The reuse of water in manufacturing processes plays an important role in controlling costs and minimising waste. Mark Bosley, business support divisional manager for Purite, explains how grey water recovery systems can help processors boost efficiency, meet legislative requirements and help the environment
Raw material costs are on the rise and water is no exception. Water is a common raw material in many manufacturing industries, especially in the food and drinks sector where it is the most commonly used commodity – so an increase in its reuse is needed both commercially and environmentally. The manufacturing industry is under pressure to control costs and minimise waste, and managers are searching for ways to achieve both of these goals. One way to do so is to introduce a grey water recovery scheme.
Even those operators who have not yet prioritised grey water recovery are being encouraged to do so by legislative requirements, which penalise high levels of water usage. Driven by customer demand, such legislation aims to encourage businesses to embrace their environmental responsibilities and reduce commercial costs.
Unlike blackwater, which contains human waste and, therefore, high levels of undesirable contaminants, greywater, which is derived from sources such as washing, is easier to treat and recycle.
A typical grey water recycling system feeds water that has been used for practices such as cleaning and washing to a storage or header tank where it can be used, for example, to flush toilets. However, grey water recovery systems can be specified to recover and reprocess water for purposes other than the flushing of toilets. This may require additional treatment and the capability to measure the quality of stored water so that it can be disposed of before becoming stale but, nevertheless, the possibilities are there for operators to reclaim grey water for uses beyond the black water system.
For example, despite the fact that grey water contains high levels of micro-organisms, it can be filtered or irradiated by ultra–violet light, to provide water for general washing where the need for purity is not critical, but requires some control of the microbial population. If the mineral purity of the grey water is too high then reverse osmosis can be employed to enhance the quality.
Reverse osmosis (RO) purification is increasingly being employed in recycling systems to process grey water. Pressurised feed water is passed through specialised semi-permeable membranes to remove inorganic ions and dissolved organic contaminants, typically eliminating over 99% of micro-organisms. The latest membrane elements used in RO systems provide high levels of flow at lower operating pressures and they can achieve 100% purity while also cutting the cost of purification, since pump speeds, and thus energy demand, can be lowered. Variable speed drives for purification units can cut costs yet again, as they enable the speed of each unit to be matched exactly to the output demands of the water treatment system.
RO not only produces water of high quality but also generates large volumes of waste water. Typically, 30% of feed water is rejected, but it is a relatively straightforward process to recover and recycle this for secondary duties, including machine washdown, toilet flushing, filter backwashing and potentially boiler feed.
Depending on the type of business concerned, there are several factors that need to be considered when specifying grey water treatment systems. Consultation with an expert provider of water treatment systems will establish whether the constituents of your wastewater impose any limitations on its use. For example, in food production, the washing of vegetables generates water with high solids loading, dissolved organics and possibly surfactants, all of which will restrict further use of the water.
There is also a variety of configurations to choose from, ranging from systems that perform minimal treatment to more complex arrangements that can treat grey water to a standard sufficient to allow extended storage. The decision as to which system to adopt will be a balance between need and cost, as there is always a trade-off between energy required and energy saved. However, a specialised supplier will help you to achieve the right balance, cutting costs for your business, keeping you in line with legislation and protecting the environment.