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%).