The first step in a typical sludge treatmentline is sludge thickening,
which is performed to increase the concentration of primary or
secondary sludge to 3% total solids (TS) or more using gravity settling,
centrifugation, air flotation, rotary drum filtration, or other
procedures [1]. A recent investigation by Marti and Batista [97] in
full-scale plants revealed that thickening under anaerobic conditions
(e.g. gravity settling and centrifugation) had no influence on
the fate of estrogens in sludge. The same study showed that that
thickening under aerobic conditions (e.g. dissolved air flotation)
decreased estrogen concentration in both liquid and solid phases
of sludge due to biodegradation