Characteristics And Mechanism Of Wastewater Reclamation Of A Capacitive Deionization Enhanced Ultrafiltration System

Conventional ultrafiltration?UF?technology suffers from membrane fouling and limited separation performance,thus difficult to fulfill the increasingly stringent requirement of sustainable development in the wastewater reclamation area.The current study proposed a novel capacitive deionization?CDI?enhanced UF?CUF?water purification technology through combining the advantageous characteristics of the electric-based antifouling and CDI techniques,aiming at developing an intensive wastewater reclamation technology with low energy consumption and high treatment efficiency.On the basis of different electrode materials,the synergistic water purification behavior of the CUF process in terms of fouling inhibition,foulant retention,and desalination was systematically invetigated.The specific purification and operation mechanisms of the CUF process were also analyzed.A CUF system was first established on the basis of the carbon fiber electrodes and polyvinylidene fluoride membranes.The series of multi-cycle water purification tests demonstrated that the applied electrical power brought about an up to 68%reduction of average transmembrane pressure?TMP?increasing rate,indicating a strong capability in inhibiting membrane fouling.This fouling reduction can be mainly ascribed to the applied electrophoretic force and changes in solution chemistry,which repulses foulants away from the membrane and hampers foulant adsorption owing to enhanced electrostatic repulsion,respectively.The 1.2 V voltage was identified as an effective voltage for stably inhibiting membrane fouling.Owing to the electrophoretic repulsion and/or electrosorption effect,the applied electrical power led to an up to?32%increase in foulant retention rate as compared the control?0 V?operation.Moreover,the CUF system achieved a conspicuously enhanced desalination capability with a significantly higher desalination rate and an up to?43%greater maximum salt adsorption capacity?m SAC?as compared with the control CDI system.This could be ascribed to the foulant retention and dielectric property of the UF membranes Additionally,the CUF system achieved a good performance in removing heavy metals?Ag,Cu,Pb,Se,Sb?.To improve the desalination performance of the CUF electrodes,a novel super-aligned carbon nanotube?SACNT?/activated carbon?AC?composite electrode was prepared by coating AC on a cross-stacked SACNT film.In the CDI tests,as compared with the control AC electrode,the SACNT/AC electrode achieved an approximately 100%increase in both m SAC and average salt adsorption rate.The CUF tests revealed that the treatment runs at 0.8,1.0,and 1.2 V achieved a 2.40-fold,2.08-fold,and 2.43-fold reduction in membrane fouling?calculated according to the final TMP data at the end of every purification stage?,respectively.The CUF system also maintained its good foulant retention and desalination capability,resulting in an overall improved water purification efficiency.With model organic foulants and typical inorganic salts,the cooperative operation mechanism of the CUF process was systematically investigated.The results revealed that the water purification performance of the CUF process is related to the charge properties of the foulants in the salt solution.The presence of inorganic ions influenced the internal resistance of the CUF system and brought about competition with foulants for adsorption sites on the electrode surface,thereby affecting the treatment performance of fouling inhibition and foulant retention.The presence of organic matter could facilitate the removal of Ca²⁺via complexation interaction.But the formation of large complexes might will increase membrane fouling.Comprehensive regulation is needed according to the specific characteristics of the influent.