The different methods for sludge disposal

As Lavoisier so aptly put it, “Nothing is lost, nothing is created, everything is transformed.”

Whether in physicochemical or biological wastewater treatments, the removal of pollutants from the water undergoing treatment inevitably produces sludge that must be disposed of.

When it comes to the operating costs of wastewater treatment, whether industrial or municipal, the cost of sludge disposal remains one of the most expensive operational expenses.

The possible methods for sludge disposal are:

• Agricultural land application – the most common method used today
• Incineration
  • Currently used in two of the most important treatment plants in Quebec – Montreal and Longeuil – the sludge from these plants is first dehydrated and then incinerated.
  • This was also the method used in Quebec City before the recent launch of the CBMO (Centre de Biométhanisation de la Matière Organique)
• Biomethanization – if you would like to learn more about this method, we invite you to read the following articles:
  • https://aquasan.ca/articles/what-is-biomethanization/
  • https://aquasan.ca/articles/methanogenic-potential/
• Landfills – which come with a certain cost and which, when it comes to organic sludge, are further removed from the environmental objectives of the Quebec government (to recover or recycle 70% of generated organic matter by 2030)
• Composting

Superintendents of municipal wastewater treatment plants or of industrial wastewater treatment facilities may soon face numerous challenges if they choose to use the method of agricultural land application.

In fact, effective November 1, 2025, the government has regulated the application of residual fertilizing materials (RFMs) through a new Code for the Management of Residual Fertilizing Materials:

https://www.environnement.gouv.qc.ca/matieres/mat_res/fertilisantes/index.htm(in French only)

One of the new regulations in this Code, which, based on our experience in the field, is going to cause a lot of headaches for superintendents, concerns the minimum dryness value required for land application.¹

In fact, for many wastewater treatment plants, achieving a minimum sludge dryness of 18% by the end of 2027 (and even the current 15%) remains a major challenge, as their current dewatering equipment cannot attain these sludge dryness values, and significant investments in their equipment will be required to reach them.

Another new feature of this guide, which certainly represents a step in the right direction regarding the control of emerging contaminants, is Criterion I, which encompasses the preventive investigative parameters (I) which are classified into 3 categories:

• I1 (specific to agricultural recycling)
• I2 (specific to agricultural recycling, with stricter conditions for distance and concentration)
• I-OC – out of class – cannot be used in land application in Quebec.

Article 11 of the Code stipulates, among other things:

Municipal biosolids from outside Québec are presumed to be Class I-OC, unless another classification is determined based on the results of the analyses of the preventive investigative parameters conducted in accordance with this Regulation.

Therefore, new analyses are required during sludge characterization to determine the levels of emerging contaminants, including PFAS², in the sludge.³

In this new guide for residual fertilizing materials, the responsibility to provide information of each key player, whether they are the generator of RFMs, the agronomist, the farmer, or the project sponsor, is now also clearer and more precise.⁴

For your sludge dewatering process, don’t hesitate to consult our experts. At AQUASAN, we have extensive training and technical know-how, and we bring creative solutions to help you achieve your sludge dryness targets.

New Fertilizing Residual Materials Management Code:

https://www.legisquebec.gouv.qc.ca/fr/document/rc/Q-2,%20r.%209.02?langCont=en 

¹ articles 52 and 119 of the Code

² To learn more about PFAS, we recommend reading our article : https://aquasan.ca/articles/pfas-tackling-a-major-environmental-and-health-challenge/

³articles 11 and 117 of the Code, and Table 7 – Classification Criteria for RFMs according to preventive investigative parameters

⁴ https://www.environnement.gouv.qc.ca/matieres/code-gestion-mrf/cartographie-nature-flux-information-valorisation-mrf.pdf (in French only)