Co‐generated fast pyrolysis biochar mitigates green‐house gas emissions and increases carbon sequestration in temperate soils

Abstract

Char is a product of thermochemical conversion of biomass via pyrolysis, together with gas (syngas), liquid (bio-oil), and heat. Fast pyrolysis is a promising process for bio-oil generation, which leaves 10-30% of the original biomass as char. Char produced for soil application, is defined biochar (BC), and it may increase soil C storage, and reduce soil emissions of greenhouse gases (GHG), such as N 2 O and CH 4 -potentially making fast pyrolysis bioenergy generation a C-negative system. However, differences in production conditions (e.g., feedstock, pyrolysis temperature and speed, post handling, and storage conditions) influence the chemical properties of BC and its net effect when added to soils. Understanding if fast pyrolysis BC can increase C sequestration and reduce GHG emissions will enable full assessment of the economic value and environmental benefits of this form of bioenergy. We characterized a BC produced by fast pyrolysis for bio-oil generation and examined GHG (CO 2 , N 2 O and CH 4 ) efflux, C partitioning using d 13 C, and soil C sequestration across four temperate soils and five BC rates; 0%, 1%, 5%, 10%, and 20% w/w. The fast pyrolysis process created a highly aromatic, low N, ashrich BC with a O : C ratio of 0.01, which we expected to be highly recalcitrant. Across soils, CO 2 emissions increased linearly and N 2 O emissions decreased exponentially with increasing BC addition rates. Despite still being actively respired after 2 years, total BC-derived C-CO 2 comprised less than the BC volatile C content (4%). Expressed as CO 2 equivalents, CO 2 was the primary GHG emitted (97.5%), followed by N 2 O. All GHG emissions were small compared to the total SOC sequestered in the BC. Fast pyrolysis produced a highly recalcitrant BC that sequestered C and reduced GHG emissions. The recovery and soil application of BC would contribute to a negative carbon balance for this form of bioenergy generation.

Interactions between biochar and soil organic carbon decomposition: Effects of nitrogen and low molecular weight carbon compound addition

“…Positive (Luo et al, 2011), negative (Cross and Sohi, 2011) and unchanged effects (Santos et al, 2012) of biochar addition on the mineralization rate of the native SOC had been found. These inconsistent effects might be due to differences in biochar feedstock, pyrolysis temperature, or soil type (Stewart et al, 2013). Luo et al (2011) reported a shortterm positive priming effect of biochar addition on SOC mineralization, when biochar was produced from Miscanthus giganteus at 350 C. On the other hand, Lu et al (2014) found a negative priming effect with biochar produced from corn straw.…”

Effect of pruning-derived biochar on heavy metals removal and water dynamics

“…Biochar is a fine-grained carbonaceous solid residue, produced by pyrolysis of carbon-rich biomass under oxygen-limited conditions (Chen et al 2011;Xu et al 2013). In recent years, biochar has also received considerable interest as a large-scale soil amendment to enhance crop productivity and soil fertility (Major et al 2010;Vaccari et al 2011;Farrell et al 2014;Prayogo et al 2014;Song et al 2014), to increase soil water holding capacity (Kammann et al 2011;Baronti et al 2014), to decrease nutrient leaching (Laird et al 2010), and to serve as a recalcitrant carbon stock (Lehmann 2007a, b;Laird 2008) to potentially mitigating climate changes Cimò et al 2014) by reducing greenhouse gas emissions Stewart et al 2013). Biochar has many properties, such as a relatively structured carbon matrix, high degree of microporosity, extensive surface area, and high pH and cation exchange capacity (CEC); therefore, it may act as a surface adsorbent (Jiang et al 2012a, b).…”

Effect Of Wood-Based Biochar And Sewage Sludge Amendments For Soil Phosphorus Availability

“…Pedological analyses revealed a decrease of soil pH in the order superphosphate > SS > BC A + SS > BC B + SS > BC A > BC B for both application rates. An increase of soil alkalinity following biochar amendment has been reported for many soil types (FARRELL et al, 2014;STEWART et al, 2013;XU et al, 2013). As mentioned before, this effect is due to the alkaline character of biochar because of the presence of negatively charged phenolic, carboxyl and hydroxyl functional groups on surfaces (BREWER et al, 2012).…”