
Optimizing Activated Sludge Systems – The significance of C:N:P and how to maintain it
June 18, 2026
Optimizing Activated Sludge Systems – The significance of C:N:P and how to maintain it
June 18, 2026
We sometimes forget that it wasn’t that long ago that wastewater in Quebec was discharged, without being treated, into our lakes, our rivers and our waterways – directly into this precious blue resource, which is one of our region’s greatest treasures.
Even though the Québec Water Board issued guidelines governing water management as early as 1960, and the Environment Quality Act was enacted in 1972, it took many years before effective and concrete measures were implemented.1
At the end of the 1970s, less than 2% of Quebec’s population had access to a sewer system connected to a wastewater treatment plant. In addition, there were the discharges from major industries and the agricultural practices which were still largely unregulated.1 The deterioration of Quebec’s waterways was then happening at breakneck speed.
Then, until the end of 1999, the Quebec government worked hard to attain its objective of treating the wastewater of 98% of the population that is served by a sewer system.1
Where do we stand today?
In 2025, 101,105 kilometres of pipes and 10,659 structures enable the management of the region’s drinking water, wastewater and stormwater. Today, if all of this infrastructure needed to be replaced, it would require an investment of $197.6 billion.2
Fortunately, according to a report done by the Centre for Expertise and Research on Infrastructures in Urban Areas (CERIU), much of the infrastructure, that is to say 67%, is still in good condition. However, close to 10% is in poor or very poor condition. By itself, this 10% represents a replacement cost of $20.6 billion. We must also not overlook the 23% of infrastructure that is deemed acceptable.2 Although it is still functional, maintaining it is essential to prevent its deterioration in the coming years.
Of the $20.6 billion required to replace the infrastructure that is in poor condition, 72% is attributable to cities with more than 100,000 residents.2 This finding highlights the concentration of deficiencies found in major urban centres. Having been among the first to implement water management systems between the 1950s and 1980s, these cities now also have the oldest infrastructures.2 The aging of these systems, combined with increased rehabilitation needs and high population density, inevitably present their own challenges to ensuring effective water management.
The sustainability of our water treatment works is at risk due to the growing imbalance between revenue and expenses related to our infrastructure. In 2023, revenue generated by water services covered only 40% of the total costs. To close this gap, municipalities rely on government grant programs (PRIMEAU 2023, TECQ 2024-2028) which are struggling to meet the demand.3
Which factors are contributing to the soaring costs of infrastructure modernization?
Firstly, it is true that the standards imposed on treatment plants have become much stricter over the years. Better control of the pollutants sent to treatment plants has led to the continuous optimization of the technologies that need to be implemented. The requirements are higher due to a better understanding of environmental impacts.
It is not the advances that should be called into question, but rather the system to which they are applied. The water management model in Quebec, as elsewhere in America, is centralized4:

The called-upon solution often remains the same when a population grows denser: expand the treatment plants, upgrade pipelines and increase capacity. Unfortunately, the centralized model is currently reaching its economic and physical limits.4
Cities are seeing their development being hampered by the saturation of treatment plants. These plants are barely able to manage peak flow rates generated by ever more frequent periods of intense rain. Climate change is therefore becoming a key factor that must be considered, as it has a direct impact on the quality and the availability of water resources.
There is therefore a need for a collective reflection on the future of the management of this resource. For years, water was seen as an inexhaustible resource without consideration for the implications of its use, whether upstream or downstream. Once it entered the system, it became the sole responsibility of municipal water treatment plants. This model gradually created a disconnect between users and their consumption.
In 2023, the Quebec government’s Annual Report on Drinking Water Usage revealed that the residential sector accounted for 68% of the water consumed in the province.3 This data highlights the importance of raising awareness about responsible water use. This essential resource must not be neglected.
In 2024, some municipalities in Quebec were still struggling to provide their residents with quality drinking water. In La Martre, in Gaspésie, the mayor revealed that residents have been under a boil-water advisory since August 2000 due to the aging water supply system and the numerous breaks that affect it. For more than twenty years, these residents have been paying for a service that does not even give them access to safe drinking water.5
This reality reminds us that water remains a precious and vulnerable resource. While certain communities struggle daily to access clean water, others continue to consume it without considering the consequences of their use.
Each of us is responsible for the protection of this blue gold. Preserving this essential resource begins with understanding the impact that our consumption habits can have on its quality and its availability.