Effect Of DOM On The Adsorption Performance Of Oxytetracycline Onto Sediment

With the development of the society and the improvement of people's living quality,the rise of livestock and poultry breeding industry caused heavy use of antibiotics,resulting in more and more immediate threats of pollution to the water and soil environment.As a universal adsorbent in nature,the adsorption of soil and sediment plays an important role in the transportation and transformation of antibiotics in environment.Usually,the adsorption ability of soil and sediment often depends on type,particle size distribution,organic matter content(especially the content of dissolved organic matter)and so on.So it is very important to explore the adsorption performance of antibiotics on different sediments and their adsorption characteristics under the influence of dissolved organic matter(DOM)for understanding the environmental behavior of antibiotics and evaluating the harm.Therefore,three different sediments were selected from Weihe River,including river bed sediment,level terrace sediment and sewage sediment,to explore the different adsorption processes of a typical antibiotics(oxytetracycline,OTC),then adding DOM from different sources(plants,animals)into the sediments to discuss the effects on adsorption process.Three dimensional fluorescence,elemental analysis and scanning electron microscopy were employed to describe the characteristics of the sediments and DOM,then mechanisms of the effcts of DOM on the adsorption were concluded combining the adsorption process.Finally the change rules of Zeta potential of the system in the adsorption process were discussed,and based on that,the influence factors were studied such as pH and ionic strength on the adsorption process of OTC to sediment.The main results have been gained as follows:1.The adsorption dynamics of OTC on riverbed sediment fits the pseudo-first-order model better,while the adsorption dynamics of level terrace sediment and sewage sediment are more conform to the pseudo-second-order model.Three isothermal adsorption of the three sediments all fit Langmuir and Freundlich model well.The adsorption capacity of OTC on riverbed sediment is the largest,while the level terrace sediment is medium and the sewage sediment is the minimum.The adsorptions of OTC onto the three sediments are spontaneous endothermic reaction,and mainly are physical adsorption,but the spontaneous possibilities are not the same.The adsorption process of the riverbed sediment is more likely to happen,and the sewage sediment is less likely to occur.Combined the adsorptions of three kinds of sediments,the adsorption capacity of OTC is more depended on particle size of the sediment,the smaller the particles,the greater the adsorption quantity.If particle size distribution of sediments were similar,the higher the organic carbon content,the higher adsorption capacity the sediment can reach.2.The adsorptions speeded up after adding exogenous DOM to the three sediments,adsorption balance time have reached about 6 hours early.Langmuir model and Freundlich model also can make good descriptions of the isothermal adsorption processes after adding exogenous DOM.The adsorption of OTC on the sediments have promoted after adding the DOM from decay plants(which has low polarity,low hydrophilicity,high aromaticity and contains a lot of kind of humus),but have a tendency to inhibit the adsorptions after adding the DOM from chicken manure composting(which has high polarity,high hydrophilicity,low aromaticity and contains a lot of classes of protein).After adding exogenous DOM,the adsorptions of OTC on the sediments still are spontaneous endothermic reaction.But it has different effects on the spontaneous possibilities of adsorption: after adding the DOM of decay plants,the adsorption became more likely to happen,while it is less likely to occur after adding the DOM of chicken manure composting.3.The Zeta potential was studied in the adsorption system,showing Zeta potentials of the three sediments are all negative and the more negative the Zeta potential,the better performance of adsorption the sediment has.There is a large number of positively charged OTC due to the acidic or neutral system,so the adsorption will be strong in the negative Zeta potential of system.Compared the adsorption without exogenous DOM,the change of Zeta potential(?Zeta)has increased after adding the DOM of decay plants and has reduced a little after adding the DOM of chicken manure composting.Combined with the above adsorption influence law of adding exogenous DOM,it is found that the higher adsorption quantity of OTC onto the sediment,the bigger ?Zeta the system has,which means there is a positive correlation relationship between the ?Zeta and adsorption quantity.Base on that,it shows that adding a high concentration of DOM from decay plants has a poor promotion for adsorption compared the low,but a high concentration of DOM from chicken manure composting can intensify the inhibition.pH and ionic strength have a significant influence on the Zeta potential of the system.The Zeta potential of riverbed sediment decreased with the increase of pH,so there is a better interval for the adsorption due to the existence form of OTC,while the increasing of ionic strength will inhibit the adsorption because the Zeta potential will increase with the increase of ionic strength.