Influence of biochar particle size on the hydraulic conductivity of two different compacted engineered soils

Abstract

Biochar is a recalcitrant material obtained after pyrolysis of labile biomass under oxygen-limited condition. The conversion of biomass into biochar is considered to be a sustainable way of generating bioenergy, minimizing the emission of greenhouse gases and managing the waste. Recently, the amendment of biochar in soil gained attention due to its multiple soil ameliorating features. Many studies have investigated the effect of biochar particle size on the physicochemical and hydraulic properties of relatively loose agricultural soil. However, such study is rarely conducted for compacted soil suitable for bioengineered structures. The objective of the current study is to investigate the effect of biochar particle size on the hydraulic conductivity of compacted soil for bioengineered structures. Saturated hydraulic conductivity (Ksat) of different compacted soils amended with biochar of different particle sizes ranging from 0.075 to 4.75 mm has been investigated. The results showed that the amendment of 5% to 15% (w/w) biochar of different particle sizes led to the change in Ksat of the silty sand. When compared with bare soil, a higher Ksat with biochar of particle size larger than 0.425 mm and a lower Ksat with particles of size smaller than 0.425 mm was observed. However, in pure sand, a lower Ksat irrespective of particle size of biochar was observed and the lowest Ksat was noted with biochar of particle size smaller than 150 mm. These changes in the Ksat after biochar amendment were attributed to the alteration of pore structure mainly, inter-pores of the soil, which is controlled by the particle size of the biochar. The findings of the present study could be useful for the field application i.e. in bioengineered structures.