Retrofitting a Clarifier with Lamella Plates for Increased Capacity
Increasing treatment capacity does not always require a new tank, a larger site or a major change to the process train. For many water and wastewater utilities, an existing clarifier can deliver substantially more throughput when its settling area is used more efficiently. Lamella plates, also called inclined plate settlers, create additional effective clarification area within the existing basin footprint.
This case study examines a hypothetical retrofit at a regional Australian wastewater treatment plant serving a growing coastal community. The facility was approaching its hydraulic limit during wet-weather events, while projected development threatened to push average flows beyond the original design capacity. The project team selected a plate-pack upgrade as a lower-impact alternative to constructing another sedimentation basin.
The example reflects issues familiar to operators in Australia, including seasonal inflow and infiltration, constrained brownfield sites, rising electricity costs and the need to keep essential treatment processes operating during construction. It also shows why hydraulic modelling, sludge management and controls integration matter as much as the plates themselves.
For professionals working across the Los Angeles Basin and other urban water markets, the same principles apply. A clarifier retrofit can be a practical capacity project, but only when the existing structure, upstream loading, downstream filters and operational controls are assessed as one connected system.
The Capacity Problem Behind The Retrofit
The plant in this example treated an average dry-weather flow of 18 megalitres per day, with peak daily flow reaching 32 megalitres. Its two primary clarifiers had been designed for an earlier population forecast. During intense rainfall, inflow and infiltration caused short-term hydraulic surges, reducing settling performance and increasing suspended solids carryover to biological treatment.
Operators were also seeing a narrower operating window. Increasing the surface overflow rate improved throughput but produced cloudy effluent. Reducing the flow protected effluent quality but increased bypass risk during storms. A conventional expansion would have required additional land, new pipework and a long construction programme beside an operating plant.
This constraint is common in Australian cities such as Sydney, Melbourne and Brisbane, where established treatment sites may be surrounded by housing, roads or protected land. In regional areas, the local market can also make specialist construction resources scarce, so a retrofit that limits concrete works may offer a significant programme advantage.
The project team began with a condition assessment. Ultrasonic thickness testing, crack mapping and level surveys confirmed that the concrete tank, launder and inlet channel could remain in service. The assessment also identified corroded access steelwork and outdated scum-removal equipment that needed replacement during the same shutdown.
Designing The Lamella Plate Upgrade
The selected system used inclined polypropylene plate packs installed inside one existing clarifier. The plates increased the effective settling area without expanding the tank footprint. At the design flow, the retrofit reduced the required upward settling velocity and created a more stable separation zone for suspended solids.
Designers first reviewed the inlet hydraulics. Lamella units are sensitive to uneven flow distribution, so the existing centre-feed arrangement was modified with a perforated distribution header and baffle improvements. Without this work, part of the plate pack could have been overloaded while other areas remained underused.
The sludge blanket was another critical consideration. Inclined plates concentrate solids into a smaller collection area, which can increase hopper loading and desludging frequency. The upgrade therefore included new sludge withdrawal valves, additional pressure monitoring and a programmable sequence linked to blanket-level instruments.
The plant also required a revised automation strategy. Operators integrated flow, turbidity, sludge blanket depth and differential pressure into the existing control system. A useful reference for smaller facilities planning similar changes is this SCADA selection guide, particularly its focus on maintainability, communications and whole-of-life cost rather than initial purchase price.
Construction And Commissioning Results
Construction was scheduled around the Australian summer holiday period, when industrial customers often reduce production and some community facilities operate at lower demand. The plant kept one clarifier online while the second was isolated, drained, cleaned and inspected. Temporary flow controls prevented the operating basin from being overloaded during installation.
The contractor removed damaged access platforms, installed new stainless-steel supports and lifted the plate modules into position using a mobile crane. The work sequence accounted for confined-space requirements, dewatering and odour control. These details were important because a short shutdown could easily become a prolonged operational risk if cleaning or structural repairs revealed unexpected defects.
Commissioning proceeded in stages. The upgraded basin initially operated at a conservative flow, allowing operators to check distribution, sludge withdrawal and effluent turbidity before the second operating step. A jar-testing programme helped establish polymer dosing for peak conditions, although the plant avoided relying on chemicals to compensate for poor hydraulics.
| Performance measure | Before retrofit | After optimisation |
|---|---|---|
| Average flow handled by upgraded basin | 9 ML/d | 14 ML/d |
| Peak flow handled by upgraded basin | 16 ML/d | 23 ML/d |
| Typical suspended solids carryover | 85 mg/L | 42 mg/L |
| Effective settling area | 420 m² | 1,180 m² |
| Average sludge withdrawal interval | 6 hours | 3.5 hours |
| Additional civil footprint | — | 12 m² |
After three months of monitoring, the upgraded clarifier handled a 55 per cent increase in average throughput for that basin. Suspended solids carryover fell by approximately half under normal conditions. During a significant rainfall event, the plant maintained compliance without increasing coagulant use, although operators used shorter sludge withdrawal cycles to control the blanket.
Managing Operational And Asset Risks
The results did not mean that the plant could simply increase flow indefinitely. Lamella plates improve clarification capacity, but they do not remove the limits imposed by pumping, biological treatment, disinfection or effluent discharge conditions. The engineering team therefore updated the hydraulic profile for the entire plant and identified the next likely bottleneck at the secondary treatment stage.
Plate fouling was managed through routine visual inspections and an annual low-pressure wash during planned maintenance. High-pressure cleaning was prohibited because it could damage the plate surfaces or dislodge solids into downstream equipment. Operators received practical training on isolation, access and safe removal of a module.
Sludge handling required the greatest behavioural change. Before the retrofit, staff could tolerate a slower withdrawal pattern. After installation, delayed desludging quickly reduced available settling volume. The operating procedure was changed to use blanket depth as the primary trigger, with time-based fallback settings for instrument faults.
The project also highlighted the value of professional networks and shared technical experience. Water authorities considering regulatory or funding implications may find broader sector context in this resource on CWEA advocacy. Australian utilities can apply the same principle through Water Industry Operators Association events, state-based water associations and local supplier workshops.
Lessons For Future Capacity Projects
The strongest lesson was that the retrofit succeeded because it was treated as a process upgrade rather than a plate-installation exercise. The tank condition, inlet distribution, sludge withdrawal, instrumentation and downstream capacity were reviewed together. This avoided the common mistake of purchasing a high-capacity plate pack that the rest of the plant could not support.
The business case also benefited from comparing several options. A new clarifier offered greater long-term expansion potential but required land, civil works and a longer approval pathway. Increasing chemical dosing appeared inexpensive but would have raised operating costs and sludge production. A lamella retrofit provided a staged response while preserving the option of future civil expansion.
Site planning remains relevant even when an upgrade is successful. In dense urban regions, water recycling, odour buffers, truck movements and community expectations can influence the value of every square metre. Guidance on urban recycling facility siting provides useful context for planners comparing brownfield upgrades with new treatment assets.
The project team also kept community and workforce considerations visible. Local contractors completed much of the access and mechanical work, while specialist suppliers provided the plate modules and controls support. For organisations developing regional partnerships or technical education programmes, a community partnership resource and a regional development example illustrate how collaboration can support skills, local participation and wider infrastructure outcomes.
A clarifier retrofit with lamella plates is most effective when the target is clearly defined: additional wet-weather resilience, higher average throughput, improved effluent quality or deferred capital expenditure. The practical takeaway is to verify tank condition, model inlet and sludge hydraulics, integrate reliable monitoring and commission in controlled steps before claiming the full capacity gain.