Study On Process Simulation Of Anaerobic Digestion Of Food Waste Based On ADM1

The system instability caused by changes in external environmental conditions and product inhibition in the system seriously restricts the promotion and application of anaerobic digestion?AD?technology in the field of food waste?FW?treatment.The development of a mathematical model that is reliably applicable to the simulation of AD process of FW is of great significance in process technology development,online process diagnosis,intelligent control and process mechanism research.This is also an effective means to overcome the difficulty in promoting and applying AD technology for FW.This study presents an ADM1-FW model suitable for simulating the AD stable process of FW and two unstable processes?overload stress and ammonia stress?.Specifically,the model considered the material characteristics of the FW and AD process characteristics.It modified the model structure,optimize the dynamic feedback relationship and calibrate the corresponding kinetic parameters based on the widely recognized anaerobic digestion model No.1?ADM1?.The new model?ADM1-FW?was validated by the experimental data reported by our research team and other domestic and international research results.The main research contents and research results are as follows:?1?The characteristics of FW and sewage sludge?SS?are different.The original ADM1 model based on SS cannot accurately simulate the AD process of FW.Based on the original model structure of ADM1,this study completed the model structure modification,dynamic feedback relationship optimization and key dynamic parameters calibration for the FW AD system,and proposed a new model,named ADM1-FW,to simulat the AD process of FW.The model modification includes:1)The disintegration stage changes the form of the single substrate input in the original ADM1 to the input form of the granular material with different components of the FW and theSS.2)The hydrolysis and acidification stages were combined.3)Expand the metabolic pathway of propionic acid-degrading microorganisms in the ADM1-FW model.4)The model has expanded the ammonia-tolerant methanogens and the ammonia-tolerant methanogens,and simulated their methanogenesis process separately.Dynamic feedback relationship optimization includes:1)A continuous sigmoid function was used in ADM1-FW instead of the pH segmentation function in the original model.2)The newly constructed VFA inhibition function describes the suppression feedback relationship of VFA to the AD process.3)Ammonia inhibition uses a threshold suppression function instead of a non-competitive inhibition function,and considers the feedback feedback relationship of NH₃and NH₄⁺to the AD process,respectively.?2?The ADM1-FW accurately models the AD process of a stable operating reactor.Microbial decay constant?kdec?,decomposition constant?kdis?,carbohydrate hydrolysis constant?khyd_ch?,acetic acid maximum specific absorption rate?km_ac?and semi-saturation constant?KS_ac?significantly affect methane production,which is the model key parameters for calibration.The calibration results for the above parameters are 0.001d^-1,0.16 d^-1,3 d^-1,1 g COD_sub gCOD^-1_bio d^-1 and 0.23 g COD_sub L^-1,respectively.The calibrated model achieved better simulation results than ADM1 during model validation.The correlation coefficient R² for ADM1-FW is above 90%,the RMSE is 0.645±0.48,the Taylor inequality coefficient TIC is 0.08±0.07,which is much smaller than the model accuracy evaluation value of 0.3.However,the ADM1 simulation result were R²=0.780,RMSE=1.985,TIC=0.316,which exceeds the model accuracy evaluation value of 0.3.Obviously,the ADM1-FW model can accurately simulate the stable AD process of FW,and the simulation results are better than ADM1.?3?The ADM1-FW model accurately simulates the process of overload stress and ammonia stress AD process.Extended Monod specific absorption rate?km_ac2?,half-saturation?KS_ac2?,decay rate?kdec_ac2?,microbial to substrate yield?Yac2?,and ammonia suppression function threshold contant?KImax_NH₃,KImax_NH₄,KImin_NH₃,KImin_NH₄?;VFA inhibition coefficient?KI_VFA?and lower pH inhibition?pH_LL?have a greater impact on methane production and VFA simulation results.The calibration results of the above parameters are:4.71±5.64 g COD_sub gCOD^-1_bio d^-1?0.80±0.37 g COD_sub L^-1?0.0076±0.0153 d^-1?0.14±0.07 g COD_bio gCOD^-1_sub?166±106mg L^-1?5279±905 mg L^-1?40±39 mg L^-1?1172±393 mg L^-1?0.85±0.23 gCOD L^-1 and7.24±0.39,respectively.The above parameter values can be used as recommended parameter values for the simulation of the process of AD of the FW.In the model verification,the correlation coefficient R² of CH₄ is above 90%,the R² of TVFA is above85%,and the TIC<0.3 of all groups.It shows that the difference between the simulated value and the experimental value is small,and the predicted result is within the acceptable range.It is also confirmed that the ADM1-FW model is reliable for the digestion process simulation of the unstable AD process.?4?In the ammonia-stressed reactor,with the increase of TAN,the fermentative bacteria increased from 0.7905±0.0125 to 0.8393±0.0011,the acetogenic bacteria decreased from 0.0262±0.0043 to 0.0156±0,and the methanogenic decreased from0.1138±0.0078 to 0.0719±0.0005.After the ADM1-FW model was simulated under the corresponding TAN conditions:the concentration of the fermentative bacteria increased from 3.54±0.02 gCOD/L to 3.59±0 gCOD/L;the acetogenic bacteria decreased from2.03±0.01 gCOD/L to 1.51.±0.18 gCOD/L;methanogenic decreased from 2.40±0.04gCOD/L to 2.24±0.08 gCOD/L,and the simulated trend was consistent with the trend of the measured analysis.In addition,the relative abundance of ammonia-tolerant methanogens was significantly increased?p<0.01?.It was increased from 0.0031±0.0011in the low TAN group to 0.0259±0.0000 in the high TAN group.The change rule of this kind of ammonia-tolerant methanogens is also consistent with the trend of simulation results.In summary,it is further confirmed that the ADM1-FW model is used to describe the rationality of the AD process of FW,and it also shows the practicability of the model for the future succession of microbial community structure.In summary,based on theoretical analysis and a large number of experimental studies,this study constructs a mathematical model suitable for simulating the stable process and unstable process of AD process of FW.Finally,taking the case of ammonia stress as an example,it is confirmed that the simulation results of microbial community structure succession are consistent with the experimental results.It not only confirms the consistency of microbial community structure succession between the simulation results and experimental results,but also confirms the rationality of model construction.The ADM1-FW model developed in this study can provide important technical support for system design,operation management and ensuring efficient and stable operation during AD of FW.