Virus removal from sewage effluents during saturated and unsaturated flow through soil columns

Recharge of sewage effluents may lead to contamination of groundwater with viruses. The goal of this research was to quantify virus removal in representative subsurface transport conditions. Soil column and batch studies were conducted to evaluate how virus type, effluent type and water saturation affect virus adsorption and removal. Three viruses were used: MS2 and PRD1 bacteriophages and poliovirus type 1. In the first column study, secondary- or tertiary-treated sewage containing the viruses percolated through coarse-sand columns under unsaturated conditions. In the second column study, the viruses suspended in secondary-treated sewage percolated through the columns under saturated or unsaturated conditions. A batch adsorption study was conducted to determine equilibrium adsorption of these viruses to the sand. Effluent type had no significant effect on first-order virus removal coefficients or retardation of virus transport. Virus "removal" was considered to be inactivation or irreversible adsorption. Unsaturated conditions resulted in an average removal coefficient (μ_s = 0.31 h^-1) more than three times greater than saturated conditions (μ_s = 0.095 h^-1), a significant difference at the 0.01 level. Poliovirus had a greater retardation coefficient (R = 5.2) than the bacteriophages (MS2, R = 1.4; and PRD1, R = 2.2), a significant difference at the 0.001 level. Column retardations of virus transport were only 0.8-8.0% of that predicted by adsorption coefficients determined from the batch studies. Equations developed in this paper may aid in estimating virus removal during recharge of effluents if the water residence times in ponds, the vadose zone and the aquifer are known.