Biochar from animal manure: A critical assessment on technical feasibility, economic viability, and ecological impact

Abstract

Animal manure has been used to manage soil fertility since the dawn of agriculture. It provides plant nutrients and improves soil fertility. In the last decades, animal husbandry has been significantly expanded globally. Its economics were optimized via the (international) trade of feed, resulting in a surplus of animal manure in areas with intensive livestock farming. Potentially toxic elements (PTEs), pathogenic microorganisms, antibiotic residues, biocides, and other micropollutants in manure threaten animal, human, and environmental health. Hence, manure application in crop fields is increasingly restricted, especially in hotspot regions with intensive livestock activities. Furthermore, ammonia volatilization and greenhouse gas (GHG) emissions during manure storage, field application, and decomposition contribute to air pollution and climate change. Conventional manure management scenarios such as composting and anaerobic digestion partially improve the system but cannot guarantee to eliminate sanitary and contamination risks and only marginally reducing its climate burden. Hence, this review discusses the potential of pyrolysis, the thermochemical conversion under oxygen‐limited conditions as an alternative treatment for animal manure providing energy and biochar. Manure pyrolysis reduces the bioavailability of PTEs, eliminates pathogenic microorganisms and organic micropollutants, and reduces GHG emissions. Pyrolysis also results in the loss of nitrogen, which can be minimized by pretreatment, that is, after removing soluble nitrogen fraction of manure, for example, by digestion and stripping of ammonia–nitrogen or liquid–solid separation. However, conclusions on the effect of manure pyrolysis on crop yield and fertilization efficiencies are hampered by a lack of nutrient mass balances based on livestock unit equivalent comparisons of manure and manure biochar applications. Hence, it is essential to design and conduct experiments in more practically relevant scenarios and depict the observations based on the amount of manure used to produce a certain amount of biochar.

Biochar-Derived Persistent Free Radicals: A Plethora of Environmental Applications in a Light and Shadows Scenario

“…In this regard, biochar (BC), mainly obtained from organic waste and possessing the capability of sequestering carbon, represents a rich carbon source and an alternative to fossil fuels [ 51 , 52 ]. Table S1 in the Supplementary Materials reports the biomasses commonly used for BC production [ 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 ].…”

Bamboo-Based Biochar: A Still Too Little-Studied Black Gold and Its Current Applications

“…To date, the types of biomasses used to prepare BC and involved in the investigation of BC-bound PFRs mainly include lignocellulosic biomasses, such as pine needles, wheat straw, lignin, waste wood, cow manure, rice husk, and maize straw [ 23 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. Lignocellulosic biomasses are made of hemicellulose, cellulose, and lignin.…”

Managing organic resources in agriculture: future challenges from a scientific perspective

“…From the solid fraction, the main recycled P products are struvite and sometimes calcium phosphate (Sigurnjak et al, 2019;Brienza et al, 2020). Recycled C-rich products such as biochars and other soil improvers are produced through drying, gasification or pyrolysis of the solid fraction (Rathnayake et al, 2023).…”