Recovery of aluminum sulfate and utilization of sludge generated in the Cañete Water Treatment Plant

Abstract

The present study evaluated the recovery of aluminum sulfate (Al2(SO4)3) from sludge generated at the Cañete Water Treatment Plant (PTAP) and the reuse of the treated residue in the production of handmade bricks. The research was conducted using a quasi-experimental and mixed approach, combining quantitative analyses—through atomic absorption spectrophotometry to measure the concentration of recovered aluminum and jar tests to determine turbidity removal efficiency—and qualitative analyses, observing color, floc formation, and sedimentation behavior. For coagulant recovery, the dried sludge was acidified with sulfuric acid (H2SO4 at 95%), reducing the pH from slightly alkaline values (7.32–7.48) to an acidic range of 2.13–3.27, which allowed the dissolution of aluminum species and the production of an effective coagulant. Acid digestion results showed an average recovered aluminum concentration of 0.0125 mg/L, with a recovery efficiency of up to 91.4% under conditions of pH ≈ 2.1 and 6.5 mL of H2SO4, demonstrating the effectiveness of the process. The remaining sediment was dried, pulverized, and mixed with cement, sand, and water to produce handmade bricks through molding, setting, and curing. The recovered aluminum sulfate achieved a turbidity removal efficiency of 94.08%, higher than that of commercial coagulant (90.03%), confirming its technical viability. The bricks produced with recovered sludge exhibited an apparent density of 1.82 g/cm3, indicating good compaction and consistency. This study demonstrates the potential for sustainable sludge reuse, promoting circular economy practices, waste reduction, and the production of construction materials with acceptable physical properties.