Biochar pyrolyzed at two temperatures affects E. coli transport through a sandy soil

Authors: Bolster, Carl; Abit Jr, Sergio

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/10/2011
Publication Date: 1/10/2012
Citation: Bolster, C.H., Abit Jr, S.M. 2012. Biochar pyrolyzed at two temperatures affects E. coli transport through a sandy soil. Journal of Environmental Quality. 41(1):124-133.

Interpretive Summary: Biochar is a charcoal-like material generated during the pyrolysis of biomass, and because of its high carbon (C) content and its recalcitrant nature, there is much interest in using biochar to sequester C from the atmosphere by incorporating it into soils. In addition, studies have shown agricultural and environmental benefits to biochar addition to soils including improved soil physical properties, increased plant-available soil water, and increased soil retention of environmental contaminants such as nutrients, heavy metals, and pesticides. This study focused on whether the addition of biochar to soils can affect the retention and transport of microorganisms through soils. Results show that the addition of biochar to soils can affect the retention and transport behavior of E. coli in soils and that biochar application rate, pyrolysis temperature of the biochar, and the surface characteristics of the E. coli all are important factors determining the impact of biochar amendments on this behavior. Our results indicate that further research is warranted on this important environmental topic.

Technical Abstract: The incorporation of biochar – a charcoal-like material generated during the pyrolysis of biomass – into soils has been proposed as a means of sequestering carbon from the atmosphere and reducing greenhouse gas emissions. In addition, several studies have demonstrated environmental benefits to biochar addition to soils including increased soil retention of environmental contaminants such as nutrients, heavy metals, and pesticides. To date, however, little work has been done on the role that biochar addition to soils has on the retention and transport of microorganisms through soils. The goal of this study was to evaluate whether the addition of poultry litter biochar produced at two different temperatures (350 and 700 oC) affects the transport of E. coli through water-saturated soil. Specifically, we looked at the transport of three E. coli isolates through 10-cm columns packed with a loamy sand amended with 2 or 10 % biochar pyrolyzed at either 350 or 700 oC. For all three isolates, mixing the high temperature biochar at a rate of 2 % into the soil had no impact on transport behavior. When added at a rate of 10 %, however, a five-order-of-magnitude reduction in the amount of E. coli transported through the 10-cm columns was observed for two E. coli isolates and a reduction of approximately 50 % was observed for the third isolate. The effect of mixing the low temperature biochar into the soil varied depending on the isolate. For one isolate, no significant differences in transport behavior was observed between the low temperature and high temperature biochar-soil mixtures, whereas for the remaining two isolates, mixing the low temperature biochar into the soil resulted in enhanced transport of these isolates through the soil column. While we were unable to definitely determine the factors controlling the changes in transport behavior which we observed, our results clearly show that the addition of biochar to soils can also affect the retention and transport behavior of E. coli in soils and that biochar application rate, pyrolysis temperature of the biochar, and the surface characteristics of the E. coli all are important factors determining the impact of biochar amendments on E. coli retention and transport behavior.