Study On The Removal Of Organic Pollutants From Petrochemical Reverse Osmosis Concentrate

Double-membrane process (Microfiltration/Ultrafiltration-Reverse Osmosis) is a typical process for wastewater reclamation, which provides 70%-75% high-quality reclaimed water with environmental and economic benefits. However, about 25%-30% reverse osmosis concentrate (ROC) is generated consequently, and the pollutants concentration in ROC can be 2-3 times higher than that in RO influent. Generally, those organic pollutants are refractory dissolved organic matter (DOM), and maybe contain some environmental priority pollutants. Therefore, direct discharge of ROC without proper treatment will cause potential water environment pollution. Direct oxidation of ROC without concentration will consume large amounts of energy. Direct reclamation of ROC by RO process will result in RO membrane fouling.The electrocatalysis technology needed higher energy consumption, while the ozone oxidation technology was significantly affected by influent quality compared to activated carbon adsorption for ROC treatment. DOM was removed better by powder activated carbon (PAC) adsorption than that of granular activated carbon or activated carbon fibers because of the varied merits of PAC, for instance, high dispersion, little micropore blocking and shorter time to reach adsorption equilibrium. In addition, the effluent quality of PAC-MF process can meet the influent requirements of RO process without suspended solids and colloids, the used PAC can be directly discharged into the biological unit to enhance the treatment effect and improve the sludge dehydration property.For unknown multi-component adsorption system, the experimental method and a simple prediction model were established for accumulative countercurrent two-stage adsorption based on proved PAC multi-stage adsorption capacity equation by jar test. Microfiltration cup and column experiments were carried out to research the stability and viability of this process. For the ROC from refinery wastewater, COD and DOC removal were 70% and 71%, respectively, when the dosage of PAC was 0.6 g/L. The consumption of PAC was 42.8% lower than that of single-stage adsorption process.The functional equations from response surface methodology (RSM) were applied to improve the prediction model for PAC-MF accumulative countercurrent two-stage adsorption because those isotherm constants changed with the initial adsorbate concentration in multi-component system. The stability of this process and the accuracy of prediction model were studied by automatic control column experiments. For the ROC from petrochemical wastewater, the values of COD and DOC reduced averagely from 94.14 mg/L and 25.61 mg/L to 36.85 mg/L and 6.976 mg/L (model theoretical values were 39.23 mg/L and 7.996 mg/L), respectively, when the dosage of PAC was 0.48 g/L. The experimental values slightly lower than prediction ones due to the adsorption of PAC accumulated in column. The effluent quality can meet the influent requirements of RO process completely, and can be monitored through the changes of UV₂₅₄ values.The titanium substrate dimensional stable anodes (DSA) with catalytic coating (Ti/Sb-SnO₂) were prepared through orthogonal experiments. That coating prepared by polymer precursor was homogeneous with better crystallinity. The regeneration efficiency of the used PAC saturated by phenol was 47.97% through electro- regeneration experiments, and the energy consumption was 5.3 kW·h/kgPAC.