Transformation and degradation of recalcitrant organic matter in membrane bioreactor leachate effluent by the O3/H2O2 process

Membrane bioreactor effluent from treating leachate (MBR leachate) is characterized by a high humification degree, and further treatment of refractory organics is required. Refractory organic components in the MBR leachate were identified by using the three-dimensional excitation emission matrix (3D-EEM) coupled with parallel factor (PARAFAC) analysis, namely fulvic-like substances (C1, Ex/Em = (245)325 nm/410 nm) and humic-like substances (C2, Ex/Em = (255)365 nm/460 nm). With a higher O-3 dosage and an increase in H2O2 dose, the removal efficiency for C1 and C2 can be enhanced. However, an overdose of H2O2 or alkaline conditions exhibited some inhibition of refractory component removal in the O-3/H2O2 process. The unsaturated structure of the humic substances was destroyed, and the aromaticity degree, hydrophobicity degree, humification degree, molecular mass, and condensation degree of the benzene ring compounds in the MBR leachate were reduced considerably by the O-3/H2O2 process. Therefore, the biodegradability of the MBR leachate increased considerably to 0.32. Correlation analysis, principal component analysis, and linear regression were applied and indicated that the chemical oxygen demand (COD) had a significant positive correlation with C1 and C2, and the absorbance at 254 nm (UV254) had a more significant positive correlation with C2. Hence, monitoring and determination of relative C1 and C2 contents can achieve rapid COD prediction in the MBR leachate. This study provides suggestions and guidance for MBR leachate treatment and references for the rapid prediction of refractory organic concentration.