publication replaces EC 1140, Putting Sludge to Good Use. July 1996. Reprinted February 2002.

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