Cooperative Extension Service
Purdue University
and U.S. Department of Agriculture

Land Application of Municipal and Industrial Biosolids

Brad Joern and Joe Yahner, Department of Agronomy
Prepared by the Residuals Management Committee
Indiana Water Pollution Control Association

Land application is a desirable method of returning "biosolids" to the land. Biosolids, also known as sewage sludge, consist primarily of liquid organic material produced by wastewater treatment. When properly treated, sludge is made into products that can be beneficially recycled on the land. Biosolids can also exist as a semi-solid, which has had a large amount of water removed, or it can be a dry material.

This publication answers frequently asked questions regarding biosolids land application programs. It will explain the agronomic and environmental merits of a community's land application program.


Where can I go for general information about biosolids land application permits as well as specific information about a community's program?

The Indiana Department of Environmental Management (IDEM) Land Application Program issues permits and enforces regulations throughout the state. Ask if your wastewater treatment plant has a land application permit. Also ask to see copies of their annual report. If you have any questions regarding the status of a permit, call the IDEM Land Application Program at (317) 233-6121.

Who obtains the land application permit?

Land application permits are issued to the generator of the sludge. If the sludge is generated at a municipal wastewater treatment plant, the permit is issued to the town or city. A consultant or contractor may work with the town or city, but the permit is issued in the name of the city or town. Permits are also issued to industries where the material produced meets required quality standards. Do not apply for a permit yourself. If problems occur the permit holder is liable.

What does a biosolids land application permit regulate?

The permit regulates where and how biosolids are land applied. Application permits can restrict applications based on site characteristics such as soil slope and separation distances from wells and waterways. These permits also specify application rates for all fields that may receive biosolids. These application rates are based on biosolids content, type of crop grown and crop yield goals. Biosolids can be applied to pasture and hay ground, with some grazing and harvesting restrictions.

Ask for a copy of the municipality's or industry's permit to learn about the regulations that control their land application program. Be aware that the state of Indiana currently does not allow municipal biosolids from other states to be land applied in Indiana.

Pathogen Control

What is done to make sure that disease-causing organisms do not present a problem when biosolids are applied to land?

Biosolids that are applied to the land must be treated by one of several processes to significantly reduce pathogens, also known as PSRP. These include aerobic digestion (with oxygen), anaerobic digestion (without oxygen), air drying, composting and lime stabilization. At present, there are no known cases of pathogenic outbreaks related to a properly managed biosolids land application program.

Toxic Materials

Do all biosolids contain "toxic" materials and are there federal or state regulations to insure that biosolids are not contaminated with high levels of these toxic materials?

Sludge is generated by municipal or industrial treatment plants. If your city or town has little or no industry, the sludge may contain very low concentrations of metal contaminants. Even larger municipalities with industries generally produce sludge with relatively low "pollutant" levels. This is true because the United States Environmental Protection Agency (US-EPA) regulates cities and towns with industries to "pretreat" their waste streams to meet the requirements of the Clean Water Act. This pretreatment is accomplished either by industries building their own treatment facilities or by building a separate municipal plant just for industrial waste.

The chemical, physical and biological characteristics of biosolids determine their suitability for land application. The US-EPA currently requires municipalities and industries to test biosolids for ten metal "pollutants" to insure the safety of this material. IDEM requires that all biosolids to be land applied meet specific minimum requirements that are similar to the risk based standards released by the US-EPA in 1993. For biosolids meeting the established criteria for class A, or "clean biosolids," the requirements for land application will be minimal.

Biosolids Testing

In the previous section, biosolids testing is mentioned. What compounds are tested for and how often are they tested?

The ten pollutant metals that must be tested for are arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, nickel, selenium and zinc. In Indiana, biosolids are also tested for pH, percent solids, total Kjeldahl nitrogen (TKN), ammonia nitrogen, total phosphorus and total potassium. The frequency of the tests that a municipal treatment plant must conduct depend on its size and on what initial analyses reveal. Large cities may collect samples daily, composite them and report results on a weekly basis. Others may collect samples weekly, composite the samples and report on a monthly or quarterly basis. If a compound is found above an approved level, or one of concern is found, IDEM will revise the analytical program and require investigation of the origin of the pollutant.

How are the results of biosolids analyses used and how can I find out what is being applied to my land?

Biosolids analyses are used to determine nutrient application rates and contaminant loadings on a site specific basis. If biosolids are to be applied to your land, you are entitled to see and receive a copy of the complete analysis of the material. All values on the analysis report are expressed on the basis of the dry weight of the biosolids unless otherwise indicated. All concentrations are expressed as parts per million (ppm).

You should ask that the biosolids analyses be interpreted for you. An agronomist working with the municipality or contractor should be able to provide you with the amounts of nitrogen, phosphorus and potassium being applied to your land. The agronomist should also be able to help you interpret the amounts of metals and other compounds applied to your land. For example, is 1000 ppm of zinc a lot? What application rate of zinc does this represent?

Nutrient Management

What method is used to determine the amount (application rate) of biosolids applied to my land?

In Indiana, the nitrogen requirement of the crop, based on a realistic yield potential, is the primary method used to determine biosolids land application rates. This minimizes the potential loss of nitrogen by leaching to ground water. In only a few situations does the metal content of the biosolids limit application rates. In these cases IDEM will work with the municipality to establish "pretreatment" programs to reduce or eliminate the compound of interest.

