Fish, chitin, and chitosan production 2772 mg/L at dawn, otherwise some kinds of mechanical aeration (e.g. surface
aerator) has to be provided during this critical period.
Experiments were conducted at the Asian Institute of Technology (AIT),
Bangkok, to observe the effects of adding septage at the loadings of 50, 150,
250 and 350 kg COD/(ha-day) to concrete ponds (the working dimensions of
each pond were 2x2x0.9 m^3 : length x width x depth). Septage loading to these
ponds was conducted once daily, and the data reported in Figure 6.7 are the
mean values obtained during steady-state conditions (based on relatively
constant COD concentrations in the pond water). The concentrations of algae
and NH 3 -N were found to increase with increasing septage loadings, while the
levels of DO at dawn decreased at high septage loadings, according to the
phenomena described in section 6.4. It appears from Figure 6.7 that, under this
ambient condition, septage loadings in the range of 50-150 kg COD/(ha-day)
should result in suitable DO levels at dawn for Tilapia growth.
Figure 6.7 Effects of septage loadings on pond characteristics (no fish culture) from
Polprasertet al. (1984); reproduced with permission of Pergamon Books Ltd
Algae conc. mg / LPond loading, kg COD / (ha – day)algae conc.
NH 3 – N
pond surface DO
at 8.30 am