Faecal coliform attachment to settleable suspended sediments in fresh surface waters: linear partition model validation and sediment concentration effects

Controlled experiments were conducted to examine the validity of the linear partition model for faecal coliform (FC) attachment to suspended sediments and assess the impact of sediment concentration on the attachment. Sediments were collected from a river in Beijing, China and the suspended particles < 62 mu m were separated out and mixed with FC suspensions. The experimental mass specific concentration of attached FC linearly increased with the free-floating FC concentration, with the partition coefficient for four different sediment concentrations ranging from 0.2286 to 0.2695 L/g. Actually, the results can be well described using a single partition coefficient of 0.2565 L/g. The rate of sediment particle surface covered by attached FC was in the range of 0.32 x 10(-5)-0.58 x 10(-5), and the relatively low rate gave a possible explanation of the linear relationship. The experimental fraction of attached FC significantly increased with increasing sediment concentration, ranging from 7.5 to 54.2%, and this was well explained by the linear partition model. These results proved that the linear partition model was valid in describing FC attachment to suspended sediments in surface waters and the attached fraction was sediment concentration dependent, while the impact of suspended sediment concentration on the partition coefficient was insignificant.