Preparation Of Magnesium-rich Biochar Derived From Straw And Its Synchronous Recovery Of Nitrogen And Phosphorus From Biogas Liquid

Nitrogen and phosphorus organic matter are the main pollutants in swine wastewater,which are also necessary elements for the growth of plants.Therefore,it is crucial to explore a reasonable and effective way to realize the simultaneous recovery of nitrogen and phosphorus nutrients from wastewater.In this work,cornstalk,a kind of agricultural waste was used as the raw material to prepare magnesium-rich biochar using magnesiumsalt impregnation coupled with thermal pyrolysis technology.The effects of preparation conditions on the N and P recovery performance by Mg O-biochar were systematically investigated.Meanwhile,the effects of environmental factors on the N and P recovery performance from biogas slurry were also studied.Based on the results of characterization and kinetic study,the mechanism of N and P recovery by magnesium-rich biochar was discussed.In addition,the fertilizer efficiency of magnesium-rich biochar after recovery of N and P was evaluated using pot experiment of soybean.The results showed that Mg O-biochar(with 20% content of Mg O)under 500℃had the highest removal rate of N and P from biogas slurry(TP 100%,TN 69.4%,and TAN 91.6% respectively).The synchronous recovery efficiencies of N and P was highest,when p H of biogas slurry was 7-8,N/P molar ratio was 1-2 and the dosage of Mg O-biochar was 2.5 g/L.This mainly attributed to the synergistic effects of the rich porous structure of Mg O-biochar,electrostatic adsorption,struvite reaction and re-enrichment process by struvite crystals.The study of adsorption kinetics and isothermal adsorption curves showed that the simultaneous recovery of nitrogen and phosphorus was in accordance with pseudo-second-order kinetics and Langmuir model.The result explain ed that the adsorption of nitrogen and phosphorus in fermentation broth by 20% Mg O-biochar is mainly chemisorption,but also accompanied by physical adsorption.After recovery of N and P,Mg O-biochar fertilizer can obviously promote the growth of soybean.This work provides a novel method to recovery N and P from biogas slurry,which may have a potential application prospect and significant value for the development of a new slow-release fertilizer.