284 Organic waste recycling: technology and management
reproduction, and the enhancement of bioaccumulation and biomagnification in
the food chains as described in section 6.3.
Figure 6.12 Effect of pH on hydrogen sulfide-sulfide equilibrium (after Sawyer et al.
2003; reproduced by permission of McGraw- Hill Book Company)
6.5.2 Design criteria
Organic loading, DO and fish yield models
Almost all kinds of organic wastes can be fed to fish ponds. These wastes can be
in any of the following forms: raw sewage, effluents from wastewater treatment
plants or high-rate algal ponds, nightsoil and septage, biogas slurry, composted
products, animal manures, and agro-industrial wastewaters. Fish may be reared
directly in waste stabilization ponds. In any case, organic loadings to be applied
to waste-fed fish ponds should be in the range that anaerobic conditions do not
prevail in the ponds.
Data in Table 6.1 show that well-operated fish ponds fed with wastewater
had organic loadings in the range of 25-75 kg BOD 5 /(ha-day), while those fed
with organic solids e.g. septage or biogas slurry had organic loadings from 50 to
150 kg COD/(ha-day). Data of fish yields vary widely depending on the modes
of pond operation, climates, fish species and stocking densities employed.
pHH 2 SHS- S
ő%