Pro/hydrophobic Convertible Chitosan Flocculant For The Removal Of Antibiotics - Heavy Metals

At present, the problem of livestock wastewater has become more and more serious, while antibiotics and heavy metals often coexist in this kind of wastewater. The removal of antibiotics and heavy metals from water is urgently needed. The flocculation method is one of the most widely used method for water treatment, owning the benefits of cost-effectiveness, facial operation and remarkable water purification performance.However, most of the traditional flocculants are refractory and residual toxicity. In recent years, increasing numbers of researchers focus on the natural polymer flocculants. Natural polymer materials are renewable, biodegradable and have the advantages of non-toxicity and wide sources. But their application is also limited due to poor solubility, low molecular weight and low amounts of surface charges. In this essay, the improvement of the flocculation performance is studied via chemical modification on natural polymer chitosan.(1) Flocculation method, using a reusable thermal-responsive chitosan-based flocculants (CS-g-PNNPAM), was applied for separation and sequential recovery of tetracycline (TC) and Cu(?) from water. High synergistic removal rates of both TC and Cu(?) from water (>90%) were reached. Interactive effects among targeted water's temperature (Ti), stock solution's temperature (T2) and flocculants dosage on flocculation performance were assessed using response surface methodology. In order to optimize flocculation, operation strategies of adjusting T2 and dosage according to Ti, based on the interactive effects, were given through mathematical analyses. Flocculation mechanism, as well as interfacial interactions among CS-g-PNNPAM, TC and Cu(?), were studied through experimental investigations (floc size monitoring, XPS and UV spectra) and theoretical calculations (density functional theory (DFT) and molecular dynamics (MD)simulations): Coordination of Cu(?) with TC and the flocculants promoted flocculation;switchable interactions (H-bonds and hydrophobic association) of TC-flocculant at different temperatures were key factors affecting operation strategies.(2) RSM method is used to study the structure (grafting chain length) of the flocculant on flocculation effect. Interactive effects among water temperature (T1),flocculant stock solution temperature (T2), and dosage are studied in detail. Furthermore,flocculation performance of CS-g-PNNPAM for other kinds of pollutants in wastewater of livestock and poultry (heavy metal zinc and antibiotic sulfadiazine) are investigated.Cu(II)-sulfadiazine and Zn(?)- tetracycline can be synergistically removed, and the removal efficiencies of all contaminant reach more than 80%.(3) Finally, by weaken these interactions step by step, TC and Cu(?) were sequentially recovered from flocs using certain solutions. The flocculant regenerated from flocs can be reused with remained high flocculation efficiency.Above all, CS-g-PNNPAM showed desired flocculation performance for the removal of antibiotics and heavy metals from water. The flocculant can also be resued.Therefore, it is believed that the flocculant has a good application prospect in the real wastewater treatment.