## 2 Principal Textile Colored WW Characteristics and Composition
### Coagulation-Flocculation Technologies and Its Performances in Colored Textile WWs Treatment
* Precipitation: hydrated metal hydroxides (precipitates) are formed that can adsorb on the solid surface with other existing colloids and neutralize the surface charge (pH-sensitive, with the characteristic value of the isoelectric point of metal hydroxide) (coagulation-floculation process). * Enmeshment in an agglomerate precipitate and adsorption: is when organic polymers are used (cationic, anionic, and nonionic ones). The existing ions in the WW interact with the polymeric chains, forming solid aggregates (floculation process). Flocculation usually refers to the post-destabilization process in which large flocs are produced as a result of the collision of small aggregates due to rapid stirring (peri-kinetic flocculation via Brownian motion) or slow stirring (orthokinetic flocculation via velocity gradients). Both rapid and slow stirring are required for good and complete flocculation with conventional coagulants/floculants [95; 96; 97]. When hybrid materials are applied as coagulant-floculants, a single stirring regime can be used at an adequate constant velocity, yielding increased treatment efficiency. Commonly, the separation of dense produced aggregates or flocs from WW is achieved by (i) sedimentation, which is the settling of the flocs without stirring for quiescence settling or (ii) filtration/biofiltration, which is the separation of flocs using a free vacuum or under pressure by passing them through a granular solid layer of certain porosity and density (e.g., graded sand, garnet, coal, and resins) supported by gravel layers and/or porous underdrains (depth filters) or precoat filters [123; 124; 125; 126; 127; 128; 129; 130; 131; 132; 133; 134; 135; 136; 137; 138; 139; 140; 141; 142; 143; 144; 145; 146; 147; 148; 149]. Certain characteristics of coagulation-floculation processes are summarized in Table 5[150]. The efficiency of WW coagulation-floculation processes in relation to solid separation via sedimentation is important. The highest removal of suspended solids and turbidity after this WW treatment step must be higher than 60-90%, ideally 100% (in a mechanical-chemical WW treatment system). In practice, the effect of coagulation-floculation on sedimentation performance is beneficial, improving the removal of suspended solids and turbidity but not completely (48-92%) [12; 60; 71; 96; 105; 123; 124; 125; 126; 127; 128; 129; 130; 131; 132; 133; 134; 135; 136; 137; 138; 139; 140; 141; 142; 143; 144; 145; 146; 147; 148; 149; 150; 151; 152; 153; 154; 155; 156; 157; 158; 159]. The main disadvantage of this WW treatment step is that the process control is a little difficult, possibly due to precipitation rate and floc size growth involving contaminants or residuals such as non-ionic detergents remaining in the effluent, sludge production, which must be settled, dewatered, and pressed into a cake for subsequent landfill tipping, the necessity for further detoxifying and vaporization (useful compounds recovery), or incineration [98; 99; 100; 101; 102; 103; 104; 105; 106; 107; 108; 109; 110; 111; 112; 113; 114; 115; 116; 117; 118; 119; 120; 121; 122; 123].