Research On Removalefficiency Andmechanism Of Organic Pharmaceuticals In Iron And Manganese Ore Constructed Wetlands

Along with large use of pharmaceutical, the pollution problem of organicpharmaceutical is increasingly outstanding and its impact on environment has beenwidely concerned. As an energy-saving and environment-friendly technology,constructed wetland is applied more and more in the field of wastewater treatment.Owing to high oxidation state of iron and manganese elements, iron and manganeseores have showed a huge potential in the treatment of pharmaceutical wastewater. As animportant role in physical geochemistry cycle, dissimilatory metal reduction inanaerobic environment has also gradually been applied in the field of bioremediation. Inthis research, carbamazepine(CBZ) and diclofenac(DCF) were selected asrepresentatives of organic pharmaceutical, their removal efficiency were researched inconstructed wetlands, which were combined with iron and manganese ores as well asdissimilatory metal reduction bacteria. Besides, the removal mechanism of DCF inmanganese ore wetland was also further explored. The research was expected to providea new method and theoreticaldirection for the deep treatment of organic pharmaceuticalwastewater.The experiment consisted of four stages: stage one, the removal efficiency of CBZwas researched in iron and manganese ore wetland; stage two, after adding ferric citrateand manganese dioxide to iron and manganese ore wetland, respectively, the removalefficiency of CBZ was researched; stage three, after inoculating both wetlands withdissimilatory metal reduction bacteria（Geobacter metallireducens）, the removalefficiency of CBZ was researched; stage four, after adding DCF to influent andinoculating both wetlands with Geobacter metallireducens, the removal efficiencies ofCBZ and DCF were researched, and the removal efficiency of DCF was also researchedin manganese ore wetland device with only manganese ore, as compared with stage four.At last the removal mechanism of DCF in manganese ore wetland was explored.The key results and conclusions were as follows:①CBZ was hard to be degraded, the removal efficiency of CBZ in iron orewetland was a little higher than that in manganese ore wetland. In the four stages, thehighest average removal efficiency of CBZ in iron ore wetland was9.72%, while it wasonly1.05%in manganese ore wetland. Besides, the effect of bacteria on the removal ofCBZ in iron ore wetland was not remarkable, and there was no remarkable difference of the removal efficiency of CBZ in every segment of iron ore wetland.②DCF was easier to be degraded when compared to CBZ, and manganese orewetland showed a remarkably higher removal efficiency of DCF than iron ore wetland.In the fourth stage, the average removal efficiency of DCF reached to23.56%, and inthe segment of0-420mm along the depth of manganese ore wetland, DCF was largelyremoved, its removal efficiency accounted for84%of the total, the main function wasdissimilatory metal reduction of bacteria.③DCF was oxidated to three main products in manganese ore wetland, namely5-hydroxydiclofenac(5OH-DCF),diclofenac-2,5-iminoquinone(DCF-2,5-IQ) and1,3-dichlorobenzene(1,3-DCB).1,3-DCB was a newfound degradation product of DCF, itstoxicity was larger than that of DCF, it waseasily evaporated into air and very harmfulto aquatic organisms and human beings, so this kind of substance should be concerned.④The removal mechanism of DCF in manganese ore wetland was that: DCF wasfirstly adsorbed on the surface of manganese ore, and then the phenylethanoic acid ringwas hydroxylated with the function of dissimilatory metal reduction of bacteria,resulting in the formation of5OH-DCF, the5-hydroxy group of5OH-DCF was thenoxidated, and the hydrogen connected to nitrogen was laid off after dehydrogenation,leading to the formation of DCF-2,5-IQ, the bond of C-N in the benzene with Cl inDCF-2,5-IQ broke down, and was dehydrogenized to the product of1,3-DCB and2-(6-imino-3-carbonyl-1,4-cyclohexadienyl)-acetic acid.1,3-DCB was stable andexisted in environment for a long time, while2-(6-imino-3-carbonyl-1,4–cyclohexadienyl)-acetic acid was not so stable that it was easily to be oxidated andmineralized to other substances. The research result that DCF-2,5-IQ could be furtherdegraded was a new discover, it was expected to provide a guidance for the deeptreatment of organic pharmaceutical wastewater in a certain extent.