| With the rapid development of economy,large amounts of wastewater from industries,agriculture and domestic sewage are discharged into water bodies,which leads to the decrease of aquatic environment quality and causes water pollution.Nowadays,serious water pollution has become a significant problem in the water resources in China.Saline wastewater(referred to many inorganic salts are included),originating from various sources and containing complxed contaminants,can’t be ignored due to its destroying of aquatic,terrestrial and wetland ecosystems.Therefore,it’s an urgent task to treat saline wastewater.Constructed wetlands(CWs)are a potential alternative technology to treat saline wastewater,owing to their high efficiencies,low investments,wide ranges of applications and aesthetic value.In the present research,we focus on the treatment of saline wastewater,and the potential use of CWs in the removal of typical pollutants(nutrients including nitrogen and phosphorus,sulfamethoxazole,various heavy metals including copper,zinc,cadmium,lead and chromium)was evaluated by using simulated experiments.Salt-tolerant wetland plant species were selected,the effects of different pollutant loads,wetland plant species,salinity levels and configurations on the performances of CWs were investigated,the removal efficiencies of pollutants in CWs when multiple contaminants were co-existed and when each respective contaminant was existed in isolation were compared,and the relationships between salts and pollutants in plant assimilation process were revealed.The main conclusions are as follows:(1)Six tested wetland plant species(Phragmites australis,Scirpus validus,Vetiveria zizanioides,Typha orientalis,Canna indica and Iris wilsonii)showed various physiological responses to different salt stress in hydroponic solution.Among the tested species,Phragmites australis,Vetiveria zizanioides,Typha orientalis and Canna Indica showed relatively strong ability of salt tolerance and were selected to be applied in the construction of CWs.Tissue concentrations of K and Na in the selected wetland plant species were different and the values of K/Na ratios generally decreased with the increasing salinity levels.(2)There were no significant differences among CWs with different plant species in the removal of phosphorus and various heavy metals.However,CWs planted with Canna indica outperformed all the other CWs in the removal of nitrogen.Considering the removal efficiencies(e.g.,nitrogen removal),biomass,physiological characters under heavy metal stress and aesthetic value,Canna indica was selected as potential plant species in CWs for treating saline wastewater containing either nutrients,heavy metals or sulfamethoxazole,respectively,or a multiple co-existing contaminants.(3)The removal efficiencies of nitrogen,sulfamethoxazole and heavy metals(except for lead)were lower when these pollutants co-exist in the same influent water,as compared to the condition that they exist in isolation.This observation might result from the mutual influences among the three types of pollutants,as well as the influence of their degradation product on the physico-chemical characters and microorganisms in CWs.(4)High salinity level(EC=30 mS/cm)could affect microbial activities and further affect the degradation of nitrogen and sulfamethoxazole in CWs.Simultaneously,salt could also influence the photo-catalytic process of sulfamethoxazole in CWs.However,there were no significant changes observed in the removal of phosphorus and heavy metals(except for cadmium)with the increasing salinity levels.(5)The assimilation of pollutants(nutrients and heavy metals)into plants varied with the salinity levels,as well as the species and concentrations of pollutants.The addition of a proporiate amount of nutrients could improve the salt-tolerance ability of plant.(6)Significant differences in the removal of various pollutants were observed in CWs with different configuration.Generally,horizontal subsurface CWs outperformed the other mesocosms for treating saline wastewater containing nutrients,heavy metals and sulfamethoxazole. |
