Town of Antigonish Sewer Treatment Plant
Update October 18, 2024:
In response to concerns regarding the odour coming from the Sewage Treatment Plant (STP), and the Town’s commitment to keep the public informed, please see the following update regarding the plant’s operations and our efforts to deal with the odour.
In the Spring of 2024, there were weeks when a very strong odour was coming from the plant. We know it negatively impacted residents in the area. We hired a consultant to assess the issue at the STP. A report of their findings has recently been received by the Town.
This report has been reviewed in accordance with Part XX (Freedom of Information and Protection of Privacy – FOIPOP) of the Municipal Government Act (MGA) and is now publicly available pdf here (2.90 MB) . 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.
The following causes were identified as contributing to the odour:
- Climate change and warmer summers are causing summer lagoon temperatures to be approximately six to seven degrees warmer than was typical 20 years ago. Hotter water temperature decreases oxygen transfer efficiency, possibly in the range of 15 - 20%. At times there isn’t enough oxygen getting transferred into the wastewater in the lagoon to limit odours.
- Sludge accumulation and its effects on equipment (buried aerators, etc.) are also projected to have a combined 10 - 20% decrease in oxygen transfer efficiency. The STP has historically had sludge removed on a ten year cycle, the last desludging took place in the Fall of 2015.
- The influent strength has periodically increased this summer (2024) over the design loading for the plant. The STP was designed for a certain concentration of material coming in and we can periodically exceed that level. Some of this may be due to the required and ongoing removal of stormwater connections from our sanitary sewer system, which increases the concentration of influent.
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):
- 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 (one to three 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
- Town Council approved a motion at the September 16 regular council meeting to have staff proceed with this work. When the lagoon is desludged, over 60 tractor trailer loads of material will be removed, and oxygen demand will be decreased.
- Tender was released Friday, October 11, 2024 with closing October 25, 2024
- This work is expected to be completed during the month of November
- Front End Plant Upgrades
- Tender for design of a new screening system / front end
- Release RFP by end of October with construction expected for 2025
- Tender for design of a new screening system / front end
Long Term (four to 18 months):
- Assess for additional upgrades and reconfigurations of the aeration system (Fall 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)
About the STP
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 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 centre.
- 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.
Below are from Frequently Asked Questions regarding the STP
Will it ever not smell?
Let’s be clear, healthy lagoons will always have a smell; but not an offensive smell like we have had. Due to the nature of the plant and the business of treating sewage, there will always be a musky smell, but that smell should generally not leave the plant under normal operating circumstances.
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 it 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.
Can it 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 – see details above) we do have the ability to expand what we have and support our community’s growing population.
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.