An important but brief study was published last year by individuals working with the RDIC factory in Cambodia to find what factors make a more efficient ceramic water filter. In this study several empirical tests were preformed to investigate the relationships between filter mix ratios and firing schedules. Perhaps the most relevant results demonstrated by these tests demonstrated the lack of correlation between flow rate and bacterial removal efficiency. In the test, filter discs ranging from 2 to 18 liters per hour showed similar e-coli removal efficacy.
This has long been suspected in the industry where standard flow rate best practices specify a 1.5 to 3 liter range of acceptability. These flow rates were set in an attempt to ensure that new factories making filters were producing effective ceramic water filters without the ability to effectively test their real ability to remove bacteria.
Other Tendencies of Efficient Ceramic Water Filters
- Increasing burnout to clay ratio seems to increase flow rate while reducing strength
- Firing to a higher temperature may increase flow rates, (it is assumed that firing higher increases pore size)
- Increasing firing temperature may result in a stronger filter.
- Firing higher seemed to reduce bacterial removal effectively, but the correlation was weak.
- There is strong variation in flow rates of filters formed in wet or dry season.
- Similar flow rates can be achieved by 1: Increasing burnout to clay ratio and reducing burnout particle size 2: Reducing burnout to clay ratio and increasing burnout particle size.
This study clearly presents an argument for further testing of these same variables to produce a more efficient ceramic water filter.
The onus is now on each factory to further develop their manufacturing practices. If the established best practices are to be modified on a case by case basis it should only be by careful experimentation and with the partnership of an independent monitoring agency to ensure that filters being produced meet minimum bacterial removal standards.
Although these results direct us towards a path of study that develops efficient ceramic water filters, any operation in the manufacturing process which relies on additional mechanical or technological resources also removes a layer of appropriateness to the ceramic water filter technology as a whole.
Imagine, for instance, that to make a more effective filter we find that burnout must be screened to finer tolerance. The factory in Somalia must then find a new reliable source a new mesh for their screening machines. The mesh they are currently using comes from out of the country and is very expensive and difficult to obtain. I argue that although the finer mesh would result in a more effective filter, if the basic standards were to change to reflect the greater efficiency it would reduce the appropriateness of the technology as a whole.
Development of a more effective filter is a part of factory scalability, once production of a basic filter has been stabilized a factory is ready to begin the process of improvements. These improvements will be determined by the local environment. After all, there are plenty of more effective filters on the market when cost, manufacturing limitations, and community adaptability are removed from the qualifications.
Studies such as these are important for us to better understand the path ahead with regard to improvement/changes to ceramic water filter production practices. That said, many of the studies assessing these practices are conducted in research facilities using laboratory methods. While this is a necessary first step, it must be followed by a replication of the results in a working filter factory. If this was a part of all academic research there would be a lot less ambiguity.
Link to original study:
Isabelle Gensburger – October 2011