Community onsite anaerobic sewage treatment in a uasb-septic tank system: system behaviour during winter period in Palestine

Abstract

The effect of the Mediterranean climate low temperature period on the performance UASBseptic tank treating concentrated domestic sewage (COD ~ I 00mg/L) in Palestine was 3 studied. Two community onsite UASB-Septic tank reactors (capacity: 0.8 111 , height: 2.5 m)
were operated in parallel over a year and monitored over the colder half of the year. The
reactors were operated under two different HRT (2 days for RI and 4 days for R2) at average
sewage temperature of 17 .3 °C with 12 and 25 °C extreme values. The COD,, in the raw
sewage represented a high fraction of the total COD, viz. about 43.7% from the COD,01. RI
achieved mean removal efficiencies for COD,m, CODsus, CODcol, CODdis, of 51 %, 83%, 20%
and 24% respectively and BOD5 and TSS average removal efficiencies of 45% and 74%
respectively. R2 achieved mean removal efficiencies for COD,0., COD,u,, CODcol, CODdis, of
54%, 87 %, I 0% and 28%, respectively with BOD5 and TSS average removal efficiency of
49% and 78% respectively. The sludge production from both reactors was very low with
VS/TS ratios of 67.9 and 67.02 of the sludges in RI and R2, respectively. Based on the
removal efficiencies and sludge production it can be concluded that the here researched
UASB-Septic tank system is a potential compact and effective community onsite pretreatment unit for domestic wastewater in Palestine. The reactor can be designed at either 2 or
4 days HRT, but slight preference might be given to 4 days HRT when sludge production is of
concern.