Nitrogen, phosphorus, and bacteria tile and groundwater quality following direct injection of dewatered municipal biosolids into soil

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Received for publication February 14, 2008. Application of municipal biosolids (sewage) to agricultural land is a common practice to improve soil physical quality and fertility. The chosen method of land application can have a strong impact on the extent of adjacent water contamination by nutrients and bacteria. Dewatered municipal biosolids (DMB) were applied to silt-clay loam experimental field plots in Ontario, Canada using two application methods: (i) surface spreading followed by shallow incorporation (SS) and (ii) a newly developed implement that directly injects DMB into the topsoil (DI). The objective of this study was to compare N, P, and bacteria quality of tile drainage and shallow groundwater associated with each land application technique. There were no significant differences (P > 0.05) in N, P, and bacteria tile mass loads among the application treatments for time periods <100 d postapplication, when the greatest peak loads and peak tile water concentrations were observed. Both land application treatments caused groundwater Escherichia coli contamination to at least 1.2 m depth below surface after the first postapplication rainfall event, and NO3–N contamination to at least 2.0 m depth below surface. The DI treatment did, however, have significantly (P < 0.05) higher tile mass loads of total Kjeldahl N (TKN), total phosphorus (TP), E. coli, Enterococci, and Clostridium perfringens relative to the SS treatment for time periods >100 d postapplication. Nevertheless, relative to tile effluent data collected <100 d postapplication (no application treatment differences), peak loads, and concentrations during this time were, overall, considerably lower for both treatments. This finding, along with no significant differences in N, P, and bacteria groundwater concentrations among the application treatments, and that the direct injection technique could potentially reduce vector attraction problems and odor, suggests that the direct injection technique should be considered a dewatered municipal biosolid land application option.

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