Ballast Water Treatment System by Cathelco

Alternate Management Systems (AMS) Acceptance from U.S. Coastguard Enabling Ballast Water Treatment System on Ships Entering U.S. Waters.



1- Precise adjustment to different water qualities

This is vital to the effectiveness of the system and has important implications in terms of power savings.

Cathelco has a unique UVT sensor which measures a sample of water before it reaches the UV chamber. Unlike some systems which simply measure the turbidity of the water (amount of suspended solids), the Cathelco UVT sensor measures the amount of UV light actually passing through it. This is a far more accurate way of calculating the correct UV dose.

The UVT sensor operates in conjunction with UV intensity meters, located in the UV chambers, to provide a data feed-back loop. The data provides empirical evidence that the correct dosage has been applied to the ballast water at any given time.

Furthermore, the overall power consumption is reduced because as soon as the water quality improves the power to the lamps is reduced.

2 - Helix flow for maximum UV exposure

Using advanced computer simulation, Cathelco has designed the inlet manifolds of the UV chambers so that the ballast water flows in a helix. This means that the maximum surface area of the water is exposed to the UV light as it passes through.

What’s more, each chamber is a dual design so that water flows down one side and back along the other – doubling the UV exposure. 

Because of the effectiveness of the helix in increasing the UV ‘contact time’ only one lamp per 100 m3/h of seawater is required – saving space and reducing power usage.

3 - Stepless power control – saving energy

With some BWT systems power to the lamps is increased in large incremental steps with inevitable wastage. In contrast, the Cathelco system uses the latest switchmode  technology to provide a ‘linear’ electrical supply. This means that the demand from the lamps is met in much smaller steps without excessive and unnecessary use of power. As the power output is linked to data from the UVT and UV intensity meter feed-back loop, the optimum amount of power is used at any time.

4 – Medium pressure lamps

Medium pressure lamps have a much broader UV spectrum than low pressure lamps. This is important because the multiple ‘peaks’ in the wavelengths of medium pressure lamps result in a more thorough irradiation of the ballast water. This level of performance becomes even more essential in fresh or brackish water conditions. The lamps incorporate a unique anti-blackening device to maximise their life and efficiency.

5 – Salt and fresh water operation

The Cathelco BWT system is one of the few that have IMO Type Approval for both salt and fresh water operation. This could be a deciding factor if your vessel frequently operates in lakes or estuaries.

6 – Automatic ball cleaning system (CIP)

Cathelco have simplified the cleaning process for the quartz sleeves and interior of the UV chambers with an innovative ball cleaning system. It is completely automatic, does not rely on mechanical moving parts (which can break or cause scratches) and totally eliminates the need for chemicals.

Control System

The control system does much more than simply governing the functions of the Cathelco BWT system. It monitors the ‘health’ of all the major components and comprehensively logs the data. Beyond this, it has the ability to extract key data in a summary software file (Click to read more) which can be used to maintain a Ballast Water Handbook – essential in conforming to IMO requirements.

Main controls
The main controls include:-
  • Ballasting
  • De-ballasting
  • CIP Cleaning
  • Refill
  • Optional tank stripping
  • Automatic switch over fresh water to salt water.
Control options
Depending on vessel size and customer preference, Cathelco can provide a number of control options.

Local control
All of the functions are controlled from the single automation control unit situated close to the BWT equipment using a touch screen or screen with key pad.


Remote control
With remote control, a duplicate control panel is provided in a more convenient location such as the cargo control room or engine control room. This operates in a master/slave relationship with the automation control panel and displays the same data.


Full integration
By fully integrating the BWT automation system with the ship’s computer system, a single operator can control all of the functions from one location saving considerable time and effort. Integrating the BWT controls with the ship’s IPMS system uses the standard MODBUS protocols. It allows for greater flexibility of control with multiple screens in different areas of the vessel, any of which can be used to control the system.

