紊流脉动对生物膜理化性质的影响

Effect of turbulent pulsation on physical and chemical properties of biofilm

在实际紊流中同时存在时均流速和脉动流速,为仅研究紊流脉动流速对生物膜理化性质的影响,设计时均流速为零、仅存在脉动流速的振动格栅生物膜反应器;采用粒子图像测速(PIV)技术测定反应器在5个格栅振动频率下的二维紊流流速场,并计算载片处的有效紊流强度;针对不同的紊流脉动速度,对振动格栅反应器中生物膜的生物量、厚度、密度和其胞外聚合物(EPS)的组成成分进行测定与分析。结果表明:改变紊流脉动流速会使生物膜的理化性质发生变化,随着紊流脉动流速的增大,生物膜生物量和厚度先增加后减小,且均在有效紊流强度为1.92 cm/s时达到最大值;生物膜密度和EPS中蛋白质、多糖的质量分数却随紊流脉动流速的增大而增大,且蛋白质和多糖在紧密结合型EPS(TB-EPS)中的质量分数多于在松散结合型EPS(LB-EPS)中,而无论在LB-EPS、TB-EPS还是总-EPS中蛋白质的质量分数均多于多糖。研究成果可为生物膜反应器的设计与运行优化提供理论参考。

Time-averaged flow velocity and pulsating flow velocity coexist in actual turbulence.In order to study the effect of turbulent pulsating flow velocity on the physical and chemical properties of biofilm,an oscillating-grid biofilm reactor was designed which only has pulsating flow velocity with the time-averaged flow velocity being zero.The two-dimensional turbulent flow field of the reactor was measured by particle image velocimetry(PIV)at five oscillating-grid frequencies,and the effective turbulent intensities at biofilm carriers were calculated.The biomass,thickness,and density of the biofilm,as well as the composition of the extracellular polymeric substances(EPS)in the oscillating-grid reactor were measured and analyzed at different turbulent pulsating flow velocities.Research results show that changing the turbulent pulsating flow velocity would change the physical and chemical properties of biofilm.With the increase of the turbulent pulsating velocity,the biomass and thickness of the biofilm first increased and then decreased,and the maximum value was reached when the effective turbulent intensity was 1.92 cm/s.While the biofilm density and the content of protein and carbohydrates in EPS increased with increasing turbulent pulsating flow velocity,and the content of protein and carbohydrates in tightly bound EPS(TB-EPS)was more than that in loosely bound EPS(LB-EPS).The ratios of protein to carbohydrates content in LB-EPS,TB-EPS,and total-EPS were greater than one.This research can provide theoretical reference for the design and operation optimization of biofilm reactors.