A laboratory study on the behavior of estuarine sediment flocculation as function of salinity, EPS and living algae

The interactions between organic and inorganic particles in the context of flocculation is an on-going topic of research. Most current researches do not distinguish between the effects of EPS (produced by microorganisms) and living microorganisms (like algae). In this study, the effect of salinity, EPS and living algae on sediment flocculation are investigated separately. Several types of measurements were performed, which can be divided into the following categories: sediment at different salinities, sediment in the presence of EPS at different salinities, sediment in the presence of living algae at a given salinity. Results show that increasing salinity enhances slightly sediment flocculation. In the presence of EPS there was hardly any flocculation in demi-water, but the flocculation was significant in saline water. The living algae cells were shown to flocculate with themselves and form large flocs. These algae flocs can bind to sediment particles to form larger flocs, both in demi-water and sea water. Size-wise algae-sediment flocs were largest, EPS-sediment flocs came second, and salt-sediment flocs were smallest. •The presence of EPS and living microalgae can promote larger flocs than salinity effects only.•The EPS acts as a traditional flocculant, while the microalgae cells can aggregate with each other and also bind to sediment.•The ratio algae concentration (CC) to sediment concentration (SSC) is driving floc properties.•The combined action of salt and EPS does not follow the DLVO theory, but the presence of cations is required to promote flocculation.