Impact of cationic polyelectrolytes on activated sludge morphology and biological wastewater treatment in a Sequential Batch Reactor (SBR)

Abstract

The variability of the sedimentation characteristics of activated sludge is a phenomenon that often occurs in biological wastewater treatment plants. Deterioration of sedimentation properties requires the application of polyelectrolytes. They affect the morphology of sludge flocs, facilitating and accelerating their deposition. On the other hand, the type of reagent used and its dose may affect the quality of the treated wastewater. This study investigates the effect of dosing two different cationic polyelectrolytes on the properties of activated sludge and treated wastewater parameters in lab-scale sequencing batch reactors (SBRs). During studies, doses of polyelectrolytes that significantly changed activated sludge flocs' morphology were applied. It caused an improvement of the sludge volume index (SVI) from 42 to even 80 % in relation to the control reactor. However, polymers overdose resulted in the SVI increase by 10–14 % and obtaining sludge flocs with a highly branched structure, difficult to thicken. The applied polymers Praestol 855BS and Superfloc C-18530 did not affect the chemical characteristics of the treated wastewater. The only significant effect was observed for the turbidity of the wastewater. Polymers doses reduced the value of that parameter by 54–64 %. In addition, a simulation of a technological failure for several days was introduced to assess the durability of the produced flocs and their impact on the effectiveness of wastewater treatment. The experiment showed that Praestol formed stable and durable flocs, while for Superfloc polymer, a slight temporary deterioration of wastewater quality was observed due to the lower cohesion of the activated sludge.