**1. Introduction**

Textile wastewaters are defined as complex industrial effluents due to their wide variability of chemical compounds. Most of the compounds present in the textile effluents can be classified as refractory and priority pollutants, and thus showing low biodegradability. Uncontrolled disposal may provoke severe environmental effects, on receiving the water bodies and thus in human health. This low

biodegradability of textile wastewater is generally attributable to the presence of recalcitrant organic compounds, including dyes, phenolic pollutants, and dyeing aids, where conventional treatment methods are ineffective in degrading them successfully [1, 2]. The latter has led experts to explore diverse practices technologies for removing this type of pollutants. These practices have comprised physical, biological, and chemical processes, in which the conventional biotechnologies and advanced oxidation processes (AOPs) are the commonly selected treatments.

Regarding AOPs, the ozonation (O3), hydrogen peroxide (H2O2), UV-irradiation, Fenton-based process, and combinations among them, are well known for their capacity to reach efficient pollutant removals. However, these processes may generate high loads of toxic wastes during their application. Also, AOPs usually require significant processing costs due to the overall cost of AOPs being typically represented by their capital, operating, and maintenance costs [3].

On the other hand, conventional biotechnologies such as activated sludge processes, facultative lagoons, wetlands, etc., are considered reliable technologies able to treat wastewater from economic and environmental aspects. However, the conventional biotechnologies exhibit not only high operating costs derived from aeration requirements but also a large footprint [4]. Although the activated sludge processes have been widely used for industrial wastewater treatment, most of the dyes are poorly removed by using this technology. Besides, when textile wastewaters are mixed with sewage, the conventional biological processes have been shown to be inefficient in decolorizing textile effluents. Moreover, direct biological oxidation is not possible due to the presence of recalcitrant organic molecules of dyes [5]. Therefore, textile industry effluents after biological treatment are not inconsistent with the wastewater quality standards established in the legislation applicable [6]. On the other hand, biological and chemical processes have been combined to achieve better removal efficiencies and even to accomplish pollutants mineralization with more competitive treatment costs compared to AOPs, although operating costs are still considerable.

Therefore, in the last decade, great attention has been paid to novel biological technologies for wastewater treatment based on microalgae in combination with bacteria, forming the called microalgae-bacteria symbiotic granular sludge. The algal-bacterial granular sludge (ABGS) process has been positioned as a costeffective technology capable of simultaneously removing nutrients and mineralizing recalcitrant organic pollutants from municipal and industrial wastewater [4]. The presence of algae in ABGS systems not only provides oxygen for the bacterial metabolism but also maintains the structure of the original biochemical pool while further reducing the pollutants. Besides, the low concentration of organic matter in the resulting effluent may reduce the cost of the subsequent chemical treatment [7].

In this sense, the goal of this chapter is to present an overview of ABGS-based processes as an economic and friendly treatment alternative for textile wastewater with potential for resource recovery. In the following sections of this chapter, the environmental effects caused by textiles effluents, AOPs characteristics, and ABGSs potential are discussed in detail. Section 2 briefly presents the environmental, human health, and marine biota effects caused by untreated textile wastewater effluents or treated by conventional processes. In Section 3, the advantages, disadvantages, and operating costs of the main AOPs used for textile wastewater treatment are discussed. The selection of the most suitable physicochemical treatment process is determined in each particular case, thus the operating cost of AOPs for textile wastewater treatment varies depending on the energy/reagent amount used. Section 4 provides a complete description of the ABGS system's potential for the remediation of textile wastewater treatment from environmental, economic, and resource recovery aspects. Finally, Section 5 presents the main conclusions of the conducted research.

*A Critical Review on Algal-Bacterial Granular Sludge Process as Potential Economical… DOI: http://dx.doi.org/10.5772/intechopen.99973*
