Advanced Treatment Of Pulp And Paper Effluent With Three-dimensional Electrodes

Pulp and paper enterprise is one of the main sources of industrial effluents in China,which caused serious pollution to the aquatic environment. After secondary treatment,the concentration of organic pollutant in pulp and paper effluents are still at high level,and it contains a certain amount of refractory materials （such as lignin and itsderivatives, etc.）. It is difficult to meet the new strict standard （GB3544-2008） aftertreatment with conventional approach, such as physical, chemical or biologicaltreatment. For these reasons, it is very important to develop an economic and efficientadvanced treatment of pulp and paper effluent, which can provide theoretical andtechnical support for wastewater discharged or partially reuse. In this paper, tertiarytreatment was carried out to treat pulp and paper effluent from secondary treatmentprocess by a three-dimensional electrode system equipped with modified bentonites asparticle electrode. It was demonstrated that three-dimensional electrode system treatpulp and paper effluent is a feasible and effective method through a contrast researchwith two-dimensional electrode.Firstly, six modified bentonite particles were synthesized and characterized byXRD, SEM and FTIR spectroscopy analysis. The cetyl trimethyl ammonium bromidemodified bentonite （CTAB-bent） and hydroxy-aluminum pillared organic bentonite（OH-Al-CTAB-bent） were elected as two kinds of excellent particle electrode bycomparison. It was confirmed that the modified bentonite was elected as particleelectrode in three-dimensional electrode system is suitable because of its goodperformance on conductive and physical properties.Secondly, the pulp and paper effluent was treated by electrocoagulation, and theinfluence variables such as current density, electrolysis time, the distance betweenelectrode plates and the dosage of NaCl on the removal of COD, color, theconcentration of lignin and UV₂₅₄was determined. A current density of40mA/cm²,electrolysis time of40min, the concentration of NaCl of1.6g/L, the distance betweenelectrode plates of4cm and the voltage of25V were selected as an optimum conditionsthrough several single factors experiments. It was found that the degradation efficiencyof the organic pollutants in paper effluent showed an increase tendency with increasingthe electrolysis time. The electrical conductivity of wastewater was improved afteradded NaCl electrolyte, and the highest COD removal efficiency can reached75.8%at62mg/L. The removal efficiency of lignin and UV₂₅₄in effluent can reached73.1%and 60.8%respectively. It is indicated that pollutants in pulp and paper wastewater removedby Al electrode is better than Fe electrode. In addition, advanced treatment was carriedout to treat pulp and paper effluent from secondary treatment process by athree-dimensional electrode system equipped with modified bentonites as particleelectrode. A current density of40mA/cm², electrolysis time of40min, airflow rate of1.0L/min and the particle electrode dosage of16g/L were selected as an optimumconditions through several single factors experiments. It was found that the highestCOD removal efficiency can reached83.2%at43mg/L, which can reach the standard ofdischarge. The removal efficiency of lignin and UV₂₅₄in effluent can reached81.9%and85.5%respectively. In addition, it is manifested that advanced treatment of pulp andpaper effluent with three-dimensional electrode system is a new and efficient processingmethods.Finally, the organic pollutants in the pulp and paper effluent can be divided intohydrophobic acid, weak hydrophobic substances, hydrophilic substance and non-acidhydrophobic substances by XAD-4and XAD-8resin combination technology. The fourchanges of organic pollutants in paper effluent before and after three-dimensionalelectrode processing was also discussed. It was found that hydrophobic acid accountsfor a major proportion in the pulp and paper wastewater, and the color of the effluent ismainly caused by the hydrophobic acids. The hydrophobic acid and hydrophilicsubstance of organic pollutant in paper effluent were all removed to a certain level, butfocuses on the degradation of hydrophobic acid.