| China has become the largest country of drug producer and the major exporter, as well as preparation production ranking the first in the world. Since a mass of different types and complex structures raw materials were used during the process of pharmaceutical production, leading to the pharmaceutical wastewater containing large amount of organic pollutants. After the current A2/O etc. biological treatment process, the wastewater after biochemical processes still contained a lot of organic matter content in which the chemical oxygen demand (CODCr) was over 600 mg/L and the direct discharge of secondary effluent would cause the serious harm to the environment. This study used magnetic adsorption enhanced coagulation process to advanced treat the pharmaceutical wastewater, analyzing the removal effect of proteins, humic acid and polysaccharides etc. pollutants in the wastewater after biochemical processes by single factor and response surface, finally, combining optimized formulas with traditional coagulation method to the techno-economic analysis. The main research content and results are as follows:(1) The wastewater after biochemical processes of a pharmaceutical wastewater treatment plant in Zhejiang was as the research object. The concentration of organic matter was still high, total organic carbon (TOC) was 143-157 mg/L, and CODCr was 624-691 mg/L; High salinity recalcitrant and dis-biodegradation were observed in the study, mainly containing sodium, calcium and magnesium ions etc. The organic contents were more concentrated, molecular weight> 2 kDa organics accounted for 43.06%, the main organics of the effluent were humus acid and fulvic acids, simultaneously containing partially proteins and polysaccharides; The main functional group of organics were hydroxyl and carboxyl etc containing a portion of aromatic compounds.(2) To prepare the economic and efficient magnetic adsorption material, this study selected solvothermal to prepare Fe3O4 and used improved stober to prepare Fe3O4@SiO2, by an amino group grafted (3-aminopropyl) triethoxysilane (APTES) to obtain Fe3O4@SiO2-NH2. Three materials were characterized by SEM, TEM, XRD, FTIR, BET and Zeta potential. The results suggested:according to the SEM and TEM photomicrograph, the particle size of three prepared materials was homogeneous distribution, the materials were globular which had good dispersion. The particle size of the magnetic materials were 500.0±3.1 nm (Fe3O4),504.0±3.2 nm (Fe3O4@SiO2) and 510.0±3.6 nm (Fe3O4@SiO2-NH2), respectively, belonging to the powder material; Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2-NH2 presented the characteristic diffraction peaks of Fe3O4, a cubic spinel structure, and there are the diffraction peak corresponding to the carrier on spectrum; SiO2 successfully coated Fe3O4@SiO2 and Fe3O4@SiO2-NH2 surface grafting the amino group; the specific surface area of three prepared materials presented Fe3O4@SiO2-NH2>Fe3O4@SiO2>Fe3O4 trends; The electric potential of Fe3O4、Fe3O4@SiO2 and Fe3O4@SiO2-NH2 were close to 5.5,6.5 and 8.5, respectively.(3) To research the proteins and humic acid adsorption property of three materials, the study used bovine serum albumin and humic acid standard liquid as adsorption object, analyzing material adsorption kinetics and adsorption isotherm, and by controlling the initial pH value of proteins and humic acid to study the effect of pH on the materials adsorption properties. The results are as follows:Three materials for protein adsorption kinetics followed pseudo second-order equation; Protein adsorption isotherms of Fe3O4 and Fe3O4@SiO2-NH2 conformed to Langmuir model; the saturated capacity of Fe3O4 and Fe3O4@SiO2-NH2 were 28.61 and 123.80 mg/g, respectively according to the calculate of the Langmuir model; Three materials for humic acid adsorption kinetics meted the proposed second-order equation; Freundlich and Langmuir models could be used to describe the adsorption behavior of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2-NH2; according to fitting, the adsorption capacity of Fe3O4 and Fe3O4@SiO2-NH2 were 44.14 and 59.36 mg/g, respectively, with the increase of pH, the trends of protein and humic acid adsorption of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2-NH2 were firstly increasing and then decreasing, in which the adsorption effect of Fe3O4@SiO2-NH2 was the best.