Wastewater Treatment With Biomass Char Prepared By The Physical Activ-ation Process

In this study, rice husk and mulberry branch, which are the agricultural wastes, were utilized to prepare the biomass chars as the precusors. The physical activation method of usig steam as the activation gas was adopted in this study for its easy operation and causing little pollution. Also the researches about using the biomass chars to remove Cu2+, Cr6+and NH4+-N from aqueous solution were carried out in this study.The biomass chars and precusors were charaterized with scanning electron microscope, a computer controlled automated porosimeter, X-ray energy dispersion spectrometer and Fourier transform infrared spectrometer. It was found that the microsturcture and functional gourps of the precusors changed after the preparation. A great number of pores were observed in the biomass chars and some oxygen functional groups appeared on the surface of them.The effects of preparation temperature and the amount of steam in the activation gas on the performance of the biomass char were investigated. High preparation temperature and involvement of some steam in the activation gas made the biomass char has better pollutant removal capability. The optimal temperature for pyrolysis and steam activation was chosen as 700 and 750℃, respectively, using 3% (V/V) steam as the best activation gas.The influences of several experimental parameters, such as the dosage of biomass char, initial pH, temperature, and adsorption time, on the removal of Cu2+, Cr6+and NH4+-N from aqueous solution by biomass char were also studied. The optimal initial pH value for removing Cu2+and NH4+-N with rice husk char were 5.0 and 7.0, respectively, and high temperature favored the removal of Cu2+by rice husk char. The optimal dosage of rice husk char for removing NH4+-N was 1.0g, while that of mulberry branch char for removing NH4+-N, Cu2+and Cr6+was 1.0g,0.6g and 0.3g, respectively.The adsorption kinetics, isotherms and thermodynamics of pollutants by biomass chars were also investigated, and good correlation coefficients were obtained for the pseudo-second-order kinetics models for Cu2+, Cr6+and NH4+-N. The Langmuir isotherm model fitted very well with the experimental data about the removal of Cu2+ by rice husk char, while the experimental data about the removal of NH4+-N by rice husk char could be best described by D-R isotherm model. The adsorption of Cu2+by rice husk char was proved to be endothermic.