Abstract
Anaerobic digestion has been recently proposed as a more sustainable energy supply chain able to strengthen the existing security of supply provisions. Anaerobic digestate (AD) is the by-product of the anaerobic digestion process and presents organic fertilizer characteristics, but its agronomic usage has been hindered by both agronomic and environmental concerns. In this study, the impact of agricultural liquid (LD) and solid (SD) AD and beef manure (Man) was evaluated on some agro-environmental characteristics. First, the AD fractions functional groups were characterized by FT-IR, and then LD and SD performances were evaluated on soil organic carbon (SOC) stock and carbon dioxide (CO2) emissions and compared to beef manure (Man). The fertilizer impact was also considered with the presence or absence of a shallow water table. Results showed that SD increased of ca. 3 t ha−1 the SOC stock in the 0–20 cm soil profile with respect to LD, while it was comparable to Man despite the lower C input (6.7 vs. 8.7 t C ha−1), due to the presence of more stable compounds (e.g., lignin). The CO2 fluxes were affected by both fertilizer type and water table level. In the absence of a water table, the CO2 emissions (5.5 g CO2 m2 d−1) were driven by carbon content and quality in the fertilizer, while the presence of a shallower water table hindered mineralization of stable SOC and, in turn, reduced emissions (4.4 g CO2 m2 d−1). AD can be considered a beneficial solution to both maintain soil fertility and, at the same time, give new insight into a circular economy model, although further investigation on GHG emissions is required.
Highlights
Biomethane is produced in anaerobic digestion plants where the anaerobic digestion process takes place, producing biogas and anaerobic digestate as a byproduct
Conventional anaerobic digestate management has been addressed to agriculture as an inexpensive way to close nutrient cycles by being applied to agricultural land as an organic fertilizer [5,6,7,8]
Treatments consisted of a combination of three groundwater conditions—a free drainage (FD) and two shallow water table levels set at
Summary
Biomethane production has been recently proclaimed by the European Commission as a renewable and low-carbon gas able to strengthen the resilience of the gas system [1]. According to the 2018/844/EC [2], biogas and biomethane will account for 32% of the renewable energy share of EU energy consumption after 2020. It has been estimated that approximately 180 million tons of anaerobic digestate are produced annually in the EU [3]. For these reasons, the treatment of digestate is receiving increasing attention to cope with environmental standards and, possibly, fulfill the goal of Agenda 2030 for sustainable development [4]. Conventional anaerobic digestate management has been addressed to agriculture as an inexpensive way to close nutrient cycles by being applied to agricultural land as an organic fertilizer [5,6,7,8]
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