Anaerobic digestion: A promising technology of utilizing radioactively contaminated plant biomass

Anaerobic digestion (AD) is a widely used technology that allows for the reprocessing and reduction of waste biomass. A study was conducted to see if the AD technology might be used to process radioactively polluted agricultural biomass. For this purpose, laboratory tests were carried out with a 20-liter model biogas plant (BGP) with the radionuclide ¹³⁴Cs and operational tests with the South Bohemian commercial biogas plant monitoring the radionuclide ¹³⁷Cs. The activities of ¹³⁴Cs in inputs, contaminated grass or maize silage and in emerging fractions were investigated in the model fermenter. The activity of ¹³⁴Cs in the dry matter during the fermentation process increased by 46% on average, which corresponds to a reduction of dry matter by 43% due to the production of biogas. ¹³⁷Cs activities were measured in commercial BGP maize, grass, and whole plant silage, wheat, digestate, biogas, and aerosol samples. The commercial BGP fermentation process was more efficient, with an 80% reduction in dry mass weight. Dry biomass (1.37 Bq/kg) had a ¹³⁷Cs massic activity that was 4.4 times lower than the activity of dry digestate mass (6.01 Bq/kg). The activity of the ¹³⁷Cs in biogas aerosol was 1.1 × 10^-7 Bq/m³ or less, and the decontamination factor was 6.9 × 10⁶ or greater. Most Cs remain in the digestate. No other ways of radioactivity leakage have been identified.