Study On Pretreatment Of Pre-plating Wastewater

The electroplating wastewater has a very complex composition with great harmand the treating of it is quite difficult. The heavey metals it contains may formcomplexes with some of the additives in the wastewater, which is hard to treat usingtraditional precipitation. Besides, the treatment effect of traditional chemical treatmentto the removal of COD, NH3-N and TP in electroplating wastewater isn’t very good.There is an urgent need for new electroplating wastewater treatment process.This paper based on the electroplating wastewater treatment project of a largeelectroplating industrial park in Shenzhen. After fully investigated and researched thetypes and characteristics of wastewater discharged by the workshop, we re-divided thewastewater into generally plating wastewater, complexation wastewater, pre-platingwastewater, cyanide-containing wastewater, and chromium-containing wastewater,and designed a new treatment process with chemical treatment followed byA2O-MBR process. Reserched the pre-treatment process of the pre-treatmentwastewater using neutralization-flocculation-precipitation process, Fenton process andmicro-electrolysis process to make sure that the treated water reached the biochemicalsystem feed water requirement.Experiments showed that this pre-plating wastewater mainly contains Cu, Ni,COD and TP, the heavy metals together with the organic components of which have acertain degree of complexation, treating with neutralization-flocculation-precipitationprocess, the residual concentration of pollutants is still above the biochemical systemfeed water requirement. Using Fenton before neutralization-flocculation-precipitationprocess, the effluent proved to be much better, all the indicators can reach thebiochemical system feed water requirement. The optimum reaction conditions forFenton are as follows:30%hydrogen peroxide dosage at1.4mL/L, pH at3.5, molarratio of hydrogen peroxide and ferrous sulfate at1:1.2, residence time of1hour. ForCOD degradation, hydrogen peroxide dosage is the most prominent influencing factor,for the removal of TP, molar ratio of hydrogen peroxide and ferrous sulfate is the mostsignificant factor. Using micro-electrolysis before neutralization-flocculation-precipitation process, the removal efficiency of Ni, COD, TP is satisfying, while theresidual concentration of Cu is higher than the biochemical system feed water requirement. The optimum reaction conditions for micro-electrolysis are as follows:pH at2, iron carbon ratio at1:1, and reaction time at40min. Reaction time has thegreatest impact on degradation of COD. When using micro-electrolysis together withFenton, the effluent water quality is even better than the biochemical system feedwater requirement, but as COD is too low, this effluent is not suitable for biochemicaltreatment.As a result of the facts above, in actual operation, when the water quality ofinfluent is normal, we can use only Fenton process, micro-electrolysis treatmentserved as a backup process of Fenton, only used when the influent water quality isworse than normal.