Study On The Remediation Of Eutrophic Water By Aquatic Plants And Their Biochars

In recent years,people’s unreasonable production and life have caused excessive nitrogen and phosphorus nutrients to flow into natural waters,making the eutrophication of water bodies more severe.This has become a current global environmental problem.With the continuous expansion of exploration and research,many scholars have found that aquatic phytoremediation technology has the characteristics of simple and easy operation,low treatment cost,good purification effect,low energy consumption and small impact on the environment.It is a more ecological friendly means of environmental governance.However,if the aquatic plants can not be cut and harvested in time,as the dead branches and fallen leaves of plants enter the water body,it will cause the re-release of pollutants in the plant itself,affecting the purification effect of the water body,and also have the harm of secondary pollution.Therefore,it is particularly important to cut and harvest plants in time and deal with plant residues scientifically.At present,the harvested aquatic plants are mainly used in animal feed and raw materials for the production of biogas,bioethanol,biomass carbon,etc.Among them,due to its unique surface characteristics,biomass carbon can effectively adsorb and remove various pollutants in water.It plays an important role in agriculture,environmental protection,energy and other fields.Therefore,in this study,we selected four aquatic plants with better purification ability,such as Pistia stratiotes,Myriophyllum verticillatum L.,water hyacinth and duckweed.Through outdoor static experiments,the purification effect of four plants on simulated eutrophic water was studied.On the basis of this,the newly-adopted floating plant barley was selected as the biomass raw material and the activating agent such as H₂SO₄,KOH and Mg Cl₂were used to prepare the corresponding modified biomass charcoal.The adsorption and purification effect of ammonia nitrogen（NH₄⁺）,nitrate nitrogen（NO₃^-）,total phosphorus（TP）in the water body was studied,and a series of more in-depth discussions on their influencing factors and adsorption mechanism were further developed.First,H₂SO₄,KOH,and Mg Cl₂were respectively used to activate biomass raw materials.The different plant biomass carbons were prepared under different production methods（including carbonization temperature and pyrolysis time）.We can explore its optimal production conditions through its yield,adsorption effect and other factors,finding the best preparation temperature and pyrolysis time of H₂SO₄modified biomass carbon,KOH modified biomass carbon and Mg Cl₂modified biomass carbon are 450℃,1 h;450℃,2 h;550℃,1 h,named respectively HPS-450-1、KPS-450-2、MPS-550-1.Second,the corresponding modified biomass charcoal was prepared under the best production conditions to study its adsorption and purification research on its influencing factors such as temperature,p H was studied.The results show that MPS-550-1 has a strong comprehensive adsorption capacity for TP,NO₃^-,and NH₄⁺,and its maximum adsorption capacity is as high as4.685,0.988,and 26.325 mg/g,followed by KPS-450-2,whose maximum adsorption capacity is 4.897,1.208,25.641 mg/g,and finally HPS-450-1,its maximum adsorption capacity is 4.361,0.796,27.521 mg/g.The internal diffusion kinetic model can better describe the adsorption process of TP by HPS-450-1 and KPS-450-2,and the adsorption law of NH₄⁺by KPS-450-2 and MPS-550-1,but other adsorption data can not be fitted by the quasi-first-order,quasi-second-order,and internal diffusion kinetic model,indicating that the existing three models cannot describe their adsorption laws well,and the adsorption laws may be complicated.KOH modified biomass charcoal,H₂SO₄modified biomass charcoal,and Mg Cl₂modified biomass charcoal have the best adsorption effect when p H is 7,7,and 11,respectively.The fluctuation of p H can obviously change the adsorption effect of modified biomass charcoal.Too low temperature will inhibit the adsorption effect of various modified adsorption reaction for the various modified biomass carbon at room temperature and high temperature.Third,the technologies such as specific surface area,pore size and pore volume,infrared spectroscopy,scanning electron microscopy are used to obtain the characteristics of the biomass carbon before and after modification,developing the further study about its adsorption mechanism.The activation treatment of H₂SO₄and KOH can form a richer and more developed pore structure,significantly increase the specific surface area of biochar.The specific surface area of H₂SO₄modified biochar and KOH modified biochar are respectively up to 331.1884 and 331.8988 m²/g,the total pore volume of them is up to 0.192805 and 0.263105 cm³/g;Mg Cl₂activation treatment has a certain pore-forming effect and can form Mg O particles on the surface of biomass carbon,the total pore volume of which can reach 0.264877 cm³/g.Compared with the corresponding unmodified biomass carbon,the surface of the biomass carbon is rougher after activated by H₂SO₄,KOH,Mg Cl₂,and its surface voids are denser,and the porosity is larger,which makes the spatial relatively abundant oxygen-containing functional groups such as ether,carbonyl,carboxyl,and hydroxyl groups on the surface of Pistia stratiotes biochar.After modified by KOH,H₂SO₄,Mg Cl₂,the pore structure of the biomass carbon,the types and number of oxygen-containing functional groups on the surface are obviously enriched,which can increase its active adsorption sites on the surface,and effectively improve the adsorption performance of biomass carbon.