Water treatment options

Summary of Week 2 of Introduction to Household Water Treatment and Safe Storage (Coursera – École Polytechnique Fédérale de Lausanne)

Water safety

In water treatment (and in life), the question is what level of risk is acceptable. WHO defines safe drinking water as water that presents no significant risk to health over a lifetime of consumption.

The water safety framework comprises health-based targets, water safety plans and verification. Health-based targets include performance measures in terms of log reduction values.

It is important to note that measuring water quality is not the same as water safety because water quality varies in space and time, and no E.coli does not mean no contamination. Multiple treatment barriers should be put in place to remove contaminants.

Health-based targets include performance measures in terms of log reduction values. Water quality measurement does not mean water safety because water quality is variable in space and time, and no E.coli does not mean no contamination

Water treatment options: Sedimentation and filtration

A household-level treatment process typically comprises sedimentation, filtration, disinfection and safe storage.

  • Sedimentation removes turbidity (suspended particles in water), and some pathogens. Turbidity itself has no health risks, but has impacts on subsequent treatment steps. Mechanisms include gravity settling, and coagulation and flocculation.
  • Membrane filtration works on size exclusion, electrostatic effects and biological activity.
  • Ceramic filters work on physical and electrostatic removal. It is common to brush silver onto filters, which contributes to bacteria reduction and prevents biofilm growth and clogging.
  • Biosand filtration also uses size exclusion, electrostatic effects and biological activity.

Introduction to Household Water Treatment and Storage

Summary of Week 1 of Introduction to Household Water Treatment and Safe Storage (Coursera – École Polytechnique Fédérale de Lausanne)

There are many diseases caused by poor water, sanitation and hygiene. In particular, diarrhea is a leading cause of mortality and morbidity.

Diseases related to poor water, sanitation and hygiene can be classified according to its transmission pathways: waterborne, water-washed, water-based and water-related. This is the Bradley classification, and informs the selection of appropriate control mechanisms.

These diseases are caused by pathogens that can be described by its biological type: protozoa, bacteria, viruses and helminths. These are transmitted through pathways illustrated by the F-diagram.

Because it is impractical to measure all pathogens, faecal indicators area used. Escherichia coli (E.coli) is generally considered the most suitable, although it does not necessarily co-relate to contamination risk. A more complete picture can be obtained by also doing a sanitary inspection. Contamination can occur at the point of the water resource, delivery, collection and transport, household storage, and consumption.

Household water treatment offers the opportunity to remove contamination that occurs before consumption. Treatment processes include sedimentation (pre-treatment), filtration, boiling, UV radiation (solar disinfection) and chlorine. Each process has different levels of effectiveness and different applications.