Evaluation of the potential of coagulant recovered from WTP sludge for use in low and high turbidity water

ABSTRACT

This study aimed to verify the feasibility of recovering the coagulant used in the water treatment plant of Palmitinho, Rio Grande do Sul, through the use of the sludge acid extraction process, observing the possibility of its application for the treatment of raw water, with two distinct characteristics: low and high turbidity. The regeneration of coagulant by acid route may represent a viable alternative treatment to be used, providing a concentration of 683.31 mg.L⁻¹ of aluminum sulfate to the recovered solution. In low and high turbidity tests, the recovered coagulant, when tested in high turbidity and color waters, showed a higher applicability range than commercial coagulant, with removal ≥ 90% of turbidity in virtually all pH tracks tested, as well as efficiency in apparent and true color removal. However, there was a limitation in the use of coagulant recovered when transferring color to the water to be treated, when low turbidity, to which the commercial coagulant was more efficient. The use of the recovered coagulant did not meet the requirements for permissible impurity concentration per product, taking into account the CIPPA calculated for manganese and cadmium elements, proposed by NBR 15784; Therefore, it was not viable in natural water treatment. In addition, even having provided a reduction of approximately 45% in the final volume of sludge, the insoluble residue obtained had physicochemical characteristics that can make its final disposal difficult.

Keywords:
water treatment; water treatment plant’s sludge; coagulation; acid pathway