Biosolids

Biosolids are the nutrient-rich organic materials resulting from the treatment of domestic sewage at a wastewater treatment facility. Through biosolids management, solid residue from wastewater treatment is processed to reduce or eliminate pathogens and minimize odors, forming a safe, beneficial agricultural product. Farmers and gardeners have been recycling biosolids for ages. Biosolids can be applied as fertilizer to improve and maintain productive soils and stimulate plant growth. They also are used to fertilize gardens and parks and reclaim mining sites. Biosolids are carefully monitored and must be used in accordance with regulatory requirements.

We have biosolids as a result of treating sewage sludge (which refers to the solids generated during the treatment of domestic sewage in a treatment plant) in order to meet the land application regulatory requirements. Wastewater treatment technology has made our water safer than ever for recreation and seafood harvesting. Thirty years ago, thousands of American cities dumped their raw sewage directly into the nation's rivers, lakes, and bays. Through regulation of this dumping, local governments are now required to treat domestic sewage and to make the decision whether to recycle the solids generated as fertilizer, to incinerate them or to bury them in a landfill. If the solids meet the regulatory requirements for land application and are recycled, they are biosolids. 

Biosolids are generated when solids produced during the treatment of domestic sewage are treated further to meet regulatory requirements. The wastewater treatment can actually begin before the wastewater reaches the treatment plant. In many larger wastewater treatment systems, pre-treatment regulations require that industrial facilities pre-treat their wastewater to remove many hazardous contaminants before it is sent to a wastewater treatment plant. Wastewater treatment facilities monitor incoming wastewater streams to ensure their recyclability and compatibility with the treatment plant process. 

Sewage sludge is not generated until domestic sewage is treated in a treatment plant, and biosolids are not produced until the sewage sludge meets the land application Part 503 requirements. For these reasons, the treatment of biosolids cannot occur before the domestic sewage reaches the wastewater treatment plant.

Once the wastewater reaches the plant, domestic sewage goes through physical, chemical and biological processes that clean the domestic sewage and remove the solids. If necessary, some of the solids are then treated with lime to raise the pH level to eliminate objectionable odors. Pathogen reduction (reduction of disease-causing organisms, such as bacteria, viruses, and parasites) and reduction of other organisms capable of transporting disease for the solids usually occurs in a different process (e.g., a digester). 

After treatment and processing, biosolids can be recycled and applied as fertilizer to improve and maintain productive soils and stimulate plant growth. The controlled land application of biosolids completes a natural cycle in the environment. By treating sewage sludge, we create biosolids that can be used as valuable fertilizer instead of taking up space in a landfill or other disposal facility.

Biosolids may have their own distinctive odor depending on the type of treatment it has been through. Some biosolids may have only a slightly musty, ammonia odor. Others have a stronger odor that may be offensive to some people. Compounds that contain sulfur and ammonia, which are both plant nutrients, cause most odors. Once applied to land, the odor typically dissipates after a short time, depending on weather conditions. 

Charlotte Water produces "Class B" biosolids at each of its five wastewater treatment plants. Class B biosolids can be applied to land that produces animal feed crops but not land producing crops for human consumption. Biosolids from four of these plants are recycled through land application on more than 19,000 acres of private farmland in North and South Carolina. Each of these sites must be permitted with the South Carolina Department of Health and Environmental Control (SCDHEC) and the North Carolina Department of Environment Quality (NCDEQ). This means that in addition to the stringent requirements our biosolids meet, each particular farm where it is applied meets specifications, and the method in which it is applied at each site also is regulated. 

The biosolids program is managed using an EMS which is ISO 14001:2015 certified by an external audit process. In addition to the stringent treatment requirements, biosolids also need to meet strict specifications for each field that they are applied to. This is also regulated by federal and state agencies.