Animal Waste, Water Quality and Human Health

Transport of microbial pollution in catchment systems 171Table 5.6 Summary of faecal indicator organism concentrations (cfu 100 mL −1 ) for different treatment levels and individual typesof sewage-related effluents under different flow conditions: geometric means (GMs), 95% confidence intervals (CIs) a ; and results oft-tests comparing base- and high-flow GMs for each group and type b ; and (in footnote) results of t-tests comparing GMs for thetwo untreated discharge types and the two tertiary-treated effluent types (the results of other comparisons for the groups and othereffluent types are present in Tables 5.7 and 5.8).Indicator organismTreatment levels andspecific typesn c GeometricmeanBase-flow conditions High-flow conditionsLower 95%CIUpper 95%CIn c GeometricmeanLower 95%CIUpper 95%CITOTAL COLIFORMSUntreated 253 3.9 × 10 7 *(+) 3.2 × 10 7 4.6 × 10 7 279 8.2 × 10 6 *(–) 7.0 × 10 6 9.6 × 10 6Crude sewage discharges d 253 3.9 × 10 7 *(+) 3.2 × 10 7 4.6 × 10 7 79 1.2 × 10 7 *(–) 8.2 × 10 6 1.6 × 10 7Storm sewage overflows d 200 7.2 × 10 6 5.9 × 10 6 8.4 × 10 6Primary 130 3.0 × 10 7 *(+) 2.3 × 10 7 3.9 × 10 7 14 1.2 × 10 7 *(–) 4.0 × 10 6 3.7 × 10 7Primary settled sewage 61 3.8 × 10 7 3.0 × 10 7 4.7 × 10 7 8 2.2 × 10 7 – –Stored settled sewage 26 2.4 × 10 7 1.2 × 10 7 5.1 × 10 7 1 1.1 × 10 6 – –Settled septic tank 43 2.5 × 10 7 1.3 × 10 7 4.2 × 10 7 5 7.5 × 10 6 – –Secondary 853 1.1 × 10 6 9.5 × 10 5 1.2 × 10 6 183 1.3 × 10 6 1.0 × 10 6 1.7 × 10 6Trickling filter 472 1.4 × 10 6 1.2 × 10 6 1.7 × 10 6 76 1.4 × 10 6 1.0 × 10 6 1.9 × 10 6Activated sludge 256 7.8 × 10 5 *(–) 6.2 × 10 5 1.0 × 10 6 92 1.4 × 10 6 *(+) 8.6 × 10 5 2.1 × 10 6Oxidation ditch 35 8.1 × 10 5 4.6 × 10 5 1.4 × 10 6 5 3.1 × 10 6 – –Trickling/sand filter 10 6.4 × 10 5 2.8 × 10 5 1.4 × 10 6 8 2.7 × 10 5 – –Rotating biological 80 6.8 × 10 5 4.6 × 10 5 1.0 × 10 6 2 4.0 × 10 6 – –contactorTertiary 182 5.5 × 10 3 3.4 × 10 3 9.0 × 10 3 8 3.8 × 10 3 – –Reedbed/grass plot e 73 3.7 × 10 4 1.5 × 10 4 8.1 × 10 4 2 2.3 × 10 4 – –Ultraviolet disinfection e 109 1.5 × 10 3 9.9 × 10 2 2.6 × 10 3 6 2.1 × 10 3 – –(Continued)