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Tuesday, March 04, 2014

Making “Low-Tech” Biochar Adsorbent For Decentralized Water Treatment

 By Josh Kearns

Readers of this blog probably don’t have to be told that the proliferation of synthetic chemicals over the past century has hugely impacted drinking water sources around the world. But you might be shocked to learn that these toxic contaminants are completely ignored by international, governmental and non-governmental agencies concerned with expanding the provision of safe drinking water in developing communities.

This is because, from a WASH (water-sanitation-hygiene) perspective, microbial pathogens typically represent the most immediate threat to health. However, although they receive no attention for the international WASH development establishment, a huge variety of synthetic organic contaminants (SOCs) such as pesticides, pharmaceutical residues, fuel compounds, and industrial wastes heavily impact the safety of surface waters collected for drinking in communities around the globe.

Hundreds of millions of tons of SOCs, including several million tons of pesticides, are produced annually, impairing water quality on a global scale. Consequently, for example, “pesticide pollution” appears twice in the top ten of The World’s Worst Toxic Pollution Problems Report (2011) by the Blacksmith Institute. Long-term chronic exposure to trace quantities of SOCs such as pesticides can lead to cancer, diseases of the endocrine and reproductive systems, and damage to the liver, kidneys, or central nervous system, and a variety of other toxic effects.

In the rural hill country of SE Asia where my colleagues and I work these problems are acute. Few scientific studies have been undertaken among the impoverished hill tribe villagers here, but the data we do have indicate, for example, detection of a wide array of biocides in mothers’ milk samples. One study found that infants’ exposure to DDT and several other organochlorine compounds exceeded by up to 20 times the acceptable daily intakes as recommended by UN-FAO and WHO. Along with residues in food and occupational exposure, drinking water is a major pathway for harmful agrichemical residues to enter into our bodies.

Using charcoal for water treatment is a technique that is at least 4,000 years old – there are references to ritualistic purification of water using charcoal in ancient Hindu and Egyptian religious texts. My colleagues and I have hypothesized that charcoals produced by traditional methods could be effective for removing modern organic contaminants, as charcoal has properties similar to activated carbon (AC) – a highly micro-porous structure, and a large internal surface area with a plenitude of adsorption sites for removing toxicants from water.

But unfortunately, traditional charcoal production can cause substantial environmental damage through deforestation and atmospheric emissions. Moreover, traditional charcoaling systems are geared towards the production of charcoal-for-fuel, not an optimal adsorbent for water treatment.

Thus part of our work at Aqueous Solutions has been to develop low-cost, “low-tech,” environmentally friendly systems for production of optimal water filter char. Using scrapyard tin and steel, surplus 55-gal oil drums, and simple hand tools, we’ve made chars from waste agricultural and forestry residues that rival the performance of commercial ACs for uptake of herbicide and a range of other trace SOCs from surface water.

Here I am on a typical day of field research in northern Thailand – collecting temperature data on a 55-gallon drum pyrolyzer used for making adsorbent biochar. (Photo credit Lyse Kong.)

If you want to learn more about our work please visit, where you can download open-access handbooks and watch instructional videos for making your own biochar adsorbent and using it in decentralized water treatment.

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