The research program was initiated with the objective of evaluating a new process, the sulfide precipitation of heavy metals from industrial wastewaters. The process was expected to effect a more complete removal of heavy metals than conventional lime processing because of the much lower solubilities of metal sulfides than hydroxides. Five processes were compared in bench-scale, continuous-flow equipment: conventional lime processing, conventional lime processing plus filtration, lime with a sulfide polishing and filtration, lime with sulfide, and lime with sulfide plus filtration. Samples of actual wastewaters from 14 metal working industries (including Boeing) were processed through the bench-scale equipment using all five processes. Reductions in the concentrations of cadmium, chromium, copper, nickel, and zinc, plus selected other metals were measured by atomic absorption chemical analysis. Capital and operating costs for the five processes were comprised for three plants sizes: 37.85 cu m/day (10,000 gal/day), 757 cu m/day (200,000 gal/day), and 1,893 cu m/day (500,000 gal/day). The report recommends that, to reduce the levels of cadmium, copper, nickel, or zinc, from a wastewater treatment plant using conventional lime processing, the addition of a final filtration should be considered first. The sulfide process did not significantly reduce the levels of these metals. Details are included on the use of a specific ion electrode for the control of sulfide additions. The report does not include comparison testing of the commercial Sulfex process.

Includes bibliographical references (pages 40-41). Prepared for U.S. Environmental Protection Agency, Office of Research and Development, Industrial Environmental Research Laboratory, Cincinnati, Ohio, submitted by Boeing Commercial Airplane Company, Manufacturing Research and Development, under grant Contract Number: S805413.