不同组成活性污泥胞外聚合物吸附Cd^2＋、Zn^2＋特征

Adsorption Characteristics of Cd^(2+) and Zn^(2+) by Extracellular Polymeric Substances with Varied Constituents from Activated Sludge

以蛋白质和糖含量比分别为2.5∶1、7∶1和9∶1的3种活性污泥胞外聚合物(extracellular polymeric substances,EPS)EPS1、EPS2、EPS3作为吸附剂,研究其对水中Cd2+、Zn2+的吸附效能.结果表明,EPS对Cd2+和Zn2+的吸附与其组成有关,EPS1、EPS2和EPS3对Cd2+和Zn2+吸附量分别约为19.5、27、17mg/g和40.5、47.5、37mg/g.3种胞外聚合物对Cd2+、Zn2+吸附过程可在1h内快速平衡.动力学拟合结果表明,EPS1对2种重金属的吸附速率最快,而EPS2对Cd2+、Zn2+的平衡吸附容量最高.Freundlich和Langmuir方程均可描述3种EPS对Cd2+、Zn2+的吸附过程,方程参数拟合结果表明2种金属同EPS之间存在多种作用方式.3种EPS的吸附热力学方程拟合系数均表明EPS对Zn2+的吸附稳定性、吸附能力和亲和力均比对Cd2+的吸附强;当EPS中糖所占比例增加时,其对重金属的吸附能力也提高,表明糖在吸附过程中起着重要作用.

Three typos of extracellular polymeric substances （EPS）, EPS1, EPS2 and EP3, with protein/sugar content ratio of 2.5 ： 1, 7 ： 1 and 9： 1, respectively, were investigated as sorbent for adsorbing Cd^2＋ and Zn^2＋ from wastewater. The experimental results showed that the adsorption efficiency of EPS toward Cd^2＋ and Zn^2＋ were dependent on the composition of EPS. The adsorptive capacities of EPS1, EPS2, EPS3 to Cd^2＋ were 19.5 mg/g, 27 mg/g, 17 mg/g and to Zn^2＋ 40.5 mg/g, 47.5 mg/g, 37 mg/g, respectively. Kinetic study showed that EPS1 has the highest reaction rate, while EPS2 has the highest adsorption capacity. All of the adsorption processes reached equlibrium within 1 h following both the Freundlich and Langmuir isotherms. The fitted parameters indicated that varied reactions may occur in EPS-metal adsorption process and EPS as adsorbent has much higher adsorption stabilization, adsorption ability and appetency to Zn^2＋ than to Cd^2＋. The adsorption capacity of EPS toward Cd^2＋ and Zn^2＋ increased with the sugar content, which suggests sugar is of great importance in the adsorption.