Environmental Sustainability of the Removal of Alpaca Fiber Dye Using a Thermally Modified Sludge from a Drinking Water Treatment Facility

In this work, the removal of dye using thermally modified sludge from a drinking water treatment facility (DWTS) was evaluated. This study gives value to the waste from the coagulation flocculation process (waste sludge) in order to remove an emerging organic agent (Bordeaux B). The sustainability of the process leads to a circular economy, which represents an important environmental contribution. The physicochemical characterization of the DWTS was carried out by standard methods. DRX and FTIR spectroscopy, SEM, and superficial specific area S_BET N₂ at 77 K were used. Thermal activation processes were carried out (200–600 °C) to obtain the best activated thermal conditions for dye removal (T: 500 °C). Muscovite and other minerals were found in the DWTS. Experimental conditions (batch mode) were determined: contact time (CT), pH, adsorbent dose (AD), and dye initial concentration (Co). S_BET = 54.77 and 67.90 m²/g by DWTS and TA-500. The best removal efficiency was achieved at 500 °C (R = 85.57 ± 0.76 %, q max = 37.45 ± 0.14 mg/g), which, compared to other unconventional adsorbents, is more reliable and competitive. The adsorption process was adjusted to the Langmuir mathematics model, following pseudo-second-order kinetics (R² = 0.99).