Composting 111An experienced compost operator can, most of the time, recognize the
maturity of a composted product. However, it is advisable that the quality of the
composted products be regularly checked for the nutrient contents and presence
of any pathogenic microorganisms. Chemical fertilizers can be added to a
composted product to make it suitable for applying to a particular crop,
according to its nutrient requirement (see Table 8.7).
Details about the composting systems of both batch and continuous operation
are given in section 3.6.
3.6 Composting systems and design criteria
In this section the composting systems will be described as the on-site and off-
site processes. On-site systems are the ones that compost organic wastes at the
places of generation, e.g., at home or in the toilets; the composting process is
usually not controlled and occur naturally. Off-site systems involve the
collection and transportation of organic wastes to be composted at central
treatment plants; the composting process is usually controlled either manually or
mechanically. Nowadays, there are many manufacturers producing various
composting units for the treatment of nightsoil, sludge, or municipal refuse;
some of these units will be described herein.
3.6.1 On-site composting
Aerobic composting toilets
These types of composting toilets, often referred to as the ‘multrum’, were
originally invented by Lindstrom and put into commercial production about 20
years ago (Rybczynski et al. 1978). The multrum (Figure 3.7) consists of a
water-tight container with a sloping bottom. Human excreta (without flushing
water) is introduced at the upper end of the container, and mixed with organic
kitchen and garden wastes, introduced lower down, to increase the C/N ratio.
Air ducts and a vent pipe are provided to promote aeration. The composted
material moves toward the lower end and from where it is periodically removed.
The decomposition period is long, up to 4 years, and the container is quite large
(3 x 1 x 1 m: length x width x height). The air ducts also help to evaporate the
humidity and eliminate odors, while the sloping bottom permits continuous use
of a single container by separating the fresh and the decomposed materials.
Another modification of the multrum is the biopit composting toilet (Figure 3.8)
which incorporates a gravel soakage pit to treat and dispose of the liquid waste
present in the excreta.