Organic Waste Recycling

368 Organic waste recycling: technology and management

Note: 1US$ = 40 Baht

a) Water hyacinth

Organic loading of the pond =
ha

kg

L

mg

d

m

1. 2

1

10

10

(^1002003)
3 6
̧× ×
¹

·

̈

©

× §

̧ ̧

¹

·

̈ ̈

©

§

−

−

= 16.66 kg BOD 5 /(ha-day)

Hydraulic loading =
day ha

m

1. 2

1

100

3

̧ ̧×

¹

·

̈ ̈

©

§ = 83.3 m3/(ha-day)

Note: these loading rates are within the ranges reported in Tale 7.9.
Because the doubling time is 10 days, the no. of water hyacinth harvesting is
36 times per year. The amount of water hyacinth harvested is half of the total
pond area.
Amount of water hyacinth harvested/year

= 36 x ̧
¹

·

̈

©

§

2

(^1) x 1.2 x 10 (^4) x 2.0 kg = 432x10 (^3) kg.
Assuming solid content = 5%
Total protein obtained = 0.05 x 0.17 x 432 x 10^3 kg = 3.672 kg.
Income from protein = 1.0 x 3672 = 3672 Baht
Annual income = 3672 Baht
b) Duckweeds
Because the doubling time is 15 days, the frequency of duckweed harvesting is
24 times per year. The amount of duckweeds harvested is half of the total pond
area.
Amount of duckweeds harvested per year =
2
(^1) x 24 x 0.7 x 1.2x10^4 kg
= 100.8x10^3 kg
Solid content in duckweed = 20%
Total protein obtained = 0.2x0.2x100.8x10^3 = 4032 kg/year
Cost for harvesting = 100.8 x 10^3 x
1 , 000

0. 2 × 100

Income from protein = 4032x3.0 Baht/year

= 12,096 Baht/year

Net income = (12,096 – 2,016) Baht/year

= 10,080 Baht/year