Experimental Study On Seperation Of Antibiotics And Concentration Of Alginate By Forward Osmosis

Forward osmosis?FO?has attracted wide attention recently due to low energy consumption,low membrane fouling and high efficiency.For removing trace antibiotics from wastewater and concentrating extracellular polymer substance?EPS?from excess sludge,this study focused on the new application field of FO membrane separation.By literature researches,the research direction of FO application was obtained,and then this study focuses on the synchronous separation of multiple antibiotics,and the dewatering of high-value products?aginate?in FO.The separation behaviors of four tipical antibiotics ciprofloxacin?CIP?,sulfamethoxazole?SMX?,acetaminophen?ACP?,carbamazepine?CBZ?during FO were investigated at trace concentrations using ultra-high performance liquid chromatography-tandem mass spectrometry?UPLC-MS/MS?.The results showed that for single pharmaceuticals,the molecular sieve dominates their retention rate—the retention rate increases with increasing Stokes radius of the molecules?29.1?94.8%for 0.35?0.47 nm?.For binary pharmaceuticals,the retention rates of both pharmaceuticals without charge decrease with increasing total molecule number?for ACP+CBZ,31.4?52.1%?ACP?,75.1?83.0%?CBZ??.Negatively charged pharmaceuticals are mutually exclusive with the negatively charged FO membrane,resulting in the increase of the retention rate of pharmaceuticals?83.1?90.1%?CIP?when CIP+ACP?CIP+SMX?.In the presence of a positively charged pharmaceutical,the retention rate of negatively charged pharmaceuticals decreases?85.7?80.4%?SMX?when SMX+ACP?SMX+CIP?because the positively charged pharmaceutical neutralizes the negative charge on the FO membrane surface,resulting in the weakening of electrostatic repulsion between the negatively charged pharmaceutical and FO membrane surface.The positively charged molecule attracts the negatively charged molecule,forming a couple of molecules with larger molecule weight and increasing the retention rate of the pharmaceuticals?80.4?88.2%?SMX?when pH=7?5 for SMX+CIP?.The results suggest that the interactions between pharmaceuticals cannot be ignored in the process of removing PPCPs by FO.Taking sodium alginate?SA?as the model EPS,the FO separation and concentration behaviors were investigated experimentally.The FO concentration experiments of alginate were carried out with the draw solution of CaCl₂.The filter cake layer was formed by reverse osmotic calcium ions in the draw solution and SA in feed side of FO and the flux decline deceased,because alginate can form egg-box structure with calcium ions.Therefore,choosing the appropriate draw solution in FO concentration process can alleviate the membrane fouling and realize alginate concentration recovery.To further explore the concentration characteristics of FO,NaCl was used as the draw solution.The results showed that the effect of the concentrated external concentration polarization?ECP?in FO process is greater than the diluted ECP.The overall water flux of the membrane toward the feed solution is higher than that toward the draw solution.The water flux increased significantly when the NaCl concentration rised from 1M to 2M,while little change from 2M to 3M,because membrane fouling and other factors have more influence on the water flux than the osmotic pressure.The concentration and viscosity of SA had little effect on the water flux.