Animal Waste, Water Quality and Human Health

168Animal Waste, Water Quality and Human Healthprovide sufficient information for a reliable assessment of the level of risk posed bythese animal sources.5.3 EMPIRICAL DATA ON HUMAN MICROBIALSOURCESA recent paper on FIO concentrations in sewage effluents provides empirical dataon the contribution of human wastewater as a source of faecal contamination incatchments. Kay et al. (2008a) note the lack of published empirical data on FIOconcentrations in sewage-related discharges to natural waters and the significantinformation gap for the research and management communities. They reportedFIO data (presumptive total coliforms (TC), faecal coliforms (FC) and enterococci(EN)) for 1933 samples taken from a range of different types of sewage-relatedeffluent in the United Kingdom and on the island of Jersey at the locationsspecified in Figure 5.8. These data cover discharges/effluents associated withthe following “levels” of treatment:• untreated sewage – including various storm sewage overflows as well ascrude sewage discharges;• “primary” treatment – that is “physical” treatment such as settlement ofsolids as might be achieved in a primary settlement tank at a municipalwastewater treatment plant or a domestic septic tank;• “secondary” treatment – that is involving biological processes such as wouldbe produced in an activated sludge plant or trickling filter system; and,• “tertiary” treatment – that is final “cleaning” of effluent from secondarytreatment, in some cases designed specifically to remove FIOs, notablyUV disinfection, but often to reduce levels of nutrients (e.g. inreedbed/grass plot systems) in addition to FIOs.Given the worldwide utilisation of the treatment technologies investigated,these data provide indicative geometric means (GMs) and ranges for FIOconcentrations likely to be encountered in other comparable geographicalregions. It should be noted, however, that sewerage systems in the UnitedKingdom predominantly take both sewage and runoff from built-up areas (i.e.“combined” systems), which leads to high variations in flows. Thus, the reporteddata may be less applicable to systems where foul sewage and surface drainageare collected separately. Some specific technologies are not covered, notablychemical dosing and combined chemical/UV systems, both of which are notcommonly employed in the United Kingdom; and lagoons/constructed wetlands,which were not encountered in the areas studied.