Copper can be found in many wastewater sources including, printed circuit board manufacturing, electronics plating, plating, wire drawing, copper polishing, paint manufacturing, wood preservatives and printing operations. Typical concentrations vary from several thousand ppm from plating bath waste to less than 1 ppm from copper cleaning operations. Copper can be removed from wastewater by precipitation as an insoluble hydroxide salt or by ion exchange. Hydro-Flo Technologies designs and manufactures many types of metal precipitation systems including small and large batch type and a range of continuous flow treatment systems.
Precipitation of the insoluble cupric hydroxide salt is the most common form of treatment. This salt is formed by adjusting the pH of the water to about 9 to form the precipitate. The resulting precipitate can leave about 0.1 ppm of dissolved copper in solution if chelates are absent. If chelates are present, the final copper concentration can be much higher. When chelating agents are present, Hydro-Flo can design a treatment system using special metal trapping chemistry.
Ion exchange can be used to remove copper from wastewater. Hydro-Flo ion exchange systems are designed to treat plating rinse water with trace amounts of metals. The water is sent through cation and anion resin beds, along with activated carbon and/or media filtration to produce deionized water that can be returned to the process. The advantage offered by Hydro-Flo ion exchange systems is that the resin is regenerated on-site, eliminating the need for bottle haul off. Since the regenerate waste will contain any copper and other metals removed during treatment, a vacuum distillation system can be used to concentrate the regenerate even further to reduce the amount of liquid waste hauled away. The purified water from the vacuum distillation system can also be returned to the process.
The equipment normally used for these processes is a batch treatment system for high copper concentrations (greater than 1000 ppm), continuous precipitation if the copper concentrations are less than 1000 ppm and the volume is greater than 5000 gpd. Ion exchange is feasible if concentrations are less than 20 ppm and the desired effluent requires low copper concentrations, less than 20 ppb.
The typical method to remove copper from wastewater is as follows:
Stage 1 Precipitation:
pH is adjusted upward to a pH of 8-9.5 to the optimum chrome hydroxide precipitation point. Often, a coagulant such as ferric sulfate is added to enhance metal co-precipitation and the formation of “pin floc”.
Stage 2 Flash mix:
The wastewater with it’s precipitated pin floc is introduced to the flash mix zone where a polymer flocculent is added. This stage maximizes flocculent dispersion throughout the coagulated wastewater.
Stage 3 Flocculation:
The wastewater is now introduced to the slow mix zone to agglomerate the pin floc into larger rapid settling particles.
Clarifier, Inclined Plate:
The flocculated wastewater is introduced into the clarifier where the settling particles accumulate in the sludge chamber. The clarified water then exits the clarifier and flows downstream to sewer or further treatment if necessary.
Clarifier Sludge Handling:
The accumulated sludge is periodically removed from the clarifier and sent to a sludge holding tank where it further thickens for disposal or dewatering.
Sludge dewatering is typically handled by a Filter Press. After processing a batch of "sludge" the filter press is emptied of “chrome cake” which is a semi solid of approximately 20-35 % solids. Chrome cake is high in chrome and sulfite and should be disposed of according to environmental regulations.
Plating shops are found in typically two categories, captive and independent shops. Some industries operate their own captive, in house plating operation while others outsource to an independent plating operation.
Typical industries include: