| Parabens are a class of compounds that have been used fornearly 100 years for their anti-microbial and anti-fungal properties.They are mainly used as preservatives in foodstuffs,cosmeticsand pharmaceutical drugs.Considered as emerging contaminants,Parabens may act as weak endocrine disrupter chemicals,but controversy still surrounds the potential suspected adverse ecological or human health effects of these compounds.It has been reported that these compounds have weakly oestrogenic activity and reproductive toxicity.Biochar is a widely source of raw materials of new environmental functional material,which has abundant micropore structure and large specific surface area,can be used as high performance adsorbents,and has a strong adsorption capacity for organic pollutants.Biochar is produced from thebiomass pyrolysis under limited or in absence of oxygen conditions.Due to its porousstructure,biochar has beenused in many studies as an impressive adsorbent to remove different pollutants from aqueous solution.In this paper,two type of biochars were prepared.One was prepared at a temperature of 300,500 and 700 degrees,which were named BC300,BC500 and BC700,respectively.Another type of biochar was prepared at 500 degrees from wheat straw,cow dung and sycamore leaf,followed by modification with CTMAB.They were named MWB,MSB,MCB,respectively.Then the biochars were applied to study the adsorption of the simulate ethyl paraben waste water.The biochars were tested for its ability to remove ethyl parabenfrom aqueous solution by batch static adsorption and dynamic column adsorption,and the mechanism of the adsorption process was determined.Several mainconclusions of this study are as follows:(1)With increasing temperature,the biochars provided more hydrophobic surfaces,and promoted the point of zero charge from 8.42 to 9.52.In addition,alkaline conditions(pH=8-12)decreased the adsorption capacity significantly.Decrease of adsorption capacity also came along with an increase of ionic strength.Sorption isotherm of ethyl paraben onto biochars agreed well with Langmuir isotherm model,and the order of maximum adsorption capacities is BC700>BC500>BC300.Adsorption kinetics is well described by the pseudo-second-order model,and the thermodynamics constants show that the adsorption processes are endothermic and spontaneous.After 4 cycles of adsorption-regeneration test,the regenerated biochars still maintained 90%of their initial adsorption capacities,and BC700 showed the largest recovered adsorption capacity,92.76%.(2)After the modification of three biochars of MWB,MCB,and MSB,C16H33(CH3)3N+-Br-was mainly adsorbed on the surface of biochars,and only a few of them entered into the biochar.Moreover,the adsorption behavior of modified biochar on EP was mainly caused by C16H33(CH3)3N+ on the surface of biochar and biochar adsorption sites,and the internal adsorption of C,6H33(CH3)3N+had little effect.The maximum adsorption capacities of MWB,MCB and MSB were:26.17mg ·g-1,23.14mg · g-1 and 25 mg · g-1,respectively.and the order of removal efficiency is MWB>MSB>MCB.The adsorption accorded with the Langmuir isotherm equation,which followed the pseudo two order kinetics equation.It was spontaneous endothermic adsorption process.Compared with the wheat straw biochar without modification,the adsorption efficiency of modified wheat straw biochar was increased,and the hydrophobic property of biochar was increased.(3)Through the dynamic adsorption experiments of modified wheat straw biochar,the effect of bed height,initial ion concentration,feed flow rate and other operating parameters on the EP adsorption characteristics was studied to show that the dynamic adsorption effect of modified biochar adsorption of EP depended on the experimental condition.The higher the height of the packing layer was,the greater the flow rate was.The higher the initial concentration was,the less the penetration time was.The less the column consumption time was,but the lower the adsorption efficiency was. |
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