Heterogeneous persulfate activation by nano-sized Mn3O4 to degrade furfural from wastewater

Abstract

The simultaneous use of persulfate (PS) and nano-Mn3O4 was investigated as an advanced oxidation process for furfural degradation and oil refinery wastewater treatment. The synthesized Mn3O4 nanoparticles were characterized by XRD, BET, BJH and FESEM-EDS and then successfully used as a heterogeneous catalyst for PS activation. The effects of five independent variables on the performance of nano-Mn3O4/PS system were investigated and optimized using a 5-level-5-factor full Central Composite Design (CCD). Accordingly, CCD developed a reduced quadratic polynomial model with P-value < 0.0001 and R2 = 0.9996. The optimal values for the nano-Mn3O4 dosage, PS concentration, solution pH, stirring rate and furfural concentration were 1.2 g/L, 6.34 mM, 4.82, 337 rpm and 50 mg/L, respectively. The maximum experimental removal efficiencies under these conditions for PS alone, nano-Mn3O4 alone and the combined nano-Mn3O4/PS system were 8.36, 4 and 91.14%. Considering the kinetic coefficients of furfural removal in the individual and combined systems, a significant synergistic effect was observed in the nano-Mn3O4/PS process. Acetic acid, formic acid, maleic acid, and oxalic acid were the major intermediates of furfural degradation by LC-MS analysis. Alcohol-based probe experiments demonstrated that the sulfate radical was the dominant active radical at optimum pH. The optimized nano-Mn3O4/PS process can effectively increase the biodegradability index (BOD/COD ratio) of oil refinery wastewater.