Unformatted text preview: d HRT was found to within the usual intervals, but without a good corresponding be inﬂuential in terms of efﬂuent BOD, SS and FC concen- efﬂuent quality. Similarly to the primary ponds, the statisti- trations. The efﬂuent quality from the pond system was cal tests conﬁrmed the inﬂuence of the organic loading on inﬂuenced by the inﬂuent ﬂow (plant size) and monitoring the efﬂuent coliform concentration. Flow and monitoring index. index were more inﬂuential in the efﬂuent quality than in
the primary ponds. Activated sludge Anaerobic ponds Figures 8 and 9 present the relationship between efﬂuent
BOD concentration and removal efﬁciency and the follow- Figure 7 presents the scatter plots for the relationship ing variables: food/microorganism ratio (F/M ratio) in the between efﬂuent BOD concentration and BOD removal efﬁ- aeration tank, hydraulic retention time (HRT), hydraulic ciency and the following variables: Lv, HRT, inﬂuent ﬂow loading rate (HLR) in the ﬁnal clariﬁers, solids loading and MI parameters. It is seen that organic underloading rate (SLR) in the ﬁnal clariﬁers, inﬂuent ﬂow and monitor- conditions were observed on most anaerobic ponds investi- ing index (MI).
The results show that the different food/microorgan- gated, and no pond exceeded the maximum organic load
recommended. The statistical tests conﬁrmed that there Table 7 | ism ratios and HRT values did not inﬂuence Efﬂuent concentrations signiﬁcantly inﬂuenced by loading conditions – FP and AP þ FP
Primary facultative ponds Parameter BOD COD Ls √ √ Lv – – HRT √ SS Secondary facultative ponds
TN TP √ √
– – FC BOD SS TN Anaerobic ponds
TP – – – – – – – FC BOD COD SS TN TP FC √ √ – – – – – – – √ √ √ Flow
√ MI COD √
√ √ √ √ √ √ √ √ √ √ √ Test: Kruskal–Wallis with post-hoc multiple comparison of mean ranks (95% conﬁdence level); √: signiﬁcant; blank: not signiﬁcant; –: not applicable. Table 8 | Removal efﬁciencies signiﬁcantly inﬂuenced by loading conditions – FP and AP þ FP
Primary facultative ponds Parameter BOD COD SS Secondary facultative ponds
TN TP BOD – – – SS TN Anaerobic ponds
TP – – – – – – – – FC BOD COD SS TN TP FC √ √ HRT – – – – – – –
√ √ √ Flow
MI COD √ Ls
Lv FC √ √ √ √ √
√ √ Test: Kruskal–Wallis with post-hoc multiple comparison of mean ranks (95% conﬁdence level); √: signiﬁcant; blank: not signiﬁcant; –: not applicable. √ 48 Figure 5 S. C. Oliveira & M. von Sperling | | Performance of wastewater treatment technologies Journal of Water, Sanitation and Hygiene for Development | 01.1 | 2011 Relationship among Ls, HRT, ﬂow, monitoring index and efﬂuent BOD concentration and BOD removal efﬁciency – primary facultative ponds. Note: the dotted lines represent the
minimum and maximum values considered typical by the technical literature for efﬂuent...
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