How the control system works
The automation control panel screen shows a graphical representation of the system and can be supplied with a touch screen or a screen with a key pad according to customer preference.
At the ‘overview’ level the screen shows a schematic drawing of the pipework and all of the major components.  The user can then access screens covering specific areas including UV reactor performance, the operation of the cleaning in place (CIP) system and other screens which are used for the set-up and commissioning of the system.
The control panel is password protected at three levels for security. The user level allows for day to day operation, the engineering level opens a wider range of functions and there is also a manual mode which enables any element of the system to be controlled for testing purposes.
The automation unit continuously logs all of the data concerning the performance of the BWT system. This includes the ballast tank number, time/date of event, mode of operation, flow rate, temperature, power to UV lamps, UV transmission and calculated UV dose. The UV transmission rate is recorded at 32mm (the distance between the UV source and the edge of the reactor) and also at 10mm according to the Class Body requirements.

Summary Software File

This software simplifies the process of maintaining a Ballast Water Handbook by gathering the essential data from the log files stored in the control panel and presenting it in a form which is easily understood. This includes:

  • Date/time of BWT transfer
  • Tanks used for transfer
  • Mode of operation
  • Average dose rate
  • Average flow rate
  • Average water temperature
  • Total volume of water treated
  •  Date/time process completed

How it Works

UV Lamp Control Units
Each cabinet powers two UV lamps and is equipped with a state-of-the-art modular switch mode power supply. Step-=less power control enables output ot the lamps to be raised or lowered in small incremental steps, ensuring that it is used economically without wastage. This is an important advance on older types of BWT units using transformers where power is raised or lowered in much larger increments.

Mains Switchboard

The mains switchboard has a single electrical feed and provides all of the consumable emerge for the BWT unit. This simplifies installation and maintenance in comparison with systems which require multiple power lines.

Foam Ball Cleaning System - Cleaning in Place (CIP)

Specialized foam balls gently polished the quartz sleeves (surrounding the UV lamps) to remove residue. They also clean the interior of the chamber increasing reflectiveness and migrating corrosion. The balls are automatically recovered at the end of the cleaning cycle. Importantly, there are no mechanical parts to go wrong or scratch the sleeves. No chemicals are used not even citric acid.

Sampling Points

Allows for routine sampling of solutions. Installed in pipe work before and after BWT system.

Temperature Sensor

These ensue there is sufficient cooling of the UV lamps when the system is on operation. Mounted on the outline manifolds, the sensors send a single to the control panel if they temperature exceeds a prescribed level.




Automation Control Unit

Controls ballasting/deballasting, CIP cleaning and many other functions. Built in data logging ensures compliance with IMO regulations. Provides salt water and fresh water operational modes. Available as standalone, mote or fully integrated. 

Filter Unit

On most systems for commercial vessels this will be a Hydrac RFCA filter with automatic back flushing. On mega yachts and some naval vessels where space is at a premium a Filterx ACB filter will be installed, also with automatic back flushing. Both filters units have mesh sizes of 40 microns.

UV Intensity Meters

UV intensity meters are mounted on the edger of the UV chambers and measure the amount of light received during irradiation. If the amount of UV light falls before a prescribed level the automation control unit indicates that a cleaning cycle is required or that lamp renewal is necessary. 

Water Level sensor

These prevent the BWT system from being started or operated if there is no seawater within the UV chambers. These sensors, mounted on the outlet manifolds, are part of the system’s comprehensive fail-safe protocols. 

UVT sensor

The UVT sensor measures UV light transmittance through a seawater sample taken before it reaches the chamber. The sensor operated in conjunction with UV intensity meters in a feed-back loop ensuring that correct dosage is being achieved.


The BWT system - from start to finish

During uptake the sea water passes through the filtration unit where the larger organisms and sediments are removed.

To allow for different water qualities, a sample of sea water is taken before it reaches the UV chambers and measured using a UVT sensor. The sensor measures the UV light transmittance of the sample -  the amount of UV light actually passing through the water. The power to the lamps is automatically raised or lowered, optimising the power usage.

At regular intervals the retained material in the filter is automatically back flushed and discharged at the original ballasting site, with very minimal reduction of the ballast water flow during the back flushing process.
The sea water continues to UV treatment where smaller organisms, bacteria and pathogens, are rendered harmless before the water passes to the ballast tanks.

