On a global basis, 2022 has been one of the driest periods for over 300 years. The controversy around this being a result of climate change continues, but sooner or later, the fact that we can measure the trend in global warming is undeniable.
Terry ClarkeToday, rivers, lakes, and other freshwater supplies in most industrialized countries are under increasing pressure from population growth, increased consumption, and reduced rainfall. With only 3% of the earth's water classified as freshwater and 2.5% of this locked up in glaciers, only 0.5% is available for us to use.
Not wishing to misuse statistics, this still results in 2.2 million gallons of fresh water for every human on earth. It sounds like more than enough, but like most resources, it's not evenly distributed or easily accessible.
So, what does all this have to do with Surface Finishing?
Considering that the most widely consumed chemical in surface finishing is water, our businesses need to know if this essential commodity will continue to be available and affordable well in the future. And these questions are not as simple to answer as you might think.
In the U.S., we believe there are no water shortages; the Great Lakes hold 20% of the world's freshwater, so we're all set, right? Maybe, but no one can deny the relentless march of the environmental lobby and its impact on both individuals and businesses to become more sustainable.
Let's Consider Fresh Water Use in Surface Finishing
There's no getting away from the fact that water is a vital commodity for surface finishers. It's impossible to operate aqueous chemical processes without fresh water. It typically represents most of the chemistry in surface finishing processes and almost 100% of associated rinses. Surface Finishing applicators typically pay for both incoming and outgoing water, making it a serious operating expense. And many modern processes generate wastewater that can't easily be treated by existing wastewater treatment systems, especially if the plant was built 10 or 15 years ago. This waste often requires external treatment at a significantly higher cost than equivalent on-site treatment.
Another consideration is rinsing, and who determines the amount of water needed for effective rinsing after each process step? Most likely, you don't have any 'official' information about this, so we use the best rule of thumb available, which is more than enough to ensure you don't have quality problems. This will unquestionably result in using more water than is actually needed because you have no way of measuring the safety margin being applied.
Finally, we have a somewhat controversial observation that some consumers use higher water throughput to help dilute waste to reliably meet local wastewater discharge consent limits. It gives an added measure of assurance designed into the production process. This is not simply an activity that was common 25 years ago but is no longer used or only found in emerging economies, where less diligent water authorities may be more relaxed about water quality or volume. This approach was described by my former boss as, "dilution is the solution to pollution" God rest his soul, I'm sure he wasn't the originator of the saying, but it certainly has been part of our industry practices for a long time.
Most, if not all, of these measures inflate the total cost of water and will most likely impact its longer-term availability.
Next-Gen Water Management
So, what could the future of Surface Finishing look like as water becomes a more precious resource and a less commoditized raw material? Can the utilization of water for Surface Finishing be more carefully managed in an affordable way?
Indeed, it's essential for a finishing operation to get a clear understanding of the distribution and function of water usage within the facility. Creating a water usage map can be very revealing and create immediate opportunities for process improvement and cost savings. A Water Map identifies where water is used, along with its specific function and volume.
This may sound deceptively simple, but it's rare to find this detailed information in widespread use. For example, if rinsing consumes the majority of influent water, this would be an ideal optimization target.
- There are methods to measure dilution rates for process drag-out and rinse volumes alongside theoretical dilution rates for optimum rinsing.
- Optimum rinse rates, by process type, can be established, giving improved water utilization and providing options for effective recycling.
- Assessment can be made for the impact and efficiency of counter-flow (cascade) rinsing and where these are best utilized.
- Automated systems to monitor water quality and manage flow rates can be used to minimize consumption whilst maintaining good rinsing efficiency.
Furthermore, if we consider that 95% of the influent water will eventually go to waste treatment, reducing the volume by as little as 10% would have a significant benefit in terms of waste treatment chemicals, energy costs, and discharge volumes.
Is Water Recycling Viable for Surface Finishing Operations
The simple answer is yes. But let's understand more about why and how.
Firstly, the principles and technologies behind water recycling are widely understood and utilized in many industrial applications. Let's be clear, it rarely, if ever, results in lower water costs. It can, however, be financially neutral for specific industrial applications if addressed in the correct way.
Surface Finishing is, in fact, an attractive proposition for practical water reuse. This means our ambitions should be to reuse water in an economical way, rather than 100% recycling or zero liquid discharge. 100% water recycling and ZLD are always more expensive and rarely net environmentally beneficial.
Practical water reuse can be implemented in many Surface Finishing operations. The first aim is to identify water that is not being used efficiently and repurpose it. For a broader water recycling plan, identify the cleanest water sources, define what they can be used for, and divert them for reuse. It's not always necessary to clean or treat these streams before reuse, although that is an option in some instances. Treating the cleanest water may sound counterintuitive, but in fact, it is the most effective and efficient approach. Trying to remove large amounts of metal or organic contaminants from rinses following high concentration processes involves invasive, energy-intensive processing, often for very little net clean water gains. Where possible, these processes are best targeted with metals, organic, or salt recovery systems rather than water recycling.
Rinse waters following low concentration processes can much more readily be repurposed for reuse with minimal treatment. This can often provide high rinse flow rates for more efficient rinsing.
Recent testing of water recycling in a PCB surface finishing application resulted in almost 90% water recycling of all process rinses with no impact on rinse water quality, process efficiency, finish quality, or reject rates. This was achieved by careful identification of chemical process components, targeted rinse segregation, careful mitigation selection, and regular monitoring to capture rinse-quality data. Once a baseline for continuous processing was established, it remained stable over a prolonged period. Being intimately aware of the process chemistry made it possible to create high water reuse characteristics with zero processing impact.
This may be a more advanced example of practical water reuse; however, almost all water used in surface finishing processes benefits from rinse segregation before attempting water recycling. The traditional "end of pipe" method for recycling water doesn't allow selective pretreatment and relies entirely on the system after wastewater treatment to remove and polish out significant amounts of organics, salts, and trace metals. This approach is rarely effective and is perhaps one reason for the Surface Finishing industry being reluctant to consider practical water reuse when, in fact, it can be economical, practical and beneficial to the industries environmental impact.
Terry Clarke is Managing Director at MacDermid Envio Solutions. Visit https://www.macdermidenvio.com
