Lagoon Sludge Removal Without Dredging or Downtime
If sludge keeps climbing and dredging is in budget talks, your lagoon likely has a mixing problem. Full-depth mixing returns oxygen to the sludge layer so bacteria digest the volatile portion in place. In La Grande, Oregon, average sludge depth dropped from 41 to 28 inches in five months. Titus Wastewater Solutions sizes systems to your lagoon’s acreage and depth.
Fixed aerators only move the water right around them. Solids settle in the dead zones between units, oxygen runs out, and the sludge layer keeps growing.
Signs Your Lagoon Needs Sludge Removal
Rising sludge depth, lingering odor, and climbing BOD or TSS are the most common signs a lagoon needs sludge removal. If two or more of these sound familiar, it’s time to act before the fix gets more expensive.
Sludge depth keeps rising
Each sludge survey shows a thicker blanket and less volume left to treat wastewater.
Odor that won’t go away
Anaerobic sludge produces hydrogen sulfide, even when surface DO readings look fine.
Floating sludge or gas bubbles
Mats rising to the surface mean gas is forming in the sludge layer below.
BOD or TSS creeping up
Lost volume and short circuiting push effluent numbers toward permit limits.
Dredging is on the budget
If someone has already priced dredging, the sludge has won a few rounds.
More aerators haven’t helped
Adding units of the same type rarely reaches the dead zones between them.
Most of that sludge doesn’t have to be dug out. With the right mixing, sludge reduction can happen in place, while the lagoon keeps running.
What Causes Lagoon Sludge Buildup
Lagoon sludge builds up when solids settle faster than bacteria can digest them, usually because poor mixing keeps oxygen from reaching the bottom. Every lagoon is designed to hold some settled solids, but three conditions turn normal accumulation into a problem.
Dead Zones
Fixed aerators move the water closest to the unit, but much of a large lagoon sees little circulation. Solids settle in those quiet areas and stay there.
Oxygen That Never Reaches the Bottom
Without full-depth circulation, oxygen stays near the surface. The sludge layer goes anaerobic, digestion slows, and sulfate-reducing bacteria start producing hydrogen sulfide.
Volatile Solids Left Undigested
Lagoon sludge is a mix of volatile solids, which bacteria can break down, and inert material like grit, which they can’t. When the bottom runs out of oxygen, the volatile portion piles up alongside the inert material instead of being digested.
That’s the key to sludge reduction: the volatile portion is the part you can recover without a dredge, as long as oxygen and mixing reach the bottom.
Lagoon Sludge Removal Options: Why Common Fixes Fall Short
Only full-depth mixing changes the conditions that create lagoon sludge; dredging and most fixed aerators deal with the sludge that’s already there. Here’s how the common options compare.
Approach
Mixing reach
Maintenance
Long-term sludge control
Approach
Dredging
Mixing reach
None, removes sludge physically
Maintenance
Major project, disposal costs, lagoon disruption
Long-term sludge control
Sludge rebuilds if mixing doesn’t change
Approach
Bottom diffusers and tube aerators
Mixing reach
Fixed in place, limited circulation
Maintenance
Clog, foul with rags, and get buried in sludge
Long-term sludge control
Struggles in high-solids lagoons
Approach
Surface or brush aerators
Mixing reach
Upper water column near the unit
Maintenance
Power in the water, boat access often required
Long-term sludge control
Solids below settle untouched
Approach
Aspirating aerators
Mixing reach
Fixed thrust, poor overall mixing
Maintenance
Prone to ragging, boat access often required
Long-term sludge control
Limited reach into dead zones
Approach
Twister-FL floating aerator
Mixing reach
360-degree, full-depth circulation, repositionable while running
Maintenance
No moving parts or power in the water, blower on shore
Long-term sludge control
Keeps volatile solids suspended so bacteria digest them in place
What this looks like in a real lagoon: The City of La Grande, Oregon, ran through most of this table. It dredged its pre-air cell in 2002 and again in 2020, and it added diffusers and tube aerators along the way. In 2026, the city replaced all 72 tube aerators with four Twister-FL units and two Twister SDF units. See the results below.
Video: fouled aerator being pulled from the lagoon
Old tube aerators came out fouled with rags and sludge.
How to Reduce Lagoon Sludge Without Dredging
To reduce lagoon sludge without dredging, keep the volatile portion suspended in oxygenated water so bacteria can digest it in place. Lewis Titus compares it to a fire that has burned down to a few chunks of wood: stir the chunks back into the middle and give them air, and they burn down to almost nothing. Volatile sludge works the same way, and in many lagoons, 60 to 70% of the sludge layer is volatile.
Titus WWS does that with AirLift technology:
- Air is delivered from shore. A shore-based blower sends air to each floating unit, so no electrical components or moving parts go in the water.
- Water is lifted from the bottom. Air released inside the unit pulls water up from the lower water column, drawing the sludge layer back into circulation.
- Water discharges in every direction. Oxygenated water spreads 360 degrees just below the surface, setting up full-depth circulation. Each Twister-FL moves about 1.7 million gallons per hour.
Mixing the Edges, Not Just the Middle
Floating units in the middle of a lagoon can push sludge toward the banks, where it settles out of reach. Twister SDF directional flow units fix that. Placed along the edges, they set the whole lagoon spinning so solids never get a chance to settle on the banks. They transfer less oxygen than a floating unit, but they make the entire system mix more efficiently.
