Colloids and Surfaces A: Physicochemical and
Engineering Aspects abstract The coagulation and flocculation processes in conventional drinking water treatment generate aggregates
which settle to form a sludge waste. This sludge can be dewatered further by thickening, centrifugation
and filtration operations in order to recover water and minimise the volume of the waste stream.
A range of water treatment sludges generated in the laboratory were characterised according to a
phenomenological method that is valid from the dilute free-settling regime to the concentrated cake
compression stages. These were compared with plant samples.
Experimental results show that raw water natural organic matter (NOM), coagulant dose and coagulation
pH affected both the rate and potential extent of dewatering. Similar effects were observed for both
aluminium sulfate and ferric chloride. These results suggest that increasing dose or pH leads to an increase
in the proportion of rapidly precipitated material in the sludge or flocs, which form looser aggregates and
hence exhibit inferior dewatering properties.