不同人工湿地基质对甲苯的比较吸附研究

Adsorption of Toluene on Different Substrates for Constructed Wetland

通过火山岩、天然沸石、碎石对甲苯的吸附实验,比较分析了三种人工湿地基质对甲苯的吸附机理和去除效果。结果表明:基质粒径小于200目时,甲苯在三种基质上的吸附平衡时间均为12 h,线性和Freudlich吸附方程均可用来描述甲苯在三种基质上的等温吸附行为,吸附量从大到小为火山岩≈沸石>碎石,Dubinin-Radushkevich方程拟合求出平均吸附自由能E均小于8 k J·mol-1,表明三种基质对甲苯的吸附作用均为物理吸附;基质粒径增大时,火山岩和天然沸石的吸附量变化不大,碎石的吸附量急剧下降。小试系统模拟对甲苯的动态去除结果表明:水力停留时间为2 d时,经火山岩或天然沸石系统处理后,达到GB 8978—1996《污水综合排放标准》三级排放标准(≤0.5 mg·L-1)的废水中甲苯浓度可降低并达到一级排放标准(≤0.1 mg·L-1),而碎石系统对甲苯的去除率较低,仅为12%~16%。

Constructed wetlands are a low-cost and easy-operation technology for treating low concentration organic substance wastewater.The present study compared the adsorption and removal efficiency of toluene by volcanic, natural zeolite and gravel. The results showed that the equilibrium time of toluene adsorption on three substrates were 12 h. Both Freudlich and linear isotherms could be used to fit toluene adsorption. The adsorption capacities of three substrates for toluene were:natural zeolite≈volcanic>gravel; E(mean free adsorption energy)of toluene for each substrate obtained by Dubinin-Radushkevich equation was less than 8 k J·mol-1, implying that the toluene adsorption was physical process. With the particle size of substrates increasing, the toluene adsorption by volcanic and zeolite changed little, while that of gravel sharply decreased. The removal efficiency of toluene from water was obviously greater in volcanic and natural zeolite systems than in gravel system. When the Hydraulic Retention Time(HRT)was 2 d, the toluene concentration in the wastewater satisfying the third grade Integrated Wastewater Discharge Standard(GB 8978—1996)(≤0.5 mg·L-1)could meet the first grade standard(≤0.1 mg·L-1)for the volcanic and natural zeolite systems, whereas the toluene removal rate in the gravel system was only 12%~16%.