3.1.7. Toxicity analysis
The eco-toxicity test was applied to the effluent before and after
the electrocoagulation process for the best operating conditions
referred before. The results obtained for EC20 and EC50 indicators
are shown in Table 2. One can observe that the addition of the electrolyte
NaCl increased the toxicity of the effluent by itself, reducing
EC20 from 10% to 9% and EC50 from 36% to 18%. After treatment,
even if the effluent remains toxic for bacteria a decrease on this
parameter is detected subsequently to the ECG with EC20 = 20%
and EC50 = 38%. Fulladosa et al. [36,37] determined EC20 and EC50
threshold values for Zn2+for Vibrio fischeri bacteria, which corresponded
to 0.46 ± 0.02 mg/L and 0.86 ± 0.11 mg/L, respectively.
The concentration of Zn2+ obtained in this work was 36 mg/L, value
that is above EC50 reported in literature. This aspect can be an
important contribution to the toxicity present in the effluent at
the end of the treatment.