analysis of a pilot-scale anaerobic baffled reactor treating domestic ...

2.5 THE ANAEROBIC BAFFLED REACTOR
The anaerobic baffled reactor is a high rate anaerobic digester that has been used to pre-treat or codigest
high strength or toxic industrial effluents. Its application in the treatment of low-strength
wastewaters has been tested on a laboratory-scale and in a number of full-scale applications for the
primary treatment of domestic wastewater. A modified ABR forms the central unit of the DEWATS
(DEcentralised WAstewater Treatment Systems) plant that has been implemented to provide low cost
domestic wastewater treatment in low income communities in South-East Asia, India, China and
Africa (Sasse, 1998; BORDA, 2008).
Figure 2.7: Diagram of an anaerobic baffled reactor (ABR) showing hanging and standing
baffles. Curved arrows indicate liquid flow, while straight arrows represent gas
production.
The ABR is similar in design and application to the upflow anaerobic sludge blanket (UASB) reactor,
but it is reported that no special granule formation is necessary for its operation (Barber and Stuckey,
1999). The first baffled digesters to be called ABR were described by Bachmann et al. (1985).
The ABR has alternating hanging and standing baffles (Figure 2.7), which divide it into
compartments, and direct liquid flow through a series of upward and downward passes. A sludge bed
accumulates through the settling of solids in the bottom of each compartment, and the liquid flow is
forced through this blanket as it passes under each hanging baffle. Good contact between wastewater
flow and active biomass is ensured by this design. In principle, all phases of the anaerobic degradation
process can proceed simultaneously in each compartment. However, the sludge in each compartment
will differ depending on the specific environmental conditions prevailing and the compounds or
intermediates to be degraded (Barber and Stuckey, 1999).
The hydrodynamics and degree of mixing that occur within a reactor of this design strongly influence
the extent of contact between substrate and micro-organisms, thus controlling mass transfer and
potential reactor performance. Micro-organisms within the reactor rise and settle depending on flow
direction (up or down) and velocity, particle settling velocity and gas production. Their rate of
movement along the reactor from compartment to compartment is generally slow. The main driving
force behind reactor design has been to enhance the solids retention capacity. (Barber and Stuckey,
1999)
The reported advantages of the baffled reactor design are as follows (Barber and Stuckey, 1999):
• The reactor design is simple, with no moving parts or mechanical mixing.
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