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Title: Transport and retention of bacteria and viruses in biochar-amended sand

Author
item SASIDHARAN, SALINI - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item TORKZABAN, SAEED - Flinders University
item Bradford, Scott
item KOOKANA, RAI - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item PAGE, DECLAN - Commonwealth Scientific And Industrial Research Organisation (CSIRO)
item COOK, PETER - Flinders University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2015
Publication Date: 1/25/2016
Citation: Sasidharan, S., Torkzaban, S., Bradford, S.A., Kookana, R., Page, D., Cook, P. 2016. Transport and retention of bacteria and viruses in biochar-amended sand. Science of the Total Environment. 548:100-109.

Interpretive Summary: Biochar has previously been investigated as a soil amendment to mitigate climate change, enhance soil fertility and crop production, and as a sorbent for pesticides, heavy metals, and pathogenic microorganisms. The aim of this study was to gain a better understanding of the underlining mechanisms that control transport and retention of microbes (bacteria and viruses) in biochar-amended sand. Batch and column results demonstrate biochar does not act as an effective sorbent for viruses over a range of solution chemistries and biochar types, and this suggests a potential risk of biochar amendment. Similarly, biochar did not act as an effective sorbent for bacteria in batch studies or in column studies when the sand was amended with coarse biochar particles. In contrast, amendment of sand with fine biochar particles enhanced bacteria retention in column studies due to a reduction of the pore-size distribution that enhanced straining. This information will be of use to scientists, engineers, and government officials concerned with benefits and risks of biochar amendment to soil.

Technical Abstract: The transport and retention of Escherichia coli and phages (PRD1, MS2 and 'X174), as surrogates for human pathogenic bacteria and viruses, respectively, were studied in sand that was amended with biochars produced from various feedstocks. Batch and column studies were conducted to differentiate the roles of attachment and straining, respectively. Batch experiments conducted at various solution chemistry conditions showed negligible attachment of phages and bacteria to biochar before or after chemical activation. At any given solution ionic strength, the attachment of phages was significantly higher on sand than biochar, whereas bacteria showed no attachment to either sand or biochar. Consistent with batch results, biochar addition (10% w/w) to sand reduced phage retention in the column experiments, suggesting a potential negative impact of biochar application to soil on virus removal. In contrast, the retention of bacteria was enhanced in biochar-amended sand columns. However, elimination of the fine fraction (< 60 µm) of biochar particles in biochar-amended sand columns significantly reduced bacteria retention. Results from batch and column experiments suggest that land application of biochar may only play a role in microbe retention via straining, by alteration of pore size distribution, and not through attachment. Consequently, the particle size distribution of biochar and soil is an important factor in determining whether land application of biochar enhances or diminishes microbe retention.