Mum of the range in view of the large performance

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Unformatted text preview: (UASB þ POST). mum of the range). In view of the large performance variability observed in Additionally, in order to analyse whether there was a the systems investigated, it is also analysed whether good or difference in the performance of smaller and larger plants, poor performances are related to underloading or overload- all systems were ranked by flow, and split into two groups: ing conditions, respectively. Thus, operational conditions lower flows (0 to 50 percentile of mean flows) and higher are evaluated in order to verify the existence of a relationship flows (50 to 100 percentile of mean flows). between design/operational parameters and the performance Also a monitoring index (MI – average number of of the plants or, in other words, whether there is evidence of a samples collected per year in each plant) was investigated better performance when the systems operate within loading as a possible indicator of the operational level in the plant rates recommended by the technical literature. (higher MI values could be associated with more operator’s involvement and, therefore, possibly a better operation). Also in this case, the plants were separated into two groups (50% lower and 50% higher MI percentiles), as METHODS shown in Table 2. Performance evaluation The treatment technologies described and evaluated in this RESULTS AND DISCUSSION work are located in Southeast Brazil (latitudes 20° to 22° south, tropical climate, average liquid temperatures between Performance evaluation 20 and 25°C), in the states of São Paulo and Minas Gerais. The data used were obtained directly from the operational Table 3 presents the monitoring frequency and the number records of the water and sanitation companies responsible and percentage of treatment plants within each category. for the operation of the treatment plants. The data obtained In total, almost 42,000 data from the 166 WWTP were ana- span a period ranging from 1976 to 2003, with variations lysed and the results showed a great variability in terms of within this period for each specific plant. sampling frequency, monitoring period and measured 39 S. C. Oliveira & M. von Sperling Table 1 | | Performance of wastewater treatment technologies Journal of Water, Sanitation and Hygiene for Development | 01.1 | 2011 Typical design and operational parameters used to evaluate WWTP performance Parameter Technologies Type Unit Usual range À1 À1 Ls – surface BOD loading HRT: hydraulic retention time FP ATc Activated sludge (AS) SCd UASB reactor (UASB) a kg BOD mÀ3 dÀ1 days kg BOD haÀ1 dÀ1 days 0.10–0.35 3–6 150–300 15–45 F/M ratio: food/microorganism ratio kg BOD kg MLVSSÀ1 dÀ1 hours HLR: hydraulic loading rate m3 mÀ2 hÀ1 kg MLSS mÀ2 hÀ1 0.3–0.8 (CAS)a 0.08–0.15 (EAAS)b 6 a 8 (CAS) 16–24 (EAAS) 0.67–1.33 (CAS) 0.33–0.67 (EAAS) 4–6 (CAS) 1–5 (EAAS) HRT: hydraulic retention time v: upflow velocity AP Lv: volumetric BOD loading HRT: hydraulic retention time Ls – surface BOD loading HRT: hydraulic retention time SLR: solids loading rate Anaerobic þ facultative ponds (AP þ FP) kg BOD ha days HRT: hydraulic retention time Facult...
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