**9. Algal alginate as a coagulant in wastewater treatment**

Coagulation is a process used in water treatment, in which aids are used to change the surface structure of suspended materials to form aggregates and to remove them by destabilization. In this process, inorganic metals and polymers are generally used as coagulation aids [128–130]. The large amount of chemicals, significant pH changes, and the high amount of sludge produced are among the significant disadvantages of the coagulation process with metal salts [128, 129]. In addition, some negative effects of synthetic polymer on human health have increased the tendency to use natural polymeric materials as a coagulation agents. Natural polymeric materials such as polysaccharides are low cost, easy to obtain, have low molecular weight and high shear stability. For these reasons, they have been suggested to be more advantageous materials. They also have advantages such as being safe for human health, biodegradable, and having a wider effective flocculation dose range for various colloidal suspensions [129, 131]. High volume wastewater is one of the most important problems for many industrial sectors. Especially, textile industries produce large volumes of wastewater with varying physicochemical properties. This diversity in physicochemical properties is due to the enormous continuous effort to identify suitable technologies for the treatment of textile industry wastewater and the many components involved in this process [130, 132]. The different types of wastewater treatment performed for industrial wastewater include coagulation/flocculation, oxidation, membrane separation,

#### *Algal Alginate in Biotechnology: Biosynthesis and Applications DOI: http://dx.doi.org/10.5772/intechopen.101407*

ion exchange, photochemical, adsorption, biological treatment method, and so on [130, 133]. Among the various methods, one of the effective methods for removing substances from wastewater is coagulation using algal alginate [130].

Alginate naturally derived from algae offers significant potential for wastewater treatment as a coagulant. Calcium and sodium ions can be used as coagulation aids in processes where alginate is used as a coagulant. Especially when calcium ions interact with metal cations in the alginate structure, the gel structure forms and tends to precipitate the pollution factors in the wastewater. Thanks to having the ability of formation insoluble molecules, it becomes an important option as a coagulant in wastewater treatment [130, 134–136].

Laboratory-scale studies on the use of the obtained algal alginate in wastewater treatment processes have been carried out. In these studies, the process continues with measuring the coagulation efficiency depending on the determined parameters after the extraction stage. In the study conducted by Vijayaraghayan and Shanthakumar [130], *Sargassum sp.* was used as an alginate source and the efficiency of removing Congo red dye from the aqueous solution was studied depending on the pH, alginate dose, calcium dose, and initial dye concentration of the extracted alginate. As a result of the study, it has been shown that the performance of alginate as a coagulant is highly dependent on the calcium dose used as the gelling agent and the initial dye concentration in the solution [130]. A process for reactive magenta dye removal in textile wastewater was carried out depending on the alginate dose, calcium dose, and pH by the same authors. In this study, a color removal of 92.7% was achieved and it was confirmed that the alginate extracted from *Sargassum sp.* could be used as a coagulant for dye removal in textile wastewater [137]. In another study conducted by Natesh et al., 3 different algae such as *Sargassum* sp*.*, *Turbinaria* sp*.*, and *Kaapaphycous alvarezii* were used and the results supported the study obtained by Vijayaraghayan and Shanthakumar [129]. In the study by Devrimci et al., the coagulation efficiency of algal alginate was investigated in terms of drinking water treatment. The study was carried out depending on parameters such as calcium and alginate doses, and the initial turbidity of the samples. Experiments on synthetically prepared turbid water samples have shown that calcium alginate can act as a potential coagulant. The coagulation efficiency was highly dependent on the initial turbidity and calcium concentration. At high initial turbidity, the coagulant worked well, and the targeted final turbidity was achieved at most doses of calcium and alginate. It is stated that the performance is weaker at low turbidity. The authors noted that the use of higher viscosity alginate and prolonged rapid mixing may improve the performance for low turbidity waters [135].
