Investigation On Separation And Purification High Salt And Ammonia Wastewater With Ultra Low Pressure And High Flux Nanofiltration Membrane

Preparation of polyelectrolyte multilayer films (MPFS) involves immersing asubstrate into the solutions containing a pair controlled alternating oppositely chargedpolyelectrolyte. In this process, the thickness of the polymer electrolyte membrane can beeasily controlled at the nanoscale, and the composition of the active layer and the chargedensity of the skin also can be flexibly changed, excellent performance NF membrane canbe prepared by LBL. For the nanofiltration membrane, the rejection rate of monovalentions is small, while divalent and valent ions’ rejection rate is high, which make the goal ofseparation of monovalent and divalent ions can be achieved.In this work, two polyelectrolyte, PSS and PDADMAC are selected as polyelectrolytefor multilayers Nanofiltration based on polysulfone ultrafiltration membrane through theelectrostatic layer-layer self-assembly process of preparation. The prepared NF membraneswere characterized by FE-SEM, AFM and Zeta potential, and the self-assemblymechanism of layer was also analyzed.In the preparation process, the static effects of deposition time, the molecular weightof cationic polyelectrolyte, and the concentration and types of the supporting electrolyte tomembrane performance were investigated. The results show that15minutes is a suitabledeposition time, the200,000Da molecular weight of cationic polyelectrolyte is appropriate,sodium chloride and magnesium chloride are the suitable supporting electrolyte and theoptimal concentration is0.5mol/L. FE-SEM and AFM showed the nanofiltrationmembrane’s surface is relatively uniform, no defects and the roughness is only26.798nm.The Zeta potential with the number of alternating layers also reflect the electrostaticlayer-layer self-assembly process. Under the best of circumstances,(PDADMAC/PSS)6NFmembrane repared by static process exhibites excellent performance, the rejection ofNa2SO4is90.6%and membrane flux is60.8L/m2h, the rejection of NaCl is about11% while the membrane flux is67.5L/m2h, indicating that the LBL NF membranes haveexcellent ion selectivity.The experiment is using LBL (PDADMAC/PSS)6nanofiltration membrane to rejectthe CO32-, NH4+and Cl-, the changes of the separation factor, recovery rate and flux feedwith different operating pressures and feed concentrations are studied in the experiment,the raw material solution includes sodium chloride:10g/L, sodium carbonate specifications:20g/L and NH4Cl:10g/L. Experimental results show that the feed concentration andoperating pressure on the performance of nanofiltration membranes have a greater impact.Ion separation factor, flux and recovery rate increase with the increasing operating pressureand lower feed concentration. Experimental results’ effect of feed flow, by changing theflow conditions near the surface of the membrane and the concentration polarization,which is less significant impact than the other factors. Under the optimal conditions, theseparation factors of CO32-/Cl-and NH4+/Cl-are64.8and23. Thus, separation andpurification and recovery of ammonia from the laboratory preparation of high salt water by(PDADMAC/PSS)6nanofiltration are feasible to achieve.