134 Organic waste recycling: technology and management
Although such epidemiological study for compost workers in developing
countries has not been reported, the health risks originating from the secondary
pathogens should be similar or even greater than those reported in U.S.A.
Therefore, skin contact with the composted materials should be avoided and
proper measures, such as wearing gloves, boots and masks, are undertaken to
prevent the inhalation of the spores of secondary pathogens, especially during
turning of compost piles. The composting processes without pile turning, such
as the BARC (Figure 3.14) and the Chinese (Figure 3.12) composting system,
should pose less health hazards to the compost workers than those with pile
turning.
3.8 Utilization of composted products
Compost has been used as: a) fertilizer, b) soil conditioner, c) feed for fish in
aquaculture, d) landfill material, e) horticultural medium on parkland,
ornamental and recreational areas and in highway right-of-ways.
Screening, grinding, or combination of similar processes should be done to
remove plastics, glass, and other materials from the compost that might be
objectionable in its use. For some uses such as land filling and land reclamation,
compost needs not be finished or processed further. For general
agriculture/aquaculture, a coarse grind is satisfactory, whereas for horticulture
and luxury gardening, the compost product must be finer. Compost to be used as
fertilizer or soil conditioner is usually mixed with chemical fertilizers to make
its nutrient contents suitable for crop growth. A schematic diagram of compost
fertilizer production process is given in Figure 3.22.
3.8.1 Utilization as fertilizer and soil conditioner
Compost can improve overall soil fertility through the addition of organic matter
and plant nutrients, and modify the soil pH. The long-term effect on soil fertility
is also important. The result is that soil erosion can be reduced, the water
retention capacity raised, the soil structure improved, and subsequently,
vegetation can be established quickly.
The utilization of composted municipal wastes as fertilizers and soil
conditioners will depend on three principal factors:
- Socio-economic considerations,
- Product quality, and
- Soil and plant responses