Sewer

Town of Antigonish Sewer Treatment Plant

Update February 20, 2025:

The Town of Antigonish is committed to keeping the public informed about our Sewage Treatment Plant (STP) and ongoing efforts to improve capacity and address odour concerns.

What is Capacity?

When we talk about sewer capacity, we mean how much wastewater the system can handle before reaching its limit. Our sewage treatment plant can process up to 1.8 million gallons per day (MGD). Currently, we average 1.65 MGD, meaning we are approaching full capacity, especially during peak times.

Why is Capacity Important?

If our system exceeds capacity, it can:

Cause backups and overflows in homes and streets.
Reduce treatment effectiveness, impacting water quality.
Limit future development in Antigonish by restricting new connections.

What Affects Our Capacity?

One of the biggest challenges is Inflow and Infiltration (I/I)—extra water entering the sewer system from sources like:

Leaking pipes – Groundwater seeps into cracks in underground pipes.
Stormwater connections – Roof drains, sump pumps, and catch basins send excess water into the sewer.
Foreign materials – Wipes, rags, and other non-flushable items clog systems and reduce efficiency.

On dry summer days, our flow is about 1.46 MGD, but in wet weather, it jumps—showing how much extra water enters the system. Reducing I/I helps free up capacity for homes and businesses without needing major expansions.

How is the Sewer System Performing?

Our sewage treatment plant is working well and producing high-quality treated water. However, seasonal challenges impact performance:

Spring & Fall Odours - Natural turnover in the lagoon can cause temporary odours.
Summer Heat Issues - Higher temperatures make treatment less efficient, especially during heat waves.
Increased Sludge Buildup - More waste is accumulating, requiring frequent desludging to maintain efficiency.

Odour Issues in 2024

In Spring 2024, strong odours affected nearby residents. A consultant study identified the main causes:

Warmer Summers – Lagoon temperatures are 6-7°C hotter than 20 years ago, reducing oxygen transfer efficiency by 15-20%.
Sludge Accumulation – Buried aerators and excess sludge further reduce oxygen levels by 10-20%.
Higher Waste Concentration – Removing stormwater from the sanitary sewer means the remaining sewage is more concentrated.

The report is is publicly available pdf here (2.90 MB) . This report has been reviewed in accordance with Part XX (Freedom of Information and Protection of Privacy – FOIPOP) of the Municipal Government Act (MGA). The few redactions in the report, cost estimates and plant designs, have been made in accordance with sections 477 (1) and 475 (1) of Part XX of the MGA.

What Are We Doing About It?

The Town of Antigonish remains committed to ensuring the long-term functionality and sustainability of this critical infrastructure as it provides essential services to the community. A number of action items have been identified to address the causes identified above and have been sorted according to the timeframe in which they can be done.

Short Term (Daily/Ongoing Actions):

Monitor and record odour conditions (Done daily)
Apply deodorizer products (Done daily)
Adjust plant aeration equipment (Done regularly)
Skim surface floatables (Done regularly)
Flow recirculation to front of plant (This action was started in September and is ongoing)

Medium Term (1 to 3 Months):

Assess how to increase aeration feed configuration to the front end of the plant, including the following options:
- Consider what we need to add another blower to the front of the plant, including piping and wiring connections
- Assess how to increase the output from the blowers we currently have
- Purchase/rent/remodel a new blower unit. All of these options are being considered/investigated.
Desludging
- The Town of Antigonish is pleased to announce the completion of the desludging process for the first cell of the lagoon at the Sewer Treatment Plant. GFL Environmental Inc., the successful proponent selected through a competitive RFP process, began the work in late November.
- While equipment delays caused a pause in the process over the holiday season, desludging resumed in January and was completed mid-month. Over 300 bone dry tonnes (36 tractor trailer loads) of sludge were removed from the first cell—slightly exceeding initial estimates, but within budget.
- The Sewer Treatment Plant has traditionally undergone desludging on a ten-year cycle, with the last desludging performed in the fall of 2015. Regular sludge removal is essential for maintaining the plant’s efficiency, as it prevents interference with aerators and enhances oxygen levels. This supports the overall treatment performance of the plant.
Front End Plant Upgrades
- Tender for design of a new screening system / front end
  - Release RFP by end of January with construction expected for Spring 2025

Long Term (4 to 18 Months):

