| The status of water pollution in China is serious, and needs to be improved in urgent. Calcium peroxide has attracted wide attention in the aerobic remediation of water body due to its oxygen releasing capacity with the presence of water. However, since powder CaO2reacts with water rapidly and self-agglomerate appears easily, thus, the direct use of powder CaO2in water body remediation could not meet the requirement of long-term oxygen-releasing and high utilization efficiency. According to the requirement above, an oxygen-releasing compound (ORC) was developed and prepared based on CaO2in this study. The effects of preparation conditions of ORC on the oxygen releasing efficiency were investigated to optimize the parameters of ORC preparation. The reaction model was adopted to simulate the oxygen release process in the experiment and calculate the oxygen-releasing rate of the ORC. The prepared ORC was applied in the remediation of the simulated water bodies of eutrophication and contaminated by the hydrophobic organic compounds.Based on the embedding effects, including molding stability, oxygen-releasing time and total amount of released oxygen, of agar, xanthan gum, polyethylene glycol and polyvinyl alcohol (PVA), the reaction rate of CaO2with water could be retarded and the oxygen-releasing time would be prolonged. The experiment results indicated that the CaO2embedded by2%PVA with granular activated carbon (GAC) could provide better oxygen-releasing efficiency and longer oxygen-releasing time, compared with the powder CaO2adsorbed on the columnar granular activated carbon (CGAC). In order to improve the inner porosity of ORC and increase the contact possibility of CaO2with water, powder CaO2and GAC were mixed uniformly according to the weight ratio of3to2and prepared by PVA embedding, which could raise the utilization efficiency of CaO2and extend the oxygen-releasing time.To optimize the preparation conditions of ORC, the effects of mixing proportion and particle size of GAC, as well as curing temperature on the oxygen releasing efficiency of ORC were investigated. The experimental results indicated that the addition of GAC in the preparation of ORC with mixed particle size (20to40meshes and60mesh of GAC) could provide not only better oxygen-releasing efficiency but also longer oxygen-releasing time than the ORC prepared with sole particle size. The curing temperature would also affect the oxygen-releasing efficiency of ORC. Higher curing temperature would destroy the cross-linking structure of the embedding material in ORC, lowering the embedding effect and leading to the excessive rapid oxygen-releasing speed. The curing temperature of60℃would enable the ORC to have a more stable oxygen-releasing rate and higher CaO2utilization efficiency.The reaction model was adopted to simulate the oxygen releasing process of ORC in this experiment. From the view of kinetics, the correspondence analysis was carried out between the oxygen consumed by the sediment and the oxygen released from ORC. The oxygen-releasing time of ORC would increase with the dimension of the ORC. The ORC in the size of Φ20×5mm could provide an oxygen-releasing time of60days. With the ORC dosage of58g·m-2, oxygen-releasing rate of6.36g·(d·m2)-1was achieved during the period of0to0.5h, and oxygen-releasing rate of0.47g·(d·m2)-1during the period of0.5h to60d, which could meet the oxygen consumption rate for the reduction matter and the microbe in sediment. The oxygen-releasing rate of ORC above could meet the oxygen demand of sediment, indicating that the ORC was sufficient for the aerobic remediation of the contaminated water body. Therefore, the following experiments were all carried out with this size of ORC.The effect of ORC on the water quality index of overlying water and the remediation efficiency were studied by applying ORC in the simulated eutrophication water body. The result showed that when the ORC dosage was greater than180g·m-2, the dissolved oxygen concentration and the redox potential were both improved significantly, and the chemical oxygen demand (COD) was effectively decreased. The declining amplitude of the dissolved inorganic phosphate (DIP), dissolved total phosphate (DTP) and the ammonia nitrogen (NH4+-N) were close with the dosages of180g·m-2and270g·m-2of ORC. The declining amplitudes of DIP and DTP reached to91%, and83%, whereas those of NH4+-N and total nitrogen (TN) reached to93%and50%respectively with the ORC dosage of270g·m-2. The ORC showed significant effect on the control of the phosphorus and nitrogen release in the eutrophication water body.The oxygen restoration at the water-sediment interface was carried out with the application of ORC in the simulated anaerobic eutrophication water body, and the spatial and temporal distribution of different phosphorus fraction in sediment was studied. The vertical distributions showed that the summation of P fractions (EP) in the four sediment layers exhibited the increasing tendency with the application of ORC and the ΣP of the upper sediment layers (0-6cm) were more sensitive to the ORC. Due to the oxygen consumption along the oxygen transfer path, the accumulation of phosphorus in bottom sediment layer (6-8cm) was weakened, compared with the upper layers. Especially, with the ORC dosage of180g·m-2, P was accumulated significantly in sediment. With the ORC application, the concentrations of Fe-P and O-P were much higher than the control, which demonstrated an accumulation effect. The variations in the P fractions indicated that the concentrations of De-P, A-P and EX-P were relatively stable in the sediment and were thus not sensitive to the aerobic treatment. Due to the application of ORC, the redox potential of the water body was raised, which promoted the increase of Fe-P, and the microbial activity in sediment was stimulated such that the microbial biomass also increased, by which phosphorus was stored by microorganisms in the form of O-P. Although the mineralization of P was accelerated with the existence of ORC, the accumulation of P surpassed the release of P, which led to the accumulation of P. Thus, for the control of phosphorus release from sediment could be achieved effectively. In the simulated water body contaminated by naphthalene, the effect of the naphthalene on the dehydrogenase activity (DHA) in sediment, and the effect of ORC on the naphthalene-contaminated sediment were both studied. The results indicated that the DHA was significantly inhibited as the concentration of naphthalene reached9.5μg·g-1, whereas significantly improved with the presence of ORC. The naphthalene degradation efficiency reached62.7%with the ORC dosage of225g·m-2.In the simulated water body contaminated by bisphenol A (BPA), the effects of ORC on the bacterial growth, sediment toxicity and BPA degradation efficiency were investigated, and the degradation products and microbial diversity for the water body contaminated by BPA were also studied. The results indicated that the total bacterial count (TBC) in the water body was stimulated by the ORC dosage below459g-m’2, whereas inhibited with the application of powdery CaO2. Similar rule could be observed in the variation of sediment toxicity. With the ORC dosage lower than459g·m-2, the bacterial growth, sediment toxicity inhibition, microbial diversity and the BPA degradation efficiency in the water body would be all improved. The BPA degradation efficiency reached94%, which was significantly higher than the control. The degradation of BPA with ORC followed the first order reaction kinetic model. According to the PCR-DGGE analysis, the accumulation of Thauera aromatic was observed with the ORC dosage of459g·m-2, which would contribute to the degradation of BPA. In conclusion, with the appropriate dosage of ORC, the DO concentration of the water body contaminated by hydrophobic organic pollutant would be improved, which would be favorable to their degradation and conversion, being conducible to the remediation of polluted water body. |
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