Reduction of spruce phytotoxicity by superheated steam torrefaction and its use in stimulating the growth of ecological bio‑products: Lemna minor L

Abstract

The use of biochar in agriculture is associated with the concepts of "carbon sink" and "carbon negative," which will constitute additional income for farms in the near future and may provide them with a key role in the fight against global warming. The existing model in the Scandinavian countries is one of the first to combine biochar with carbon dioxide biosequestration. Fertilizers with excessive nutrient content, salinity issues, impurities, or irregular pH levels can induce phytotoxicity, damaging plant health and growth. Torrefied woody biomass can work as a bulking agent, carbon carrier, or as an mendment for composting materials containing high amounts of water and/or nitrogen contents. Superheated steam torrefaction as a valorization process increases the amount of pores in which minerals can be stored and the plant will grow faster and bigger by using these pores agglomerated minerals. The torrefaction process was conducted using the DynTHERM TG Rubotherm high-temperature and high-pressure thermogravimetric analysis apparatus under conditions of superheated steam flow. Various residence times (10, 20, and 40 min) and torrefaction temperatures (250, 275, and 300 °C) were explored to assess their efficacy in reducing the phytotoxicity of torrefied spruce. To confirm this assumption, a toxicity test with Lemna minor L. was carried out according to Radić et al. (2011) and extended to the determination of chlorophyll index and chlorophyll fluorescence to assess the physiological status of the plants after treatment with different doses of spruce wood biocarbon. Research indicates that biochar positively impacts soil quality and plants. Thanks to its unique properties, biochar provides nutrients, enhancing fertilization efficiency [1]. Biochar, after concentrating and adsorbing the nutrients from the wastewater, can be used as a soil amendment or fertilizer. Biochar blended with organic residues full of nutrients is more effective in improving soil properties and crop yields than the exclusive application of pure biochar or other fertilizers. Traditional chemical fertilizers have drawbacks, such as rapid nutrient leaching, severe environmental pollution, and high costs. Therefore, biochar is gaining increasing recognition worldwide.