Comparing unamended and Fe-coated biochar on removal efficiency of bacteria, microspheres, and dissolved phosphorus in sand filters

Authors: Bolster, Carl

Submitted to: Biochar Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2021
Publication Date: 6/8/2021
Citation: Bolster, C.H. 2021. Comparing unamended and Fe-coated biochar on removal efficiency of bacteria, microspheres, and dissolved phosphorus in sand filters. Biochar Journal. 3:329-338. https://doi.org/10.1007/s42773-021-00100-7.
DOI: https://doi.org/10.1007/s42773-021-00100-7

Interpretive Summary: In many areas of the US, tile drainage is employed to remove excess water and improve trafficability in fields which otherwise would be too water-logged to support profitable agriculture. Because tile drainage significantly alters field hydrology it can have a significant impact on the fate and transport of sediment, nutrients, pesticides, and bacteria. In particular, the transport of pathogens from agricultural fields to drinking water can be greatly enhanced in tile-drained fields because the distance from the soil surface to tile drains is relatively short and thus the ability of the soil matrix to filter out bacteria (through both physical and chemical processes) is reduced. One mitigation strategy for dealing with contaminated tile-drainage waters is the use of end-of-tile filters to treat the water prior to being discharged into the environment. In this study, the use of sand filters amended with biochar is investigated as a potential management practice for reducing microbial concentrations in tile-drainage waters. Specifically, this research focuses on whether coating of biochar with iron hydroxides can increase the sorption and retention of bacteria in sand filters. The sorption and transport of dissolved phosphorus is also investigated. Results suggest that coating BC with Fe-oxyhydroxide may have a small benefit for increasing retention of bacteria in BC-amended sand filters but will result in significant reductions in dissolved phosphorus concentrations.

Technical Abstract: The effects of uncoated and Fe-coated biochars (BC) on the removal of bacteria, microspheres, and dissolved reactive phosphorus (DRP) in sand filters were compared. Filters were packed with 1.2 or 2.0-mm sand mixed with 30% (vol/vol) uncoated BC, Fe-coated BC, or a control without BC. Removal of E. coli, Salmonella, and Enterococci increased from 23, 42, and 25% in the unamended 1.2-mm sand to 48, 80, and 75% in the uncoated BC treatment, though only the increase for Enterococci was significant (p'<'0.05). For the Fe-coated BC, removal efficiencies were 89, 93, and 94%, respectively, which were all significantly (p'<'0.05) greater than the unamended sand but only the removal of E. coli was significantly greater than the uncoated BC sand filter. For the 2.0-mm sands, the only significant increase in removal following BC addition was observed for Salmonella. Trends in microsphere removal were generally consistent with bacteria. Removal of DRP in the unamended and uncoated BC filters was 33 and 13% (p'>'0.05), respectively, whereas removal in the Fe-coated BC filters was 98% (p'<'0.05). Results from batch sorption experiments indicate that both BCs similarly increased bacterial sorption to sand. In contrast, DRP sorption to the unamended and uncoated BC-amended sands were similar (p'>'0.05) with DRP sorption to the Fe-coated BC-amended sand being significantly greater (p'<'0.05). Results indicate that Fe-coated BC is more effective at retaining DRP than bacteria and microspheres in sand filters.