Focus on the Environment: A return to basics with biochar

Tuesday, March 3, 2009

Just as charcoal proved its worth in the development of civilization, so is biochar demonstrating its potential for yield enhancements and carbon absorption

by PETER ION

With carbon soil sequestration on the agenda of the latest Kyoto Protocol talks in Poland, the case for soil enhancement through biochar application has gained in momentum. Biochar is charcoal produced by pyrolysis, the process of chemical decomposition by heating. Biochar improves soil and can be used to lock carbon in the soil. Proponents see it as a powerful tool in the fight against global warming.

The latest pyrolysis technology was on display at the technical sessions in Poznan and garnered a good deal of attention from potential investors. It is looking increasingly likely that geological and soil sequestration of carbon will be included as a viable and credible  process within the Clean Development Mechanism of Kyoto. Ontario farmers should keep well abreast of this technology as some hard figures are beginning to get affixed to the processes and the possibilities involved.

The key is in closing the loop of the emissions cycle using pyrolysis – burning biomass in the absence of oxygen. From an environmental perspective, closed-loop pyrolysis systems are the only way to make a fuelwhich is actually carbon negative, in that it genuinely permanently absorbs carbon – a critical sticking point with all of the biologically-based mechanisms within Kyoto's allowable practices.

The case for biochar gains credence when the raw economics are considered against the alternative ofburning these biological residues in an electrical-generating power station. Based on some current European analysis, a tonne of biochar has an energy value of about 28 Gigajoules (GJ), slightly less than the best quality coal at around 32 GJ.

At an average cost of around $3 per GJ, and assuming that the operator is willing to pay the coal-equivalent price, biochar is valued at around $84 per tonne. Burning a tonne of biochar produces about 3.5 tonnes of CO² and, at a current trading price of around $32 (which means that sequestering it is worth $112) costs some $28 more than its value as a feedstock for electrical power generation.

The situation is even less economically logical for some European Union countries, where power stations which burn "energy crops" such as willow or miscanthus grass are rewarded with Renewable Obligations Certificates – currently valued at around $90 each for a MWh of generation. (Specialist biomass power stations in the U.K. can generate 2.3 MWh, earning over $200 to the generator!).

Even before the generator's greenhouse gas emissions are taken into account, it would be better to plow the char into the soil. The additional greenhouse gas avoidance from substituting fertilizer application (and N2O emissions with a global warming potential 310 times that of CO²) for biochar further skews the balance towards biochar. 

Agri-Therm of Dorchester, Ont., specializes in mobile pyrolysis units and is at the stage of pre-commercialization of their units. They are using agricultural wastes, residues and transition crops as feedstock. Dynamotive Inc. of Vancouver, with offices in Guelph and West Lorne, is leading the charge in Canada. There has been added impetus in recent months because of the prospect of harvesting pine-beetle-infested deadwood from interior B.C. as a source of raw feedstock.

ABRI (Advanced Bio Refinery Inc.), an Ottawa-based R&D organization, received federal funding through Sustainable Development Technology Canada to produce systems that will generate solid biochar and biooils costing between $150,000 for small units and $2 million for larger, transportable systems with the potential to pay back the investment costs through savings in energy and fertilizer applications in less than five years. Initial efforts are being focused on Ontario's 60,000 farms.

The case for biochar is strengthened by the fact that the syngas produced in the process as a byproduct can be tapped to power the pyrolysis process – a truly virtuous closed loop process.

The techniques continue to receive federal subsidies, especially in the United States. The updated U.S. Farm Bill (2008) includes provisions for research into biochar and has highlighted the importance of the material's unique capabilities in maintaining the carbon-nitrogen balance, whilst stressing its use as a soil amendment (rather than a direct replacement) together with manure or fertilizer, to improve tilth and nutrient retention.

Dr. Johannes Lehmann, a Cornell University world authority, recently completed research identifying the specific properties of biochar and its nutrient affinity (adsorption) and general persistence or stability in the soil, relative to "normal" soil organic material. Specifically, the phosphorus retention capabilites of biochar have been identified.

The portable pyrolysis technology which produces biochar was intro-duced at the Poznan conference last December. The techniques of production have gained acceptance from a carbon cycle perspective, partly because the carbon-negative (absorption) function can replace nitrogen fertilizer.

This is achieved though the production and application of ammonium bicarbonate from the use of waste-stream hydrogen generated in the pyrolysis process. A very virtuous circle indeed.

Recent results from Virginia with a pyrolysis unit that can generate three to four tons of biochar a day,  showed that a chicken farmer can generate enough energy to heat his hen-houses and then sell the char as fertilizer for $600 US a  ton.

At the Poznan meeting, Dr. Lehmann was the leading light in championing biochar and has produced data demonstrating yield enhancements for 10 field crops. Using data drawn from fieldwork in the north-eastern United States with a similar climatic regime to much of Ontario, he has described positive results for various bean varieties (including moong and soy), pea, rice, alfalfa, cowpea and carrot.

The biochar has proven effective when applied in high fertility trenches in contour rows of steep land for vegetables or grain crops, or in planting holes for tree crops. Dr Lehmann has noted that biochar's benefits are not so much a scientific novelty as a return to basics. "From cave drawings to iron smelting," he says, "charcoal has always played an important role in the development of civilization, and maybe it is about to do so again."

Laura Telford, executive director of the Canadian Organic Growers Association in Hamilton, is a supporter of biochar and agrees that "the long-term carrying capacity for carbon is high," and says that her association has been lobbying the carbon-trading bodies for some time.

She points out that the idea of plowing biochar into the soil to enhance fertility and yield improvement (for example, through increased water retention of biochar-applied soils) is one of the real benefits of the product. BF