Phosphorus can be present in biosolids at levels that exceed the crop requirement when applications are based on nitrogen. Phosphorus is generally thought to be "tied up" in soil and poses little threat to the environment as long as soil erosion is controlled. At high phosphorus test levels, however, the potential problems associated with phosphorus movement from erosion of phosphorus enriched sediment and solution to surface waters are increased. A rotational land application program is recommended to minimize soil phosphorus test build-up from biosolids high in phosphorus.

What about metals? What do the terms "cumulative pollutant loading rate" and "most restrictive metal" mean?

When application rates are based on crop nitrogen requirements, most biosolids do not add excessive levels of metals. However, there are limits on the maximum total metal additions that can be made on a given site. Analytical data for metal content of the biosolids material will determine how many years it will take to reach each metal's maximum limit. This is known as "cumulative pollutant loading rate." It is determined for each metal and the "most restrictive metal" is the one that reaches this limit first, and "restricts" the number of years biosolids can be applied to a particular field.

How do applicators adjust their equipment to assure the correct application rate?

The percent solids and nutrient composition (from the biosolids analyses) as well as the desired nitrogen (or other nutrient) application rate all influence the amount of biosolids applied per acre. The contract applicator or municipality should be able to explain the calibration process. The actual application rate is determined during the application process and will be recorded in the report for your inspection. If the applicator or municipality cannot explain the calibration process, it likely means the machines are not calibrated properly and that the actual rate of application is not known. Do not accept biosolids from this source.

Should soil testing be done prior to biosolids application? Why must soil pH be 6.5 or above?

Soil tests are conducted before biosolids application to identify soil characteristics such as soil test nutrient levels, pH and cation exchange capacity (CEC). In Indiana, soil pH must be maintained at or above 6.5 to minimize potential metal uptake by plants. This is also the optimum pH range for most crops. Soil CEC is used in Indiana to determine maximum metal applications to different soil types. Soil test information should be provided to the grower as a service by the municipality or contractor.

Record Keeping

Who keeps records on where and when biosolids are applied?

Daily records should be kept by the municipality or contractor for each land application of biosolids. These records should include number of loads, field location, percent solids, number of wet and dry tons applied, and the application rate on a per acre basis. This information, along with the biosolids laboratory analyses, should be made available to anyone receiving biosolids on their land. Ask to receive a copy of these records. This information is also sent to IDEM for their files.

As with all land use practices, you should keep records of the biosolids analyses, applications and soil analyses of the field(s) receiving biosolids. With the enactment of the Indiana Responsible Property Transfer Law, land use records are becoming increasingly important when buying and selling property. Biosolids that have cleared EPA requirements and been applied to meet crop nutrient needs, should not adversely affect property value.

Who monitors the soil or site?

As mentioned previously, soil testing should be done by the municipality or contractor prior to biosolids application. The results of the soil tests should be provided to you. The agronomist or contractor should then consult with you to develop a nutrient management program that incorporates nutrients from the biosolids and from any chemical fertilizers required to achieve your crop's yield potential. Remember, do not apply more nitrogen (or other nutrient) than the crop requires as the biosolids application is often calculated to provide all of the crop's nitrogen needs.

Remember, you have total control over where and when biosolids are applied on your land. For example, applications made to wet fields can cause compaction problems and possible yield losses. The effects of extreme soil compaction are not easily overcome. Any activities that do not coincide with your knowledge of proper soil management should not be tolerated.

To maximize the benefit for all concerned parties, good communication is critical. Under proper management, land application of biosolids can benefit the grower, the contractor, the municipality, and the citizens within the community.

In addition, the following bulletins in the Water Quality series may be of interest:

WQ 1 "Water Testing Laboratories"
WQ 2 "What Is Ground Water?"
WQ 3 "How to Take a Water Sample"
WQ 4 "Why Test Your Water?"
WQ 5 "Interpreting Water Test Results Part One: Inorganic Materials"
WQ 6 "Buying Home Water Equipment"
WQ 7 "Animal Agriculture's Effect on Water Quality Pastures and Feedlots"
WQ 8 "Animal Agriculture's Effect on Water Quality Waste Storage"
WQ 9 "Water Quality for Animals"
WQ 10 "Wetlands and Water Quality"
WQ 11 "Sulphur Water Control"
WQ 12 "Distillation For Home Water Treatment"
WQ 13 "Home Water Treatment Using Activated Carbon"
WQ 14 "Reverse Osmosis for Home Treatment of Drinking Water"
WQ 15 "Bacterial Contamination of Household Water"
WQ 16 "Land Application of Manure"
WQ 17 "Agriculture's Effect on Environmental Quality: Key Management Issues"

The White House lawn thrives on applications of biosolids. Biosolids provide nutrients needed to encourage plant growth on public lands, such as parks, ball fields and highway medians.

Land application of biosolids is similar to fertilizer application. In addition to crop nutrients, such as nitrogen and phosphorus, biosolids add organic matter to soil. Organic matter improves physical characteristics of soil such as structure and moisture-holding capacity.

Cooperative Extension work in Agriculture and Home Economics, state of Indiana, Purdue University, and U.S. Department of Agriculture cooperating; H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an affirmative action/equal opportunity institution.