Effective utilization of Moringa seeds waste as a new green environmental adsorbent for removal of industrial toxic dyes

Abstract

The Moringa seeds waste (MSW), which resulted from the oil extraction industry, contains many varieties of natural organic components such as flavonoid, tannins, phenolic and hydrolyzable carbohydrates. The MSW could be considered a promising and an efficient green adsorbent for wastewater treatment as it reduces the environmental impact of hazardous chemicals existing in the industrial wastewater. The present work is designated to clarify the possibility of using MSW for the removal of industrial dispersed red 60 (DR60) and Congo Red (CR) dyes from aqueous solutions. The factors affecting the adsorption process such as initial dye concentration, catalyst weight, pH value, and solution temperature were investigated. It was found that the adsorption rate for both dyes was very high at the initial stages of the process and then decreases until reaches the equilibrium. The adsorption rate of the DR60 dye was not affected by catalyst weight, pH or the solution temperature. Whereas the percentage of the CR dye removal is found to be 100% for all dyes concentrations except for the CR dye with high initial concentration (100mg/L), which reached only 85.3%. It was observed that the adsorption % of CR dye increases by increasing the temperature from 25 to 40°C. With more increases in the reaction temperature from 40 to 80°C, the CR removal decreases from 88.7 to 57.7%, respectively. This behavior can be attributed to the desorption behavior of the adsorbed dye molecules at a higher temperature. Accordingly, the optimum temperature for the CR dye adsorption is found at 40°C. A detailed study of the dye adsorption isotherms and kinetics was carried out and the results show that the dyes adsorption isotherms and kinetics are followed by Freundlich and pseudo-second-order models. Maximum amounts of dyes adsorbed were found to be 170.7 and 196.8mg/g for both CR and DR60 dyes, respectively, at 100mg/L concentration, 25°C and pH 7. The overall rate of adsorption process seems to be controlled by a chemical process mechanism involving valence forces through exchange or sharing of electrons between dyes and MSW adsorbent.