Study On Reusing Of Electroplating Wastewater By Nanofiltration (NF)

With the high-speed development of national economy, China's industrial wastewater emissions increased sharply, and it also brings large quantity of pollution. Electroplating wastewater is difficult to handle with because it has the characteristic of toxic compound and large quantity of emission. Membrane separation technology as one kind of high efficient water treatment methods has been widely used in power plant sewage treatment cycle and sea water desalination and recycling of industrial waste water treatment. And the membrane separation of MF+RO is applied mostly to deal with electroplating wastewater. But RO membrane is susceptible to many kinds of pollution factors, and the inflow water for RO membrane requires high standard, which limits the reuse efficiency of the whole membrane treatment system to only 50%-65%.Nanofiltration is a kind of membrane technology which developed rapidly in the recent years. It has the screening effect and Donnan effects of separation electric charge, and with which the Donnan effect functioned mainly. And together with its strong resistance to pollution that makes the interception of NF membrane for divalent ion represent much better. So it has certain advantage in the application of NF membrane system which based on RO system which can make the reuse efficiency of the whole membrane treatment system to almost to 90%. This thesis studies the application of NF membrane system which based on RO system. we investigated the influence of operating pressure, concentration polarization and different nano filtration membrane modules (NF90 & NF270) on efficiency of interception. And the reuse possibility of electroplating wastewater was initially tested through the engineering case.According to the research on working state of single nano filtration membrane that dispose the synithetical electroplating wastewater, we investigated the influence of operating pressure and different nano filtration membrane modules (NF90 & NF270) on efficiency of interception. The experiments showed remarkable differences between NF90 and NF270 when treating synithetical electroplating wastewater. NF90 with its characteristics of high fixed surface charge density showed a higher and more stable heavy metal ions interception rate compared with NF270 and interception rate was stable around 90%. But the water production rate of NF90 is relatively small compared with NF270, and only about 1/3 of NF270's. The both NF270 and NF90 system showed a high efficiency of interception when the operating pressure was about 1.6MPa. Even the inflow water conductivity is around 30000μs/cm, the concentration ofZn2+ of water production can still be controlled around 1.2mg/Land concentration of Ni2+ was around 0.4 mg/L, which accorded with the national discharge standard.We further investigated the influence of concentration polarization of NF90 and NF270 system when treating the electroplating wastewater. In the best operating pressure under 1.6Mpa, we investigated the relationship between mass transfer coefficient and surface velocity. The results show that the mass transfer coefficient k increased with surface velocity, together with decrease of polarization degree. And at the same time, the Penetration Flux J also had a certain effect. When permeability increase, the mass transfer coefficient k decreased, and polarization degree increased. And NF90 was relatively highly influenced by the concentration polarization compared with NF270. Even we increased the surface velocity cannot control NF90's polarization degree under 1.2 while the surface velocity of NF270 membrane reached 0.20m/s the polarization can be controlled to a relatively small degree, which was suitable for the engineering practical operation.We further tested the NF270 membrane system on an actual engineering practical operation project, in which the conductivity of inflow water was around 16000 [i s/cm, pressure was around 1.6MPa. The conductivity of water production by NF system was steadily under 7000μs/cm, The reuse efficiency of NF membrane system was about 75%, while the reuse efficiency of RO/NF combination system can reach 95%, and can reach the reuse water requirements both in quality and quantity that engineering practical operation project was designed for.