Study On Ultrafiltration Process For Luan River Water Treatment

Due to the shortage of water resource, the deterioration of water environment, the enhancement of drinking water quality standards and the limitations of traditional drinking water treatment processes, it has been a great subject that new water treatment technologies were explored to improve or replace traditional treatment processes in the area of drinking water treatment. Membrane technology is known as "water treatment technologies in the 21st century", particularly the concern caused by water treatment workers.Ultrafiltration membrane process was tested for treatment of Tjanjin Luan River micro-polluted raw water. The pollutant removal characteristics and operating economics of the pressured membrane system and the submerged membrane system for treatment of Luan river water were studied. The two systems were evaluated comprehensively by using of fuzzy comprehensive Evaluation Method.The characteristics in relative molecular weight of the submerged membrane system on the removal of organic matter were investigated.The prediction model between effluent quality and membrane fouling of the immersed membrane system was established by using of BP artificial neural network. The effects of influent quality, membrane fouling and membrane integrity on the stability of submerged membrane system were analyzed in the periods of low temperature and low turbidity period and the period of high temperature and high amount of algae. In order to improve water production rate of UF system, Coagulation/PAC adsorption/immersed membrane was tested for treatment of inside-out UF membrane backwash water. The process design characteristics, the operation management and process design experience of the demonstration project, as well as the problems of ultrafiltration membrane technology in municipal water supply industry application were discussed.The results and conclusions were as follows: (1) The pollutant removal characteristics and operating economics of the pressured membrane system and the submerged membrane system for treatment of Luan river water were studied contrastingly in the same water conditions. The results showed that pressured membrane system and immersed membrane system showed operation stability in setting operating conditions. By two systems, the removals of organic matter were 41.6% and 36.5% respectively. The two systems had shown a great advantage comparision with conventional water treatment process in turbidity removal, and the mean effluent turbidity was respectively 0.07NTU and 0.08NTU. The water production rate of the pressured membrane system and immersed membrane system were 89.6% and 91.4% respectively, the operating costs were 0.136 yuan/m3 and 0.122 yuan/m3 respectively. Pressured membrane system and immersed membrane system were made a comprehensive evaluation from the technical performance, economic performance and environmental performance by Fuzzy comprehensive evaluation method. From the initial evaluation results, the pressured membrane system showed better environmental performance; while immersed membrane system showed better economic performance.From the comprehensive evaluation results, immersed membrane system demonstrated superior overall performance.(2) The molecular weight distribution of organic matter in the different period of Luan River water quality was analyzed. The characteristics of the relative molecular weight of organic matter removal from the immersed membrane systems were studied. The results showed that the organic matters in Luan River raw water were mainly composed of the small molecules with MW less than lkDa during the different water quality periods, in which the proportion of the total organic matter was the mininum in the periods of low temperature and low turbidity, while the maximum in the periods of high temperature and high amount of algae. It was found that the THMFP/DOC was the maximum on the organic molecular weight range of 3k-1k, and followed by molecular weight range of 10k-3k. Thus increasing the removal rate of small-molecule organic compounds helps reduce the risks of producing THMs. The organic removal efficiency of Al salt coagulants was significantly better than Fe salt coagulants, especially for the organic matter with MW 30k was best.(3) The prediction model between effluent quality and membrane fouling of the immersed membrane system was established by using of BP artificial neural network.BP artificial neural network prediction model which was trained had good simulation accuracy.The correlation coefficient R of the effluent COD, effluent turbidity and TMP were greater than 0.8. The simulation results and experimental results showed a good correlation.The RMSE of the effluent COD, effluent turbidity and TMP were 0.0083,0.0009 and 0.4617 respectively, which indicated unapparent discrete trend of the simulated values and experimental values series.The predicition performance of the models was tested for using test samples. It was found that the average relative deviation of predicted values and experimental values of the effluent COD, effluent turbidity and TMP were 4.63%,9.32% and 8.08% respectively. It showed that the BP artificial neural network prediction model built had a high prediction performance.(4) The system operating parameters was optimized by using BP artificial neural network model and orthogonal design. The optimization results showed that the optimal operating parameters(membrane flux, membrane filtration cycle, coagulant dosage, backwashing time, backwashing water flux, coagulation reaction time, backwashing air flux) were 53.3L/m2.h,30min,4mg/L,80s,15m3/h,6min,7m3/h respectively.(5) The organic matter and turbidity of the submerged membrane effluent remained relatively stable in the period of low temperature and low turbidity, but the higher initial TMP caused by the situations which were water temperature below 5℃and constant flux affected the normal operation of the system. Increasing the coagulant dosage can not effectively improve the membrane fouling. Decreasing membrane flux properly can effectively reduce the initial TMP, thereby easing the fouling of membrane system. High algae raw water will not only affect the membrane system's effulent quality, but also cause the serious membrane fouling. Pre-chlorination processes increased could not only improve the organic matter removal, but also play a certain improvement to membrane filtration performance.Air-water backwashing can mitigate membrane fouling, but it does not make TMP fully recovered. Periodic EFM can timely recover the membrane performance. It was found by analyzing the composition of chemical cleaning waste liquid that organic was the main material causing membrane fouling, while the deposition of inorganic elements such as Fe salt in the membrane surface can not be ignored.(6) The concentration of organic matter in membrane backwash water was relatively high. The molecular weight of DOC in membrane backwash water was mainly more than 30ku and less than lku. The average permeate turbidity was 0.07 NTU. The average removal efficiency of CODMn was 50.7% and the average permeate CODMn was 2.81mg/L under the conditions of 15mg/L FeCl3 and 15mg/L PAC. Microcystin levels and pH were lower than the water quality requirements of "Sanitary standard for drinking water". Practice has proved that Coagulation-UF short flowsheet process is feasible. The ultrafiltration membrane technology is the optimum choice to improve or replace traditional treatment process.