Introduction to Biochar

Long before the Europeans arrived, the natives of Ecuador and Peru would set piles of vegetation on fire, cover them with dirt and let them slowly smoulder and turn into charcoal.  We know this was very common practice because areas with a thick layer of dark, exceptionally fertile, high carbon soil, called terra preta (Portuguese for "black earth") are widespread. 

When fossil fuels or organic solids are burned, or as they decompose, the carbon in them escapes into the atmosphere as carbon dioxide. Physically capturing and storing carbon long term so it can’t return to the atmosphere as carbon dioxide gas (CO2) is called carbon sequestration.  The IPCC reported that carbon sequestration will be essential to bring CO2 levels down to 1.5C, citing several negative emission approaches. 

 

There are a few high tech methods to capture and store CO2 from the exhaust gases of burning fuels, but they’re still experimental, and might be both very costly and very difficult to scale up fully. 

The other carbon storage methods studied by the IPCC were planting forests, agriculture practices that increase soil carbon, and making biochar. These are safe, proven, and highly effective, and would have many indirect ecological benefits.  Of the three, only the last one can be applied directly in urban environments – and can be put into practice by NYC officials and other progressive municipal governments.   

Cities can turn their organic waste streams, such as wood, food scraps, or sewage sludge, into biochar.  When carbon-containing materials are pyrolyzed - heated in the absence of oxygen - instead of catching on fire, they turn to charcoal.  Most of the carbon, instead of being released to the atmosphere, is captured in solid form, which can be stable for thousands of years.

Most charcoal is burned as a fuel.  When charcoal is made according to certain standards, with certain types of feedstock, process temperature ranges, and chemical profiles, and is intended for certain uses - it’s referred to as biochar. 

Biochar preserves the structure of wood as a carbon framework at a microscopic level. It has an extremely high surface area per unit of weight, and provides great habitat for beneficial soil microbes and fungi. Cornell University has compiled research about how biochar improves soil quality, agricultural productivity and water retention. 

Even if biomass has been contaminated with chemicals, and can’t be used as agricultural soil amendments, they can still be pyrolyzed.  Even such contaminated end products can still be used to replace a long list of non-renewable products in commercial and industrial uses. The more biomass that’s pyrolyzed, the more carbon is drawn down.

As I learned during a visit with leading biochar author Albert Bates, the most immediate way that turning organic waste into biochar could benefit NYC would be the reduction of NYC’s waste disposal costs. Since pyrolyzing organic wastes will reduce both their volume 75-95%, significant savings are possible.