Organic Waste Recycling

138 Organic waste recycling: technology and management

There are two principle objectives in applying sludge compost as a source of
N for crops: to supplement the amount of potentially available N, and to ensure
that the level of N applied as compost does not greatly exceed that necessary for
attainable crop yields. Based on the N requirements of different crops (Table
8.7), the application rates will be different and the rates should be able to
produce maximum growth and yield.

Table 3.11 Average nutrient contents (dry weight basis) of compost piles at the starting
period and during the 30-60 days of composting

Initial C/N ratio

20 30 40

Nutrients

Starting

period

30-60 days

of

composting

Starting

period

30-60 days

of

composting

Starting

period

30-60 days
of
composting
% N 2 2.2 1.3 1.9 1.3 1.9
% P 0.3 0.6 0.2 0.4 0.3 0.3
% K 1 1 0.6 0.6 0.6 0.6
From Polprasert (1984); reproduced by permission of Pergamon Books Ltd.

Table 3.12 Fish Yields from compost fed ponds (Edwards et al. 1983)

Experiment

number

Pond

number

Compost

feeding rate, kg

COD/(ha-yr)

Fish yield,

kg /pond per 6

months

Extrapolated

fish yield,

kg/(ha-yr)

1 50 a 26.5 2,840

2 0 7.6 820

3 50 b 51.9 5,570

1

4 0 8.15 875

1 25 b 15.7 1,510

2 100 b 32.2 3,090

3 0 6.6 630

2

4 50 b 30.2 2,900

1 25 b 36.1 3,530

2 50 b 35.9 3,500

3 100 b 57.7 5,640

3

4 0 11.2 1,100

aCompost whose initial C/N ratio was 30
bCompost whose initial C/N ratio was 20