**1. Introduction**

#### **1.1 Wastewater**

Water which is the key element responsible for life in the world is becoming more valuable due to the increased consumption and demand. In order to provide a locally controlled water supply, wastewater recycling offers great environmental advantages. Recycling of water can corporate in decreasing the consumption of water from sensitive ecosystem, reducing the environmental pollution, and even preventing accumulation of pollutants in our ecosystem. The US Environmental Protection Agency (USEPA) has suggested three stages of water recycling; in the primary stage that can be achieved by a sedimentation process, normally the produced water is not suitable for any use. The biological oxidation and disinfection process are used to reach the secondary stage. The produced water from that stage can be used mainly for irrigation of nonfood crop and industrial cooling system. The tertiary stage in wastewater treatment is reached using chemical, coagulation, filtration, and disinfection processes. Produced water in the tertiary stage can be employed mostly for irrigation of food crops and landscape, washing of vehicles, and flushing toilet [1]. Good quality water (i.e., water free of contaminants) is essential to human health and a critical feedstock in a variety of key industries including oil and gas, petrochemicals, pharmaceuticals, and food. The available supplies of water are

decreasing due to (1) low precipitation, (2) increased population growth, (3) more strict health-based regulations, and (4) competing demands from a variety of users, e.g., industrial, agricultural, and urban development. In addition, our water today became such type of cocktail of chemicals that has more than 100 of toxic compounds, viruses, bacteria, and metals. Consequently, water scientists and engineers are seeking alternative sources of water and new technologies for wastewater treatment and recycling. These wastewaters include but not limited to sewage effluent, contaminated surface or groundwater, and industrial wastewater. Water recoveryrecycle-reuse has proven to be effective and successful in creating a new and reliable water supply while not compromising public health [2].

#### **1.2 Heavy metals**

Water pollution with contaminants became a global issue. Among of these contaminants, heavy metals have a greater concern mainly due to their bioaccumulation, toxicity, and non-biodegradability. Their non-biodegradability nature makes their existence in water to cause great risk to living organisms. Accordingly, many government environmental agencies such the US Environmental Protection Agency (USEPA) and World Health Organization (WHO) have set the maximum acceptable concentration level for heavy metals in recycled water. Therefore, different methodologies, with varying level of success, have been employed to remove these contaminations from water and wastewater. Biological treatment (aerobic and anaerobic), coagulation, precipitation, oxidation, membrane, and filtration are common methods of removing microorganisms and ionic and cationic compounds from wastewater streams. The performance of these methods is generally acceptable at low concentration of heavy metals below few hundred ppm, which is the main drawback of them. Even though most of the wastewater treatment technologies available today are effective, they are often costly and time-consuming methods. Bioadsorption is considered as among the most promising low-cost process for wastewater treatment. Numerous materials were used as adsorbents to remove heavy metal ions from water, such as metal oxides, activated carbon, zeolite, chitin*,* metal sulfide, resin, etc. The search for new and more effective materials to be used as bioadsorbent materials has a continuous effort and been considered by many researchers. Since 1990 till now, there are more than 5000 publications in the field of bioadsorption of heavy metals, and approximately 6% of these publications have been concerned on using marine algae [3]. **Figure 1**(**a** and **b**) shows the dramatic increase in both the number of publications and their citations versus time.

#### **1.3 Marine algae**

Marine algae are one of the most highly available natural resources in tropical ecosystem where around 2 million tons of them are collected from seas and oceans and cultured in artificial system [4]. They are useful in different applications such as pharmaceutical, food, and cosmetic industries. Algae have rich biochemical composition; therefore, its biomass is a promising material to be used as bioadsorbent to decontaminate water and wastewater by removing pollutants such as heavy metals [5, 6]. Marine algae are commonly known as seaweeds, and they had a great potential to be used in pollutant removal process as a promising bioadsorbents material. This is due to their renewable availability, distinct properties, and high biosorption capacity. Seaweeds are divided into three main broad groups, namely, (i) green (Chlorophyta), (ii) red (Rhodophyta), and (iii) brown (Phaeophyta) algae. Marine algae have many advantages for bioadsorption. Among them brown algae provided the best adsorption capacities due to their cell wall structure and components.

**153**

increases [8].

