Coupling Effect Of Biofilm Growth And Gas-liquid Two-phase Flow In Microchannel

Methane,as a powerful greenhouse gas,has a great influence on environment when it been released into the atmosphere.For this reason,it is a problem faced by the scientists to find a way of efficiently utilizing the dispersed energy.A new and effective technique methane conversion technology based on the combination of biofilm technique and microchannel reactor was devised and this bioreactor is a complex biochemical reaction system involving biofilm growth and gas-liquid two-phase flow,where many key problems need to be studied.In this work,the coupling effect of biofilm growth and gas-liquid two-phase flow,the influence of characteristics of gas-liquid two-phase flow and transport on bioconversion performance,improving the bioconversion performance of bioreactor by enhanced mass transfer and increased biofilm were explored using visualization method.Firstly,the effect of gas-liquid interface on the movement,distribution and adhesive growth of bacteria was analyzed.Due to the tremendous shear stress of the gas-liquid interface on the wall of the microchannel,most of the biofilm formed in the corner region,whereas the a few biofilm formed on the wall of the main stream.The growth process of biofilm could be divided into five stages: reversible adhesion,rapid growth,slow growth and mature stability.The length of bubble and liquid slug was decreased with the biofilm growth because of the decrease of circulation area.During the growth process of biofilm,the bioconversion and space-time bioconversion gone through five stages: slow growth,rapid growth,slow growth,slow decline and steady fluctuation.The steady value of bioconversion and space-time bioconversion were 8.7% and 263 mol/(h·m3)in the bioreactor with roughness modification.Moreover,the influence of operating conditions on the gas-liquid two-phase flow and the transport characteristics in the microhannel bioreactor with formed biofilm was revealed.With increase of gas flow rate,the length of bubble increased,resulting in the increase of bioconversion and space-time bioconversion of methane and oxygen.However,when the gas flow rate increased to a critical value,the bioconversion and space-time bioconversion began to reduce.With the increase of liquid flow rate,the residence time of methane and oxygen was reduce,which led to the decrease of bioconversion and space-time bioconversion.When the temperature was 30°C and p H was 7.0,the bioactivity of biofilm was the highest and the microchannal bioreactor had best bioconversion performance.In addition,the mass transfer characteristics and the bioconversion ability of biofilm were two key factors affecting the performance of microchannel bioreactor.The wavy microchannel bioreactor and mansard microchannel bioreactor were designed to enhance the mass transfer of reactant.The experimental results showed that the biofilm was fewer and distributed on the wall in the form of colonies in wavy microchannel bioreactor,However,a great quantity of biofilm was formed in the corner of turning region,and a large number of colonies are distributed on the wall of the main stream in mansard microchannel bioreactor.Meanwhile,the steady value of bioconversion and space-time bioconversion was improved to almost 12.5%and 380 mol/(h·m3).The obstacle structure enhanced the mass transfer in the mansard microchannel bioreactor,and a great quantity of biofilm formed around the obstacle structure,which increased the steady value of bioconversion and space-time bioconversion to almost 14.5% and 465 mol/(h·m~3).