If you’re staring at a designer’s recommendation that includes “Ecoflo,” “Waterloo Biofilter,” “RUCK,” or “Bionest,” your lot has told them the simple version isn’t enough.
Advanced treatment units (ATUs), sometimes called tertiary treatment systems, take partially treated effluent from a septic tank and process it further before it reaches the leaching bed. The output is so clean that the bed required after them is dramatically smaller, sometimes a quarter the size of what a conventional Class 4 bed would need. That’s why these units exist: they fit on lots where a conventional bed can’t.
The trade-off is cost (typically $30,000 to $60,000+ all-in), maintenance complexity, and dependence on power. This guide covers what each major brand does, when they’re the right answer, and what owning one looks like long-term.
The Quick Answer: When You’d Need One
| Site condition | Typical solution |
|---|---|
| Plenty of soil, good perc, no setback issues | Conventional Class 4 (cheapest) |
| Soil too slow or shallow bedrock, large lot | Raised or mound bed |
| Tight setbacks, marginal soil, lakefront | Tertiary treatment + smaller bed |
| Very tight site, no leaching bed possible | Tertiary treatment with discharge to constructed wetland or surface (rare, special permit) |
| Lakefront with severe space constraints | Tertiary often the only legal path |
| Poor soil + commercial-scale flow | Tertiary unit + engineered bed |
Tertiary treatment is what makes a lot of small lakefront and constrained-site builds possible at all. Without these technologies, many lots would be unbuildable for residential.
What “Tertiary” Actually Means
Sewage treatment is described in three stages:
- Primary, physical separation. Solids settle, grease floats. Happens in your septic tank.
- Secondary, biological breakdown by anaerobic bacteria. Also happens in the tank, plus initial bacterial action in the leaching bed.
- Tertiary, additional treatment that removes nutrients and pathogens to a much higher standard. This is what these units do.
Conventional Class 4 systems do primary and partial secondary in the tank, then rely on the soil under the leaching bed to finish the job. Tertiary systems do primary in the tank, then a much more aggressive secondary and tertiary stage in their treatment unit, before sending nearly clean water to a final dispersal step (which can be a small leaching bed or, in rare permitted cases, surface discharge).
The cleaner output means:
- The dispersal area can be much smaller (sometimes half or a quarter the size)
- Setbacks can sometimes be reduced
- Dispersal can happen in soils that would be too slow or shallow for conventional treatment
- Lake water quality impact is significantly reduced (relevant for shoreline cottages)
The Major Brands and How They Differ
Ecoflo (Premier Tech)
A peat-based passive system. Effluent flows through a layered peat moss filter inside a concrete or fibreglass shell. Beneficial bacteria colonize the peat, treating the effluent as it passes through. Output is dispersed to a small bed.
Strengths:
- Mostly passive, minimal moving parts, low power consumption
- Long-tested in Canadian conditions, including cottage-country installations
- Reliable through power outages (most of the unit doesn’t need power)
- Modular, multiple units can scale to larger flows
Weaknesses:
- Peat media needs replacement every 10–15 years (~$3,000–$6,000 per unit when due)
- Larger physical footprint than some pump-driven alternatives
- Not great in deep cold without insulation
Common in Ontario cottage country, including Kawartha Lakes installations.
Waterloo Biofilter
Engineered foam-cube filter media designed at the University of Waterloo. Effluent is dosed onto the foam where bacteria colonies treat it. Cleaner output is collected and dispersed to a smaller bed.
Strengths:
- Compact physical footprint
- High treatment quality, meets stringent discharge standards in many jurisdictions
- Foam media doesn’t need replacement on a fixed schedule (much longer lifespan than peat)
- Some tolerance to flow surges
Weaknesses:
- Pump-dependent (needs power for dosing)
- More mechanically complex than a pure-passive system
- Requires regular service contracts in some installations
Common on tighter sites and where space is at a premium.
RUCK
A specialty Quebec/Ontario design using a sand-filter approach with engineered hydraulics. Effluent passes through controlled sand layers that achieve very high treatment quality. Output goes to a small bed or controlled dispersal area.
