Department of Environmental Investigation, CIATEC A.C., 201. Omega Boulevard, León, Guanajuato 37545, Mexico.
J Environ Manage. 2013 Oct 15;128:22-9. doi: 10.1016/j.jenvman.2013.04.049. Epub 2013 May 27.
In central Mexico, agricultural irrigation reusing Mexico City's municipal wastewater has been occurring for the last century, resulting in the recharge of the local aquifer. However, groundwater of this zone is of good quality, indicating that the microorganisms contained in wastewater are retained by soil after infiltration. This study aims to assess the capacity of three agricultural soils to retain three microorganisms frequently found in wastewater, namely Escherichia coli (E. coli), Giardia lamblia (G. lamblia) cysts and Ascaris lumbricoides (A. lumbricoides) eggs, through batch sorption-desorption assays. The tested soils were: an organic-clayey soil (C-OM), a clayey soil (C-om) and a sandy soil (c-om). For the three soils, sorption equilibrium of E. coli was reached before 1 h, while for G. lamblia cysts and A. lumbricoides eggs, sorption equilibrium took 2.5 h. Sorption of E. coli was better described by the Freundlich model than by the Langmuir one. Higher retention of bacteria was observed in the C-om soil (KF = 4340) than in the C-OM and c-om ones (KF = 1821 and 0.01, respectively). Regarding G. lamblia cysts and A. lumbricoides eggs, data could not be fitted to the tested sorption models. For both organisms, retention was lower in the C-OM soil than in the C-om and c-om ones. In the desorption tests, a sudden liberation of E. coli from soils was observed, probably due to bacterial re-growth. Desorption of G. lamblia was higher in the sandy soil than in the clayey ones; desorption was not increased when a surfactant was applied to the soil, suggesting that hydrophobic interactions are not necessarily responsible for retention of the cysts onto the tested soils. For A. lumbricoides eggs, desorption using NaOCl solution suggested that retention was caused by interactions between the mineral fraction of the soil and the external walls of eggs. This study showed that the three target microorganisms are retained by the tested soils and that mineral domain of soil has an important role in such retention.
在墨西哥中部，农业灌溉再利用墨西哥城的城市废水已经持续了一个世纪，导致当地含水层得到了补给。然而，该地区的地下水水质良好，这表明废水中的微生物在渗透后被土壤截留。本研究旨在通过批量吸附-解吸实验评估三种农业土壤保留三种常见于废水中的微生物的能力，即大肠杆菌（E. coli）、贾第鞭毛虫（G. lamblia）包囊和蛔虫（A. lumbricoides）卵。测试的土壤为：有机-粘土土壤（C-OM）、粘土土壤（C-om）和沙质土壤（c-om）。对于三种土壤，大肠杆菌的吸附平衡在 1 小时前达到，而对于贾第鞭毛虫包囊和蛔虫卵，吸附平衡则需要 2.5 小时。大肠杆菌的吸附更符合 Freundlich 模型，而不是 Langmuir 模型。在 C-om 土壤中观察到对细菌的更高保留（KF = 4340），而在 C-OM 和 c-om 土壤中保留较低（KF = 1821 和 0.01，分别）。对于贾第鞭毛虫包囊和蛔虫卵，数据无法拟合到测试的吸附模型。对于这两种生物，在 C-OM 土壤中的保留率低于 C-om 和 c-om 土壤。在解吸实验中，观察到大肠杆菌从土壤中突然释放，可能是由于细菌的再生长。在沙质土壤中，贾第鞭毛虫的解吸率高于粘土土壤；当向土壤中添加表面活性剂时，解吸率并没有增加，这表明疏水性相互作用不一定是将包囊保留在测试土壤上的原因。对于蛔虫卵，使用次氯酸钠溶液的解吸表明，保留是由土壤的矿物质部分与卵的外壁之间的相互作用引起的。本研究表明，三种目标微生物被测试土壤保留，并且土壤的矿物质域在这种保留中起着重要作用。
