Influence of production conditions on the yield and environmental stability of biochar

Abstract

Biochar, a solid product of biomass pyrolysis, is a promising concept for climate change mitigation and adaptation, as it can sequester atmospheric CO 2 while improving quality of soil where it is stored. However, for this potential to be realised, it is necessary for biochar to have high environmental stability, i.e., resist various decomposition processes over long time. The main objective of this work has been to relate biochar production conditions to the yield, and properties of biochar, particularly its long-term stability. We used our lab-scale pyrolysis facilities to produce biochar at three temperatures between 350 and 550 °C, from selected feedstock (pine, mixed larch and spruce chips, hardwood pellets). We measured the yield of biochar and then used an accelerated ageing assay to obtain information on the stability of biochar. Such information is very important for the assessment of the climate change mitigation potential of biochar, as it has not yet been clearly defined what proportion of biochar actually remains "permanently" sequestered and how much is released back to the atmosphere in the short to medium term. The results of this work showed that despite increase in the stability of biochar with increasing pyrolysis temperature, the yield of stable biochar fraction is nearly independent of the temperature. These findings are essential for the optimisation of pyrolysis conditions for production of biochar with selected properties, as well as for modelling biochar systems and their climate change mitigation potential as compared to other uses of biomass, such as bioenergy, biofuels and/or chemicals.

Biochar: Pyrogenic Carbon for Agricultural Use - A Critical Review

“…Alternatively, the labile fraction of biochar can also be determined by simple and indirect methods such as thermal decomposition (Benites et al, 2005;Calvelo Pereira et al, 2011) and chemical oxidation (Calvelo Pereira et al, 2011) or a combination of both (Mašek et al, 2013b).…”

The Benefits of Biochar on Rice Growth and Yield in Tropical Riparian Wetland, South Sumatra, Indonesia

“…Recent research has identified several environmental and agricultural benefits of applying biochar, including carbon sequestration for reducing carbon emission into the atmosphere (Mašek et al, 2013;Mukherjee and Lal, 2013;Zhang and Ok, 2014;Jiang et al, 2016;Wang et al, 2016); phytoremediation of soil contaminants (Ahmad et al, 2014;Mohan et al, 2014;Wiszniewska et al, 2016); adjusting soil physicochemical and biochemical properties for agriculture (Herath et al, 2013;Githinji, 2014;Bai et al, 2015;Abujabhah et al, 2016;Bera et al, 2016;Haider et al, 2017); creating soil health by inducing growth of beneficial and suppressing pathogenic organisms (Lone et al, 2015;Abujabhah et al, 2016;George et al, 2016;Xu et al, 2016); and improving crop growth and yield (Vaccari et al, 2015;Agegnehu et al, 2016).…”

“…For instance, biochar produced at different temperatures varied in their effect on N uptake by Eruca sativa (Zhou et al, 2017) and on growth of lettuce (Hunter et al, 2017). High temperature during pyrolysis increased stability of biochar in soil (Mašek et al, 2013), but had short-lived effects on crop yields (Hall and Bell, 2015;Griffin et al, 2017). Moreover, Hagner et al (2016) reported that pyrolysis temperature only marginally influenced biochar-induced effects on soil pH, water holding capacity (WHC), soil organisms, and plant growth.…”

Technical Greenhouse-Gas Mitigation Potentials of Biochar Soil Incorporation in Germany

“…For the dry pyrolysis 34 Biochar that is produced during HTC is often called hydrochar or HTC char (e.g., Kammann et al 2012). 35 Further reaction conditions influencing biochar yields include, for example, the heating rate (e.g., Williams and Besler 1996), pressure (e.g., Mahinpey et al 2009) or the use of catalysts (e.g., Nowakowski et al 2007). processes, for example, it holds that the higher the temperature -and, thus, the lower the biochar yield -, the higher the carbon content of the biochar (e.g., Mašek et al 2013). Since the focus of this paper is on the use of biochar for soil carbon sequestration, we restrict our attention to slow-pyrolysis processes -as is common in the related literature (e.g., Shackley et al 2011;Hammond et al 2011;Woolf et al 2010a;Gaunt and Cowie 2009).…”

“…Moreover, hydrochar tends to be considerably less stable in soil than biochar obtained from dry pyrolysis processes (e.g., Kammann et al 2012;Steinbeiss et al 2009;Kuzyakov et al 2009), rendering it less suitable for a carbon-sequestration strategy. 37 Among the dry pyrolysis processes, in turn, slow pyrolysis not only maximizes the biochar output (35% on average, see Table 7), but -more importantly -also the total amount of carbon that is transferred from the raw biomass into the biochar (e.g., Cantrell et al 2012;Mašek et al 2013). In other words, the share of the biomass carbon that is recovered in the biochar is maximized with slow pyrolysis, amounting to 50% on average (Lehmann et al 2006; Table 8, column 16).…”