| The annual discharge of tens of billions of tons of industrial saline wastewater and the substitution of seawater in coastal areas aggravate the workload and difficulty of sewage treatment.Aerobic granular sludge（AGS）is favored in the biological treatment of saline wastewater because of its compact structure,good sedimentation performance,high biomass content,rich functional bacteria composition and strong ability to resist external adverse environmental factors.However,the formation of AGS i s generally time-consuming and restrained by harsh operating conditions.The response and regulation of AGS system lags behind when dealing with the problem of large fluctuation of industrial saline wastewater quality in different production seasons.In ad dition,the low temperature in winter in northern China will further inhibit the activity of biological enzymes,which limits the popularization of AGS in the actual treatment of saline wastewater.To solve the above problems,a simple cultivation method o f AGS was developed,assisting by the flocculation of Aspergillus tubingensis mycelium pellets for activated sludge granulation.The granules’physicochemical properties,biological activity,size effect and mechanism were studied.After the formation of s alt-tolerant biomass by salt gradient acclimation,the feasibility and mechanism of exogenous Fe 3O4promotion system to deal with the C/N fluctuation impact of high salt wastewater were explored.A number of salt-tolerant functional strains of different sp ecies were isolated and screened,and compounded bacteria agent with high nitrogen removal efficiency at low temperatures was formed,which was added to the salt-tolerant granular sludge systemt to explore the feasibility and mechanism of enhancing the bio logical treatment of actual seafood processing wastewater.The research results can provide theoretical guidance and technical support for solving the bottleneck problem of aerobic granular sludge in the actual application of saline wastewater treatment.（1）Study on the performance and formation mechanism of aerobic granular sludge constructed by iron-based modified AT mycelium pellets.In view of the relatively loose entanglement of the hyphae in the protomycelium pellets and the low surface flocculation performance,different Fe3O4 nanoparticles were used to modify the Aspergillus tubingensis（AT）mycelium pellets,results showed that Fe3O4@Si O2-QC modification made the internal structure of AT mycelium pellets became more compact,the surface hydrophobic ity and apparent viscosity of hyphae increased by 45.41%and 42.38%respectively,and the flocculation performance of mycelium pellets was improved.In view of the current formation conditions and time-consuming issues of aerobic granular sludge,u nder the optimized conditions,the biomass of activated sludge initially accumulated on AT mycelium pellets could reach 1.54 g/g,and the specific oxygen consumption rate（SOUR）of AT-based AGS（AT-AGS）could reach 58.03 mg O2/g VSS·h.The mature AT-AGS with high bi ological activity（64.45mg O2/g VSS·h of SOUR）and better sedimentation performance（58.22 m/h of settling velocity）was formed when the initial AT-AGS was screened and cultured alone until the9th day.Combined with XDLVO mathematical theoretical model and comprehensive analysis of the changes of sludge surface properties and quorum sensing signal molecule concentration during granulation process to explore the formation mechanism of granular sludge.The electrostatic adsorption by the positively charged AT mycelium and the three-dimensional network skeleton structure promoted the initial aggregation of flocculent activated sludge.The increased c-di-GMP quorum sensing signal molecules stimulate the more secretion of extracellular polymeric substance（EPS）u nder the interaction between AT mycelium pellets and initially aggregated sludge microorganisms,which promoted the aggregation of flocculent activated sludge in the later stage.The sludge microorganisms aggregated on the mycelial surface continued to gro w and reproduce,which further increased the granule’s biomass and formed the mature AT-AGS.Under the condition of high influent loading,the removal rates of total nitrogen and total phosphorus of AT-AGS were 12.24%and 16.29%higher than those of inocul ated flocculent activated sludge,respectively.High throughput sequencing results showed that the richness and diversity of functional species responsible for carbon,nitrogen and phosphorus removal of AT-AGS were higher than those of inoculated flocculen t activated sludge.（2）Research on the size effect and mechanism of AT-AGSIn view of the large differences in pollutant removal performance and structural stability of traditional AGS of different sizes,this paper analyzes the internal particles by studying the internal pores of the particles,the composition and spatial distribution of cellular EPS,and the hydrophobicity and apparent viscosity of the particle surface.The influence of microenvironment on the colonization and abundance of functional bacteria.The research results showed that with the increase of particle size,the total pore volume of AT-AGS first decreased and then increased,while the average pore size first increased and then decreased.EPS secretion as a whole increased first and then decreased with the increase of particle size,but the extracellular protein content of GS was the largest（67.53 mg/g VSS）,while the extracellular polysaccharide content of GM was the largest（65.02 mg/g VSS）,resulting in the difference of microbial surface characteristics,which formed the different microenvironment with different