Polyaluminiumchloride (PACl) has been used as a conditioner for waste activated sludge prior to dewatering and drying. PACl addition to waste sludge is a technically feasible and very effective method to avoid fouling in direct sludge dryers.
Researchers in Belgium have reported on a new application of polyaluminiumchloride (PACl) as a conditioner for waste activated sludge prior to dewatering and drying.
The process is demonstrated at lab scale with a shear test-based protocol, where a dose ranging from 50 to 150 g PACl/kg MLSS (mixed liquor suspended solids) mitigates the stickiness of partially dried sludge with a dry solids content between 25% and 60% dry solids (DS).
For example, at a solids dryness of 46% DS, the shear stress required for the pre-consolidated sludge to slip over a steel surface is reduced by 35%.
The salient feature of PACl is further supported by torque data from a full scale decanter centrifuge used to dewater waste sludge. The maximum torque developed by the screw conveyor inside the decanter centrifuge is reduced by 20% when the sludge feed is conditioned with PACl.
The researchers propose that the beneficial effect of waste sludge conditioning with PACl is due to the bound water associated with the aluminium polymers in PACl solutions. This acts as a type of lubrication for the intrinsically sticky sludge solids during drying.
It can be anticipated that PACl addition to waste sludge will become a technically feasible and very effective method to avoid fouling problems in direct sludge dryers. It will also reduce torque issues in indirect sludge dryers, as well as in sludge decanter centrifuges.
