Practical Water Recycling for Surface Finishing Processes
Water is by far the most important chemical used in Surface Finishing.
Almost all of the processes used in electroplating and surface finishing are aqueous based, meaning the primary solvent for the chemical system is water. They therefore require water to be used for rinsing concentrated process chemistry from the surface of components before they can more to the next process stage. This ensures downstream chemical processes do not become contaminated by the chemistry of earlier process stages. Water is therefore by far the largest volume chemical used in surface finishing. With today’s increasing focus on improving environmental standards along with the inevitable increasing costs associated with water treatment, taking steps to optimize water use can offer significant economic and competitive advantages.
Water Quality Standards for Surface Finishing
Minimum quality standards of water used in processes is not always well documented. Some chemical suppliers will quote deionized, demineralized or distilled water for specific processes. Other than this, it’s rare to find more detailed information about water quality requirements. In truth, this is because most surface finishing processes are fairly tolerant to variations in water quality. Indeed, many of the raw materials used in them contain higher levels of potential contaminants than typical water sources from municipal sources. However, some processes are sensitive to dissolved salts and minerals contained in water sources. Before embarking on measures to recycle water, it’s good practice to liaise with chemical suppliers about water quality requirements for sensitive processes.
What is Practical Water Recycling?
Put simply, it’s a method for identifying the most advantageous way to prepare a water recycling plan. While it’s possible to recycle 100% of the water used for surface finishing, the investment and energy cost to do so make it technically challenging, uneconomic and environmentally unsustainable. Energy consumption alone for recycling 100% of the water used in typical surface finishing waste streams would far outstrip the value of the recovered water. ZLD (Zero Liquid Discharge), the term typically used to describe 100% water recycling, sounds like an admirable goal; however, the full impact of achieving does not deliver a more sustainable outcome. The earth’s natural processes for water recycling is far more efficient than any man made solution. Therefore, by returning suitably treated water back to the environment, we can naturally maintain effective and sustainable water recycling. Practical water recycling for surface finishing can provide significant advantages providing it is planned and executed well.
Water Recycling for Surface Finishing
When considering water recycling, the best place to start is by creating a detailed process roadmap including all water use points for each process line. Water volumes, flow rates, dump schedules, drag out rates, contamination levels and cascade layouts all require assessment to determine the best water streams to target for recycling. The first target is to optimize water flow and rinse efficiency. It’s incredible how many surface finishing operations don’t optimize rinse rates but simply assume that more rinsing is better. In fact, a poorly setup high flow rate rinse station can be far less efficient than a well configured low flow rate rinse. The judicious use of drainage time, sprinklers, distributors or agitation can significantly improve rinse efficiency and allow significant reduction in water use. Drag out tanks are another area where use should be determined by process and treatment needs rather than simply assuming that a concentrated chemistry rinse offers some additional treatment benefits. Drag outs to aid useful chemical recovery and reuse are ideal.
Focusing on recovering the cleanest rinse waters are at the heart of Practical Water Recycling. It’s far easier to recover water for reuse from relatively clean rinses. Cascade rinsing is one approach but again the need to size and control the flow correctly is essential. Rinse segregation is also a key step. Collecting compatible rinses to feed a single recycling point is essential to minimize capital costs and optimize recovery volume and quality.
Finally, determining the best reuse points for recovered water is an important aspect. If during recovery, salts like calcium, magnesium & sodium are built up, selecting the points of water reuse is important, avoiding processes that may be sensitive to them.
Process Chemical Know-How is Critical
Many surface finishing operations are complex, utilizing many different chemical process types that may differ significantly in their sensitivity to rinse water quality and rinse volume requirements. Knowing the details of each chemical process provides a significant advantage when looking at the best options for water recovery and reuse.
Contact MacDermid Envio Solutions today to find out more about practical water reuse.
Written by Terry Clarke, MacDermid Envio Solutions