In urban areas domestic wastewater pollution reaches 60 % and about 75 % of the total volume of domestic wastewater is greywater . As an alternative wastewater treatment, UASB ( Upflow Anaerobic Sludge Blanket ) is an effective waste processing because it has many advantages . Several factors affect the performance of UASB reactors is Hydraulic Retention Time ( HRT ) and influent concentration. In the COD removal and BOD , reactors with HRT 4 hours having the smallest removal efficiency , i.e. by 36 % and 20 % . Reactor reaches the optimum point processing when operated at HRT 12 hours , where COD removal efficiency of 73% and BOD removal efficiency of 66% . In the reactor with medium concentration range ( S ) with an influent COD of 760 - 880mg / L of COD and BOD removal efficiency reached a maximum of 77 % and 75 % . While the smallest efficiency reactor obtained at low concentrations ( R ) with the organic content of the feed ( influent ) of 133-160 mg / L with a COD removal efficiency of 48% and BOD by 44 % .