Formation Process, Function Mechanism And Mathematic Modeling Of The Aerobic Granular Sludge

Aerobic granular sludge is a type of microbial aggregate through self-immobilization and granulation of the microorganisms in activated sludge. Aerobic granule usually has regular shape,good settling ability,compact structure, high biomass retention,and diversity of microbial population.It ensures a higher substrate removal efficiency,less excess sludge disposal,less area consumption and lower costs for capital construction,compared with activated sludge floes.Therefore, this process has been regarded as a promising wastewater treatment system.However, aerobic granulation is a very complex phenomenon.There are numerous internal interactions among process variables,such as growth,storage,microbial products formation and endogenous respiration,and sludge characteristics,including biomass detachment,oxygen transfer and diffusion.In this thesis,the formation,the function mechanism and the mathematical modeling of aerobic granular sludge were systematically explored.The storage processes of aerobic granules under both aerobic and anoxic conditions were investigated.The production of extracellular polymeric substances(EPS) and soluble microbial products(SMP) in aerobic granular sludge were also explored.Furthermore,this work was the first attempt to cultivate aerobic granules on low-strength municipal wastewater in a pilot-scale sequencing batch reactor(SBR).Main contents and results are as follows:1.Aerobic granules were successfully cultivated in SBRs fed with both soybean-processing and fatty-acids-rich wastewaters.,Based on experimental observations and formation mechanism analysis,the aerobic granulation process in terms of mean radius profiles was quantitatively characterized.In the granulation process,the mean diameter of bioparticles gradually increased.Their settling velocity increased to 40 m h^-1,while their sludge volume index(SVI) decreased to 20 mL g^-1. The chemical oxygen demand(COD) removal efficiency increased to 98%.The developed model is applicable to describing the aerobic sludge granulation process and substrate diffusion within granules appropriately.Three phases in the granule formation process could be clearly distinguished:initial exponential growth phase, linear growth phase afterwards and final stable phase.2.The autotrophic and heterotrophic growth and competition in aerobic granular sludge were explored using a batch experimental approach.The activated sludge model No.3(ASM3) was modified based on experimental results in order to describe the simultaneous autotrophic and heterotrophic growth in aerobic granules.The distribution within granules and competition for dissolved oxygen of autotrophs and heterotrophs were analyzed.It was found that full oxidation of ammonia and COD by autotrophs and heterotrophs occurred within 1.5 h.The heterotrophs accounted for major oxygen consumption than the autotrophs.The autotrophs were mainly located on the outer layer of granules,whereas the heterotrophs were present in the center of granules,or on the outer layer of granules.3.With the bioenergetic methodology established by McCarty,the microbial yield was predicted and the overall stoichiometrics for biological reactions involving the key chemical and biological species in activated sludge were established.The bioenergetic methodology was integrated with a modified activated sludge model No.1(ASM1) to formulate a new approach to analyze the activated sludge process, with the treatment of soybean-processing wastewater as an example.This approach was able to approximately describe the treatment of soybean wastewater by activated sludge in terms of the concentration dynamics of C₁₆H₂₄O₅N₄,CH₂O,cell(C₅H₇O₂N), H⁺,NH₄⁺,HCO₃^-and CO₂.4.The internal storage mechanisms and electron flows from the external substrate occurring in aerobic granule sludge were explored with extensive storage experiments under different initial conditions.The simultaneous growth and storage processes in aerobic granules were accurately modeled.Aerobic granules in an SBR were subjected to alternative feast and famine conditions,and were able to rapidly take up carbon substrate in wastewater and to store it as intracellular storage products when the substrate was in excess.After the depletion of the external substrate,the accumulated storage polymer was utilized for heterotrophic growth. 5.The internal storage mechanisms in aerobic granule sludge under anoxic conditions were investigated with respirometric experimental results.Hydrolysis, simultaneous anoxic storage and growth,anoxic maintenance,and endogenous decay were found to be the main bioreaction processes governing the anoxic storage in the aerobic granules.Kinetic analysis of nitrate utilization rate(NUR) indicates that the NUR of granules-based denitrification process included four linear phases of nitrate reduction.Furthermore,the methodology for determining the most important parameter in anoxic storage,i.e.,anoxic reduction factor,was established based on an analysis of anoxic storage mechanisms.The performance of storage process in a granule-based denitrification system was accurately modeled.6.EPS produced by mixed microbial community were characterized using gel-permeating chromatography(GPC) and 3-dimensional excitation emission matrix (EEM) fluorescence spectroscopy measurement.The production of EPS,as well as its molecular