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 into garbage disposals, taking showers and baths, and flushing toilets.

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



What Is the Difference Between Biosolids and Sludge? - Sewage sludge is made from deposits collected after primary and secondary treatment. Biosolids are sewage sludge that has been carefully processed and tested according to federal and state regulations.

How Are Biosolids Generated And Processed? - The Metro District's modern, 140 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 natural, mostly organic material. When this material is further treated, it is called biosolids.

Why Are Biosolids Recycled? - Biosolids recycling is a beneficial way of returning nutrients and organic matter to the soil that were originally removed by the harvest of agricultural products. It is recycling a resource, just like recycling newspapers, plastics and glass. Aside from recycling, the other option for the disposal of biosolids contributes to the depletion of 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 to meet environmental protection requirements – they are also running out of space. Keeping biosolids out of landfills and placing them where they are environmentally beneficial helps reduce the landfill shortage problem.

Why Is Land Application of Biosolids Beneficial? - Farmers and gardeners have been recycling biosolids for ages. Biosolids are used to increase crop production, fertilize gardens and parks, and reclaim damaged lands.

Biosolids add organic matter to the soil increasing water holding capacity and slowing the release of nutrients for crop growth; resulting in healthier crops, less water runoff, less soil erosion, and more water conservation. Biosolids recycling is a safe, reliable, and cost-effective method for managing biosolids.

Are There Pathogens in Biosolids? - Yes, because biosolids are a product of the wastewater treatment process. Most 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.

How Are Biosolids Treated to Destroy Pathogens? - At the Metro District, wastewater flows through aerobic conditions to promote microbial decomposition of pathogens. Solids separated from these processes are then anaerobically digested at extremely high temperatures to kill pathogens.

Are Biosolids Regulated? - Prior to land application, biosolids must meet strict regulatory and quality standards established by federal, state and local governments. The rules that govern the use of biosolids contain numerical limits for metals, pathogen destruction and vector attraction reduction standards, site restrictions, crop planting and harvesting restrictions, as well as 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. 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.