Biochar, a carbonaceous soil amendment, has been extensively used in agriculture and stormwater treatment systems. During and after application, biochar may become subjected to compaction, which may break biochar grain due to surface abrasion or particle fragmentation and release the fine biochar particles into the environment. Yet, the extent to which compaction can change the particle size distribution of biochar and release biochar particle is unknown. Moreover, it is unclear how compaction would affect biofilter performance: reduction of runoff volume and contaminant removal. In this study, we quantify a change in particle size of biochar because of compaction, the amount of biochar loss from biofilter after compaction due to erosion, and the mechanism of fine particle (&lt; 0.07 mm) generation from biochar during compaction. To examine the effect of biochar particle size, we packed a mixture of sand (0.6-0.8 mm) and biochar with two size ranges (0.07 mm&lt; d &lt; 0.8 mm or d &gt; 0.8 mm) in plastic columns with and without compaction. Our results showed that compaction generated fine biochar particles and lower the average biochar particles size in the biofilter. The quantity of released biochar particles decreased when the average biochar particle size was lower than sand size. We surmise that biochar particles that occupy pore space between interlocked sand particles experience low compressive energy and contributes a limit to the generation of fine particles. Dying biochar before compaction and comparing the color intensity of dye on fine particles released and bulk biochar from where they were released from, we revealed dominant mechanisms of biochar particle generation during compaction. While compaction decreased hydraulic conductivity of biofilter media, thereby compromising its ability to reduce runoff volume, but compaction also improved contaminant removal. Overall, these results indicate that the negative impacts of compaction on the release of fine biochar particles and on hydraulic properties of soil should be considered in performance assessment of biofilters.

Compaction affects the performance of biochar-augmented biofilter: Mechanism and implications

2019 Fall National Meeting

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