Process Economics—A Case History

A manufacturer of painted and plated store and office fixtures, located in the Midwest conducts plating operations involving nickel, trivalent chromium and zinc. 

A conventional wastewater treatment system with an average flow rate of 160,000 gpd produces effluent suitable for NPDES discharge. Metal hydroxide sludges are dewatered in a 15 cu. ft filter press producing more than one half ton of filter cake per day. The filter cake is further dewatered in a 7 cu. ft, batch-type sludge dryer. Based upon recommendations by their consultant, the firm also uses the sludge dryer to dehydrate nickel strip solutions. Two reverse osmosis systems are used for partial nickel recovery. Trivalent chromium is recovered by drag-out control and evaporation. 

The output volume from the sludge dryer operating two shifts is 8 to 12 cu. ft per day. Approximately 30,000 lbs. of dried F006 material are shipped to a secure landfill every two months. The present cost for transportation, disposal and taxes is approximately 30,000 per year or almost 200 per ton. Several loads have been rejected either because 

In the fall of 1988, plant management made a decision to get out of the RCRA loop. As a division of a major corporation, the primary concern was the future liability should the TSD facility which they employ become a Superfund site. A consultant was retained to evaluate methods to delist, recycle or recover the F006 sludge. 

Those costs to operate the system which include additives, fuel, electricity and refractory replacements are estimated at 1500 per month, representing about 0% of the present disposition costs. More importantly, the client has been discarding over 1200 lbs. per month of nickel (at 8/lb of nickel, this is 9 00/mo.) and paying a transporter to haul it to the secure landfill. 

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