This research aims to develop a compact on-site anaerobic treatment of department store wastewater and biogas recovery by a two-step UASBeEGSB (Upflow Anaerobic Sludge Blanket e Expanded Granular Sludge Blanket) as an energy-saving system. The wastewater came from a department store in Bangkok city having COD in the range of 450e700 mg/L and high suspended solids content in the range of 230 e300 mg/L. The applied organic loading rate to the pilot-scale UASBeEGSB system was designed at 5 kg COD/m3 -day. The upflow velocity of EGSB reactor was varied to 4, 6, 8 m/hr. The results of the pretreatment with the UASB reactor show that the UASB reactor is efficient to remove suspended solids and COD in raw wastewater, viz.77.4 and 65.9%, respectively. This means that the UASB reactor plays an
important role to entrap and digest main part of suspended solids from raw wastewater prior to the EGSB
reactor. The overall efficiencies of UASBeEGSB system for removal COD, BOD and SS were 90.5, 90.7 and
92.2%, respectively. Moreover, an increase in upflow velocity of EGSB reactor could slightly increase COD
and BOD removal efficiencies; however, did slightly decrease in SS removal efficiency. Furthermore,
specific methanogenic activity (SMA) of the granular sludge inside the EGSB reactor was found in the
range of 0.06e0.09 gCOD-CH4/gVSS-day.