Organic Waste Recycling

292 Organic waste recycling: technology and management

Solution

From data presented in Table 6.4 and Figure 6.7,

Use organic loading rate = 50 kg COD/ (ha-day)

10 x 25,000
Area requirement = = 50,000 m^2 = 5 ha
50 x 1,000
Select a fish pond size of 25.0 m (width) x 50.0 m (length) x 1.5 m (depth);
water depth = 1.0 m
50,000
Number of ponds = = 40 ponds
25 x 50
Each pond is separated from each other to facilitate harvesting and drying
operation.
Select Tilapia (Oreochromis niloticus) with a stocking density of 5 fish/m^2.
The products will be sold as trash fish to produce animal feed. This will reduce
possible health hazard from direct consumption of these fish.
Number of fingerling (about 0.5-5 g) used = 1,250 x 5 = 6,250 fish/pond.
Select harvesting period of 3 months and 10 days of pond drying or 100 days
in total before subsequent operation.
Calculate fish yield from Equation 6.6:
Wt = 12.032 (t.N/SD)0.707

(500 + 1,500) 10

N = x = 4 kg/(ha-day) (6.6)

1,000 5

t = 3 months

SD = 5 fish/m^2

Wt = 12.032(3x4/5)0.707 = 22.3 g/fish

Assume mortality rate = 20%

22.3

Estimated fish yield = 6,250 x 0.8 x

1,000

= 112 kg/pond per 100 days

365

Extrapolated fish yield = 112 x = 408.8 kg/(pond-year)

100

408.8

= = 3,270 kg/(ha-year)

0.125