(4) To research the effect of pH on three materials adsorbing the pharmaceutical wastewater after biochemical processes, this study controlled the initial pH of wastewater and selected the best adsorption material to be parsed and recycling, examining the recycling performance. The results are as follows:when pH was 5-6, Fe3O4@SiO2-NH2 had high removal of TOC, CODcr, chroma, proteins, humic acid and polysaccharides on secondary effluent of pharmaceutical wastewater after biochemical processes, they were 44.14%,34.07%,62.94%,35.58%,33.07% and 26.03%, and are more excellent than Fe3O4 and Fe3O4@SiO2. The experiment about desorption and regeneration of Fe3O4@SiO2-NH2 suggested that the removal of TOC was 38.91% and the removal of chroma was 55.07%, achieving 87.50% of the first time use and indicating that the material has the value of recycling.(5) To select the suitable coagulant, this study compared the coagulation effect of polymeric aluminium (PAC) and ferric sulfate (PFS) on pharmaceutical wastewater after biochemical processes by controlling the initial pH and the coagulant dosing concentration, and selected the better adsorption property of Fe3O4 and Fe3O4@SiO2-NH2 to do the enhanced coagulation adsorption experiments. The results are as follows: The effect of PFS was better than PAC. The removal trends of TOC, CODCr, TP, protein, humic acid and polysaccharides were firstly increasing and then decreasing with the increase of pH when Fe3O4 or Fe3O4@SiO2-NH2 were used as the adsorbent in the enhanced coagulation process with magnetic adsorption. When pH was 5, the removal of TOC, CODcr, TP, protein, humic acid and polysaccharides achieved the best during the enhanced coagulation process with magnetic adsorption of Fe3O4, that is,50.92%, 45.97%,93.43%,67.61%,44.50% and 34.87%, respectively. When pH was 6, the removal of TOC, CODcr, TP, protein, humic acid and polysaccharides achieved the best during the enhanced coagulation process with magnetic adsorption of Fe3O4 @SiO2-NH2, that is,65.04%,59.72%,97.93%,91.00%,68.75% and 50.93%, respectively.(6) To research the effect of coagulant, coagulant aids and magnetic adsorbent dosing concentration on the enhanced coagulation process with magnetic adsorption treating proteins, humic acid and polysaccharides etc. pollutants in pharmaceutical wastewater after biochemical processes, this study compared the effect of the enhanced coagulation process with magnetic adsorption for three single factors by a separate control of the dosing concentration of PFS, polyacrylamide (PAM) and Fe3O4 (or Fe3O4 @SiO2-NH2). The results are as follows:When pH was 5, the best project of the enhanced coagulation process with magnetic adsorption of Fe3O4 was that the dosing concentration of Fe3O4 was 0.5 g/L, PFS was 200 mg/L and PAM was 20 mg/L. When pH was 6, the best project of the enhanced coagulation process with magnetic adsorption of Fe3O4@SiO2-NH2 was that the dosing concentration of Fe3O4@SiO2-NH2 was 1.5 g/L, PFS was 200 mg/L and PAM was 15 mg/L, establishing a clear function of multi-factor and response value. The fitting quadratic regression equation could reasonably reflected the relationship between the removal of TOC, TP, protein, humic acid and polysaccharides and the dosing concentration of PFS, PAM and Fe3O4 (or Fe3O4@SiO2-NH2); The equation also could be used to analyze and predict the removal of various contaminants during the enhanced coagulation process with magnetic adsorption.(7) For the cost of engineering application and in accordance with the scale of daily processing capacity of 1000 m3 pharmaceutical wastewater after biochemical processes, this study compared the operating cost of the traditional coagulation and the enhanced coagulation process with magnetic adsorption of Fe3O4@SiO2-NH2. The results are as follows:The latter was higher than the former on agent fee, while the enhanced coagulation process with magnetic adsorption of Fe3O4@SiO2-NH2 had higher degradation performance, so the latter was a lower cost from the cost of the unit CODcr degradation point of view. After accounting, the unit CODCr degradation cost of the traditional coagulation was 6.62 rmb/(kg CODCr), while the unit CODCr degradation cost of the enhanced coagulation process with magnetic adsorption of Fe3O4@SiO2-NH2 was 5.70 rmb/(kg CODCr). |
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