State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing 210008, China.
Nanjing University of Science and Technology, 200 Xiaolingwei Road, 210094 Nanjing, China.
Water Res. 2017 May 15;115:329-338. doi: 10.1016/j.watres.2017.03.014. Epub 2017 Mar 6.
The cost-effective and geographically available substrates are vital for the design of constructed wetlands (CWs), especially the saturated subsurface flow CWs, which are deemed as an efficient way to remove the inlet-lake phosphorus concentrations. In this study, phosphorus removal of thermally-treated calcium-rich attapulgite (TCAP) with varied particle sizes (0.2-0.5 mm, 0.5-1 mm and 1-2 mm) was assessed using batch and long-term column experiments to evaluate its feasibility as a CWs substrate. The phosphorus-bound mechanism in TCAP was identified in various initial phosphorus concentrations. Batch studies indicated that more than 95% of P can be rapidly (<1 h) removed by TCAP from solution with a concentration of 20 mg P/L, and P sorption can be well fitted by a pseudo-second-order equation. The maximum P sorption capacity of TCAP was in the range of 4.46-5.99 mg P/g, and the availability of Ca concentration might limit the P removal capacity of TCAP at high phosphorus concentrations. Both the P removal rate and capacities decreased with the increase of TCAP particle sizes. Column P removal experiments indicated that hydraulic retention time (HRT) exerts great influence on P removal performance and longer HRTs favor the dissolution of CaO in TCAP, consequently increasing the P removal rate. In a 150-day P removal experiment, TCAP removed an average of 93.1%-95.4% of the influent P with a HRT of eight hours. Both the batch and chemical extraction of the P fraction of TCAP showed that the P removed by TCAP was mainly through formation of Ca phosphate precipitation. However, the species of Ca-P precipitation formed might be varied in different phosphorus concentrations. All results indicated that TCAP can be a suitable substrate when used in CWs, and field experiments should be carried out to test its real P removal performance in the future.
用于设计人工湿地（CWs）的具有成本效益和地理可用性的基质至关重要，特别是对于饱和地下流 CWs 而言，因为它被认为是去除入湖磷浓度的有效方法。在这项研究中，使用批处理和长期柱实验评估了不同粒径（0.2-0.5mm、0.5-1mm 和 1-2mm）的热处理富钙凹凸棒石（TCAP）的除磷效果，以评估其作为 CWs 基质的可行性。在不同初始磷浓度下确定了 TCAP 中磷的结合机制。批处理研究表明，在 20mg/L 的磷浓度下，TCAP 可以在不到 1 小时的时间内迅速（<1h）将溶液中的磷去除 95%以上，磷吸附可以很好地用拟二级方程拟合。TCAP 的最大磷吸附容量在 4.46-5.99mg P/g 范围内，高磷浓度下 Ca 浓度的可用性可能限制了 TCAP 的磷去除能力。TCAP 的磷去除速率和容量均随 TCAP 粒径的增加而降低。柱磷去除实验表明，水力停留时间（HRT）对磷去除性能有很大影响，较长的 HRT 有利于 TCAP 中 CaO 的溶解，从而提高磷去除率。在 150 天的磷去除实验中，TCAP 在 HRT 为 8 小时的情况下，去除了进水磷的 93.1%-95.4%。TCAP 的磷分批次和化学提取实验表明，TCAP 去除的磷主要是通过形成磷酸钙沉淀。然而，在不同磷浓度下形成的 Ca-P 沉淀的形态可能有所不同。所有结果均表明，TCAP 可用作 CWs 的合适基质，未来应进行现场实验以测试其在实际去除磷方面的性能。
