Environmental Performance in the Production and Use of Recovered Fertilizers from Organic Wastes Treated by Anaerobic Digestion vs Synthetic Mineral Fertilizers.

Axel Herrera,Oscar Schouman,Ambrogio Pigoli,Fabrizio Adani,Micol Schepis,Erik Meers,Andrea Giordano,Federica Barone,Giuliana D’Imporzano,Massimo Zilio,Bruno Rizzi

doi:10.1021/acssuschemeng.1c07028

Abstract

Recovered fertilizers (RFs), in the form of digestate and digestate-derived ammonium sulfate, were produced from organic wastes by thermophilic anaerobic digestion (AD) at full scale. RFs were then used for crop production (maize), substituting synthetic mineral fertilizers (SFs). Environmental impacts due to both RF and SF production and use were studied by a life cycle assessment (LCA) approach using, as much as possible, data directly measured at full scale. The functional unit chosen was referred to as the fertilization of 1 ha of maize, as this paper intends to investigate the impacts of the use of RF (Scenario RF) for crop fertilization compared to that of SF (Scenario SF). Scenario RF showed better environmental performances than the system encompassing the production and use of urea and synthetic fertilizers (Scenario SF). In particular, for the Scenario RF, 11 of the 18 categories showed a lower impact than the Scenario SF, and 3 of the categories (ionizing radiation, fossil resource scarcity, and water consumption) showed net negative impacts in Scenario RF, getting the benefits from the credit for renewable energy production by AD. The LCA approach also allowed proposing precautions able to reduce further fertilizer impacts, resulting in total negative impacts in using RF for crop production. Anaerobic digestion represents the key to propose a sustainable approach in producing renewable fertilizers, thanks to both energy production and the modification that occurs to waste during a biological process, leaving a substrate (digestate) with high amending and fertilizing properties.

Highlights

The linear economy model based on the use of fossil fuel and raw sources has led our planet to encounter major environmental problems such as climate change, land degradation, and alteration of biochemical cycles.[1]
life cycle assessment (LCA) analysis aims to measure the environmental impacts related to both production and to subsequent agronomic use of digestate and ammonium sulfate (RF) produced by the anaerobic digestion process using a mix of organic wastes (Scenario Recovered fertilizers (RFs)), compared to the production and use of synthetic fertilizers (SFs), i.e., urea, triple phosphate, and potassium sulfate (Scenario synthetic mineral fertilizers (SFs))
Because this study considered the impacts derived from the production and use of fertilizers on maize crop, the functional unit chosen was referred to the fertilization of 1 ha of maize, i.e., for the Scenario SF: 402 kg of urea (185 kg of N), 476 kg of chemical ammonium sulfate (100 kg N), 195 kg of triple phosphate (89 kg of P2O5), and 165 kg of potassium sulfate (82.5 kg of K2O), and for Scenario RF: 48 Mg of digestate, i.e., 370 kg of total N, i.e.,185 kg of effective N, 317 kg of P2O5, and 43 kg of K2O, 1.38 Mg of recovered ammonium sulfate (100 kg of N), and 80 kg of potassium sulfate (40 kg of K2O)

Summary

Introduction

The linear economy model based on the use of fossil fuel and raw sources has led our planet to encounter major environmental problems such as climate change, land degradation, and alteration of biochemical cycles.[1] With particular reference to N and P global flows, it has been reported that the current uses of these two elements are over Earth’s boundaries because of anthropogenic perturbation due, mainly, to fertilizer application.[2] The use of chemically produced N and mined P is modifying and misbalancing the agroecosystem and the natural ecosystems, putting biodiversity at risk.[3]. The production of P and K fertilizers relies upon nonrenewable and extracted resources that are becoming depleted[7] and are concentrated (e.g., P) in only a few countries.[8] The consequence of that is the need for new management strategies to reduce the additions of N and P into the ecosystem with particular reference to agriculture. The Circular Economy has been indicated as a new productive paradigm to produce goods, and it consists in the redesign of productive processes to allow the successive recovering of wastes for new productive processes, avoiding the use of new resources.[9]

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