Agregação helicoidal e adensamento por filtração do lodo de uma estação de tratamento de água

Abstract

The treatment of sludge generated in water treatment plants (WTP) aims to eliminate a considerable portion of water so that this solid residue can be disposed or used, and thus minimize environmental impacts with its release into the environment. The initial stage of this process occurs with the flocculation of these residues by the application of water-soluble polymers. In the sequence, the sedimented or floated flocs are separated from the clarified liquid phase in thickening operations, followed by dewatering. In this way, it is possible to include stages of treatment of the sludge at the station itself, such as the recovery or regeneration of the coagulant, which can be reused in the treatment of wastewater or in the own treatment performed by the WTP, when attested its viability. Thus, this work aimed at the development of a compact unit with the continuous flow for aggregation, thickening and recovery of aluminum ions from the sludge of a WTP in operation in the city of São Gabriel, RS. The first stage consisted of a characterization of the main physical and mineralogical characteristics of the sludge. In the sequence, an investigation of flocculating polymers of different ionic loads was carried out. Subsequently, the flocculation of the sludge was evaluated in helical tubular flocculators (HTF), units that dispense external energy to promote the mixture between the reagents and effluents in the solid particles aggregation stage. The model tested and selected for the following tests had 12 m of 1.25 cm diameter flexible tubing encased in a rigid polyvinyl chloride (PVC) column. The flocculation was investigated through the unitary application of the cationic polymer P 2900 and in combinations with the anionic polymer P 22 (dual flocculation). This investigation led to the use of the polymer combination due to the total volumetric reduction of these reactants by approximately 50%. Sludge thickening was performed through a built static thickener, and comparative evaluations of sedimentation thickening. The thickened sludge in the static thickener resulted in a solids content (SC) higher than 18%, while in the by sedimentation thickening the highest TS was 7%, both submitted to flocculation in the fed HTF with 4.5 L / min. The recovery of Al ions, or recovery of the coagulant, was carried out through the acidification of the sludge with the application of sulfuric acid. In the study, it was proposed to evaluate this recovery simultaneously to the development of aggregation and thickening, an innovative process considering that the recovery of coagulant from ETA sludge is usually carried out in isolation to the treatment of this waste. In this way, it is sought to minimize the physical structure for the development of the treatment to reduce the volume of the sludge and obtain the recovered coagulant. The results allowed recoveries above 87% of Al ions at pH 2, in addition, the occurrence of the application of the reagents (acid and polymers) allowed a reduction in the volume of polymer applied.