Experimental Study On The Treatment Of Polluted Water By Composite Modified Biological Sand Filtration Process

Organic pollutants and nitrogenous pollutants from human activities enter water bodies,making many surface water source waters polluted to varying degrees and having a series of negative impacts on the water treatment process,and efficient removal of pollutants from raw water is urgently needed.Biosand filters are used to cultivate biofilms on the surface of quartz sand filter media to enhance the removal of pollutants through the adsorption and biochemical effects of biofilms,however,due to the smooth surface of ordinary quartz sand,it is difficult for biofilms to adhere to its surface and it is easy to fall off due to the shear force of water flow,This thesis presents a proposal to modify the surface roughness of quartz sand.In this thesis,a composite modification method of common quartz sand was proposed to address the above problems,and the surface structure of common quartz sand and the composite modified sand was analysed.The results of the study showed that:(1)Inspired by the glass etching process and surface coating method,amino-modified sand(AMS),aluminium cation-modified sand(ALS)and aluminium-calcium double hydroxide materialised modified sand(CAS)were prepared on the basis of ordinary quartz sand.Scanning electron microscope characterisation results show that the surface of the quartz sand appears grooves of a certain depth and width after modification by different methods,and the roughness and porosity of the surface become larger,with the formation of lamellar crystals on the surface of CAS.Infra-red spectroscopy,X-ray diffraction and X-ray photoelectron spectroscopy characterisation results indicate the formation and content variation of specific elements on the modified sand,with the formation of functional groups and metal chemical bonds on its surface.(2)After successful stabilisation,the surface material composition of the composite modified sand is more complex than that of ordinary quartz sand.The good hydrophilic properties of the composite modified quartz sand,the positively charged surface and the presence of a large number of functional groups such as amino or hydroxyl groups on the surface promote the secretion of extracellular polymers by microorganisms,resulting in an increased surface biomass and biological activity of the quartz sand.The surface roughness of the quartz sand is increased after the composite modification,which increases the ability of the microorganisms to adhere to the surface and is less likely to be dislodged by the shear of water.(3)After stable operation of the bio-sand filter,compared with ordinary quartz sand,the bio-sand filter with composite modified quartz sand as filter media has improved the treatment effect of both COD and nitrogen,among which CAS has the best treatment effect with the removal rate of 70.45% and 47.73% for COD and total nitrogen respectively.(4)High-throughput sequencing Miseq technique was performed to screen the functional genera of biofilms on the surface of the modified bio-sand filter media for pollutant removal and identify the changes in their abundance.The results showed that the relative abundance of the dominant genera of AOB,NOB and denitrifying bacteria were CAS>AMS>ALS>QS.