When the copper electroplating washing water is not reused online, it is directly discharged into the mixed sewage for treatment together; During on-line reuse, the RO concentrated water of the reuse system is also discharged into the mixed sewage for treatment. When the plastic nickel electroplating washing water is not reused online, it is discharged into the chemical nickel sewage for treatment together; During on-line reuse, RO concentrated water of the reuse system is also discharged into chemical nickel sewage for treatment. Therefore, the treatment system of plastic electroplating sewage is similar to that of metal electroplating sewage, which can be divided into nickel containing sewage treatment system, chromium containing sewage treatment system and mixed sewage treatment system.
1.Treatment of nickel containing wastewater
Different from the general nickel containing sewage, the nickel containing sewage of plastic electroplating contains chemical nickel sewage. There are a large number of hypophosphites and organic complexes in the sewage. The complex nickel ions in the water cannot be removed only through simple pH adjustment and coagulation sedimentation treatment. At the same time, the removal of hypophosphites also needs to be targeted. Generally, it is necessary to adjust the pH of the sewage and add oxidant at the same time, The hypophosphite and phosphite in the sewage are converted into phosphate, and the complex in the sewage is destroyed to free the nickel ion, and then the phosphate and nickel ion are removed by adding calcium salt, coagulant and flocculant. It is worth noting that because the nickel containing sewage treatment system needs to treat the RO concentrated water of the electroplating nickel water washing water reuse system, the COD in the water is difficult to reach less than 100mg / L through only one coagulation and sedimentation process. Therefore, the general practice is to discharge it into the mixed sewage after treatment for re treatment.
2.Treatment of chromium containing wastewater
The chromium containing sewage uses the usual chemical reduction method to reduce Cr6 + to Cr3 + with low toxicity, and adjusts the pH value to form Cr (OH) 3. After precipitation, chromium is removed. Like the nickel containing sewage treatment system, when the chromium containing sewage is reused online, the RO concentrated water produced by it is difficult to reach cod below 100mg / L after one-time coagulation and precipitation, so its effluent should also be discharged into the mixed sewage for inheritance treatment.
3.Treatment of mixed sewage
The pollutant types of plastic electroplating mixed sewage with on-line reuse system are much more complex than those without on-line reuse system. Because the RO concentrated water of on-line reuse system finally needs to be collected into the mixed sewage treatment, its treatment is more complex. Common processes are:
Chemical oxidation – > coagulation and sedimentation before Biochemistry – > hydrolytic acidification – > Contact Oxidation – > coagulation and sedimentation after Biochemistry – > discharge