Environmental and Health Concerns

Municipalities have several options for meeting land application standards according to the EPA 503 Rule (Table 1). These standards depend on pathogen levels, concentrations of pollutants, and the type of treatment for reducing the attraction of vectors or carriers of pathogens (e.g., flies and rodents). In order to be land applied, all biosolids must be treated to reduce pathogen levels and all biosolids must at least meet the ceiling concentration limit for each of the pollutants listed in Table 2.

Class A biosolids have pathogen levels below detect- able limits and have no site application or use restrictions (Table 1). Class A biosolids can be bagged and sold, and can be used on lawns and home gardens. If one or more of the pollutants listed by EPA 503 Rule is above the Pollutant Concentration Limit (Table 2), Class A biosolids can still be bagged, but the application rate is restricted so that the amount of the pollutant applied in one year does not exceed the Annual Pollutant Loading Rate (APLR). Bags containing APLR biosolids must be labeled with the APLR for the pollutants of concern.

Class B biosolids contain a low pathogen level and have some restrictions (Table 1). These can only be handled in bulk. Crops whose edible parts do not touch the ground can be harvested 30 days after application, but harvest of edible parts that touch the ground or are underground is restricted to 14 and 20 months, respectively. Class B biosolids have a 30-day grazing restriction and a one-year restriction on public access to public contact lands. Reporting and tracking of land application of biosolids is required if one or more of the nine pollutants is above the Pollutant Concentration Limit (Table 2). The total amount of the pollutant applied to a piece of land over time cannot exceed the Cumulative Pollutant Loading Rate (CPLR).

Biosolids produced in Nebraska are generally Class B. The ranges of pollutant values for several wastewater treatment plants in Nebraska are given in Table 3. In some cases, one or more pollutants may exceed the Pollutant Concentration Limit and tracking is required.

Table 3. The range of pollutant levels, on a dry weight basis, for biosolids of several wastewater treatment plants in Nebraska¹.

¹The wastewater treatment plants were: the Theresa Street and the northeast plants in Lincoln; the Papillion Creek and Missouri River Valley plants in Omaha; and the treatment plants in Seward and Scottsbluff.

Agronomic Considerations

Agronomic benefits. When applied to soils, biosolids can supply nutrients and improve soil condition. Biosolids contain the full complement of nutrients required for crop growth and are a good source of nitrogen and phosphorus, the nutrients most commonly applied in Nebraska. Biosolids decompose over several years, gradually releasing nitrogen, sulfur, and micronutrients.

In addition to supplying nutrients, biosolids may improve soil organic matter, microbial activity, and soil physical properties. Effects of biosolids on soil physical properties such as increased soil aggregate formation and aggregate stability may be greater than for animal manures due to the stability of organic compounds in biosolids. Improved water infiltration may be especially valuable on upland areas where the topsoil is shallow and low in organic matter due to soil removal by erosion, grading, or terrace formation.

Nitrogen. The EPA 503 Rule states that biosolids cannot be applied at more than the “agronomic” rate—the rate that supplies sufficient nitrogen to achieve a realistic yield goal. Most nitrogen in biosolids is in organic forms (50–85 percent) and the remaining is mostly ammonium-N (Table 4). Ammonium-N is immediately available to the crop, but much may be converted to ammonia and lost by volatilization if not incorporated into the soil (Table 5). Organic nitrogen is slowly released, typically with 40 percent available to the first crop following application and 75 percent of organic nitrogen released over four years (Table 6). The sewage treatment process influences the rate of organic nitrogen release, with slower release from more stable biosolids. When biosolids are applied at the agronomic rate, nitrogen is used as effectively as with fertilizers.

Table 4. Typical nutrient levels for biosolids of several wastewater treatment plants in Nebraska on an “as is” basis.

As an example, calculation of biosolids application rate, assume that 150 pounds per acre of added nitrogen is needed to achieve a realistic yield goal after giving credit for soil nitrate-nitrogen, the effects of organic matter, and other nitrogen sources. If the biosolids are immediately incorporated, biosolids from the Theresa Street Wastewater Treatment Plant in Lincoln would need to be applied at the rate of 17.4 tons per acre (Table 7). In performing such calculations, use recent analytical results from the wastewater treatment plant for ammonium and organic nitrogen, rather than the values in Table 4.

When non-legume crops are grown in the second and subsequent years, nitrogen may need to be applied to supplement the nitrogen from decomposing biosolids. Credit should be given to the release of organic nitrogen in subsequent years although actual rates of release can vary widely from the estimated rates (Table 6). Soil nitrate-nitrogen in the top 2 to 4 feet of soil and other nitrogen credits also should be considered in determining the nitrogen needs of the subsequent crop.

Phosphorus. Most phosphorus in biosolids becomes crop-available during the year of application. If biosolids are regularly applied to meet crop nitrogen needs, the supply of phosphorus will exceed crop demand. Careful planning is needed with repeated application of biosolids to avoid excessive build-up of soil phosphorus, resulting in increased potential for phosphorus loss in runoff and erosion, and contamination of surface waters. Applying 17.5 tons per acre, as in the example in Table 7, would apply 175 pounds of phosphate per acre while 45 pounds may be removed in 150 bushels of corn. Soils should be tested after three to four years to ensure adequate phosphorus availability and to avoid excessive soil phosphorus levels.

Potassium. Biosolids do not supply much potassium. Potassium is soluble and most is removed in the treated wastewater. Most Nebraska soils supply sufficient potassium for optimal crop growth, but added fertilizer potassium may be needed where soil supply is low.

Site-specific application. Crop responsiveness to applied biosolids and the potential for contamination of surface and groundwater varies with land and soil conditions. Producers will need to weigh the costs of using biosolids against the anticipated benefits for each field, and even for zones within fields. Greater crop response to applied biosolids can be expected if: 1) soil test phosphorus is low; 2) one or more micronutrients are deficient; and/or 3) water infiltration is slow and runoff is high due to low organic matter and/or high clay content in the surface soil. The potential for environmental contamination is less if: 1) soil test phosphorus is low; 2) there is little or no chance of flooding; 3) the depth to a drinking water aquifer is more than 6.5 feet and the soil has fine texture; 4) best management practices for erosion and runoff control are applied when slope is more than 6 percent, and biosolids are not applied when slope is more than 12 percent; 5) water holding capacity is greater than 1 inch per foot of soil depth; 6) biosolids are not applied to wetlands; and/or 7) the application site is more than 100 feet from open water bodies or water flow channels. Treated effluent from a domestic wastewater treatment facility should not be applied within 500 feet of a public drinking water well, 100 feet of a private drinking water well, and 100 feet from an inhabited building.

Table 5. Ammonium-nitrogen available for crop use with preplant application as affected by time to incorporation of the land-applied biosolids.

Less of the ammonium nitrogen will be available when biosolids are applied under hot, wet, and windy conditions as compared to cold and dry conditions.

Table 6. Estimated percent of organic nitrogen applied in biosolids that is crop available.

Additional Information

Table 7. Calculation of application rate for biosolids, on an “as is” basis, to supply the added nitrogen needed to achieve a realistic yield goal (Steps 1 to 4), and calculation of the nitrogen supplied from the biosolids in the second year (Step 5). (Nitrogen values for biosolids from the Theresa Street Wastewater Treatment Plan in Lincoln were used for the example.)

This publication has been peer reviewed.

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