ABSTRACT

Slow sand filtration is a common technology providing potable water in rural households across Latin America, Asia and Africa. Two PVC household slow sand filters (HSSF) were operated in continuous (C-HSSF) and intermittent (I-HSSF) flow modes for eight consecutive months. A non-woven blanket was installed on the fine sand top to facilitate cleaning with scheduled maintenance undertaken every 30 days. The efficiency of each HSSF was evaluated via physico-chemical indicators (reduction of turbidity and colour) with biological performance assessed via total coliform and E. coli enumeration post treatment. There were no statistically significant differences between the continuous flow and intermittent flow models for physical–chemical and total coliform reduction parameters. However, when evaluating E. coli, C-HSSF performed better (p = 0.02). The non-woven blanket was subjected to weekly analysis using a Clark-type amperometric microsensor (diameter < 20 µm), which measured dissolved oxygen (DO) concentration in the adherent biofilm. DO microprofiles illustrated a variation in biofilm growth, which were associated with a progressive increase in the HSSF efficiency. The maximum DO depletion value measured during several months of operation showed no significant difference between I-HSSF and C-HSSF (p = 0.98). The microsensor measurements provided unprecedented results in real time. These results can help to understand the efficiency of the filter in relation to the biofilm growth, the dissolved oxygen depletion and turbidity removal.

摘要

慢沙过滤是为拉丁美洲、亚洲和非洲的农村家庭提供饮用水的常用技术。两个 PVC 家用慢砂过滤器 (HSSF) 在连续 (C-HSSF) 和间歇 (I-HSSF) 流动模式下连续运行八个月。在细沙顶部安装了无纺布毯，以方便清洁，每 30 天进行一次定期维护。每个 HSSF 的效率通过物理化学指标（浊度和颜色的降低）进行评估，生物性能通过总大肠菌群和大肠杆菌计数后处理进行评估。物理化学和总大肠菌群减少参数的连续流动和间歇流动模型之间没有统计学上的显着差异。但是，在评估时大肠杆菌、C-HSSF 表现更好 ( p  = 0.02)。使用 Clark 型安培微传感器（直径 < 20 µm）对无纺布毯进行每周分析，该传感器测量粘附生物膜中的溶解氧 (DO) 浓度。DO 微图说明了生物膜生长的变化，这与 HSSF 效率的逐渐增加有关。在运行数月期间测得的最大 DO 消耗值显示 I-HSSF 和 C-HSSF 之间没有显着差异（p  = 0.98）。微传感器测量提供了前所未有的实时结果。这些结果有助于了解过滤器与生物膜生长、溶解氧消耗和浊度去除相关的效率。