Operisation Of Membrane Cleaning Process And Kinetic Model For Chemical Cleaning Process

Membrane technology process has many advantages including simple operation, high efficiency, energy conservation, environmental protection, small footprint and so on. As a separate unit, it is widely applied in various industries. However, membrane fouling is an inevitable problem in the process of membrane separation. Membrane cleaning is the direct and effective method to solve the problem. In this paper, a cleaning procedure consists of hydraulic pre-rinsing and chemical cleaning was used to cleaning microfiltration membrane in MBR. A cleaning procedure consists of ultrasonic cleaning and chemical cleaning was used to cleaning a kind of polysulfone membrane fouled by dust and oil. Large amount of experiments were carried out to optimize the operating conditions during the membrane cleaning process. For the chemical cleaning process of the fouled membrane in MBR, a dynamics model is established. And the validity of the model was verified through simulation and comparison the experimental data and model predictions. Besides, influence contributions of the studied operating conditions(temperature, operating pressure and stirring speed) on the model parameter were calculated and estimated. The following conclusions:(1) For chemical cleaning process of the fouled membrane in MBR, ① sodium hypochlorite was the best cleaning agent, followed by sodium dodecyl sulfate and sodium hydroxide. ② flux recovery increases rapidly with the increase of cleaning solution concentration at first and tends to be stable in the later period during the chemical cleaning process. ③ flux recovery increases rapidly with the increase of cleaning time at first and tends to be stable in the later period during the chemical cleaning process. ④ flux recovery increases with the increase of temperature during the chemical cleaning process. ⑤ flux recovery decreases with the increase of TMP during the chemical cleaning process. ⑥ flux recovery increases gradually with the increase of agitation speed during the chemical cleaning process. Above all, we suggest the optimal operating condition is that in the case of no pressure, 0.5 wt % sodium hypochlorite with agitation speed of 400 rpm cleaning for 15 minutes.(2) For the cleaning process of the polysulfone membranes fouled by dust and oil, ① flux recovery increases with the increase of ultrasonic current during the ultrasonic cleaning process. ② flux recovery increases with the increase of cleaning time during the ultrasonic cleaning process. ③ within the range of experimental concentrations of alkali and acid, when the citric acid cleaning conditions is fixed, flux recovery rate increases with the increase of concentration of sodium hypochlorite and then decreases generally. And 0.3 wt% sodium hypochlorite shows the best cleaning efficiency. When sodium hypochlorite cleaning conditions is fixed, with the increase of the concentration of citric acid, the variation of flux recovery has no regularity. The effective recipe is 0.3 wt % sodium hypochlorite and 15 wt% citric acid. ④ The cleaning efficiency of alkali washing firstly and acid pickling secondly is better than that of acid pickling firstly and alkali washing secondly. ⑤ The cleaning efficiency of ultrasonic cleaning combined with chemical cleaning is better than that of ultrasonic cleaning and chemical cleaning. ⑥ flux recovery increases with the increase of temperature.(3) Based on Hom-Haas model, this paper presents a dynamic model of chemical cleaning. The proposed model describes the variation of flux recovery with the cleaning time and cleaning solution concentration in the chemical cleaning process. By theoretical analysis, the reasonability of model is confirmed and it is applied in the chemical cleaning process of fouled membrane in MBR. Mainly conclusions as follows:The model can accurately describe how the flux recovery varied with the cleaning time and concentration of Na Cl O during the chemical cleaning process. Intuitive comparison of the predicted values and the new experimental data is further proved the validity of the model. And the contribution of the influence of operating conditions on the model is calculated by multiple linear regression analysis. The results show that model parameters including m and n are influenced by both operating pressure and temperature. However, the rate constant k is influenced by agitation speed, operating pressure and temperature. The proposed model can accurately describe sodium hydroxide and sodium dodecyl sulfate cleaning processes. In addition, contribution of the influence of operating conditions on the model for Na OH and SDS cleaning processes are analyzed by multiple linear regressions.