| Water-based ink as the environmental-friendly material has been widely used in printing the packaging of food, drug, toy, wine product and so on. However, wastewater obtained from the printing process is highly colored by the pigments, highly contaminated with organic materials and difficult to break down biologically. Attempts were made in this study to degrade water-based printing ink wastewater by home-made tubular electrochemical reactor. Parameters affecting the electrochemical process, such as the value of chemical oxygen demand (COD) and color, pH, flow velocity and the settling time, were determined to examine the efficiency of electrochemical reactor, and to investigate the mechanism and reaction kinetics of the electrochemical process.Results indicated that, under batch condition, the color and COD removal efficiency of wastewater increased with the increase of current density, the color and COD removal value of wastewater tend to stabilize after the current density was 20.0 mA/cm2. The efficiency affected by electrolyte concentration was low than current density, the treatment efficiency of water-based printing ink wastewater by tubular electrochemical reactor achieved the maximum value with an electrolyte concentration of 4.5 g/L, the removal efficiency of color and COD reached to 88.52%, 81.75%, respectively. Comprehensively considered initial pH effecting on the removal efficiency of color and COD, the optimum initial pH of the wastewater was in neutral condition. During the treatment of real wastewater, the suitable electrolysis time was 90 min. Under the optimum process conditions, the electrochemical degradation of water-based printing ink wastewater fit well with a pseudo-first-order kinetic pattern, the correlation coefficient of linear curve fitting R2 was 0.9967.Considered the influence of different flow velocities on the color and COD removal, the removal efficiency of color and COD increased with increasing the flow velocity at low flow velocity. However, when the flow velocity exceeded a constant value, overhigh flow velocity go against the degradation of wastewater. The Re was in the range from 25.4 to 289.8 at the flow velocity varying from 0.5×10-3 to 6.1×10-3 m/s, known as laminar flow, and the corresponding mass-transfer coefficient in the cell was about 2.0×10-5 to 2.7×10-5 m/s. the instantaneous current efficiency (ICE) increases with raising liquid flow velocity, and decreased with increasing electrolysis time. For a water-based printing ink wastewater in 4.5 g/L Na2SO4 at current density of 20.0 mA/cm2 and the electrode potential of 7.0 V, the actual energy sonsumption was 38.4 kWh/kg COD within 90min under a flow velocity of 0.5×10-3 m/s, and the energy usage ratio of the tubular reactor was 39%.During the electrochemical degradation process of water-based printing ink wastewater, pH dropped gradually, and small molecular organic acids such as formic acid, acetic acid were generated by ion chromatography. Before electrolysis, the water-based printing ink wastewater by GC-MS contained n-amyl alcohol, isoamyl alcohol, azo-organic compounds, linear and banched-chain hydrocarbons. After 90 min of electrolysis, the composition of organic matter changed obviously, kinds of organic compounds decreased and small molecular organic acids increased, the biodegradablity of the water-based printing ink wastewater improved. The tubular electrochemical reactor treated effectively water-based printing ink wastewater,the color and COD removal efficiency was high, small molecular organic acids were generated, and the energy sonsumption of reactor was low. So it provided certain theory reference for industrial application of tubular electrochemical reactor. |
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