The Effect Of Alternating Wet And Dry Conditions On The Blocking Of Antibiotic Transport In Porous Media By Biochar

There are different conclusions regarding the environmental effects of biochar ageing,and few studies have focused on the possible changes in biochar properties caused by different alternating wet and dry environments.In this study,fresh biochar was prepared by three alternating wet and dry methods to obtain aged biochar:ultrapure water aged carbon,silica aged carbon and humic acid aged carbon,and sulfadiazine and florfenicol were used as target contaminants.The effect of alternating wet and dry aging on the adsorption of target antibiotics was investigated through batch equilibrium adsorption experiments and fitting analysis using different isothermal adsorption models.The effect of alternating wet and dry ageing on water transport and antibiotic transport behaviour in porous media was investigated.This study can provide some basis for the effect of biochar ageing on the transport and sorption behaviour of contaminants and potential risks.The main findings are as follows.Alternating wet and dry ageing caused significant changes(p<0.05)in the elemental C,H and O of biochar,and significant decreases(p<0.05)in the elemental ratios H/C,O/C and(N+O)/C.The surface morphology of biochar was altered,while the oxygen-containing functional groups of biochar increased by 5.25%-6.86%and the specific surface area increased by 39.15%-102.67%.The isothermal adsorption characteristics of biochar on target antibiotics were in accordance with the Langmuir model and Freundlich model(R~2>0.83,p<0.01).In the Langmuir model,the relationship between the maximum adsorption capacity of biochar for the target antibiotics,was maintained as follows:silica aged carbon>ultrapure water aged carbon>humic acid aged carbon>fresh biochar.In the Freundlich model,the sorption equilibrium constants for sulfadiazine and florfenicol were higher for both dry and wet aged biochars than for fresh biochars.The alternating wet and dry ageing affected the adsorption performance of the biochar,which was attributed to the increased specific surface area and aromaticity of the biochar.Water transport in the test sand columns was simulated by a convection-dispersion model(R~2>0.874,RMSE<0.065),indicating that alternating wet and dry ageing delayed water transport but was not significant(p>0.05).The two-point chemical non-equilibrium model better characterised the transport behaviour of sulfadiazine and florfenicol in the quartz sand column(R~2>0.876,RMSE<0.087),suggesting that alternating wet and dry ageing caused a change in the blocking effect of biochar on the transport behaviour of the two antibiotics in the quartz sand column,which was attributed to the change in adsorption of biochar by alternating wet and dry ageing.The effect of pore flow rate on water movement was not significant in the same test sand column,but affected the transport behaviour of the antibiotics.