Investigation of Oxidation Methods for Waste Soy Sauce Treatment

To obtain a suitable oxidation method for removing the color and lowering the chemical oxygen demand (COD) of waste soy sauce, Fenton (Fe(2+)), Fenton-like (Fe(3+)), and ozone (O(3)) oxidation methods are used as the target reactions. In experimental conditions for Fenton oxidation, the dose of Fe(2+) and Fe(3+) was varied between 100 mg/L and 300 mg/L. The dose of hydrogen peroxide for the reaction was injected from 100–1000 mg/L. For ozone oxidation, the pH was increased from 3 to 14 and the O(3)-containing gas was supplied continuously for 30 min through a gas diffuser at the bottom of the reactor at different applied O(3) doses (10–90 mg/L). We subjected it to a simple 1:20 dilution with deionized water to identify the comparison result in detail. O(3) oxidation shows the highest efficiencies of color removal (81.1%) and COD lowering (64.9%) among the three oxidation methods. This is mainly due to the fact that it has a relatively large amount of hydroxyl radical, resulting in the degradation of organics. Thus, O(3) oxidation could be a promising method for removing the color and lowering the COD of waste soy sauce. The critical parameters (pH and applied O(3) dose) were varied systematically to optimize O(3) oxidation. It was found that the optimum pH and applied O(3) dose are 11.0 mg /L and 50.0 mg /L, respectively (color removal = 34.2%, COD removal = 27.4%).