Dickson Weatherproof Nail/CDC Coatings
Currently, zinc is precipitated out of wastewater from the galvanizing department and "released" to the environment when it is land-filled as a component of sludge. Some zinc is also released through a permitted outfall. Trace amounts of lead, found as a contaminant of zinc, are also released in both sources. Improvements in the efficiency of the galvanizing process through the use of proprietary chemicals and a purer grade of zinc reduced the concentration of both lead and zinc in the wastewater and hence in the sludge. In a process integral to galvanizing, about 20,000 gallons per day of fresh water were used to pump a slurry. It was found that fresh water was not needed for this purpose, so a totally enclosed system was constructed by rerouting existing pipe and reallocating existing tank storage. This reduced the wastewater flow by 20,000 gallons per day and resulted in improved control of the wastewater system. Further reductions in the wastewater flow were realized by using treated wastewater in non-critical applications, such as preliminary rinses, solution make-up in galvanizing, and polymer and caustic dilution in the wastewater treatment system. This reduced the wastewater flow by another 10,000 to 15,000 gallons per day.
Through the use of treated wastewater in non-critical applications and using a totally enclosed system for pumping the slurry, wastewater flow was reduced by 30,000-35,000 gallons per day.
A reduction in the wastewater flow brought us well into compliance with our permitted wastewater discharge. The lower flow rates improved the performance of the wastewater treatment system, thus reducing the amount of zinc and lead released through the out fall. Improved zinc use efficiency in the galvanizing operation not only reduced zinc and lead concentrations in the wastewater but also in the sludge. The improvements lead to a reduction of about 12,000-15,000 pounds per year of lead and zinc released to the environment, primarily in the sludge.
Details of Reductions
Additional Information :
Cost savings were realized primarily from the improvement in zinc use efficiency. Estimates are in the range of $42,000 per year. Improved compliance with our discharge permit and reduced environmental impact were the main driving forces behind these projects.