Abstract
Digestate is an anaerobic digestion by-product rich in inorganic-nitrogen (N) that can be used as an organic fertilizer. Digestate agronomic efficiency and its impact on the environment have not yet been studied in detail, therefore this study tries to fill this gap. The agro-environmental sustainability of digestate fractions was evaluated in a holistic way by comparing the best management practices available in the Veneto Region agroecosystem. A farm experiment involving mineral fertilizer and both liquid and solid digestate fractions was established involving silage winter wheat and silage maize as main crops. Agro-environmental sustainability was investigated coupling crop performance analysis (e.g., yield, N uptake and N use efficiency (NUE)) with a novel proposed agro-environmental sustainability index (AESI) (i.e., product of the dry yield and NUE). The results showed that the liquid digestate fraction gave agronomic performances comparable to mineral fertilizers and a satisfying AESI while solid digestate showed lower performances. In conclusion, liquid digestate fractions might be an effective substitute for mineral fertilizers in the Veneto region agroecosystem reaching encouraging levels of agro-environmental sustainability. On the contrary, longer-term experiments are requested to evaluate solid digestate fraction sustainability.
Highlights
During the last decade, biogas production has steadily increased in the EuropeanUnion (EU), encouraged by renewable energy policies [1,2]
With the general aim of evaluating the agro-environmental sustainability of cropping systems that make use of anaerobic digestate (AD) as fertilizer, our study aims to (i) identify and test a practical protocol for solid and liquid AD fractions applications, (ii) determine the optimal AD rate according to a novel agro-environmental sustainability index, and (iii) evaluate the AD
Farm 1 (F1) is located in Mira (Venice) (45◦ 24.2530 N; 12◦ 9.9820 E) on a lagoon plain, which formerly originated as transition area between the alluvial plain and the sea
Summary
Biogas production has steadily increased in the EuropeanUnion (EU), encouraged by renewable energy policies [1,2]. Biogas production has steadily increased in the European. 18 billion m3 of methane in 2015, produced by 18,202 plants, mainly concentrated in Germany, Italy, and the Czech Republic [3,4]. A biogas plant, called an anaerobic digester, transforms organic materials into two different products—i.e., biogas and anaerobic digestate (AD)—through the anaerobic digestion process. The use of AD as fertilizer is often hindered by economic (e.g., high transport and storage costs), practical (e.g., large volumes to managed), and environmental issues (e.g., nitrogen and phosphorus fertilization limits in high nutrient areas) [7]. AD is generally subjected to further processes of nutrient concentration and recovery to favor its storage and transport [8]. The solid fraction is mainly composed of organic compounds and phosphorous, while the liquid fraction contains the larger part of N and K [10]
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