Research On Pollutant Removal And Influencing Factors Of Vertical Subsurface Wetlands With Different Matrix Combinations

At present,due to the extensive application of antibiotic-added feeds and fish medicines in the aquaculture industry,high levels of antibiotics remain in the tail water discharged from aquaculture.As an eco-friendly water treatment process,vertical submerged wetlands have a good removal effect on water nutrient salts,but less research on the removal effects of emerging pollutants,especially under different nitrogen and phosphorus loads,undercurrent wetland systems with different matrix fillers Few studies have been reported on the removal of antibiotics from water bodies.In this study,three small artificial subsurface wetland experimental systems（three parallels in each group）were designed with zeolite（CW-Z）,zeolite+bioceramsite（CW-B）and zeolite+volcanic rock（CW-V）as matrix fillers.Using artificial sewage,under three different nitrogen and phosphorus loads（TN\TP=3mg/L\0.5mg/L,10mg/L\2.5mg/L and 20mg/L\5mg/L）,（1）to study its Removal effects of nutrients and antibiotics（sulfadiazine SDZ and norfloxacin NFX）under different water retention time HRT,（2）removal effects of vertical submerged wetlands with different matrix combinations on nutrients and antibiotics under different pollution load conditions;（3）Influence of environmental factors（antibiotics and physicochemical factors）on microbial composition in substrates and plant roots,（4）Monitoring and evaluation of the removal effect of aquaculture tail water constructed wetland purification project on nutrients and antibiotics.The main findings are as follows:This part of the research provides basic data for the design of hydraulic loads in subsurface wetlands while removing nutrients and antibiotics from water bodies.（1）Longer hydraulic retention time of vertical flow constructed wetlands will reduce the treatment efficiency and treatment capacity of the wetlands;under various nitrogen and phosphorus loading conditions,the removal effects of total nitrogen,total phosphorus,organic matter and antibiotics increased first with the increase of HRT.When the HRT is 72h,the removal effect of pollutants is the best;the removal effect of volcanic rocks on nitrogen has no downward trend with the increase of HRT.（2）Under different pollution loads,there were significant differences in the removal effects of sulfadiazine SDZ（average removal efficiency>60%）and norfloxacin NFX（average removal efficiency>90%）among the three filler treatment groups（p<0.05）.),CW-B has a good removal effect on SDZ and NFX,and the removal rate is as high as 90%;the average removal effect of CW-Z and CW-V on compound antibiotics is 70%and 50%,respectively;In addition,in the three Under different pollution loads,CW-B has a higher removal rate for TP（51.99%～93.84%）and COD（84.96%～95.01%）,and CW-V has a higher removal rate for TN（average68.26%～91.32%）.%);the removal rate of NH₄⁺-N by the three wetland systems did not change significantly with the increase of pollution load,and the nitrate nitrogen（NO₃-N）content of CW-B effluent was significantly higher than that of CW-Z and CW-V.The comprehensive performance of zeolite is good,the biological ceramsite+zeolite group can efficiently remove phosphorus and compound antibiotics in the water body,and the volcanic rock+zeolite group can effectively remove the nitrogen in the water body.（3）With the increase of nutrient load,the removal effect of VFCW on SDZ showed a downward trend,and the removal effect of NFX had no obvious trend of change,but the biological ceramsite group always maintained a high removal efficiency.There is no significant correlation between the removal rate of antibiotics and the removal rate of antibiotics.The removal effect of low pollution load is the best,but higher pollution load will reduce the removal effect of antibiotics;with the increase of pollution load,the removal effect of TN,TP and COD showed an upward trend.（4）Under the same nutrient load,there were significant differences in the composition of microbial communities in the rhizosphere of different filler wetland plants（P>0.05）,and there were differences in the composition of microbial communities attached to the rhizosphere surface of different fillers and substrate surfaces,and the number of microbial communities attached to the substrate surface was significant higher than rhizosphere surface microorganisms.When the HRT is 72H,it runs stably for two months.The main dominant phyla in wetland plant roots are Cyanobacteria,Proteobacteria,Actinobacteriota,Firmicutes,Bacteroidota,etc.The main dominant phyla of plant roots and substrate surface microorganisms are Proteobacteria,Actinobacteriota Bacteria,Chloroflexi Aspergillus aeruginosa,Patescibacteria Pasteurella,Acidobacteriota Acidobacter,etc.The genera that were negatively correlated with antibiotics on the inner and outer surfaces of plant roots were Pseudomonas,Comamonas and Acinetobacter.Under each pollution load,the number and abundance of OUT on the matrix surface of the bioceramsite+zeolite group were the highest.It is speculated that the removal effect of antibiotics is better because the main dominant species Thauera is desulfurization bacteria,which are involved in the degradation and degradation of antibiotics.transform.In addition,the higher content of DO and p H in this group is also one of the reasons for the better removal effect of antibiotics.（5）The complex constructed wetland project uses aquaculture tail water purification and treatment.The concentration of conventional pollutants at the wetland outlet can reach the national surface water class IV standard（GB3838-2002）.The removal of TN,COD,NH₃-N and TP increases with the The increase of pollution load shows an increasing trend.The reduction of conventional pollutants mainly relies on sedimentation tanks and subsurface wetland modules,with an average reduction of 23.6%and 29.8%,respectively.The removal effect of VFCW was significantly better than that of IFCW;the removal of antibiotics mainly depended on removable metal-loaded wetland modules（57.4%）and vertical subsurface wetlands（24.6%）.VFCW can be used as the main body of the composite constructed wetland in the subsequent construction of water bodies containing new pollutants.