Influence of sludge characteristics on coagulant recovery from water treatment sludge: a preliminary study

Abstract

This study investigated the effect of raw water quality and coagulant type and dosage on the efficiency of aluminium recovery from water treatment sludge by acidification process. One of the features of this study is to prioritise several factors affecting aluminium recovery using demonstrating experiments and analysing the result using model. The previous studies comparing the aluminium recovery from PACl and alum sludge had collected the sludge from treatment plants treating different source water. However, this study compares aluminium recovery from PACl and alum sludge obtained from treating same source water. Water treatment sludge was prepared in laboratory by coagulating raw water with different inorganic and organic contents using aluminium sulphate (alum) and polyaluminium chloride (PACl) as coagulants. The effect of the different factors on the aluminium recovery efficiency was evaluated using a 23 full factorial experimental design. The aluminium recovery efficiency was higher for PACl sludge compared to alum sludge with recovery ranging from 62.5 to 74.5 % for alum sludge and from 70.7 to 84.0 % for PACl sludge. At higher concentrations of organic matter and turbidity in the raw water, lower aluminium recovery efficiency was observed for both the sludges. The study thus shows the important effects of raw water quality and coagulant type and dose on the recovery process.