Similarly to the primary ponds the statisti trations

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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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