Cousin Samantha (Sam) insisted, “you’ve got to take a look at Lake Mendocino; it will change your whole outlook.” We were in Northern California for a winter break. I groaned inwardly. I know about the drought in California. I wanted to do a wine tasting, not look at a lake. Cousin Sam is a really persistent lady; so we piled into our relatively environmentally-sensitive Prius and drove over. Yikes! Lake Mendicino had turned into Mendocino Mud Puddle. The water’s edge begins a good 100 feet beyond the end of the boat launch dock. Yup, we’re in a drought.
In terms of critical product cleaning, I think many well-intentioned water conservation efforts miss the point. Manufacturers have been admonished to fix the plumbing, rip out lawns and replace them with “water-wise” landscapes, and even use grey water for landscaping. In critical cleaning of high value parts, controlling water quality makes good sense from a quality and economic perspective. Saving water makes economic sense even if your manufacturing plant is covered with snow or your landscaping is covered with moss.
Start with High Quality Water
Treat water like the valuable chemical that it is. Water has unique properties that make it a valuable resource for critical parts cleaning. This means achieving the correct water quality at the wash and rinse stages of the cleaning process. We often advise you to buy quality cleaning, to buy carefully formulated cleaning agents. The same holds for water. Using tap water to clean or fabricate high value product is both wasteful and counterproductive. Tap water can vary in terms of dissolved solids (hardness), depending on the time of year and on the local water conditions. In general, water with high dissolved solids means an ineffective cleaning process. Especially where the water flows through agricultural communities, there can be wide seasonal swings in organic and inorganic compounds.
The problem with undefined water quality starts at the initial wash step. Some suppliers of aqueous cleaning agents actually specify mixing the concentrated cleaning agent with tap water. We disagree with this practice. While I drink tap water (brave soul that I am), good potable water is not the same as good process water. Starting with tap water means starting with inconsistent, often dirty water. The process bath itself is inherently inconsistent, and soil loading is will be more of a problem. If the washing solution cannot be used, it must be replaced. In many processes, three or more rinse tanks may be required. Using tap water can result in inconsistent rinsing, spotting, and discoloration of the component. On an all too regular basis, we see unexpected failure in cleaning processes, coating processes, and other surface treatment processes due to variable contaminants in tap water.
Maintain that high quality water
So how does a manufacturer reduce process costs while producing a quality product? By treating water as if it were a costly chemical. Start with good quality water; then maintain that high-quality, and reuse it. Look at your current cleaning process set-up. There may be several wash tanks, or a washing zone for an in-line spray cleaner followed by several rinse tanks or a rinse zone, and finally a drying chamber. Maintaining water quality while the process is running is not only a greener approach, it also improves the cleaning process quality. This means fewer rejects and, ultimately lower costs.
Don’t contaminate the rinse water
Even if your water rates are low, treat water and water-based cleaning agents like the valuable chemistries that they are. You would not purposely cross-contaminate valuable chemicals, but that’s what happens during transfer of parts between wash and rinse tanks. Cleaning agent gets trapped in the crevices of parts and drips into the nice clean rinse water. The phenomenon is known as carry-over or drag-out. One way to reduce drag-out from one tank to the next is by allowing pause time (drip time) before transfer. This can be programmed into automated processes. A second is to include a short spray rinse between tanks; adding the spray is most practical when purchasing new equipment.
Rinse more effectively, use less water
Use multiple rinse tanks in a reverse cascade process so that the final rinse is in the highest quality water. But how do you determine the flow rate from the last rinse up to the first rinse? It takes a little finesse and process optimization. If the rate is too fast, excess costly water will be used. If the rate is too slow, contamination buildup in earlier rinse stages limits the effectiveness of that rinse and the ineffectiveness trickles down to the next rinse stage. Determining the adequate rate involves monitoring the rinse water quality so that it adequately accomplishes the rinsing task while minimizing the need for new, highly conditioned water.
Appropriate filtration of the wash tank and the rinse tanks can be a money saver. We have experienced situations where clients have been reluctant to invest in filters, electing instead to replace the water. Replacing the water takes time, costs money, and means more waste stream management. Issues of waste stream management include treating the waste stream effluent prior to release, evaporation, or using hazardous waste disposal. In many cases, the costs and hassles of waste stream management are enough to make engineers reconsider water reuse.
Now, we are not at all suggesting that you use poor quality water in the interest of water conservation. We are suggesting that, with appropriate process design, filtration and monitoring, you can actually achieve consistent, high-quality recycled water that exceeds process requirements.
Evaporation and insulation
There is another often overlooked aspect to water conservation in manufacturing – and that is evaporation and insulation. Many aqueous processes are considered to be so benign that the process tanks are not covered. I know many of you are losing water through evaporation, because my hair is an excellent qualitative moisture meter – it frizzes within minutes of exposure to excess moisture! If I am observing an aqueous cleaning process and my hair begins to look as if I am in New Jersey in August, it’s a pretty good sign of excess evaporation of water (and probably also loss of volatiles in the cleaning chemistry). Environmental regulations may not require you to cover the process tanks, but any manufacturer concerned about quality and costs ought to reevaluate general process practices.
For most cleaning processes, water is heated; and process tanks may not be well-insulated. Good insulation may mean a higher initial capital investment. However, savings in energy and water can add up.
The bottom line
Conserving water during the cleaning process should not be off-limits. Managing process water properly is almost certain to use less water, you will have improved quality control, and you will save money.