Where Do Biosolids Come From? - Each of the thousands of households the Metro District serves generates wastewater by washing clothes, washing dishes and putting waste food into garbage disposals, taking showers and baths, and flushing toilets.

All this water, combined with soapsuds, food particles, toilet paper, and other matter, travels through sewers to reach the Metro District's treatment plant. The wastewater treatment process separates these solids from the water and the solids are further processed and treated until they become biosolids.

What Is the Difference Between Biosolids and Sludge? - Sewer sludge is made up of deposits collected after primary and secondary treatment. Biosolids are sewage sludge that has been carefully treated, monitored and regulated.

How Are Biosolids Generated And Processed? - The Metro District's modern, 185-million-gallon-per-day treatment plant treats the wastewater to remove pollutants. The first stage of this process is mechanical: screening, skimming and settling. The second stage is mostly biological. Microorganisms in the water "eat" the wastes, turning them into the natural, mostly organic material. When this material is further treated, it is called biosolids.

Why Are Biosolids Recycled? - Aside from reuse, the other options for the disposal of biosolids contribute to the depletion of our natural resources. Landfills are quickly disappearing. More than 1,200 of the existing 1,500 landfills in the United States have closed because of the increased cost of meeting environmental requirements and many more are running out of space. Keeping biosolids out of landfills and placing them where they can be beneficially used helps reduce the landfill shortage problem. It also provides a process for renewing the soil with nutrients and organic matter. Biosolids recycling is the best means of returning nutrients and organic matter to the soil, that were originally removed in agricultural products and consumed by the public. It is recycling a resource, just like recycling newspapers or bottles. If the right safeguards are taken, biosolids use can be environmentally protective and even beneficial.

Why Is Land Application of Biosolids Beneficial? - Farmers and gardeners have been recycling biosolids for ages. Biosolids are used to help grow crops, fertilize gardens and parks, and reclaim mining sites.

Biosolids add organic matter to the soil that allows the soil to breathe and at the same time, hold more water and nutrients. The plant nutrients are released slowly, improving crop production. The result is better crops, less water runoff, less soil erosion, and more water conservation. Biosolids recycling is a safe, reliable, and cost-effective method for managing biosolids. Biosolids enrich the soil with essential nutrients and organic matter. Plants need a complex mixture of nutrients, soil, air, and water to grow well. Biosolids contain a full range of essential plant nutrients released slowly as the plants need them during the growing season. The organic matter acts as a sponge for water, nutrients, and air, where soil organisms can prosper and plant roots can better develop. This “sponge” reduces the possibility of leaching nutrients to the groundwater.

Are There Pathogens in Biosolids? - Yes, because biosolids are a product of the wastewater treatment process. Approximately 99 percent of the pathogens (harmful micro-organisms) are destroyed during the collection and treatment of wastewater, and most of the remainder through the solids treatment process. Most pathogens cannot multiply outside of living hosts.

How Are Biosolids Treated to Destroy Pathogens? - The presence of pathogens in wastewater and the biosolids resulting from wastewater treatment requires treatment of these solids to reduce any remaining pathogens to a safe level before reuse. Municipal wastewater treatment includes a wide variety of processes to kill germs. The resulting products (biosolids) are then safely recycled as a soil amendment or fertilizing material.

Are Biosolids Regulated? - Prior to land application, biosolids must meet strict regulations and quality standards established by the federal and state governments, and local ordinances. The rules that govern the use of biosolids contain numerical limits for metals in biosolids, pathogen reduction standards, vector attraction reduction, site restrictions, crop planting and harvesting restrictions, and monitoring, record keeping and reporting requirements for land-applied biosolids.

Do Biosolids Have an Odor? - Biosolids may have a different distinctive odor depending upon the type of treatment it has been through. Some biosolids may have only a slight musty odor, while others have a stronger ammonia odor. If the biosolids are thoroughly digested at the wastewater plant, the odor is usually that of a moist soil. Wastewater treatment plants typically use an organic polymer additive in the process of dewatering biosolids, which can also cause a salt water smell.

The odor from biosolids comes from the decomposition of organic material. Compounds that contain sulfur and ammonia, which are both plant nutrients, cause most of these odors.