Coagulation kinetic study and optimization using response surface methodology for effective removal of turbidity from paint wastewater using natural coagulants

The wastewater from paint manufacturing industry contains high quantity of pollutants that are generated from washing equipment, as well as chemical additives. Hence, coagulation–flocculation was applied in the present study to evaluate the performance of some natural coagulant derived from Hibiscus esculentus L,(okra) Detarium microcarpum,(sweet dater) Xanthosoma (cocoyam) and Crassostrea Virginica, (oyster shell) in the removal of turbidity from paint wastewater (PW). The coagulants were characterized using Fourier transform infrared spectrometer (FTIR), Scanning electron microscopy (SEM) and X-ray diffraction (XRD). A laboratory jar test was employed for the experiments. Process kinetic was studied to determine coagulation-flocculation parameters such as coagulation rate constant and coagulation half-life τ1/2. The effects of the operating parameters such as initial pH of the wastewater, coagulant dosage and settling time affecting the efficiency of turbidity removal were studied in a one-factor-at-a-time (OFAT) process. Box-Behnken Design (BBD) was used in designing the experiment; evaluate the individual and interactive effect of the variables and determining the optimum conditions. Statistical parameters such as coefficient of determination R2, sum of square roots due to error (SSE) and the root mean square error (RMSE) were used to evaluate the adequacy of the process. The optimum removal of turbidity was observed at pH range 2–4, dosage 100–200 mg/L and settling time of 30 min for the coagulants, with removal efficiency of 60–92.6% a second order polynomial regression equation with R2 values of 0.9644, 0.9827, 0.9707 and 0.9718 for OSC, DMC, CYC and ODC, respectively. While the coagulation half-time, τ1/2 ranges from 0.98 for OSC, 0.87 for DMC, 13.73 for CYC and 9.15 for ODC. The study has proved the coagulant can be used in treatment of turbidity from paint wastewater