Treatment Of Micro-polluted Brackish Water With An Integrated Process Based On Ultrafiltration-nanofiltration

In the cold and arid regions of northwest China,the available surface and shallow groundwater resources are abundant,but most of these water resources are brackish water with poor water quality,and there are micro-polluted problems.For the treatment and utilization of such water resources,single technology or the typical combined water treatment processes have strong applicable limitations.The exploration of integrated and systematic new combined processes have become a very important research topic in the treatment and utilization of such water resources.Based on the investigation of the water quality characteristics of brackish water in the cold and arid regions of Northwest China,this paper selects HA(humic acid)as the organic pollutant,and uses sodium chloride to simulate brackish water as the base liquid to form the water quality of the micro-polluted brackish water.The effects of HA on the performance of ultrafiltration and nanofiltration membranes during the treatment of micro-polluted brackish water were studied.In this paper,water treatment technologies with different removal mechanisms,such as US/UV,AC,UF and NF,were applied to the desalination and decontamination of the micropolluted brackish water and the effects of HA on the performance of ultrafiltration and nanofiltration membranes were investigated.At the same time,data support was provided for the popularization and application of advanced oxidation membrane coupling process in the micro-polluted brackish water treatment in northwest cold and arid areas.The specific research results are as follows:An experimental study on the treatment of the micro-polluted brackish water by NF process was carried out,experimental results show that under the optimal operating conditions of NF determined by experiments,the physical screening removal of nanofiltration membrane is obvious,the average removal rate of NaCl by NF process can reach 48.47%,41% and 33.7% when the concentration of NaCl is 1000 mg/L,3000 mg/L and 5000 mg/L of influent,and when the HA concentration is 5mg/L,30mg/L and 100mg/L of influent,the average removal rate of HA by NF process can reach 96.39%,99.37% and 99.71%,after 8h of operation,when the HA concentration is 5 mg/L,30 mg/L and 100mg/L of influent,nanofiltration average membrane flux decreased by 20.18%,29.19% and 37.64%;although NF process has better desalination and decontamination effect on micro-polluted brackish water,but in long-term operation during the process,the nanofiltration membrane flux will be greatly attenuated,and the nanofiltration membrane performance cannot be maximized.In order to ensure the desalination and decontamination effect of NF process and to minimize the organic pollution of nanofiltration membrane.On the basis of previous research on NF process,UF-NF process suitable for slightly polluted brackish water treatment was selected for experimental study,experimental results show that under the optimal operating conditions of UF determined by experiments,the adsorption properties of UF play a role,when the HA concentration is 5mg/L,30mg/L and 100mg/L of influent,the average removal rate of HA in UF process is 5.52%,6.41% and 8.49%,after 8 hours of operation,when the HA concentration is 5mg/L,30mg/L and 100mg/L of influent,the average membrane flux of ultrafiltration membrane decreased by 10.25%,17.24%,30.45%,the average membrane flux of the membrane decreased by 9.12%,11.48% and 11.76%,respectively;It can be seen that UF as the pretreatment process of NF makes the attenuation of nanofiltration membrane flux in UF-NF process a greater degree than that in NF process,but the ultrafiltration membrane itself also has a large degree of membrane during long-term operation,so it cannot maximize the performance of ultrafiltration membrane in the UF-NF process;In order to ensure the desalination and decontamination effect of UF-NF process and to minimize the organic pollution of ultrafiltration and nanofiltration membrane.On the basis of previous research on UF-NF process,AC-UF-NF process suitable for the micro-polluted brackish water treatment was selected for experimental study,experimental results show that under the optimal operating conditions of AC determined by experiments,the effect of the combination of the two activated carbon column played a good adsorption degradation,when the HA concentration is 5mg/L,30mg/L and 100mg/L of influent,the average removal rate of HA by AC process can reach 18.63%,30.44 % and 39.7%,respectively,after 8h of operation,the average membrane flux of ultrafiltration membrane is decreased by 5.96%,14.37%,24.5%,the average membrane flux of nanofiltration membrane decreased by 3.84%,6.97% and 11.87%,respectively;It can be seen that AC as the pretreatment process of UF-NF not only has a better effect on HA,but also makes the attenuation of ultrafiltration and nanofiltration membrane flux in AC-UF-NF process larger than that in UF-NF process,the degree of improvement,however,in the long-term operation of the activated carbon column,the adsorption is easy to be saturated and the service life is short;In order to ensure the desalination and decontamination effect of the AC-UF-NF process and to maximize the adsorption performance of the activated carbon column.On the basis of previous research on AC-UF-NF process,US/UV-AC-UF-NF process suitable for slightly polluted brackish water treatment is selected for experimental study,experimental results show that under the optimal operating conditions of US/UV process determined by experiments,US/UV process has a good removal effect on HA in water,when the HA concentration is 5mg/L,30mg/L and 100mg/L of influent,the average removal rate of HA can reach 76.17%,79.8% and 80.65%,after 8 hours of operation,the average membrane flux of the ultrafiltration membrane decreased by 1.88%,5.24%,5.68%,the average membrane flux of nanofiltration membranes decreased by 1.48%,3.65% and 4.45%,respectively,it can be seen that the US/UV process as the pretreatment process of AC-UF-NF not only optimizes the US/UV-AC-UF-NF process,but also improves the service life of the activated carbon column and effectively alleviate the ultrafiltration and nanofiltration membrane pollution;On the whole,by optimizing US/UV,AC,UF,NF process units,the US/UV-AC-UF-NF combination process has obvious advantages in desalination and decontamination of micropolluted brackish water,and can effectively remove the natural organic pollutant HA in the micro-polluted brackish water,and can significantly reduce the concentration level of the inorganic salt sodium chloride which characterizes the salinity of the micro-polluted brackish water.