Pellets from Biogas Digestates: A Substantial Source of N2O Emissions

Abstract

The field application of pellets from biogas residues resulted in high N2O emissions which could not yet be parametrized through soil drivers. Therefore, the aim of this study was to determine potential N2O production from pellets themselves. N2O and CO2 release from the pure pellet body (in form of intact, crushed or finely ground pellets produced from biogas digestates) were measured during the first seven days after pellet wetting under constant laboratory conditions. Three pellet water contents were examined: 47, 62 and 72% water of the total fresh pellet weight. Additional replicates of similarly wetted intact pellets were used to determine NH4+, NO3− and DOC contents on days 0, 1 and 4 of incubation. Two further treatments of wet intact pellets (62% moisture) were sterilized prior or after moistening to investigate the emissions’ origin. N2O release was found to increase with decreasing pellet size fraction. A maximum of N2O fluxes within all three fractions was determined at 62% moisture, whereas lowest fluxes were measured at 72% moisture. The cumulative N2O emissions over seven days ranged between 1 µg N2O–N g−1 pellet (intact pellets at 72% moisture) and 166 µg N2O–N g−1 pellet (finely ground pellets at 62% moisture). In general, our findings indicate that denitrification was the main factor for N2O emissions, driven by indigenous microbial communities already present in the pellets. The results show that the N2O emissions released by the pellets themselves can explain a major portion of the N2O fluxes measured in situ. Graphic Abstract

Organic Matter Composition of Digestates Has a Stronger Influence on N2O Emissions than the Supply of Ammoniacal Nitrogen

“…The analysis of the gas samples was performed using a gas chromatograph (GC 450, Bruker Daltonik, Bremen, Germany) coupled with an autosampler (GX-281, Gilson, Limburg, Germany). Further details on the GC measurements can be found in Petrova et al [32].…”

“…The high N 2 O emissions observed after pellet application (Figures 2 and 4) are in accordance with the results of Hayakawa et al [22], who compared poultry manure with its pelleted post-treatment. In general, the strong increase in temperature during pelletizing affects the properties of organic compounds and creates constant inner microsites [32,[71][72][73][74]. According to Petrova et al [32], the water addition to the pellet activated the decomposition of its organic matter by indigenous microflora.…”

“…In general, the strong increase in temperature during pelletizing affects the properties of organic compounds and creates constant inner microsites [32,[71][72][73][74]. According to Petrova et al [32], the water addition to the pellet activated the decomposition of its organic matter by indigenous microflora. Consequently, an enhanced microbial O 2 consumption favored the development of anaerobic microsites inside the pellet and, thus, stimulated denitrification.…”

Rice straw for energy and value-added products in China: a review

“…Digestate drying is commercially available and a common hygienization method that produces portable and storable fertilizer (Salamat et al 2022 ). Pelletizing involves compressing the raw material, reducing digestate volume while increasing the bulk density and durability of the final product (Petrova et al 2021 ). Furthermore, composting solid digestate enhances digestate properties as a soil conditioner and fertilizer (Torres-Climent et al 2015 ).…”

Conversion of Renewable Biogas into Single-Cell Protein Using a Combined Microalga- and Methane-Oxidizing Bacterial System

“…In addition to biogas, the nutrient-rich biogas slurry also needs to be reasonably disposed of to avoid environmental pollution. Although the biogas slurry has been traditionally used as fertilizer in agriculture, several drawbacks exist in this process: (1) the produced biogas slurry usually needs to be stored to meet seasonal demand for fertilizer in agricultural products, which leads to fugitive emissions of methane (CH 4 ) and ammonia (NH 3 ); (2) the production and utilization of biogas slurry usually have different spatial distributions, which leads to high transportation cost; and (3) most of the nutrients contained in biogas slurry could not be captured by plants, and as reported, more than 50% of the initial nitrogen content in biogas slurry would be lost during its utilization as fertilizer . Thus, facing the rapid development of the biogas industry, alternative strategies for biogas utilization and biogas slurry disposal are urgently required.…”