Organic Waste Recycling

178 Organic waste recycling: technology and management

porosity of some packing media used for anaerobic filters. The waste flows
upward or downward through the anaerobic filter column, contacting the media
on which anaerobic bacteria grow and are retained. Because the bacteria are
retained on the media and not easily washed off in the effluent, the mean cell
residence times (șc) on the order of 100 days can be achieved with short HRT
(Metcalf and Eddy Inc. 2003). Table 4.13 shows the advantages and
disadvantages of anaerobic filter process, while Table 4.14 reports operating and
performance data of some full-scale anaerobic filters in U.S.A. and Canada.
Depending on the flow regime, the enrichment of the acid- and methane-
forming bacteria takes place at different zones in the filter. For an up-flow
column, there will be enhancement of the acid formers and methane formers at
the bottom and top regions, respectively.

Figure 4.14 Up-flow anaerobic filter

Influent feed

Liquid effluent

Gas trap

Packing media

Packing support

Biogas