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Unformatted text preview: ciencies in terms of nutrients was expected, since none conditions of the treatment processes. For example, if a FP of the analysed technologies has been designed for either operated at a loading rate above the upper limit of the nitrogen or phosphorus removal. However, the good per- recommended range (300 kg BOD haÀ1 dayÀ1), it was con- formance presented by the AS process considering TP is sidered to be in an overloading condition, whereas if it somewhat unexpected, with 100% of the wastewater treat- operated at a rate below the lower limit (150 kg BOD haÀ1 ment plants presenting efﬂuent concentrations lower than dayÀ1), it was considered to be in an underloading condition. the expected. Regarding HRT, values higher than the upper limit of the
reported range indicated underloading. Inﬂuence of the operational conditions This criterion was used for all the loading rates and
treatment technologies. After the calculation of the para- All data obtained from four treatment processes (132 plants) meters, a graphic comparison between observed and were evaluated in order to verify the existence of a relationship recommended loading rates was undertaken. It is recog- between design/operational parameters and the performance nized that, ideally, mathematical models for each process of the plants. It was not possible to analyse all 166 WWTP, and plant should be used, but the shortage of input data 45 S. C. Oliveira & M. von Sperling Figure 3 | | Performance of wastewater treatment technologies Journal of Water, Sanitation and Hygiene for Development | 01.1 | 2011 Comparison between mean efﬂuent concentration and expected values according to the literature. and the complexity of the analysis for such a large number of those variables (efﬂuent concentrations and removal efﬁ- treatment plants made this approach unfeasible. ciency) that were signiﬁcantly inﬂuenced by the surface The scatter plots produced for each treatment process organic loading rate (Ls), volumetric organic loading rate are presented separately. Each plot includes, in the form (Lv), hydraulic retention time (HRT), ﬂow or monitoring of dotted lines, the minimum and maximum values con- index (MI), considering the technologies FP and AP þ FP. sidered typical by the technical literature (Arceivala ; For the other technologies (AS and UASB), the statistical Qasim ; WEF & ASCE ; Mara ; Metcalf & tests did not indicate any inﬂuence of the parameters on Eddy ; Von Sperling & Chernicharo ) for efﬂuent the efﬂuent quality. All results are discussed in the following concentrations from each speciﬁc technology. sections, separated by technology type. The ponds are dis- A statistical analysis (Kruskal–Wallis followed by mul- cussed separately, considering the primary facultative, tiple comparison of mean ranks for all groups), at the 95% secondary facultative and anaerobic type, and they have conﬁdence level, was undertaken for the efﬂuent concen- already been analysed, in detail, in a previous st...
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