tailieunhanh - Sediment and Contaminant Transport in Surface Waters - Chapter 4

Phần lớn các hạt vật chất lơ lửng trong các sông, hồ, và các đại dương tồn tại trong hình thức flocs. Những flocs là tập hợp của các hạt nhỏ hơn, vững chắc có thể được vô cơ hoặc hữu cơ. Sự nhấn mạnh ở đây là sự năng động của tập hợp chủ yếu vô cơ - đó là, các trầm tích hạt mịn. Đây là những đặc biệt phổ biến ở các con sông, trong khu vực gần bờ hồ, đại dương, và trong suốt các cửa sông. Bởi vì họ là hạt mịn, những trầm tích. | 4 Flocculation Settling Deposition and Consolidation Much of the suspended particulate matter in rivers lakes and oceans exists in the form of flocs. These flocs are aggregates of smaller solid particles that may be inorganic or organic. The emphasis here is on the dynamics of aggregates that are primarily inorganic that is fine-grained sediments. These are especially prevalent in rivers in the near-shore areas of lakes and oceans and throughout estuaries. Because they are fine-grained these sediments have large surface-to-mass ratios and hence adsorb and transport many contaminants and other substances with them as they move through an aquatic system. Flocculation is a dynamic process that is flocs both aggregate and disaggregate with time and their sizes and properties change accordingly. The net rate of change of floc properties depends on the relative magnitudes of the rates of aggregation and disaggregation with the steady state being a dynamic balance between the two. It is this dynamic nature of a floc that is particularly interesting and one of the major concerns in the present chapter. Section considers the basic theory of the aggregation of suspended particles. This is useful for a preliminary understanding of the experimental results on the flocculation of suspended particles presented in Section . As flocs are formed their sizes and densities change with time and are quite different from the sizes and densities of the individual particles that make up a floc this greatly modifies the settling speed of the floc. Experimental measurements on the settling speeds of flocs are presented in Section . Based on the elementary theory of aggregation presented in Section and especially the experimental data presented in Sections and numerical models of the aggregation and disaggregation of suspended particles have been developed these are discussed in Section . As sediments both individual particles and flocs are transported through .