Missouri state rules for biosolids land application were first created in 1982 followed by federal rules issued in 1993 by the EPA (40 CFR Part 503). The combination of these regulations works to ensure the safety of this practice to human and environmental health. Biosolids generated at the Southwest and Northwest Treatment Plants meet Class B pathogen control standards. Class B biosolids have undergone treatment to reduce pathogens. Site restrictions and management practices, including minimum time durations between application and land usage, allow natural processes to further reduce pathogen levels. Class B guidelines also restrict the types of cropland on which these biosolids can be applied. Locally, the biosolids are applied to lands producing all hay producing grasses (warm and cool season), corn, soybeans, and other types of crops not used for human consumption. The EPA has designated 10 pollutants for regulation based on risk analysis studies of the composition of a national sampling of sewage sludge. These regulatory limits along with average detected levels in locally generated biosolids are shown in Table 1. The City's Industrial Pretreatment Program helps to meet these limits by reducing the amount of pollutants in the wastewater before it is discharged to the treatment plant. Additionally, regulations include reducing the attraction of vectors such as rodents and flies through treatment or application options, and calculating application levels not to exceed the agronomic rate of nitrogen. Table 2 shows the nitrogen content of local biosolids. Monitoring, record keeping, and reporting requirements must also be fulfilled.
To ensure protection of the area's bountiful and scenic waterways, the Missouri Department of Natural Resources requires compliance with additional guidelines beyond EPA regulations (Missouri extention center). These guidelines include increased buffer zones around wells and waterways, and phosphorus restrictions.
Do Biosolids Contain Pollutants?
Biosolids can contain organic and inorganic pollutants other than the current, regulated list shown in Table 2. This list is the result of the first of two rounds of evaluation by the EPA of pollutants to consider for regulation. The Round 1 evaluation began with 411 pollutants on which data was collected in a National Sewage Sludge Survey (NSSS) in 1990. The list was narrowed down based on a set of criteria for exemption from regulation. Round 2 was conducted in 1996 and started with the same list of 411 pollutants. Initial screening narrowed the list to thirty by eliminating pollutants that were not detected in the NSSS, detected in less than 10% of samples from the NSSS, and that lacked sufficient toxicity data. Further hazard identification studies eliminated all pollutants but dioxins, furans, and coplanar PCB's from consideration for regulation. A proposed limit and monitoring requirements for these compounds, considered collectively as "dioxins," in biosolids applied to land was issued in 1999 by the EPA for peer review. The proposal has yet to be mandated due to continuing evaluation and debate on the subject.
Are Biosolids Safe?
The current EPA and state regulations are based on extensive studies of the possible long-term effects of the land application of biosolids. However, studies are ongoing and the City will implement any new guidelines as required. Any questions or comments about the environmental and health concerns of biosolids usage are welcome and can be directed to Ed Malter, Superintendent of Clean Water Services, at 417.891.1600.