Gaps in Aqueous
Cleaning Research

Efforts to better understand and document the successes of aqueous cleaning are ongoing. Several areas that merit future study are:

• Extending the life of aqueous cleaning solutions using closed-loop approaches. The use of oil skimmers or similar equipment to remove large quantities of oil from aqueous cleaners is widely used and well known, but more sophisticated approaches such as membrane filtration are still not fully understood by many manufacturers. To date, the majority of work done to extend cleaner life has been done within private companies, and has not been made publicly available. Some work has been done recently. For example, Underwood and Thomas reviewed the concepts and techniques for closed loop aqueous cleaning and presented three short industry case studies where filtration was used to extend the life of aqueous cleaners. (Ref. 16) In one example, a metal parts manufacturer reduced daily wastewater discharge due to cleaning from 2,000 to 75 gallons by installing a cleaner recycling system that uses hollow fiber ultrafiltration. Additional applied research and documentation of industry experiences is necessary to provide an available knowledge base to help manufacturers reduce the wastewater streams they generate as a result of aqueous cleaning. Extending the life of the cleaning solution will reduce both cleaning purchasing and wastewater treatment costs.

• Obtaining a better understanding of temperature's effect on the aqueous cleaning process. The significance of temperature in aqueous cleaning was discussed in the technical section of this review, but several important questions remain unanswered. Why did some experimentation show that operation at temperatures above the cloud point resulted in higher cleaning efficiencies? Is this finding, which contradicts conventional wisdom, true for cleaning solutions other than those already tested? Gaining a better understanding of the effects of temperature will allow manufacturers to operate their cleaning processes more efficiently.

• Ongoing development of cleaning solutions that are biodegradable This issue of cleaning solution biodegradability was briefly mentioned in the limitations section of this review. Increased biodegradability of cleaning solution will reduce treatment requirements for spent cleaning solutions, as long as non-biodegradable contaminants added during cleaning are separated from the solution or can be passed on to the discharge point (sewer or surface water).

• Additional case studies of manufacturers' efforts to implement and improve aqueous-cleaning systems. Continued documentation of industry experiences in this area are essential to promote the transfer of information between companies as continued improvements are made by individual manufacturers in their aqueous-cleaning processes. More detail regarding the experimentation with key cleaning process parameters that many companies do to implement a new system would be useful to include in these case studies. Ultimately, what does and does not work in the manufacturing environment will be defined by manufacturers themselves, and continued transfer of this knowledge will reduce the number of companies that waste time when trying to implement or improve their own aqueous-cleaning process.