Performance of electrochemical treatment of refractory organic matter in printing and dyeing reverse osmosis concentrate

The printing and dyeing wastewater treatment process produces a reverse osmosis concentrate (ROC) that contains high organic matter content and requires proper treatment before discharge. Electrochemical oxidation was applied in this study to treat organic pollutants in the ROC. In addition, the concentration variation of phthalate esters (PAEs) in ROC was investigated. The results demonstrated that the electrochemical oxidation process could effectively reduce the organic content in ROC; the total organic carbon (TOC) removal efficiency reached 83.38% at pH 2.4 and a current density of 40 mA/cm2. Increasing the current density can markedly enhance the oxidation of the bulk organic matter (i.e., TOC, chemical oxygen demand (COD), UV254, and fluorescence). The effect of pH on the decomposition of organic materials was slightly less as than that of current density. The molecular weight (MW) distribution in the ROC indicated that the percentage of components larger than 5 kDa was approximately 10%, but decreased to 2.16% with persistent electrolysis. Further, 3D fluorescence spectroscopy suggests that the organic matter in ROC was mainly aromatic proteins (APⅡ) and soluble microbial products (SMP), which account for 25.78% and 51.39% of the total fluorescence, respectively. Notably, acidic conditions are more favorable for the breakdown of fluorescence, which is attributed to the higher oxidative capacity of·OH. The decomposition of PAEs was enhanced by lowering the pH, and degradation efficiency increased by 36.45% when the pH was lowered from 9.8 to 2.4. Qualitative analysis by gas chromatography-mass spectrometry (GC-MS) showed that the abundance of organic matter in the treated ROC was significantly decreased. •COD, TOC and UV254 can be effectively eliminated from ROC by electrochemical oxidation.•Soluble microbial products and aromatic proteins degradation led to significantly decrease in fluorescence intensity.•The primary components of PAEs in ROC are DIBP, DBP and DEHP.•The average current efficiency and energy consumption for different current densities are evaluated.