2.2. Reactors
Seven reactor configurations were assessed (see Fig. 1), including
aerobic only units, anaerobic AnCSTR, HUASB and AHR units,
and three anaerobic–aerobic sequence reactors systems. The AnCSTR
was a completely-mixed, suspended-cell system with a 5-L
working volume (Sartorius, Germany). The HUASB and AHR units
were anchored-cell anaerobic units (1.5-L working volumes) where
bottom zones contained granular anaerobic sludge and top zones
had polypropylene pall rings (capped by aluminium mesh screens
to reduce biomass loss). Up-flow conditions in the HUASB and AHR
reactors were maintained by recycling reactor effluents using peristaltic
pumps (Watson Marlow, UK). The up-flow velocities were 4
and 1 m/h in the AHR and HUASB reactors, respectively, and both
had 2-day hydraulic retention times (HRT). An 8-day HRT was used
for the AnCSTR reactor, which had no recycle. Temperature and pH
were maintained at 35 C and 6.8–7.2, respectively, in all anaerobic
units.