Investigation of the use of biochars in soil applications and determination of their toxic effects

Project no. 23874 · Status: Kapanmış (Yayın bekleniyor) · 2023

Summary

The commercialization of biochar from different wastes as both a soil conditioner and a carbon sequestration technology is quite promising. In recent years, research has focused on the impact of biomass type and production conditions on the soil-enhancing properties of biochar and its effect on plant growth. However, investigating the risk of soil contamination by toxic substances from biochar and its potential inhibition of soil microorganisms is crucial for long-term application without negative effects on the environment.In this study, the potential use of biochars obtained from five different biomasses (sewage sludge, chicken manure, hemp stalks, pine sawdust, and two-phase olive oil process waste) in soil applications was evaluated. Biochars were obtained by pyrolysis at 300 and 500 °C and hydrochars were produced by hydrothermal carbonization at 220 °C. In order to investigate the soil enhancement potential, analyses of pH, bulk density, electrical conductivity, cation exchange capacity (CEC), stable carbon content, water retention capacity, and inorganic contents were conducted. Additionally, the toxic properties of biochars, including heavy metal and volatile organic compound (VOC) contents, were determined. The results showed that the soil-enhancing properties of biochars varied depending on the biomass type and process conditions. Biochars were found to be alkaline, while hydrochars were acidic. The bulk density of biochars and hydrochars mostly varied depending on the biomass type. The CEC values of biochars and hydrochars ranged between 11.1 and 52.9 cmol/g. However, no strong correlation was found between CEC values and functional group or O/C ratio. Water holding capacity was found to be relatively higher in hydrophilic and low-density biochars and hydrochars. The inorganic content of biochars and hydrochars varied significantly depending on the biomass type. Due to the dissolution of some inorganic contents during hydrothermal carbonization, the ash contents of hydrochars were found to be lower than those of biochars.The inorganic structures in biochar formed a more stable structure at high-temperature pyrolysis, which reduced the macro nutrient content transferred to water. Based on VOC results, significant volatile matter content was observed in hydrochars and biochars obtained at 300 °C. Hydrochars obtained from olive oil pulp and hemp stalks, which had high VOC content, were found to significantly inhibit the growth of plant growth-promoting bacteria.On the other hand, biochars and hydrochars derived from sewage sludge were observed to increase bacterial growth, probably due to the major and minor nutrient contents. According to European Biochar (EBC) Standard, the heavy metal contents of sewage sludge and chicken manure derived biochars and hydrochars exceeded the limits.

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