At Water Treatment 411 we see small wastewater treatment plants across the U.S. all staring down the same problem: aging infrastructure with zero redundancy. Many operate with just one aeration basin and one clarifier (often nearing or past their design life) and limited space for expansion. When the liner starts leaking or grit buildup impacts performance, operators face an impossible choice: risk noncompliance or shut down the plant. A recent project on the Big Island of Hawaii shows there’s a smarter path forward.
The Challenge: Maintain Treatment While Replacing a Failing Lagoon Liner
At a 300,000 GPD extended aeration activated sludge facility, the aging lagoon liner had begun deteriorating, with visible wear along the outer edge and accumulating grit reducing capacity. The utility manager needed to take the lagoon offline for cleaning and relining, but the site had no secondary aeration basin or spare clarifier to fall back on. No redundancy, no safety net.
Expanding the footprint wasn’t an option either. This is typical of older, land-constrained sites. So the question became: How do you temporarily remove a critical treatment process without breaking compliance?
The Fix: Turn the Clarifier Into an Aeration Basin
Enter WSI International, which engineered a clever workaround: Convert the existing secondary clarifier into a temporary aeration basin and drop in a compact DAF unit to handle clarification. The project avoided major construction and used just a 38’ x 14’ flat space next to the control building.
The DAF system was designed to manage MLSS from the activated sludge process and included pumps to send effluent uphill to the chlorine contact tank and handle RAS/WAS flows. Once the DAF came online, the clarifier was taken down and retrofitted for biological treatment duty.
The converted clarifier had structural limitations (a sloped floor, existing rake systems, and limited internal access) making traditional blower-based aeration impractical.
The Innovation: External Jet Aeration With Landia AirJet
To meet oxygen demand and ensure proper mixing in the repurposed clarifier, WSI went with Landia’s AirJet system. The venturi-style jet aerator pulls atmospheric air into the flow and reintroduces it into the tank, delivering both aeration and mixing energy. Crucially, the AirJet’s nozzles are installed from the outside, with no need to gut or retrofit the internal structure.
This solved multiple problems at once:
- It avoided interference with existing rake assemblies.
- It allowed fast deployment without costly custom fittings.
- It enabled full biological treatment performance in a nontraditional tank.
Why It Matters: Realistic Solutions for Aging Plants
Many utilities, especially in rural areas, are dealing with similar constraints of older facilities with limited budgets and no room for expansion. This project offers a useful case study for how to temporarily shift treatment functions and execute maintenance without breaching permits or causing environmental risk.
For operators and engineers, the core lesson here is that strategic repurposing can solve major constraints. You can add redundancy without pouring concrete or overhauling your plant. A clarifier can become an aeration basin. A compact DAF system can hold the line on solids separation. External jet aeration can eliminate the need for invasive installations.
Keep Your Eyes Open for Scalable Solutions
This isn’t just a one-off success. With the EPA’s increasing scrutiny on aging infrastructure and resilience, the ability to adapt and retrofit with minimal footprint will only become more important.
Whether you’re working on an island or a landlocked township, this kind of creative, space-conscious, and technically robust thinking should be in every operator’s toolkit.
SOURCES: H2O Global News
