Sewage Biosolids – Managing Urban Nutrients Responsibly for Crop Production
Sewage biosolids are created when municipal wastewater treatment facilities separate municipal wastewater (water from sewage systems, road drains, etc.) into liquid (clean water that can be discharged to a nearby stream or river) and the leftover solids. Solids go through an additional treatment process to reduce the presence of potentially harmful micro-organisms and potential causes of odour. The final treated materials are sewage biosolids. Sewage biosolids that do not exceed the regulatory limits for contaminants, pathogens and odour can be applied to farm land as a non-agricultural source material (NASM). See our NASM web page for more information about land applying NASM.
Biosolids contain nutrients and organic matter that are beneficial and important to plant growth, such as:
- mineral and organic nitrogen
- micronutrients such as zinc, magnesium, and copper
They may also contain trace amounts of other elements such as arsenic, lead and mercury. The land application of sewage biosolids as a NASM and the elements NASM contains is regulated under the Nutrient Management Act, 2002, (NMA) and the Nutrient Management Regulation.
Municipal wastewater treatment plants receive raw sewage from residential, industrial and commercial sources. Bylaws regarding municipal sewer use do much to control the quality of the raw sewage received at sewage treatment plants. However, treated biosolids may still contain some chemicals that are not beneficial to crops, but pose minimal risk to the environment when applied to land in accordance with the regulation.
The Nutrient Management Regulation ensures that any land applied biosolids are of benefit to crops, do not degrade the natural environment and don’t pose any harm to human or animal health.
The regulation sets out criteria for:
- the concentrations of 11 metals of concern
- the amount, method and timing of application
- separation distances from sensitive areas, such as wells, surface water, and neighbouring homes and businesses
- suitable soil types and topography
The key to using sewage biosolids successfully is management, which is a combination of:
- proper application methods
- best management practices
- nutrient management planning
People who practice good management will get the most benefit from the applied biosolids while minimizing risks to the environment and to the health of people and animals.
When applied according to the regulation, sewage biosolids will:
- improve soil fertility, offsetting the need for commercial fertilizers
- add organic matter, which enhances soil structure, moisture retention and permeability while reducing the potential for wind and water erosion
Sewage biosolids have been used on agricultural land in Canada, the United States and Europe for more than 30 years. Applying sewage biosolids to farmland is an important means of recycling nutrients in the environment, and offers economic and environmental advantages to communities.
These crops are well-suited to using nitrogen supplied by biosolids. Nutrients such as nitrogen should be applied within crop recommendations.
Some sewage biosolids contain a lot of nitrogen. Take care to apply the correct amount of nitrogen to cereal crops, and make sure to follow crop recommendations.
Soybeans and hay crops containing more than one-half legumes do not require added nitrogen, but will use added nitrogen rather than fix nitrogen from the atmosphere. Biosolids that supply phosphorus and/or organic matter can be of benefit to these crops. Some materials may cause management concerns. For example, viable tomato seeds, if present in sewage biosolids, can pose a weed problem in a soybean crop.
Some biosolids may be applied in late fall. However, as is the case for other crops, nitrogen management is critical to avoid over or under application that may cause poor fruit quality, delayed hardening of trees or vines, or winter injury.
- The maximum application rate per hectare for sewage biosolids must not exceed the maximum rate specified in a NASM Plan.
- Nitrogen application rates for individual crops should not exceed recommended rates. Refer to OMAFRA’s Publications 811 – Agronomy Guide for Field Crops, 360 – Fruit Production Recommendations, and 363 – Vegetable Production Recommendations, for recommended nutrient application rates.
- OMAFRA’s nutrient management planning software, NMAN, can be used to determine suitable application rates.
As with spreading manure, applying biosolids may produce odours. Odours can be reduced by timely incorporation into the soil. When planning biosolids application, it is important to follow the standards set out in the regulation and to use best management practices that help to maximize benefit by conserving nitrogen while minimizing odour. The Odour Guide establishes the category of the biosolids. OMAFRA has some discretion to assign a different odour category to the material. The procedures to do this are set out in the Odour Guide.
The regulation establishes minimum separation distances between areas where biosolids are applied and dwellings, residential areas, and commercial, community and institutional uses (such as office buildings, campgrounds and schools). These setback distances are based on the potential of the material to produce odours: the greater the odour detection threshold, the greater the required separation distance.
The regulation establishes minimum separation distances of biosolids begin spread from features such as wells, surface water, saturated soil conditions and bedrock. These separation distances are based on the risk of the material entering either surface water or ground water. Minimum separation distances are determined based on the specific analysis of the material, the soil type found in the field, the slope of the land and the application method used in the area near the watercourse. Separation distances are determined on a case-by-case basis as part of a NASM Plan.
A NASM Plan deals with the management of NASM, including storage and land application. See the information about NASM for Farmers web page for more information about NASM plans.
Nutrients can be harmful to soil and water resources if improperly applied. For example:
- excessive nutrient applications can pollute surface and ground water
- nitrate nitrogen is very dynamic, and excessive soil nitrate at the end of the growing season can leach into ground water, posing a risk to human and animal health
- phosphorus binds to soil and can move with eroded soil to rivers and lakes, degrading water quality and harming fish and wildlife habitat
Over application of nutrients is also a waste of money.
As nutrient sources, sewage biosolids must only be applied in accordance with nutrient management planning principles – total available nutrients applied must not exceed what the crop can use.
The three commandments of nutrient management planning:
- Know what you have.
- Know what you need.
- Know how much you are applying.
The success of a biosolids land application program depends on:
- all parties being aware of their responsibilities
Municipalities as generators of biosolids are responsible for:
- sampling and analysing the sewage biosolids in accordance with the regulation
- providing alternative destinations if biosolids don’t meet the criteria or can’t be applied due to weather or field conditions
Biosolids haulers and applicators are responsible for:
- land applying uniformly so that the maximum application rate is not exceeded
- timely application that is mutually beneficial for the hauler and the farmer
- keeping records of biosolids quality, location of all application sites and volumes applied to each site
- providing the farmer with a report indicating the fertilizer equivalent values of the land-applied biosolids, which is essential for the farmer to make sound nutrient management decisions
Farmers are responsible for:
- ensuring that biosolids are land-applied at times that are beneficial for crop production, but not disruptive to normal farming practices
- complying with all waiting periods between biosolids application and harvesting or grazing
- using best management practices in order to optimize the benefits and minimize the risks of land applying sewage biosolids
- having an approved NASM Plan before the applying sewage biosolids
- ensuring soil application sites meet the requirements of regulation
Farmers also have the right to request flexibility in the land application program, and to stop or refuse biosolids application at any time.
The Nutrient Management homepage links to information on nutrient management planning, regulation, and certification and training, and other web pages dealing with agricultural and non-agricultural source materials.
The Agronomy Guide for Field Crops, Publication 811, has the latest information on producing field crops, tillage options, soil management and other tools for crop production.
The Soil Fertility Handbook, Publication 611, explains the fundamentals of how nutrients behave with soil and crops.
OMAFRA developed a series of Best Management Practices books to help farmers make practical and affordable farming decisions while conserving soil and water resources. Here is a selection to help you with nutrient and soil management:
- Application of Municipal Sewage Biosolids to Cropland
- Soil Management
- Water Management
- Nutrient Management Planning