particle sizes.Fluorescence in situ hybridization analysis showed that the internal microenvironment difference of AT-AGS regulated the spatial distribution of functional species.The relative abundances of degrading bacteria genus of GS and GM were about11%higher than that of GL.The relative abundances of nitrifying and denitrifying bacteria of GM were 1.09%～11.54%higher than those of GS and GL.The results of biological enzyme activity analysis showed that the activities of dehydrogenase,ammonia monooxygenase,nitrite oxidoreductase,nitrate reductase and nitrite reductase of GM were 1.32～3.09 times higher than those of GS and GL.The results of real-time quantitative PCR showed that the expression levels of the corresponding functional genes such as amob,hao,nxr A,nxrb,nar G and nir S of GM were 1.31～37.55 times higher than those of GS and GL.（3）Research on the formation and resistance mechanism of salt-tolerant AT-AGSIn response to the problem of high salt stress factors that severely inhibit the growth and metabolism of functional bacteria and destroy the stable interaction between bacterial species.In this study,salt gradient acclimation method was used to c ultivate salt-tolerant biomass.It was found that AT-AGS took 4,5,8,7 and 8 days less to reach the stable state under the salinity of 6.25,12.5,25,37.5 and 50 g NaCl/L than flocculent activated sludge,showing higher high salt-tolerance acclimation efficiency.The removal rates of COD and ammonia nitrogen of salt-tolerant AT-AGS were 11.83%and 7.18%higher than that of salt-tolerant flocculent activated sludge under the salinity of 50 g NaCl/L.Salt-tolerant AT-AGS showed stronger biomass retention cap acity（7.92 g/L of MLVSS concentration）and higher metabolic activity（48.06 mg TF/g VSS·h of dehydrogenase activity）.The total extracellular polysaccharide content of salt-tolerant AT-AGS（80.7 mg/g VSS）was close to twice that of salt-tolerant flocculent a ctivated sludge（46.3 mg/g VSS）,which played a key role in maintaining the stability of the system.High throughput sequencing analysis showed that after salt acclimation,AT-AGS maintained high microbial richness and diversity,and salt-tolerant Marinobacterium（32.04%of relative abundance）become the main genus.The adsorption capacity of Cd2+and Pb2+of salt-tolerant AT-AGS could reach 30.3 mg/g and 50.9 mg/g respectively.Aiming at the simultaneous C/N fluctuation problem of salty wastewater,this study proposes a coping strategy to use iron to cope with the dual extreme factors,When 1.5 g/L Fe3O4 was added to the salt-tolerant AT-AGS system,it was found that the time for sludge to achieve stable performance after responding to the C/N fluctuation impact of high-salt wastewater was greatly shortened,and the removal rates of COD,ammonia nitrogen and total nitrogen in each stage were 2.27%～8.55%higher than those in the control group.The addition of Fe 3O4 improved the functional bacteria’s retention capacity of salt-tolerant AT-AGS in response to C/N fluctuation,which maintained high flocculation activity of sludge and ensured high stability of the system.In addition,Fe3O4 increased the activity of electron transport system of sludge under the condition of C/N fluctuation,and which promoted the cells to maintain high biological enzyme activity.（4）Study on the performance of bioenhancement of salt-tolerant AT-AGS coupling compound microbial agentIn view of the problem that the salt-tolerant biomass cultivated in the laboratory is difficult to efficiently treat the fully complex and changeable actual wastewater,this paper isolates and screens two salt-tolerant ammonia-nitrogen-utilizing bacteria and two salt-tolerant nitrous acid bacteria from the soil around seafood processing enterprises.Nitrogen-utilizing bacteria and three strains of salt-tolerant nitrate-nitrogen-utilizing bacteria were isolated and screened.According to the results of environmental factor tolerance test,the compound bacteria agent with high comprehensive nitrogen removal performance at low temperature（15℃）was prepared in proportion.5%（w/w）compound bacterial agent was added to the salt-tolerant AT-AGS system in batches（2.5%on day1and day10 respectively）to enhance the treatment of actual seafood processing wastewater.It was found that the removal rates of ammonia nitrogen and total nitrogen of the bio-augmentation group were 12.13%and 17.20%higher than those of in the control group.The activities of ammonia monooxygenase,nitrite oxidoreductase,nitrate reductase and nitrite reductase of the bio-augmentation group were also 60.00%,66.39%,61.97%and95.24%higher than those of the control group,respectively.（5）Research on the universality and performance of mycelial pellets assisted flocculent activated sludge granulationFinally,the feasibility of flocculent activated sludge granulation assisted by different representative mycelium pellets such as Aspergillus niger,Aspergillus fumigatus,Phanerochaete Chrysosporium and Streptomyces albicans was investigated.It was found that the sludge biomass initially aggregated in the four mycelium pellets under the optimized conditions could reach 1.24,1.73,1.75 and 1.89 g/g respectively,The SOURs of the formed initial granules could reach 36.52,54.11,45.36 and 56.95mg O2/g VSS,respectively.After screening,continuous culture could form mature AGS with stable perfor mance,showing good sedimentation performance,high biological enzyme activity and strong pollutant removal performance.The results showed that the flocculent activated sludge granulation assisted by mycelium pellets had broad spectrum. |
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