# 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  
Coagulation methods have always attracted attention for their high efficiency in removing primarily turbidity and color, but also organic matter and SS from wastewater. Coagulation-flocculation is a common treatment method for wastewaters containing dyes, paint particles, and SS [46; 47; 48]. The process of water and wastewater treatment is based on forming flocks that are settled down during sedimentation [30]. Therefore, the dye molecules and toxic aromatic compounds can be eliminated from the effluent without decomposition [49]. The amount of coagulant and adequate pH of the wastewater affects the quality of treated wastewater; therefore, these are important factors in the coagulation process (each coagulant requires a specific pH range for the coagulation process). Figure 4: Hierarchy of stages involved in a typical industrial wastewater treatment plant. Figure 3: Distribution of industrial wastewater treatment methods according to treatment mechanism. \begin{table}
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**Treatment Method** & **Treatment Parameters** & **Results** & **Source of Wastewater** & **References** \\ \hline Coagulation– flocculation & FeCl3 at pH 5.9, filtration & COD removal 40–59\% & Water-based paint and allied products industry & [38] \\ \hline Coagulation– flocculation & FeCl3, FeSO4, and PAC1 pH 4.5–10 & COD removal 88\% SS removal: 100\% Color removal 46–72\% & Paint industry wastewater & [32] \\ \hline Coagulation– flocculation & NaOH and album as coagulant agents followed by lamella clarification process, aeration process (1–2 h) and palm hemp filtration process & Removal of COD 85\% TSS 91\% BOD up to 90\% & Different paint factory industrial wastewater & [10] \\ \hline Coagulation– flocculation & 2 coagulants Al2(SO4)3 and FeCl3 & BOD and COD reduction 2 flocculants: anionic and cationic optimal pH 5.3 & Wastewater from the main collector of a local steel tiles & [39] \\ \hline Coagulation– flocculation & Filtration coagulation —PAC disinfection with sodium hypochlorite & BOD = 78.6\% coagulant—PAC pollutant—anionic PAM, pH = 7.3 & BOD = 78.6\% COD = 90.6\% TSS = 99.9\% TDS = 65.0\% aluminum = 99.9\% & Wastewater reservoir of a production plant (Latex paint company) & [40] \\ \hline Coagulation– flocculation & FeCl3 and several natural-based materials, namely, limestone, pumice, sepiolite, bentonite, and mussel shell were used as flocculant aids & Most of the SS removed sepiolite—highest COD reduction 80\% & Wastewater of paint and construction chemicals producing factory in Turkey & [41] \\ \hline Coagulation– flocculation & 3 coagulants: FeSO4, FeCl3 and Al2(SO4)3, optimal pH = 7.54 mixing 100 rpm 5 min, followed by slow mixing 20 rpm 30 min & The coagulant FeCl3 provided the best treatment efficiency under optimized conditions removal of COD 94.1\%, TSS 95.3\%, color 97.1\%, and turbidity 99.5\% & [42] \\ \hline Coagulation– flocculation & Natural coagulant—_Moring oleifera_ fortified with Ca2+ (CaCl2) rotation 100 rpm, natural coagulant & COD removal 41\% turbidity removal > 99\% After 1.5 h electrolysis, COD removal of wastewaters previously & [35] \\ Combined with electrolysis & sedimentationiopptimal pH 6.5 coagulant dosage = 80 mL/L BDD electrode & treated with MOAE/CaCl2 and MOAE/Ca(NO3)2 was 70\% and 75\%, respectively & [11] \\ \hline Coagulation– flocculation &
\begin{tabular}{} \end{tabular} & Removal of turbidity 9.2\%, COD 78.6\% in industrial area & [11] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physicochemical treatment methods for paint industry wastewater. Typically, chemical coagulants are widely used, especially hydrolysisable metal salts based on aluminum or iron [29; 42; 50].