Figure 4.
(a) The photograph of pig farm wastewater before and after digestion. (b) The DPSV results of pig farming wastewater (with high Cu2+ and Zn2+) after different digestion methods. (c) Characteristic peak currents of Cu2+ and Zn2+ after digestion with nitric acid (pig farming wastewater with no detectable heavy metal ions but with exogenously added 1 mg/L Cu2+ and 1 mg/L Zn2+). (d) The results of DPSV of pig farm wastewater (with no detectable heavy metal ions) spiked with different concentrations of Cu2+ and Zn2+.