# Recent Developments and Emerging Trends in Paint Industry Wastewater Treatment Methods
## 3 Paint Industry Wastewater Treatment Methods
### Physicochemical treatment
#### 3.1.1. Coagulation and Flocculation
Generally, inorganic coagulants, such as aluminum sulfate (Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\):18H\({}_{2}\)O), ferrous sulfate (FeSO\({}_{4}\):7H\({}_{2}\)O) [5], ferric chloride (FeCl\({}_{3}\)), and polyaluminum chloride (PACI) [31] have been applied during coagulation to reduce dye and SS levels [51]. Adequate pH is an important parameter for the coagulation-floculation treatment. The COD removal was estimated in effluents from a manufacture of water-based paints using different coagulants such as FeCl\({}_{3}\):H\({}_{2}\)O, sodium bentonite, Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\):18H\({}_{2}\)O, and FeSO\({}_{4}\).7H\({}_{2}\)O. It was found that the most useful coagulant used was FeCl\({}_{3}\) at a wastewater pH of 5.9. However, this method only decreased the COD by 40-59% and was found inefficient and additional biological treatment was required [41]. On the other hand, in another study [31] applying coagulation-floculation treatment using coalpaths Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\):18H\({}_{2}\)O, FeSO\({}_{4}\):7H\({}_{2}\)O, PACI, and FeCl\({}_{3}\):6H\({}_{2}\)O at different wastewater pH levels (range of 4.5-10) showed up to 88% COD removal, 100% removal of SS, and color removal of 46-72% from paint industry wastewater with the best values at pH 8 for Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\):18H\({}_{2}\)O and FeSO\({}_{4}\) and 8.5 for FeCl\({}_{3}\)[29]. [PERSON] et al. [38] reported sufficient COD and BOD removal using coagulants Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) and FeCl\({}_{3}\) with anionic and cationic flocculants for the pre-treatment of steel painting factory effluents by the coagulation-floculation method at the wastewater's pH. The optimal dosage of 700 mg/L was estimated using a cationic flocculant, reducing BOD and COD values by over 95% [38]. Volume and concentration of the added coagulants are also important for the efficiency of the treatment process. In some cases, the addition lower doses of coagulants (Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\), FeSO\({}_{4}\), PACI, and FeCl\({}_{3}\)), under 500 mg/L, a higher removal efficiency has been achieved [31]. For the optimization of the treatment processes a jar test can be applied, which has been used for the comparison of coagulant efficiencies, FeCl\({}_{3}\):6H\({}_{2}\)O, Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\):18H\({}_{2}\)O, and FeSO\({}_{4}\).7H\({}_{2}\)O [49]. The best treatment efficiency was provided by the coagulant FeCl\({}_{3}\):6H\({}_{2}\)O; hence, optimization experiments were carried out with FeCl\({}_{3}\). The treatment conditions were optimized by using a central composite design. The dependent variables were COD, TSS, color, and turbidity in the optimization experiments for wastewater treatment. Treatment conditions were optimized using the design expert program. The optimum treatment parameters were reported as coagulant amount 1080.49 mg/L, pH 7.54, and mixing speed 146.16 rpm. Under optimized conditions, the treatment process was 4% more efficient than the non-optimized process. The COD, TSS, color, and turbidity removal were 94.1%, 95.3%, 97.1%, and 99.5%, respectively [49]. Other coagulant agents, NaOH and Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\):18H\({}_{2}\)O, have been studied for the coagulation-floculation treatment method for paint industry wastewater, followed by the lamella clarification, aeration, and palm hemp