Use of talc for filamentous bulking control in effluent treatment plant

Abstract

One of the main existing operational problems in activated sludge effluent treatment processes is the poor sedimentation of the biological sludge in the secondary clarifiers. This poor settleability of the sludge is, generally, associated with excessive growth of filamentous bacteria in the bioreactor causing sludge filamentous bulking. In Brazil, many pulp and paper mills have faced problems related to sludge filamentous bulking in their effluent treatment plants experiencing a significant reduction in COD and BOD removal efficiency and a loss of suspended solids in the treated effluent. The addition of talc to increase floc density for the control of filamentous bulking has been studied. The objective of this study was to test the use of talc for the control of filamentous bulking. The bio-sludge used was obtained from a recycling paper mill and had an abundance of filamentous bacteria Type 021N. The experiment consisted of five bioreactors operating batch wise with sludge age of ten days. Different talc applications were used: 0%, 25%, 50%, 75% and 100% in relation to the total suspended solids in the aeration tank. The following analyses were carried out to monitor the system: suspended solids, sludge volumetric index (SVI) and chemical oxygen demand. Successive additions of talc contributed for the reduction of IVL. Dosages of 75% and 100% showed to be most efficient to improve settleability of the sludge. The presence of talc did not interfere with biological activity of the sludge. However, it was observed an increase of the total suspended solid concentration in the aeration tank. The addition of talc had a temporary effect on sludge settleability, so it was necessary to add repeatedly talc in the reactor in order to maintain a low sludge volumetric index.