Thermal Metrology Research On Interaction Of Heavy Metals And PhACs With Extracellular Polymers Substances

The pollution problems of trace pollutants, such as heavy metals and pharmaceutically active compounds(PhACs), in municipal wastewater become worse and worse. Because of inhibitory effect on microorganism, the removal effect of conventional activated sludge process for these pollutants is very limited that would result in pollutants' vestigital in the effluent of the wastewater treatment plants(WWTPs) and might induce environmental risk. Extracellular polymers Substances(EPS) are macromolecular substances covering the surface of microbial cells and filling within sludge flocs, and are produced along with the process of matrix degradation of activated sludge in the wastewater. EPS have large numbers of active functional groups and hydrophobic regions so that EPS have a strong adsorption and complexation ability of pollutants. Trace pollutants, heavy metals and PhACs, in wastewater biological treatment system will interact with the microbial in the first place with mechanism of adsorption and complexation.In this work, the mechanism of heavy metals and PhACs interacting with EPS was studied by an efficient, online, nondestructive and advanced analysis technique — isothermal titration calorimetric method(ITC) to understand the role of EPS in the process of pollutants removal and reveal the interference factors and regulars in this pollutants removal process so as to provide theoretical basis and technical guidance for the trace pollutants strengthen removal in activated sludge system.The main research contents and results were as follows:1. The condition of model EPS interact with heavy metals and PhACs was studied using isothermal titration microcalorimetric instrument(ITC-200).The results showed that the pollutants combination with model polysaccharide(glucan) was not obvious, and combination with model humic acid(HA-Na) was weak, and combination with model protein(BSA) was the strong.2. The influence of solution conditions including temperature(T), ionic strength(IS), and different valence cations on EPS adsorption for heavy metals removal was dicccused by ITC-200 to reveal the solution conditions interference regulars in the removal process and competition mechanism between different valency cationics and heavy metal ions. The results demonstrated that the high concentration of heavy metal ions was easiler to damage model EPS structure and limit system conformation change so that the combined capacity was reduced that was not good for the lasting heavy metals removal by EPS adsorption. In general low ionic strength didn't affect the combination of BSA and heavy metal ions. When the ionic strength exceeded a certain range, system conformation change would be more and more restricted and the adsorption quantity was significantly reduced with the increase of ionic strength. The complexation of EPS and heavy metal ions would be influenced by different valence cations in varying degrees. The Ca2+ interference was mainly through electrostatic intereaction while Fe3+ interference was mainly through the strong combination with EPS and competed EPS limited binding sites with heavy metal ions and so as to hinder the combination of EPS and heavy metals.3. The mechanism of EPS and PhACs combination and the influence regular of IS and pH to the combination were discussed using ITC-200. The results determined that the protein-substances model EPS combined with 4-acetamidophenol(ACT) and sulfamethazine(SMZ) strongly, and the combinination process depended on entropy driven with the hydrophobic interaction as main driving force. The EPS and ACT combination was significantly affected by pH and combination approached the best when closed to neutral condition. The stoichiometric number(N) of EPS and SMZ combination was not significantly affected by pH while the EPS and SMZ combination was a most favorable reaction on thermodynamics, conformational change was largest, and the complex EPS-SMZ was most stable in the neutral condition. The combination of EPS and PhACs affected significantly by IS. The stoichiometric numbers(N) of EPS and ACT combination were decreased under IS pressure generally, and compound stability affected by the ionic strength of solution and overall decline. EPS and SMZ combination was weak(IS, 5 m M). The EPS and SMZ combination was more spontaneous and the complex was more stable, whereas the combination stoichiometric number(N) was smaller if the IS was higher from 50 mM to 500 mM.