From waste water to cost reduction
Mark Bosley, Business Support Divisional Manager at Purite looks at how waste water recovery can reduce operating costs
As accountants like to remind us, ‘turnover is vanity, profit is sanity’. Somewhat trite, perhaps, but this simple phrase disguises a greater reality: the importance of controlling your operating costs if you are to maximise profits. Of course cost control applies throughout your business, but for many companies in the surface treatment sector one of the biggest areas of cost, and therefore of potential reduction, is the purchase and use of both energy and raw water.
Large volumes of high purity water are essential for processes such as coating, plating, anodising and galvanising; for example rinse processes in powder coating lines often require purity better than 50μS/cm. This is normally achieved using a variety of techniques including filtration, reverse osmosis and deionisation to remove particulates, salts and organic matter from the raw water feed, which would otherwise cause imperfections in the quality of the finished coatings.
Reducing the volume, and thus the cost, of the water used in surface treatment should firstly involve a review of the process mechanisms; for example, making sure that the most effective systems are in place, including counter-flow rinsing, spray rinse equipment, efficient flow control, drag-out reduction techniques and accurate conductivity measurement and monitoring of water purity.
Once these systems are in place then it is time to consider techniques to reduce water volumes by efficient recycling or repurification of waste water streams. Although this may be impractical for some of the most heavily contaminated waste streams, for most applications the introduction of a filtration and purification unit could typically enable a high percentage of the waste water to be returned to the main process for normal or non-critical rinsing duties, without affecting product quality. This clearly offers a considerable saving on raw water costs.
The technology used in repurification systems will vary depending on the nature of application. For example, some small batch systems use ion exchange cartridges or exchangeable cylinders. These are packed with cationic and anionic resin beads that allow either hydrogen ions to be exchanged for positively charged ions such as nickel, copper, sodium and cadmium, or hydroxyl ions to be exchanged for negatively charged sulphates, chlorides and chromates. Cartridge based systems do, however, require regular recharging, which can become expensive over time, especially if high volumes of waste water are being generated.
A more cost-effective solution is the use of a reverse osmosis (RO) system, sometimes installed in conjunction with electrode ionisation (EDI) or cylinder based deionisers. Reverse osmosis (RO) purification is increasingly being employed in recycling systems to process waste water and the capabilities of these systems to clean water are impressive. Pressurised and pre-treated feed water is passed through specialised semi-permeable (RO) membranes to remove up to 98% of both dissolved inorganic ions and soluble organic contaminants and typically eliminating over 99% of water borne micro-organisms.
The process can be refined further with the addition of an EDI unit. Through a combination of applied voltage/current soluble inorganic ions are drawn from the water towards their respective electrodes via chambers incorporating repeating layers of mixed bed ion-exchange resins sandwiched between sheets of Cationic and Anionic ion-selective membranes. The soluble ions flowing through these cells are eventually captured in waste or concentrating chambers where they are flushed to drain. The result is a constant stream of purified water with no associated resin regeneration costs.
It’s worth pointing out that although RO technology has been used in industrial applications for many years it has been continually developed. As a result the latest RO membranes provide high levels of flow at lower operating pressures. This gives exceptional purity but also cuts operating costs as pump speeds, and thus energy demand, can be significantly lowered. Additionally, the adoption of pumps with variable speed motors allows the duty of each unit to be matched exactly to the output demands of the water treatment system, again minimising energy consumption.
For some companies, although it may be impossible to repurify all waste water it may nonetheless be feasible for waste streams to be recycled as grey water. This can be used for non-process duties, ranging from machine or vehicle washdown to toilet flushing and, with additional treatment, boiler feed.
When specifying waste water recycling solutions it pays to discuss your requirements with an expert provider of water treatment systems. This will enable waste streams to be correctly analysed, ensuring the most effective systems are put into place. Inevitably, there will be a balance to be struck between need and cost, as there is always a trade-off between the water and energy required for your processes and the potential for savings. However, a specialised supplier will work with you to achieve this balance, cutting the operating costs for your businessand, as a bonus, helping you comply with legislation and your environmental responsibilities.