Ecoflo vs Waterloo Biofilter vs Bionest vs AES: Ontario ATU Comparison 2026
Your Lot Needs a Class 4 System. Now You Are Googling Brand Names. Here Is What You Need to Know.
Once your perc test points you toward an advanced treatment unit, the conversation shifts from “what class of system” to “which brand.” This guide covers the four systems you will most commonly encounter in Ontario — how they work, what they cost to maintain, and how to think about choosing between them.
One thing to say upfront: this is an independent guide. We do not sell, install, or represent any of these systems. What follows is based on publicly available technical documentation, Ontario Building Code requirements, BMEC authorizations, and industry sources. Every system covered here is genuinely good technology — the differences matter, but no option is obviously wrong for every situation.
The right system for your property depends on your specific site conditions, your installer’s experience with each technology, and how you weigh factors like power dependence, maintenance frequency, and upfront cost. Your designer should be walking you through this analysis — if they are not, this guide gives you the questions to ask.
How Ontario Approves Advanced Treatment Systems
Before comparing systems, it is worth understanding the approval framework, because it determines which systems can legally be installed in Ontario and what maintenance obligations come with them.
Advanced treatment units in Ontario are approved through two pathways under Part 8 of the Ontario Building Code:
- CAN/BNQ 3680-600 certification — a national standard administered by the Bureau de normalisation du Quebec. Systems certified under this standard are approved across Canada, including Ontario, as meeting Level IV treatment requirements. Ecoflo and Bionest are certified under this pathway.
- BMEC authorization — the Building Materials Evaluation Commission (BMEC) is an Ontario-specific body that evaluates and authorizes treatment technologies and dispersal systems that are not covered by the national standard. Waterloo Biofilter, Advanced Enviro-Septic, Eljen GSF, and Infiltrator ATL systems are approved through BMEC. Ecoflo’s linear biofilter model also holds BMEC authorization 23-02-404 in addition to BNQ certification.
Both pathways are legitimate and result in systems that are legally approvable under Part 8. The authorization also specifies the required maintenance contract terms — how often the system must be serviced and by whom.
Check Current Authorization Status
BMEC authorizations have expiry dates and must be renewed by the manufacturer. Before specifying any system, confirm that its authorization is current. The OOWA website maintains a list of currently authorized treatment technologies in Ontario. Your designer should also be verifying this as part of any permit application.
The Two Categories: Passive vs Active
The most important distinction among Ontario ATUs is whether they require electricity to operate. This single factor affects installation cost, operating cost, power-failure risk, cottage suitability, and long-term maintenance requirements.
Passive (gravity-fed) systems — Ecoflo, Waterloo Biofilter, Advanced Enviro-Septic — use gravity to move effluent through a treatment medium. No blower, no pump, no continuous electricity draw. Treatment occurs through biological and physical processes in the filter medium. These systems continue to function during power outages as long as the site allows gravity flow. They are generally preferred for seasonal cottages and remote properties.
Active (aerated) systems — Bionest and similar aerobic treatment units — use an electric air pump running 24 hours a day to inject oxygen into the treatment chamber. The aerobic environment supports a different and more aggressive bacterial population, which can achieve higher nitrogen removal rates than passive systems. These systems stop treating wastewater during power outages and require electricity to function.
Neither category is inherently superior. The right choice depends on your site, your power supply reliability, your nitrogen reduction requirements, and your tolerance for mechanical components that require periodic replacement.
System-by-System Breakdown
Ecoflo Biofilter (Premier Tech)
How it works: Septic tank effluent flows by gravity into the Ecoflo biofilter unit. Inside, a tipping bucket distributes the effluent across the filter medium — coconut husk fragments in the compact model, coconut husk with a coco filtration pad in the linear model. As effluent trickles through this organic medium, physical filtration removes suspended solids and a biological film of bacteria breaks down organic waste. The treated effluent then exits to the dispersal system.
Two models in Ontario: The compact biofilter is a self-contained unit placed after the septic tank, with effluent then directed to a leaching bed or area bed. The linear biofilter (EL30 series, BMEC authorization 23-02-404) is a combined treatment-and-dispersal system that eliminates the need for C33 septic sand in many configurations — a significant advantage given the scarcity and cost of certified septic sand in Ontario.
