# Recent Developments and Emerging Trends in Paint Industry Wastewater Treatment Methods
## 1 Introduction  
Industrial wastewater is created during different types and stages of manufacture or as a by-product of instrument cleaning in factories, such as rinsing sludge, manure, or as aqueous waste from the engineering industry [1]. Industrial wastewater causes significant water pollution due to entering surface water (streams, lakes, rivers) and underground reservoirs. Chemicals, heavy metals, and microorganisms from industrial wastewater are toxic to aquatic organisms reducing organisms' life spans, abilities to reproduce and participate in the food chain. With the growing population and industrialization, global awareness has shifted towards exploring substitute methods for reducing water consumption [2]. Therefore, every effort must be made to reduce water consumption and treat wastewater to be reusable or safer for discharge into the environment.  
Industrial wastewater is characterized not only by the containment of grease and oils, but also by high turbidity, high levels of chemical oxygen demand (COD) and biochemical oxygen demand (BOD), and suspended and dissolved solids. These high amounts must be reduced or eliminated before discarding the wastewater into water bodies. The main characteristics of industrial wastewater are classified into physical, chemical, and biological categories (Figure 1.). The treatment is a demanding, multi-step process with the primary purpose to reduce COD and BOD levels by removing as many contaminants as possible. Conventional industrial water treatment does not remove sufficient amounts of pollutantsentering watercourses; thus, industrial wastewater is considered potentially hazardous to freshwater ecosystems [3].  
High amounts of wastewater are created by the paint-producing industries. These factories use large volumes of water, about 284-321 million liters per day, of which only about 4% is recycled [4]. The chemical content of the paint industrial wastewater varies widely and is related to the individual industrial units and the manufacturing processes [5]. The main stream of wastewater from paint industries is generated from equipment cleaning and represents around 80% of the effluents [6]. These effluents are toxic not only to the environment but can also have adverse effects on human health. The effluents contain diluted paint, which can irritate eyes, and skin or can cause headaches. The toxins present in paint industrial wastewater can also contribute to respiratory problems, muscle weakness, and liver and kidney damage. Heavy metals also pose many health risks [7]. Toxic heavy metals discharged into the environment can cause detrimental health problems in animals and ultimately humans via the food chain. They can be teratogenic and carcinogenic, and can cause oxidative stress, organ damage, nervous system impairments, and reduced growth and development [8].  
The presented paper aims to review and discuss the recent trends in paint industrial wastewater treatment methods used to adequately clean wastewater. The main part of the review is classified into subchapters according to the various treatment techniques. The next part is devoted to highlighting future trends in this area.