Wärtsilä Aquarius BWTS Overview

Updated 2026-06-16

Wärtsilä's Aquarius ballast water management range offers two treatment routes from a common platform: Aquarius UV, which combines filtration with ultraviolet disinfection, and Aquarius EC, which uses filtration with side-stream electrochlorination generating total residual oxidant. Both reach the IMO D-2 standard and hold IMO and USCG type approval, letting owners match technology to salinity profile and operating constraints.

Key takeaways

Aquarius offers UV and electrochlorination (EC) disinfection from a shared filtration platform.
Aquarius UV is chemical-free and salinity-independent but sensitive to UV transmittance.
Aquarius EC uses compact side-stream electrochlorination, is salinity-dependent and needs TRO control and neutralization.
Both variants start with a 40 to 50 micron self-cleaning filter and target the IMO D-2 standard.
The EC variant manages hydrogen from electrolysis and uses sodium thiosulfate neutralization on discharge.
Both hold IMO and USCG type approval and require MEPC.325(75) commissioning testing once fitted.
Technology choice should follow the vessel's salinity profile, water clarity and voyage length.

Two Technologies, One Platform

The Aquarius range gives owners a choice between UV and electrochlorination disinfection while sharing a common filtration front end and control philosophy. Aquarius UV pairs a screen filter with UV reactors, while Aquarius EC pairs the filter with a side-stream electrochlorination unit that generates total residual oxidant (TRO) and injects it into the main ballast flow.

This dual offering lets a buyer match the technology to the vessel's trading pattern. UV is salinity-independent and chemical-free but sensitive to water clarity, while electrochlorination is highly effective in seawater but salinity-dependent and reliant on TRO control and neutralization. The shared platform simplifies fleet standardisation where a mixed fleet has different ballasting profiles.

Both variants follow the standard approach of mechanical filtration on uptake followed by disinfection, targeting the IMO D-2 performance standard of fewer than 10 viable organisms per cubic metre for the 50 micron and larger class plus the smaller-class and indicator-microbe limits.

Filtration Front End

Both Aquarius variants begin with an automatic self-cleaning screen filter, typically in the 40 to 50 micron range, removing sediment and larger organisms on ballasting. Differential pressure triggers backflushing, with the backwash returned to the area of uptake to avoid translocating concentrated organisms.

Filtration reduces the biological and solids load reaching the disinfection stage, improving efficiency for both UV and EC routes. The filter is the principal mechanical wear component, with screen elements, drive and seals being the most frequently serviced parts.

On deballasting the water generally bypasses the filter; the UV variant may re-treat with UV on discharge, while the EC variant passes the water through neutralization before it goes overboard.

Aquarius UV Variant

Aquarius UV inactivates organisms with high-intensity ultraviolet light, damaging their genetic material so they cannot reproduce. It adds no chemicals, generates no residual oxidant and needs no neutralization, and it works at any salinity, which makes it suitable for vessels operating in fresh, brackish and sea water alike.

As with all UV systems, performance depends on UV transmittance. In turbid low-UVT water the system raises lamp power and may reduce ballast flow to maintain the required dose, which extends ballasting time. UV lamps are consumables rated in operating hours, and quartz sleeves require cleaning and periodic replacement to maintain UV transmission.

The UV route is often chosen for vessels on short voyages or with fresh-water ballasting, where a chemical-free, salinity-independent solution is preferred and where dual treatment can avoid holding-time constraints.

Aquarius EC Variant

Aquarius EC uses side-stream electrochlorination: a small fraction of the filtered flow is electrolysed at high concentration to produce a concentrated oxidant stream, which is then dosed back into the main ballast line to achieve the target TRO. This keeps the electrolysis cell and rectifier compact compared with a full-flow electrolysis chamber.

Because it relies on electrolysing seawater chloride, the EC variant is salinity-dependent and may face limits in low-salinity water. A TRO analyzer controls dosing on uptake and verifies the residual on discharge, and a neutralization step using sodium thiosulfate reduces residual oxidant below the discharge limit before deballasting.

The electrolysis produces hydrogen, so the EC variant includes safe gas separation and dilution. The electrode cell is the principal consumable, scaling and eroding over time, and TRO analyzer reagent management is a routine task.

Type Approval, Service and Support

Aquarius systems hold IMO type approval under the BWMS Code (MEPC.300(72)) and have achieved USCG type approval, enabling use in US waters when the installed model and capacity are covered by the certificate. The EC variant, using an active substance, also went through the IMO active-substance approval process. Both variants must pass commissioning testing under MEPC.325(75) once installed.

Maintenance differs by variant: the UV route centres on lamps, quartz sleeves and CIP, while the EC route centres on the electrode cell, TRO analyzer reagents and neutralization dosing. Both share filter maintenance. Energy demand is higher for UV in poor water, while EC adds chemical handling for neutralization.

Sea Clean AS supports BWTS operators across technologies with spare parts sourcing, reagent supply and field service. Matching genuine or correctly specified filter screens, UV lamps, electrodes and reagents to the installed configuration preserves both performance and type-approval validity.

Frequently asked questions

What is the difference between Aquarius UV and Aquarius EC?

Aquarius UV uses ultraviolet light for disinfection, which is chemical-free and works at any salinity but depends on water clarity. Aquarius EC uses side-stream electrochlorination to generate TRO, which is highly effective in seawater but salinity-dependent and requires TRO monitoring and neutralization with sodium thiosulfate on discharge.

Which Aquarius variant is better for fresh-water trading?

The UV variant is generally preferred for fresh or brackish ballasting because UV performance is independent of salinity. The EC variant relies on electrolysing seawater chloride and can be limited in low-salinity water unless salt dosing is provided. The trade-off is UV's sensitivity to turbidity.

Are Aquarius systems approved for US waters?

Yes. Aquarius systems have obtained USCG type approval in addition to IMO approval, so they can be used in US waters when the installed model and capacity are covered by the certificate. The EC variant also completed the IMO active-substance approval, and both require MEPC.325(75) commissioning testing.

How do maintenance needs differ between the variants?

The UV variant's main consumables are UV lamps and quartz sleeves plus CIP chemicals, while the EC variant's main consumable is the electrode cell, with TRO reagents and neutralizing chemical. Both share filter screen maintenance. Sea Clean AS can supply parts and reagents for either configuration.

Sources

Sea Clean BWTS service desk · All Insights