Strengths:
- Excellent treatment quality
- Good for shoreline applications
- Long media life (decades, not years)
Weaknesses:
- Larger physical footprint than peat or foam systems
- Higher initial install cost
- Less widely used than Ecoflo or Waterloo Biofilter (fewer local installers)
Bionest
Another aerobic/biological treatment unit using engineered media and active aeration. Common in Quebec and parts of Ontario.
Strengths:
- High treatment quality
- Compact
Weaknesses:
- Power-dependent (aeration runs continuously)
- Service contracts often mandatory
- Less common in Kawartha Lakes than Ecoflo
Aerobic Treatment Units (ATUs), generic
A category rather than a brand. Active aeration in the tank itself supports an aerobic bacterial colony that treats sewage to a higher standard than passive anaerobic treatment.
Strengths:
- Smaller bed required
- Effective on smaller lots
Weaknesses:
- Continuously power-dependent
- Service contracts typically required
- Treatment quality drops fast during power outages
Cost Reality
| Component | Typical Ontario range |
|---|---|
| Conventional Class 4 baseline | $25,000–$35,000 |
| ATU upgrade only (replacing tank with aerobic unit) | +$8,000–$15,000 |
| Ecoflo system (unit + reduced bed) | $35,000–$55,000 |
| Waterloo Biofilter system | $40,000–$60,000 |
| RUCK system | $45,000–$70,000 |
| Bionest or similar aerobic with reduced bed | $40,000–$60,000 |
| Tertiary + raised bed combination | $55,000–$85,000+ |
| Service contract (where applicable) | $300–$800/year |
| Media replacement (Ecoflo, every 10–15 years) | $3,000–$6,000 |
The premium over conventional ranges from $10,000 to $40,000+ depending on system and site. For context, this is what makes some lakefront and constrained-lot builds legally possible at all, without tertiary treatment, the alternatives are a Class 5 holding tank (with ongoing pumping costs that often exceed the tertiary unit’s lifetime cost) or no system at all.
Maintenance: What Owning One Looks Like
This is where tertiary systems differ most from conventional Class 4. Maintenance is more involved and more important to keep up.
Ecoflo
- Annual visual inspection of peat surface (DIY or service)
- Pumping of upstream tank on standard schedule (every 3–5 years)
- Peat media replacement every 10–15 years (the big-ticket maintenance item)
- Effluent filter on tank still needs periodic cleaning
Waterloo Biofilter
- Service contract often required (typically annual visit)
- Pump checks and float monitoring
- Tank pumping on schedule
- Foam media generally doesn’t need replacement on fixed schedule
Aerobic units
- Service contract often required, sometimes mandatory
- Regular checks of aerator function
- Tank pumping on schedule
- Effluent filter cleaning
- Treatment quality drops within hours of power loss; recovery takes days
Generally for all
- More electrical components = more things that can break
- More documentation required for permits and resale
- Service contracts add ongoing cost but maintain manufacturer warranty
A homeowner with an Ecoflo on a Bobcaygeon lakefront installed in 2015 has had the following touch points:
- Tank pumped 3 times (every ~4 years): ~$1,500 total
- Annual visual checks (DIY): $0
- One service call for a frozen distribution line: $400
- No major issues
- Peat replacement coming due around 2028: budgeted ~$5,000
Total ownership cost over 11 years: roughly $6,900 plus the original $42,000 install. Comparable conventional system on a sufficient lot would have run roughly $30,000 install + similar maintenance, minus the eventual peat replacement. The $12,000 install premium over conventional bought him a working system on a lot that conventional couldn’t have accommodated.
When Tertiary Is the Right Answer
Three honest scenarios:
1. The lot won’t accept conventional treatment
Soil is too slow, bedrock too shallow, water table too high. A perc test and soil profile have already told you the answer. Tertiary plus a small bed is the path.
2. Lakefront with serious setback constraints
A standard leaching bed needs more space and more setback distance than the lot offers. Tertiary’s smaller bed footprint solves the geometry problem.
