Biochar For Adsorptive Sequestration Of Heavy Metals,Antibiotics,and Antibiotic Resistance Genes:Effect Of Ferrihydrite Loading And Wet-State Modification

Heavy metals,antibiotics and resistance genes,which are the three pollutants that need to be controlled urgently in the water and soil environment,can induce environmental risks such as increased resistance to pathogenic bacteria.Biochar has the functions of fixing heavy metals,adsorbing antibiotics,and degrading antibiotic resistance genes,but the adsorption and removal capacity of biochar for anionic compounds such as tetracycline antibiotics and resistance genes is relatively small.Ferrite mineral particles such as goethite and magnetite are positively charged,and their load modification is expected to make up for the shortcomings of the small anion adsorption capacity of biochar.This article focuses on the"high stability and high adsorption capacity ferrihydrite-biochar composite material",while ensuring the stability of the ferrihydrite on the biochar,it avoids the decrease in the ultra-high adsorption capacity of the wet composite material caused by drying.The specific research results are as follows:（1）The chemical precipitation method can prepare wet,stable and high surface area ferrihydrite-rice straw biochar composite material:in an aqueous solution,the ferrihydrite deposited on the surface of the rice straw biochar can withstand the aging treatment at 70°C for 60 hours,Different from the ferrihydrite control group without biochar（converted to goethite after aging）;the silicon component of rice straw biochar is dissolved after alkali treatment and forms Fe-O-Si on the ferrihydrite surface The bond,in turn,may block the transformation of ferrihydrite to goethite by hindering the dissolution of Fe³⁺and occupying crystalline sites.The wet ferrihydrite-biochar composite material has good dispersion performance,small Zeta potential,and is rich in small particles with a diameter of 60-200 nm,and the surface of small and large particles（200-2000 nm in diameter）is wrinkled,but after drying After drying,cold drying,vacuum drying,room temperature air drying and organic washing,the small particles with a particle size of 60-220 nm almost disappeared.The dried sample showed a smooth surface（wrinkles disappeared significantly）,and the active surface limit was reduced.（2）The wet ferrihydrite-biochar composite material can efficiently adsorb and remove Cu²⁺,oxytetracycline and resistant plasmid p BR322 in water:Compared with the natural adsorbent moisture soil and red soil,pure rice straw biochar has an advantage in adsorption of Cu²⁺（1.54 mg/g）;The adsorption of ferrihydrite to oxytetracycline and resistant plasmid p BR322 is more advantageous（2817,124 mg/g）.The wet ferrihydrite-biochar composite material integrates and improves the advantages of the adsorption performance of the two raw materials.The adsorption capacity of Cu²⁺,oxytetracycline and resistant plasmid p BR322 can reach 3455,1.84and 66.0 mg/g,respectively.The wet composite material avoids the reduction in adsorption capacity caused by the decrease in specific surface area during the drying process（the adsorption capacity for oxytetracycline and resistant plasmid p BR322 is reduced by 47.6-91.9%）.The silicon component eluted from the biochar may promote the dispersion of ferrihydrite and the adsorption of oxytetracycline through the formation of Fe-O-Si bonds.At the same time,the silicic acid complexed with ferrihydrite may promote the adsorption of Cu²⁺as a new adsorption site（3）Inspecting the adsorption of three pollutants by moisture soil and red soil after mixing with 1%soil material（w/w）showed that:Simple rice straw biochar is difficult to significantly improve the adsorption of oxytetracycline and resistant plasmid p BR322 in the soil;Pure ferrihydrite is also difficult to significantly increase the adsorption of Cu²⁺in the soil;The wet ferrihydrite-biochar composite material can significantly increase the adsorption capacity of the soil（moisture soil and red soil）:in the moisture soil,the maximum adsorption capacity for Cu²⁺,oxytetracycline and resistant plasmid p BR322 are 0.40 and 7.17 and 0.28 mg/g,which are 37.9%,1426%and 86.7%higher than pure moisture soil;In red soil,the maximum adsorption capacity of the three pollutants is 0.08,2.97 and 0.75 mg/g,which are 119%,607%and 74.4%higher than pure red soil.After the wet composite material enters the soil,it may be fully dispersed by the soil particles,so that the effect of the soil drying process on the adsorption performance of the composite material due to agglomeration is effectively alleviated.After 5 cycles of dry and wet,the wet ferrihydrite-biochar composite material can adsorb and lock Cu²⁺,OTC,and plasmid p BR322 in the soil.The increase can still be maintained at 34.6%,71.3%and 31.0%（moisture soil）,50.2%,86.5%And 34.5%（red soil）.