Organic Waste Recycling

290 Organic waste recycling: technology and management

operation. Separate water supply and drainage system should be provided in
each pond.

Pond arrangement

Various pond arrangements can be made to suit the local condition as well as
type of organic wastes available. Figure 6.15 shows some possible arrangements
of the ponds with appropriate measures such as depuration to safeguard the
public health (see sections 6.6 and 6.7). In some cases, it might be necessary to
drain the fish ponds during or after harvesting. Therefore additional pond area or
water storage space should be provided for the drained water to prevent
contamination of the fish pond water to the nearby water courses. Depending on
the water quality and local conditions, the fish pond water can be used for
irrigation. Fish ponds that have been drained should be sun-dried for 1-2 weeks
to inactivate any pathogens inhabiting at the pond bottom and side walls. The
bottom mud should be removed to maintain the working pond volume and
avoiding excessive accumulation of sludge at the pond bottom.
Based on the above information and the data from Edwards (1992), design
guidelines and performance data of waste-fed fish ponds are given in Table 6.4.

Table 6.4 Design guidelines and performance data of waste-fed fish ponds

Pond depth (m)

Pond width (m)

Pond area (m^2 )

Minimum DO at dawn (mg/L)

NH 3 concentration of pond water (mg/L)

pH of pond water

Organic loading rate

(kg BOD 5 /ha-day)

(kg COD/ha-day)

Fish stocking density (fish/m^2 )

Recommended fish species

Culture period (months)

Fish yield (kg/(ha-yr))

1-1.5

< 30

400-4000

1-2

< 0.02

6.5-9 (optimum 7.0-8.0)

25-75

50-150

0.5-50

Tilapia and carps

3-12

1000-10000

Removal efficiencies

Suspended solids (%)

BOD 5 (%)

Total nitrogen (%)

Phosphorus (%)

70-85

75-90

70-80

80-90