Environmental Management: Principles and practice

Agricultural wastes
These include: animal dung and urine; silage effluent; cereal straw and other crop
residue. Agricultural waste problems can be countered by:
♦
quotas—limits on quantities a farm may produce;

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CHAPTER ELEVEN
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♦
incineration or composting (discussed earlier), ideally linked to electricity or
district heating or used to reduce use of chemical fertilizers.
♦
set-aside—withdrawal of land from production A risk is that remaining
agricultural land will be more intensively used.
Livestock wastes
In Europe and the USA livestock waste has become a major problem because farms
have increased in size and arable and livestock production have tended to be separated
spatially. Livestock waste is a major cause of nitrate pollution of ground and surface
waters in Europe, North America and some other parts of the world. The dependence
of developed country livestock producers on imported feed should be noted. Forest
clearance and land degradation in some developing countries may, at least in part, be
driven by the market for feedstuffs like soya and cassava.
Manure, once a resource used to sustain cropping and pasture, is now often a
problem. A UK farm of 40 ha with just 50 cows and 50 pigs can present waste
disposal problems equivalent to a town of nearly 1,000 people. UK livestock produce
2.5 times the total human sewage; in the USA about ten times (Conway and Pretty,
1991: 276). In 1993 The Netherlands had a ca. 40 million tonne manure mountain—
more than twice that which could be safely disposed of onto all the farmland.
Consequently The Netherlands (and Denmark) have established waste processing
plants (some contributing to district heating or greenhouse heating) and some manure
is returned to farmland or sold in composted form to gardeners.
Stored in pits or lagoons, livestock waste generates methane, ammonia and
hydrogen sulphide, which cause nuisance smells, damage vegetation downwind
(because of the ammonia) and act as greenhouse gases. If slurry escapes, as it often
does, it can cause serious stream, lake or groundwater pollution (through chemical
oxygen demand—COD, biological oxygen demand—BOD, harmful bacteria and
parasites, excreted antibiotics or growth-promoting hormones, steroids and sometimes
heavy metals—especially copper and zink added as growth accelerators to pig feed).
Disposal by spraying onto farmland is impractical as it may transmit diseases, and
the heavy metals from feedstuffs can concentrate in the soil, and nitrates and
phosphates leach to contaminate surface and groundwaters—de-watering, composting
or incineration are needed.
Silage effluent
Silage has become popular in Europe over about the last 25 years as livestock feed.
When it is made moisture is released, the amount depending upon how dry the grass
or other crop was on collection and on the mode of production. It is common for 330
litres of effluent to be formed for each tonne of silage made. This means farmers
must store and dispose of large quantities of acidic (often pH 3.4) effluent. Escapes
damage soil, aquatic life and groundwater. Stored in lagoons or pits, the effluent
gives off ammonia and hydrogen sulphide, both active as greenhouse gases. The
solution may have to be de-watering and incineration or composting.

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POLLUTION AND WASTE MANAGEMENT
231
Straw and crop residue
Around the world farmers burn off coarse vegetation to encourage new growth or to
clear land for cultivation. Cereal straw burning has been a problem in Europe for
some years until recently when legislation began to curb it. In Brazil, Mauritius,
parts of Australia and the Caribbean sugar fields are burnt before harvesting. Crop
residue burning helps control weeds and pests but also destroys harmless or useful
wildlife, damages soil, causes accidents through smoke affecting visibility, and
generates soot and greenhouse gases. Modern cereal straw may not be as strong as in
the past (because of rapid growth due to fertilizer use), and thus less useful for
thatching, but there is still potential for manufacturing strawboard, paper, cardboard,
or for on-farm or district heating. The problem has been the cost of collection and
transport.
Brush clearance
Clearing land for agriculture is often done with fire, which each year generates vast
amounts of soot and greenhouse gases, damages soil and kills wildlife. The problem
has recently got seriously out of control in South East Asia, northwestern Amazonia,
and Venezuela and Mexico. In Europe, Australia and the USA fires are more likely
to be accidental or set by arsonists, rather than be intended for agricultural clearance.
In some situations regular brush burning may be vital as part of land management to
prevent occasional serious fires.
Agricultural products processing waste
Processing rubber, sugar, meat, fish, coca (for cocaine) and many other products
generates effluent. In West Malaysia and Sabah palm-oil processing takes place in
local factories, to ensure that treatment takes place without delay to get a high-quality
product. Consequently few major streams have escaped pollution in spite of legislation
since the late 1970s. In Brazil the processing of sugar, cassava and yams to produce
alcohol for automobiles results in about 13 litres of high-BOD effluent for each litre
of fuel produced; rivers, especially in the northeast, have suffered.
Crop processing often demands fuelwood and large areas can be deforested
for tobacco curing, tea drying, and preparing many other crops. Leather tanning
with oak bark, wattle bark or other natural compounds produces acidic, high-BOD
effluent, smell and nuisance from flies. Toxic chemicals are increasingly adopted for
tanning: some contain chromium or mercury, and can cause damage to aquatic ecology
and contaminate groundwater.