Research On The Restoration Effect Of Three Kinds Of Aquatic Plants On The Repair Of Black And Odorous Water

In this study,two kinds of water bodies with different black and odorous grades were selected in Guimiao canal and shovel bay channel in Shenzhen city,and three aquatic plants were selected under the conditions of laboratory simulation,such as Canna indica?Eichhornia crassipes?Vallisneria natans.It was studied on the removal rate of important black-odor water pollutants indicators and the changes of rhizosphere microorganisms in the same black and odorous water,and the purification effect of hyacinth and its rhizosphere microorganism on different pollutant indexes in different black-odor water was investigated.Through the bacteriostasis and routine treatment,during the experimental period,the quantity of rhizobacteria,actinomycetes and fungi in the plants were tracked and monitored,to investigate the correlation between the number of microbes and the removal of pollutants,and to evaluate the synergistic decontamination ability of aquatic plants and their rhizosphere microorganisms at different eutrophication levels.The results were as follows:?1?Under the laboratory simulation conditions,three common aquatic plants,Canna indica?Eichhornia crassipes and Vallisneria natans,which have good engineering application experience,were used as experimental objects.The growth status of this three kinds of aquatic plants was studied,and the removal capacity and purification effect of dissolved oxygen,transparency,ammonia nitrogen and other monitoring indicators of black and odorous water bodies were investigated.The results showed that during the trial period,the dissolved oxygen in water increased from 2.1 mg/L to 5.8 mg/L,and the recovery effect of dissolved oxygen content by the three aquatic plants in water was as follows:Canna indica>Vallisneria natans>Eichhornia crassipes.For the transparency in the water,Canna indica and Eichhornia crassipes were able to restore the transparency to an ideal level compared with the initial value at the end of the experiment.The highest transparency of the Canna indica group was higher than 48%of the control group in the same period,that of the Eichhornia crassipes group was 52%higher than that of the control group in the same period,while that in the Vallisneria natans group was only 23%higher than that of the control group in the same period.Therefore,the effect of improving water transparency was as follows:Eichhornia crassipes>Canna indica>Vallisneria natans.And for the COD removal efficiency,at the end of the experiment,the COD removal efficiency of Canna indica?Eichhornia crassipes and Vallisneria natans reached 70%?43%and 61%respectively,so the removal efficiency of COD in water was Canna indica>Vallisneria natans>Eichhornia crassipes.Three kinds of aquatic plants could absorb ammonia nitrogen in water,compared with the initial value of experiment,the removal rates of ammonia nitrogen in the Canna indica?Eichhornia crassipes and Vallisneria natans group reached 88%,93%,65%and 40%,respectively.As for the redox potential in water,compared with the initial value,the lowest redox potential in each group during the experimental period decreased by 36?10 and 15 MV respectively,and among them,the Canna indica group could significantly increase the water redox potential value while compared with the other two groups.?2?The purification of black-odor water was mainly concentrated on the cultivation of aquatic plants with single ecotype and different configurations,but it was seldom reported that the combination of aquatic plants with different ecotypes,and the situation of microbes was similar.In this study,three kinds of aquatic plants in different ecotypes of mosaic were selected,the aquatic plants were as follows:submerged plant-Vallisneria natans,emergent aquatic plant-Canna indica,floating plant-Eichhornia crassipes.A combination of them was to study the purification of black and odorous water,the results showed that the collocation of Eichhornia crassipes and Vallisneria natans was more favorable to exert the advantage of isolated area,and the nutrient resources and light could be used reasonably in space.Therefore,in the application of combination plants,attention should be paid to the different niche of plants and reasonable arrangement of growth range.For the rhizosphere microbes of three aquatic plants,the change trend of actinomycetes was opposite to that of bacterial quantity,because the actinomycetes inhibited bacterial synthesis of cell wall.At the end of the experiment,the water quality was improved.And the total number of bacteria in the water was maintained at a lower level,therefore,it was indicated that the number of bacteria in water environment could indicate the degree of water pollution.?3?Under the same light and temperature conditions,choosing the Eichhornia crassipes as the research object,the effects of bacteriostasis and routine two different treatments on the removal of ammonia nitrogen,COD and DO under different levels of black-odor water were studied.The dynamics of rhizosphere bacteria,actinomycetes and fungi in the experimental period were analyzed,and the synergistic removal ability of pollutants by Eichhornia crassipes and its rhizosphere microorganisms were discussed.The results showed that the removal effect of ammonia nitrogen in mild black and odorous water was better than that in severe black and odorous water.During the test period,the removal rates of ammonia nitrogen in light black-odor water could reach 52%and 63%in Eichhornia crassipes routine group and bacteriostasis group,respectively.It can be seen that the removal of ammonia nitrogen in water by Eichhornia crassipes group is dominated by plants and supplemented by microorganisms.The removal rates of COD in the water body of Eichhornia crassipes routine group and bacteriostasis group were 65%and 38%,respectively.This also showed that the removal of organic matter in water by Eichhornia crassipes had close relationship with the rhizosphere microorganism.It can be seen that the removal of COD in water was mainly caused by the nitrification and denitrification of microorganism,and microbial growth and metabolism is the key to removing organic matter in water.What's more,the ability to improve DO content by the Eichhornia crassipes itselves in severe black-odor water was stronger than that in mild black-odor water,which was mainly related to the dormancy of most microorganisms in anoxic state.?4?To explore the effects of sedimentation plants on water quality in different water environments,the decomposition processes of Vallisneria natans were respectively investigated in the manipulated environment of high pure water,overlying water and sediment suspension under laboratory conditions.Moreover,the differences of N and P content between sediment and overlying water environment were discussed.The results showed that,during the decomposition process of V.natans,the pH value of the overlying water and sediment decreased first then increased,and the DO concentration was simultaneously sharply down.In the overlying water environment,the pH value increased to 8.7 after decreasing from 7.8 to 7.2 with about 56%reduction of DO concentration in the 10^th day compared with the beginning of the experiment.The pH value of the sediment suspension decreased from 7.8 to 7.3 and then rose to 8.3 with a decrease of 60%of DO concentration in the 10^th day.In the overlying water and sediment suspension,the nitrogen in the process of the decomposing of V.natans was mainly organic nitrogen,followed by ammonia nitrogen.The concentration of total phosphorus?TP?showed a trend of an initial increase followed by a decrease in the early stage of the experiment;nevertheless,the TP concentration showed a dynamic balancein the middle stage of the experiment,around 1 mg/L in thesediment suspension.In addition,variation of the biomass density of 0.1,0.2 and 0.4 g/L resulted in a change of nutrient content.The concentrations of COD_Cr and TP were positively correlated with biomass,while the concentrations of TN and NO^2--N increased along with the peak value in the early stage of the experiment.The results showed that decomposition of V.natans had a similar effect on the physicochemical properties of the two kinds of water environment,and there was a significant difference in the forms of nitrogen and phosphorus.