Sorption of E. coli from liquid swine manure in natural and artificial soils

Animal waste applications in agricultural lands can contribute microbial contamination to water bodies. After manure application, Escherichia Coli (E. coli) can be transported by surface runoff and infiltration or can be retained in soils by its filter capacity. The soil filter capacity is a dynamic function of the physical-chemical properties of the soil, effluent composition and bacteria properties. In this study, E. coli isotherms were determined after mixing natural and artificial soils with manure effluents at different dilution ratios and decanting the clay particles by centrifugation. Two natural soils (e.g., loamy sand and sandy loam) and seven artificial soils were used with different clay (e.g., kaolinite: KGa-1) and organic matter (e.g., Sphagnum peat moss) content. In addition, the organic matter in the natural soils was removed using a hydrogen peroxide reagent. Sorption data fit a nonlinear Freundlich isotherm with a coefficient of determination, R², higher than 0.93 except for the pure sand and natural soils after the organic matter was removed (e.g., R² was higher than 0.84). Sorption data suggested that the presence of organic matter favored E. coli sorption in soils with clay contents lower than 10%. Sorption equations based on clay content without considering the effect of organic matter may underestimate E. coli sorption for varying solution E. coli concentrations. A general equation to estimate the Freundlich coefficients were obtained from the experiments based on the natural logarithms of clay content for total carbon content in the range of 0 to 2.1%. These equations are intended to be valuable in estimating E. coli sorption in manure-amended soils for improved modeling of E. coli fate and transport in soils.