粪大肠菌群吸附于悬沙的规律、机理及其在湖库水体中运动转化的数值模拟研究

Fecal coliforms (FC) are used as indicators of fecal contamination and microbiological impairment of water in China and many other countries. It has been known for a long time that FC exist in water in two forms, either as free-swimming bacteria within the water column or attached to suspended sediment particles and that transport and inactivation of attached bacteria are very different from the free-swimming. Because of the biological activity of FC, the attachment of FC to particles is different from other physicochemical attachment processes. Though it is commonly admitted that it is essential to understand the attachment of FC to suspended sediment particles, especially to know what fraction of bacteria like FC is attached to the particles, little research effort has been put on this issue. There are very different results from the existing observation data. Some observations show most of the indicators are free-swimming while others contrast this by demonstrating the majority of indicators in water are attached to suspended sediment particles. This cannot be statisfatorily explained yet for lacking of understanding of the mechanisms of the attachment, and as a result existing numerical models cannot accurately predict the fate and tranport of indicator bacteria in waters. Experimental research and field sampling are planned in this proposal to investigate the characteristcis and mechanisms of the attachment, and from this we will develop a numerical model and apply it to model the fate and tranport of FC in lakes and reservoirs.

我国和很多其他国家目前都采用粪大肠菌群(FC)，也称为耐热大肠菌群作为微生物指示菌，水体中的FC以两种状态存在，一部分呈自由态，另一部分吸附于水体中的悬沙，吸附态FC运动和转化规律都与自由态不同。由于细菌的生物活性, 细菌-矿物吸附作用有别于物理化学吸附过程，理解悬沙吸附解吸FC的规律，尤其是确定吸附态FC的含量是准确模拟和预测FC在水体中的运动和转化过程、控制水体FC污染的关键问题。虽然指示菌-悬沙吸附作用的重要性得到了学者们的公认，但对这一过程的规律和机理研究还很不充分。某些现场采样分析显示水体中绝大部分指示菌都是自由态的，但另外一些结果却与之完全相反，由于对吸附机理的认识不足，还不能对这一现象进行解释，这也影响了数值预测指示菌运动转化规律的准确性。本项目将综合采用室内试验和现场采样研究水体中悬沙吸附态FC的规律和机理，在此基础上建立湖库水体中FC的迁移转化模型并应用于实际模拟。

地表水体中的指示菌，如粪大肠菌群(FC)和大肠杆菌等，以两种状态存在，一部分呈自由态，另一部分吸附于水体中的悬沙，吸附态指示菌的运动和转化规律都与自由态不同。理解悬沙吸附指示菌的规律，尤其是确定吸附态指示菌的含量是准确模拟和预测指示菌在水体中的运动和转化过程、控制水体微生物污染的关键问题。项目通过室内试验，研究了悬浮泥沙吸附粪大肠菌群(FC)的规律，结果表明，该吸附可以用线性模型描述，即单位质量泥沙颗粒上吸附态FC浓度和自由态浓度成正比，线性分配系数随泥沙颗粒减小而增大。 因为天然泥沙组成复杂，为了进一步研究粒径的影响，项目利用石英、钾长石和方解石矿物颗粒，开展了吸附试验，结果与天然泥沙类似。项目利用DLVO理论对吸附的机理进行了分析，结果表明势垒随泥沙粒径减小而减小，一定程度上解释了为何指示菌更容易吸附于细颗粒。项目还利用微流体和显微技术，在单细胞水平上，对颗粒吸附大肠杆菌的过程进行了研究，结果也表明细菌更容易吸附于细颗粒，另外，与理想的玻璃微球相比，细菌更容易吸附于表面不规则的天然泥沙。在上述研究的基础上，构建了指示菌运动转化的数值模型，并进行了验证和应用。项目研究加深了对颗粒吸附指示菌的认识，为控制控制水体微生物污染提供了技术支撑。