**1. Introduction**

The increase in population and human activities have caused various pollutants to enter the environment. Substances that exist in industrial, agricultural, and domestic wastewater can be toxic to humans and other organisms and have negative effects on them [1].

Hazardous pollutants can be classified into organic and inorganic materials. However, wastewater from chemical industries, the textile industry, industrial effluent, agricultural runoff, sewage treatment plants [2], urban runoff, boating activities [3], and mines include a high amount of chemicals, heavy metals, soaps, nutrients (nitrogen and phosphorous). There is no doubt that it poses a great threat to the ecological environment and human health. Therefore, the treatment of polluted water is very important.

Application of some methods to eliminate these pollutants like flocculation, membrane separation, and adsorption [4] for wastewater treatment has been used and studied for decades. In recent decades, the study and use of living organisms like microalgae and biodegradable components such as alginate as an absorbent of pollutants has increased. There are some modifications and changes also being made. Chemical modifications of biomaterials, including grafting, cross-linking, combining with other adsorbents, polymerization, and copolymerization. They can increase solubility, stability, and adsorbing capacity of natural polymers. Combining specific

components with alginate creates composite materials containing functional groups that improve the elimination of a wide range of pollutants [5].

The objective of this chapter is introduction of new methods using alginate and adding algae and some materials in order to increase the capacity to absorb pollutants. It is hoped that the best method of pollutant absorption will be introduced in coming future.

## **2. Sources of alginate**

Marine macroalgae or seaweeds are photosynthetic algae that are abundant in every ocean. There are three main classes, or phyla, of seaweed: *Phaeophyta* (brown algae), *Rhodophyta* (red algae), and *Chlorophyta* (green algae) [6].

It is estimated that 1800 brown, 6200 red, and 1800 green macroalgaehave existed in the marine environment [7]. Macroalgae have occurred across all coastlines, seas, and oceans. They are found from the intertidal zone to the greatest depths (>200 m) that has enough light for supporting their growth [8].

Macroalgae and macroalgal debris are important sources of food for benthic organisms [9]. Seaweeds have been used traditionally as food, drugs, fertilizers, and dyes [6]. Currently, seaweeds are used in many countries especially for food industry, human health (medicine, antioxidant, antibacterial properties), agriculture, biofuel production, bioactive compounds extraction, cosmetic industry, biofertilizing, and wastewater treatment [9, 10].

The cell wall of seaweeds produces large amounts of polysaccharides. Several of these compounds are of commercial value as phycocolloids [11].

Phycocolloids, such as alginate, carrageenan, and agar have gelling properties and are the most commonly used components because of their gelling properties in foods, pharmaceutical and biotechnological applications. Alginic acid, fucoidans, and laminarin are the main polysaccharides in brown algae [6]. Alginates and fucoidans are the major constituents of brown seaweed cell walls representing between 17 and 45%, respectively 5–20% of the algal dry weight [10].

E.C.C. Stanford, a Scottish chemist, discovered alginates from British kelp in the 1880s. During World War II, production units of alginate were set up in Scotland and California using local seaweed resources of brown algae. After the war, other production units were launched close to natural seaweed beds in Norway, France, Germany, Japan, and, more recently, China. The main raw materials were obtained from *Macrocystis pyrifera*, the Giant Kelp, in California, from *Ascophyllum nodosum*, *Laminaria hyperborea* and *L. digitata* in north-eastern Atlantic, and from *Durvillaea* and other kelps in the southern hemisphere [12].

In China, the kelp *Saccharina japonica* (previously called *Laminaria japonica*), was considered the main source for the production of alginates and was introduced from Japan to China in the 1950s and grown in the Yellow Sea. In China, the mariculture of this alga yields over 2 million wet tons which makes it the single largest maricultural crop in the world by far [12] and it constitutes ~40% of the world's seaweed production.

In Chile, brown seaweeds such as *Lessonia* spp., *Macrocystis pyrifera* and *Durvillaea antarctica* are used for alginate production and abalone feed and they harvest a total of 100,000 tones y−1. Several other kelps are cultivated or harvested from nature for food and alginates. The cultivation of *Saccharina latissima* is occurring in eastern Canada and the eastern United States. *Alaria esculenta* is also cultivated in eastern

Canada. Other brown seaweeds include *Ascophyllum nodosum*, harvested from wild populations for alginate production in eastern Canada and northern Europe. Chile is an important producer of brown seaweeds representing about 10% (250,000 wet tonnes y−1) of the world supply. *Lessonia* spp. with a large natural population and *Macrocystis* with a much smaller wild population are used to feed abalone industry and for its alginate content [11].
