What ballast water is and why it must be treated today
Ballast water is the water that a ship takes on and discharges into ballast tanks to maintain stability, trim and navigational safety. The problem is that, along with the water, organisms and pathogens can be transferred between different ports and seas, with the risk of introducing invasive alien species and altering local ecosystems. That is why, when asking how ballast water is treated, the answer is not just about water quality in a generic sense: it is mainly about biological control, meaning the reduction of living organisms and microorganisms that could colonize a new environment.
In this context, IDRO Group develops and integrates ballast water treatment systems designed to operate with fresh, brackish or seawater, with compact skid-mounted and modular solutions suitable for both new installations and marine retrofits.
Ecological and operational risks: what ballast water management is meant to prevent
Ballast water can carry microscopic algae, small organisms, eggs, spores and bacteria, which enter an environment different from the one where they were taken on when the water is discharged. The BWM Convention was created specifically to reduce this risk, which has become more critical with the growth of global shipping traffic.
In addition to environmental impact, proper ballast water management has practical operational implications: Port State Control inspections, documentation requirements, and the need to guarantee stable performance even with turbid water or high ballasting flow rates. For this reason, the technology must be selected and sized according to the ship profile and real operating conditions.
IMO regulations and the BWM Convention: what it actually requires and why it is not “just MARPOL”
The main reference is the Ballast Water Management Convention (BWM) of the IMO, adopted in 2004 and entering into force in 2017. The Convention requires ships to have a Ballast Water Management Plan and a Ballast Water Record Book, as well as management procedures compliant with the required standards. In practical terms, onboard systems must be supported by a formal type-approval process: within the IMO framework this refers to BWMS type approval according to the applicable procedures, while for certain routes and flags, compliance with the requirements of national authorities such as the US Coast Guard (USCG) may also be relevant.
Online, people often refer to a “new MARPOL regulation on ballast water treatment.” In reality, MARPOL is the International Convention for the Prevention of Pollution from Ships and governs different categories of pollutants through technical annexes. The specific issue of ballast water is regulated by the BWM Convention and the related IMO guidelines.
From a technical and operational standpoint, the BWM Convention introduced a crucial change: today, compliance is achieved mainly by meeting the D-2 standard, which requires measurable treatment performance at discharge.
The D-1 standard (open-ocean ballast water exchange) was used as an operational risk-reduction measure, but D-2 is the standard that drove the adoption of onboard treatment systems because it sets limits on living organisms and indicator microorganisms. In practice, while D-1 is based on a management procedure, D-2 normally requires the installation and operation of an approved BWMS.
Ballast water treatment technologies: filtration, UV, chlorine and hybrid systems
Ballast water treatment technologies follow a barrier-based approach: first, solids and larger organisms are removed, then biological inactivation or neutralization is carried out. The most common solutions include:
- Filtration + UV: filtration retains sediments and larger organisms, while UV disinfection inactivates microorganisms. It is often chosen when the goal is to avoid the use of chemical reagents and simplify onboard management, while keeping in mind that UV effectiveness can be affected by high turbidity and requires proper maintenance of lamps and optical surfaces. IDRO Group offers systems based on this architecture, such as PUREBALLAST, which integrates filtration and UV disinfection to render microorganisms harmless and comply with regulatory limits, with solutions designed for reliable onboard operation, including retrofit applications.
- Active substances and hybrid systems: the use of oxidants or biocides, alone or combined with filtration and/or UV, is considered when greater robustness is needed for highly variable water conditions or specific operating profiles. In these cases, it is essential to manage storage, dosing, safety and, where required, neutralization before discharge.
In practice, selection depends on water quality in the ports visited, ballasting flow rates, available space, energy consumption and type-approval requirements.
IDRO Group application examples and why modularity helps with retrofits
In onboard installations, especially retrofits, the challenge is not just to “have” a treatment system, but to integrate it into limited spaces with reduced vessel downtime. For this reason, pre-assembled and compact skid-mounted solutions are often preferred, as they simplify installation and commissioning.
A concrete example delivered by IDRO Group is a ballast water treatment system designed as a compact, pre-assembled module, including a filter, UV reactor, CIP unit for automatic lamp cleaning, and integrated control panel. The design took into account the applicable regulations and requirements, adopting internationally recognized standards and defining the sizing according to the required flow rate and the ship’s plant layout.
For applications involving higher flow rates and the need for flexibility, IDRO Group builds skid-mounted systems in various sizes, with capacities up to approximately 1000 m³/h, typical power supply of 400–440 VAC 50/60 Hz, and operating pressures up to 6 bar, with larger configurations available depending on the project. This modular approach improves scalability and makes onboard integration in retrofit projects easier.
Do you want to understand which solution is best suited to your ship or retrofit project, based on flow rates, available space and routes? IDRO Group can support you from technical and regulatory assessment to design, supply of skid-mounted/modular systems, and assistance during start-up and operation, in line with the applicable IMO requirements.
Contact IDRO Group for more information!
