text: * Mechanical filtration addresses only two issues in wash rack wash water: suspended solids larger than 30 µm, and free oil and grease. Emulsified oil and grease cause damage to the media filters, resulting in high maintenance costs. Electrocoagulation does not use particle size to provide physical separation.
  * Chemical treatment addresses suspended solids, oil and grease, and some heavy metals, but may require the addion of various flocculants and coagulants as well as pH adjustments for proper treatment. This technology requires the addition of chemicals which can be expensive, messy, hazardous and labor-intensive treatment. This process also requires addition of compressed air for flotation of coagulated contaminants. Generally filtration is used only as a post-treatment phase for polishing.