Table 4: ANOVA of surface response methodology for the photocatalytic process of dairy wastewater.

CoefficientSE Coefficient -value value

Constant29.5971.37721.4900.000
pH1.7980.7462.4090.025
ZnO coating thickness1.2830.7461.7190.100
pH * pH−22.6391.567−14.4520.000
pH * thickness0.0720.7460.0970.924

Where: S = 3.37352, Rsq. = 91.08%, Rsq.adj. = 89.45%, Rsq.pred. = 86.73%.