Argonne National Laboratory develops new system to enhance AD process

US-based science and engineering centre Argonne National Laboratory has developed technology that synergistically uses two waste biomass streams to generate two bioproducts and enhance the process of anaerobic digestion (AD).

According to the organisation, the digestion of wastewater can be improved sludge by incorporating biomass-derived, carbon-sequestering char within the digester, thus creating pipeline-quality renewable natural gas while using the remaining biosolids for a high-quality fertiliser.

With funding from the US Department of Energy’s (DOE’s) Bioenergy Technologies Office (BETO) totalling $1.5 million (€1.42m) over three years, researchers at ANL said they have been able to develop and de-risk this technology, which is now ready for scale-up.

Biochar, charcoal derived from plant material, is created in processes such as gasification and pyrolysis, which also produce energy in the form of syngas or liquid fuels.

In a statement, ANL said that it has demonstrated success using biochar from gasification of agricultural waste such as both corn stover and waste wood sources.

Anaerobic digestion usually creates biogas that is mainly a combination of carbon dioxide (CO2) and methane, and extra steps are required to upgrade the biogas to renewable natural gas by removing the CO2 and other contaminants.

However, according to ANL by adding biochar directly to the anaerobic digester sequesters the CO2 and creates a biogas stream that is more than 90% methane and less than 5 parts per billion hydrogen sulphide, thus reducing the need for upgrading steps.

The biochar was also said to improve many of the operating conditions for AD, and furthermore, it is nutrient-rich, so the digestate left after the process is completed can serve as a high-quality fertiliser.

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