At the wastewater treatment plant in Bingen, Germany, conveyor belts carry semi-dry sewage into steel containers, and the air is filled with the smell of maturing sludge. The sewage transforms into shiny black granules within the containers, and after this brief ecological "alchemy," the waste ultimately becomes charcoal, which is then buried underground. This sequesters the carbon, preventing it from entering the atmosphere. Supporters of the technology say this method of carbon storage is highly effective, and that biochar should be included in future global climate agreements.
Burying biochar can also improve soil fertility, as its honeycomb-like particles act as reservoirs for water and nutrients. Field trials are about to begin at Rothamsted in southeast England to assess the benefits of biochar on soil structure and moisture. Experiments in Australia, the United States, and Germany have already shown promising results, particularly in otherwise infertile soils.
Biochar has gained support from those concerned about climate change. Helmut Gerber, the design engineer of the Bingen biochar plant, says his pyrolysis equipment was originally designed to address the problem of waste ash clogging conventional boilers.
Typically, wastewater treatment is a significant source of greenhouse gases, and the ash produced from incineration (which generates even more emissions) is used in the construction industry. In Bingen, 10% of the wastewater stream is fed into an experimental pyrolysis plant, which heats the waste with minimal oxygen, separating out carbon monoxide and methane, which are then burned to provide heat for the pyrolysis process.
