highly significantp < 0.003
Regarding sodium removal, the pH (K 3 ) and the coefficients of the factor K 3 K 3 influenced the EC process ( p > 0.05), whereas the current density (K 1 ) with the electrolysis time (K 2 ) and the quadratic terms of the current density and electrolysis time (K 1 K 1 ) had highly significant effects on sodium removal ( p < 0.003).