Microwave Tech - PCB Circuit Board waste water treatment method

PCB Circuit Borad wastewater is also called printed circuit board wastewater, WHICH contains heavy metal ions and has low biodegradability. I have introduced the technology of using the micro-electrolysis process to preprocess PCB electroplating circuit board wastewater treatment. Today, I will introduce other treatment technologies.

1., Characteristics of PCB wastewater

1. PCB printed circuit board production process from the beginning of the purchased substrate to the final product needs to experience dozens of production processes such as inner layer treatment, electroplating, outer layer treatment, surface processing and forming, and final treatment, will produce a variety of wastewater, and the composition of various wastewater is very different.

The production process of the printed circuit board (PCB) is complex, and there will be different wastewater in different production stages, and the composition of various wastewater is very different.

3. PCB production wastewater can be divided into a single panel, double panel, and multi-panel production wastewater according to the wiring level.

4. According to the types and forms of pollutants in its wastewater, it can be divided into wastewater containing heavy metals (containing Cu2+, Pb2+, Ni2+, etc., without EDTA, NH4+, and other complexing agents), wastewater containing fluorine, wastewater containing complex metals (containing heavy metal ions, complexing agents, including heavy metal-EDTA complex and heavy metal-ammonia complex) and acid and alkali wastewater (containing dissolved organic Inorganic acid-base, CN-, etc.).

5. In addition, the printed circuit board production process will also produce a large number of waste liquids, mainly for membrane waste liquid, chemical copper waste liquid, and other tank bath baths.

2, Treatment technology of printed circuit board wastewater

Due to PCB wastewater node number, and the composition is complicated, so the wastewater treatment at present has two kinds big, namely, physical-chemical method and biological method, mainly including coagulation precipitation, ion exchange, air flotation, adsorption, iron-carbon micro electrolytic method, catalytic oxidation, biological degradation, and joint treatment, etc.

2.1 Physicochemical method

1) coagulation method. Some organic wastewater and heavy metal wastewater with high concentrations are produced in the process of PCB production. For this kind of wastewater with complex water quality, coagulation reaction can effectively remove colloidal particles in the wastewater, and also form insoluble precipitation with organic matter dissolved in the water phase. Common coagulants include inorganic coagulants and organic coagulants, among which inorganic coagulants are FeCl3, Al2(SO4)3, and their polymers. Organic coagulants include cationic polymer coagulants, amphoteric organic polymer coagulants, anionic polymer coagulants, and non-ionic coagulants.

2) Air flotation. Air flotation is to the wastewater into the air, and precipitation in the form of tiny air bubbles from the water as the carrier, make the emulsified oil, tiny suspended particles, and other pollutants in wastewater adhesion on the bubble, with bubbles rising to the surface, forming foam particle (oil) - air, water, three-phase hybrid, by collecting bubble or scum in the purpose of impurity separation and purification of wastewater. Guo Yongfu et al. pretreated the membrane removal developing wastewater in PCB wastewater through coagulation precipitation and air flotation and added flocculant at the outlet of the collecting tank to form water-insoluble flocculating material. Then the water dissolved with a large amount of gas is released to the air floating pool through pipes and nozzles through the gas tank in the air floating pool, forming a mixture of mud, water, and air and floating on the surface of the water. After air flotation treatment, the concentration of organic pollutants in wastewater is greatly reduced.

3) Adsorption method. Adsorption method is the use of porous solid adsorbent treatment of pollutants, pollutants in one or several components under the action of molecular gravity or chemical bond are adsorbed on the solid surface, to achieve the purpose of separation. The commonly used adsorbents are activated carbon, humic acid, sepiolite, polysaccharide resin, and so on.

The advantages of the adsorption method are fast speed, good stability, small equipment footprint, its main disadvantages are a higher investment, adsorbent regeneration difficulty, high pretreatment requirements.

4) Iron-carbon micro electrolysis. The electrolytic materials of the iron-carbon micro-electrolysis process generally use cast iron filings, activated carbon, or coke. When the material is immersed in wastewater, internal and external electrolytic reactions occur. Electrode reaction products have high activity, can REDOX reaction with a variety of components in the wastewater, many difficult to biodegrade and toxic substances can be effectively degraded; At the same time, the metal can exchange with the heavy metal ions in the wastewater after iron.

Iron carbon micro electrolysis is to remove pollutants from water through these effects. Bao Xuping et al. used a combination of acidification demulsification - iron-carbon micro-electrolysis - neutralization precipitation -SBR to treat the PCB developing wastewater. After demulsification, the effluent entered the iron-carbon micro-electrolysis column with V(iron)BV(carbon)=1B1, and the reaction time was 45min. After the pretreatment, M (BOD5)Bm(COD) increased from 0.114 to 0.136, and the heavy metal content in wastewater decreased greatly, which improved the biodegradability of wastewater and laid a foundation for subsequent biochemical treatment.

5) Catalytic oxidation method. Catalytic oxidation refers to the oxidation reaction under certain pressure and temperature conditions, with metal materials such as Pt, Pd, Ni as the catalyst, with air, oxygen, ozone as oxidant, including/oxygen 0 / dehydrogen 0. Catalytic oxidation is used to enhance the decomposition of oxidants to speed up the chemical reaction between pollutants in wastewater and oxidants and remove pollutants in water.

It is difficult to treat the membrane removal wastewater in the process of PCB preparation, and it is difficult to reach the standard by using the traditional physical and chemical process. Bamboo activated carbon was prepared by microwave irradiation and modified by microwave irradiation. Bamboo activated carbon and modified bamboo activated carbon were used as absorbing materials to oxidize PCB demoulding wastewater by microwave induction. The effects of conventional heating and microwave heating on wastewater treatment were investigated, and the effects of absorbing materials, microwave power, and heating time on wastewater treatment were emphatically discussed. When 1g of modified bamboo activated carbon is used as catalyst and 15min of heat treatment is added in the microwave field with a microwave power of 500W, the COD removal rate of the pretreatment wastewater reaches 96%.

2.2 Biological method and combined treatment method

As the quality and quantity of PCB wastewater vary greatly, the traditional treatment methods cannot maintain stable effluent quality, produce a large amount of sludge and cause secondary pollution, resulting in high cost. The biological method has the advantages of low cost, high efficiency, and no secondary pollution. At present, the effective method to treat PCB wastewater is biodegradation, which mainly uses sludge or natural microorganisms returned from sewage treatment plants to treat PCB wastewater. The removal rate of high concentration PCB wastewater by the biological method is not high, and the degradation is not complete, so it is necessary to add chemical treatment to make up for the above deficiencies, that is, to treat PCB wastewater by the bio-chemical combined treatment process. Therefore, the combined treatment of circuit board wastewater by biological methods and other methods is attracting more and more attention. There have been reported coagulation-contact oxidation method, reverse osmosis - electric deionization (RO-EDI) desalting system, acidification demulsification - iron-carbon micro-electrolysis - neutralization precipitation -SBR combined process.

The biological method is suitable for the treatment of organic wastewater containing low metal ions, such as electroplating, etching, template, demoulding, development, and ink removal processes of the integrated wastewater formed by water, the application of the biological method is mainly based on the water quality, combination of different pretreatment methods, improve the biodegradability of refractory organic matter. The development and application of various forms of activated sludge process can be used as both secondary treatment and advanced treatment methods to achieve the target of 60% water reuse rate in the PCB circuit board industry.