Monitoring of greenhouse gas emissions and compost quality during olive mill waste co-composting at industrial scale: The effect of N and C sources
Ana García-Rández, Luciano Orden, Evan A.N. Marks, Javier Andreu-Rodríguez, Samuel Franco‐Luesma, Encarnación Martínez‐Sabater, José Antonio López Sáez, M.D. Pérez-Murcia, E. Agulló, M.A. Bustamante, Maite Cháfer, R. Moral
Abstract
• Co-composting of olive mill wastes with different C and N substrates. • Influence of substrates on GHG emissions studied at industrial scale. • GHG emissions and greenhouse warming potential was driven by the N sources. • Organic matter mineralization was greater with recalcitrant woody C sources. • Polyphenol degradation was greater with recalcitrant C substrates. Olive mill wastes (OMW) management by composting allows to obtain valuable fertilizing products, but also implies significant fluxes of greenhouse gases (GHG). For a proper OMW composting, high C- and N co-substrates are necessary, but little is known concerning their effect on GHG emissions in OMW-industrial scale composting. In this study, different co-composting agents (cattle manure (CM), poultry manure (PM), sheep manure (SM) and pig slurry solid fraction (PSSF) as N sources and olive leaves (OLW) and urban pruning residues (UPR) as bulking agents and C sources) were used for OMW composting at industrial scale. Physico-chemical and chemical properties in the composting samples, and GHG (CO 2 , CH 4 and N 2 O) fluxes were monitored in 12 industrial-scale windrows. GHG emissions were firstly influenced by N source, with the highest accumulated global warming potential (GWP) associated with PM (512 kg CO 2 eq pile -1 ), since PM composts were associated with the greatest N 2 O (0.33 kg pile -1 ) and CH 4 emissions (15.67 kg pile -1 ). Meanwhile, PSSF was associated with the highest CO 2 emissions (1113 kg pile -1 ). UPR as a bulking agent facilitated 10 % greater mineralization of the biomass than OLW, however this C-source was not associated with higher GHG emissions. The results showed that while mineralization dynamics may be impacted by C sources, GHG emissions were mainly conditioned by the characteristics of nutrient-heavy feedstocks (PM and SM). Moreover, manures as nitrogen-laden co-substrates had widely differing effects on total GWP, and that of individual gases, but further research is necessary to understand the mechanisms explaining such differences.