Whiter than White

David Keely at Lubron Water explains how to keep laundries running efficiently and economically

Whether it’s a summer’s afternoon cricket match, a hospital doctor on his rounds or a bunch of schoolboys in uniform shirts, nothing impresses quite like clean whites. We take it for granted that the laundry will do a good job, but let’s just pause for a moment and consider the laundry’s water.

Typical “in-premises” laundries – that is those in institutions like hospitals, large hotels, prisons and schools – and commercial laundries will use, depending on the soiling that has to be removed, around 15-20 litre of water per kg of wash load, at least 50% of which is heated. Let’s just go back to basics of water chemistry. A lot of UK water supplies are “hard”, that is they contain significant concentrations of calcium and magnesium salts. These salts, unusually, show a decreasing solubility as the temperature increases. But the real problem is calcium bicarbonate, aka temporary hardness. When water containing calcium bicarbonate is heated, the salt decomposes to form very insoluble calcium carbonate (chalk) and carbon dioxide. The insoluble carbonate forms the familiar white scale that we find in hot water systems. Let’s put that into some sort of perspective. A typical UK hard water, if there is such a thing, might have a total hardness of about 300mg/l as CaCO3, of which about half is temporary hardness. This means that washing a tonne of laundry, using 15m3 of hot water, would result in the deposition of just over a kilogramme of calcium carbonate. Whether your hot water is heated by indirect steam, high temperature hot water or electricity, 1mm of calcium carbonate scale will reduce heat transfer efficiency by about 90%. That means a higher temperature in the heat source, resulting in a significant increase in fuel costs and a concomitant increase in carbon footprint. If scale deposits are allowed to build up they can cause valve failure and even block pipework. Water softening removes calcium and magnesium from the water, thus preventing scale formation.

Of course many commercial washing powders contain polyphosphates to make the washing machines live longer. These chemicals allow calcium carbonate to form microcrystals rather than adherent scale, and they are very effective. But the polyphosphate turns into orthophosphate in the drain, creating a problem at the sewage treatment works which has to comply with the Urban Wastewater Treatment Directive. This sets a maximum allowable phosphate concentration in discharges to the environment in order to prevent eutrophication in rivers and lakes. So reducing the use of polyphosphates by water softening is environmentally friendly.

If you’re not already convinced, there is another important point in our chemistry lesson. Calcium and magnesium react with detergents to form scum. Not only does this adversely affect the finish on the laundered clothes but it uses up the expensive builders (sequestering agents) in the detergent. A 2012 Danish study1 found that softening laundry water could reduce detergent use by as much as 50%, so water softening not only helps to save the planet but also, and perhaps more immediately relevantly, helps to save operating costs. But these are not simply hypothetical savings. Harrow School and the William Harvey Hospital, Ashford, which launders all the linen for the hospitals in the East Kent Hospitals University NHS Trust, are two typical examples of in-premises laundries that have discovered the economic advantages of water softening.

Softeners are readily available, fully automatic standard units and are, generally, given little attention, but they are critical to the laundry’s operation. Like any automatic plant, a water softener’s performance is only as good as the servicing it receives. So it is essential to ensure that your water softener supplier can not only supply equipment to meet water quality specifications but can also routinely service it and provide emergency cover in the event of a breakdown.

Testimonial: “With 800 boys plus resident staff our laundry is very busy”, says Maria Davies, General Service Manager at Harrow School. “Soft water means lower fuel bills, no shutdowns for descaling and no need of fabric conditioner.”

Email: info@lubron.co.uk Web: www.lubron.co.uk

1 Godskesen, Hauschild, Rygaard, Zambrano, & Albrechtsen. (2012). Life cycle assessment of central softening of very hard drinking water. Journal of Environmental Management, 105, 83-89.