Review on process intensification for adsorptive wastewater treatment: focus on bed geometries

Abstract

Treating wastewater contaminated with toxic pollutants is becoming increasingly challenging for chemical processes and allied industries due to stringent environmental legislation and the focus on sustainability. Conventional wastewater treatment processes involve multiple stages with many unit operations and processes. To meet the growing technical, economical, and environmental sustainability needs, industries are interested in innovative processes and technologies offering compact, small-sized equipment with improved mass transport, heat, and momentum and reduced capital and operating expenses. The Process Intensification (PI) approach is gaining importance in wastewater treatment as it offers these advantages. Among the various separation methods involved in wastewater treatment, adsorption is considered to be one of the most robust methods in the series of treatments for removing low concentrations of contaminants. The design of adsorption columns with alternate bed geometries is desirable to meet the requirements of less installation cost, small footprint area, and compact adsorption columns without compromising performance. However, there is limited literature are available related to bed geometries (helical and tapered) other than the vertical fixed type. Therefore, a systematic literature review was performed with an interest in adsorption bed configuration and separation performance. Key technical aspects are explored, including the influence of bed geometry, adsorbent stratification (normal and reverse), and flow dynamics on mass transfer kinetics. Computational Fluid Dynamics (CFD) modeling employs governing equations such as the Advection-Dispersion Equation and Darcy’s Law, which aids in optimizing column performance. The incorporation of adsorption isotherms, such as Langmuir and Freundlich models, provides a deeper understanding of pollutant-adsorbent interactions. The study also evaluates economic aspects, comparing CAPEX and OPEX across configurations. Fixed beds feature low initial costs but face challenges like clogging and pressure drops. Tapered beds, while more expensive to fabricate, achieve efficient flow distribution and reduced adsorbent usage. With their intricate design, Helical coil columns demand higher manufacturing and operational investments but excel in compactness and efficiency. The review can help the researchers to leverage the potential of process intensification to enhance the adsorption column design and advance in wastewater treatment.