Term Yield Regression coefficients t-value p-value Constant 49.5143 108.708 0.000 Ccp(mg/L) -3.6783 -14.933 0.000 pH -11.9833 -48.651 0.000 t (min) 2.7100 11.002 0.000 D (g) 2.0975 8.516 0.000 Ccp2(mg/L)2 0.6943 3.077 0.007 pH2 -5.6932 -25.229 0.000 t2(min)2 -1.2307 -5.454 0.000 D2(g)2 0.3181 1.410 0.178 pH × Ccp(mg/L) 1.0888 3.609 0.002 Ccp(mg/L) × t(min) -1.2462 -4.131 0.001 Ccp(mg/L) × D (g) -1.7562 -5.822 0.000 pH × t (min) 0.3338 1.106 0.285 pH × D (g) -1.6163 -5.358 0.000 t (min) × D (g) -0.8013 -2.656 0.017

Table 5: Observed Regression Coefficients, t-Test, and p-Values for 2-CP removal by Fe powder.