**Figure 1.**

**Figure 2.**

*citations each year on these publication [3].*

*Marine Algae Bioadsorbents for Adsorptive Removal of Heavy Metals*

The cell wall of brown algae has a lot of active chemical functional groups such hydroxyl, carboxylic acid, amine, imidazole, phosphate, phenolic, thioether, and sulfhydryl which offer a selective binding and interaction with metals and pollutants in the bioadsorption process. It contains mainly cellulose, a group of salts of sodium, potassium magnesium, and calcium, and alginate, which is a type of

*Histograms for (a) number of publications in the field of biosorption of heavy metals and (b) the number of* 

**Figure 2** illustrates the main four mechanisms of heavy metal uptake by bioadsorbents. The first one is ion-exchange process including ionic or cationic exchange. The surface of the cell wall contains mainly organic nitrogen group in the case of ionic exchange or hydroxyl and organic sulfate or phosphate in the case of cationic exchange. The uptake mechanism can be a complexation through a covalent or electrostatic interaction where the metal ions form a complex compound with organic molecules. The third mechanism is chelation which involves an interaction between the metal and an organic compound that has more than one electron donor functional group. The last one is through precipitation that occurs when the pH of the solution varies due to cellular metabolism or when the concentration of metals

**Table 1** summarizes some of the marine algae (red, green, and brown), those used for removal of transition, actinide, or lanthanide metals. Many researchers found that the *Sargassum* brown algae has a high adsorption capacity

polysaccharide (anionic copolymer) [7].

*Classification of metal uptake mechanism by bioadsorbents.*

*DOI: http://dx.doi.org/10.5772/intechopen.80850*

*Marine Algae Bioadsorbents for Adsorptive Removal of Heavy Metals DOI: http://dx.doi.org/10.5772/intechopen.80850*

#### **Figure 1.**

*Advanced Sorption Process Applications*

**1.2 Heavy metals**

**1.3 Marine algae**

water supply while not compromising public health [2].

decreasing due to (1) low precipitation, (2) increased population growth, (3) more strict health-based regulations, and (4) competing demands from a variety of users, e.g., industrial, agricultural, and urban development. In addition, our water today became such type of cocktail of chemicals that has more than 100 of toxic compounds, viruses, bacteria, and metals. Consequently, water scientists and engineers are seeking alternative sources of water and new technologies for wastewater treatment and recycling. These wastewaters include but not limited to sewage effluent, contaminated surface or groundwater, and industrial wastewater. Water recoveryrecycle-reuse has proven to be effective and successful in creating a new and reliable

Water pollution with contaminants became a global issue. Among of these contaminants, heavy metals have a greater concern mainly due to their bioaccumulation, toxicity, and non-biodegradability. Their non-biodegradability nature makes their existence in water to cause great risk to living organisms. Accordingly, many government environmental agencies such the US Environmental Protection Agency (USEPA) and World Health Organization (WHO) have set the maximum acceptable concentration level for heavy metals in recycled water. Therefore, different methodologies, with varying level of success, have been employed to remove these contaminations from water and wastewater. Biological treatment (aerobic and anaerobic), coagulation, precipitation, oxidation, membrane, and filtration are common methods of removing microorganisms and ionic and cationic compounds from wastewater streams. The performance of these methods is generally acceptable at low concentration of heavy metals below few hundred ppm, which is the main drawback of them. Even though most of the wastewater treatment technologies available today are effective, they are often costly and time-consuming methods. Bioadsorption is considered as among the most promising low-cost process for wastewater treatment. Numerous materials were used as adsorbents to remove heavy metal ions from water, such as metal oxides, activated carbon, zeolite, chitin*,* metal sulfide, resin, etc. The search for new and more effective materials to be used as bioadsorbent materials has a continuous effort and been considered by many researchers. Since 1990 till now, there are more than 5000 publications in the field of bioadsorption of heavy metals, and approximately 6% of these publications have been concerned on using marine algae [3]. **Figure 1**(**a** and **b**) shows the dramatic increase in both the number of publications and their citations versus time.

Marine algae are one of the most highly available natural resources in tropical ecosystem where around 2 million tons of them are collected from seas and oceans and cultured in artificial system [4]. They are useful in different applications such as pharmaceutical, food, and cosmetic industries. Algae have rich biochemical composition; therefore, its biomass is a promising material to be used as bioadsorbent to decontaminate water and wastewater by removing pollutants such as heavy metals [5, 6]. Marine algae are commonly known as seaweeds, and they had a great potential to be used in pollutant removal process as a promising bioadsorbents material. This is due to their renewable availability, distinct properties, and high biosorption capacity. Seaweeds are divided into three main broad groups, namely, (i) green (Chlorophyta), (ii) red (Rhodophyta), and (iii) brown (Phaeophyta) algae. Marine algae have many advantages for bioadsorption. Among them brown algae provided the best adsorption capacities due to their cell wall structure and components.

