Characterization of phytotoxicity of metal engraving effluent samples

Two effluent samples were collected from an acid bath of a metal engraving industry. Sample A was lime-treated to pH 6 and sample B, pH 9. Zn concentrations in samples A and B were 1207 and 4.24 mg L^-1, respectively. Both samples A and B caused 100% inhibition on millet seed germination. Sample A was more toxic than B. The 60% concentration of sample A caused 96% inhibition, whereas the 60% concentration of sample B caused 60% inhibition. The toxicity of sample B was not likely due to the presence of cyanide and zinc ions. The results of using various adsorbents and resins for the effluent treatment showed that only powdered activated carbon was partially effective in toxicity removal. By a combination of treatment methods, including using sodium hydroxide precipitation and carbon column adsorption, toxicity removal was calculated to be 29%.