Application Of ADM1 For The Simulation Of Anaerobic Digestion Of Food Waste Under Ammonia-nitrogen Stress

Anaerobic digestion of food waste is a process technology popularized in China.However,due to the high protein content in food waste,the actual operation of the food waste anaerobic digestion plant is susceptible to ammonia inhibition by ammonia stress.Modeling of the anaerobic process can effectively predict system performance,and is a powerful tool to guide the process design of anaerobic digestion and ensure efficient and stable operation of the reactor.The Anaerobic Digestion Model No.1?ADM1?is a widely applicable mathematical model.However,the model is based on sludge anaerobic digestion system,the substrate characteristics are different from food waste.In order to make the ADM1 model can be used to simulate the anaerobic digestion of food waste,this study proposed a anaerobic digestion process for food waste under ammonia inhibition by modifying the model structure,adding the inhibition function,and calibrating the model parameters.Finally,the modified model was verified.The results are as follows:1)Modified of the model:According to the characteristics of anaerobic digestion of food waste,the model correction is based on the ADM1 model,combined with the four-stage theory of anaerobic digestion.The hydrogen-producing acetogen process were combined,the ADM1 was extended the metabolic pathways of propionate oxidizing bacteria?POB?;Separate simulations in the model based on the characteristics of different amino acid tolerances of acetoclastic methanogenesis microorganisms;pH inhibits the whole process of anaerobic digestion,and uses a growth-curve function to replace the pH inhibition function;The VFA inhibition function was added to inhibits the whole process of anaerobic digestion,and the inhibition of ammonia used threshold-style inhibition instead of non-competitive inhibition,and consider the inhibition of anaerobic digestion by NH₃ and NH₄⁺,respectively.The revised model is named ADM1-FW model.2)Parameter calibration:Sensitivity analysis determined that the specific Monod maximum uptake rate(k_mac2),Monod half saturation constant(K_Sac2),Decay rate constant(k_decac2)yield of biomass on substrate(Y_ac2),ammonia inhibition function upper limits?KImax_NH3,KImax_NH4,KImin_NH3,KImin_NH4?,VFA inhibition constant?KI_VFA?,and pH inhibition lower limits(pH_LL)of the extended acetic acid degradation bacteria Monod had a great influence on the methanogenesis process.Then,through the parameters determined by the sensitivity analysis,the parameters are calibrated by calculating the sum of the squares of the minimized weighted deviation between the calibration experiment value and the model simulation value.The results after parameter estimation were k_mac2=4.71±5.64 kg COD?sub?·[kg COD?bio?d]^-1?K_Sac2=0.80±0.37 kg CDO?sub?·m^-3?k_decac2=0.0076±0.0153 d^-1,Y_ac2=0.14 CODbio·CODsub^-1;K_ImaxNH3?K_ImaxNH4?K_IminNH3?K_IminNH4=166±106?5279±905?40±39?1172±393mg·L^-1;K_IVFA=0.85±0.23 g COD·L^-1;pH_LL=7.24±0.39?,respectively.3)The ADM1-FW model was used to simulate in batch experiments,and compared with the original ADM1 simulation results.The results show that the modified model has better fit than the ADM1.Threshold-style inhibition function can better quantify the different contributions of NH₃ and NH₄⁺to the degree of inhibition.The extended microbiological processes involved in methanogenesis of organic substrates.This set of parameter values can be used as a recommended parameter for simulating anaerobic digestion under ammonia-nitrogen stress.4)Validation and evaluation:The modified model was validated in other food waste experiments.The gas production and total VFA of the two batches were simulated.The model was evaluated using the goodness of fit R²,Theil's inequality coefficient?TIC?and Root mean square error?RMSE?.The results show that the goodness of fit for methane production is above 90%,the TIC is also below 0.3,the RMSE is 1.66±0.28,the goodness of fit for VFA simulation is above 80%,and the TIC coefficient is below 0.30.The RMSE is at 0.95±0.17.The model can be used to simulate the anaerobic digestion of food waste under ammonia inhibition.In summary,the modified ADM1 model was applied to the anaerobic digestion of food waste under ammonia inhibition.A set of kinetic parameters was proposed through calibration experiments and verified in another three sets of batch tests.The obtained ADM1-FW model can provide a reference for the simulation of the process of anaerobic digestion of food waste in the future.