Lodo secundário de esgoto sanitário como adsorvente alternativo para remoção de corante vermelho reativo 120 em solução aquosa

Abstract

Considering the problem of inadequate final disposition of sewage sludge and pollution caused by contaminated effluents with dyes, in this work, evaluated the use of sewage sludge as an alternative adsorbant to high-cost commercial activated carbon. Thereby, reuse of this waste ally a sustainable alternative to its recycling potential. It was evaluated the potential of this residue in the removal of the Red Reactive 120 dye in the in natural form (without activation technique), after thermal treatment (pyrolysis) and chemical treatment with 0.1 mol L-1 HNO3. The adsorbents were physico-chemically characterized by the moisture content, volatile and ash content, real specific mass, pH, zero charge point pH (pHpcz), Fourier Transform Infrared Spectrometry (FTIR), Boehm Method, morphology by Scanning Electron Microscopy (SEM) and by Dispersive Energy System (EDS); X-ray diffractometry; Thermogravimetric analysis and adsorption/desorption analysis of N2. The kinetic assays were carried out based on the statistical design elaborated with central composite rotational design (CCRD), varying pH and temperature for each of the studied adsorbents. Subsequently, adsorption equilibrium tests were carried out using isotherms and thermodynamic properties (ΔS°, ΔH° and ΔG°). The kinetic data obtained were adjusted to the pseudo-first and pseudo-second order Lagergren models. From the results, it was verified that natural sludge adsorption presented low efficiency in terms of dye removal. However, the efficiency of adsorption of dye with pyrolyzed and functionalized sludge resulted in 75 to 92% and 92 to 97%, respectively, with different values of pH and temperature. The adsorption kinetics data were better fitted to the pseudosecond order model with R² higher than 0.98 for most of the investigated conditions and the adsorption equilibrium data to the Langmuir model. The ΔG ° results were negative at 25°C, 45°C and 55°C, indicating that the process is endothermic and spontaneous. The increase in temperature favored adsorption with sewage sludge. Thus, it was concluded that the sewage sludge used in this study, with thermal and chemical treatment, is an alternative in the removal of Red Reactive 120 dye, and it can be used as an alternative low-cost adsorbent.