The performance of the lamps is constantly monitored by UV intensity meters indicating when cleaning, replacement or refurbishment is necessary.

During ballast discharge the sea water by passes the filter unit and goes directly to the UV chambers where it is treated for a second time. This avoids the risk of any contamination due to re-growth in the ballast tank.

Located on pipework before and after the BWT unit, the sampling points enable laboratory specimens of sea water to be taken by the Port State Authority, if required.


Cathelco have received Alternate Management Systems (AMS) acceptance from the U.S.Coastguard enabling the BWT system to be used on ships entering U.S. territorial waters.

The system has been approved for the full range of salinities - sea water, brackish water and fresh water - enabling it to be used on vessels passing through the Great Lakes and other U.S. waterways. Cathelco are one of the few BWT system manufacturers who have achieved AMS approval without restrictions on the types of salinities which are permitted for operation.

The AMS approval also recognised that the system will operate effectively in challenging water conditions where UV light transmittance values are as low as 45% (75% being value for normal seawater).

AMS acceptance by the U.S. Coast Guard is a temporary designation given to BWT systems approved by a foreign administration. It enables BWT system to be used on vessels for a period of up to 5 years, while the treatment system undergoes approval testing to U.S.Coast Guard standards.


The Cathelco Ballast Water Treatment system received IMO Type Approval in April 2014.

The approval was granted by the Federal Maritime & Hydrographic Agency of Germany (BSH), covering both sea water and fresh water operation.

Key extracts from certificate

Salt water and fresh water operation
“At high salinity as well as in fresh water five independent consecutive and successful experiments were carried out.”

Effective in challenging water conditions

“45% minimum UV-Transmittance of the ballast water after filtration at a wavelength of 254nm and a layer of 10mm thickness.”

This means that the system has been proved to operate effectively in extremely challenging water conditions. Normal water conditions are around 75% UVT.

Shipboard testing in wide ranging conditions
“Tests were conducted on board the vessel in Gran Canaria (ES), Marchwood (UK), Gibraltar (UK), English Channel.”

The trading pattern of the M.V. Eddystone enabled shipboard testing results to be obtained in the North Atlantic, Mediterranean Sea, English Channel and the Solent Estuary.

The Type Approval Certificate issued by the Federal Maritime and Hydrographic Agency (BSH) of the Federal Republic of Germany is a nine page document containing detailed information about the results of land based and shipboard testing. It is far more comprehensive than certificates issued in the past, reflecting the introduction of more rigorous testing procedures. Furthermore, the test results are open to public inspection.

An advanced system - far exceeding minimum standards

  • As one of the latest and most advanced BWT systems on the market, Cathelco conforms to the more stringent IMO standards which have been introduced during the last few years. Our emphasis has been on refining the system and test protocols to meet these higher standards, rather than merely passing a minimum standard. You benefit by having a system that operates effectively in all water conditions – including the most demanding.
  • Our system remains effective in extremely high sediment levels. In conditions where UV transmittance is only 45%, our system will continue to provide effective irradiation.
  • Our land based testing was conducted under natural conditions at the Royal Netherlands Institute for Sea Research (NIOZ) facility on the island of Texel in Holland. The area is a highly productive shallow sea with a large variety of plankton and very challenging brackish water conditions. During the test period, the number of organisms present in the sea water considerably exceeded those required by the IMO standard. In addition, NOIZ have the facility to introduce natural sediments into the test water to simulate the most difficult water conditions.  In short, our land based testing was conducted under the most rigorous natural conditions.
  • The test regime at NIOZ included fresh water protocols enabling our IMO Type Approval to include fresh water accreditation. This allows us to immediately apply for USCG Approval under the Alternate Management System (AMS) where fresh water operation is an essential requirement. 
  • Shipboard testing was completed on the M.V. Eddystone, a ro-ro vessel owned by Foreland Shipping. The vessel has a diverse trading pattern  frequently operating in the Atlantic Ocean and Meditterrean Sea. As a large vessel, entering a variety of ports, the M.V. Eddystone provided test conditions representative of typical commercial operations.
  • The Cathelco BWT system is tested and approved in fresh water, brackish water and sea water.