Biochar granulation reduces substrate erosion on green roofs

Abstract

Green roofs are exposed to high winds and harsh environmental conditions that can degrade vegetation and erode substrate material, with negative consequences to ecosystem services. Biochar has been promoted as an effective substrate additive to enhance plant performance, but unprocessed biochars are susceptible to wind and water erosion. Applications of granulated biochars or chemical dust suppressants are suggested as a means to mitigate biochar and substrate erosion; however, research on biochar type and chemical dust suppressant use on biochar and substrate erosion is lacking. Vegetation is a crucial factor that influences substrate erosion, yet plant responses may vary with biochar type and chemical dust suppressant; thus, the effects of possible mitigation measures on biochar and substrate erosion are unclear. We investigated the effects of surface-applied granulated and unprocessed biochars and an organic dust suppressant (Entac™) on biochar and substrate erosion on green roofs with Sedum album L. and a native plant mix. Our results show that 94% of unprocessed biochars were lost from green roofs after 2 years regardless of the Entac™ amendment, likely due to the lightweight nature and fragmentation of biochar particles. In contrast, granulation of biochars reduced the biochar erosion and total substrate erosion by 74% and 39%, respectively, possibly due to enhanced biochar bulk density and particle size and improved moisture retention of biochar-amended substrates. Additionally, Sedum album better reduced biochar and substrate erosion than the native plant mix, likely due to rapid development of high vegetation cover that reduced wind exposure and enhanced substrate moisture retention. We conclude that applications of granulated biochars can substantially reduce biochar and substrate erosion on green roofs, improving green roof sustainability. Graphical Abstract

Biochar Benefits Green Infrastructure: Global Meta-Analysis and Synthesis

“…Substrate water retention capacity (WRC) (ln RR = 0.211 ± 0.043, p < 0.001) and plant available water (PAW) (ln RR = 0.288 ± 0.064, p < 0.001) increased with biochar amendment by 23 and 33%, respectively (Figure 2a). Consistent patterns were also reported in the qualitative summary, with Liao et al 44 also revealing that biochar reduced substrate erosion loss (Table 1). 45−79 Biochar showed no mean effect on substrate saturated hydraulic conductivity (ln RR = −0.285 ± 0.505), total porosity (ln RR = −0.079 ± 0.104), or air-filled porosity (ln RR = −0.015 ± 0.067).…”

“…The highly variable effects of biochar on saturated hydraulic conductivity (Figure a) are likely associated with a large variation of GI substrate composition and texture. Although biochar erosion loss is a concern on green roofs, a recent study showed a reduction of total substrate erosion losses from biochar-amended green roofs due to increased moisture retention and vegetation cover . Losses of biochar particles in discharge water are also a concern; in the meta-analysis, we found a variable but increasing trend of TSS concentrations in discharge with biochar application (Figure b), likely due to fragmentation of friable biochars …”

“…Although biochar erosion loss is a concern on green roofs, a recent study showed a reduction of total substrate erosion losses from biochar-amended green roofs due to increased moisture retention and vegetation cover. 44 Losses of biochar particles in discharge water are also a concern; in the meta-analysis, we found a variable but increasing trend of TSS concentrations in discharge with biochar application (Figure 2b), likely due to fragmentation of friable biochars. 60 Biochar increased substrate nutrient content on GI, in part due to high biochar concentrations of P 83 and K, 84 as well as enhanced nutrient retention.…”

A Field Study to Investigate the Hydrological Characteristics of Newly Established Biochar-Amended Green Roofs

“…As compared to fine particles, larger particles are more resistant to biochar loss caused by wind and water [59]. Medium to large biochar particles or heavy biochar (processed biochar) were suggested to be used to limit the biochar loss [60,65,76].…”

A Wooden Carbon-Based Photocatalyst for Water Treatment

“…In addition, a shadowing effect may appear in the photocatalytic reaction of a wood biochar-based photocatalyst [159,160]. This phenomenon is usually due to the fact that the light cannot fully penetrate the thick or dense part of the photocatalyst, thus reducing the effective light absorption on the surface of the catalyst, resulting in some areas not being irradiated by light and affecting the catalytic reaction [161][162][163]. The shadowing effect can be reduced by the following strategies: (1) Adjusting the structure of the catalyst [164]: by designing the catalyst structure with a larger pore size and lower density, the penetration depth of light can be increased and the shadowing effect can be reduced.…”