The Mechanism Of In Situ Remediation Of Sediment In Black And Odorous Water By Layered Double Hydroxides And The Application Of MBBR

With the rapid economic development and accelerated urbanization,a large amount of industrial wastewater and domestic sewage are discharged into natural water without treatment,and the influx of a large number of pollutants exceeds the self-purification capacity of rivers,thus causing the water to become black and odorous,known as black and odorous water.Studies have shown that the generation of black and odorous water is closely related to the substrate environment,and improving the substrate environment plays an important role in a healthy water environment system,so corresponding measures must be taken to restore the water ecological environment.In situ remediation technology based on environmental functional materials has become a hot research topic,layered double hydroxide（LDH）has adsorption properties and adjustable laminate structure,thus attracting widespread attention.In this paper,we investigated the effect of LDH on the morphology and structure of black and odorous sediment and the removal of pollutants in the overlying water of a channel in Xiangtan,Hunan Province,and developed LDH-loaded fillers for moving bed biofilm reactor（MBBR）to investigate the interaction between LDH fillers and biofilm.（1）Mg Al-LDH and Mg Fe-LDH with ionic ratios of M²⁺:M³⁺=2:1,3:1 and 4:1were prepared by co-precipitation method,and Mg Al-LDH and Mg Fe-LDH with M²⁺:M³⁺=2:1 were selected by structure optimization.follow-up experiments were conducted with an actual black and odorous water in a channel in Xiangtan city to investigate the treatment effect of LDH on the black and odorous water.The monitoring of the water pollution indexes showed that the COD removal rate increased by 21.5%and 19.8%,ammonia nitrogen removal rate increased by 16.9%and 12.9%,and total phosphorus removal rate increased by 12.0%and 9.6%,respectively,and the LDH promoted the degradation of organic matter in the black and odorous water by three-dimensional fluorescence verification.Microscopic analysis of the sediment showed that Mg Al-LDH and Mg Fe-LDH promoted the reduction of sediment particle size from 70.3μm to 59.2μm and 60.6μm,respectively,and the results of Fourier transform infrared spectrometer（FT-IR）showed that the phosphate absorption peak at 1030 cm^-1in the sediment was significantly reduced,while the phosphate absorption peak in LDH was enhanced accordingly.The FTIR spectra showed that the phosphate absorption peak was significantly reduced at 1030 cm^-1,while the phosphate absorption peak was enhanced in LDH.In addition,the presence of LDH facilitated the release of pollutants from the substrate and the transformation of anaerobic state.The effect of LDH on the purification and improvement of black and odorous water was verified by the removal of both the overlying water and the substrate.（2）In-depth investigation of the remediation mechanism of LDH and black and odorous substrate.Firstly,we investigated the binding of Mg Al-LDH and Mg Fe-LDH to the substrate microorganisms,and extracellular polymeric substances（EPS）from the substrate for LDH adsorption experiments,and characterized the adsorbed LDH by X-ray diffraction analysis（XRD）and Fourier transform infrared spectrometer（FT-IR）,and found that the binding of LDH to EPS was mainly manifested as the adsorption of protein-like substances on the laminate.And the adsorption of protein-like in the system was verified by three-dimensional fluorescence.Next,the effects of Mg Al-LDH and Mg Fe-LDH on the changes of electrochemical properties and characteristics of the substrate were investigated,and LDH increased the electron chain transfer activity and extracellular reactive oxygen species（ROS）content of the substrate.Compared with the blank group,the extracellular ROS production increased by 38%and 5%,respectively,in the experimental group.Cyclic voltammetry and electrochemical AC impedance spectroscopy calculations showed that the substrate power increased from 0.194μC to 0.495μC and 0.242μC,respectively,and the resistance decreased from 8.006*10¹⁴kΩto 3.242*10³kΩand 1.519*10¹⁴kΩ,indicating that LDH promoted the interspecies electron transfer of substrate microorganisms.Therefore,LDH can improve the activity of substrate microorganisms and thus promote the removal of various pollutants in black and odorous water,which plays an important and positive role in the purification ofblack and odorous water.（3）The composite system of filler-loaded LDH microorganisms was designed to investigate its effect on the treatment of black and odorous water.The contact angle and scanning electron microscopy（SEM）showed that the loading of LDH increased the hydrophilicity and roughness of the filler,and the contact angle of the filler was133.75°,the contact angle of the filler loaded with Mg Al-LDH was 56.87°,and the contact angle of the filler loaded with Mg Fe-LDH was 57.67°.The water quality indexes were monitored during the operation of MBBR,and compared with the composite system without loaded filler,LDH had better treatment effect on the water,the removal rate of COD increased by 11.5%and 12.3%,the removal rate of ammonia nitrogen could achieve 100%,the removal rate of total phosphorus increased by15.3%and 17.0%,and also had better removal effect on the characteristic pollutants of black and odorous water such as humic substances.The removal effect of the biofilm was also well.The study of biofilm performance showed that LDH improved the hanging rate and biofilm volume,and the biofilm volume increased by 55.0%and47.2%respectively,which is beneficial to the MBBR treatment performance.ensured that the composite system of filler-loaded LDH microorganisms was durable for the removal of black and odorous water.