Revised by Zhiqiang Hu
Professor of Civil and Environmental Engineering

Biosolids is a term for domestic wastewater sludge that meets standards for use as a fertilizer or soil conditioner. Biosolids standards include limitations for metals and other compounds, pathogen reduction, vector requirements and best management practices. Biosolids are regulated under 40 CFR Part 503 Standards for the Use and Disposal of Sewage Sludge.

This publication outlines biosolids land application monitoring requirements.

Applying biosolids to land uses the available nitrogen, phosphorus and potash to fertilize growing crops. This is an environmentally sound practice sanctioned by the U.S. Environmental Protection Agency (EPA) and the Missouri Department of Natural Resources (DNR).

Reusing biosolids on crops, pastures and timberland reduces pollution of the waters of the state. It eliminates the environmental risks and costs associated with sludge disposal options, benefiting all citizens of Missouri.


EPA regulations, under Title 40 Code of Federal Regulations Part 503 (40 CFR 503), establish the minimum national standards for the use and disposal of domestic sludge. These standards include limitations for the land application of biosolids.

Biosolids are a product of the wastewater treatment process. The terms ‘biosolids’ and ‘sewage sludge’ are often used interchangeably. Biosolids are divided into “Class A” and “Class B” based on treatment methods. Existing regulations and guidance help ensure that biosolids are processed, handled, and land-applied in a manner that minimizes potential risk to human health.

The DNR has incorporated the EPA standards into the state requirements under the Missouri Clean Water Law and regulations. The state rules include additional requirements that are not covered in the EPA standards. Complying with state regulations automatically meets the EPA sludge standards.

Recommended minimum monitoring frequency

Recommended minimum monitoring must be in accordance with A Plain English Guide to the EPA Part 503 Biosolids Rule (EPA 832-R-93-003, September 1994). Monitor the biosolids to determine the quality for regulated pollutants listed in the biosolids standards. Base the number of samples on the quantity of sludge produced by the facility.

Another sampling plan may be approved for an equal number of samples per year. For example, you sample quarterly, but apply biosolids during July only. You may collect all four samples during the land application period (Table 1).

Table 1
Recommended monitoring frequency

Design sludge production
(dry tons per year)
Monitoring frequency (See notes 1 and 2.)
Metals, pathogens
and vectors
Priority pollutants and TCLP3
0 to 1001 per year1 per year1 per month1 per year
101 to 200biannualbiannual1 per month1 per year
201 to 1,000quarterlyquarterly1 per month1 per year
1,001 to 10,0001 per month1 per month1 per week-- 4
10,001+1 per week1 per week1 per day-- 4
1Test total Kjeldahl nitrogen, if biosolids application is 2 dry tons per acre per year or less. 2Calculate plant available nitrogen, if biosolids application is more than 2 dry tons per acre per year.
3Priority pollutants (40 CFR 122.21, Appendix D, Tables II and III) and toxicity characteristic leaching procedure (40 CFR 261.24) is required only for permit holders that must have a pre-treatment program.
4One sample for each 1,000 dry tons of sludge.

Note 1
Total solids: A grab sample of sludge shall be tested one per day during land application periods for percent total solids. This data shall be used to calculate the dry tons of sludge applied per acre.

Note 2
Total phosphorus: Total phosphorus and total potassium shall be tested at the same monitoring frequency as metals.

Optional sampling for lagoons

If you own a wastewater treatment lagoon or sludge lagoon that is cleaned out once a year or less, you may choose to sample only when the sludge is removed or the lagoon is closed.

Test one composite sample for each 100 dry tons of sludge or biosolids removed from the lagoon during the year or left within the lagoon at closing. Composite samples must represent various areas at one-foot depth.

Sample type

Collect composite samples for all monitoring under this section. Each composite sample must consist of at least seven to 20 grab samples. Collect the samples during the same week from various locations in the sludge.

Data from individual grab samples may vary by as much as 50 percent from mean values. A composite sample made up of 20 grab samples will be 90 percent to 95 percent accurate.

Dry weight basis

Report all sample results on a dry weight basis unless otherwise specified. If the laboratory report does not specify dry weight, consider the data in a wet weight basis. The permit holder must convert the measurements to a dry weight basis. Use the following formula:

Wet weight in ppm or milligrams per kilogram ÷Percent total solids/100

An example for 100 ppm at 2 percent total solids:

100 ppm ÷2/100= 100 ÷ 0.02= 5,000 ppm dry weight

Soil testing

Test soils for soil pH, cation exchange capacity and available phosphorus once every four or five years, if biosolids are applied during that period. Base available phosphorus on Bray's P-1 test.

Recommended soil testing methods must be in accordance with Recommended Chemical Soil Test Procedures for the North Central Region (North Dakota Agricultural Experiment Bulletin 499-Revised).

Original authors: Ken Arnold, Chief of Land Application, Missouri Department of Natural Resources; John H. Dunn, Environmental Engineer, Environmental Protection Agency Region VII; Dennis Sievers, Department of Agricultural Engineering