Assess for additional upgrades and reconfigurations of the aeration system (Winter 2025)
Prepare and issue the tender for the construction of the new screening removal system (Spring 2025)
- Currently, the STP does not have a screening system. The plant has a grinder that shreds incoming materials into smaller pieces so they can be pumped into the lagoon. This means the plant doesn’t have a method to prevent material that shouldn’t be flushed from entering the lagoon, and we are currently dealing with treating the increased loading and smells from that material.  
- A screening system includes equipment that will remove, de-water, and dispose of solids and inorganic screenable materials (pads, tampons, condoms, wipes, etc). Upgrading the STP infrastructure will also include new lift station pumps and aeration blowers.  
- In June 2024, the Province of Nova Scotia announced the Town will receive $2.71 million from the Municipal Capital Growth Program for this upgrade. The Town of Antigonish is contributing $1.8 million to this project and $903,507 is coming from the Municipality of the County of Antigonish. That’s over $5.4 million in upgrades coming in 2025.
- Installation of new screening system (Completed by end of 2025).

How the Sewer Treatment Plant Works

The Town’s STP is an aerated lagoon that uses biological processes to consume waste and clean wastewater, before it is released back into the environment. Here’s how it works: 

Headworks / Pre-Treatment: The first step of our STP process occurs when the sewage enters our plant. It flows by gravity through a grinder, which shreds material into pieces, so they are small enough to pass through our pumps. The pumps then lift the sewage 25 feet underground up into the front end of our lagoon.
Aerated Lagoon: The next step involves using aerobic bacteria and other microorganisms (biomass) to break down the sewage in the aerated lagoon. These microorganisms feed on waste, cleaning the water naturally. This process happens in the first five (out of six) cells of the lagoon, with most of the aeration and waste breakdown focused in the first cell. In the lagoon, air is used to help the bacteria grow and do their job. There are four blowers pumping air through a pipe that runs the length of the lagoon, supplying 13 chains of aerators that are strategically placed for both mixing and aeration.  
Clarification: After the biological treatment, the water moves to the final cell in the lagoon. Here, any remaining solid particles, including the biomass (dead bacteria), settle to the bottom, leaving the clarified wastewater on top to flow through three modules of three banks of sand filters. 
Disinfection: To make sure the wastewater is safe to release, it is disinfected with UV light, which reduces (kills) pathogens and bacteria down to acceptable levels. 
Release: Finally, the treated wastewater (effluent) is released back into nature, into the river to rejoin the water cycle. This is a standard practice regulated by the Nova Scotia Department of Environment and Climate Change.

It takes about a month for the wastewater to go through this process. This method is effective and environmentally friendly, using natural processes to treat wastewater.

STP Fast Facts:

The lagoon at the STP is shaped like a kidney and is 1,500 feet long. That is the equivalent of five U.S. football fields.  
The lagoon is 14 feet deep in its center.  
It is divided into six cells.  
Of the 13 chains of aerators, 70% of those are located in the first two cells where most of the sludge accumulation is stored.
Our STP was originally built in 1974 with $3 million of upgrades made in 1996.

Frequently Asked Questions regarding the STP

Will the plant ever be completely odour-free?

No. A healthy lagoon will always have a mild, musky smell. However, the strong odours from 2024 were not normal, and the measures we are taking will help prevent such issues in the future.

We recognize the offensive smell we have experienced is not normal. We have short-term measures, the addition of deodourizing products, medium-term actions such as plant desludging, and long-term actions including upgrades to the STP, we are taking to address this odour (as further detailed above).

Can the STP handle further growth?

A statement we often see online is that the STP can’t handle the expansion we’ve seen in the fringe.  With modest upgrades (which are coming) we do have the ability to expand what we have and support our community’s growing population.    

Do we need a new plant?  

No, we do not need a new plant. For what the plant is supposed to do, treating sewage, the lagoon performs well and has a good treatment efficiency.  

The plant’s capacity can be affected by the accumulating sludge as this reduces oxygenation and effectiveness of pumps and aerators in the lagoon.

The STP was built to hold approximately 10 years of sludge. Like a residence with a septic tank which needs to be pumped on a regular cycle, our lagoon also needs to be dredged and this has been typically done every 10 years. With the growth of our community along with climate change, we have to alter our maintenance plan and desludge more often; not based on a timeframe but based on the amount of material in the lagoon.

What NOT to Flush

Without a screening system in place, we have a large quantity of non-organic materials like menstrual products and garbage floating in the lagoon. These items block our aerators and affect the plant’s efficiency.

Residents should be mindful of what is being flush; please only flush toilet paper and human waste. Every small action makes a big difference.