Virus transport from on-site wastewater treatment systems
Thesis DisciplineWater Resource Management
Degree GrantorUniversity of Canterbury
Degree NameMaster of Water Resource Management
Viral pathogens present in wastewater, discharged to land from domestic wastewater systems, can contaminate groundwater and drinking-water supply wells. By understanding how viral pathogens move through soils, we can optimise assessment of the risk of groundwater contamination. This is particularly pertinent in areas where drinking-water supply wells are situated near wastewater discharge. Free draining soils such as those in much of Canterbury, New Zealand, may increase the risk of groundwater contamination. Current bacterial indicators do not provide a good indication of viral contamination. This research investigates the transport of pathogenic viruses in free draining Canterbury soils. Intact soil cores of silty and sandy loam overlying sandy gravels were used to carry out saturated virus transport experiments dosed with on-site wastewater.
Analysis of intact soil cores revealed heterogeneous soil structure and macropore characteristics. Hydraulic loading of secondary treated wastewater resulted in successive clogging of intact soil cores under saturated conditions. Hydraulic conductivity of both intact soil cores decreased dramatically over a period of 56 days with wastewater conditioning. Saturated virus transport experiments conducted every two weeks in intact soil cores showed that male-specific-2 coliphage (MS2 phage) was a more conservative indicator of virus transport and removal than rotavirus and rotavirus surrogate from on-site wastewater treatment systems (OWTS). Mass recovery of MS2 phage was substantially higher than that of rotavirus and rotavirus surrogate. Consequently, log reduction values (LRVs) for MS2 phage through intact soil cores were also lower than rotavirus and rotavirus surrogate. Rotavirus surrogate better represented rotavirus transport and removal than MS2 phage, however, MS2 phage still provides a conservative indication of viral contamination from OWTS. The similarity of rotavirus to rotavirus surrogate during the intact core experiments showed that rotavirus surrogate is a useful tool for predicting virus transport and removal in wastewater experiments. However, caution must be exercised when using rotavirus surrogate for separation distances from drinking water supply wells as it does not provide a conservative indication of viral contamination as MS2 phage does. The Guidelines for separation distances from OWTS to drinking water supply wells used in New Zealand appear to be too conservative having been modelled using data based on conservative indicators. Determining appropriate separation distances from pathogenic virus, virus surrogate, and indicator virus data would allow the modelling of a more realistic scenario. However, further investigation into the transport and removal of viruses from OWTS is first required to provide data in different soil types and under various conditions to enable the improvement of current separation distance guidelines.