| Reverse osmosis(RO)membrane has been widely used in food,electricity and sewage treatment industry because of its very small pore size,which can effectively remove dissolved salts,colloids,microorganisms,organic substances and so on.However,due to the adsorption and deposition of impurities on the surface of the membrane element during operation,the membrane performance is inevitably lowered.At present,the main method of treating membrane fouling is to add scale inhibitors and regular cleaning,but these two methods will increase cost of expenditure and cause environmental pollution to a certain extent,and regular cleaning will increase the number of membrane cleaning and damage the membrane structure.Therefore,finding a more effective way to treat membrane fouling has become a research hotspot.A large number of studies have shown that electromagnetic fields have the functions of descaling and scale inhibition.Therefore,it is a beneficial attempt to carry out electromagnetic field treatment of membrane fouling.At present,there are still some shortcomings in this research,and the theoretical and experimental research is not perfect.Therefore,it is of great theoretical and practical significance for the development of RO membrane technology to study the fouling characteristics and cleaning prediction of RO membrane under high frequency electromagnetic field.Firstly,the process of membrane fouling and the electromagnetic mechanism were analyzed.Based on the RO non-equilibrium thermodynamic model,combined with the Kern-Seaton and Helmholtz liquid-solid model,the membrane flux was used as a quantitative index to establish a model of the relationship between key fluid parameters and RO membrane fouling under the presence or absence of a electromagnetic field.The simulation results show that the flux of the membrane increases obviously under the electromagnetic field,and the magnetization effect changes with the change of soluble matter concentration and flow rate.This will play a guiding role in the manufacture of electromagnetic scale suppression device and the development of membrane fouling experiment.Secondly,based on the simulation parameters of the RO membrane fouling model,a highfrequency electromagnetic scale-inhibiting device was developed.At the same time,the RO membrane pollution experiment platform was designed and fabricated,and a double-loop membrane pollution cycle comparison experiment was carried out with or without electromagnetic field.The results show that the high frequency electromagnetic field effectively improves the water quality of the RO membrane and improves the separation performance of the RO membrane.In the experiment,the membrane flux and the desalination rate are increased by 64% and 26.4%,respectively;Through the SEM image analysis of the film surface,it is found that the CaCO3 crystal on the surface of the film is mainly in the aragonite state after magnetization,while the CaCO3 crystal on the surface of the film without the electromagnetic field is mainly in the calcite state.At the same time,the cleaning cycle of membrane fouling shows that,compared with the membrane without electromagnetic field,the cleaning efficiency increases by 18.3% in the range of 0.8g/L-6.0g/L and 21.5% in the range of 0.6m/s-1.2m/s after electromagnetic field is applied.Finally,based on the RO membrane pollution model and related experimental data,a set of RO membrane cleaning prediction system was designed for the problem of frequent membrane cleaning caused by periodic cleaning.By comparing and verifying the actual cleaning time and predicted cleaning time of RO membrane,it is found that the prediction accuracy of the system is good,and the average absolute error under the action of electromagnetic field or not are 0.6 and 0.7 respectively,which meet the industry requirements.This has certain theoretical reference value for the cleaning time of RO membrane and has practical significance for reducing the cleaning frequency of the membrane. |
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