| During the pulping and papermaking process,the organic pollutants were produced in bleaching of pulp.The production of absorbable organic halogens is greatly reduced when elemental chlorine free(ECF)process is employed.As the papermaking industry discharges a large amount of wastewater annually,the total AOX which released into the environment was increasing.As a kind of the persistent organic pollutants(POPs),it has the characteristics of long-term remains,bioaccumulative,high toxicity and long-distance transfer,AOX causes enormous threat to the environment which could be reduced a little by natural degradation.Shell activated carbon is a kind of functional carbon materials with large pore size,large specific surface area and strong adsorption capacity,which is widely used in the field of environmental protection.This paper investigates the natural degradation of AOX in ECF bleaching wastewater.The optimum process conditions of AOX adsorption were exlpored by using the shell activated carbon.The kinetic model of 2,4,6-TCP and 1,2,4-TCB was established to provide a theoretical basis for monitoring the distribution of AOX pollutants in the actual environment.1.The content of AOX was reduced from 25.98 mg.L~-1 to 21.97 mg.L~-1 after the bleaching wastewater was degraded for 45 days.It was found that the content of small molecular substances such as chloroacetic acid,chloro acetone and so on was reduced after the free degradation of bleaching wastewater.But the chlorinated organic compounds are difficult to degrade,such as chlorobenzene and chlorophenol.2.It was observed that the activated carbon is mainly amorphous by XRD.It is showed that the surface was rich in pore structure by SEM.The results show that the specific surface area of activated carbon is 1241 m2.g~-1,The average pore size is 2.21 nm and the pore size is mainly concentrated in 1-4 nm,which has a large number of micropores and mesopores.It belongs to the type of adsorption isotherms of the fourth types by BET.3.The optimum adsorption conditions of AOX:activated carbon particle size is 75 um,the adsorption equilibrium time is 100 min,adsorption temperature is 50 ?,the best activated carbon dosage is 1.50 g.L~-1,pH value of wastewater is 2.47,the best adsorption capacity can reach 4.385 mg.g~-1 at this time.The GC-MS analysis of bleaching wastewater which was treated by activated carbon show that chloropropanone,2-chlorobenzene,two chlorophenyl ester,trichlorobenzene,and trichlorophenol were mostly removed.EDAX spectra show that:the chlorine content increased from 0.01%to 2.32%on the activated carbon after adsorption of AOX.4.2,4,6-TCP and 1,2,4-TCP were used as the AOX simulation,the adsorption kinetics model and adsorption isotherm model were used to fit the adsorption process.They were used as the AOX simulation,the adsorption kinetics model and adsorption isotherm model were used to fit the adsorption process.The pseudo-second order and Freundlich models were used to describe the adsorption of 2,4,6-TCP.The pseudo-first order and Langmuir models were used to describe the adsorption of 1,2,4-TCB.The adsorption mechanism was found that there were other control steps in the adsorption process based on the Dumwald-Wagner equation,and the adsorption thermodynamics shows that the adsorption process is exothermic reaction. |
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