Understanding the Agricultural Use of Biosolids

Sewage Biosolids

Q. What are sewage biosolids?

A. Municipal wastewater treatment facilities separate the solids from the liquid in municipal wastewater to produce clean water that can be discharged to a nearby stream or river. The solids resulting from this treatment process undergo additional treatment (stabilization) to reduce the presence of potentially harmful microorganisms and the potential for the material to cause odour. The treated materials that result are sewage biosolids.

Q. Why are sewage biosolids good for agricultural lands?

A. Sewage biosolids contain important plant nutrients including nitrogen, phosphorus, calcium, magnesium, copper and zinc, all of which are essential for healthy plant growth. These biosolids also contain organic matter that helps improve the physical condition of the soil, so that it is better able to hold water and nutrients. Soils that have good organic matter content are easier to work and plant roots can find water and nutrients more easily.

Applying sewage biosolids on agricultural lands:

• Reduces the need for commercial fertilizers
• Reduces production costs
• Improves soil fertility
• Enhances soil structure, moisture retention and soil permeability, and
• Adds organic matter, reducing the potential for soil erosion.

Q. How can you be sure applying sewage biosolids to land is safe?

A. Government scientists, health experts and agrologists continually review the regulatory requirements and standards for applying sewage biosolids to land to make sure they protect food safety, human health and the environment. Requirements are revised as needed, based on new science or technology.

The standards include:

• Requirements for spreading to take place at specified minimum distance away from homes, wells and watercourses, and
• Mandatory waiting periods after application before crops can be harvested or livestock allowed to graze.

Q. What can be grown on land where sewage biosolids have been applied?

A. In Ontario, sewage biosolids are commonly applied to land that is used to grow crops for livestock feed or fuel production (e.g. ethanol) and is not used for fruits and vegetables, or pasture. The mandatory waiting periods after the application of sewage biosolids before crops like fruits and vegetables can be harvested, or before livestock can be grazed, makes the use of sewage biosolids impractical in these situations. The length of the required waiting period varies depending on the type of crop grown on the field. For example, hay cannot be harvested until three weeks after spreading; tree fruits cannot be harvested for three months, and vegetables cannot be harvested for a full year after biosolids have been spread on the land.

The length of the waiting period also depends on the type of animal to be grazed on the field (e.g. two month waiting period for horses, six month waiting period for swine).

Q. What testing is required on sewage biosolids before they can be applied to agricultural land?

A. Before they can be spread on agricultural land, sewage biosolids must be tested for total solids, nitrogen, and phosphorus concentrations, as well as concentrations of 11 regulated metals. Sewage biosolids produced by wastewater treatment plants that have been phased-in under the Nutrient Management Act must also be analyzed for their E.coli concentration. If any of the levels is above the regulated level, the biosolids cannot be applied.

Municipalities are responsible for the testing of sewage biosolids.

Q. Do the agricultural lands have to be tested before having sewage biosolids applied to them?

A. Agricultural soils that are going to have sewage biosolids applied must be tested for pH, phosphorus and regulated metal concentrations. Pre-approval inspections are carried out to by MOE staff to make sure that the site conditions (e.g. surface slope, depth of soil) are suitable and that all required protective distances (e.g. setback distance from surface water) have been properly identified before sewage biosolids can be spread.

Q. How do you know that the requirements are followed? What happens if they are not followed?

A. MOE conducts about 200 inspections a year of sites that receive sewage biosolids. These ongoing checks confirm that the rules are being followed.

Any reports received by either OMAFRA or MOE about possible infractions are promptly investigated by MOE. If a problem is found, the ministry takes appropriate action. This may range from simple actions like requiring the applicator to adjust how or where they should spread sewage biosolids, to more serious actions like fines.

Government Research

Q. What kind of research does the government do to be sure that applying biosolids to land is safe?

A. In addition to its own research, the government conducts regular evaluations and periodic reviews of all applicable scientific research in Ontario and in other jurisdictions to ensure that the best available scientific knowledge is applied to provincial regulations and standards.

The findings of the studies continue to support the application of sewage biosolids as a plant fertilizer as a safe and beneficial practice under the province's regulatory requirements and standards.

For more information about sewage biosolids, their use as a fertilizer in agriculture, and studies and research undertaken in Ontario, please visit:

http://www.weao.org/committees/biosolids/biosolids.html