Activated carbon minimization in two-stage batch adsorption without intermediate adsorbent separation to treat real industrial wastewater containing phenolic compounds

Abstract

The need to treat industrial effluents containing toxic substances has stimulated the search for alternative strategies that can reduce process costs. Among these pollutants, phenolic compounds present a high risk to human health and the environment. The present work explores strategies to minimize costs and the consumption of commercial activated carbons in batch adsorption processes, proposing the use of a new two-stage adsorption approach without intermediate filtration to separate the exhausted adsorbent. Investigation of the thermodynamics and kinetics of these processes enabled the understanding of operational fundamentals that allowed the identification of application niches and the proposal of optimization procedures. Firstly, phenol was used as a model molecule to develop adsorption strategies that minimized the adsorbent dosage and cost, which were then validated using real industrial effluents containing phenolic compounds. Evaluation was made of the effects of operational parameters such as contact time and pH, using different adsorbents. The optimal contact time varied according to the adsorbent uptake capacity, which varied from 23.53 mg g⁻¹ to 146.4 mg g⁻¹ for the different carbons evaluated, while the highest efficiencies were achieved at pH between 3 and 4. The viability of applying the two-stage process without intermediate filtration depended on the capacity of the adsorbent added in the first stage to retain the adsorbed solute, being appropriated for application in industrial processes where the effluent composition does not vary significantly, while the two-stage approach with intermediate filtration could potentially reduce the process cost by 33 %, compared to the conventional one-stage method. The findings are expected to benefit companies operating in the sector, offering ways to reduce adsorbent consumption and minimize environmental impacts.