Benefits Of Biochar

The article “Capturing CO₂” describes a number of absorbent molecules (C&EN, May 2, page 30). I’m disappointed, however, that biochar was not mentioned among the possibilities. The article does state in its next-to-last paragraph that “cellulose and sawdust can be used to make activated carbon with record-setting carbon dioxide uptake.” This comes close, but it doesn’t really represent biochar, about which much is misunderstood.

Some significant aspects are that biochar and activated carbon are not the same. Conditions of preparation differ, and biochar is considerably cheaper. Biochar can be made from a greater spectrum of sources including farm and forestry waste, municipal waste, and algae.

Biochar is considerably cheaper than the specialized absorbents described in the article. CO₂ absorption by biochar occurs by photosynthesis during the growing of the biomass. Although this is a slow and not highly efficient process, the cost of naturally growing biomass is much less than that of these specialized absorbents. Furthermore, the absorbents discussed do not permanently capture CO₂. It must be subsequently released and then disposed of by other means.

With biochar, the carbon from CO₂ serves as a soil additive where it remains in place for very long periods of time. Thus, I refer to the practice as “coal mining in reverse,” whereby one is removing CO₂ from the atmosphere and burying its carbon in the ground. In the ground, biochar serves an agriculturally useful purpose as a template for the growth of fungi and bacteria, shown to enhance plant growth. In addition, it aids water retention, absorbs pollutants, and helps retain fertilizer, decreasing its polluting runoff.

Consequently, biochar serves to decrease the amount of fertilizer (as well as compost) needed, thereby decreasing the energy needs to manufacture the fertilizer. As a result of its role in enhancing biomass growth, biochar serves to increase biomass resources, which serve as CO₂ absorbers. It also brings into use marginal land not otherwise suitable for agriculture. Thus, in considering biochar, its virtue as an agricultural aid may be even more important than that of a CO₂ absorber.

By Richard S. Stein
Amherst, Mass