Treatment Technologies and Type Approval

6 min read

What you'll take away Describe the three main BWMS technology families and their operating envelopes, and trace the approval trail: the BWMS Code, active-substance approval, and the commissioning test required since 1 June 2022.

Regulation D-2 fixed the outcome and named no method, and the market answered with a generation of treatment systems. Underneath the hundreds of brand names, nearly everything afloat is one of three families, and almost all of them put a filter first.

Three families

The filter, typically a backflushing screen of 20 to 50 micrometres, does the unglamorous half of the job: it removes the larger organisms and the sediment at uptake, so the disinfection stage downstream faces a lighter load and the tanks stop accumulating mud.

Filtration plus UV passes the filtered water along banks of ultraviolet lamps that destroy organisms or render them unable to reproduce. Its charms are real: no chemicals aboard, nothing to neutralise at discharge, and indifference to salinity, which suits ships trading into rivers and brackish ports. Its weakness is optical, in turbid water the light cannot reach the organisms, so UV transmittance sets the operating envelope, and lamp power sets the flow rate.

Filtration plus electrochlorination takes a side stream of seawater and electrolyses it into sodium hypochlorite, bleach, made on demand, which is injected back into the main flow. It scales beautifully to tanker and bulk-carrier flow rates, but the chemistry needs raw material: sufficient salinity and, usually, a minimum water temperature. Ships that ballast in cold or fresh water need workarounds: brine tanks, or recirculating from a dedicated tank of seawater. At discharge, the total residual oxidant (TRO) must be measured and neutralised, typically with sodium bisulphite, before the water goes over the side.

Chemical injection systems dose a purchased biocide directly. The hardware is simple and the envelope wide; the price is a consumables supply chain and the same neutralisation duty at discharge.

None of this is a beauty contest: it is a matching exercise. Every certificate issued under the BWMS Code carries System Design Limitations, the salinity, temperature, UV-transmittance and flow envelope inside which the approval is valid; older G8 certificates state their limits less systematically. A system that is superb on a VLCC trading blue water can be a liability on a feeder working silty estuaries. The comparative guidance in the ABS best-practice advisory is blunt about how many early installation regrets were really selection errors.

Three families, one filter first 1 · filter 2 · disinfect 3 · at discharge operating envelope set by Filter 20–50 µm Ultraviolet lamps no chemicals aboard nothing to neutralise UV transmittance: turbidity closes it; lamp power sets flow Filter 20–50 µm Electrochlorination bleach made on demand measure and neutralise the residual oxidant enough salinity, and usually a minimum water temperature Filter 20–50 µm Chemical injection a purchased biocide same neutralisation duty at discharge wide envelope, but a consumables supply chain Type approval states each system's design limitations: the envelope inside which the approval is valid.
The families share the filter and diverge downstream: only the chemistry routes owe a neutralisation duty at discharge, and each buys its capability at the price of a different envelope. Matching that envelope to the trade the ship actually does is the whole selection exercise.

The approval trail

A BWMS earns its place on board through type approval by an administration, against the IMO's testing and performance requirements. The regime tightened over time: the original G8 guidelines became the mandatory BWMS Code, which applies to systems installed on or after 28 October 2020, with land-based and shipboard testing across salinities and temperatures. The IMO's ballast water FAQ sets out the framework and the family of guidelines around it.

Systems that rely on an active substance, the chlorine-makers and chemical dosers, face a second, parallel examination. The GESAMP Ballast Water Working Group reviews the chemistry under Procedure (G9) and the IMO's Marine Environment Protection Committee grants the approvals on its advice, in two tiers, Basic Approval and then Final Approval, asking whether the substance and its by-products are safe for the crew, the ship and the water it will be discharged into. Only with that in hand can the administration grant type approval. A purely physical process such as UV never enters this pipeline, one reason the technology split persists.

And the United States runs its own type-approval regime entirely, which is worth a lesson of its own: lesson 5 takes it up.

Proving it on board: commissioning testing

A certificate proves the design; it says nothing about the yard's plumbing. Since 1 June 2022, the installation survey of a new BWMS must include commissioning testing: a sample of actual treated discharge, taken from the ship and analysed, an indicative analysis against the D-2 limits, before the system is signed off. The requirement exists because early retrofits produced systems that were approved, installed, alarmed to silence and quietly incapable; cross-connections and starved sensors that no document review would ever catch. DNV's ballast water FAQ covers the practicalities, including who may take and analyse the sample.

The operator's summary: the technology families are few, the envelopes are real, and the paper trail runs from GESAMP through type approval to a water sample drawn from your own discharge line. Choose the system for the trade the ship actually does: an approved system outside its envelope is just a contingency generator, and contingencies are the subject after next.

Check yourself

1. An electrochlorination system needs what kind of water to generate its disinfectant?
2. A UV system's performance degrades most directly when…
3. Before chlorinated ballast may be discharged, the system must…
4. Basic and Final Approval under Procedure (G9), granted by the MEPC on the GESAMP Ballast Water Working Group's advice, applies to…
5. The BWMS Code (the revised G8 requirements) is mandatory for systems installed on or after…
6. Which of these are established BWMS technology families?

Select all that apply.

7. Commissioning testing checks the installation paperwork rather than the actual discharge.
8. Commissioning testing has been required for new BWMS installations since 1 June of which year?
year

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