| 1. |
- Abubaker, Jamal, et al.
(author)
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Short-Term Effects of Biogas Digestates and Pig Slurry Application on Soil Microbial Activity
- 2015
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In: Applied and Environmental Soil Science. - : Hindawi Limited. - 1687-7667 .- 1687-7675. ; 2015, s. 1-15
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Journal article (peer-reviewed)abstract
- The effect of four biogas digestates (BD-A, BD-B, BD-C, and BD-D) and pig slurry (PS) on soil microbial functions was assessed at application rates corresponding to 0–1120 kg-N ha−1. At dose corresponding to 140 kg-N ha−1, 30.9–32.5% of the carbon applied in BD-A, BD-C, and PS was utilized during 12 days, while for BD-B and BD-D corresponding utilization was 19.0 and 16.9%, respectively. All BDs resulted in net nitrogen assimilation at low rates (17.5–140 kg-N ha−1) but net mineralization dominated at higher rates. PS resulted in net mineralization at all application rates. All residues inhibited potential ammonium oxidation (PAO), with EC50-values ranging between 45 and 302 kg-N ha−1. Low rates of BDs appeared to weakly stimulate potential denitrification activity (PDA), while higher rates resulted in logarithmic decrease. The EC50-values for PDA were between 238 and 347 kg-N ha−1. No inhibition of PDA was observed after amendment with PS. In conclusion, biogas digestates inhibited ammonia oxidation and denitrification, which could be an early warning of potential hazardous substances in the digestates. However, this effect can also be regarded as positive, since it may reduce nitrogen losses.
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| 2. |
- Risberg, Kajsa
(author)
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Quality and function of anaerobic digestion residues
- 2015
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Doctoral thesis (other academic/artistic)abstract
- The growing number of biogas plants in Europe has resulted in increased production of nutrient-rich digestate, which has potential as fertiliser on arable land. Many different organic materials can be degraded in the anaerobic digestion process, with most macronutrients and micronutrients retained in the digestate. Depending on the ingoing organic substrate and management of the biogas process, the nutrient content of digestate varies widely. It can also contain compounds such as heavy metals and organic pollutants that are potentially toxic to soil microorganisms. Previous studies on the effect of digestate on soil microorganisms and crop yield have yielded contradictory results, so further investigations are needed to determine its true fertiliser value. In this thesis, the fertiliser effect of different types of digestate originating from biogas plants operating with various substrates and operating parameters was determined by measuring: 1) general and specific soil microbial activity, 2) bacterial and archaeal community composition, 3) crop growth and 4) chemical and physical composition of different digestates. Soil respiration generally displayed a positive response to digestate addition, but soil respiration curves revealed differences in quality and quantity of organic carbon between digestate, pig slurry and cow manure. However, the total utilisation rate of the organic carbon in digestate, pig slurry and cow manure did not differ. Moreover, digestate showed both stimulatory and inhibitory effects on potential ammonia oxidation, while pig slurry and cow manure had a more consistent inhibitory effect. Addition of digestate to soil resulted in increased wheat yield compared with control soil and mineral fertiliser, but final yield was not as high as that from pig slurry. Digestate was also generally characterised by a higher content of ammonium and lower content of organic carbon than pig slurry and cow manure. Addition of digestate to soil resulted in changes in the microbial community structure, with less pronounced effect in sandy soils, but no change in diversity was detected. It can be concluded that the digestate from biogas plants has great potential as a fertiliser in crop production and does not seem to pose a greater risk of disturbing soil microorganisms than pig slurry and cow manure when spread on arable land.
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