Surface Modification Of Novel Basalt Fiber Bio-carrier And Evaluation Of Wastewater Treatment Performance Of Bio-nest

Basalt fiber(BF) is a high-performance inorganic micron-level flexible fiber.It can enrich a large amount of activated sludge in the biological contact oxidation tank to form microbial aggregate with a diameter of several centimeters,which is named "bio-nest".The "bio-nest" has a large number of aerobic/anoxic/anaerobic microenvironments,which can achieve organic degradation and nitrogen removal more efficiently than traditional biological carriers.Therefore,BF has attracted much attention as a new type of carrier material for wastewater treatment.However,the existing BF materials are limited by surface physical and chemical properties and biological affinity,which inhibit the rapid and stable attachment of microorganisms,thereby restricting its promotion and application in the field of wastewater treatment.In view of the ideal properties of carriers for wastewater treatment,modified basalt fiber(MBF) were prepared by surface treatment in this thesis.The modification method and recipe were optimized.By studying the changes of the internal microbial community during the cultivation of the "bio-nest",the formation of "bio-nest" and the evolution of the internal microbes were revealed.The influence of modified basalt fiber carrier on the growth of "bio-nest" and the microbial community was discussed.This work evaluated the pollutant removal efficiency of various carriers by comparing biological contact oxidation reactors with modified basalt fiber carrier and conventional carrier.It provides theoretical and experimental basis for the practical application of the modified basalt fiber carrier and its "bio-nest" reactor.The main content and specific results of this research are as follows.(1)Preparation and surface properties of modified basalt fiber carrierThe surface of basalt fiber was modified by the method of liquid deposition with calcium ions and surface coating with chitosan.The surface properties of calcium modified basalt fiber(Ca-MBF)and chitosan modified basalt fiber(CTS-MBF)were characterized.Through bacterial adhesion and activated sludge culture experiments,the effect of surface modification on the bio-affinity of the carrier was evaluated.The experimental results showed that the Ca-MBF prepared by liquid deposition with calcium ion had better properties in terms of surface roughness,hydrophilicity,surface and bio-affinity.With the increase of calcium ion concentration during modification,Ca-MBF exhibited increasing surface potential,reducing contact angle,and increasing surface energy.On this basis,the formula for modification was optimized.In the activated sludge culture experiment,the microbial activity and biomass of the Ca-MBF carrier were significantly higher than that of the unmodified carrier,and the amount of extracellular polymeric substances(EPS) secreted by the microorganisms also increased.(2)Study of the formation and microbial community of modified basalt fiber "bionest"Ca-MBF and commercial MBF were used for “bio-nest” culture in the bioreactor to study the growth of microorganisms in the “bio-nest”.Through Confocal laser scanning microscope analysis and high-throughput 16 S rRNA gene sequencing,the composition of the bacterial community in the “bio-nest” at different culture periods was studied,and the mature “bio-nest” was analyzed from the inside to the outside.The results showed that the biomass aggregated Ca-MBF “bio-nest” was 1.24 times as that of MBF.Both MBF and Ca-MBF “bio-nest” had formed aerobic/anoxic/anaerobic composite structure,and the relative abundance of nitrogen removal bacteria in CaMBF “bio-nest” was higher.(3)Evaluation of wastewater treatment performance of modified basalt fiber carrierThe wastewater treatment performance of the reactors filled with Ca-MBF carrier,MBF carrier and conventional combined carrier was tested using synthetic domestic wastewater.The feasibility of practical application of Ca-MBF carrier was evaluated.The results showed that the basalt fiber “bio-nest” reactor had higher pollutant removal efficiency than the reactor filled with conventional carrier.In addition,the Ca-MBF "bio-nest" reactor had higher and more stable removal efficiency of COD,total nitrogen,and total phosphorus than the MBF “bio-nest” reactor,especially for influent with higher ammonia nitrogen concentration(COD:N =10:1).Ca-MBF carrier showed better wastewater treatment efficiency.