100 Organic waste recycling: technology and management

For the sludge that has 90 % volatile solids, the percent ash is 10, Equation
3.6 gives:

100-10
% C = = 50% of total solids
1.8

Letx be kg dry weight of rice straw needed to be mixed with 1 kg dry weight
of septic tank sludge (or total solids)
For 1 kg dry weight of septic tank sludge, C content = 1(0.5) kg,
N content = 1(0.5) (1/15) kg.
Forx kg dry weight of rice straw, N content = x (0.2/100) kg,
C content = x(0.2/100)(80/l) kg.

Therefore C/N of the mixture is,

1(0.5) + x (0.2/100) (80/l) 30

1(0.5) (1/15) + x (0.2/100) 1

x = 5 kg
5
Volume of rice straw required = = 100 L
0.5(100 kg/1000L)

1

1 kg dry weight of septic tank sludge = = 9.09 L

0.1(1.1)

Therefore, 9.09 L septic tank sludge requires 100 L of rice straw to be mixed
to raise the C/N ratio to 30/l.

3.4.2 Particle size and structural support of compost pile

The particle size of composting materials should be as small as possible so as to
allow for efficient aeration (in case of aerobic composting) and to be easily
decomposed by the bacteria, fungi and actinomycetes. Therefore municipal solid
wastes and agricultural residues, such as aquatic weeds and straws, should be
shredded into small pieces prior to being composted. Nightsoil, sludge, and
animal manure usually contain fine solid particles suitable for microbial
decomposition. However, other materials such as organic amendments and/or