Local discharge limits for oil and grease vary from 10 ppm to 100 ppm. Ultrafiltration (UF) treatment of these waste streams will typically result in a permeate with an oil and grease content less than 10 ppm. Recycle is generally the objective for both cleaner and rinse water applications as neutralization can be problematic in some cases.
In addition to waste minimization, the use of recycle has two additional benefits. First, the recycled permeate will, in most cases, contain most of the alkaline detergent thereby reducing the volume of cleaner purchases. Second, by continuously recycling the cleaner, the bath oil levels are kept low throughout the life of the run that improves the washing quality.
By using an UF membrane, recycling the rinse water can reduce water consumption. Additionally, in worst cases, a carbon and/or ion exchange may be required to produce rinse water with the desired clarity. Rinse water can also be used as make-up water for the primary wash cycle.