Filters in ballast water systems

Oct 21 2021

Filters for ballast water systems may not be a legal requirement, but they may prove very helpful, particularly if the vessel is loading ballast in sediment-rich waters. We spoke to filter system manufacturer Filtersafe.

It may make a lot of sense for tanker operators to consider the sediment in the ballast water they load onto vessels, and whether they should filter it out, says Mark Riggio, head of marine at filter systems manufacturer Filtersafe.


The regulations for ballast water systems require a system which is approved to kill organisms and remove sediment to a certain level, and has been tested in factory conditions to ensure that it can do that.


But the only ships which don’t need filters are very large vessels, trading between large deep water ports, where there isn’t a lot of sediment in the water being collected for ballast, Mr Riggio says.


Particularly high levels of sediment are likely if you trade in rivers, deltas, or shallow harbours where flowing water and run-off may impact water or where the ship’s uptakes may be close to the bottom. “And this is where most cargo is being discharged,” he says.


The ballast water regulations do include requirements about sediment levels in ballast water being discharged. The full name of the regulations is “International Convention for the Control and Management of Ships' Ballast Water and Sediments (BWM)”.


There are a number of ballast water systems which are type approved for use without a filter. But tanker operators not using filters may find that their ballast tanks slowly collect a layer of sediment at the bottom, which cannot be pumped out, so it must be removed at dry dock.


“In dry dock, you end up shovelling 6-8 inches of sediment at the bottom of the tanks,” he says.


This is dead weight that the vessel needs to carry. But an additional concern is that this sediment may be classed as hazardous waste in future, so incur high disposal fees. Its disposal regulations could be similar to those for bilge water. Also, the waste disposal contractor may be chosen by the dry dock yard, putting the shipowner in a poor position to negotiate the fee.


Tankers may need two dry dock visits every five years. For many tanker operators, their next visit will be the first visit they make after installing the ballast water system (since the systems were installed at their previous dry dock), and so the first time they learn about sediment levels in their tanks, he says.


Ballast testing

Ballast water systems are thoroughly tested by the IMO and testing facilities before they are approved to be installed on ships. This test “has the highest challenge conditions. We want to stress the system and make sure it works. This is done in a scientific lab,” Mr Riggio says.


But if the system needs to be tested after being installed on a ship, the test might not be so rigorous. Companies may schedule a test while the ship has its most competent crew, on a route which is less demanding from a ballast water perspective.


For example if the ship is transiting equatorial waters, the high temperatures may kill the organisms, so no-one will know if the ballast water system is not working.


“A shipboard test is good but it’s a limited test. There's a whole lot that can go into gaming the test to make sure that you pass,” he said.


A better filter

If tanker operators are persuaded about the need for a filter system, the next question is what kind of system to use.


The filters are used when the ballast water is being loaded. This has to happen at the same time as the tanker is being discharged (with the ballast water taking the place of the removed cargo in keeping the vessel stable).


If the filter system is not able to filter ballast water at the rate needed to balance the rate the cargo is being discharged, then discharging needs to be stopped to catch up.


Port facilities tend to really dislike tankers giving them a variable flow rate of cargo, Mr Riggio says. So this would happen if “you can’t bring ballast on fast enough.”


Tanker operators need a filter which will give them predictable results and predictable flow rates.


Just with any filter, the flow rate will decline if it is clogged – and so to be predictable there needs to be a reliable way to remove the sediment.


Filtersafe’s system

One of the big differences between a poor and good quality filter is the cleaning system, because a filter can only maintain maximum flow rate if it is free of debris, Mr Riggio says.


The Filtersafe product has its own automatic cleaning system.


The ballast water being loaded comes in through the inlet to the filter from the inside of the cylindrical filter mesh. It passes…through the screen and into the tank.


The cleaning process is initiated when a pressure sensor detects a higher pressure inside the screen than outside, indicating that water is not flowing freely through the screen.


A suction pump is activated, which sucks clean water back across the filter mesh, through precision designed cleaning nozzles, and back to the seawater source that the water came from, taking the sediment with it.”


Any sediment which has built up on the screen is drawn through the suction nozzle down a pipe and back to the sea it was originally taken from.


Also, to improve durability of the filter, Filtersafe has removed 316L grade stainless steel and switched to 904L grade stainless steel, which is up to 82% more durable than 316L.


It has 3 configurations, labelled “regular”, “turbo”, and super turbo” giving different levels of cleaning capability, using more nozzles.


It has been tested at solids levels of up to 2500 mg (2.5g)/ litre.


The system is used for 25 per cent of all ballast water worldwide. In the maritime industry, its systems are used by ballast water system suppliers Wartsila, Techcross, Ecochlor and Evoqua.


Filtersafe makes filtration systems in a variety of sizes, for a variety of industries other than shipping – including oil and gas, agriculture, desalination, and other industry.


The company is headquartered in North Israel, and has offices in Pittsburgh (USA), Brazil, Chile, Hamburg (Germany), Netherlands, Russia, Hong Kong, Singapore, Beijing, and South Australia.


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