During the manufacture of gun barrels, high pH alkaline solutions containing sodium hydroxide are used in bath tanks to clean metal parts prior to further processing. The contents of the bath must be replaced every 6-8 weeks. The objective of this project was to demonstrate that the Vibratory Shear Enhanced Processing (VSEP) system developed by New Logic International Incorporated of Emeryville, California was an effective recycling and recovery process for prolonging the bath life of caustic cleaning solutions and for reducing the volume of hazardous waste generated.
Standard separation technologies such as reverse osmosis cannot operate effectively under harsh caustic conditions, and traditional cross flow filtration systems plug and foul because the majority of the shear is created by turbulent flow away from the boundary layer, preventing retained solids from being removed. The VSEP process offers a new dimension to membrane separation by imparting a shear force at the membrane surface to prevent fouling while maintaining high separation efficiency.
Chemical tests verified that contaminants were removed, while the active chemical cleaning components were returned to the bath. This increased the alkaline bath life to 12 months with only small additions of new chemicals and water makeup to compensate for evaporative losses.
Implementation of the VSEP system will result in significant cost savings as compared to the current practice of offsite disposal of hazardous wastes and purchase of new chemicals for replacement solutions. The payback period on the $72,000 capital cost of the VSEP system, while allowing for replacement of the membrane pack every year, was estimated at 5.5 years. Additionally, parts cleaning will be improved by maintaining a less contaminated cleaning solution.