Edge Collective

DIY Water treatment using biochar.

DIY techniques for filtering contaminants from drinking water (image credit, Josh Kearns).

Biochar and Decentralized Water Filtration

(Image above from Kearns et al 2016 Presentation on Biochar and water filtration)

Why decentralized water filtration?

Gaining access to clean drinking water is increasingly more difficult, around the world. Microbial contaminants, chlorination by-products, and pesticides are growing problems everywhere.

Because chlorine helps to keep water safe from potentially harmful bacteria, water engineers typically design centralized water systems to maintain a chlorine residual in the water that is distributed to households. This chlorine often interacts with organic matter in distribution pipes to produce some concentration of toxic chlorination by-products in the water delivered to homes; but this is typically viewed as an acceptable trade-off, as long as these concentrations are low. (The Florida Health Department has a useful document on the regulation of trihalomethanes in drinking water).

Further: centralized water treatment infrastructure is dependent on a well-functioning electrical grid for its operation, the anticipated increasing frequency and severity of grid disruptions due to climate change will likely render centralized drinking water systems increasingly vulnerable to extended disruptions.

For these reasons there has been a growing interest in developing solutions for clean drinking water at the local community or household level.

Why biochar?

One common technology for the removal of contaminants from water is the use of activated carbon as a filter. As water passes through such a filter, contaminatns are adsorbed to the carbon in the filter and removed from the water.

Such carbon filters only have a limited capacity for adbsoprtion, and therefore must be replaced after a certain amount of use. Their cost is not trivial; so a household or small community using such filters for their drinking water will incur an ongoing cost. Also, traditional methods for producing activated carbon typically rely on sophisticated industrial chemical processes and fossil fuel-based inputs.

Research in the last decade has indicated that biochar, when produced at sufficiently high temperatures, can serve in large part as a replacement for standard activated carbon filters.

Such biochar filters can be produced from a wide variety of biomass materials -- including common agricultural waste -- using equipment that can be manufactured locally from widely-available materials (some designs use two 55 gallon steel drums).

Development of biochar-based water filtration systems

Dr. Josh Kearns (UNC) has led efforts in the last decade to assess the ability of biochar to filter out various water contaminants such as pesticides and chlorination by-products, and has developed designs that have now been built and used by communities around the world. His team has produced manuals in several langauges for constructing water filtration systems.

Kearns and his collaborators have formed a non-profit, Aqueous Solutions, to disseminate their work. Manuals, instructional videos, and peer-reviewed research are avaiable on their "Charcoal / Biochar water treatment" page.

Their designs include water filtration systems with capacities that range from small household use (300 liters or less) to larger-scale community use (2000 liters or more).


Elegant overview of the design of a biochar-based water filtration system

A researcher in Thailand describes a system design that has since been widely reproduced throughout Thailand and the region.

Kearns et al Biochar Water Treatment academic presentation

A nice history and overview of the project.

(Slides from the above presentation)

Construction a biochar gasifier

In the below video, Kearns demonstrates a simple design for a biochar gasifier which is capable of operating at the high temperatures required to produce biochar that is effective for water filtration:

A simplified design using only hand tools, mud, and two oil drums is described here:

A small-scale gasifier for testing and development

In the below video, Kearns describes the project while demonstrating a smaller-scale version of a biochar gasifier:

Water testing for disinfection byproducts

Simple Labs offers useful information on disinfection byproducts in drinking water and offers a VOC Water Test for $140.


Further References