A proposed compact on-site anaerobic treatment of department
store wastewater and biogas recovery by a two-step UASBeEGSB
system can be considered as an energy-saving system, compared to
aerobic treatment system. The results of the pre-treatment with the
UASB reactor showed that the UASB reactor is efficient to remove
both 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 effi-
ciencies of UASBeEGSB system for removal COD, BOD and SS were
90.5, 90.7 and 92.2%, respectively. Specific methanogenic activity
(SMA) of the granular sludge inside the EGSB reactors was found in
the range of 0.06e0.09 gCOD-CH4/gVSS-day. Moreover, The
UASBeEGSB system could save energy consumption up to 75%,
compared to traditional activated sludge process due to no aeration