After settling for approximately 2–5 min while preparing for
pumping, the mixture was pumped to the filter press by a
diaphragm pump and the content in the holding tank was periodically
stirred gently without breaking the flocs to avoid excessive
settling. At the initial stage the pumping rate was controlled by
adjusting the air pressure to the diaphragm pump. As the pressure
built up inside the filter chambers, the pumping rate reduced
over time. The pressure profiles during the dewatering process
are shown in Fig. 2. The filtrate forced through the weave in the
filter cloth was collected and weighed periodically during the process.
For the tests with high dewatering rate (optimum flocculation
with lignite conditioning), the filtration process was terminated
when the mass of the filtrate collected over a period of 10 min was
0.1–0.5 kg. When the dewatering rate was low for the tests without
lignite conditioning or under-flocculated, the runs were stopped
after 3–4 h. After the pressure was released, the solid cakes inside
each chamber were removed from the filter cloth and weighed. The
solids were homogenised prior to sampling for moisture content
measurements.