That’s the layout La Grande, Oregon, uses: four Twister-FL units mixing the middle of the cell, and two Twister SDF units circulating the edges.
Twister-FL Floating Aerator
- Air-driven, with no moving parts in the water
- Floats, so it never gets buried in sludge
- Loosely tethered and easy to reposition
- Serviced from shore, with no boat work
Lagoon Sludge Reduction Results
Full-depth mixing has cut sludge depth within months in working lagoons, with dissolved oxygen and odor improving along the way. Here are the numbers from two of them.
City of La Grande, Oregon
Six years after its last dredge, La Grande’s pre-air cell averaged 41 inches of sludge, and dissolved oxygen had fallen to about 0.2 mg/L. The city installed its first Titus units in April 2026 and completed the layout in July.
41 → 28 in
Average sludge depth, April to September 2026
1.9 mg/L
Average dissolved oxygen, September and October, never below 1.5
30 to 40%
Lower BOD and TSS leaving the pre-air cell
No odor
Coming off the pre-air cell
“At this time we have no odor coming off of our pre air cell.”
Lyle Bridge, City of La Grande WWTP
The city is surveying sludge depth every three months for the next year, so these numbers will keep updating.
Village of Lakeview, Michigan
Twister-FL floating aerators cut sludge 55% in four months.
Results vary with lagoon size, loading, and temperature. In both of these lagoons, dissolved oxygen stabilized first, odor dropped, and the sludge layer shrank over the months that followed.
Get a Lagoon Sludge Assessment
Send us your lagoon’s size and depth, plus your latest sludge survey if you have one. We’ll tell you how many units it takes, where they go, and what to expect.
No sludge survey yet? We’ll walk you through how to take one.
Lagoon Sludge Removal FAQs
How do you measure sludge depth in a lagoon?
Most operators use a sludge judge, a clear, marked tube lowered to the bottom that captures a core sample showing how thick the sludge layer is. Readings are taken at points across the lagoon and averaged into a sludge survey. Surveying on a regular schedule, such as every three months, shows whether sludge is building or shrinking.
Can lagoon sludge be reduced without dredging?
Yes. The volatile portion of the sludge is organic material that bacteria can digest in place when full-depth mixing keeps it suspended in oxygenated water. Inert solids like grit don’t break down and may eventually need removal, but far less often than in a lagoon that relies on dredging alone.
Does mixing a lagoon increase TSS in the discharge?
Not when the sludge is being digested. Full-depth mixing keeps solids suspended long enough for bacteria to break them down, rather than flushing them out. In La Grande, Oregon, grab samples show TSS leaving the pre-air cell running 30 to 40% below the incoming wastewater, before the flow reaches the primary lagoons.
Why does sludge build up along lagoon banks?
Banks and corners are low-flow areas, and floating aerators in the middle of a lagoon can push solids outward toward them. Directional flow units placed along the edges set the whole lagoon circulating, so solids stay in motion instead of settling on the banks.
How fast does sludge build up in a wastewater lagoon?
Sludge builds fastest in lagoons with heavy organic loading, cold water, and poor mixing, because solids settle faster than bacteria can digest them. Without full-depth mixing, a lagoon can lose significant capacity within a few years of being dredged, which is why regular sludge surveys matter.
How long does it take to reduce sludge in a lagoon?
Lagoons with full-depth mixing can see measurable reduction within months, not years. La Grande’s average sludge depth dropped from 41 to 28 inches in five months, and Lakeview, Michigan, saw a 55% reduction in four months. Results depend on lagoon size, sludge volume, temperature, and loading.
How much does lagoon sludge removal cost?
The cost depends on the method, the lagoon’s size, and how much sludge has built up. Dredging carries mobilization, dewatering, hauling, and disposal costs every time it’s done, while in-place reduction is an equipment investment sized to the lagoon’s acreage, depth, and loading. For a full breakdown, see what lagoon sludge removal really costs.
Titus Products for Lagoon Sludge Control
If sludge is spread across the whole lagoon
Start with the Twister-FL Floating Aerator. Floating units set up full-depth circulation that reaches the sludge layer across the entire lagoon.
If the problem starts upstream at a lift station
Treat it before it reaches the lagoon. The Twister Mixing Aerator breaks up grease and keeps wastewater aerobic in the wet well, so less grease reaches the lagoon.
If grit and stormwater are getting into the system
Stop it at the manhole. TwistLift Locks/EJ Access secures and seals manhole access points, reducing the inflow that can carry grit into the lagoon, where it settles as sludge bacteria can’t digest.
If liners, joints, or pipes need sealing
Protect the lagoon’s infrastructure. Titus Industrial Tapes handle geomembrane seaming, concrete joint sealing, and below-grade pipe protection, so repairs hold up in wet, demanding conditions.
Related Problems
- Lagoon aeration cost: Why the cheapest aerator can become the most expensive one you own.
- Lagoon aerator maintenance: What happens when servicing equipment means sending a crew out on the water.
- FOG and surface mats: How one plant spent 30 years fighting a lagoon surface problem that wasn’t what everyone thought.
Stop Budgeting for the Next Dredge
The next dredge doesn’t have to be on the calendar. A short conversation with the Titus WWS team is enough to show what full-depth mixing could recover in your lagoon, using results from systems with similar size and loading.
Rather talk it through first? Call (877) 582-9899 or reach the team through our contact page.