Soybean Peroxidase‐Catalyzed Treatment of Azo Dyes with or without Fe° Pretreatment

Abstract

Representative azo dyes (Acid Blue 113 [AB113] and Direct Black 38 [DB38]) were treated in a single step with soybean peroxidase (SBP) and hydrogen peroxide (H2O2), or in two steps, zero-valent iron (Fe°) pretreatment followed SBP/H2O2. The purpose of this research was to compare both treatment processes and to determine which one was the optimal for degradation of each azo dye. For AB113, the preferred process was the single-step process, 1.0 mM AB113 required 2.5 mM H2O2, 1.5 U/mL SBP at pH 4.0 for ≥ 95% color and dye removal and 30% total organic carbon (TOC) removal. For DB38, due to the products formed after Fe° reduction, which are enzyme substrates (aniline and benzidine; two of four products) a two-step process was preferred, which allowed reduction in the required SBP and H2O2 concentrations by 5- and 2-fold, respectively, compared to a single-step treatment for ≥ 95% color, dye, and aniline/benzidine removal and 88% TOC removal.

Soybean peroxidase‐catalyzed degradation of a sulfonated dye and its azo‐cleavage product

“…The removal of dyes has been observed to be favorable at acidic pH values. pH 4.0 and 3.6 were optimal for removal of CI Acid Blue 113 and CI Direct Black 38 using SBP 7 . Chiong et al .…”

“…In the present study, for 0.50 mmol L –1 MO, [H 2 O 2 ]:[substrate] = 2 was found to exhibit the maximum conversion of 98%. This ratio can be compared to the optimum [H 2 O 2 ]:[substrate] of 2.5 observed for CI Acid Black 2 at pH 4.4 13 and CI Acid Blue 113 at pH 4.0 7 for 95% decolorization. An increase in the ratio to 4 reduced the conversion marginally to 96%.…”

“…The azo bond has been reported as a labile component of azo dyes undergoing peroxidase‐mediated reactions 7,17 . In some cases, the products of azo‐cleavage are more toxic than the original dye 13 .…”

“…These dyes resist aerobic treatment processes and their fate remains uncertain 6 . Dye concentrations <1 ppm are easily noticeable and undesirable, yet concentrations of ≤300 ppm released from textile industries have been reported 7 . Dyes are xenobiotic and highly recalcitrant owing to the presence of electron‐withdrawing sulfonic and carboxylic acid groups 8 .…”

Soybean Peroxidase Catalyzed Decoloration of Acid Azo Dyes

“…Only one recent report used the same SBP preparation as the present study, which highlights the need for continued exploration of the scope for enzymatic azo dye treatment in order to arrive at a generalized treatment process. 32 Soybean seed coat peroxidase is well suited for this study because of its stability, ease of extraction, widespread availability and potential for adding to the soy value chain. 33 The present study evaluated the feasibility of SBP catalyzed oxidative dye polymerization and removal of Acid Orange 7 and Acid Black 2.…”