Three-dimensional Multi-bacteria Modeling Of Aerobic Granular Sludge Based On Cellular Automata

Aerobic granular sludge is a kind of microbial polymer formed by self-immobilized cultivation in aerobic wastewater system,which has been well studied due to the great application prospects in wastewater treatment.However,the granulation process of aerobic sludge was still the key factor to affect its practical application.A three-dimensional multi-bacteria mathematical model of aerobic granular sludge was developed based on the cellular automata in the dissertation.Moreover,the growth of aerobic granular sludge and the effect factors were investigated.The endogenous respiration process of aerobic granular sludge was investigated.The results showed that the cells would oxidize themselves and intracellular storage products to release energy and matters during the process of endogenous respiration.Activated Sludge Model No.1(ASM1)and Activated Sludge Model No.3(ASM3)were used to fit the experimental data and results indicated that the ASM3 showed better performances on the simulation of aerobic granules endogenous respiration.The respiration rate of heterotrophic bacteria fitting by ASM3 was 0.15 d-1 and the respiration rate of intracellular storage products was about 1.55 d-1.In addition,two different phases can be distinguished in the oxygen uptake rate(OUR)profiles during endogenous respiration.The intracellular storage products in granular sludge occupied little proportion,whereas it contributes greatly to OUR.A dual-morphology and multi-bacteria model based on ASM3 was developed to explain the inhibitory effect of toxic substances on the performance of aerobic granular sludge and aerobic flocculent sludge.In this model,diffusion,storage and growth,endogenous respiration,and biomass decay are taken into account.The model was successfully validated with the OUR profiles for the aerobic granules in treating synthetic wastewater.The model simulation indicates that aerobic granules showed high persistence against the toxic effects compared with flocs.The compact structure of granules as a protection barrier against the diffusive toxins of toxicant.The large granules have a good potential for treating toxic wastewater.On the basis of dual-morphology and multi-bacteria model,a three-dimensional mathematical model of aerobic granules was established through the application of the theory of cellular automata.This model was used to simulate the growth of aerobic granular sludge and the spatial distribution of microbial population under different conditions.The simulation showed that the size of granules was smaller under a high shear stress,while the content of autotrophic bacteria in granules interior was higher.Under the condition of high concentration oxygen,the granular sludge with larger size,also the autotrophs within granules are higher.In addition,the inhibition of toxic substance would result the slow growth of granules.The modeling results show that the autotrophs and toxic-degrading bacteria are mainly present in the outer layers of granule,whereas the ordinary heterotrophs mainly located in the granule center.