Study On The Electrochemical Treatment Of COD In Bio-treatment Outflow Of Coking Wastewater

Coking wastewater is a typical refractory industrial wastewater with high biological toxicity. The advanced treatment and reuse of bio-treatment outflow of coking wastewater attracts more attention. Electrochemical methods have been widely used in the field of water treatment because of its advantage of little secondary pollution and easy operation. In this paper, advanced treatment of bio-treatment coking wastewater by electrochemical technology was studied. The reaction mechanism of electro-catalytic oxidation of quinoline, which is the typical pollutant in coking wastewater, was preliminary discussed as well.The main conclusions were drawn as follows:(1) When initial pH was 8, current density was 7 mA/cm² and plate distance was 3 cm, the COD removal of electric flocculation was 41.6% with iron plate anode and graphite plate cathode respectively. Aeration rate had little effect on COD removal. Otherwise the COD removal of coagulation was 33.0% when the initial pH was 8, the dose of PFS was 0.3 mL/L, reaction time was 6 min and still time was 3 min. Polyacrylamide had no obvious effect on COD removal.(2) When initial pH was 3, current density was 5 mA/cm² , dosage of H₂O₂ was 1 mL/L and plate distance was 1 cm, the COD removal of electro-fenton was 76.5% with iron plate anode and graphite plate cathode respectively. When initial pH was 8, current density was 10 mA/cm², and plate distance was 1 cm, the COD removal of electro-catalytic oxidation system was 100% with idium modified Ti anode and graphite plate cathode respectively(3)The cost of coking wastewater treatment by coagulation,electric flocculation,electro-fenton and electro-catalytic oxidation was 0.95 yuan,0.30 yuan,2.62 yuan and 1.67 yuan. The COD of coking wastewater after advanced treatment by electric flocculation cooperated with electro-catalytic oxidation could meet with Code for design of industrial recirculating cooling water treatment. However, the salinity of coking wastewater was very high and needed further treatment. (4) When initial pH was 9, current density was 20 mA/cm², the initial concentration of quinoline was 100 mg/L, plate distance was 1 cm, and the concentration of Na₂SO₄ was 0.06 mol/L, the quinoline removal could reach 88.1% in electro-catalytic oxidation system. The kinetics of quinoline removal follows pseudo-first order model. Quinoline was not mineralized completely while intermediates appeared.