Biofuels production 177(b)Figure 4.13 (a) Schematic diagram of anaerobic digester at Huay Kwang, Bangkok,
Thailand. (b) Anaerobic digester at Nongkham, Bangkok, Thailand.
Besides the above types of digesters, there are numerous modifications of
biogas digesters made to suit particular needs and local conditions. Schematic
drawings of these modifications can be found in the book "Biomethanation" by
Brown and Tata (1985). A summary of design criteria and performance data of
dispersed-growth biogas digesters is given in Table 4.11.
Attached-growth digesters
Anaerobic filter (Young and McCarty 1969)
This is essentially a filter column packed with stationary media such as rocks,
gravels or different types of proprietary plastic materials (Figure 4.14). Columns
with media having a larger specific surface area (surface area per unit volume of
the medium) will have more fixed-film bacteria attached to the media and some
entrapped within the void spaces of the media. In general, the packing media to
be installed in anaerobic filters should have a high specific surface area (surface
area to volume ratio) to provide a large surface for the growth of attached
biofilms, while maintaining a sufficient void volume to prevent the reactor from
plugging either from particulate solids entering with influent waste stream or
bacterial floc growing within the reactor (Vigneswaran et al. 1986). Commercial
media available for use in anaerobic filters include loose fill media such as Pall
rings and modular block media formed from corrugated plastic sheets, in which
the channels in modular media may be tubular or crossflow (Figure 4.15). The
specific surface area of media used in full scale anaerobic filters averages
approximately 100 m^2 /m^3. Table 4.12 lists size, specific surface area and