A review of the biochemistry of heavy metal biosorption by brown algae

doi:10.1016/S0043-1354(03)00293-8

Water Research

Volume 37, Issue 18, November 2003, Pages 4311-4330

https://doi.org/10.1016/S0043-1354(03)00293-8 Get rights and content

Abstract

The passive removal of toxic heavy metals such as Cd²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cr³⁺, and Hg²⁺ by inexpensive biomaterials, termed biosorption, requires that the substrate displays high metal uptake and selectivity, as well as suitable mechanical properties for applied remediation scenarios. In recent years, many low-cost sorbents have been investigated, but the brown algae have since proven to be the most effective and promising substrates. It is their basic biochemical constitution that is responsible for this enhanced performance among biomaterials. More specifically, it is the properties of cell wall constituents, such as alginate and fucoidan, which are chiefly responsible for heavy metal chelation. In this comprehensive review, the emphasis is on outlining the biochemical properties of the brown algae that set them apart from other algal biosorbents. A detailed description of the macromolecular conformation of the alginate biopolymer is offered in order to explain the heavy metal selectivity displayed by the brown algae. The role of cellular structure, storage polysaccharides, cell wall and extracellular polysaccharides is evaluated in terms of their potential for metal sequestration. Binding mechanisms are discussed, including the key functional groups involved and the ion-exchange process. Quantification of metal–biomass interactions is fundamental to the evaluation of potential implementation strategies, hence sorption isotherms, ion-exchange constants, as well as models used to characterize algal biosorption are reviewed. The sorption behavior (i.e., capacity, affinity) of brown algae with various heavy metals is summarized and their relative performance is evaluated.

Introduction

Biosorption is a term that describes the removal of heavy metals by the passive binding to non-living biomass from an aqueous solution. This implies that the removal mechanism is not metabolically controlled. In contrast, the term bioaccumulation describes an active process whereby removal of metals requires the metabolic activity of a living organism. In recent years research on the mechanisms of biosorption has intensified since biomass can be employed to sequester heavy metals from industrial effluents (e.g. from the mining or electroplating industry) or to recover precious metals from processing solutions.

Of the many types of biosorbents (i.e. fungi, bacteria, and yeasts) recently investigated for their ability to sequester heavy metals, brown algal biomass has proven to be highly effective as well as reliable and predictable in the removal of, for example, Pb²⁺, Cu²⁺, Cd²⁺, and Zn²⁺ from aqueous solutions. Some reviews that deal with biosorption by different types of biomass include [1], [2], [3]. This review is devoted to biosorption by brown algal biomass and an effort was made to outline their classification. As model predictions of heavy metal biosorption become more sophisticated, there is an underlying need to appreciate the basic cell biology and biochemistry of the brown algae and how these compare to other algae. To this end, the emphasis is placed on outlining the fundamental parameters that are at play in biosorption by the brown algae.

Section snippets

A comparison with other algae

The term algae refers to a large and diverse assemblage of organisms that contain chlorophyll and carry out oxygenic photosynthesis. It is important to note that algae are distinct from Cyanophyta, class Cyanophyceae, the blue-green algae, which are also oxygenic phototrophs, but are eubacteria (true bacteria), and are therefore evolutionarily distinct from algae. Although most algae are microscopic in size and are thus considered to be microorganisms, several forms are macroscopic in

Cellular structure

A typical brown algal cell is depicted in Fig. 3. The chloroplast envelope (Ce) contains the chloroplasts which have three thylakoids (an interconnected set of disc-like sacs) per band. This structure (known as a plastid; the most common of which is the chloroplast) stores food material and contains chlorophyll a, c₁, and c₂. In addition to the chloroplast envelope, the chloroplasts are surrounded by the two membranes of the chloroplast endoplasmic reticulum (Cer). The outer membrane which

Key functional groups

The carboxylic groups are generally the most abundant acidic functional group in the brown algae. They constitute the highest percentage of titratable sites (typically greater than 70%) in dried brown algal biomass. The adsorption capacity of the algae is directly related to the presence of these sites on the alginate polymer, which itself comprises a significant component (up to 40% of the dry weight, [12]) of the dried seaweed biomass. Furthermore, the majority of metals of interest (i.e. Cd²⁺

Sorption isotherms

From a scientist's perspective, the field of biosorption is a challenging one, since it requires the application of first principles of organic chemistry and geochemistry. The main objectives are the elucidation of binding mechanisms, the relative affinity of heavy metals for the biomass, and how both are affected by varying environmental conditions. Ultimately, the goal is the successful implementation of a remediation program.

The first step towards these objectives is to quantify the capacity

Conclusions

The brown algae represent an especially efficient and resilient class of biosorbents relative to other biomass types. Fortunately, due to their economic value in many industrial applications, there is much information about their basic structure and biochemical constitution. This in turn makes the interpretation of the sorption behaviors and elucidation of metal binding mechanisms more rigorous. The order Laminariales and Fucales of the brown algae (division Phaeophyta) are the most important

Acknowledgements

We wish to acknowledge our colleague, Dr. Silke Schiewer whose previous work greatly influenced this text. This work was made possible by a Natural Sciences and Engineering Research Council of Canada (NSERC) Seed Grant to A.M. Additional financial support was provided by individual NSERC Research grants to A.M. and B.V. as well as funding from NSERC and the Fonds pour la Formation des Chercheurs et l’Aide à la Recherche du Québec (FCAR) to T.D. in the form of a post-graduate scholarships.

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ReviewA review of the biochemistry of heavy metal biosorption by brown algae

Abstract

Introduction

Section snippets

A comparison with other algae

Cellular structure

Key functional groups

Sorption isotherms

Conclusions

Acknowledgements

Trends Biotechnol

Carbohyd Res

Carbohyd Res

Carbohyd Res

Carbohydr Res

Carbohyd Res

Int J Biol Macromol

Carbohydr Res

Water Res

Carbohyd Res

Water Res

Water Res

Proc Biochem

Water Res

Water Res

Carbohyd Poly

Carbohyd Res

Biosorption of heavy metals

Biotechnol Prog

Biosorption by marine algae

Algal products

Tagblatt der 58. Versammlung deutscher naturforscher und bei Eugleninen

Osterr Botan Z

Seasonal variation in chemical composition of some of the littoral seaweeds common to Scotland. Part II. Fucus serratus, Fucus vesiculosus, Fucus spiralis, and Pelvetia canaliculata

J Soc Chem Ind

The seasonal variation in weight and chemical composition of the common British Laminariaceae

J Mar Bio Assoc UK

Cell wall and intercellular region polysaccharides

Chemistry and physical properties of alginates

Carbohyd Eur

Biochemical taxonomy

Biochemistry of sea algae

Hoppe-Seyler's Z Physiol Chem

The seasonal variation in chemical composition of the sublittoral seaweeds common to Scotland

J Soc Chem Ind

Contribution of sulphonate groups and alginate to heavy metal biosorption by the dry biomass of Sargassum fluitans

Environ Sci Technol

Metal selectivity of Sargassum spp. and their alginates in relation to their α-l-guluronic acid content and conformation

Environ Sci Technol

A study of the constitution of alginic acid by partial acid hydrolysis

Acta Chem Scand

Review
A review of the biochemistry of heavy metal biosorption by brown algae