微生物堵塞过程中生物膜生长特征对多孔介质渗流特征影响

A study of microbial clogging on the variation of seepage characteristics with biofilm growth in porous medium

为研究回灌水刺激下生物膜在砂柱中的生长规律,并分析生物膜生长特征对堵塞介质典型渗流特征的影响,采用室内土柱实验方法,供给营养液刺激砂柱内生物膜生长,模拟入渗介质生物堵塞的过程,监测介质渗透系数的变化,并开展不同回灌时长下介质水分吸持实验和弥散试验,并对其内生物膜形态进行表征.结果显示,在0~5h时,渗透系数呈先下降后回升趋势;在回灌至18h前,渗透系数急剧衰减,水力弥散系数明显增大,水分吸持能力的变化并不明显;18h后渗透系数降低速率减缓,水分吸持能力明显升高,溶质运移过渡到以弥散作用为主导机制.综上,可将生物膜在介质内的生长分为三个阶段:菌适应期,接种菌体并未生长繁殖,单纯由于菌体的流入与流出引起渗透系数的变化;菌体大量生长繁殖期,大量生长繁殖的菌体占据了部分介质孔隙体积;胞外聚合物大量分泌期,逐渐形成具有透水性的生物膜,生物膜的生长与回灌水提供的养分形成动态平衡.

The seepage characteristics of porous media varies with the inner biofilm growth irritated by recharge water during groundwater recharge.Indoor soil column experiments were conducted to stimulate the bio clogging process of porous media by continuous injection with nutrient solutions.Growth morphology biofilm and the corresponding seepage parameters of media(including permeability coefficient,water retention and dispersion coefficient)were measured over a series of time periods during experiments.The results showed that the permeability coefficient slightly decreased and rose in the first 5hours.In 5~18 hours,the permeability coefficient decreased sharply,and the hydraulic dispersion coefficient,and greatly increased,but the change of water holding capacity was not obvious.After 18hours,the decrease rate of the permeability coefficient slowed down,whist the water holding capacity began to increase rapidly,and the solute transport in the porous media transited be recharged by dominant mechanism of dispersion.To sum up,the clogging process by the growth of biofilm in the medium can be divided into three stages:(1)First stage is the adaptation period of bacteria,in which the inoculated bacteria did not dramatically grow and reproduce,and the permeability coefficient changed simply because of the retention and migration of bacteria cells;(2)Second stage is the period of mass growth and reproduction of bacteria,in which the increasing bacteria cells occupy more and more pore volume of medium,resulting the decrease in permeability and the increase in dispersion of the porous media;(3)Last stage is the period of extracellular polymer secretion,in which a permeable biofilm is gradually formed,and the growth and shedding of biofilm forms a dynamic balance with the nutrients provided by recharge water.