| Eutrophication of water bodies is a hot environmental problem to be solved urgently.Eutrophication will cause the rapid increase of algae in lakes,reservoirs and rivers.In recent years,the continuous outbreak of blue algae has seriously affected the quality of water bodies,which is one of the major global environmental problems.P is one of the key factors of eutrophication.The utilization of blue algae as biomass can not only solve the problem of blue algae accumulation problem,but also realize the removal of phosphate in the water and ease the eutrophication of the water body,which can be used as a new way to treat blue algae.In this work,blue algae from Taihu Lake are used as biomass raw materials.The blue algae biochar is prepared by pyrolysis under high-temperature nitrogen.Mg Cl2and La Cl3 are used to modify blue algae to prepare Mg and La modified biochar.The surface morphology,structure and physicochemical properties of the modified blue algae biochar were characterized by modern analytical instruments.The adsorption performance,kinetics and main factors affecting the adsorption of phosphate by modified biochar were discussed,and the adsorption mechanism of phosphate by modified materials was analyzed.The improved effects of recovered blue algae biochar on soil p H,P and N and other basic indicators,as well as the effects on the germination and growth of typical vegetables were investigated.The feasibility of recycling blue algae biochar as a soil improver and effective utilization of phosphate fertilizer resources was confirmed.?1?X-ray diffraction?XRD?characterization results showed that corresponding metal oxides Mg O and La2O3 were dispersed on the surface of blue algae biochar after Mg and La modification.Scanning electron microscopy?SEM?and Nitrogen adsorption and desorption curve characterization results showed that the blue algae biochar and metal modified blue algae biochar were rich in C and O element and had large specific surface area and rich pore structure.Mg and La modification make the corresponding metal elements effectively doped into biochar.Fourier transform infrared spectroscopy?FT-IR?analysis results showed that the surface of biochar contains was rich in functional groups.Zeta potential results confirmed that the blue algae and Mg,La modified blue algae bicohar were positively charged at p H<6.8-9.5which were favorable for phosphate adsorption.?2?The adsorption capacity of phosphate by Mg and La modified blue algae biochar increased obviously compared to the unmodified blue algae biochar.The adsorption rate of phosphate by La and Mg-La modified blue algae biochar was the highest,which was up to 97.4%.In order to explore the optimal adsorption conditions,the conditions of pyrolysis temperature,p H and the dosage of biochar were selected by Design Expert software.The results presented that when the pyrolysis temperature was600°C,p H=6.0 and dosage was 2.0 g/L,the best adsorption efficiency was obtained.Under the condition that four common competitive anions coexist with phosphate,the effect of coexisting ions on the adsorption of biochar was as follows:CO32->HCO3->SO42->Cl-.The adsorption of phosphate by the prepared biochar was fitted by pseudo-second-order kinetic equation.The most suitable adsorption isotherm model was Redlich-Peterson model.Based on the material characterization results and adsorption behavior,it can be speculated that the adsorption mechanism of biochar to phosphate were Hydroxylated metal oxides indicated the formation of mononuclear and polynuclear complexes with negatively charged phosphates and the phosphate in solutions reacted with metallic oxides to form precipitation through a chemical reaction,thus improving the phosphate adsorption capacity of biochar.?3?The blue algae biochar was recycled and added to the soil after absorbing the phosphate.Results showed that the p H of soil decreased and the content of soil phosphorus increased after adding recycled biochar.The addition of recycled biochar can increase the germination rate of vegetable seeds.The germination rate of the cabbage seeds reached 100%after the addition of biochar,which increased by 24.1%-38.0%compared with the control group.Besides,the seedling height increased by38.3%-105.8%,the seedling width increased by 77.7%-105.9%and the seedling biomass increased by 135.6%-199.5%.Besides,the chlorophyll content increased significantly as well.The results confirmed that the post-adsorption biochar could be used as an effective P-fertilizer to promote the growth of plants.In this study,blue algae were used to prepare environmentally friendly adsorption material for the adsorption of phosphate in the water,which is of great significance for reducing eutrophication of water.Besides the biochar was recovered after adsorbing phosphate and was used as a soil improver and effective phosphate fertilizer,so that the phosphorus in biochar and wastewater can be used as resources,which is both economical and environmentally friendly. |
PDF Full Text Request