Experimental Studies On Treating Simulated Industrial Wastewater By Ultrafiltration And Nanofiltration

The water scarcity is more and more severe. Thus, the advanced treatment ofindustrial wastewater for water reusing is more and more popular, and the membranetechnology plays an important role in the treatment. However, the flux decline arisingfrom membrane fouling is a serious problem, which cause the application ofmembrane technology to be uneconomic. Therefore, it is very significant to studydeeply the influence factors of the membrane process treating industrial wastewaterand the membrane fouling mechanism.In this work, two experimental setups were designed and established, and theultrafiltration and nanofiltration membrane process treating simulated wastewatercontaining humic acid substances were investigated using the setups. The factorswhich can influence the processes were studied systemically.The experiments on the removal of turbidity and organic substance usingultrafiltration process were carried out. The results indicated that the turbidityrejection of the ultrafiltration membrane can approach to 100%, and the organicsubstance rejection would vary according to the variation of the nature of the solution.It was found that the membrane flux decrease was accelerated with increasing Ca2+concentration, humic acid concentration, ionic strength and decreasing pH value.Meanwhile, the results also showed that the extent of membrane fouling decreasedwhen the back-wash frequency increased at a constant total consumed water volume.Based on the ultrafiltration experiments, the nanofiltration experiments for thetreatment of the simulated wastewater were carried out. The results indicated that theD-series nanofiltration membrane had high rejection for both the organic substanceand divalent ions. Meanwhile, divalent cations can cause the organic substance toadsorb on the membrane surface more easily, then cause more severe flux decline.And the effects of the monovalent ions and divalent anions were less than that ofdivalent cations. The humic substances fouling of nanofiltration membranes can bereduced by decreasing initial flux and increasing crossflow velocity.According to the characteristic of the operation and the membrane fouling, severalkinds of cleaning strategies were applied during the experiments, and the ATR and theSEM analyses were carried out. The cleaning efficiency and the fouling mechanismwere thus investigated. It was found that the ultrafiltration membrane fouling causedby humic acid is due to the adsorption and deposition of the humic acid on themembrane surface and inside membrane pores. In the cleaning experiment ofultrafiltration membrane, the flux was well recovered after using the NaOH aqueoussolution to immerse the membrane and then make a back-wash. It was also found thatthe adsorption and deposition of humic acid on the membrane surface caused thecharacteristics of nanofiltration membrane to present as the nature of the humic acid,and resulted in the decline of membrane flux. In the cleaning experiment ofnanofiltration membrane, the flux was almost recovered after cleaning with theEDTA (ethylenediaminetetraacetic acid) solution, which is a strong chelating agentfor calcium.