Optimization of multiple parameters of coking wastewater (CWW): catalytic thermolysis (CT) at high pressure reactor (HPR)

Present study deals with the treatment of coking waste water (CWW) for the reduction of pollutants COD, phenol and cyanide using catalytic thermolysis (CT). For screening of catalyst and optimization of pH the CT was performed at 100 °C, pH = 3–11 using catalyst mass loading Cw = 3 g/L. In this study Cu (NO3)2 gave best performance. Further, CT was carried out using Cu (NO3)2 catalyst in high pressure reactor (HPR). The investigated parameters range were initial pH (pHi) = 3–11, Cw = 1–5 g/L, temperature (T) = 100–160 °C and treatment time (tR) = 6 h. The maximum percentage reduction for COD, phenol and cyanide were 83.33, 80.57 and 97.61%, respectively at pH = 9, Cw = 4 g/L, T = 140 °C and tR = 6 h. The CT did not give complete reduction of pollutant; therefore it was further treated using adsorption process as second stage treatment. The initial value of COD = 610 mg/L, phenol = 70.58 mg/L and cyanide = 0.45 mg/L were further reduced to 98.85, 100.00 and 55.55%, respectively, when adsorption process was performed at pH = 9, adsorbents dose Aw = 4 g/L, tR = 2 h. The response surface methodology (RSM) was performed through central composite design (CCD) for the designing of experiments and optimization of both the process. The kinetics studies of CT at HPR showed first order with respect to COD and phenol, and 0.24–0.608 order with respect to CW.