**152**

*Histograms for (a) number of publications in the field of biosorption of heavy metals and (b) the number of citations each year on these publication [3].*

#### **Figure 2.**

*Classification of metal uptake mechanism by bioadsorbents.*

The cell wall of brown algae has a lot of active chemical functional groups such hydroxyl, carboxylic acid, amine, imidazole, phosphate, phenolic, thioether, and sulfhydryl which offer a selective binding and interaction with metals and pollutants in the bioadsorption process. It contains mainly cellulose, a group of salts of sodium, potassium magnesium, and calcium, and alginate, which is a type of polysaccharide (anionic copolymer) [7].

**Figure 2** illustrates the main four mechanisms of heavy metal uptake by bioadsorbents. The first one is ion-exchange process including ionic or cationic exchange. The surface of the cell wall contains mainly organic nitrogen group in the case of ionic exchange or hydroxyl and organic sulfate or phosphate in the case of cationic exchange. The uptake mechanism can be a complexation through a covalent or electrostatic interaction where the metal ions form a complex compound with organic molecules. The third mechanism is chelation which involves an interaction between the metal and an organic compound that has more than one electron donor functional group. The last one is through precipitation that occurs when the pH of the solution varies due to cellular metabolism or when the concentration of metals increases [8].

**Table 1** summarizes some of the marine algae (red, green, and brown), those used for removal of transition, actinide, or lanthanide metals. Many researchers found that the *Sargassum* brown algae has a high adsorption capacity


#### **Table 1.**

*Marine algae used in bioadsorption removal of heavy and lanthanide metals.*

**155**

**Figure 3.**

*Adsorption isotherm.*

*Marine Algae Bioadsorbents for Adsorptive Removal of Heavy Metals*

to remove heavy metals such as Cu, Ni, Cd, Pd, Cr, Sm, and Pr from their solution efficiently due to its cell wall structure that is rich in active bioadsorption sites [9, 10, 15, 17–19]. Mostly, bioadsorption offers many advantages over the bioaccumulation process since bioadsorbents are available commonly as byproduct or waste, as well as they do not need growth media and growth conditions. As a result, they are considered low-cost materials with high possibility to be reused for many cycles. The literatures show that marine algae can be used for the removal of heavy metals in dead or live forms. However, in industrial applications, the nonliving marine algae provide more practical bioadsorbent materials for the removal of pollutants. This is because toxicity of heavy metals and other pollutants do not affect dead biomass. In addition, the performance of those bioadsorbents can be improved by physical treatments such as heating or chemical processing such as acid or base treatments. This enhancement in their biosorption capacity is attributed to activation of the adsorption sites as well as rearrangement of the cell wall structure to be more accessible and compatible

An idea about the adsorption process is predicted using the correlation between the pressure or the concentration of adsorbate and the adsorption capacity (X/m) at

The amount of adsorbate (X) adsorbed should be normalized by the mass of adsorbent (m) to allow comparison of different materials. From **Figure 1**, it can be predicted that after the saturation point, the number of adsorption sites on the adsorbent is occupied, and the vacancies became limited so that the adsorption does not occur anymore. There are five general types of adsorption isotherms. They are

*DOI: http://dx.doi.org/10.5772/intechopen.80850*

for pollutants capturing and removal [35].

constant temperature as shown in **Figure 3**.

**2.1 Adsorption isotherm models**

as follows:

**2. The nature and kinetics of bioadsorption**

*Marine Algae Bioadsorbents for Adsorptive Removal of Heavy Metals DOI: http://dx.doi.org/10.5772/intechopen.80850*

to remove heavy metals such as Cu, Ni, Cd, Pd, Cr, Sm, and Pr from their solution efficiently due to its cell wall structure that is rich in active bioadsorption sites [9, 10, 15, 17–19]. Mostly, bioadsorption offers many advantages over the bioaccumulation process since bioadsorbents are available commonly as byproduct or waste, as well as they do not need growth media and growth conditions. As a result, they are considered low-cost materials with high possibility to be reused for many cycles. The literatures show that marine algae can be used for the removal of heavy metals in dead or live forms. However, in industrial applications, the nonliving marine algae provide more practical bioadsorbent materials for the removal of pollutants. This is because toxicity of heavy metals and other pollutants do not affect dead biomass. In addition, the performance of those bioadsorbents can be improved by physical treatments such as heating or chemical processing such as acid or base treatments. This enhancement in their biosorption capacity is attributed to activation of the adsorption sites as well as rearrangement of the cell wall structure to be more accessible and compatible for pollutants capturing and removal [35].
