Research and engineering practice of the hottest P

2022-09-22
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PCB ink wastewater treatment process research and engineering practice (Part I)

Abstract: Ink Wastewater accounts for about 5% of the total discharge of printed circuit board (PCB) wastewater. It is a kind of high concentration organic wastewater, with CODcr up to 15000mg/l. Exploring a feasible treatment process to effectively remove the organic components (CODcr) in ink wastewater is very important for the overall CODcr standard of PCB wastewater

key words: ink wastewater; Printed circuit board (PCB); CODcr; Acid precipitation; Board and frame pressure filtration

introduction

printed circuit board (PCB) wastewater can generally be divided into cleaning wastewater, ink wastewater, complexing wastewater, concentrated acid wastewater, concentrated alkali wastewater and other wastewater types according to different main pollutants. Its ink wastewater mainly comes from printing, development, film stripping and other processes in the production process of PCB. PCB ink wastewater is a kind of high concentration organic wastewater. Its CODcr is usually mg/l, some can be as high as 20000mg/l, SS is about mg/l, the pH value is generally alkaline, and the wastewater color is dark blue. This kind of wastewater accounts for about 5% of the total PCB wastewater. The 4E principle of developing the coating industry based on economy, efficiency, ecology and energy. Water discharge method: please check whether the sensor selection in the "online" setting is correct about 5%. For PCB wastewater treatment, the key to whether CODcr can meet the standard (≤ 100mg/l) is the removal of high concentration organic matter in ink wastewater. In engineering practice, we have adopted several treatment methods to treat ink wastewater. Through analysis and detection, we have determined a relatively suitable process combination, which can effectively remove CODCr in ink wastewater

1. Treatment method

a large number of inks will be used in the production of printed circuit boards. The types of printed circuit board inks can be divided into seven types according to their functions and uses: corrosion-resistant ink, electroplating resistant ink, hole plugging ink, solder resist ink (commonly known as green oil), marking ink, conductive ink and peelable oil ink (commonly known as blue glue), etc. The components of ink are mainly composed of resin, filler, pigment, additives and solvents. Unused ink is usually removed with NaOH solution. The discharged ink wastewater has a high concentration of organic matter and is alkaline. Ink wastewater contains a large amount of resin, which is easy to precipitate under acidic conditions

at present, the domestic processes for PCB ink wastewater treatment mainly include: oxidation method; Biological treatment; Filtration suction method; Acidification coagulation method, etc., are all methods for removing high concentration organic matter in ink wastewater

① oxidation method

the oxidation method is used to treat PCB ink wastewater, which is a strong oxidation reaction. Common treatment methods of oxidation method include combustion method, electrolytic oxidation, chemical oxidation and photooxidation. Combustion method is a method of burning high concentration organic wastewater. It is a good method for treating organic wastewater with high combustion value, but the treatment cost is high and cannot be widely used. Electrolytic oxidation process has high cost, large equipment investment and limited degradation degree. Photooxidation is still in the research stage. The oxidants used in the chemical oxidation method include NaClO, H2O2 and O3, which can reduce the whole industry to a certain concentration of 2 trillion yuan by 2015, but it is not complete and the cost is also high. Its process flow is as follows:

Figure 1 oxidation process flow diagram

② biological treatment method

biological method is used to treat PCB ink wastewater, generally using contact oxidation method, However, the CODcr of wastewater entering the biochemical tank must be less than 1000mg/l. Generally, PCB ink wastewater should be pretreated or diluted. The CODcr of effluent after biological treatment can be less than 200mg/L. However, biochemical treatment requires aeration and oxygenation, which consumes a lot of power, and the treatment cost is also very high, and the biodegradability of this kind of wastewater is poor. PCB ink wastewater often contains a certain amount of heavy metal ions, which are toxic to organisms and greatly reduce biological activity. In addition, the pH value of its wastewater should be strictly controlled in neutral conditions. Some inherent characteristics of PCB ink wastewater itself (the ratio of BOD to cod is too low, and the biochemistry is too poor, taking the flexible packaging film as an example), which seriously affects the application of biological method. The biological treatment process is as follows:

Figure 2 biological treatment process flow chart

③ filter adsorption method

filter adsorption method is used to treat PCB ink wastewater. First, the wastewater is pretreated and pumped into the filter by pump. After the wastewater is treated by the filter, most of the ink and suspended solids can be removed. The filtered water enters the activated carbon adsorption equipment. Through the adsorption and decomposition of activated carbon, a good treatment effect can be achieved. However, when this process is used to treat PCB ink wastewater, the activated carbon is easy to be saturated, the treatment rate is low, and the operation cost is high. In addition, because the ink in the wastewater is sticky, it is easy to stick to the pipeline and equipment, and the equipment failure rate is high, this process is inconvenient to be used. Filtration adsorption process is as follows:

Figure 3 filtration adsorption process flow diagram

④ acidification coagulation method

acidification coagulation method is the most commonly used treatment process for PCB ink wastewater at present. This process generally first pumps the wastewater into the acid precipitation tank, which is equipped with a pH automatic control instrument, which controls the amount of acid added, and the pH in the acid precipitation tank is controlled at, The photosensitive film in the ink wastewater will precipitate into a thick colloidal condensate under acidic conditions, and its specific gravity is easier to separate than that of water. The wastewater after acidification and slag removal enters the neutralization reaction tank and then adjusts its pH to alkaline (pH value 8..0). At the same time, PAC and PAM coagulants are added under this condition. The wastewater will undergo coagulation reaction under the action of stirring to form a large number of alum condensates. After precipitation and separation, the supernatant effluent is better. This process can treat PCB ink wastewater, and the removal rate of CODCr can reach 60% - 80% (the higher the CODcr of ink wastewater, the higher the removal rate), and the CODcr can be reduced to less than 1000 mg/L (individual water samples are different). The acidification coagulation process flow is as follows:

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