Retrofitting bilge water treatment systems
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - Circulars - Marine Environment Protection Committee - MEPC.1/Circular.677 – Guide to Diagnosing Contaminants in Oily Bilge Water to Maintain, Operate and Troubleshoot Bilge Water Treatment Systems – (22 July 2009) - Annex – A Guide to Diagnosing Contaminants in Oily Bilge Water to Maintain, Operate and Troubleshoot Bilge Water Treatment Systems - Appendix III – Recommended Major Preventive, Redmedial and Corrective Actions - Retrofitting bilge water treatment systems

Retrofitting bilge water treatment systems

▸Pre-Treatment    
  •Improved holding tanks
    1. Higher aspect (height to width ratio) holding tanks
    2 .Proper tank sizing
    3. Heating of bilge water
    4. Large particulate screens and filters (in tank weirs, skimming, solids removal)
  • Point source reduction – portable or semi-fixed filters for treatment of highly polluted sources before entry into the bilge; e.g., particulate filters for soot wash down operations. Note: This does not have to be perfect. 90% efficiency is a lot better than nothing.
  • Use of low shear diaphragm pumps or progressive cavity pumps when possible
▸ Treatment    
  • OWS system – periodic hot water flush
  • Periodic diagnostic on OWS effluent
  • Pressures and flows – changes could indicate sludge build-up
▸Post-Treatment Polishing: small particulate filters and emulsion polishers (confirm that the operating pressures of post-treatment units will be compatible with the OWS). These include polishing/filtration technologies listed below. Some of the polishing systems may not be available as stand-alone units for retrofitting, may not be compatible with all existing OWS, or may not be suitable for high-volume bilge water treatment. There are several variables that can impact the effectiveness of some of these polishers, such as fouling in the presence of too much oil, desorbtion (release of previously absorbed oil under certain conditions), bacterial growth on the polishing surface, the presence of other small non-oil droplets, and/or maintenance and operating costs. It is therefore important carefully to evaluate each technology. Before considering a post-treatment polisher/filter, it is also important to evaluate the ship’s and company’s circumstances.
  • Adsorbers – Adsorbers capture oily emulsions in an extremely thin layer of molecules on the surfaces of the polisher.
  • Surface modified oil-affinity filtration is a type of adsorber that uses a molecule imbedded on a filter. The molecule binds together and coagulates hydrocarbons, specifically altering oils and semi-volatile organics into a cohesive viscoelastic mass that repels water. This action allows for extremely efficient capture without developing differential pressure across the filter.
  • Flocculation – A chemical immersion process to cluster individual dispersed emulsified droplets together, followed by a process to coagulate the clusters for removal.
  • Ultra-filtration membrane – Membrane filtration uses hydrostatic pressure forces the treated bilge water past a semi-permeable membrane that filters small particles including emulsified droplets. The rate of passage depends on the pressure, concentration, and temperature of the emulsion, as well as the permeability of the membrane to each emulsified droplet and other particles.
  • Filter coalescers – oil droplets are removed by adhering to the underside of a series of plates in the separator. Upon contact, small oil droplets bind together forming larger droplets, resulting in an increased buoyancy and rise rate to the surface of the unit for removal.
  • Change out shearing pumps to low shear pumps (e.g., diaphragm pumps).
     
Parent topic: Appendix III – Recommended Major Preventive, Redmedial and Corrective Actions
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