Using tree stems as water filters

Contaminated water causes 1.2 million deaths every year through infectious diseases including cholera, diarrhoea and typhoid. A majority of these cases occur in developing countries that lack the resources to build water treatment facilities. Instead, they resort to cheaper alternatives like solar disinfection and chlorination, that aren’t foolproof in removing harmful pathogens. So, how can we create a reliable water treatment method that can meet the needs of resource-limited settings?

Researchers from the Massachusetts Institute of Technology may have just found the answer: tree stems. Inside the barky stem of conifers lie multiple tubes that carry water throughout the tree. The walls of these tubes have ‘pit membranes’, which are like extremely tiny kitchen sieves. These membranes trap contaminants, so only water flows between the tubes. Therefore, conifer stems were selected for making low-cost water filters.

The team conducted experiments to understand how the method of preparing these filters and thickness affected their performance. The result — a 4 cm disc-shaped filter that weighs the same as one pencil and can be stored for at least two years. Upon testing with synthetic waters, this filter removed 99.99% of rotavirus and 99.9% of E.coli and MS-2 phage.

Method of preparing the tree stem filters

The researchers recognised that obtaining positive results in the lab was only half the battle won. They needed to gauge the impact of their technology in realistic settings, so they went on to conduct field testing in India. A locally made filter was tested on sources of drinking water used by the community. It was able to remove coliform bacteria from the contaminated water altogether. After interviewing the users, the team developed a working prototype that could be used to treat water at home.

Suggested prototypes for treating water using tree-stem filters

In addition to being practical, this technology fulfils essential user requirements such as accessibility and affordability. Given the readily available raw materials and simple manufacturing process, the filters can be locally made. From a cost perspective, it is estimated that these filters will be 100 times cheaper than conventional filter cartridges. Regarding the obvious concern about deforestation, a billion filters can be made annually from just 0.01% of the timber used in conifer wood global trade.

While conventional filters can be used for 3–5 months, these tree stem filters have to be replaced every 1–5 days. Researchers have acknowledged that this could be a hindrance to the widespread adoption of this technology and further engineering effort is required to prolong its life span. Moreover, the filters need to be tested under many different conditions to evaluate their safety and understand the effect of degradation.

One day, these tree stem filters will be able to provide low-cost safe drinking water in places that cannot afford complex water treatment facilities.
Maybe STEM is the answer to most problems!

References

Ramchander, K., Hegde, M., Antony, A., Wang, L., Leith, K., Smith, A. and Karnik, R., 2021. Engineering and characterization of gymnosperm sapwood toward enabling the design of water filtration devices. Nature Communications, 12(1).

Hannah Ritchie and Max Roser (2019) — “Clean Water”. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/water-access' [Online Resource].

A team of 3 trying to make academic research more relatable to the public. Our aim is to create content that displays how STEM brings value to society.