The use of biosolids on agricultural land has many proven benefits. However, strict guidelines must be followed in order to protect human health and the environment. In Canada, The Ministry of Environment (MOE) sets the criteria before biosolids are considered suitable for farming. The exact location where the biosolids will be spread must also be identified and approved by the Ministry. If a site meets the conditions set by the Environmental Protection Act and Ontario Regulation 347, the applicant will be given a Certificate of Approval for an “Organic Soil Conditioning Site.” The MOE will then provide the recommended application rates, spreading procedures and suitable soil characteristics. To allay concerns of the public about biosolids, we discuss some of the issues in this article.
Do Biosolids Emit a Foul Odour?
Odours from biosolids are the result of organic matter breakdown which gives it the peculiar smell of rotting eggs or ammonia. The smell can be quite strong that even small traces can result in complaints from nearby communities. If not addressed properly, this can be a significant issue among locals and create a negative opinion of the wastewater treatment facility.
To combat offensive odours, treatment plants use various methods including chemicals or deodorizing misting systems. The simplest and most effective solution is to place a cover on the water tanks that hold the sludge. It would be vital that the cover be airtight to prevent the escape of foul odours yet be accessible and safe for necessary inspections.
Chemical solutions can also be employed. Chlorine dioxide (ClO2) is a potent disinfectant and bactericide in wastewater treatment. It provides safe and environmentally friendly wastewater treatment applications since it does not react with inert compounds. Sodium nitrate is a biological solution to managing odours in sewage sludge. Iron and zinc salts can be used to precipitate sulphides. These salts are proven to be efficient in controlling dissolved hydrogen sulphide which stops the creation of H2S gas that usually causes pungent odours.
The MOE stipulates that biosolids spread on agricultural land must have a low potential to generate odours.
Do Biosolids Contain Harmful Pathogens?
Wastewater goes through several processes including: anaerobic digestion, composting, or alkaline stabilization to reduce odours and minimize the presence of pathogens such as salmonellae, the eggs of the human-beef tapeworm, Taenia saginata, potato cyst nematodes and a range of other viruses. 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.
The MOE emphasize that wastewater must undergo proper treatment before it is considered safe for use in agriculture.
Do Biosolids Contain High Heavy Metal Concentrations?
Biosolids may contain trace amounts of heavy metals. These include: arsenic, copper, lead, cadmium, mercury, selenium, cobalt, molybdenum, zinc, chromium and nickel. The MOE has set guidelines for the concentration levels that are deemed acceptable to limit metal accumulation. To avoid heavy metal accumulation in soil due to repeated biosolids applications, best management practices are implemented to ensure that these elements do not exceed limits and negatively impact the environment in the long run. Soil pH is a significant factor in determining the availability of these metals in soil. It is known that acidic soils (except in the case of molybdenum and selenium) increase the availability of most of these metals. Thus, soil pH must be regularly monitored.
Do Biosolids Contain Dangerous Pharmaceutical Residues?
Pharmaceutical residues mainly enter the environment through excretion, either as the original pharmaceutical compound, or as a by-product of that compound. If wastewater sludge is not treated properly, these compounds may make their way into rivers and oceans, or through the spreading of contaminated biosolids fertilizers on agricultural land. Human medications are not the only contributors, veterinary pharmaceuticals can also add to the residues found in wastewater.
To address this issue, wastewater treatment plants use multi-process methods to treat sewage sludge residuals. Normally, treatment entails primary, secondary, and tertiary levels of filtration to turn the wastewater into biosolids that is suitable for agriculture. The primary treatment is a physical separation of solid materials from the sewage resulting in the production of a liquid effluent and solid sludge (biosolids). Secondary treatment involves biologic treatment of the wastewater byproducts. Tertiary treatment uses chemical and/or ultraviolet processes. If the sludge goes through the correct process. pharmaceutical residues will no longer pose any danger since most chemicals are degraded during the tertiary phase.
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.