Research On Process Optimization Of Electroplating Wastewater Treatment

Electroplating was one of the three major polluting industries. And electroplatingwastewater had severe toxicity and harmfulness. Based on electroplating wastewater of aelectroplating industrial park in Qing yuan town, Guangdong province, the main polluntantswhich included Cr⁶+, Ni²⁺, CN^-, Cu²⁺and COD could not meet Emission standard ofpollutions for electroplating （GB21900—2008）. This paper was about the optimization ofwastewater treatment processes to reach the emission standards at low operation cost. Thispaper designed four kinds of process optimization.Process optimization （I）----study on the application of iron fillings for sludge reductionin the electroplating wastewater treatment. This method was about mixing iron fillings andacidic electroplating wastewater. This method could make the value of pH ascend obviously.And the content of Fe（2+）went up with the increase of acidity. The mixing of iron fillings andacidic wastewater had the effect on the treatment of chromium-containing wastewater, whichreduced the dosage of lime and Ferrous Sulfate greatly.Process optimization （II）----study on the separated treatment of electroplatingwastewater and optimum parameters of process. Changing from mixed treatment to separatedtreatment and dividing into three kinds of wastewater: cyanide-containing wastewater,chromium-containing wastewater and nickel and copper-containing wastewater. The methodof FeSO₄7H₂O and Ca（OH）2joint treatment was applied to treat Cr⁶+. The optimumparameters were as follows: m（FeSO₄7H₂O）:m（Cr⁶+）=20:1, the initial pH was3⁴, the valueof pH during precipitation was10. The alkaline chlorination process was applied to treat CN^-.The optimum parameters of this process were as follows: the value of pH of the partialoxidation was11, m（NaClO）:m（CN-）=3:1; the value of pH of complete oxidation was8,m（NaClO）:m（CN-）=10.76:1. The method of FeSO47H2O and multistage precipitation jointtreatment was applied to treat Ni（2+）and Cu（2+）. The reaction was divided into three phases: thetreatment of complex compound, lime precipitation and sulfide precipitation. The values ofpH of these three phases were3,9¹0and10respectively. m（FeSO47H2O）:m(Cu²⁺)=9.72:1;m（FeSO₄7H2O）:m(Ni²⁺)=7.68:1; m（Na₂S9H₂O）:m(Cu²⁺)=3.81:1. In the above conditions, the indices of Cr⁶+, Ni²⁺, CN^-and Cu²⁺in effluent reached the discharge stands and all theremoval rates were more than99%.Process optimization （III）----study on the advanced treatment electroplating wastewaterby the biological aerated filter （BAF）. The results showed that BAF had steadily good effecton CN^-, Cu²⁺and COD. When the working volume of the reactor was3L, the optimum flowrate of wastewater was2L/H, the hydraulic retention time （HRT） of BAF was1.5h. Under theconditions of that HRT, the removal rate of CN^-, Cu²⁺and COD was more than80%,50%,60%. When the influent concentration of CN^-, Cu²⁺and COD was less than1.5mg/L,1mg/L,200mg/L, the effluent quality could reach the emission standard of pollutants forelectroplating. And the form-film time of BAF was14days. When BAF was applied toengineering project, its designed flow rate of wastewater was25m3/h. The treatment effectwas the same as laboratory studies. And dosage of NaClO reduced from8‰（the volume ratioof NaClO to cyanide-containing wastewater） to6‰and Na2S9H2O reduced from2‰（thevolume ratio of Na2S9H2O to nickel and copper-containing wastewater） to0.5‰, whichreached goals of reducing costs and making COD meet the discharge standard.Process optimization （IV）----study on location of the biological aerated filter （BAF）.Changing the location of BAF reduced the operation cost of the project in the case of effluentmeeting the discharge standard. The highest limit value of CN-which microorganism couldbear was7mg/L. By dosing3‰NaClO could treat cyanide-containing wastewater from65mg/L to7mg/L. And the removal rate of CN-was65%, the mass concentration of CN-wasremoved to2.3mg/L. And when COD met the discharge stands, there was1.5‰NaClO tomake the mass concentration of CN-from2.3mg/L to less than0.3mg/L. That was to say,4.5‰NaClO in total was needed, which saved1.5‰NaClO in comparation withoptimization plan （III） and3.5‰NaClO in comparation with optimization plan （II）, almosthalf of dosage of NaClO.