Removal of heavy metals and organic compounds from wastewater printing circuit board manufacturers via a hybrid ferrate(VI)-trithiocarbonate process: An optimization study and toxicity assessment

In this work, the removal of heavy metal ions (Cu2+, Ni2+, Zn2+, Pb2+, and Fe3+) and organic contaminants (HCHO and EDTA) from printed circuit board wastewater (Cu2+ 57.9 mg/L, Ni2+ 1.09 mg/L, Zn2+ 1.00 mg/L, Pb2+ 0.09 mg/L, Fe3+ 17.3 mg/L, HCHO 21.9 mg/L, and EDTA 35.0 mg/L) by a combination of a green oxidizer, potassium ferrate(VI) (K2FeO4), and sodium trithiocarbonate (Na2CS3) as precipitation agents was studied. Central composite design (CCD) and response surface methodology (RSM) were applied for modeling and optimizing the designed wastewater treatment process. Analysis of variance (ANOVA) and experimental verification of the model confirmed the consistency of the experimental and estimated data calculated from the model (R2 0.800, R 2adj. 0.667). The use of K2FeO4 under the optimal conditions calculated from the model (initial pH of 2.9, K2FeO4 dose of 1.00 g/L, time of 35 min) followed by the addition of a stoichiometric dose of Na2CS3 at pH 9-9.5 resulted in decreases in the concentrations of Cu2+, Ni2+, Zn2+, Pb2+, and Fe3+ by 99.65, 91.74, 98.00, 77.78, and 99.13 %, respectively. Moreover, the concentrations of HCHO and EDTA decreased by 92.69 % and 85.43 %, respectively. Eco-toxicity tests with Daphnia magna, Lemna minor, Sinapis alba and Allium cepa revealed a significant reduction in the overall toxicity of treated sewage compared with that of raw sewage. Thus, the unique properties of the effective use of K2FeO4 and Na2CS3 in hybrid K2FeO4-Na2CS3 processes make them promising options for the treatment of industrial wastewater containing chelated heavy metal ions and organic recalcitrants.