COD Removal Efficiency of Pararubber Wastewater by Ozonation using the Central Composite Design Model
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Abstract
Pararubber is one of the major plants contributing to both Thai and Asian’s economy. Pararubber wastewater having a high strength can cause several environmental problems to community nearby the industry. The research aimed to study the characteristics of pararubber wastewater and investigate the optimal conditions for treatment of pararubber wastewater using the ozonation process. The results revealed that the pararubber wastewater has a black color with a pungent odor like sludge from a septic tank. Wastewater characteristics obtained from the preliminary analysis are as follows; pH of 4.99, Chemical Oxygen Demand (COD) of 55,448.52 mg/L, Total Dissolved Solid (TDS) of 10,240 mg/L, and SS of 1,516.67 mg/L. Factors affecting the ozonation process studied are dosage rate of ozone and contact time. The Central Composite Design (CCD) model or box-wilson design, which is an experimental design at 3 levels (popularly represented by symbols -1, 0, +1) and useful in response surface methodology (RSM) for generating a second order (quadratic) model for the response variables, was applied to investigate the optimal condition for the treatment process. From the results, it was found that both of factors significantly affected the COD removal efficiency and can be expressed in the form of equations or a mathematical model for predicting COD removal efficiency, in which %COD R.E. = 13.3408 + 0.0613A + 0.5587B + 0.000619A*B - 0.000063A2 - 0.004270B2. The coefficient of determination was 92.14%. The mathematic model was applied to develop the graph displaying the relationship between these two factors and COD removal efficiency using the Responsive Surface Methodology. It was found that the removal efficiency of COD was increased with increasing contact time and dosage rate of ozone, which has a maximum value of 89.67% at ozone dosage rate of 900 mg/hr and contact time of 120 minutes.
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