Characterization And Electrochemical Treatment Of Persistent Organic Pollutants In Wastewater From Pulp And Paper Industry

Pulp and paper industry plays an important role in economy of China and Shandong province. Because of generating significant quantities of wastewater and heavy pollution, it’s difficult to promote sustainable development for pulp and paper industry. Especially for some persistent organic pollutants(POPs) in effluents, they are extremely toxic and refratory to degradate. The wastewater from pulp and paper industry consists of pulping wastewater, washing wastewater, pulp bleaching effluents and whitewater. There are plenty of chlorinated organic pollutants in pulp bleaching effluents, especially for chlorophenolics, which are carcinogenic, teratogenic and mutagenic. Chlorophenols(CP), chloroguaiacols(CG) and chlorocatechols(CC) are the main chlorophenolics in pulp bleaching effluents.Biodegradation, catalytic reduction and advanced oxidative process(AOP) are used by many reseachers to degrade chlorophenolics. Recently, there have been an increasing interest in the application of electrochemical methods for the treatment of toxic or biorefractory organic pollutants. PbO2electrode, which has been extensively used in electrolysis, is favored to be a nonactive anode owing to its high electrical conductivity, high oxygen overpotential, chemical inertness, high performance and low cost. Characterization and electrochemical treatment of POPs in effluents from pulp and paper industry were investigated in this paper. Electrochemical treatment of pulp bleaching effluents and chlorophenolics was the key point. The main research contents were as follows:(1)The key producing process, compositions and concentrations of pollutants were investigated. COD, pH, color and chlorophenolics in all kinds of effluents from pulp and paper industry were determined and analysed.Pulp bleaching was the key process generating POPs, and chlorinated organic pollutants especially for chlorophenolics were the main pollutants. Chlorophenolics in Cl2and ClO2-H2O2bleaching effluents(C, E effluents and D, P effluents) were determined respectively by GC-MS. The concentrations of all chlorophenolics in C effluents were1.814mg/L, in which3,4,5-Trichlorocatechol(3,4,5-TCC),3,4,5,6-Tetrachlorocatechol(3,4,5,6-TeCC),3,5-Dichlorocatechol(3,5-DCC),3,6-Dichlorocatechol(3,6-DCC) and2,3,4,5-Tetrachlorophenol(2,3,4,5-TeCP) were the main compositions. The concentrations of all chlorophenolics in E effluents were2.985mg/L,in which2,4-Dichlorophenol(2,4-DCP),2,4,6-Trichlorophenol(2,4,6-TCP),4,5-Dichloroguaiacol(4,5-DCG),2,3,4,5-Tetrachlorophenol(2,3,4,5-TeCP), Pentachlorophenol(PCP) and3,4,5-Trichlorocatechol(3,4,5-TCC) were the main compositions. In D and P effluents, the concentrations of all chlorophenolics were40.3μg/L and53.82μg/L respectively.(2)A Bi-doped PbO2eletrode was prepared by continuous pretreatment, thermal decomposition and electrochemical deposition, which might be described as Ti/SnO2-Sb2O3/Bi-PbO2. The COD removal efficiency in an solution containing380mg/L phenol and5g/L Na2SO4could reach75%at pH7with an applied current density of30mA/cm2and electrochemical treatment time of120min. In addition, the average current efficiency(ACE) was17.2%.(3)The influence of pH, current density and treatment time on electrochemical treatment efficiency was investigated by experiment with bleaching effluents. At pH7with an applied current density of20mA/cm2and electrochemical treatment time of180min, the COD removal efficiency, average current efficiency(ACE) and energy consumption(EC) could reach78.51%,36%and120.83Kwh/KgCOD respectively in Ch bleaching effluents. As in ClO2-H2O2bleaching effluents, the COD removal efficiency, ACE and EC were58.6%,40.64%and148.4Kwh/KgCOD respectively at pH5with an applied current density of20mA/cm2and electrochemical treatment time of180min.(4)Chlorophenolics in Cl2bleaching effluents were almost removed by electrochemical treatment with an applied current density of20mA/cm2and treatment time of180min.