The attenuation of microorganisms in on-site wastewater effluent discharged into highly permeable subsoils

• Published in: Journal of contaminant hydrology 2012-11, Vol.142-143, p.126-139
• Main Authors: O'Luanaigh, N.D., Gill, L.W., Misstear, B.D.R., Johnston, P.M.
• Format: Article
• Language: English
• Subjects: Bacteriophage; Bacteriophages; Biomat; E. coli; Escherichia coli; Groundwater; Groundwater - microbiology; Microbial contamination; On-site wastewater treatment and disposal; Septic tank effluent; Soil - chemistry; Waste Disposal, Fluid - methods
• ISSN: 0169-7722; 1873-6009
• DOI: 10.1016/j.jconhyd.2011.12.003

An extensive field study on percolation areas receiving both septic tank and secondary treated on-site effluents from single houses in Ireland was carried out to investigate the attenuation capacity of highly permeable subsoils with respect to E. coli bacteria and spiked bacteriophages (MS2, ΦX174 and PR772). The development of biomats across the percolation areas receiving the secondary effluent was restricted compared to the percolation area receiving septic tank effluent, promoting a much higher areal hydraulic loading which created significant differences in the potential microbiological loading to groundwater. Greatest E. coli removal in the subsoil occurred within the first 0.35m of unsaturated subsoil for all effluent types. Analysis showed, however, that more evidence of faecal contamination occurred at depth in the subsoils receiving secondary treated effluents than that receiving septic tank effluent, despite the lower bacterial influent load. All three bacteriophages were reduced to their minimum detection limit (