Two community onsite UASB-septic tanks namely R1 and R2 were operated under two different HRT (2 days for R1 and 4 days for R2) in parallel over a year and monitored over the cold half of the year. During the monitoring period, the sewage was characterised by a high CODtotof 905 mg/l with a high fraction of CODss, viz. about 43.7%, and rather low temperature of 17.3 °C. The achieved removal efficiencies in R1 and R2 for CODtot, CODsus, CODcol, CODdis, BOD5and TSS were "51%, 83%, 20%, 24%, 45% and 74%" and "54%, 87%, 10%, 28%, 49% and 78%", respectively. The difference in the removal efficiencies of those parameters in R1 and R2 is marginal and was only significant (p < 0.05) for CODsus. The sludge filling period of the reactors is expected to be 4-7 years. In view of that, the UASB-septic tank system is a robust and compact system as it can be adequately designed in Palestine at 2 days HRT. © 2008 Elsevier Ltd. All rights reserved.
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