6 107 55 106 09 53 107 12 106 16 20 108 43 105 22 37

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Unformatted text preview: 11 7 36 3 1 46 7 6 –1 7 5 23 FC d Influent (MPN 100 mLÀ1) Effluent (MPN 100 mLÀ1) Removal efficiency (log units) a b 2.6 Â 107 5.5 Â 106 0.9 5.3 Â 107 1.2 Â 106 1.6 2.0 Â 108 4.3 Â 105 2.2 3.7 Â 107 1.3 Â 105 2.0 1.2 Â 108 3.4 Â 107 0.6 1.8 Â 108 9.7 Â 106 2.8 Activated sludge process includes: conventional and extended aeration. UASB þ POST includes as post-treatment: aerated filter; anaerobic filter; trickling filter; flotation unit; facultative pond or maturation pond. c TKN and TN were used. d Geometric mean used for coliforms. contributions, type of sampling practised (prevalence of for the six technologies, the ranges effectively observed for grab samples, collected at peak hours), low per capita the wastewater treatment plants in operation (considering water consumption, low infiltration rates and low waste- the 10 and 90% percentiles) and the percentage of wastewater water/water return coefficients, as discussed in more detail treatment plants that presented mean effluent concentrations by Oliveira & von Sperling (). above the upper value of the reported range. Table 6 shows, The variability of the mean effluent concentrations and in a similar way, the removal efficiencies. Figures 3 and 4 the mean removal efficiencies of the six treatment technol- show the percentages of wastewater treatment plants ogies can be visualized in the box-and-whisker plots with presented in Figures 1 and 2. The figures show that, in reference ranges reported in the literature, in terms of mean general, variable effluent concentrations and removal effi- effluent concentrations and removal efficiencies, respectively. ciencies were obtained within all treatment processes, considering all the analysed constituents. performance below, within or above the In general, a great difference was noticed between the ranges reported by the literature and those effectively The effluent concentrations and the removal efficiencies observed, taking into consideration all the constituents (Table 4) observed in the treatment plants in operation and all the treatment technologies, with a prevalence of were compared with values considered typical by the technical effluent concentrations higher than expected. literature (Arceivala ; Qasim ; WEF & ASCE ; The ST þ AF (septic tank þ anaerobic filter) systems had Mara ; Metcalf & Eddy ; von Sperling & Chernicharo a high percentage of WWTPs with a lower performance ) for the different wastewater treatment technologies. than expected, considering both mean effluent concen- The results related to the effluent concentrations are pre- trations and removal efficiencies. This low performance sented in Table 5, which shows the typical values expected was observed for all constituents, except for FC, which 41 S. C. Oliveira & M. von Sperling | Performance of wastewater treatment technologies Journal of Water, Sanitation and Hygiene for Development | 01.1 | 2011 presented a high percentage of WWTPs with performance efficiencies, above or within the expected...
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