Simulation Study On Anaerobic Methane Production Enhanced By Batch Exogenous Hydrogen

Carbon neutral operation of wwtps is one of main directions for the future wastewater treatment industry,while anaerobic digestion of excess sludge is the most directed method to recover energy contained in the wastewater.When exogenous H₂ and CO2 are intervened in anaerobic digestion,the production of CH₄ can be stimulated.Study based on model is a powerful tool for anaerobic digestion,which has many advantages when compared to experimental study.An extended model containing homoacetogenic process based on the anaerobic digestion model NO.1 was established,and the anaerobic digestion system status under intervention of exogenous H₂ was simulated with the model,both simulation and experiment were used to assessing the feasibility of improving CH₄ production by exogenous H₂.The yield of CH₄ increase as the dosage of H₂ increasing,but when the dosage is increased to a certain extent,the effect is very limited,and the optimal dosage of exogenous H₂ is 0⁰.33 bar?0¹00ml?.Continuously monitoring the gas phase composition of the reactor,the differences among various dosages were not obvious at the initial stage of a single cycle,while the differences are shown at the end of the cycle in the form of CH₄ production amount.At the beginning of the cycle,the inhibition caused by hydrogen partial pressure on microbes reduces the conversion efficiency of organic compounds,while the differences of CH₄ production under different H₂ dosage are presented as H₂ gradually converted to CH₄,thus releasing the inhibition effect.The built extended model is used to simulate the experimental data,all the four systems?H₂ partial pressure of 0,0.17,0.33 and 0.5 bar?gain good fitting degree.The maximum error of 9.1% was gained when no exogenous H₂ was used,while the minimum error of 1.5% occurred when the dosage of H₂ is 0.5bar.The CH₄ yield has a limited enhancement and energy waste appeared when excessive H₂ was used.It seems that the degradation of the substrate was inhibited by excessive H₂,but simulation and experimental results show that there is potential of producing more CH₄.In order to realize the full degradation of substrate,the method of extending the single cycle length?SRT?can be used,thus get the best results of CH₄ yield.The best range of H₂ dosage is contacted directly to SRT and operation mode of anaerobic digestion system.