Study Of Advanced Treatment Of Tannery Wastewater By Electrocoagulation

In China,tannery industry development is fast and it also brings a series of environmental problems.The waste discharged from the tannery industry contained a large amount of poisonous and harmful substances.Tannery is a heavily polluting industry,and its effluent is difficult to treatment.Because the wastewater has high concentration of COD and it contains a lot of organic,inorganic,heavy metal chromium(Cr)and sulfide.The effluent of Anoxic-Oxic tank couldn't reach the standard in the conventional treatment process.With reference to(GB 30486-2013),the total Cr emission limit has been decreased from 1.5mg/L to 0.5mg/L and the COD discharge limit has been decreased to 60mg/L.It is imperative that the tannery wastewater be treated by advanced treatments.In this paper,the refractory organic and Cr in a tannery wastewater from Shandong province were removed by the technologies of biological treatment using the dominant bacteria combined with electrocoagulation(EC).Wastewater was treated by chemical precipitation method which was mainly for the removal of Cr.After precipitation,the effluent was treated with biological treatment that included the sludge acclimation in 15 days,biofilm culturing process,and stable operation in 20 days.The concentration of COD and Cr were about 200 mg/L and 10 mg/L,respectively,in the effluent that was used for EC to remove Cr.The effects of electrode material,reaction voltage,pH,reaction time on the total Cr removal efficiency were studied.The influence of current density and current efficiency on the experimental process was also explored during the experiment.At the same time,material conservation was verified,and the content of Cr after treatment were proved.The transformation form of Cr was inferred.For the removal of COD from refractory organics,the effects of reaction voltage,pH,reaction time,and current density on COD removal efficiency were studied.Anode consumption was also calculated during the experiment to assess the economic feasibility of the EC.The study results showed that theCOD removal could reach 60.79%after three stages of the dominant bacteria of biological enrichment culture and domestication.The COD concentration of effluent was about 200 mg/L.The aluminum-titanium anode had the best effect for treatment of tannery wastewater.The total Cr,Cr(III)and COD removal rates were 98.88%,98.93%and 83.38%,respectively,under the conditions that the reaction voltage was 5 V,the pH was 6,the time was 30 minutes and current density was 800 A/m2 The effluent met the first class discharge standard of the tanning industry(GB 30486-2013).Finally,the reaction kinetics were fitted.The results showed that the removal of Cr by EC was in accordance with the first-order kinetics model.The process of COD removal conformed to the first-order reaction law.The relationship between the time and the removal rate of COD accords with the equation:R =-0.049t2+2.5595t + 56.674.The relationship between the time and the rest concentration of COD accords with the equation:C= 0.2868t2-13.448t-11.514.The relationship between the variation of COD concentration and the time was a parabola relation,which conformed to the first-order reaction law.The linear correlation was closed to0.9877.