Study On The Coupling Mechanism Of Plant-microorganism In The Treatment Of Saline Wastewater By Constructed Wetland

Constructed wetlands(CWs)with halo-resistant halophytes and microorganisms are moderately salinity tolerant and possess a huge application potential in saline wastewater treatment.However,current studies of its salt tolerance merely cover the botanical and microbiological roles in removal mechanism,and the removal efficiency cannot be stably controlled.Therefore,CWs have not been applied extensively in saline wastewater treatment yet.In this study,the effects of salt stress on typical wetland plants and microorganisms under different salt concentrations and treatment time were studied,and the response rules of plants and microorganisms to salt stress were revealed in the treatment of saline wastewater in constructed wetland.Using intertidal wetland sediments as the matrix,the coupling effect between plants and microorganisms under salt stress was studied,the biological response pathway of constructed wetland system under salt stress was analyzed,and the mechanism of treatment of saline wastewater by constructed wetland was clarified.It provides a theoretical basis for the technological optimization of the purification function of constructed wetland.In this paper,the sediment of intertidal zone is sampled in the central area of the Yellow River delta in Shandong province,China.Samples were collected at four different depths of 0-5 cm,5-10 cm,10-15 cm and 15-20 cm by five-point method,respectively,and their microbial communities were analyzed,so as to select the appropriate depth of intertidal sediment to be added into the constructed wetland system for microbial inoculation.The intertidal sediment was inoculated into the constructed wetland experiment system,and the constructed wetland system was established by taking typical wetland plant reed as the research object.The removal effect of pollutants from sewage,the response of plants to salt stress,the response of microorganisms to salt stress and the coupling effect of both sides were studied.The following conclusions are drawn:1)In the intertidal sediment of the Yellow River delta,the diversity of soil microbial community at a depth of 0-5 cm is significantly lower than that at other depths.The soil microbial diversity is most abundant at a depth of 5-10 cm,and decreases with the increase of soil depth.This may be related to the concentration of oxygen and organic matter in the soil.At the phylum level,Cyanobacteria was the dominant species in 0-5 cm of soil samples,Proteobacteria was the dominant species in 5-10 cm and 10-20 cm of soil,and acidobacteria was the dominant species in 15-20 cm of soil.In addition,with the increase of soil depth,the proportion in soil increased.There are abundant halophilic bacteria in each soil layer,and there are different dominant bacteria in different soil layers.The 0-5 cm layer is mostly aerobic bacteria,which can participate in photosynthesis.A large number of microorganisms related to organic matter removal were found in the 5-10 cm layer.In 10-20 cm,most anaerobic bacteria were denitrified and dephosphorized.The differences of soil depth flora are related to the adaptability of soil environment and microorganism.Therefore,the selection of suitable intertidal sediment of the Yellow River delta to be added into the constructed wetland system will provide the possibility for improving the purification effect of the constructed wetland on the treatment of saline wastewater.2)The removal rate of ammonia nitrogen in sewage was higher than 80% in constructed wetland systems with different salt concentrations,and there was no significant difference.The removal efficiency of COD in different wetland systems was significantly different.At a high salt concentration of 150 mM/L,the removal rate of COD in the wetland system with intertidal sediment was significantly higher(51.8%)than that in the ordinary wetland system(27.4%).In addition,salt stress significantly reduced the pollutant removal effect of constructed wetland system.The addition of sediment in intertidal zone is beneficial to the enhancement of pollutant removal effect due to the introduction of salt-tolerant microorganisms.3)Some microorganisms in the intertidal sediment can produce GA,resulting in high content of GA3 in the root.In addition,the plant antioxidant enzyme system effectively reduces the damage caused by salt stress,and the reed actively reduces the endogenous GA3 level to resist salt stress in the stages of adapting to salt stress and heading,leading to the accumulation of DELLAs protein and the protective mechanism of inhibiting plant growth.This indicates that the presence of sediment in intertidal zone is beneficial for plants to complete the whole physiological cycle,alleviate the damage caused by salt stress,and improve the salinity tolerance of plants.4)Chloroflexi phylum,especially the Anaerolineaceae family,plays an important role in the anaerobic degradation of hydrocarbons in constructed wetlands with intertidal sediment.The dominant Anaerolineaceae family may be involved in methanogenic degradation of organic matter in symbiotic cooperation with archaea.With the increase of salt concentration,a large number of Anaerolineaceae families were induced and accumulated in the intertidal sediment,which is crucial to the enhancement of COD removal in the constructed wetland system under high salt stress.5)During the treatment of saline wastewater in constructed wetlands,plants can selectively accumulate beneficial microbiota around the rhizosphere through relevant signaling pathways and change the characteristics of soil microbial activities.The inoculation of intertidal sediment introduced a large number of halophiles,which gathered in the rhizosphere and were conducive to the degradation of pollutants.The microorganisms in the intertidal sediment modified by sea water formed the corresponding salt tolerance mechanism and regulated the level of osmotic pressure of cells to resist salt stress.Therefore,the addition of intertidal sediment in the constructed wetland system can introduce the acclimated halophilic bacteria,which can tolerate the salty wastewater and thus improve the sewage treatment effect.