Purification Of Primary RO Effluent By Membrane-free Electrodeionization

High-purity water is widely used in thermal power generation,medicine,microelectronics and other industries.The core of high-purity water preparation is to remove soluble salts in water.Membrane-free electrodeionization(MFEDI)is a novel desalination technology with outstanding advantages such as no need for acid and alkali for regeneration,high desalination efficiency,low investment cost,and easy operation and maintenance.In previous research,MFEDI was mostly used as a deep desalination technology to treat dual pass reverse osmosis(RO-RO)effluent.In view of the high investment cost and complicated maintenance of reverse osmosis,This thesis used MFEDI as a pre-desalting technology to replace the secondary RO to treat the primary reverse osmosis effluent.In addition,based on the original MFEDI system,a current-water flow vertical MFEDI was designed for improving the regeneration efficiency.Major research works include three sections,they are,the selection of the anion resin and the ratio of anion and cation resin,the performance investigation of current-water flow parallel MFEDI,the performance investigation of current-water flow vertical MFEDI.The suitable anion resin and ratio of mixed resins for the treatment of primary RO effluent by the MFEDI system were selected.The results showed that the performance of strong-acid resin A was better,its regeneration performance was equivalent to that of strong-acid resin B resin,and the transformation expansion rate and resistivity of different ion types were smaller.1:1.2(weak-acid resin:strong-acid resin)was the best resin ratio,Under this ratio,he quality of the produced water was better,the regeneration voltage was lower,and the regeneration efficiency was higher.The performance of the current-water flow parallel MFEDI was investigated.The results showed that when the influent water conductivity was lower than 15μS/cm,the average conductivity of the effluent was lower than 2.0μS/cm,and the salt rejection rate was higher than 86.7%.The influence of various parameters was investigateed,and the opimum parameters were confiemed:processing velocity,regeneration current density,regeneration duration,regeneration velocity and regeneration temperature were60 m/h,150 A/m~2,20 min,40 m/h and 35℃,respectively.The system had been running continuously for 40 cycles without any deterioration in water quality,the energy consumption was 0.317 k Wh/m3,and the water recovery rate was 86.7%.Compared with the secondary RO,the current-water flow parallel MFEDI system had the same water recovery rate and lower energy consumption.The performance of the current-water flow vertical MFEDI was investigated.The results showed that when the influent conductivity was lower than 15μS/cm,the average conductivity of the effluent was lower than 1.6μS/cm,and the salt rejection rate was higher than 89.3%,which was better than the current-water flow parallel MFEDI.In a single operation cycle,the average conductivity of effluent,average regeneration voltage and average conductivity of concentrate were 1.584μS/cm,441 V and 113.3μS/cm,respectively.The optimal current density and regeneration velocity rate were100 A/m~2 and 40 m/h,respectively.The system had been running continuously for 20 cycles,due to the directional electromigration of ions,the conductivity of the produced water,the regeneration voltage,and the conductivity of concentrate all rose slightly in the last 11 cycles.The energy consumption and water recovery rate of the first 9 cycles were 0.311 k Wh/m3and 86.7%,respectively.It can be seen that the water recovery rate of this system was equal to that of the current-water flow parallel MFEDI system,and the energy consumption was lower.