The ultimate “closed-loop” cleaning system would produce no effluents requiring disposal. In many manufacturing facilities, disposing of waste liquid containing chemicals and other contaminants removed from parts being cleaned is either very costly or just not possible using municipal sewer or other available facilities. Even in the best cases, most cleaning system effluents require pre-treatment prior to disposal. Municipalities frequently monitor waste coming from manufacturing locations on a connection by connection basis and, believe me, you want to be in compliance or you will pay! In many instances, the only solution is to have collected waste hauled away for treatment – an expensive option unless your effluent stream happens to include precious metals such as gold or silver!
A “closed loop” cleaning system may reduce the cost of disposal of used process liquids significantly or, in some instances, completely. The basic concept is that water is used in progressively dirtier process steps and, in the end, is disbursed by evaporation as water vapor. In order to successfully accomplish this goal, water usage must be minimized. The article Ten Minutes to better Rinsing demonstrates how water usage for rinsing can be significantly reduced by using a reverse cascade system. If the required amount of water required to refresh the cascaded rinse tanks can be reduced sufficiently, then it may be possible to use the overflow from the first (final in the sequence of flow) rinse tank to makeup the cleaning tank. If the evaporation rate from the cleaning tank is sufficient to vaporize all of the liquid received from the rinse tanks then a “closed loop” system has been achieved. There are no effluents.
The problem with this scheme, of course, is that eventually all contaminants removed from the parts being cleaned will end up in the cleaning tank. Although solid contaminants (particles) may be removed from the cleaning tank by filtration, water soluble or emulsified contaminants will continue to build up in the tank until cleaning is no loner effective. Therefore, even in a well-engineered “closed loop” cleaning system removing contaminants that can mix with water, the solution in the cleaning tank will occasionally need to be dumped and replaced. Disposal of the dumped, contaminant-laden liquid can be achieved by evaporating the liquid in an evaporator, by neutralizing it and sending it to drain, or by hauling it away for disposal. In any event, there is a distinct benefit to reverse cascade flow even if a totally “closed-loop” system is not achieved.
Water is an expensive commodity. Disposing if it once it’s used is often even more expensive. Any means that can be put to use to reduce water consumption, therefore, reduces the cost of cleaning. Although not applicable in all situations, consideration of a “closed-loop” system may be well worth the effort. In most cases, it will mean that the initial cost of the equipment is higher, but the higher cost is repaid multi-fold by the savings in water and waste disposal.
– FJF –