Study On Analyis And Removal Of Organics In Reverse Osmosis Concentrate

The reverse osmosis(RO) technology already has many applications in fields such as sea water desalination and advanced wastewater treatment. Despite supplying 50%~75% of high-quality permeate, the RO process generates approximately 25%~50% of the feeding as reverse osmosis concentrate(ROC). The organics concentration in ROC was several times higher than that in the feeding and the organics in ROC may include emerging and priority pollutants. Currently, for the determination and occurrence investigation of emerging and priority pollutants in the ROC, however, there were few documents reported in the latest decade. There is a problem of high activated carbon consumption for the ROC treatment by the traditional activated carbon technology.The work investigated the occurrence and concentrations of emerging and priority pollutants in the(ROC) using liquid-liquid extraction(LLE) followed by gas chromatography-mass spectrometry(GC-MS). The results indicated that there were varieties of pollutants, including chlorinated organic compounds, polycyclic aromatic hydrocarbons(PAHs), phthalate esters(PAEs), pharmaceutical and personal care products(PPCPs), herbicides and flame retardants, in the ROC. The Quality Assurance/Quality Control(QA/QC) for the LLE-GC-MS analytical method was explored. The results indicated that the LLE-GC-MS method exhibited a high degree of precision and accuracy for the analysis of the majority of the target compounds. The concentrations of most target pollutants in ROC were as low as typically tens or hundreds of ng/L, whereas others were as high as several μg/L, such as bis(2-chloroethyl) ether 1.42 μg/L, caffeine 3.73 μg/L, butyl benzyl phthalate 4.90 μg/L.A powdered activated carbon(PAC) adsorption-MF hybrid process was investigated for the removal of organics, including trace-level(approximately 10 μg/L) target emerging and priority pollutants, COD and DOC, from ROC. Regarding to the target emerging and priority pollutants, bis(2-chloroethyl) ether, atrazine, simazine, caffeine, dimethyl phthalate and diethyl phthalate, were difficult to remove compared with others pollutants. On the condition of adsorption time of 0.5 h, the removal efficiencies of all the target emerging and priority pollutants were higher than 90% when the PAC dose was 640 mg/L, then the removal efficiencies of COD and DOC were 65.8% and 64.8% when the PAC dose increased to 0.9 g/L. The octanol-water partition coefficient(log Kow) could be served as an indicator for the difficult of the removal of the target emerging and priority pollutants. But the relationship was not absolutely correct and the application should be paid special attention. The relationship between the initial concentrations of the emerging and priority pollutants and their removal efficiencies was investigated. The results showed that the removal efficiencies of them from ROC were independent of the initial concentions.A PAC countercurrent four-stage adsorption-MF hybrid process was investigated for organics removal from ROC. The results showed that the organics in ROC was effectively removed by the hybrid process. The PAC consumption was further reduced and the membrane fouling was significantly mitigated in the countercurrent four-stage adsorption process compared with countercurrent two-stage adsorption process. In the experimental setup of the process, the increasing of the total number of sub-cycle in a cycle(n) would result in the larger of Hydraulic retention time(HRT) and the severer of membrane fouling. The calculation method for correlating removal efficiency and PAC dose was deduced and validated. The validation results indicated that the calculation method could well correlating the organics removal efficiency and PAC dose.