Review of biochar role as additive in anaerobic digestion processes

TLDR: In this paper, a review of the connections between biochar and anaerobic digestion (AD) is presented, focusing on three key issues related to the better understanding of the biochar role in AD processes: 1. Investigation of the influence of BC properties on AD performances and their ability to counteract its main challenges; 2. Assessment of the optimal BC production chain (i.e., feedstock-pyrolysis-activation) to achieve the desired features; and 3. Evaluation of the economic and environmental advantages connected to BC use in AD, compared to conventional solutions applied to

Abstract: Anaerobic digestion (AD) could be considered as a mature technology and nowadays it can still play a pivot role because of the urgent need to provide renewable energy sources and efficiently manage the continuously growing amount of organic waste. Biochar (BC) is an extremely versatile material, which could be produced by carbonization of organic materials, including biomass and wastes, consistently with Circular Economy principles, and “tailor-made” for specific applications. The potential BC role as additive in the control of the many well-known critical issues of AD processes has been increasingly explored over the past few years. However, a clear and comprehensive understanding of the connections between BC and AD is still missing. This review paper analyses and discusses significant references (review articles, research papers and international databases and reports), mostly published in the last 10 years. This review is aimed at addressing three key issues related to the better understanding of the BC role in AD processes: 1. Investigation of the influence of BC properties on AD performances and of their ability to counteract its main challenges; 2. Assessment of the optimal BC production chain (i.e. feedstock-pyrolysis-activation) to achieve the desired features; 3. Evaluation of the economic and environmental advantages connected to BC use in AD processes, compared to conventional solutions applied to address AD challenges.

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Table 3. Results of pH drop and CH4 production/yield of AD processes in the presence 488 of various types of BCs 489

Table 4. A summary of selected works focusing on ammonia/ammonium inhibition mitigation by BC in AD processes (FAN: free ammonia 557 nitrogen; TAN: total ammonia nitrogen). 558

Table 1. Overview of literature studies exploring the connections between BC and AD 132

Figure 1. Relative contributions of the scientific literature selected for this work 180

Table 8. Advantages and disadvantages of conventional technologies for digestate 726 processing [188–191]. 727

Table 2. Advantages and disadvantages of conventional methods for creating buffering 426 capacity in bioreactors 427

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17 Anaerobic digestion ( AD ) could be considered as a mature technology and nowadays it 18 can still play a pivot role because of the urgent need to provide renewable energy sources 19 and efficiently manage the continuously growing amount of organic waste. The potential BC role as additive in the 23 control of the many well-known critical issues of AD processes has been increasingly 24