Elimination of Crystal Violet and Indigo Carmine from Water Using Pinus patula Biochar: Process Optimization and Application to Real Textile Wastewater

Abstract

ABSTRACT : Dyes are toxic compounds that can be present in the environment due to the discharge of untreated or inefficient treated wastewater. Among the industries responsible for the presence of dyes in the environment, the textile industry is remarkable due to the high consumption of dyes during the production processes. Crystal Violet and Indigo Carmine are widely used dyes in the textile industry, and they need to be removed from wastewater before they are discharged into the environment because of their associated toxicity. Biochar is an adsorbing material that has been found to exhibit high efficiencies in the removal of dyes in water. Therefore, biochar produced from the gasification of Pinus patula was used to treat water polluted by Crystal Violet, Indigo Carmine, and real textile wastewater. The obtained results showed that for Crystal Violet the maximum removal efficiency (> 99.9%) was obtained at a pH of 9, biochar dose of 13.5 g/L and biochar particle size of 300-450 µm. The adsorption of Crystal Violet by Pinus patula biochar followed the Langmuir isotherm model and a pseudo-second order kinetic model. For Indigo Carmine, the maximum removal efficiency (99.0%) was obtained at a pH of 3, biochar dose of 13.5 g/L, and particle size of 300-450 µm. The adsorption of Indigo Carmine by Pinus patula biochar was represented by the Freundlich isotherm model and by the pseudo-second order kinetic model. For both dyes, the adsorption involved chemical and physical interactions including hydrogen bonding, electrostatic interactions, pore filling, and π-π interactions. In the regeneration studies, it was found that despite obtaining low desorption efficiencies, the regeneration efficiency of Pinus patula biochar was high being able to accomplish 6 and 7 adsorption-desorption cycles for Crystal Violet and Indigo Carmine-loaded biochar respectively. Biochar from Pinus patula is a potential adsorbent to be used in the textile industry being able to reach colour removal efficiencies of 81.3% in real textile wastewater, as well as high elimination percentages of dissolved organic carbon. Using an adsorbing material like biochar which exhibits high efficiencies in the treatment of dyes in wastewater contributes to the development of the circular economy. Creating the possibility to use waste generated in an industrial process in another process will contribute to the decrease of environmental pollution. The use of biochar for water treatment supposes a pathway towards sustainable development.