With the development of printing technology and ink raw materials, the printing industry adopts water-based inks with advantages such as environmental protection and economy as raw materials. Ink complies with environmental requirements, has non-toxic, non corrosive, non irritating odor, non flammable, non explosive, good safety, convenient transportation, high concentration, low dosage, low viscosity, good printing adaptability, stable performance, good adhesion, fast drying, excellent water resistance, alkali resistance, and wear resistance after drying; Easy to adjust operations before and after printing, as well as during the printing process, the printed material appears full, brightly colored, with high gloss, gorgeous and luxurious. Printing complex patterns can also achieve rich levels, and can print bright and high gloss colors. The main pollutants in water-based ink wastewater are water-soluble acrylic resins (color carriers), cyclic organic compounds (pigments) with colored groups, and high molecular weight alcohol or phenyl dispersants. Among them, acrylic resin is the main component of COD in the wastewater, accounting for more than 80%. During the production and application of water-based inks, a certain amount of wastewater is generated due to equipment cleaning. The ever-changing color of water-based ink results in a complex chemical composition of its wastewater, characterized by high organic matter concentration, deep chromaticity, and difficulty in biodegradation. Once it enters the water, it can cause serious pollution to the water environment. For the treatment of water-based ink wastewater, the use of only biological treatment processes cannot meet the requirements of water-based ink wastewater treatment, and comprehensive physical, chemical, and biological treatment processes must be used. The coagulation process, as the main means of pre-treatment for water-based ink wastewater, is efficient and reliable in removing COD and chromaticity. To improve the biodegradability of wastewater, methods such as microelectrolysis, chemical oxidation, and anaerobic biological treatment have been adopted, followed by anaerobic and aerobic biological treatment. Generally, for water-based ink wastewater, treatment processes such as "acid precipitation+coagulation sedimentation+biochemistry", "acid precipitation+coagulation air flotation+biochemistry", and "acid precipitation+plate and frame pressure filtration+biochemistry" can be designed. In actual operation, the advantages and disadvantages of the above processes are compared in the table below. Acid precipitation refers to the process of adding acid to water-based ink wastewater to transform acrylic resin from a dissolved state to solid SS and precipitate it from the wastewater. The solid SS can be removed by solid-liquid separation method; After acid precipitation solid-liquid separation, most of the organic pollutants in the wastewater have been removed, and the COD value is generally around 600-800, which has the conditions for biodegradability and easy biodegradation. It can be directly treated by biochemical treatment or enter the domestic sewage treatment system and other biochemical treatment systems for joint treatment.
