Abstract Biofiltration systems are landscape depressions or shallow basins used to slow and treat on-site stormwater runoff and are considered as one of the important components of a sustainable drainage system. Biofilters generally consist of two components: a filtration media which is sand-dominant and a top vegetated soil layer. The efficiency of a biofiltration system is normally assessed by two key parameters namely hydraulic conductivity and percentage removal of pollutants. In tropical areas like Malaysia where rainfall intensity is normally high, hydraulic conductivity of the biofiltration systems needs to be high enough to prevent ponding and possible flooding of the system. To date, several studies have been done on development and maintenance of such systems; however, few have studied such systems under tropical climates with heavy and intense rainfall which needs high hydraulic conductivity. The present study aims to identify proper soil filter media that not only can remove heavy metal ions efficiently but also has reasonably high hydraulic conductivity. For this, a soil column experimental set up was developed and the effectiveness of adding different fine grained materials such as fly ash, halloysite nanotubes (Hals) from two different origins (Imerys from NZ and HalloPure from I-Minerals, Idaho), and zeolite in sand-based soil media was assessed. To assure the validity of the results for each proposed filter media three replicates were prepared. The performance in removing heavy metal ions Fe(III), Mn(II), Cu(II), Zn(II), Ni(II), and Pb(II) was then evaluated for each soil composition using Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES) test. Synthesized stormwater was used to provide consistency of pollutant concentration in experiments. The watering dosage was calculated based on hydrological data of a Malaysian catchment. Infiltration rate of each soil composition was also measured for further comparison. Results showed that increasing the percentage of fine materials can improve the heavy metal ions removal; however, the drawback would be significant decrease in infiltration rate. In general, Hals were found to fulfill the requirements for both high percentage removal and high infiltration rate compared to zeolite and fly ash. Moreover, the effect of aspect ratio, surface area, particle size and chemical composition of each fine material on its efficiency in heavy metal ions removal and infiltration rate were compared.

中文翻译：

---

埃洛石纳米管作为热带生物过滤系统中去除重金属离子的细粒材料

摘要 生物过滤系统是用于减缓和处理现场雨水径流的景观洼地或浅盆，被认为是可持续排水系统的重要组成部分之一。生物过滤器通常由两部分组成：以沙子为主的过滤介质和顶部植被土壤层。生物过滤系统的效率通常通过两个关键参数进行评估，即水力传导率和污染物去除百分比。在像马来西亚这样的热带地区，降雨强度通常很高，生物过滤系统的水力传导率需要足够高，以防止系统积水和可能的洪水。迄今为止，已经对此类系统的开发和维护进行了多项研究；然而，很少有人在热带气候下研究过此类系统，这些气候需要高水力传导率，且降雨量大且强。本研究旨在确定合适的土壤过滤介质，它不仅可以有效地去除重金属离子，而且还具有相当高的导水率。为此，开发了一个土柱实验装置，并研究了添加不同细粒材料的有效性，例如粉煤灰、来自两个不同来源（来自新西兰的 Imerys 和来自爱达荷州 I-Minerals 的 HalloPure）的埃洛石纳米管 (Hals) 和沸石在沙基土壤介质中进行了评估。为了确保每种建议的过滤介质结果的有效性，准备了三个重复。去除重金属离子Fe(III)、Mn(II)、Cu(II)、Zn(II)、Ni(II)、然后使用电感耦合等离子体 - 发射光谱 (ICP-OES) 测试评估每种土壤成分的 Pb(II) 和 Pb(II)。合成雨水用于提供实验中污染物浓度的一致性。浇水量是根据马来西亚流域的水文数据计算的。还测量了每种土壤成分的入渗速率以进行进一步比较。结果表明，增加细料的比例可以提高重金属离子的去除率；然而，缺点是渗透率会显着降低。一般而言，与沸石和飞灰相比，Hals 满足高去除率和高渗透率的要求。此外，纵横比、表面积、