Abstract
Gaseous and liquid anaerobic digestion (AD) streams, currently are at best used for electricity and heat production or simply spreading at the fields, respectively. However, electricity and heat are economically produced from other renewables and advanced fertilizers are needed to avoid leaching and boost nutrients capture. Hence, AD seeks new opportunities to support circular bioeconomy. The overall objective of this review is to present state-of-the-art resource recovery routes for upcycling the AD streams to reduce carbon footprint and formulate alternative products to increase sustainability. Technical barriers and integrated systems to upcycle AD streams through biological means are presented. New technologies and methods to capture CH4, CO2 and nutrients from the digested residual resources are presented, as a) methanotrophs cultivation to be used as feed ingredients; b) CO2 conversion and micro-nutrients capturing from microalgae to be valorized for a wide range of applications (e.g. biofuels, food and feed, fertilizers, bioactive compounds); c) CO2 transformation to biodegradable plastics precursors (e.g. Polybutylene succinate, Polyhydroxyalkanoate); d) digestate valorization for biochar production to support efficient agricultural usage. Moreover, the environmental factors and life cycle assessment perspectives of the novel biorefinery routes are revised highlighting the need for regionalized models or assessments that can reveal the most sustainable routes based on local conditions and requirements. Despite AD poses some positive characteristics related to environmental benefit and emissions reduction, the present work reveals that the novel routes can further enhance sustainability metrics supporting circular bioeconomy.
Highlights
Arable lands and seas are over-utilized due to intensified industrial activities
The present work is focusing beyond the stateof-the-art (Table 1) on topics as: a) biogas and digestate valorization for single cell protein (SCP) production; b) CO2 and micro-nutrients capturing from microalgae to be valorized for a wide range of applica tions; c) biodegradable plastics precursors (i.e. polybutylene succinate (PBS) and PHA) production from CO2; d) digestate valorization for efficient agricultural usage; e) environmental factors and LCA perspectives of the novel routes; f) biorefinery approaches focused on the circular economy
All these results indicated that the ash component in the biochar played an important role in ammonium and/or phosphate adsorption through mechanisms including physical adsorption, surface complexation, precipitation, and electrostatic interactions [175,181, 183]
Summary
Arable lands and seas are over-utilized due to intensified industrial activities. the overexploitation of natural resources is strongly contradictory to the United Nations’ sustainable development goals (SDGs); for example, SDG 12: Sustainable consumption and production and SDG 1: Climate action. Digestates can supply the needed phosphorus to substitute phosphate salts and release from the pressure of mining rocks phosphates Through such valorization route, residual resources upcycling can significantly contribute towards the replacement of traditional meal proteins which have high environ mental costs related to their production [8]. The present work is focusing beyond the stateof-the-art (Table 1) on topics as: a) biogas and digestate valorization for single cell protein (SCP) production; b) CO2 and micro-nutrients capturing from microalgae to be valorized for a wide range of applica tions (e.g. biofuels, food and feed, fertilizers, and source of bioactive compounds); c) biodegradable plastics precursors (i.e. PBS and PHA) production from CO2; d) digestate valorization for efficient agricultural usage; e) environmental factors and LCA perspectives of the novel routes; f) biorefinery approaches focused on the circular economy
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