Citation: Seruga, P.; Krzywonos, M.; den Boer, E.; Nied´ zwiecki, L.; Urbanowska, A.; Pawlak-Kruczek, H. Anaerobic Digestion as a Component of Circular Bioeconomy—Case Study Approach. Energies 2023, 16, 140. https://doi.org/10.3390/en16010140 Academic Editors: Margarida Gonçalves and Cândida Vilarinho Received: 17 November 2022 Revised: 14 December 2022 Accepted: 21 December 2022 Published: 23 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Anaerobic Digestion as a Component of Circular Bioeconomy—Case Study Approach Przemyslaw Seruga 1, * , Malgorzata Krzywonos 2 , Emilia den Boer 3 , Lukasz Nied ´ zwiecki 4 , Agnieszka Urbanowska 5 and Halina Pawlak-Kruczek 4 1 Department of Bioprocess Engineering, Faculty of Production Engineering, Wroclaw University of Economics and Business, Komandorska 118/120, 53-345 Wroclaw, Poland 2 Department of Process Management, Faculty of Management, Wroclaw University of Economics and Business, Komandorska 118/120, 53-345 Wroclaw, Poland 3 Faculty of Environmental Engineering, Wroclaw University of Science and Technology, Wyb. Wyspia´ nskiego 27, 50-370 Wroclaw, Poland 4 Department of Boilers, Combustion and Energy Processes, Faculty of Mechanical and Power Engineering, Wroclaw University of Science and Technology, Wyb. Wyspia´ nskiego 27, 50-370 Wroclaw, Poland 5 Department of Environment Protection Engineering, Faculty of Environmental Engineering, Wroclaw University of Science and Technology, Wyb. Wyspia´ nskiego 27, 50-370 Wroclaw, Poland * Correspondence: przemyslaw.seruga@ue.wroc.pl; Tel.: +48-71-368-0872 Abstract: Current and future trends in the world population lead to the continuous growth of municipal waste volumes. Only in the EU-28 approx. 86 million tons of biowaste is produced yearly. On the other hand, the recent energy crisis calls for a fast transition towards more local and renewable energy sources. Most of this stream could be recycled through anaerobic digestion (AD) to produce energy and high-quality fertilizers. This paper presents a balance of dry anaerobic digestion of municipal biowaste based on three years of system monitoring in an industrial-scale AD plant. The results indicate that the average biogas production rate of 120 Nm 3 /ton of fresh waste can be achieved. Biogas utilization in combined heat and power (CHP) units leads to an overall positive energy balance at significantly reduced CO 2 emissions. The overall CO 2 emission reduction of 25.3–26.6% was achieved, considering that biogas utilization is environmentally neutral. Moreover, biowaste conversion allows digestate production to substitute mineral fertilizers in agriculture and other applications. It is beneficial for soil protection and a broader environmental perspective. Keywords: bioenergy; biogas; fermentation; fertilizer; greenhouse gas; waste management; zero waste 1. Introduction The circular economy (CE) and bioeconomy (BE) concepts are prevalent within the European Union (EU) and other parts of the world as new business models to achieve sustainability [1]. However, there is still a lack of consensus about their universal interpre- tation. Kirchherr et al. [2] defined CE as “an economic system that is based on business models which replace the “end-of-life” concept with reducing, alternatively reusing, recy- cling, and recovering materials in production/distribution and consumption processes.” Ellen MacArthur Foundation considers it “a systems solution framework that tackles global challenges like climate change, biodiversity loss, waste, and pollution” [3]. However, it can be concluded that CE is a system governed by the following main principles: design to minimize waste and pollution generation; lifetime expansion of materials and products with reuse, regeneration, and recycling; as well as the usage of renewable resources. It was assessed that CE could halve emissions in the food sector, i.e., by 5.6.10 9 tons of CO 2 in 2050, followed by economic benefits of 700 billion dollars [4]. In comparison, BE can be defined as a “production model based on biological resources and on innovative biological processes and principles to provide sustainable goods and services in all economic sectors” [1]. Energies 2023, 16, 140. https://doi.org/10.3390/en16010140 https://www.mdpi.com/journal/energies