Abstract
Hollow-fiber membrane filters (HFMFs) for household water treatment (HWT) can efficaciously remove disease-causing organisms in laboratory settings. However, lower effectiveness in use in low- and middle-income countries (LMICs) and humanitarian contexts (HCs) has been observed and attributed to membrane fouling and the associated cleaning. In LMICs/HCs, it is not possible to prevent and control fouling using commonly known methods (e.g., testing influent water, maintenance regimes), and the literature on fouling/cleaning of HFMFs distributed in LMICs is scarce. As such, controlled laboratory experiments were conducted to determine the efficacy of locally available (in LMICs/HCs) backwashing solutions at removing fouling using different influent waters and HFMF types. Four commonly distributed HFMFs were selected; fouling layers were developed by filtering three influent water compositions, representing LMIC/HC waters, for 10-days, and bleach, water, or vinegar backwashing solutions were used for daily backwashing. Filter performance indicators included: fiber mechanical properties (strain at break, break force), water quantity performance (flow), water quality performance (turbidity, E. coli), and imaging. The study found fouling developed rapidly and altered mechanical properties and water quantity indicators within 200 h of filtration. Fouling did not decrease water quality indicators. Backwashing improved the filter’s mechanical properties and water quantity performance, but it did not fully recover the initial performance. Additionally, recovery differed between backwashing solutions, and no universal cleaning recommendation appropriate for HFMFs in LMICs/HCs was identified. Overall, fouling development and control depended on HFMF type, influent water quality, and backwashing solution type; thus, caution before distributing HFMFs for long-term use in LMICs/HCs is recommended.
Highlights
In 2017, an estimated 29% of the global population did not have access to safely managed water supplies, and 785 million people lacked even a basic drinking service [1]
The time of filtration increased in the BacChem and BacSed influent waters due to fouling, and applied pressure was lower in Filter 4 (F4) than F1–3 because a larger number of fibers were not in a U-shape in the module
While the indicators tested varied between the four hollow-fiber membrane filters (HFMFs) (F1–F4), the variation was smaller between F1–F3 than between F1–3avg and F4 (Table S2)
Summary
In 2017, an estimated 29% of the global population did not have access to safely managed water supplies, and 785 million people lacked even a basic drinking service [1]. While one aim of the United Nations Sustainable Development Goals is to ensure universal and equitable access to safely managed and affordable drinking water for all [1], household water treatment (HWT) options are currently promoted as an interim solution for those without safe drinking water [2]. There has been extensive previous research and promotion of sand and ceramic filters [5,6]. Hollow-fiber membrane filters (HFMFs) have been increasingly promoted. HFMFs consist of several hundred tubular fibers, with specified pore sizes, packed together. With advertised pore sizes between 0.1 and 0.02 μm [7], HFMFs remove >99% bacteria from contaminated water in laboratory settings [8]. HFMFs can obtain at least a targeted protection rating from the WHO Certification Scheme for household treatment products without any other treatment [8]
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