The most common issues with the metal plating industry are the high levels of aluminum, chromium, copper, nickel, phosphorus and sometimes zinc. All these metals can be removed by precipitating the dissolved parameter to a solid. The conventional method of treating this water is having 2 to 3 reaction chambers, where the pH is raised to 9-10.5 to precipitate nickel and copper and then lowered to pH 6.5 to 7 to precipitate aluminum phosphate to remove the phosphorous and aluminum. A third reaction chamber is required to add a polymer to assist in the floc development to improve settling. The conventional method to separate the solids is a Lamella Plate clarifier. Figure 1 below shows a conventional metal plating wastewater treatment system.
The problem with the conventional system is the complexity of chemical addition and the management of the reactors to create a stable floc that will settle rapidly in the clarifier. In a recent application to treat metal plating waste water (5 m3/hr -20 gpm), a comparison was made for floor space requirements for the conventional clarifier versus the RSL Membrane™. The clarifier required a floor space of 12.2 m long by 3 m wide versus the RSL Membrane™, which is 2 m by 1.2 m. The RSL Membranes™ provides > 90% reduction in floor space. Floor space in a metal plating shop is an important cost factor.
In addition, because of the robustness of the RSL Membrane™ to handle high solid loads, the need for reactors is limited to one where the pH is raised in the equalization tank.
Below is the data on an aluminum etching plant displaying the metal removal using precipitation and the RSL Membrane™.
