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Freshwater makers from Wärtsilä
Also known as 'Serck Como'

Reverse Osmosis Plants


Reverse Osmosis (RO) is a water purification technology that uses membranes to remove salts and impurities from seawater in order to create permeate (freshwater). Wärtsilä Water & Waste offers Reverse Osmosis freshwater makers for ships, that can produce between 40 and 1500 tons of freshwater per day. These RO systems stand out for their modular and flexible design and are customizable to meet operational and space requirements of any type of vessel.  

Wärtsilä Reverse Osmosis plants use semi-permeable membranes: porous sheet barriers that blocks the flow of salts and other solutes. Seawater is forced through microscopic pores in the membrane under pressure, while larger dissolved solids and heavy molecular weight contaminants are flushed away as reject water.



    • Low energy consumption
    • Easy operation and maintenance 
    • Flexible material selection regarding components and piping 
    • Modular design for minimal footprint 
    • Maximum flexibility: critical components can be chosen individually
      (pre-filtration, membranes, high pressure pumps, energy recovery devices, automation) 
    • All proven suppliers from Western Europe and US 
    • Engineering and installation support 
    • Minimal chemical consumption


    • Capacity 40–1500 ton/day  
    • Single and double-pass designs
    • Consistent production of freshwater at seawater temperature range of 0-35 °C  
    • Fully automatic or semi-automatic operation  
    • Standard automation: Siemens S7-1500, PROFINET (other by request)  
    • Easy connection to ship automation and control system  
    • UV-steriliser after prefiltration reduces chemical consumption  


    Seawater is pumped into the RO system by a seawater pump (1). Incoming water is subjected to double filtration. In the first prefilter stage (2) the seawater is filtered from all suspended solids up to 40-50 micron for large RO plants, and 5 microns for small standard plants. A second prefilter stage (4) further filters the water down to 5 microns for large RO plants, and 1 micron for small standard plants. In large RO plants a UV reactor (3) is installed between the two filtration stages to disinfect the filtered water and avoid bacterial growth on the RO membranes.

    The filtered seawater is then pumped through the RO membranes by a high-pressure pump (5). Semi-permeable RO membranes (6) remove ions, particles, and bacteria from seawater to generate permeate/freshwater. The permeate leaves the membranes, while the brine is diverted for discharge. Optional post-treatment (9) consists of pH correction, re-hardening and remineralisation. Large RO plants offer automatic flushing with low salinity water to remove the salty water from the RO housing. 

    process flow Reverse Osmosis, working principle reverse osmosis Wärtsilä Water & Waste

    RO plants typically have a single or a double pass configuration. In double pass plants the treated water passes through the membranes twice. The permeate from the first pass becomes the feed water for the second membrane-pass (8) via another high-pressure pump (7). Single pass RO plants typically supply freshwater under 500 ppm total dissolved solids (TDS). When high quality water with a TDS under 20 ppm is required (for example in boilers), a double pass RO plant is necessary. 


    System Capacity (tons/day) Electrical power* (kWh/t) Dry weight (kg) L x W x H(mm) Footprint (m2)
    ROS-1680 1680 1,5 110 1300x950x750 1,24
    ROS-3360 3360 2,2 125 1301x950x750 1,24
    ROS-5040 5040 3,0 145 1302x950x750 1,25
    ROS-6480 6480 3,0 165 1303x950x750 1,25
    ROS-9600 9600 5,5 235 1110x800x1850 0,90
    ROS-14400 14400 7,5 265 1110x800x1850 0,90

    Customized RO plants can be designed according to the specific requirements for capacity range from 20 to 100.000 tons/day.


    Delivered as standard 

    • Pre-treatment (multimedia filters/self-cleaning filters, cartridge filters, UV-sterilisation) 
    • High-pressure pump 
    • Energy recovery device (Isobaric recovery or Turbocharger) 
    • RO membranes 
    • Automatic flushing system/CIP 


    • Post-treatment (remineralisation and/or pH-correction) 
    • Remote monitoring system 
    • Flow transmitters for seawater, permeate, and brine 
    • Super duplex 
    • Containerized construction

    Options for large RO plants

    • UV sterilizer for the filtered water
    • Energy recovery device (turbocharger or pressure exchanger)
    • Dosing system for pH adjustment
    • Re-hardening system
    • Re-mineralisation filter
    • UV sterilizer for the permeate


    More freshwater makers from Wärtsilä

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    For NEWBUILD, please contact +49 4152 805-0 or

    For SPARE PARTS, please e-mail us with the Equipment Serial Number or the name of the vessel at For urgent support, contact +49 4152 805-130.

    For TECHNICAL SUPPORT & SERVICE, please email us with the Equipment Serial Number or the name of the vessel at For urgent support, contact +49 4152 805-226.

    Equipment Serial Number is taken from the equipment nameplate and includes all letters and numbers as given on the equipment nameplate.

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