Pilot Study Of Reverse Osmosis Concentrate Treatment By A PAC Countercurrent Four-stage Adsorption-MF Hybrid Process

Due to the excellent removal of salts and organic pollutants in water, reverse osmosis(RO) technology is widely used in the field of desalination and wastewater treatment and so on. This process can provide high-quality reclaimed water. However, about 30% of the inlet reverse osmosis concentrate(ROC) is produced consequently. ROC contains almost all of the organic matter in the influent, which may also include some environmental priority pollutants. Direct discharge of ROC without proper treatment will cause serious pollution to the environment.At present, the main treatments and technologies of ROC include: traditional processes, such as lime softening, activated carbon adsorption, coagulating sedimentation, ion exchange process, and and other advanced oxidation processes like ozone oxidation, photocatalysis oxidation, Fenton and electrochemical oxidation. But these processes exist consumption high, low efficiency and other problems. In this study, powdered activated carbon(PAC) adsorption and microfiltration(MF) technology combined to remove the organics from ROC, namely use PAC to adsorb the organics in ROC, and then make the PAC separated from the aqueous phase by MF to obtain a low organic matter, low sludge density index(SDI) water, and then can recover more fresh water, improve RO system's recovery. Using a countercurrent mode of operation can effectively decrease the dosage of PAC.PAC accumulative countercurrent four-stage adsorption-microfiltration is a improved process of the PAC adsorption-microfiltration process. Preliminary works have confirmed PAC adsorption-microfiltration process can effectively remove organic matter in the ROC, reduce turbidity. But in order to reduce process costs, reduce PAC dosage and minimize the generation of solid waste matter, the PAC accumulative countercurrent two-stage adsorption-microfiltration technology and the PAC accumulative countercurrent four-stage adsorption-microfiltration treatment process are explored of the ROC effect. The results showed that, the more PAC countercurrent adsorption accumulative number, the low PAC dosage, but that will increase the number of reactors, increased infrastructure costs, so choose the PAC accumulative countercurrent four-stage adsorption-microfiltration process carry out pilot test.Pilot test results show that a large loop of reactor A corresponds to three small cycles of reactor B' operation mode and a big loop of reactor A corresponds to a small loop of reactor B' operation mode are able to achieve the desired effect of organic matter removal, the latter treatment's effect slightly worse than the former, but it can greatly reduce the volume of the reactor A, so the latter has practical applications, reducing the footprint and capital costs. Due to each row of the reactor A of carbon, the latter reduced the amount of suspended solids in the reactor B, reduced membrane fouling rate, prolonged use of the membrane. By calculation, treating 1 m3 of ROC by this process costs about 2.8 RMB, and the water quality can achieve water quality requirements of RO process, improve recycling rates.