Environmental Management: Principles and practice

Pollution and waste associated with urbanization
The term ‘urban’ broadly means ‘the concentration of people in cities and towns’.
Some urbanized areas are the most altered, unhealthy and contaminated of Earth’s
environments. Cities affect other, often distant environments, and rapid urban
expansion, especially in poor countries, often stresses services and infrastructure to
the point of breakdown. Many cities, even in developed nations, have dangerous
levels of atmospheric pollution, and sewage and waste pose problems.
Heat-island effect
Built-up land has a different albedo, heat storage characteristics, and roughness than
non-urban, and there may also be considerable waste heat from homes and industry—
these combine to cause a heat-island effect. This means that city areas are warmer
than their surroundings, causing local airflows that may recycle pollution.
Urban sprawl
Spreading cities destroy farmland, biodiversity and amenity areas. Between 1958
and 1974 the USA lost an estimated 5.1 million ha to urbanization and transport land
use. The FAO estimated that world-wide between 1980 and 2000 about 1,400 million
ha of arable land would be lost through urban sprawl (WRI, IIED, UNEP, 1988:42).
Most cities have considerable areas of derelict land which could be used to reduce
demand for new land, but to decontaminate and rehabilitate it for settlement can be
costly, although it can be relatively cheaply converted to amenity areas by tree planting
and landscaping (which reduces the heat-island effect).
Urban storm run-off
Drains and sewers speed up run-off of sewage, silty and contaminated storm water
from cities. Leaking sewerage contaminates groundwater beneath a city—London
has such a problem, which means that it cannot be exploited and alternative supplies
must be taken from surrounding areas, reducing streamflow (‘sewerage’ refers to
the infrastructure/pipework concerned with conveying sewage).

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POLLUTION AND WASTE MANAGEMENT
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Sewage
Before the late nineteenth century sewage was only a problem in urban areas, which
depended on cess-pits, latrines, street collection by nightsoil carts, or open-channel
sewerage systems that emptied without treatment. Cities in Europe and North America
began to install water-borne sewage disposal systems in the 1850s, following rising
incidence of faecal-oral diseases and smell.
Urbanization shifted sewage management from reclamation to disposal, from
resource use to resource waste. Some parts of the People’s Republic of China are an
exception to this trend, in that much human waste is still collected and returned to
farmland. Many of the world’s sewerage systems are becoming overtaxed by waste
disposal that consumes large amounts of water that might be used for other purposes.
Sewers in cities which grew before the 1930s are often crumbling and need costly
refurbishment. Modern sewerage design can reduce silting up, for example by
installing stepped or ovoid cross-section pipes but there are still many problems
associated with water-borne sewage disposal:
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The cost of installing, extending and maintaining sewerage.
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Failure to separate storm water, sewage and industrial waste, which makes
treatment and disposal more difficult.
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Waste of often scarce water.
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Treatment of sewage before discharge, which is seldom satisfactory.
Many of the world’s rivers, lakes and seas are so polluted that they pose a
health risk and have begun to affect adversely the tourist trade and wildlife. Where
long sea-outfalls were once satisfactory, population increase and anti-discharge
regulations mean raising treatment costs a great deal. More appropriate alternatives
to established water-transported sewage disposal should get more attention
(composting latrines, etc.).
Most sewage treatment generates phosphate and sludge contaminated with
pathogens and often rich in toxic heavy metals. In the past this was sent to landfill
sites, spread on agricultural land or dumped out at sea. The last option has been outlawed
in the USA since 1993, and will be illegal in the EU from late 1998. In Europe and the
Americas sludge is increasingly pumped onto farmland. In the USA and Europe
treatment reduces the pathogen content, but in the UK about 25 per cent (in 1998) was
disposed of as raw, untreated sludge—mainly onto farmland (and is unlikely to be
reduced in the immediate future). Disposal of raw sewage sludge onto farmland risks
contaminating agricultural produce, groundwater, streams and ultimately, perhaps,
domestic water supplies with problem micro-organisms like Cryptosporidium or
especially harmful strains of Escherichia coli. These disposal options are increasingly
outlawed, which leaves high-temperature incineration as the only viable option. Europe
and the USA increasingly de-water sewage and incinerate the solids.
Village- or household-scale biogas production can offer safe, cost-effective
sewage disposal and also supply gas-fuelled heating, cooking and lighting.
Unfortunately, even cheap systems may be too costly for very poor communities and

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there needs to be an optimum mix of sewage and farm or household waste, which is
not always to be found.
There are a number of ‘waterless’ sewage disposal systems: low-volume water
flush to septic tank, earth-fill latrines, household or village composting toilets, electric
incineration and chemical digestion toilets (from which safe waste can be periodically
removed and spread on the land or safely disposed of in some other way). Septic
tanks (limited sewerage systems) are widely used and are effective provided the soil
and groundwater conditions are suited and the operation and regular solids removal
and treatment are well supervised. At the village, large farm or small town scale
composting sewage mixed with agricultural waste like straw may prove an effective
method of disposal, yielding a safe, useful end-product.