To filter or not to filter? That is a question

I have spent most of my 20 years in the ballast water industry working with filterless ballast water treatment systems (BWTS). Coming from waste/industrial water treatment projects, I knew how effective, but also practically limiting and frustrating, filters can be. Given the huge flow rates required for ballast water treatment, not needing a filter seemed like a good idea, though initially, filters were so prevalent in BWTS that they were often considered a legally required component. Filterless systems would only work if the underlying treatment was robust enough.

Meeting the D-2 standard is a big deal. Achieving this in a steady environment with a known inlet quality is tough, but on a vessel with limited resources and a huge variation in inlet qualities, a treatment system that can reliably meet D-2 is a high-performance system, filter or no filter.

“A filterless system can pass the prescribed test, but how does it deal with 30 times the challenge?”

Early on, several systems decreased filter sizes to reduce power use and increase treatment performance. Over the years, the expectation of discharge compliance has not been consistently established. Without this normal check and balance, envelopes have naturally been pushed. Some systems have simply removed their filters with little or no change to treatment. Still Type-Approved and legal to install, will these filterless systems provide consistent compliance?

They will in conditions similar to their testing. However, the real world is often more challenging. For example, the USCG and IMO require no less than 100,000 >50um organisms per cubic meter of testing feed water. Filterless systems I have tested in natural environments experienced up to three million plus. A filterless system can pass the prescribed test, but how does it deal with 30 times the challenge? Some may do well, but it is incumbent on owners to check the testing their candidate systems have undergone and understand the challenges of the waters where their vessels trade.

Fundamentally, a filterless BWTS will be more robust than a filtered system. Ballasting is generally far less challenging, with less to operate, less to go wrong, and less to compromise vessel operations. But what about compliance?

Paris MOU and USCG are focusing on BW compliance, and IMO is working on verifying discharge assessment instruments. It is likely that discharge compliance will become relevant. As it does, owners should carefully assess the fundamental robustness of their BWTS, particularly if it performs without a filter. Without a filter, the robustness of the primary treatment mechanism is the only thing providing compliance.

The InTank BWTS provides robust filterless treatment. Treating in the tank allows the use of the CT treatment metric, automatically returning during the hold time to check treatment efficacy and re-dose if necessary. Confirmed neutralisation in the ballast tank before discharge is another benefit.

Going forward, regulators and PSCs are committing to discharge assessments and treatment systems will need to show records of operation. Extensions, exchange-and-treat, and unexplained/unexcused bypasses should stop. Treatment systems will have to be operated, maintained, and recorded. This realisation, combined with operational feedback from vessels, is pushing demand for filterless options. Their simpler operation makes them more attractive to vessels. The right filterless system can offer the most confidence in compliance with the least impact on operations.