Treatment of domestic wastewater produces two principal byproducts: effluent (see Chapter 1) and biosolids or “sewage sludge.” Biosolids are solid or semisolid organic matter recovered from the sewage treatment process. Biosolids can be disposed in landfills or incinerated to produce energy. High in organic matter and nutrients, biosolids may also be processed, packaged, and distributed as fertilizer/compost or processed and spread directly on farms, ranches, forest lands, and public parks, subject to regulation by the Florida Department of Environmental Protection (FDEP) (Chapter 62-640, F.A.C.). Based upon the level of treatment for the protection of public health and the environment, biosolids are classified as Class B, Class A, or Class AA. Class B provides the lowest and Class AA the highest level of treatment.
In addition to meeting specific sanitary requirements under the federal Clean Water Act, Class AA biosolids must meet stringent heavy metal limits. Products that meet these standards and are licensed as a fertilizer with the Florida Department of Agriculture and Consumer Services (FDACS) avoid additional regulations imposed on compost distribution and marketing. Use of biosolids is about $60 per acre cheaper than synthetic fertilizer (FDEP 2019b). Once it meets Class AA standards, composted biosolids are essentially unregulated, allowing for broad commercial and retail usage.
Florida’s wastewater treatment facilities produce about 350,000 dry tons of biosolids each year. About 25% is disposed in landfills. About 30%, or 90,000 tons, of Class B biosolids is spread at approximately 140 permitted sites across Florida, primarily pastures and hay fields (Figure 3.1). Class B biosolids still contain some bacteria and heavy metals, and local governments can ban application within their jurisdictions.
Figure 3.1. Biosolids produced as a byproduct of wastewater treatment in Florida are disposed in landfills or dried and processed into Class B or Class AA products.
The remaining 45%, or about 150,000 tons, of biosolids, are processed in 39 permitted Class AA facilities across Florida to remove heavy metals and pathogens before being distributed as commercial fertilizer and compost products. The distribution and use of Class AA biosolids is not tracked and local governments cannot ban their use. An additional 9,000 dry tons of Class AA pellets are shipped to Florida from out-of-state facilities.
Disposal of biosolids created by the major wastewater treatment facilities (WWTFs) in Sarasota County occurs at a facility in Charlotte County. The only biosolids currently disposed in Sarasota County are those purchased from a commercial Class AA composting operation such as Synagro and used as a soil amendment.
Quantify Nutrient Loads From Biosolids Disposition
Biosolids are a valuable byproduct of wastewater treatment that can be landfilled, spread on ranches and fields, or used as a fertilizer. However, the high concentration of nutrients in biosolids may contribute to water quality problems. Quantifying nutrient loads from biosolid disposal methods is an important first step in assessing their role in an overall nutrient management plan.
Because most biosolids are generated by municipal wastewater treatment facilities, emerging markets for biosolids products may offer economic and environmental benefits to communities. Understanding the costs and benefits of various technologies for processing biosolids can inform their sustainable use.
Biosolids are transported from wastewater treatment facilities to processing and disposal locations around the state, making them a statewide issue. Changes to current regulations will improve water quality protection and establish criteria for assessing the suitability of land-spreading sites. Additional research and monitoring is needed to evaluate runoff from biosolids and to address unregulated chemical contaminants.