Abstract
AbstractWe employed life cycle assessment to evaluate the use of hydrochars, prospective soil conditioners produced from biowaste using hydrothermal carbonization, as an approach to improving agriculture while using carbon present in the biowaste. We considered six different crops (barley, wheat, sugar beet, fava bean, onion, and lucerne) and two different countries (Spain and Germany), and used three different indicators of climate change: global warming potential (GWP), global temperature change potential (GTP), and climate tipping potential (CTP). We found that although climate change benefits (GWP) from just sequestration and temporary storage of carbon are sufficient to outweigh impacts stemming from hydrochar production and transportation to the field, even greater benefits stem from replacing climate‐inefficient biowaste management treatment options, like composting in Spain. By contrast, hydrochar addition to soil is not a good approach to improving agriculture in countries where incineration with energy recovery is the dominant treatment option for biowaste, like in Germany. Relatively small, but statistically significant differences in impact scores (ISs) were found between crops. Although these conclusions remained the same in our study, potential benefits from replacing composting were smaller in the GTP approach, which due to its long‐term perspective gives less weight to short‐lived greenhouse gases (GHGs) like methane. Using CTP as indicator, we also found that there is a risk of contributing to crossing of a short‐term climatic target, the tipping point corresponding to an atmospheric GHG concentration of 450 ppm CO2 equivalents, unless hydrochar stability in the soil is optimized. Our results highlight the need for considering complementary perspectives that different climate change indicators offer, and overall provide a foundation for assessing climate change mitigation potential of hydrochars used in agriculture.
Highlights
Hydrochar is a carbonaceous material produced from biomass residues using hydrothermal carbonization (HTC; Berge et al, 2011; Titirici et al, 2014)
We found that climate change benefits (GWP) from just sequestration and temporary storage of carbon are sufficient to outweigh impacts stemming from hydrochar production and transportation to the field, even greater benefits stem from replacing climate-inefficient biowaste management treatment options, like composting in Spain
Using climate tipping potential (CTP) as indicator, we found that there is a risk of contributing to crossing of a short-term climatic target, the tipping point corresponding to an atmospheric greenhouse gases (GHGs) concentration of 450 ppm CO2 equivalents, unless hydrochar stability in the soil is optimized
Summary
Hydrochar is a carbonaceous material produced from biomass residues using hydrothermal carbonization (HTC; Berge et al, 2011; Titirici et al, 2014) It is mainly used as solid fuel for domestic heating, but its use in agriculture as soil conditioner with some carbon storage value has recently attracted attention (Reza et al, 2014; Burguete et al, 2016). In LCA, resource consumption and emissions of pollutants stemming from the extraction of the raw materials (e.g., for HTC plant), their manufacture and use or operations Studies investigating environmental performance of hydrochars using LCA have focused on its use as solid fuel so far (Berge et al, 2015; Benavente et al, 2016; Owsianiak et al, 2016; Liu et al, 2017). These four studies showed how environmental performance of hydrochar used as solid fuel depends on the type of fuel that the hydrochar substitutes and on the incumbent waste management system that HTC replaces
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