Retrofit Sewage Treatment Plants

When upgrading or retrofitting your engine room, the retrofit sewage treatment plants from Super Trident® are by far the most convenient solution available to the marine world today. A modular design allows for easy installation. The retrofit STP can easily be boarded through standard vessel access ways thanks to its modular design. Three separate modules with limited dimensions prevent the need for hull penetration.

Widely regarded as standard specification by many of the world’s shipowners, the Super Trident® retrofit sewage treatment plants from Wärtsilä Water & Waste form the most cost effective and safe answer to disposal of wastewater at sea.

The plant ensures compliance to IMO legislation – MEPC.227(64). Minimum maintenance is required.


    Sewage Treatment Plants installed on or after 1st January 2016 are required to meet the new IMO Annex IV, MEPC 227(64) effluent quality standards, which introduce a Dilution Compensation Factor into the sampling requirements.

    Dilution should not be the solution to pollution. IMO intended to tackle ‘dilution machines’ by the introduction of Dilution Compensation Factor (Qi/Qe) in MEPC.227(64). If the volume of the effluent is higher than the volume of the influent due to the use of dilution, the quality of the effluent must be improved by the same factor. Installing an STP that relies solely on dilution will leave ship operators with some difficult questions to answer, even if the STP is type approved. Therefore, for STPs where Qi/Qe <1, it is important that Qi and Qe can be measured and visible.



    The retrofit range has been specifically designed to reduce the cost of installing sewage treatment equipment into existing vessels. 

      Assembled Unit
      Separated Unit
      • IMO & MED certified
      • Modular construction
      • Single power supply input point
      • Minimal maintenance requirement
      • Solids handling Wärtsilä centrifugal discharge pump
      • Standby compressor
      • Standby discharge pump
      • Compatible with fresh and salt water and conventional or vacuum fed collection system
      • Modular construction (3 modules, easy to install)

      Each size in the retrofit range is built up from three separate water tight tanks connected by external piping, aiding installation. The dimensions of each component has been arranged to permit its transportation through standard vessel access ways.

      Wärtsilä Water Systems has more than 40 years of experience in delivering Sewage Treatment Plants for the Marine industry
      • Asian Hercules II
        “Asian Hercules II”, a 3,200 MT Floating Sheerleg Crane vessel, has 4 main hoisting winches, each capable of hoisting speeds 2m/min with a full load. Delivered in 1997, the vessel has an accommodation facility for 34 persons.

        Asian Hercules II

      • Twister
        The Wärtsilä AQUARIUS® UV Ballast Water Management System (BWMS) was installed onboard the Twister, a Chemgas BV owned LPG carrier.

        For retrofit applications and upgrades, where space availability can be a determining factor, the modular configuration of Wärtsilä’s AQUARIUS® range was a particular advantage and the entire installation process took just 3 weeks.


      • Leonidas
        Delivered in 2009, the 318,000 dwt Leonidas features a machinery installation incorporating a Wärtsilä 7RT-flex82T. The vessel is also equipped with the Super Trident Sewage Treatment Plant ST2A, certified to meet IMO MEPC 159(55) guidelines.


      • Ullswater
        The vessel, a Wärtsilä Ship Design, is to perform diving support, subsea construction work, crane lifting and ROV operations.


      Wärtsilä Water Systems

      Wärtsilä is the world’s leading manufacturer of marine sewage treatment systems. For over four decades the Wärtsilä Super Trident sewage treatment plant has been widely regarded as standard specification on all types of vessels and has been designed to meet existing and future IMO standards.

      Contact us

      Please fill in the form, we aim to respond within 1-2 business days depending on the enquiry. For an existing installation, provide all necessary details to identify the installation and the equipment. Fields indicated with an asterisk (*) are required. 

      For spare parts, please e-mail us with the Equipment Serial Number or the name of the vessel at For urgent support, contact +44 1202 662 693.

      For technical support & service, please email us with the Equipment Serial Number or the name of the vessel at For urgent support, contact +44 1202 662 616.

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

      © 2022 Wärtsilä