Dague et al. (1990) describe the successful installation
and operation of a very large covered
anaerobic pond for a US pork processing company.
The design HRT and BOD5 loading were 8.8 days
and 0.33 kg/m3.day, respectively. In practice, average
retention times were higher (12-14 days) and BOD
loadings lower (0.1 kg/m3.day), but mean BOD5
removals of 85-90% were consistently obtained and
biogas production averaged 0.51 m 3 methane/kg
BOD5 removed. The system paid for itself within 2
years through the use of the biogas in a natural-gasfired
boiler. Considerable, but variable, levels of H2S
(mean, 843 ppm) may be generated from anaerobic
ponds and this toxic and corrosive gas must be
removed, for example by iron sponge filters, before
use (Kayhanian & Hills, 1988). Recently, a slaughterhouse
in Australia has installed two covered
anaerobic ponds, which appear to operate successfully.
The gas produced is flared.