Removal of Heavy Metal Ions from Wastewaters: An Application of Sodium Trithiocarbonate and Wastewater Toxicity Assessment

The synthesis and application of sodium trithiocarbonate (Na(2)CS(3)) for the treatment of real galvanic wastewater in order to remove heavy metals (Cu, Cd and Zn) was investigated. A Central Composite Design/Response Surface Methodology (CCD/RSM) was employed to optimize the removal of heavy metals from industrial wastewater. Adequacy of approximated data was verified using Analysis of Variance (ANOVA). The calculated coefficients of determination (R(2) and R(2)(adj)) were 0.9119 and 0.8532, respectively. Application of Na(2)CS(3) conjugated with CCD/RSM allowed Cu, Cd and Zn levels to be decreased and, as a consequence, ∑(Cu,Cd,Zn) decreased by 99.80%, 97.78%, 99.78%, and 99.69%, respectively, by using Na(2)CS(3) at 533 mg/L and pH 9.7, within 23 min. Implementation of conventional metal precipitation reagents (NaOH, Ca(OH)(2) and CaO) at pH 11 within 23 min only decreased ∑(Cu,Cd,Zn) by 90.84%, 93.97% and 93.71%, respectively. Rotifer Brachionus plicatilis was used to conduct the assessment of wastewater toxicity. Following the application of Na(2)CS(3), after 60 min the mortality of B. plicatilis was reduced from 90% to 25%. Engagement of Na(2)CS(3) under optimal conditions caused the precipitation of heavy metals from the polluted wastewater and significantly decreased wastewater toxicity. In summary, Na(2)CS(3) can be used as an effective heavy metal precipitating agent, especially for Cu, Cd and Zn.