Treatment of semi-coking wastewater by synergistic process of flocculation-electrolytic oxidation
The synergistic process of flocculation-electrochemical oxidation was used to treat the semi-coking wastewater.The effects of flocculant dosage,reaction time,initial pH,applied voltage,and NaCl addition on the removal of chemical oxygen demand(COD)and ammonia nitrogen(NH3-N)and the synergistic mechanism of flocculation-electrochemical oxidation were investigated.The results indicated that the removal rate of COD and NH3-N in the semi-coking wastewater gradually increased with the increase of polyaluminium ferric chloride(PAFC)dosage and applied voltage.Under optimal conditions of 50g/L PAFC dosage,6V voltage,4h reaction time,initial pH of 9,and 30g/L NaCl addition,the removal rates for COD and NH3-N were 82.37％and 100％,respectively.By replacing the electrode plate for the secondary electrolysis,the COD removal rate could reach 100％.The organic pollutants in the semi-coking wastewater before treatment were mainly phenols,alcohols and amides.After treatment,the content of phenols decreased significantly,and the relative proportion of ketones,alcohols and acids increased.During the flocculation-electrochemical oxidation process,PAFC functioned both as a flocculant and provider of Cl.The Cl dissociated from PAFC hydrolysis,together with Cl introduced by NaCl,migrated directionally towards the anode under an electric field.The active chlorine(C12/C1O)generated by the oxidation reaction on the anode surface oxidized the organic pollutants in the semi-coking wastewater into intermediate products,chlorophenols,which combined with the hydrolysis products of Al3+from the flocculant,A1(OH)2+,A1(OH)2+,and Al(OH)3,through electrostatic and adsorptive interactions to form flocs that were removed.The remaining traces of organic pollutants such as chlorophenols,amides,cyclohexanediol,and NH3-N in the wastewater were converted into N2,CO2,and H2O by the indirect oxidation action of ClO.
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