Seasonal virus removal by alternative onsite wastewater treatment systems

Abstract

Viral contamination of public waters is a leading health concern around the world, including in Minnesota where cold climate, abundant onsite systems on poor or thin soils, and abundant surface water resources present a significant risk of wastewater pathogens reaching sensitive water sources. Three alternative onsite treatment systems, a sand filter, peat filter and subsurface-flow constructed wetland (CW) at a field research site were evaluated for seasonal virus removal by seeding each with MS2 bacteriophage. The sand and peat filters and CW removed 2.7, 7.0, and 1.4 log10 of MS2, respectively, during summer and 1.8 and 6.9 log for the sand and peat filter during winter (CW not seeded). Somatic coliphage reductions for the sand filter, peat filter and CW were 2.9, 3.5, 1.0 log10 in summer, and 1.5, 2.8, 0.7 log10 during winter, respectively over a 3 year period. During this period, fecal coliform log10 reductions were 2.9, 4.6, 2.0 in summer for the sand and peat filters and CW, and 2.0, 4.6, 1.6 in winter. The peat filter was the most effective system for removing MS2, somatic coliphage and fecal coliforms during both winter and summer but all systems removed >90% of viruses throughout the year.

Removal of Pathogens in Onsite Wastewater Treatment Systems: A Review of Design Considerations and Influencing Factors

“…Both the SF and the CW performed better in summer with 1.4-3.9 log 10 removal of all pathogens. While in winter, 0.8-2.7 log 10 removal of all pathogens was observed [28]. In another study, the removal rate of Salmonella choleraesuis increased by 1.1-6.2 log 10 during summer when a variety of filters (peat filters, SFs and CWs) were tested [48].…”

“…Both bacteriophages are frequently found in human and animal feces, and are non-invasive to humans [15,26]. Therefore, they are widely accepted as indicators for human enteric viruses and are commonly used in studies on the removal of viruses in OWTSs [25,[27][28][29]. Clostridium perfringens, whose spores are used as the proxy for protozoan (oo)cysts, are also typical pathogen indicators in wastewater quality measurements [30].…”

“…Besides the traditional septic system, surface flow CWs, subsurface horizontal flow CWs, and vertical flow CWs have been widely employed in many countries and can achieve 0.4-4.48 log 10 removal of pathogens (bacteria, viruses, protozoa, and helminths) treating domestic wastewater [3,9]. Furthermore, the filtration-based treatment system filled with sand, peat, carbonaceous or other media is another technological solution for onsite wastewater treatment [28,136,165]. The installation of an SF in drain fields greatly increased the removal of FC (99.8%) compared with the soil-only filter systems (91%) [133].…”

“…Temperature, which fluctuates with different seasons, is commonly considered as the dominant factor for the survival of viruses in the environment [30,116,200,201]. Higher temperatures can damage viral DNA or RNA, increase predation through enhanced microbial metabolism, and also increase the natural die-off rates of bacteria [28,202,203]. A significant die-off of Pseudomonas sp.…”

“…was observed at 25 • C [204], while the best survival of enteric bacteria was at 5 • C [117]. A few case studies have reported higher removal rates of pathogens in warm seasons compared to those in cold seasons [28,43,48,52,55,60,134,157]. On the other hand, several studies suggested seasonal differences did not have a significant impact on the removal of pathogens in OWTSs [57,136,137,180,205].…”