BWTS

A ballast water treatment system (BWTS) is a shipboard installation designed to treat ballast water before it is discharged, in order to reduce the transfer of aquatic organisms, pathogens, and other unwanted materials between ecosystems. Ballast water is used to improve stability and trim, and it can harbor invasive species that threaten marine environments when released in foreign ports.

Most BWTS operate by a combination of physical and chemical processes. Common approaches include filtration to remove large organisms followed by disinfection, typically using ultraviolet (UV) irradiation, electrochlorination, or chemical dosing with oxidants. Some systems use ozone or chlorine dioxide. The goal is to meet regulatory discharge standards for the concentration of viable organisms, as defined by the International Maritime Organization (IMO) Ballast Water Management Convention.

Regulatory framework and compliance requirements are central to BWTS adoption. The IMO Ballast Water Management Convention, adopted in 2004, entered into force in 2017 and mandates that ships manage ballast water to minimize ecological impact. The convention sets the performance standard (the D-2 standard) for treated ballast water and requires ships to have an approved ballast water management plan and a ballast water record book, along with periodic surveys and certification. Depending on age and voyage, ships may retrofit BWMS or install new equipment, and port state authorities may verify compliance.

Operational considerations include system selection (open-loop, closed-loop, or hybrid), installation space and power requirements, maintenance and component replacement, and potential environmental trade-offs such as disinfection by-products. While BWTS reduce biological invasions, they add capital and operating costs and require ongoing management to maintain performance.