Study Of Catalytic Ozonation Process On The Treatment Of Hypersaline Antibiotic Wastewater

Hypersaline organic wastewater is widely distributed and considerable in China,with characteristics of high chemical oxygen demand,poor biodegradability and high toxicity.The pharmaceutical wastewater is one of typical hypersaline wastewater,and the antibiotics exsisted in this type of wastewater poses a serious threat to the ecological environment and human health via enrichment effect,which has become an environmental concern that needs to be treated urgently.Among the present degradation methods of antibiotics,ozonation has the advantages of mild reaction conditions,environmental friendliness,high efficiency and no secondary pollution,which consequently has promising promotion and application.However,independent ozonation has relatively lower O₃ utilization,higher selectivity of organic pollutants and poorer oxidation efficiency,so it is difficult to achieve effective mineralization of hypersaline organic wastewater.In view of the abovementioned problems,two catalytic methods,Mn-CeO_x@yAl₂O₃ and ultraviolet light（UVC）were used respectively in this thesis to improve the O₃ utilization and accelerate the decomposition of O₃ to generate a variety of reactive oxygen species（ROS）for the treatment of ciprofloxacin（CIP）.In addition,catalytic ozonation processes were applied to the practical treatment of real hypersaline organic wastewater to explore the technical feasibility of application.The main research contents and conclusions are displayed as follows:（ⅰ）The active components of Mn/Ce bimetallic oxides were loaded simply on the sufurce of activated alumina ceramsite（γ-Al₂O₃）by impregnation-calcination method to fabricate a bicomponent doped catalyst of Mrr-CeO_x@γ-Al₂O₃（MCA）.In comparison with independent ozonation（36.9±2.2%）,the mineralization of hypersaline organic wastewater by Mn-CeO_x@γAl₂O₃@γ-Al₂O₃/O₃（MCAO）process under the optimal conditions（[O₃]=13.969±0.434 mg L1,[MCA]=80 g L-1,pH=8.5±0.5）reached to 76.0±2.3%,and the O₃ utilization was increased by 14.76%.It was due to that a large amount of ·OH was generated,and the electron transfer of redox pairs Mn（Ⅲ）/Mn（Ⅳ）and Ce（Ⅲ）/Ce（Ⅳ）promoted the production of oxygen holes,which further increased the ·OH concentration.The presence of high salinity significantly enhanced the mass transfer rate and self-decomposition of O₃.However,MCAO/SO₄^2-system generated SO₄^-· and inhibited the catalytic performance（71.2±3.4%）,which was attributed to that SO₄^-· reacted more slowly with CIP than ·OH(8.4×108 M^-1 s^-1 vs.4.1×109 M^-1 s^-1).In the SO₄^2-/Cl^-mixed-salinity system,MCAO process produced Cl· at lower Cl^-(0.5 wt.%Cl^-/3.0 wt.%SO₄^2-)and improved the mineralization of organic wastewater,which however was suppressed with the increase of Cl^-（≥1.5 wt.%）due to the generation of a large amount of residual chlorine(Cl²,Cl^2-· and ClO^-).（ⅱ）UVC_254nm and ozonation were coupled to construct the UVC/O₃ process.Due to the synergistic effect between UVC and O₃,a large amount of O₂-· and 1O₂ were generated to attack CIP and its intermediates with almost no selectivity.Consequently,in contrast with independent ozonation,the mineralization of hypersaline organic wastewater by UVC/O₃ process under the best parameters([O₃]=30.0±2.0 mg L-1,UVC intensity=2.60±0.03 mW cm^-2)was increased by 81.8%and 53.9%,respectively.In the UVC/O₃/SO₄^2-system,with the increase of SO42concentration from 0 to 10.0 wt.%,the mass transfer of O₃ was enhanced dramatically.Besides,the volume of O₃ bubbled into the reactor was decreased and the specific surface area was increased,which improved significantly the catalytic performance.The increase of Clconcentration from 0 to 3.5 wt.%in the UVC/O₃/Cl^-system promoted the mass transfer of O₃ as well,but the excessive Cl^-concentration consumed a large amount of O₃ and subsequently weakened the oxidation efficiency.The coexistence of natural organic matter,suspended solids or chromaticity in wastewater inhibited the oxidative performance of UVC/O₃ process due to UVC light shielding.Both UVC/O₃/SO₄^2-and UVC/O₃/Cl^-systems were improved with pH increased from 3.0 to 11.0.The T.E.S.T software was employed to conduct toxicity evaluation of degradation products during MCAO/SO₄^2-,UVC/O₃/SO₄^2-and UVC/O₃/Cl^-system,which showed that the toxicity of CIP after catalytic ozonation was decreased to some extent.（ⅲ）In comparison with independent ozonation,both MCAO process and UVC/O₃ process performed excellently in the treatment of actual hypersaline organic wastewater as well.The removal of BOD5,CODcr and TOC were effectively enchanced,and the effluent pH was stable at 7.75±0.75,which met the influent requ irments of subsequent biological treatment.In addition,the UVC/O₃ pressurization process was applied to promote the generation,compression and cracking of O₃ microbubbles in the oxidation system,which further improved the water indexes of effluent from the secondary sedimentation tank in the wastewater treatment plant.