Deionised resin reliability
June 1st 2008

Newcomers or small window cleaning operatives can save and store more water using DI resins, says Acquafactors. For businesses using reverse osmosis systems, softeners are imperative for long life while DI resins add the purity 'polish'

Aquafactors believes keeping things simple pays enormous dividends, particularly when selling a pole system to an industry newcomer.The company has always championed the use of deionised (DI) resins.Arguments against resins have mostly been levelled at cost.However,Aquafactors believes there are distinct advantages in only using DI resins which can take raw tap water up to a 99.9% purity rating to put straight on the glass.

• Water treatment is kept very simple.With one method of treatment and one piece of equipment it is easy to use and maintain.
• It takes up little space,and weight – critical in any mobile set up – is proportionally low.
• Resin performance is very reliable when water quality checks are undertaken regularly. Even if a DI tank freezes no harm is done and when unfrozen it works as well as before.There is no water wastage.
• In mobile use most space can be devoted to the most important commodity – the storage of water.

Aquafactors says the argument that resin is expensive must be viewed in context. In a very hard water area (350mg/l of carbonate hardness) 25 litres of resin should last one person about a week.This is a cost of around £17 a day, not unreasonable as a proportion of the overall costs for a day's window cleaning.Pure water can, of course,be produced more cheaply, but this has to be viewed against the additional water treatment equipment required, which can double or treble the price of a mobile DI system.This can be prohibitively expensive for a newcomer or smaller window cleaning operative.

Reverse osmosis Reverse osmosis (RO) has a big following in the water fed pole industry for good reasons. But it requires greater understanding.Aquafactors is a big fan of RO membrane technology.However, the company believes it has to be used in the right way and by a customer who will benefit from the increased performance that RO will give. RO can be costly to buy in the short term but cheaper in the volumes of pure water that it can produce in the long term.RO systems can waste a lot of water and therefore it is important to look closely at the technical implications.

The pore size in a membrane is 5 angstrom (500 millionth of a centimetre).This makes the membrane vulnerable to hard water blockages caused by calcium and magnesium (chalk and lime). It is therefore imperative that RO systems are used with water softeners in areas where water hardness exceeds 200mg/l (below this level they are not required).An automatic, ion exchange, salt regenerated,water softener will double membrane life and improve performance.

In an RO system only pure water molecules are able to pass through the membrane while contaminants are washed away to drain.

Environmentally the ratio of waste water to pure water production is of major consideration.

Some systems can be exceptionally poor in this respect, particularly systems only using mains water pressure.These ROs can commonly be found as part of a mobile mounted tank system.

In some cases, in order to produce water at an acceptable rate, the outflow from the membrane is purposely restricted.The back pressure created makes more pure water.The downside is not enough water flushes across the membrane to keep it clean.This can lead to premature failure and additional expense.To get around this suppliers often recommend backwashing the membrane to keep it clean.

However, this can waste a lot more water.You must also never let a membrane freeze, even for a short time, as irreparable damage can occur.

Professional RO systems are pumped systems.Aquafactors uses membranes that operate at 14 bar (200psi).At this level some of our ROs can produce 1500 litres of pure water, or more overnight, and they do not require backwashing.These high pressure membranes can have a life expectancy of two to three years. A properly set up RO system includes membrane,water softener (salt), filters and pumps.However, with all this gear on board a vehicle weight allocation is seriously compromised.Tanks have to be smaller and less water can be carried in order to remain within payload restrictions.This is why Acquafactors favours, if possible, keeping the bulk of water treatment equipment away from a vehicle. It can be set up to operate 24 hours a day as part of a static water making facility, alongside a storage tank holding around a 1000 litres.Also, as this equipment can make pure water continually (in a consistent temperature) it makes it at the best possible price, with the best possible rejection characteristics.A system like this can easily be expanded to make water for several vehicles. It does not make sense to duplicate ROs in every van when all that is needed is an on-board DI tank to 'polish' the water. A static system need only take up a third of a single garage.Pure water can be pumped across to a vehicle tank as and when required.

It is only in very soft water areas that RO water becomes sufficiently pure so it can be used directly on the glass.Most of the time the percentage of purity is only about 94 to 97 percent and generally this is not good enough for glass cleaning.RO water put through a DI tank will always be at the best possible quality. DI tanks used only for this purpose can last up to two years before the resin needs to be changed.

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