need for less synthetic fertilizer. Compost increases the efficiency of fertilizers by reducing
runoff and making the fertilizer more available to the plants over a longer period (the
compost molecularly binds to the fertilizer and holds it ready for plant use). In addition
to horticultural and agricultural uses, compost would be an excellent product for application
to eroded lands in China (for example areas near Beijing which have been degraded
and cause much of the annual dust storms) as well as to arid lands.
A significant driver for composting could be carbon emission reductions (see Section
6). Composting avoids the formation of methane since the organic fraction aerobically
biodegrades and hence no methane is generated. At today’s prices for internationally
traded emission reductions of $4.50 per tonne of ER (under the Clean Development
Mechanism emerging from the Kyoto Protocol) composting would receive an international
subsidy of about $12 per tonne. This is about 2.5 times the equivalent amount that
would likely accrue from landfill gas recovery.
Large scale composting is assisted through the establishment and enforcement of quality
standards. Table 5.1 proposes compost standards for China that would encourage
broader market development and are attainable with the use of source segregated organics.
The main aspect required through the standards is the level of heavy metals. Other
compost characteristics, such as pathogens, maturity, larger contaminants like plastic and
glass, salinity and the C:N ratio are generally dictated by the market and the compost
process used. The standards proposed in Table 5.1 are for finished compost that would
have no restrictions on use (leaving it to the market to find the optimum use). There may
be occasions where specific compost of inferior quality might be used for limited applications
such as mine tailings rehabilitation and pits and quarries restoration.
Some cities have pursued anaerobic digestion (biodegradation in the absence of oxygen)
of the organic fraction of the waste stream. Anaerobic digestion generates methane
that can be burned to produce power. More research is needed in this area as the costs are
usually higher than composting and generally more sophisticated process controls are
required.