## 2 Principal Textile Colored WW Characteristics and Composition
### Hybrid Materials Used as Coagulation-Flocculation Agents in Colored WW Treatment  
Commonly, the coagulants applied in WW treatments are classified into two groups: _synthetic_ and _natural_ coagulants. To enhance the formation of flocs, the introduction of coagulant aids is sometimes required to increase the density of flocs for better separation via gravity or filtration (rapid/lent), such as different types of clays or mineral materials (e.g., kaolin, bentonite, montmorillonite) that improve the mechanical separation of suspended solids from WW after an adequate stirring regime as well as WW discoloration treatment. This is one of the main reasons for the application of hybrid materials as coagulant-floculants, which have higher densities due to the multiple materials present in their composition (inorganic, organic, natural biopolymers, etc.) that permit the improved removal of suspended solids and dissolved colored species from WW. Good S/WW separation improvements in terms of sedimentation (>20-50%) and discoloration (>10-35%) were achieved, especially in the case of treated effluents from beverage industries, local small wine manufacturing, textile or cosmetic industries, and municipal WWs associated with improved sedimentation and multiple filtration layers (rapid multiple-bed filtration) or biofililtration. Hybrid materials used as coagulant/flocculant in WW treatment systems are materials obtained by adding or introducing certain efficient components/functional chemical groups into the original material to enhance the agglomeration capacity, thus achieving superior aggregation and (S/WW) separation performance than that of individual/initial conventional coagulant materials [71; 103; 105; 130]. These materials can be used as convenient alternative materials in WW treatment systems with combined actions (e.g., as coagulant/flocculants, adsorbents, co-precipitation, or bridging/cross-linking agents, etc. ), reducing the operation time in a single operation when discharging large volumes of industrial WW. A lot of terms have been used in the scientific literature to define these hybrid materials, such as composite coagulants [144], composite flocculants [145], composite polymers [146], hybrid coagulants [147], hybrid flocculants [148], hybrid polymers [149; 103; 149; 150; 151; 152; 153; 154; 155; 156; 157; 158; 159; 160], among others. Hybrid materials are commonly grouped into three primary groups: (i) structurally hybridized materials (composites), (ii) chemically bound hybridized materials, and (iii) functionally hybridized materials. The first group, known as composites, consists of a combination of materials at the macroscopic level, such as physical mixtures prepared by the blending of inorganic and organic materials at room or high temperature without containing new chemical species (e.g., polyferric chloride-poly dimethyl diallyl ammonium chloride (PFC-PDMDAAC) hybrid, or polyaluminium chloride-epichlorohydrin-dimethylamine (PAC-EPI-DMA) hybrid). The composite properties follow the rule of mixture, wherein the properties of all of the components' materials are combined. The composite efficiency in the coagulation-flocculation step can be enhanced due to the synergetic effect of all of the material components. The second group of hybrid materials consists of special combinations and mixtures of molecules and atoms at the molecular level with excellent properties and efficiencies due to chemical bonds at the interface between the component materials produced via chemical modification/transformation due to new chemical groups introduced to the molecular chains of the materials. Inorganic polymeric coagulants have greater performance in the coagulation-flocculation step than basic inorganic coagulants (e.g., poly aluminum chloride (PAC) vs. aluminum chloride, or poly ferric sulphate (PFS) vs. ferric sulphate) but they have weaker performance than organic polymer flocculants (e.g., polyacrylamide--PAM) due to lower-molecular-weight of inorganic polymeric coagulants.