Solid fraction of separated digestate as soil improver: implications for soil fertility and carbon sequestration
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SOILS, SEC 1 • SOIL ORGANIC MATTER DYNAMICS AND NUTRIENT CYCLING • RESEARCH ARTICLE
Solid fraction of separated digestate as soil improver: implications for soil fertility and carbon sequestration Caleb Elijah Egene 1 & Ivona Sigurnjak 1 & Inge C. Regelink 2 & Oscar F. Schoumans 2 & Fabrizio Adani 3 & Evi Michels 1 & Steven Sleutel 4 & Filip M. G. Tack 1 & Erik Meers 1 Received: 14 April 2020 / Accepted: 28 September 2020 # The Author(s) 2020
Abstract Purpose This study investigated the C and N mineralisation potential of solid fractions (SFs) from co-digestated pig manure after P-stripping (P-POOR SF) in comparison with P-rich SFs, as a means to estimate their organic matter stability in soil. Compost (COMP) and biochar (BCHR) (made from P-POOR SF) were also included in the study as reference biosolids. Methods The SFs were incubated in a sandy-loam soil under moist conditions to determine production of CO2 and mineral N. At specified intervals, CO2 evolution in the mixtures was measured via the alkali trap method and titration over a period of 81 days, while mineral N was measured using a flow analyser after KCl extraction over a period of 112 days. Results The various SFs showed similar patterns of C mineralisation (15–26% of added total C in 81 days) that were clearly higher than for COMP and BCHR (6% and 7%, respectively). Temporary N immobilisation was observed in biosolids with a high C/N ratio. The effective organic matter (EOM) of the SFs was calculated based on the C mineralisation data and varied between 130 and 369 kg Mg−1. Conclusions The SF with a reduced P content had a high EOM/P ratio which is beneficial in areas where P status of the soil is already high. Moreover, the N mineralisation patterns confirm that a high C/N ratio may also reduce risks for N leaching due to temporary N immobilisation. Keywords Soil organic matter . Solid fraction . Digestate . C/N ratio . Mineralisation
1 Introduction Over the last decade, European Union (EU) policy oriented towards developing a circular and resource-efficient economy Responsible editor: Caixian Tang * Caleb Elijah Egene [email protected] 1
Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
2
Wageningen Environmental Research, Wageningen University and Research, PO Box 47, 6700AA Wageningen, The Netherlands
3
Gruppo Ricicla, Dipartimento di Science Agrarie e Ambientali: Produzione, Territorio, Agroenergia, Università degli Studi di Milano, Via Celoria 2, 20133 Milano, Italy
4
Department of Environment, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
has encouraged a rapid increase of anaerobic digestion (AD) installations. The number of AD installations in the EU rose from 6227 to 17,662 between 2009 and 2016 (EBA 2018), with a main focus on AD of residues from food and feed industries, sewage sludge, animal manure, and landfill waste. While biogas is the primary product from AD, millions of tonnes of dige
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