The effect of extraction temperature on the sludge dewatering
ability for extractions carried out at 200 rpm is presented in Fig. 2.
With increased extraction temperature the removal of SS after
filtration for AF and DF increased and reached the maximum
removal at 70 C, then remained constant to 90 C. Between 25 C to
50 C, the SS removal for AF was higher than the DF; in contrast,
lower water recovery was observed for AF compared with DF. The
flocs formed by DF were very fine and passed through the pores of
the filter cloth during filtration whilst leading to high water recovery
and low SS removal. On the other hand, the flocs formed by
AF were bigger but fluffy (not dense flocs) and were retained by the
filter cloth and hindered the passage of water which led to lower
water recovery. As the flocs were loosely packed, some of it were
easily broken into fine particles during filtration and passed
through the filter cloth and thus lower the solid removal efficiency.
The observed phenomena for both AF and DF indicated weak floc
formation and low flocculating ability. Both observations are undesirable
if a high sludge dewatering efficiency needs to be
achieved.