| The large amount of phosphorus（P）entering water bodies with surface runoff is the main cause of eutrophication,while P is a finite and non-renewable resource.Therefore,it is important to adopt a cost-effective method to recover P from wastewater in order to alleviate the shortage of P resources and reduce the eutrophication.In this paper,the nano zero-valent iron modified reed biochar（n ZVI-BC）was prepared to carry out the adsorption kinetics and isotherms of P.The purpose of this experiment was to evaluate the P adsorption performance of n ZVI-modified BC and to investigate the mechanism of P adsorption and removal by various characterization techniques（XRD,FIRT,XPS,SEM-EDS）.In addition,the effects of Fe-700-BC on the concentrations of P in the overlying water and sediment were compared under different environment conditions.Also,the influence of Fe-700-BC addition on the microbial community in the sediment in the lab-scale experiments.In addition,the effects of applying biochar with adsorbed P to the soil on the physiological characteristics of wheat were analyzed to explore the possibility of using it as a slow-release P fertilizer.The main findings of the study are as follows:（1）To determine the best preparation method of Nano zero-valent iron modified biochar（n ZVI-modified BC）:The n ZVI-modified reed BC at different pyrolysis temperatures（300,500,700 and 900°C）was subjected to adsorption kinetics and adsorption isotherm experiments,which showed that Fe-700-BC had the best P adsorption performance.Its adsorption was in accordance with the second-order kinetics model and the Freundlich mode.The adsorption capacity of Fe-700-BC for P was 95.2 mg/g according to the Langmuir isotherm adsorption model.（2）To investigate the mechanism of P adsorption by BC,SEM images of Fe-700-BC showed that the n ZVI successfully attached to the surface of BC,making its surface rough.And the modification with n ZVI could reduce the electronegativity of BC causing Fe-700-BC easier to adsorb P.Moreover,XRD and XPS characterization showed that n ZVI was gradually oxidized to form Fe2O3during the experiment.After adsorbing P,new Fe-P crystals,mainly as Fe PO4,might be formed on the surface and internal of Fe-700-BC through precipitation reaction,ion exchange and inner sphere complexation.（3）To elucidate the effect of applying Fe-700-BC in the lab-scale experiments setting up different environmental conditions（no sediment,static and disturbance）on P in the overlying water and sediment.The results showed that the addition of Fe-700-BC lab-scale experiments reduced the concentrations of TP and SRP in the overlying water,in which the SRP was almost completely removed.And the presence of Fe-700-BC reduced the growth of algae,which may be due to the following reasons:Fe-700-BC indirectly inhibited the growth of algae by reducing the P concentration in the overlying water,and the iron contained in the Fe-700-BC also affected the chlorophyll a formation.Simultaneously,Fe/Al-Pi is the dominant form of inorganic P in the sediment,which increased at the water-sediment exchange interface under the condition with algae.Meanwhile,the contents of WA-Pi,PA-Pi and Fe-Al-Pi were decreasing in the reactor with Fe-700-BC,especially under disturbance conditions,which was mainly due to the combination of high P release from the sediment under disturbance and strong adsorption of Fe-700-BC.（4）To investigate the effect of BC on microbial communities and on wheat growth.The results showed that the Fe-700-BC had no significant effect on the diversity and richness of the microbial community in the sediment.The wheat planting experiment was carried out using P-laden biochar collected in the lab-scale experiments,which showed that the growth of wheat was promoted by low concentration of P-laden BC（0.5wt%）,while inhibited by high concentration of P-laden BC（1wt%and 2wt%）.In order to verify the safety of P-laden BC,its heavy metal content was tested,and the results showed that all the heavy metals it contained were lower than the national standard,and it was safe and environmentally friendly to apply to the soil.the addition of Fe-700-BC had no significant effect on the structure,diversity and abundance of microbial communities in the sediment. |
