Leaching of phage from Class B biosolids and potential transport through soil

Abstract

The objective of this study was to investigate leaching and transport of viruses, specifically those of an indigenous coliphage host specific to Escherichia coli ATTC 15597 (i.e., MS-2), from a biosolid-soil matrix. Serial extractions of 2% and 7% (solids) class B biosolid matrices were performed to determine the number of phage present in the biosolids and to evaluate their general leaching potential. Significant concentrations of coliphage were removed from the biosolids for each sequential extraction, indicating that many phage remained associated with the solid phase. The fact that phage was associated with or attached to solid particles appeared to influence the potential for release and subsequent transport of phage under saturated-flow conditions, which was examined in a series of column experiments. The results indicated that less than 8% of the indigenous coliphage initially present in the biosolids leached out of the biosolid-soil matrix. A fraction of this was subsequently transported through the sandy porous medium with minimal retention. The minimal retention observed for the indigenous phage, once released from the biosolids, was consistent with the results of control experiments conducted to examine MS-2 transport through the porous medium.

FIG. 1.

Number of coliphage sequentially extracted from 2% biosolids. Closed symbols represent pellet concentrations. Open symbols represent supernatant concentrations. ∗, measure is likely an underestimate of the number of PFU associated with the pellet.

FIG. 2.

Number of coliphage sequentially extracted from 7% biosolids.

FIG. 3.

Transport of pure-culture MS-2 through Vinton sand via saturated flow; results from duplicate experiments. (A) Transport expressed as C/C₀ values. (B) Transport expressed on a log₁₀ scale.

FIG. 4.

Leaching of indigenous coliphage able to infect host E. coli ATCC 15597 from biosolid-soil matrix in Vinton sand during saturated flow. Summary graph of four trials.