stage was switched off. The average HRT of the UASB was 10 h
while the entire system had a HRT of 14 h. The COD concentration
of the feed was maintained around 1000 mg L1.
Period II (from day 33 until day 194). During this period the recirculation
pump from the aerobic MBR chamber to the UASB unit
was switched on. This strategy was assayed in order to avoid
anaerobic biomass losses from the UASB stage, as well as to maintain
low biomass production in the system, as part of the excess
aerobic biomass was hydrolyzed in the anaerobic stage.
Initially, the recirculation ratio was 0.15, but from day 97 it was
set at 0.075. The overall HRT was 20 h while the HRT of the UASB
stage was 15 h. COD concentration in the feed was maintained
around 1000 mg L1.
Period III (from day 195 until day 292). The COD concentration
was increased step-wisely during this period (by reducing the
dilution), in order to check the system capacity. HRT was 11 h
for the UASB and 15 h for the entire system. During this period,
the recirculation pump from the aerobic chamber to the UASB
was on