Summary of Aqueous
Cleaning Technology Review

The following summarizes the major findings of this review:

• Aqueous cleaning was found to be a technically viable cleaning alternative for manufacturers in a number of cases. Many laboratory experiments and industry case studies documented improved cleaning of parts using aqueous systems. Changing to aqueous cleaning from a solvent-based systems also greatly reduced or even eliminated two waste streams from cleaning for manufacturers: solid hazardous waste and air emissions. Unfortunately, aqueous cleaning creates a new waste stream in the form of wastewater, that must be property treated or disposed.

• Results of economic analyses of a change to aqueous cleaning from solvent-based vapor degreasers varied significantly, with paybacks periods as low as one and as high as 12 years. One of the largest contributors to this variation was the analysis method used to calculate payback. Typically, the more detailed analyses that included a greater range of costs were the most favorable. This indicates many manufacturers may be underestimating the economic benefit of a conversion to aqueous cleaning. Aqueous cleaning has also become more economically favorable as the costs of ozone-depleting and chlorinated solvents have continued to rise as a result of increases in taxes and charges associated with their purchase.

• The most important factors in successful aqueous cleaning were found to be proper choice of cleaner solution, obtaining adequate mechanical force on the part to be cleaned, and increasing the temperature to improve cleaning efficiency. Cleaning solutions have to be chemically compatible with the part being cleaned, provide appropriate surfactants to enhance removal of the specific contaminants on the parts, and contain additives needed to prevent problems such as excessive solution foaming or part corrosion. Mechanical force, obtained using equipment such as mixers, pressure sprayers, and ultrasonic transducers, is critical in aqueous cleaning since chemical action that removes contaminants is not as strong as with traditional cleaning solvents. Increased temperature was used in the majority of industrial applications reported on in case studies and improves the removal of contaminants. To avoid damaging parts or significantly exceeding the cloud point temperature of the surfactants used in many aqueous cleaning applications, care has to be taken not to increase temperature too high.

• Aqueous cleaning systems in the manufacturing environment are typically multi-staged processes, and have historically required careful design and testing to operate effectively. The requirement for design and testing has been a barrier to the implementation of these systems because many manufacturers have not been able to allocate the time required. This requirement has decreased over the last decade and should continue to lessen as aqueous-cleaning systems become more standardized and the collective level of knowledge about them within industry increases.

• Extending aqueous cleaning solution life, better understanding of temperature effects, and continued case studies of industry experiences were identified as areas that merit future study. Continued study in these and other areas is needed to help improve the effectiveness and economies of aqueous cleaning, while reducing the wastes generated as a result of the process.