标题：Reconsidering ‘appropriate technology’: the effects of operating conditions on the bacterial
removal performance of two household drinking-water filter systems
摘要：We examined the performance of two household water treatment and safe storage
(HWTS) systems, the Danvor plastic biosand filter and the Potters for Peace
Filtron ceramic filter, under ideal as well as modified operating conditions using
systematic and comparable measurements. The operating variables for the biosand
filter were (i) pause times between filtration runs, (ii) water-dosing volumes and
(iii) the effluent volume at which a filtered water sample was collected. For the
ceramic filter we examined overflow filtration versus standard filtration. We used the
bacterial indicators of total coliforms and Escherichia coli to quantify microbiological
removal. With the biosand filter, a 12 h pause time had significantly higher total
coliform removal than a 36 h pause time at the 20 l collection point (79.1% versus
73.7%; p < 0.01) and borderline significance at the 10 l collection point (81.0% versus
78.3%; p = 0.07). High-volume filtration (20 l) had significantly lower total coliform removal
efficacy than low-volume (10 l) filtration at the 10 l collection point (81.0% versus
84.2%; p = 0.03). We observed a decreasing trend in total coliform removal by sample collection volume with the
highest removal efficacy at the 5 l sample collection point (versus at the 10 and 20 l collection
points). Using the ceramic filter, mean total coliform and E. coli removal were significantly lower
(p < 0.01) in overflow filtration than in standard filtration. The findings indicate that operating
conditions can reduce the effectiveness of the systems in a field-based setting and increase
environmental risk exposure.
