The dewatering of the sludge with loss on ignition between 50 and 65% will have a maximal drainage on the order of 0.008–0.020 L/s/m2. Dewatering of the sludge with loss of ignition higher than 65% of dry solids will have a maximal drainage on the order of only 0.001–0.004 L/s/m2, approximately five to 10 times lower. It can be seen that there is a tendency for the achievable dewatering result to increase with the decrease of loss on ignition or fat in the feed sludge. The correlation shows that if the loss of ignition is higher than 65% of dry solids in the feed sludge the dewatering results in approximately 10% dry solid or lower in the sludge residue, and in approximately 5% dry solid or lower in the sludge residue if the fat concentration is above 10,000 mg/kg ds in the feed sludge. In systems treating sludge with high contents of fat (15,000–30,000 mg/kg ds) and oil (2,300–7,000 mg/kg ds) and if the loss of ignition is higher than 65% (between 65–76%) the dewatering efficiencies only achieve 5–15% dry solid in the sludge residue. In systems treating sludge with low contents of fat (4,000–8,000 mg/kg ds) and oil (50–2,000 mg/kg ds) and with loss on ignition between 50–65% contents of organic solids the dewatering efficiencies achieve 20–37% dry solid in the sludge residue.
Keywords: dewatering, fat, loss on ignition, organic load, operation problems, reed bed