Power requirement: No electricity for gravity-fed installations. An effluent pump is required only when the site topography requires pumping to the dispersal area.
Maintenance: Annual maintenance visit recommended. The organic filter medium does not require replacement — it degrades slowly over a long period. Maintenance involves inspection of the tipping bucket mechanism, effluent filter cleaning, and visual assessment of the filter medium. The compact biofilter has no moving parts in the treatment unit itself.
Treatment performance: Certified to CAN/BNQ 3680-600 as meeting Level B-IV treatment. Average effluent quality in certified testing: approximately 3-4 mg/L CBOD5 and 4 mg/L TSS — significantly cleaner than conventional septic effluent.
Best suited for: Cottage properties, remote sites without reliable power, small lots, sites near water where high-quality effluent is required. The linear model is increasingly common in Ontario due to its reduced sand requirement.
Waterloo Biofilter
How it works: Septic tank effluent is dosed intermittently to the top of the Waterloo Biofilter unit. The effluent trickles through a patented synthetic foam filter medium — a material developed by researchers at the University of Waterloo. The foam has a very high surface area-to-volume ratio, providing an extensive habitat for the aerobic bacterial film that treats the wastewater. Treated effluent exits at the bottom for dispersal.
History: The Waterloo Biofilter is the longest-established advanced treatment technology in Ontario, first installed in 1991 and formally incorporated into the Ontario Building Code in 1998. It has one of the longest track records of any ATU system in the province.
Power requirement: No electricity for gravity-fed installations. A dosing pump is required when the site requires pumping. The filter itself operates passively.
Maintenance: Mandatory maintenance contract required, with service visits every 6 to 12 months per BMEC authorization requirements. The synthetic foam medium is warranted by the manufacturer for at least 20 years. Service visits include effluent sampling and system inspection.
Treatment performance: Certified for Level IV treatment. Achieves very low effluent BOD and TSS levels. The synthetic foam medium has been shown to be highly resistant to clogging under normal operating conditions.
Best suited for: Year-round homes and cottages, small lots, clay soils, high water table sites, locations near drinking water sources. Strong installer network across Ontario given the system’s long history in the province.
Bionest
How it works: Bionest is an aerobic treatment unit (ATU). Septic tank effluent enters a reactor where an electric air pump runs continuously, forcing air through membrane diffusers to create fine bubbles throughout the treatment chamber. This oxygenated environment supports aerobic bacteria that attach to Bionest’s proprietary plastic ribbon media and break down organic waste at a higher rate than passive systems. A portion of the treated effluent is recirculated within the reactor to enhance nitrogen removal.
Power requirement: An electric air pump runs 24 hours a day, 7 days a week. This is a genuine ongoing electricity cost and a genuine dependency — if power is lost, treatment stops. For year-round homes with reliable power, this is a manageable consideration. For seasonal cottages or remote properties, it is a more significant factor.
Maintenance: Annual inspections included. The air pump typically requires replacement every 5 years or so — this is a recurring maintenance cost that passive systems do not have. The plastic media itself carries a 30-year warranty and does not require replacement. Sludge removal from the reactor is needed every 2 to 4 years, in addition to regular septic tank pump-outs.
Treatment performance: ATU aeration systems generally achieve strong BOD and TSS reduction. The recirculation feature provides significantly higher nitrogen removal than passive systems — approximately two-thirds reduction in nitrates, compared to roughly one-third for passive biofilters. In areas with strict nitrogen requirements near sensitive water bodies, this performance advantage is meaningful.
Best suited for: Year-round occupied homes with reliable power supply, sites where high nitrogen reduction is specifically required by the health unit or Conservation Authority, sites where the designer recommends it based on specific effluent quality requirements.
Advanced Enviro-Septic (AES / System O))
How it works: Advanced Enviro-Septic is fundamentally different from the other systems in this comparison. Rather than being a treatment unit that sits between the septic tank and the leaching bed, AES functions as both the treatment medium AND the dispersal system in one integrated pipe configuration. The system uses corrugated perforated pipes wrapped with a geotextile fabric. Effluent flows through the pipes, and the fabric and the soil around the pipes act as the treatment and dispersal medium simultaneously. In many configurations, no separate sand-based leaching bed is required at all.
