Composting 143
3.6 A sludge contains 70% of volatile portion (dry weight basis) and 60%
of this volatile portion is biodegradable. The chemical composition of
the volatile portion is C 10 H 19 O 2 N. Calculate the weight and volume of
air required to oxidize 1 kg of the sludge. Assume that the nitrogen is
first converted to ammonia (NH 3 ) and then to nitrate (NO 3 - ). Air
contains 23% O 2 by weight with a specific weight of 1.2 kg/m^3 at 25°C
and 1 atmospheric pressure.
3.7 Compare the advantages and disadvantages of aerobic composting and
anaerobic composting?
3.8 What measures should be taken in using the composted products as soil
conditioner or fertilizer in order to minimize the health risk?
3.9 The Bangkok city, Thailand, produces 200 tons (wet weight) of septage
daily. This septage, whose C/N ratio is 15/1, contains 10% total solid
(TS), volatile solids (VS) are 90% of TS, and the bulk density is 1.1 kg
(wet weight)/L.
Sawdust is to be mixed with the above septage to adjust the mixture
C/N ratio to be 30/1 before composting. Characteristics of saw dust are
C/N ratio = 70/1, moisture content = 40%, N content = 0.1% (of dry
weight), and the bulk density is 0.1 kg (wet weight)/L
a) Determine the amount of saw dust, in m^3 /day, needed to be mixed
with the Bangkok septage to adjust the C/N ratio to be 30/1, and the
corresponding moisture content of the mixture.
b) Suppose windrow composting is to be employed to compost the
mixture in (a) and the composting periods for first-stage composting
and maturation are 5 and 10 days, respectively.Determine the dimension (length × width × depth) of the windrow
composting pile(s). Also suggest suitable operation procedures to
achieve optimum composting efficiency. (Note: 1 ton = 1000 kg)3.10 A municipality in Vietnam plans to employ a continuous compost
reactor to stabilize its garbage and to produce compost fertilizer for use
in public parks. The garbage characteristics are as follows:
Total wet weight (TWW) = 2,000 kg/day
Bulk density = 1.2 kg/L