Mathematical Simulation Of Anaerobic Digestion Model No.1 Based On Hydraulic Characteristics,Applied To Anaerobic Treatment Of Industrial Wastewater

Since 2002,IWA pubished Anaerobic Digestion Model No 1(ADM1),which has been 20years.ADM1 model has played an important role in scientific research and engineering application of anaerobic digestion of solid waste,liquid wastewater,or co-digestion of multiple wastes.For the technology development of anaerobic digestion engineering,such as technique design,troubleshooting,and operation optimization,ADM1 model was even more important.Though as a quite versatile model,the simulation object of ADM1 designed by IWA is anaerobic digestion of municipal sewage sludge.The implicit flow pattern of the model is continuous stirred tank reactor(CSTR).When the simulation objects are anaerobic digestion of solid substances in agitator tanks,or anaerobic treatment of wastewater at most experimental or small scale,it is feasible to directly apply ADM1.The hydraulic problem of these anaerobic digestion involved is not prominent,or can be ignored.However,using ADM1 for the simultation of current full-scale wastewater anaerobic reactors,the hydraulic characteristic should be considered.Simulation errors or even simulation failures might occur due to igoring hydraulic problem.In this paper,IC anaerobic reactor is used as the research object of anaerobic wastewater treatment to carry out simulation.Firstly,research on the hydraulic characteristics of IC reactor were carried out.And then appropriate hydraulic flow pattern is combined with ADM1 to reconstruct the mathematical simulation model for IC anaerobic reactors.The reconstructed models were respectively applied to the effluent COD_eff simulation of lab-scale IC reactor,and to the effluent COD_eff and biogas production simulation of full-scale anaerobic treatment system treating paper mill deinking wastewater.Satisfactory simulation results were achieved.The main contents of the research are as follows:(1)The IC reactor used in the experiment was set up and configured at first.Using Li⁺as the tracer,a tracing experiment was carryed out for this reactor.Application of residence time distribution(RTD)curve C(t)-t residence time function,and further normalized analysis.Using the residence time distribution(RTD)research technic,the C(t)-t residence time function curves of the reactor were drawn.The function curves were normalized and analysised further.By comparing the tracing results of the blank operation and normal operation,the study concluded that the volume of the reactor and the size of the HRT may be the two main influencing factors that affect the flow pattern of this IC reactor.The multi-tank series model(TIS)was used to simulate the flow patten of IC reactor,and it was found that the gradual increasing-size CSTRs(ISC)model was better fitting tracing result than other two.Therefore,in this study,the ISC model method was chosed for the flow simulation of the IC reactor.(2)On this foundation,ADM1 combined with ISC model(ISC-ADM1)was established.According to the ratio of 1:2:5,the overall unit of the IC reactor was divided by ISC model.Based on the results of sensitivity analysis,the Monod specific maximum absorption rate and half-saturation constant of propionate and acetate were estimated and upated.Using the established ISC-ADM1 model to simulate the start-up process and two shocking experiments of the IC reactor,the simulation results were basically consistent with variation tendency of the effluent COD_eff actual resultes.(3)Taking the full-scale IC reactor of a paper mill wastewater treating plant based in Guangzhou as the research object,according to the mixing zone,expansion zone and polishing zone at a ratio of 1:1:1,a three-level CSTRs series model is established to simulate this full-sacle IC reactor.Under stable state testing,the mixing zone showed acidified characteristic,mainly due to the accumulation of large amount of VFAs;VFAs were almost removed in expansion zone and polishing zone.The effluent p H of the simulation was close to neutral.Then,under dynamic simulation conditions,the ratio of CH₄ to CO₂ in the biogas discharged from this full-scale IC reactor was basically the same,and did not change with the variation of influent flow or influent concentration.After the influent substrates were converted to VFAs in the mixing zone,these VFAs were further decomposed and removed at expansion zone and the polishing zone.In these three layers,the microbes that degrade macromolecular organic matters(X_su,X_aa,and X_fa)regularly changed.(4)According to the designed plan of paper mill wastewater treating plant based in Guangzhou,a mathematical model of anaerobic biochemical simulation of wastewater was established,which was divided into two parts:pre-acidification tank module and IC reaction tower module.At the same time,in accordance with the theoretical assumptions of the ADM1,the COD composition of the actual deinking wastewater components is classified using the physical-chemistry composition analysis method.In view of the disadvantage the local sensitivity analysis method that cannot provide effective analysis to the model,the global sensitivity analysis method was used to conducte the correlation analysis of the anaerobic system effluent COD_eff and biogas production.The Monod absorption rate and half saturation constant of propionate,acetate and hydrogen(6 parameters)were selected to estimate and modify.Simulations were carried out on the COD_eff and biogas production of the anaerobic system of deinking wastewater.The simulation results of the modified parameters were basically consistent with the measured values,and were better than that of the original parameters.(5)As anaerobic biochemical previos treatment,pre-acidification decomposes macromolecular organic matters into small molecular organic matters.By using the modified parameter,the simulation result of pre-acidification COD_eff was also basically consistent with that of actual sampling;the simulation result of pre-acidification biogas production volume was0,which agreed with the actual situation of pre-acidification tank.(6)This study illustrates that the mathematical simulation model proposed by this research is effective in the simulation of full-scale wastewater anaerobic treatment system(IC reaction tower,pre-acidification tank).This model also can be applied to actual wastewater anaerobic treatment projects,which will provide meaningful theoretical model guidance for actual operations such as device operation,debugging,and diagnosis.