Circuit board wastewater treatment equipment

1、 Overview of Circuit Board Wastewater

There are many pollutants in the production process of circuit boards, and the discharged wastewater mainly contains pollutants such as copper, chromium, nickel, zinc, acid and alkali. If the above wastewater is not effectively treated, it will cause serious pollution to the environment. After natural water bodies are polluted by acids, alkalis, and heavy metals, the buffering effect of the water body is destroyed, leading to deterioration of water quality, inhibition or prevention of microbial activity, reduction of water's self purification ability, and also causing harm to crops. Heavy metal ions are extremely harmful to human health, and heavy metal ions in water are not degraded by microorganisms. They can be adsorbed, accumulated, and enriched in organisms, posing great harm to humans, fish, and plankton. In severe cases, it may cause crop yield reduction or livestock death. Therefore, harmless treatment must be carried out, and strict treatment must be carried out according to environmental protection requirements to meet emission standards.

2、 Composition and classification of circuit board wastewater

The composition of wastewater in the printed circuit board industry is complex and needs to be classified and treated according to water quality. Therefore, it is necessary to first separate the wastewater according to different water quality and treatment methods.

1. The common components of printed circuit board wastewater include:

Heavy metals: Cu, Ni, Pb, Sn, Mn, Ag, Au, Pd, etc.

Organic compounds: various electroplating or chemical plating additives, complexing agents, cleaning agents, inks, stabilizers, organic solvents, etc;

Inorganic substances: acids, bases, NH3-N (NH3 or ammonium salts), P (various phosphates), F, etc.

2. Wastewater diversion should be based on three or more types of substances: ionized Cu, complexed Cu, and organic matter. Ni and CN can decide whether to split according to actual processing needs.

3. The main components of the waste liquid from developing and removing the film are corrosion-resistant ink and developing solution. The COD concentration is very high and is the main source of COD in PCB industry wastewater. Its chemical properties are unique and should be separately separated for post-treatment.

4. Complex heavy metals Cu and Ni should be separated from ionic wastewater and treated separately.

5. Waste liquid should be classified and collected separately.

3、 Circuit board wastewater treatment process

　　1. Pre treatment process of ink waste liquid

Ink waste mainly refers to the waste liquid in the development and film removal processes, which contains a large amount of photosensitive film, solder mask slag, etc. The waste liquid is alkaline, with a pH value generally between 11 and 13; The COD content is very high, generally ranging from 8000-10000mg/L.

The main component of ink waste liquid is organic acid salts generated by hydroxyl containing resins under alkaline conditions, and these hydroxyl containing resins are not easily soluble in acidic solutions. By utilizing this fundamental property, a waste to waste method can be adopted in the treatment of developing and film stripping waste liquids. The waste acid discharged from the production workshop can be used to acidify the ink waste liquid, and sulfuric acid solution can be added if it is insufficient.

　2. Complex wastewater treatment process

Complex wastewater mainly refers to the rinse water discharged from acidic/alkaline etching lines and PTH production lines. The pH value of such wastewater is generally between 4 and 9. The wastewater not only contains chelating agents (mainly ammonia<50mg/L, formaldehyde, EDTA, etc.), but also contains a large number of metal ions (such as Cu2+<100mg/L). The chelating agents form very stable complexes with heavy metal ions such as copper ions. It is difficult to treat the wastewater to meet the discharge standards using general flocculation and precipitation methods.

Generally, copper ions will precipitate under alkaline conditions. However, in the production process of circuit boards, some processes require copper plating under alkaline conditions. Therefore, certain chemical agents such as EDTA are added to bind with copper ions, and the binding ability is stronger than Cu (OH0) 2, without precipitation. Therefore, in this situation, copper ions can coexist with OH -, so if copper needs to be removed from this type of wastewater, it is necessary to first break the network and then remove copper. Due to the requirements of the treatment process, wastewater such as backwash water pre treated by the reuse water system and filtrate from the filter press are mixed and treated together during the treatment process.

Some commonly used methods for breaking the network include direct breaking, displacement breaking, chemical precipitation, heavy metal capture agent precipitation, and ion exchange.

　　3. Cyanide containing wastewater treatment process

Cyanide containing wastewater mainly comes from electric nickel gold production lines and nickel deposition gold production lines, as well as rinse water after electric or deposition gold processes. This type of wastewater contains highly toxic CN - (<20mg/L), and environmental protection requirements require independent collection and treatment of this type of wastewater.

The hydrogen cyanide ion cannot be directly removed by conventional flocculation precipitation method. It must undergo oxidation to break its chemical bond structure and ultimately degrade, forming CO2 and N2 that have been removed.

　　4. Organic wastewater treatment process

Organic wastewater mainly refers to the washing water after developing and removing the film, as well as the cleaning water for processes such as cleaning nets, making nets, and removing oil. This type of wastewater contains trace amounts of copper (Cu2+<5mg/L), alkaline water quality (pH=8-10), excessive SS content, and COD content within 500mg/L. Organic wastewater contains a small amount of heavy metal ions, high COD and SS, poor biodegradability, and does not have the conditions for direct biochemistry. The coagulation precipitation method is first used to remove heavy metal ions, most SS, and some COD from the wastewater to improve its biodegradability, and then it enters the biochemical system. We choose the A/O treatment method for the biochemical system. A/O process is the abbreviation of anaerobic aerobic biological process, which was founded in the early 1980s. This process places an anaerobic reactor (hydrolysis acidification tank) at the front end of the system, with the aim of further improving the biodegradability of wastewater by decomposing large organic molecules into small organic molecules through hydrolysis acidification bacteria. The aerobic process adopts the contact oxidation method, and its central treatment structure is the contact oxidation tank. Its characteristic is direct aeration under the packing material, and the biofilm is accelerated to fall off and renew by the impact and agitation of the rising airflow, so as to maintain good activity and avoid blockage.