Abstract:
The aim of this research was to find the optimum conditions for coagulationfloccuation process and ozonation process to remove color and COD from wastewater in Flexographic printing using water-base ink. We assessed the optimum conditions for the removal efficiency using Central Composite Design, CCD along with Response Surface Methodology, RSM. Independent variables in the coagulation-flocculation study are ferric chloride dosage and initial wastewater pH, while independent variables in the ozonation study are ozonation time and initial wastewater pH. One Variable At a Time (OVAT) technique was applied to investigate the effects of independent variables on color removal efficiency and COD removal efficiency. Results from the OVAT experiments was used to define the high and low levels of factors that were studied in CCD. Results from wastewater treatment by coagulation-flocculation showed that the relationship between the independent variables and color removal efficiencies, as well as COD removal efficiencies was best described by a full quadratic model with the adjusted coefficient of determination (R2-adj) and standard error (SE) of 85.91 % and 4.32, respectively. Optimum conditions for color removal of 90.83±1.60% and COD removal of 60.18±5.80% were obtained at ferric chloride dosage of 1.24 g/L and initial pH of 7.5. At the optimized conditions, color and COD in the effluent was 300 ± 7.3 ADMI and 1,749 ± 78.6 mg/L. Results from wastewater treatment by ozonation showed that the relationship between the independent variables and color and COD removal efficiencies was best described by a Linear+Square model with R2-adj and SE of 76.65 % and 18.18. Optimum conditions for color removal of 91.45±0.59% and COD removal of 72.70±9.20% were obtained at ozonation time of 130 min and initial pH of 2.3. At the optimized conditions, color and COD in the effluent was 293 ±15.2 ADMI and 466±28.5 mg/L.