Two configurations: The standard configuration uses single pipes; the nested pipe configuration uses pipes within pipes for more intensive treatment. Both hold BMEC authorizations in Ontario per the OOWA registry. The installer manual and BMEC authorization together govern Ontario-specific design requirements.
Power requirement: No electricity for standard gravity-fed installations.
Maintenance: Periodic sampling of influent to confirm the system is not being overloaded. The BMEC authorization specifies sampling parameters. No moving parts to replace.
Best suited for: Sites where eliminating a separate sand-based leaching bed provides a significant space or cost advantage. Often used in renovations and retrofits where the footprint needs to be minimized. Popular in Quebec where it originated; growing installer base in Ontario.
Head-to-Head Comparison Table
| Feature | Ecoflo (Compact) | Waterloo Biofilter | Bionest | AES / System O)) |
|---|---|---|---|---|
| System type | Passive biofilter | Passive biofilter | Active ATU (aerated) | Passive integrated pipe |
| Electricity required | No (gravity) | No (gravity) | Yes — 24/7 air pump | No (gravity) |
| Filter medium | Coconut husk / peat | Synthetic foam | Plastic ribbon media | Geotextile pipe wrap |
| Medium lifespan | Organic — degrades gradually | 20+ year warranty | 30-year warranty | Long-term per approval |
| Moving parts | None (gravity config) | None (gravity config) | Air pump, diffusers | None |
| Air pump replacement | Not applicable | Not applicable | ~Every 5 years | Not applicable |
| Maintenance frequency | Annual recommended | Every 6-12 months (required) | Annual + every 2-4 yr sludge | Periodic sampling |
| Ontario approval pathway | BNQ + BMEC (linear) | BMEC (since 1998) | BNQ | BMEC |
| Nitrogen reduction | ~1/3 reduction | ~1/3 reduction | ~2/3 reduction | Standard IV level |
| Sand requirement | Reduced/eliminated (linear) | Area bed required | Reduced leaching bed | No separate sand bed |
| Cottage / remote suitability | Excellent | Excellent | Limited (power required) | Good |
| Ontario manufacturer | No (Quebec) | Yes (Guelph) | No (Quebec) | Ontario/Quebec |
What the Annual Maintenance Contract Means
Every Class 4 advanced treatment system in Ontario requires a mandatory maintenance contract as a condition of its approval. This is not optional and is not just a manufacturer recommendation — it is a regulatory requirement under Part 8 of the Ontario Building Code and the terms of the system’s BMEC or BNQ authorization.
The maintenance contract requires annual (or semi-annual, depending on the system) site visits by an authorized service provider. These visits typically include:
- Visual inspection of all system components
- Effluent sampling and laboratory analysis to confirm treatment performance
- Cleaning or replacement of any components that require it
- A written service report submitted to the property owner and, in some cases, to the local health unit
Annual maintenance contract costs in Ontario run approximately $150 to $500 per visit depending on the system type, the service provider, and your location. Active systems (Bionest) are generally at the higher end because more components require inspection and periodic replacement. Passive systems with no moving parts are typically at the lower end.
Missing a scheduled maintenance visit can put you in violation of your permit conditions. Health units in Ontario have the authority to order remediation if a system’s maintenance is not being performed as required. Keep your service records.
When You Sell the Property
An ATU with a lapsed maintenance contract is a red flag in a real estate transaction. A buyer’s lawyer or inspector will ask whether the maintenance contract is current and whether service records are available. A gap in service records — particularly for an active system with an air pump — can raise questions about whether the system is functioning correctly. Keep every service report and transfer the maintenance contract to the new owner at closing.
How to Choose: The Questions That Matter for Your Site
Your designer should be guiding this decision based on your specific site assessment results. But these are the questions that should be driving the recommendation:
- Is the property seasonal or year-round? For a seasonal cottage that may be vacant for months, passive gravity systems are strongly preferred. Active systems with air pumps that run 24/7 during periods of little or no wastewater input can develop operational issues.
