Study On The Interaction Of Dissolved Organic Matter-tetracycline-zinc In The Soil Solution

With the rapid development of China’s rural livestock industry, the pollution oflivestock and poultry has become an important source of rural non-point sourcepollution. Livestock and poultry manure are the main waste generated from livestockand poultry breeding, which contains a large number of metal elements, antibioticsand other pollutants that are not absorbed by livestock and poultry. These pollutantswill transport under the action of surface runoff, infiltration, further causing soil andgroundwater pollution. Therefore, it has important significance to study thetransformation behavior and interaction mechanisms of livestock and poultry manurepollutants in the soil.With taking the typical pollutants of livestock and poultry manure-solubleorganic matter (DOM), tetracycline (TC) and zinc (Zn) as the research object, and thetypical black soil in the northeast as the tested soil, this thesis studied the interactionmechanism of the joint pollution system of DOM, TC and Zn in the soil solution bybatch adsorption experiments, and the influence of solution pH and addition sequenceon adsorption of TC and Zn was investigated, also DOM samples were characterized.The results can provide a theoretical basis for revealing the transformation behavior ofpollutants in livestock and poultry manure in the soil, as well as for the soil treatmentcontaminated by livestock and poultry manure. Main conclusions of this thesis aresummarized as follows:(1) In the TC-Zn system, there is a mutual promoting adsorption effect betweenTC and Zn, which main mechanism is that the absorbed TC or Zn on the surface ofthe soil could be bridge to the Zn or TC, thus enhanced the adsorption of TC or Zn. Atlower pH where cationic form of TC dominated in TC species, TC suppressed Znadsorption on soil surface by competition of adsorption point between TC and Zn.The interaction of TC and Zn in soil solution is affected by the addition sequence.When TC concentration is higher, the enhanced sequence of TC adsorption is asfollows: adding together of TC and Zn≈first adding TC and after adding Zn> firstadding Zn and after adding TC. For Zn adsorption, there has a different impact on adsorption of Zn with different adding sequence, different concentration of TC andZn.(2) In the TC-DOM system, adding DOM significantly suppressed TC adsorptionon the soil. The adsorption coefficient Kfof TC decreased with the increasingconcentration of DOM indicated by fitting results of Freundlich adsorption model.Adding DOM has significantly increased the pH of the system, which results in thechanging of TC species. Adding DOM nearly has no impact on TC adsorption whencationic form of TC dominated in TC species (pH <4). TC adsorption on the soil isalso affected by the adding sequence of DOM, the inhibited sequence of TCadsorption is as follows: first adding DOM and after adding TC> adding together ofTC and DOM> first adding TC and after adding DOM.(3) In the Zn-DOM system, adding DOM Zn significantly enhanced Znadsorption on the soil, and Zn adsorption on the soil could be better fitted withLangmuir equation when adding DOM to soil. The promoter capacity of DOM on Znadsorption enhanced with the increase of pH. The impacted sequence of Znadsorption by adding sequence followed the order: first adding Zn and after addingDOM> adding together of Zn and DOM≈first adding DOM and after adding Zn.(4) In the TC-Zn-DOM system, for TC adsorption, the inhibited impact of DOMand enhanced impact of Zn would has none effect on TC adsorption, which may bedue to the formation of quaternary bond bridge of Soil-DOM-TC-Zn complexesduring the adsorption process, and for Zn adsorption, adding TC and DOMsignificantly enhanced the Zn adsorption on soil, which all of them was dependent onthe concentration of Zn, TC and DOM.In the TC-Zn-DOM system with different solution pH, when the TC was in thepresence of a cationic form (pH <4), the inhibited impact on TC adsorption wasminimum. The inhibited impact on TC adsorption increased with the increasing ofsolution pH. When the anionic form dominated in TC species (pH>8), addingtogether of Zn and DOM adsorption TC had a certain role in promoting TC adsorption,which also indirectly confirmed the presence of the quaternary bond bridge ofSoil-DOM-TC-Zn complexes. The results of the impact of adding sequence on TC and Zn adsorption in theTC-Zn-DOM system has also verified the presence of the quaternary bond bridge ofSoil-DOM-TC-Zn complexes.(5) Characterization of the test DOM was as following. Molecular weightdistribution result showed that DOM was mainly distributed in the larger molecularweight component (>35000Da) and smaller molecular weight component (<1000Da),and the hydrophilic fraction represented51.2~57.3%with the residual washydrophobic fraction. UV-visible spectra results indicated that a few component ofDOM could strongly absorb UV light, and FT-IR spectroscopy showed that manureDOM both contained carbohydrates and aliphatic compounds.