The real cost of water purity

Effective water purification can be a critical element in controlling operating costs, argues Mark Bosley, business support divisional manager with industrial water purification specialist Purite

For most industrial and process businesses, water is one of their key utilities along with electricity, gas and perhaps compressed air. It is estimated that the manufacturing sector uses some 14% of all water consumed in the UK for process, ingredient, steam generation, washdown and cleaning duties.

As such, any rise in the cost of water supplies, whether taken directly from the mains or abstracted from boreholes or surface water sources, will have a significant impact on operating costs. The same will also be true of a change in the cost of waste water disposal.

Although manufacturers will be well aware of these points they may not have considered the cost of water to be a critical business issue, perhaps due to the fact that regulation and competition have kept supply costs under control or because other utility and raw material costs have been rising at much faster rates.

Nonetheless, water costs are inevitably going to rise in the future as factors such as population growth, climate change and growing industrialisation put growing demand on what remains a finite resource.

Shorter term, the general economic situation with low levels of growth in many regions, means that pressure remains on manufacturers to maintain operating margins through effective control of all production resources.

Preventing leaks

In terms of water consumption this effectively requires that production and maintenance engineers implement a three-stage strategy: the reduction of cost by preventing leaks and eliminating waste during production processes; improvements in plant efficiency to minimise the consumption of water as well as the energy required to drive pumps etc; and an effective programme to recycle waste, reduce overall consumption, cut disposal costs and comply with increasingly tough legislation.

Eliminating leaks from pipes and production systems should be a straightforward process; so too should the implementation of simple management and training techniques to ensure that production staff actively seek to prevent waste. Many companies have pioneered extremely effective water awareness campaigns that are making an important contribution to profitability.

Although implementing change at a plant level can be more complex and might require higher levels of long term investment it is nevertheless a critical part of any cost control strategy. Perhaps the simplest approach is to look at ways in which the efficiency of existing machinery can be improved to reduce water consumption. This might typically involve improvements in data gathering and analysis, more accurate process control techniques such as the optimisation of spray bar functions, the replacement of faulty solenoid valves and the balancing of water circulation systems.

Beyond this it then becomes necessary to consider changes to water filtration and purification systems to reduce waste, minimise energy consumption and improve product quality. For example, the latest semi-permeable membrane elements used in reverse osmosis systems provide high levels of flow at lower operating pressures. This allows pump speeds and thus energy demand to be significantly lowered. Further gains can be made if pumps are linked to variable speed drives, enabling the speed of each pump to be matched exactly to the output demands of process and water treatment system.

Improvements in the efficiency of membrane elements have been achieved in several areas. These include the development of extremely thin membrane materials, some 120micron in thickness that are based on polyamide thin film composites with non-woven polyester support webs. Elements are manufactured using advanced adhesive techniques, allowing both the spiral wound mesh space between layers and the layer to layer bonding areas to be reduced. This is achieved without compromising the thickness of the feed spacer or affecting the mechanical or chemical properties of the membrane.

As a result, the feed pressure compared with a traditional high rejection RO element has been significantly reduced with lower fouling potential and less pressure drop while flow rates have increased several fold.

This also means that operating life in many applications can be significantly extended, while the creation of a far higher active membrane surface area gives designers the option to reduce the total number of modules in larger reverse osmosis systems, thereby cutting capital and maintenance costs still further.

Water reuse or recovery

Companies that use large volumes of raw water as an inherent part of the process can also make significant savings through water reuse or recovery. Water can be purified using conventional methods of filtration such as dissolved air floatation, bioreactors and reverse osmosis to produce a waste water stream that is typically of a higher purity than that of mains water supplies and which can normally be produced at a lower cost per cubic metre. This water can then be used for machine washdown, filter backwashing or boiler feed.

Additionally, the use of alternative water sources such as rainwater harvesting should not be overlooked as these can again be purified for many of the more basic process applications.

Water is an essential resource for all of us. As such, we each have a role to play in its conservation by reducing usage and waste. For companies throughout the process sector there is effectively a duty of care or of corporate social responsibility, as well as a strong commercial imperative to implement effective management and engineering systems that cut consumption and costs, leading to an increase in profitability.

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