Study On Enhancement Of Estrogen Removal In Constructed Wetland By Modifying Micro-Environment Of Root Zone

Steroidal estrogens (SEs) have been found to pose a threat to human’s and animals’ health, even at an extremely low level. Only few research were about using constructed wetland to remove SEs. This paper studied removal of estrone (El) and 17a-ethinylestradiol (EE2) in wetlands through modifying micro-environment of root zone, and determined the influence of root exudates, wetland plant species and electrochemical action on SEs removal.The first part of research is about the composition of root exudates and root extracts from Canna and Phragmites. The main results are as follows. Phragmites can produce much more root exudates than Canna, and there are more amino acid (including DL-citrulline and L-arginine) and polysaccharose in root exudates and root extracts from Phragmites; Secondary metabolites including alkaloid exist in root exudates from both kinds of plants; Extra root extracts would be added in wetlands to simulate the increase of concentration of root exudates, because the main composition of root extracts is similar to that of root exudates.In order to determine the influence of root exudates in root zone, the second part of research is to compare the removal efficiency and pathway of pollutants (including SEs) in wetlands. Root extracts at different concentrations were added into wetlands (c(MD)=0mg/L, c(MZ)=14mg/L, c(MG)=28mg/L). The main results are as follows. Before the gravels reach adsorption saturation, competitive adsorption is the main removal pathway of El and EE2. And EE2 has a much higher adsorption rate than E1. When added root extracts with a proper concentration to simulate the increase of concentration of root exudates, wetlands have higher removal efficiency of E1, EE2, TOC, TN and TP than regular wetlands. The highest removal rate of E1 and EE2 in MZ is 88.2% and 72.6%. Ammonium monooxygenase or nonspecific degrading enzyme may facilitate the degradation of estrogens. The dehydrogenase activity value is in sequence of MZ> MG> MD, which means that addition of exudates may increase the dehydrogenase activity or decrease it if the concentration is too high.In order to determine the influence of plant species in root zone, the second part also compares the removal efficiency and pathway of pollutants (including SEs) in wetlands planted Canna and Phragmites. The main results are as follows. The removal efficiency of E1 is easier to be affected by plant species than that of EE2, because more abundant root exudates bring more microorganisms and E1 is easier to be degraded by heterotrophic bacteria. There are much more bacteria in LZ than MZ. LZ has more AOB (Ammonia Oxidizing Bacteria) than MZ, because LZ excretes more nitrogenous organic small-molecule compounds. The amount of NOB in LZ is about twice that in MZ, because pH of root exudates of Phragmites is nearly neutral, which is more suitable for the growth of nitrobacterium. SEs removal rate is positively related to nitrifying capacity. The dehydrogenase activity of biological membrane on gravels in LZ is higher than that in MZ, because root exudates of Canna are acidic, which is not suitable for dehydrogenase.In order to determine the influence of bioelectrochemistry in root zone, the last part of research is about to compare the removal efficiency and pathway of pollutants (including SEs), as well as electricity generation performances, in Constructed Wetland-Microbial Fuel Cells with plants (MFCW1) or without plants (MFCW2). The main results are as follows. The removal efficiency of E1 and EE2 in MFCW1 and MFCW2 remains higher than 80%, which is significantly higher than that in constructed wetland MD, because SEs can be easily adsorbed on gravels, activated charcoal particles and activated sludge on anode. The removal efficiency of TOC, TN, and TP in MFCWs (Microbial Fuel Cell-Wetlands) is higher than that in MD, because the enhancement of membrane permeability and catalytic performance facilitates the use of nutrient substances. O2 secration of roots boosts the concentration of O2 in cathode zone, consequently, MFCWl has a higher cathode potential than MFCW2. The removal efficiency of SEs, TOC, TN, and TP in MFCWl is slightly higher than that in MFCW2, because plants can absorb or adsorb pollutants, and root exudates facilitates the reproduction and activity of microorganisms. The density of bacteria on cathodes in MFC Ws is similar to that in MD, but density of bacteria on anodes in MFCWs is twice that in MD. There are abundant G. sulfurreducens and BetaProteobacleria in MFCWs, which means MFCWs have high electricity generation performance.