Study On The Purification Mechanism Of Compound Multimedia Biofilters For Urban Black-odorous Water

The domestic sewage in some areas of our country,including urban villages,urban-rural junctions,and old urban areas was emissioned discretely and cannot be collected centrally and effectively treated because of the lack of construction of pipeline networks,causing serious black-odor water.The biological filter,as one of the bioremediation technologies for the treatment of black and odorous water bodies,has been widely used due to its advantages such as high efficiency,low cost and no secondary pollution.Some effords have been achieved in the repair of black and odorous water bodies in some areas of China,but the removal effect of organics is still not ideal,because the researh of organics is mostly focused on indicators such as BOD and COD.These indicators are difficult to reflect the changes in the composition,content,and structural characteristics of dissolved organic matter（DOM）in the process of treating black and odorous water with biological method.Moreover,the biological carriers on the market have defects,including low biocompatibility,small specific surface area,poor adsorption effect,and easy aging.Aiming at the above problems,this paper designed two sets of multi-media biological filters and modified the carrier to enhance the carrier performance and effectively remove the pollutants such as COD,ammonia nitrogen and DOM in black and odorous water.The biological carriers on the market were modified,and the removal efficiency of conventional pollutants（COD,TOC,TN,NH₄⁺-N,TP,TSS）and effect on DOM components and structural characteristics were studied in the treatment process of BF1（Biofilter 1）system with the modified biocarriers and BF2（Biofilter 2）system with unmodified carriers under the condition of hydraulic loading rate（HLR）using spectroscopy and PARAFAC analysis methods.The mechanism of pollutant removal was also analyzed.The biological carriers on the market were modified firstly in this study.The modified carriers have different pores inside,with a pore diameter of 0.3-5 mm.These pores play different roles.The large pores are mainly used to prevent the carrier from blocking,and it has good contact.The mesopores and micropores are mainly used to fix microbial inoculants and enhance the binding ability of carrier and microorganisms.The wet density of the modified carrier is close to that of water,with an average of 1.0 g/cm³.The experiment showed that a good anaerobic environment is formed inside the microbial carrier,and denitrification can occur.Therefore,the biological filter can achieve simultaneous ammonia oxidation,nitrification and denitrification,which can efficiently remove pollutants and reduce running costs.By comparing the operating effects of BF1 and BF2 system,it is found that the removal rates of pollutants in both systems increased firstly and then decreased with increasing HLR.The removal effect of BF1 is better than BF2,and the hydraulic shock resistant ability of modified carrier in the BF1 system is stronger than the unmodified carrier in the BF2 system.Three-dimensional fluorescence spectroscopy shwed that both BF1 and BF2 systems can identify four fluorescence peaks（one humic acid-like peak,one fulvic acid-like peak,and two protein-like peaks）,and the intensity of the four peaks exhibited different degrees of ruduction after treatment process,and the reduction of protein-like substances was the greatest.As the HLR increased from 0.8 m³/m²d to 1.4 m³/m²d,the fluorescence intensity of the four peaks declined firstlly and then increase.The removal effect of the four components of the DOM in the treatment process of BF1 system was the best at the HLR of 1.3 m³/m²d,while the removal effect of the four components of DOM in the treatment process of BF2 system was greatest at the HLR of 1.2 m³/m²d.UV-Vis spectroscopy and simultaneous fluorescence spectroscopy found that the BF1 system was better than the BF2 system in removing protein-like substances.After the treatment process of two systems,the degree of condensation,aroma,and humification of fulvic acid in the DOM increased and the molecular structure becomes more complicated.EEMs-PARAFAC showed that the BF1 and BF2systems can separate four fluorescent components.As the HLR increased,the Fmax of the four components declined firstly and then increased,and the BF1 system has an more excellent removal effect on DOM than BF2 system.Microbial community analysis found that there are more dominant phylum species（10species）in the BF1 system than those in the BF2 system system（9 species）.The Proteobacteria,Bacteroides,Pneumophila,and Nitrospira BF1 system is dominant,the phylum in BF2 system is dominated by Proteobacteria,Bacteroides,Phytophthora,and Hydrophobia,and the abundance of nitrogen and phosphorus removal bacteria in the BF1system is greater than those in BF2 system;Shannon index,Simpson index,ACE index And Chao 1 index showed that the diversity and species abundance of the BF1 system is greater than those of the BF2 system.Based on this,it was speculated that the better pollutant removal performance of BF1 system than those of BF2 system was related to the microbial diversiy and abundance.The changes of microbial diversity under the condition of different hydraulic loading rate of the system indicate that the hydraulic loading rate had a certain effect on the diversity of microbes.The ecological restoration projects of the east section（1）of qianruiying village and the east section of Guogezhuang（2）in Pinggu,Beijing adopted the combined technology of ecological floating island-solar aeration-ecological permeable dam-ecological revetment for the treatment of black-odor water,effectively removed COD,ammonia nitrogen and TP in the water body,and achieved good repair effect.I have gained a more three-dimensional and deeper understanding of the black-odor water body by participating black-odor water body restoration project in Pinggu,Beijing,and provided valuable experience for the future related work.