Material and Process Selection for Biosorption

Introduction

Biosorption ??? the use of biological materials to sequester pollutants from aqueous solution ??? has emerged as one of the most promising and economically viable strategies in environmental remediation. Yet the success of any biosorption system depends critically on decisions made well before the first drop of wastewater enters a column: the choice of biosorbent, the pre-treatment applied, and the mode of operation selected. This chapter provides a comprehensive, expert-guided framework for navigating these decisions, drawing on a breadth of experimental literature and theoretical modelling to offer actionable guidance for researchers and process engineers alike.

From Raw Material to Functional Adsorbent

Biosorbents span a remarkable range of biological origins ??? from bacteria, fungi, and algae to agricultural wastes, animal shells, fish scales, bone powders, and biopolymers ??? each presenting distinct physical and chemical characteristics that determine their suitability for specific pollutants and process configurations. This chapter systematically addresses pore size classification (microporous, mesoporous, macroporous), surface area measurement via BET analysis, point of zero charge, iodine number, and the surface functional groups responsible for metal binding. The pre-treatment landscape ??? encompassing acid and alkali treatments, carbonisation, pyrolysis, magnetic modification, and chelating group incorporation ??? is surveyed with reference to a rich comparative table of biosorbent???adsorbate pairings drawn from the current literature. Crucially, the chapter reveals which pre-treatments enhance performance and which inadvertently complicate downstream regeneration ??? a balance rarely addressed with this degree of clarity.

Mechanisms, Models, and Operational Choices

Beyond material selection, this chapter addresses the mechanistic underpinnings of biosorption ??? distinguishing between extracellular precipitation, cell surface adsorption, and intracellular uptake ??? and explains how the dominant mechanism should inform both biosorbent selection and system design. Batch and continuous column modes of operation are compared, with discussion of fixed-bed and fluidised-bed configurations and the factors ??? temperature, pH, biomass concentration, contact time, and coexisting ions ??? that govern process efficiency. The chapter concludes with a comprehensive treatment of adsorption isotherm models, presenting the equations, linearisation plots, and interpretive frameworks for Langmuir, Freundlich, Redlich???Peterson, Dubinin???Radushkevich, Temkin, Sips, Koble???Corrigan, and Harkin???Jura models. For those seeking to design, optimise, or simply understand a biosorption process from first principles, this chapter is an indispensable reference.

Keywords

Biosorbents ?? Biosorption ?? Characterisation techniques ?? Adsorption isotherm ?? Langmuir model ?? Freundlich model ?? BET analysis ?? Fixed-bed column ?? Batch mode ?? Process selection ?? Surface area ?? Pore size ?? Biosorbent pre-treatment ?? Heavy metal removal ?? Kinetics and modelling ?? Regeneration ?? Extracellular biosorption ?? Intracellular biosorption