Ballast water management systems (also called ballast water treatment systems) are now widely used on ships, but many engineers are still not familiar with how they work. This can be especially challenging for third engineers, who are often in charge of these systems.
There are three main ways ballast water is treated: mechanical, physical, and chemical. Here’s a simple explanation of each method:
1. Mechanical Methods
1.1 Filtration
Filtration is one of the most environmentally friendly ways to treat ballast water. It removes certain organisms and pollutants from seawater by using filters with specific mesh sizes (10–50 micrometers). This effectively traps larger organisms and prevents them from entering the ship’s ballast tanks.
1.2 Cyclone Separation
Cyclone separation uses high-speed water flow to spin and separate solid organisms from ballast water. This process removes organisms by using centrifugal force. It works well for separating heavy particles and organisms from seawater.
2. Physical Methods
2.1 Heating
Heating the ballast water to temperatures between 38°C and 50°C can kill harmful organisms. However, this method can be expensive and less effective if organisms are in a dormant state, which requires higher temperatures to eliminate. Plus, high temperatures can cause rust and damage the ship’s equipment.
2.2 UV Light
Ultraviolet (UV) light damages the DNA of organisms, preventing them from growing or reproducing. This is a popular method because it is effective and doesn’t involve chemicals.
2.3 Ultrasound
Ultrasound creates bubbles in the water, and the pressure and heat from these bubbles destroy organisms. However, this method can be noisy and might harm the ship’s structure over time. It’s not widely used on ships because of these issues.
3. Chemical Methods
3.1 Electrolysis
Electrolysis uses electricity to create chlorine from seawater, which kills harmful organisms. The electric field also damages the cell walls of organisms, leading to their death.
3.2 Hydroxyl Radicals
Hydroxyl radicals are highly reactive and can destroy both organic and inorganic substances in the water. This method cleans the water without leaving any harmful by-products since it breaks down into water and oxygen.
Examples of Common Systems
Most ballast water treatment systems use a combination of the above methods. For example, the COSCO Blue Ocean Shield (BOS) system uses filtration and UV light, while the Qingdao Headway system uses filtration combined with an electrochemical process.
My Experience with JEF and SunRui Systems
I have worked with two types of ballast water treatment systems: JEF and SunRui. JEF uses a combination of filtration and chemicals, but I have limited experience with this system as it was rarely used.
The SunRui Ballast Water Management System (BWMS) is more familiar to me, so I will explain how it works.
How the SunRui Ballast Water Management System Works
The BalClor® BWMS from SunRui treats ballast water in two main steps: filtration and electrolysis.
Step 1: Filtration
The system uses an automatic backwashing filter with a 50-micron mesh. This filter removes larger particles and organisms from the water.
Step 2: Electrolysis
A small portion of seawater is taken from the ballast water pipe and passed through an electrolysis unit. This process creates a concentrated sodium hypochlorite (bleach) solution, which is then mixed with the filtered water. The bleach kills any remaining organisms, ensuring the water meets environmental standards.
Discharging Treated Ballast Water
Before the treated ballast water is discharged from the ship, a neutralizer is injected into the water. This removes any leftover chlorine, ensuring the water is safe to release back into the sea. The amount of neutralizer used is automatically controlled based on the chlorine level in the water.
By using simple methods like filtration and electrolysis, the SunRui system effectively cleans ballast water, making it safe to discharge. This system is widely used on ships today, and understanding how it works can help engineers handle their duties more confidently.