Abstract 117

The aim of this work was to evaluate the removal of suspended solids (SS) and 7-day biochemical oxygen demand (BOD₇) in a three chamber septic tank depending on theoretical wastewater retention time and the degree of septic tank cleanliness. It was found out that the performance of the septic tank depended on the degree of its cleanliness: when the septic tank was clean and retention time was three days, SS and BOS₇ removal efficiency was 77±10% and 67±14% respectively, whereas two months later, after septic tank desludging, SS removal efficiency decreased to 53±22% and BOD₇ to 32±31%. The performance of the septic tank also depended on theoretical wastewater retention time: when some amount of solids was accumulated at the bottom of the septic tank and wastewater retention time was one day, SS and BOS₇ removal efficiency was 45±40% and 33±16% respectively; when retention time was three days, SS removal efficiency increased to 53±22% but BOD₇ removal efficiency remained similar to one day retention time, i.e. 32±31%.

Article in Lithuanian