- Is power supply reliable? If the property has frequent power outages or if power supply is uncertain — common on remote cottage lots — a passive system eliminates a dependency that active systems cannot.
- Is high nitrogen reduction specifically required? If the health unit or Conservation Authority has specified a nitrogen reduction target — common for properties near lakes or drinking water sources — an active ATU like Bionest may be required to meet that specification. Passive systems typically achieve one-third nitrogen reduction; active systems achieve two-thirds.
- How limited is the available lot area? The Ecoflo linear biofilter and AES systems offer the smallest footprints by combining treatment and dispersal or eliminating the sand bed requirement. On a very tight lot, these may be the only workable options.
- What is your installer’s experience with each system? A properly installed system by an experienced installer outperforms an improperly installed system of a different brand. Ask your installer which systems they have installed most frequently and what their experience with each has been. An installer who has placed 50 Waterloo Biofilters in the area is a meaningful advantage over one who has installed two.
Do I get to choose which ATU brand gets installed on my property?
In most cases, yes — the designer and installer will present options, but the final decision is yours. Some designers have preferred systems based on their installation experience, and some installers are authorized to install only certain brands. If you have a preference based on your research, tell the designer early in the process. Just confirm that your preferred system is appropriate for your specific site conditions — not every system performs equally well on every type of site.
How long does an ATU system last compared to a conventional septic system?
Because the advanced treatment component pre-treats effluent to a much higher standard before it reaches the soil, the leaching bed or dispersal area in an ATU system is expected to last significantly longer than a conventional leaching bed receiving raw septic tank effluent. The treatment unit itself — the biofilter or ATU reactor — has a long service life when properly maintained: 20+ years is commonly cited, with the dispersal area potentially lasting the same or longer. The air pump in active systems is the component with the shortest service life, typically requiring replacement every 5 years or so.
What happens if I stop paying for the maintenance contract?
The maintenance contract is a condition of the system’s authorization and your septic permit. Letting it lapse puts you in non-compliance with Part 8 of the Ontario Building Code. Practically, it also means the system is not being monitored and serviced — which increases the risk of treatment failure without your knowledge. When you eventually sell the property, a lapsed maintenance contract is a disclosure issue. The fix is straightforward: contact the manufacturer’s authorized service network and reinstate the contract. Missing years of service can be partially addressed with a more thorough catch-up inspection and any deferred component replacement.
Can I use an ATU to replace a failed conventional system?
Yes — and this is one of the most common reasons ATU systems are installed in Ontario. When an existing conventional system fails and the lot does not have space for a full-size conventional replacement bed, an ATU with a smaller dispersal footprint can often fit where a conventional replacement cannot. The permit process is the same as for a new installation: site assessment, system design, permit application, installation with inspections, and Certificate of Approval. See our full guide on the Ontario septic permit process for the complete sequence.
ATU Selection — Key Decision Points
- All four systems are legitimate Class 4 technologies approved for Ontario — none is inherently wrong
- Passive systems (Ecoflo, Waterloo, AES) need no electricity and suit seasonal/remote properties
- Active systems (Bionest) need 24/7 power and achieve higher nitrogen reduction
- Waterloo Biofilter has the longest Ontario track record — first installed 1991, BMEC approved since 1998
- Ecoflo linear biofilter eliminates the C33 sand requirement — significant advantage as sand becomes scarce
- AES eliminates the separate leaching bed — useful on very small lots
- Maintenance contract is mandatory for all ATUs — budget $150 to $500 per year per visit
- Ask your installer how many of each system they have installed — experience matters
A Class 4 system is a significant investment — typically $25,000 to $50,000+ installed in Ontario depending on system type, site complexity, and region. The brand of treatment unit is genuinely important, but it is one factor among several. The quality of the site assessment, the accuracy of the system design, the experience of the installer, and your commitment to the maintenance contract will collectively determine how well any of these systems performs over its lifetime.
Not Sure Which System Is Right for Your Lot?
A qualified site assessment will tell you which systems are technically appropriate for your specific conditions. We can help you understand the options before you commit to a designer or contractor.