# Recent Developments and Emerging Trends in Paint Industry Wastewater Treatment Methods
## 3 Paint Industry Wastewater Treatment Methods
### Electrochemical Treatment
#### 3.3.1 Electroflotation  
The first use of electroflotation was in mineral processing, but the advantages of the process showed its effectiveness in the field of wastewater treatment. During the process, thanks to electrolysis, bubbles are formed and effectively used for the removal of suspended particles by flotation [60]. The main advantages of this method over flotation are in the size of the produced bubbles (smaller), the higher surface area, and the suitability for the removal of finer particles. Electroflotation has been used as a method for the removal of synthetically prepared paint from automotive paint systems [60], with NaOH addition for adjusting the pH of the water. TSS removal of 90.39 to 97.43% was achieved [60]. The continuous flow electroflotation method has also been developed [61] for the design and application of apparatus with stainless-steel electrodes for the treatment of paint wastewater from the car coating industry regarding the key variables, e.g., initial solids concentration, applied current density, and retention time. The system efficiency is reduced with higher concentrations of the suspended solid particles. On the other hand, there is a direct relationship with the current used for the treatment and the time of the whole process. The efficiency of TSS removal increased to 95 \(\pm\) 7% when applying a higher current density and longer hydraulic time [61]. It should be concluded that the control and operation of the electroflotation systems are simple, and the construction is flexible because the electrodes can be designed based on the size and dimensions of the reaction tank. In electroflotation, suspended particles collide with gas bubbles, attachment occurs, and they slowly rise to the surface to be skimmed off. Each phase of this process is time dependent. Therefore, adequate retention time is needed for the collision and attachment of bubble-particle in the solid-water separation \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt} p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**Treatment Method** & **Treatment Parameters** & **Results** & **Source of Wastewater** & **References** \\ \hline Composing of paint sludge & Reactors with temperature 40 °C for a minimum of 5 days & 85\% of paint sludge & Water-based paint sludge & \\  & & 30°C for a minimum of 5 days & bio-dried using comcob as bulking agent & originating from the automotive industry & [32] \\ \hline Pure oxygen-based activated sludge system & Oxygen flow rate maintained at 5.0-8.0 mL./L & 87.8–93.6\% COD, and 97.7–99.2\% of BOD removal & Wastewater from the paint industry effluent and sewage & [57] \\ \hline Sequencing batch reactor chemical pre-treatment & Volume 14 L, cycle run time 24 h followed by 2 h settling, decanting and idle period, temperature 20 \(\pm\) 1 °C, pH = 6.5–7.5 & & Bus production factory located in Istanbul (Turkey), Effluents met the in-severe discharge limits for COD & Bus production factory located in Istanbul (Turkey), from coating process, treated with domestic wastewater in the existing treatment plant & [22] \\ \hline \hline \end{tabular} Abbreviations: BOD—biochemical oxygen demand, COD—chemical oxygen demand.  
\end{table} 
Table 2: Biological treatment methods for paint industry wastewater. process [61]. Furthermore, the efficiency of electroflotation treatment is also dependent on the pH of the effluent, such as in the case of coagulation.