Transport of Escherichia coli in sand columns with constant and changing water contents

Understanding how changes in volumetric water content (theta) affect bacter ial adsorption could help reduce transport of pathogenic and indicator bact eria that may be present in infiltrating wastewater, Three now regimes that simulated infiltration from a household septic system were evaluated: satu rated, unsaturated with a constant volumetric water content theta (constant unsaturated now), and unsaturated with cyclic changes in theta (variable u nsaturated flow). Escherichia coli was suspended in artificial sewage (AS) and applied as step inputs to sand columns, with regular interruptions in i nput for variable unsaturated now. A transport model was fit to the saturat ed and constant unsaturated now breakthrough curves to determine retardatio n (R), the first-order filtration coefficient (mu) and the maximum outflow relative concentration (C-max), The total tells transported as a fraction o f input (tau) in all three now regimes was calculated, Constant unsaturated now resulted in a significantly lower C-max (0.633) in comparison with sat urated flow (0.803, P less than or equal to 0.05), although unsaturated mu (0.0693 h(-1)) was not significantly different from saturated mu (0.0259 h( -1)), Constant unsaturated now also resulted in a significantly smaller tau (0.617) than saturated (0.806) or variable unsaturated now (0.734), In var iable unsaturated now, cell concentrations were out of phase with theta -as the column drained, cell concentrations in the outflow increased; and when a pulse of suspension was applied, cell concentrations decreased. Constant unsaturated now is probably the best for removal of pathogenic bacteria be cause this regime resulted in lower maximum concentrations of E, coli and g reater cell removal, in comparison with saturated and variable unsaturated flow.