3. Sensitive watershed where conventional treatment isn’t enough
Some Conservation Authority priority areas, especially around lakes with documented water quality issues, may require tertiary on new or replacement systems regardless of soil. The added treatment quality protects the lake.
When You Probably Don’t Need One
Don’t let a salesperson talk you into tertiary if:
- The soil and lot can support a conventional bed
- You’re on an inland property far from sensitive water features
- The cost difference would meaningfully affect your project budget
- The lot is large enough for a raised bed if conventional doesn’t fit
Tertiary is the right tool for the right site. It’s not a default upgrade.
Power Dependence: Real-World Considerations
Most tertiary systems depend on power for some part of their operation:
- Ecoflo: minimal power use; mostly passive
- Waterloo Biofilter: pump-dependent for dosing
- RUCK: minimal power use, mostly passive
- Bionest / generic ATU: continuous aeration; treatment degrades fast without power
For outage-prone properties, this matters. Cottages in Kawartha Lakes regularly see multi-day winter outages. A passive Ecoflo or RUCK rides those out fine. An aerobic unit may need a service visit afterward to reseed the colony.
If outages are frequent at your property, the more passive systems are usually better fits, or budget for a generator + transfer switch as part of the install.
Funding Available
Tertiary systems on shoreline or environmentally sensitive lots are often eligible for Conservation Authority cost-share programs because they directly improve lake water quality. Reimbursement of 25%–50% of project cost (up to a cap) is realistic on qualifying projects.
The specific water-quality benefit of these systems makes them strong candidates for funding compared to conventional replacements. Apply before construction starts.
Resale Implications
Properties with tertiary systems sell fine when:
- Documentation is current and complete (permit, design, service records)
- Service contracts are up to date
- The system has been pumped and maintained on schedule
- The owner can show recent inspection reports
Properties with tertiary systems where documentation is sparse, service has been irregular, or the system is approaching media-replacement timing without budget can struggle. Buyers and their lawyers do their due diligence on these systems specifically because they’re more complex than conventional.
If you own a tertiary system and plan to sell in the next 1–3 years: get current inspection and service records on file now. The cost of doing it pre-listing is far lower than the price negotiation at sale if the records are missing.
Tertiary System FAQ
Are these legal under OBC Part 8? Yes. They’re permitted Class 4 systems with engineered treatment components. Each brand has specific approval through the Building Materials Evaluation Commission (BMEC) or equivalent process.
Do I need a special installer? Most brands require certified installers, installers who’ve been trained on that specific system. Not every general septic installer qualifies.
Will my insurance cover them? Mostly the same as conventional septic. Some insurers price slightly differently, especially for systems that depend on continuous power.
Can I retrofit a tertiary unit onto an existing system? Sometimes. Depends on the failure mode of the existing bed and whether the upgrade would solve the underlying problem. Sometimes it’s the right answer; sometimes a full redesign is more economical.
How long do they last? Tank: 30–50+ years. Treatment unit: 20–30 years for the structure. Pumps and aerators: 10–15 years. Peat media: 10–15 years on Ecoflo specifically. Beds after tertiary: 25–35 years.
Do they smell? A working tertiary system does not noticeably smell more than a conventional Class 4. A failing one (or one with a clogged effluent filter or backed-up pump) can smell as bad as any failing system.
Are they worth it on a year-round home? Only if the lot conditions or watershed regulations require them. They’re not an upgrade for the sake of upgrade.
When the Lot Decides
The most reliable advice on tertiary systems: don’t pick the technology, let the site’s design requirements pick it. A licensed sewage system designer who’s done many of these in your specific area knows which brand fits which site. Trust their recommendation more than a contractor’s product preference.
We service the Kawartha Lakes region, Lindsay, Bobcaygeon, Fenelon Falls, Coboconk, and surrounding rural and waterfront properties. We pump the tanks on tertiary systems regularly, document their condition, and refer to local designers and certified installers when an upgrade is being considered. We don’t install or design these systems ourselves (specialty work), but we understand the maintenance side and can spot when one isn’t being looked after correctly.
Have a tertiary system to maintain or inspect? Call (705) 806-0800 or book online. Use the cost calculator for a 60-second estimate.