New Zealand and Australia generate large quantities of agricultural,
industrial, and municipal wastes. As authorities move to protect the
environment by regulating waste disposal practices, environmentally sound
methods of waste disposal are being sought. In particular, land application of
wastes as a means of disposal, nutrient re-cycling, and water conservation is
becoming increasingly popular.
This paper provides an overview of the types, quantities, and characteristics
of wastes generated in New Zealand and Australia, and highlights the problems
with current waste disposal practices, including landfilling, incineration,
and discharging into waters. This is followed by a detailed review of the
beneficial effects and adverse impacts of land application of wastes on plant
production and soil and environmental quality, and possible hazards to human
health.
The management of waste application on land is a challenging task and requires
rigorous scientific input. Sludges and euents contain significant
concentrations of plant nutrients, particularly nitrogen, phosphorus, and
organic matter. Their application on land has been shown, in many cases, to
result in significant increases in plant yields and improvements in soil
physical conditions and chemical fertility. The constraints with some wastes,
particularly those of industrial and municipal origin, are that they contain
undesirable constituents, e.g. heavy metals, toxic organics, pathogens, and
salts, or have extremely high or low pH. High concentrations of nitrate and
phosphate derived from wastes are also of concern for ground and surface water
contamination. The processes that control the fate of wastes in the soil are
complex and many of them are poorly understood, e.g. rate of release of
nutrients and other chemicals; leaching of nutrients, metals, and organics
through macropores and as suspended solids; emission of greenhouse gases;
impact of solvents, surfactants, and sludge organic matter on the sorption,
degradation, and leaching of hydrophobic organics; and the long-term
bioavailability and fate of metals and organics fixed by soil organic matter.
More research is urgently required to develop a sound understanding of waste
characteristics and the processes affecting their fate in the soil in order to
ensure that land application of wastes is safe.
Environmental Evaluation of Land-Applied Pulp Mill and Municipal Biosolids