weight(MW),depended on the external substrate utilization.The quantity of produced EPS increases significantly in the substrate utilization process.With the parallel factor analysis(PARAFAC) approach,two components of the polymer matrix are identified by the EEM analysis,one as proteins at Ex/Em 280/340 nm and one matrix associated as fulvic-acid-like substances at 320/400 nm.7.A novel and convenient approach to evaluate the EPS production kinetics was developed.The weighted least-squares analysis was employed to calculate approximate differences in EPS concentration between model predictions and experimental results.An iterative search routine in Monte Carlo simulation was utilized for optimizing the objective function by minimizing the sum of squared weighted errors.Parameters estimation results indicate that the kinetic coefficients of EPS production by activated sludge and their practical identifiability information could be obtained accurately and conveniently with this approach.Electrons from the external substrate were distributed in the following order:new biomass synthesis of 61%,oxygen for respiration of 21%,and EPS of 18%.8.The sub-fractions of the SMP,i.e.,utilization-associated products(UAP) and biomass-associated products(BAP),excreted by activated sludge were characterized in terms of formation sequence,MW and chemical natures,using MW and dissolved organic carbon(DOC) measurements,coupled with oxygen utilization rate determination,polysaccharide and protein measurement,3-dimensional EEM fluorescence spectroscopy and Fourier transform infrared spectroscopy(FTIR) analysis.The UAP,produced in the substrate utilization process,were found to be carbonaceous compounds with an MW lower than 290 kDa.The BAP were mainly cellular macromolecules with an MW in a range of 290-5000 kDa,and were further classified into the growth-associated BAP(GBAP) and the endogeny-associated BAP (EBAP).9.A new approach for determinating SMP,UAP and BAP and their production kinetics was established.A mathematical model was developed to further quantitatively and qualitatively describe the production kinetics and sub-fractionation of SMP.The objective functions of UAP and BAP were constructed based on the integrated substrate utilization equation.A spreadsheet program was utilized to optimize the objective function by minimizing the sum of squared weighted errors.In this way,the best estimations of the rate coefficientsμH,Ks and k_B.(?)p and the two yield coefficients for active bacteria(Y_H) and UAP(k_UAP) were determined.Furthermore, the relationships among the formation of the three sub-fractions of the SMP and the substrate utilization,as well as the SMP formation mechanisms,were elucidated.10.The formation of EPS,SMP and internal storage products(X_STO) in aerobic granular sludge was investigated using experimental and modeling approaches.An expanded unified model describing the production and the consumption of EPS,SMP, and X_STO was formulated after integrating the electron flows from the external substrate to EPS,SMP,and X_STO.The effect of the sludge retention time(SRT) of the reactor on the formation of EPS,SMP,and X_STO in the aerobic granular sludge was analyzed.The new model could be used for process control and thus for the optimization of aerobic-granule-based reactors.11.The formation mechanism,component characterization,and mathematical modeling of the microbial products of autotrophs in the aerobic granular sludge were investigated systemically.The formation mechanism of EPS and SMP by autotrophs the nitrifying sludge was explored using EEM fluorescence spectroscopy and GPC measurement.The heterotrophic growth on the microbial products in the nitrifying sludge feeding with non-organic carbon source was also evaluated.The aerobic growth of the NOB occurred at the expense of nitrite as an electron donor and resulted in the production of new biomass,UAP,EPS,and nitrate.These autotrophic microbial products could be utilized as the sole electrons and carbon source for the heterotrophic growth in autotrophic systems.12.For the first time,aerobic granules with an excellent settling ability were cultivated in a pilot-scale SBR for the treatment of low-strength municipal wastewater. The key factors in the granulation of activated sludge grown on the low-strength municipal wastewater were identifed.Mathematical modeling of this pilot-scale granule-based reactor was successfully achieved.The granules had a diameter ranging from 0.2 to 0.8 mm and had good settling ability with a settling velocity of 18-40 m h^-1.Three bacteria with rod,coccus and filament morphologies coexisted in the granules.The volume exchange ratio and settling time were found to be two key factors in the granulation of activated sludge grown on such a low-concentration wastewater in an SBR.13.The accelerating startup of anaerobic ammonium oxidation(ANAMMOX) process in an upflow anaerobic sludge blanket(UASB) reactor was achieved by seeding aerobic granules.The structure and physicochemical properties of the ANAMMOX granules and the reactor performance were characterized.Microbial community analysis was performed to reveal the composition and dynamics of the microbial consortium based on denaturing gradient gel electrophoresisanalysis and 16S rRNA genes amplified from the granular sludge.The obtained results demonstrate that aerobic granular sludge could be effectively used to inoculate ANAMMOX reactors.