Low-Cost Adsorbents for the Removal of Phenol/Phenolics, Pesticides, and Dyes from Wastewater Systems: A Review

The huge development of industrial production and human activities throughout the world has resulted in serious water pollution. Pesticides, dyes, phenol, and phenolic compounds may be life-threatening to humans and marine aquatic animals, even at low concentrations. These pollutants must be removed by using different techniques to provide high-quality water. So far, the adsorption process has been considered an effective method to remove pollutants from an aqueous solution. The adsorption method has several advantages, such as low cost, easy operation, and high performance. This article reviewed the removal of dye, pesticides, phenol, and phenolic compounds through zeolite, activated carbon, clay, ash fly, and carbon nanotubes by reviewing the existing literature from 2000 to 2022. The properties of the adsorbent, adsorption studies, the method of design, and optimization conditions were reported. The thermodynamic studies were conducted to determine Gibbs free energy change, standard entropy change, and standard enthalpy change. Adsorption isotherms (Langmuir, Freundlich, and Temkim models) revealed the relationship between the amount of adsorbates per unit adsorbent in the equilibrium process. The adsorption kinetic investigations (pseudo-first-order and pseudo-second-order kinetic model) were carried out to determine the rate of adsorption and correlate the experimental data. Experimental results indicated that a higher adsorption capacity can be observed when the adsorbents have a high surface area and high-porosity structure. The removal percentage of pollutants increased when the adsorbent dosage was increased due to the availability of a larger number of adsorption sites. In conclusion, cheaper adsorbents can be used in wastewater treatment to improve water quality and protect the environment.