Throughout much of civilization, manure has been used as fertilizer in agricultural farmlands for many centuries. In the early 1900s, farmers in the United States began utilizing sewage wastewater to improve soil fertility. As technological advances in the field improved, researchers began to recognize the valuable nutrients that can be derived from treated sewage sludge.
Modern techniques have improved the safety and quality of wastewater sewage neutralizing pathogens and minimizing toxic natural and synthetic chemicals. Though biosolids may also give off distinct odours due to compounds such as sulphur and ammonia, they are found to be harmless to the community.
According to the Water Environment Association of Ontario (WEAO), “There are no documented cases of adverse effects where biosolids have been applied to agricultural land in accordance with regulations or to anyone living nearby. Furthermore, there are no documented cases where workers involved in the wastewater treatment process or the land application of biosolids have experienced adverse effects due to the biosolids.”
Testing of Biosolids
Prior to utilizing biosolids as fertilizer, they must first be evaluated for total solids, nitrogen, and phosphorous concentrations. They must also pass the prescribed concentrations of 11 regulated metals. Under the Nutrient Management Act, E.coli levels must be below what is stated in current regulations. Each municipality is in charge of the testing of biosolids and testing must be undertaken by certified labs.
Pharmaceuticals and Synthetic Chemicals
Pharmaceuticals, synthetic hormones and antimicrobial additives in personal care products are commonly found in wastewater sludge. These compounds degrade during the treatment process depending on their chemical properties. However, traces may still remain in treated biosolids. North American and European scientists have reported that polybrominated diphenyl ethers (PBDEs, flame retardants), antibiotics, anti-depressant pharmaceuticals, and antimicrobial compounds such as triclosan and triclocarban have been found in biosolids at parts-per-billion (ppb) to parts-per-million (ppm) concentrations. Surfactants, including the nonylphenol class, are found at ppm to parts-per-thousand (ppt) concentrations.
To put these amounts in perspective, the WEAO explains that “a typical planting rate for soybeans is 200,000 seeds per acre and 1 ppm is equivalent to 1 seed in 5 acres. One ppb is equivalent to 1 seed in 5,000 acres and 1 ppt is equivalent to 1 seed in 5 million acres. The Province of Ontario is approximately 230 million acres.”
A typical person is more likely to be exposed to these chemicals in higher concentrations in their daily living through the use of personal care and household cleaning products.
Metals of Concern
Biosolids may contain heavy metals. These include: arsenic, copper, lead, cadmium, mercury, selenium, cobalt, molybdenum, zinc, chromium and nickel. The Ministry of the Environment and Climate Change (MOE) has set guidelines for the concentration levels that are deemed acceptable to limit metal accumulation. Applying waste materials in accordance with these Guidelines could elevate the metal concentrations of a typical Ontario soil to the maximum recommended limits within 25 to 55 years. However, if the metal concentrations in biosolids are reduced, waste applications may be allowed to continue for longer periods of time.
Non-biodegradable Materials
Regulations mandate that biosolids applied on agricultural land must be free from foreign nonbiodegradable material that may cause human or animal injury or damage to equipment. Wastewater must be shifted through an 8 mesh screen size Tyler sieve (2.36 mm size openings). Plastic residues should not exceed 1.0% of the total sample and the total concentration of all other foreign non-biodegradable materials shall not exceed 2% of the total sample.
Site Conditions Evaluation
Before routine land application can commence, planned site management methods must be evaluated. Approval is required for the application site and the hauling of the waste. An inspector from the MOE has to visit the site to ensure that conditions such as surface slope, depth of soil and protective distances from surface water are appropriate for biosolids application to minimize the risk of contamination. Waiting periods between biosolids application and human contact for other wastes will also be assessed, on a case-by-case basis, subject to the level of pathogens and organic and industrial chemicals present as well as the features of the site. If the site meets the requirements set by the ministry, it will be given a Certificate of Approval for an Organic Soil Conditioning Site.
Safe Distance from Residences
When biosolids are spread on agricultural lands that are near housing communities, apprehensions may crop up due to potential odours, air-borne particles and surface run-off. The minimum distance required between the spreading site and a residential area is normally 450 metres. For an individual home that is not located in a residential area, the minimum separation distance is 90 metres. However, these standards may still undergo further assessment depending on the application method and land slope. In situations where liquified treated wastewater sludge is injected directly into the soil, or when it is applied by surface irrigation within twenty-four hours, distances may be reduced. Moreover, if the farmer occupies the residence being evaluated, then the required distance may be lowered further. It is up to the applicant to prove that his request for the reduction in the separation distance is justified.
In Conclusion
To ensure the safety of the public, government officials and academic researchers continue to review the effects of biosolids in terrestrial and aquatic ecosystems. In a study undertaken by the WEAO in 2001, it was reported that the use of biosolids in agriculture posed no significant risk to the environment or human health. The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) closely coordinates with the MOE to manage Ontario’s biosolids land application program. The practice is governed by provisions and regulations set out under the Ontario Water Resources Act, the Environmental Protection Act, and the Nutrient Management Act. The WEAO Residuals & Biosolids Committee also works to safeguard food safety, human health and the environment. Requirements are reviewed and revised as needed, based on new science or technology.
If you are a municipality in Ontario and in need of a biosolids management solution, please feel free to contact us at 1 (877) 479-1388.
Sources:
Canadian Water and Wastewater Association (CWWA)
Water Environment Federation
Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)