106 Organic waste recycling: technology and management
(1/0.1)(90) + (5/0.5) (50) 14
= (100) = 70%
(1/0.1) + (5/0.5) 20
Or the compost feed solids are = 30%.From Equation 3.13,(Sm/Sc-1) (0.4/0.3) - 1
Rd = = = 0.67
(1-Sm/Sr) 1 – (0.4/0.8)
From Equation 3.11,Sm- Sc 0.4 - 0.3
Rw = = = 0.25
Sr - Sm 0.8-0.4
Also from Figure 3.6, at Sr = 0.8 and the compost feed solids of 30%, the
value of Rd = 0.7; and from Figure 3.5, Rw = 0.25.
Therefore, for composting 6 kg dry weight of the mixture of septic tank
sludge and rice straw, the quantity of compost recycle is
6 x 0.67 = 4 kg dry weight or 20 x 0.25 = 5 kg wet weight, in order to
achieve a 40% solids content of the compost mixture.
3.4.4 Aeration requirements
Aerobic composting needs proper aeration to provide sufficient oxygen for the
aerobic microbes to stabilize the organic wastes. This is accomplished through
some non-mechanical means such as periodic turning of the compost piles,
insertion of perforated bamboo poles into the compost piles, or dropping of
compost heaps from floor to floor. A more effective, mechanical way is the
forced-air aeration in which air is pumped through perforated pipes and orifices
into the compost heaps.
Because non-mechanical aeration cannot supply sufficient oxygen to the
microorganisms, aerobic conditions prevail only at the outer surface of the
compost heaps, while facultative or anaerobic conditions exist inside. The
composting rate is accordingly slow and requiring a longer composting period.