ENVIRONMENT AND ENERGY
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in wastewater treatment plants where biological reactors are
engineered to boost biochemical degradation under carefully
controlled conditions, therefore enhancing the removal of
pollutants and the stabilisation of sludge. The processes taking
place in the bioreactors can be aerobic or anaerobic. The former
often needs more energy in order to maintain the aerobic
conditions inside the reactor, and the organic waste is converted
into biomass (sludge) and carbon dioxide (CO 2 ). However, it
prevents the formation of methane (CH4), which has a greater
climate warming potential than CO 2 (Cakir and Stenstrom, 2005).
Anaerobic treatment processes generally require less energy and
have a lower sludge production and generates CH4, but this can
be captured and used as an energy source. Physical, chemical
and biological processes are combined to achieve different
‘levels’ of wastewater: preliminary, primary, secondary, tertiary
and quaternary.
The selection of the most appropriate technologies depends on
the kind of components, pollution load, anticipated use of the
treated wastewater, and economic affordability. Table 2 provides
some examples of technologies, the kind of wastewater they are
generally used for, and their advantages and disadvantages.
One of the by-products of wastewater treatment is sewage sludge.
The sludge generated is rich in nutrients and organic matter,
which gives it considerable potential for use as a soil conditioner
and fertiliser. In many cases, however, the beneficial value of
sewage sludge is not realised because of concerns regarding the
pathogens, heavy metals, and other compounds it may contain.
Other useful by-products from wastewater include biogas (that is,
CH4) and heat, which can be recovered for beneficial use either in
the treatment plant or in the adjacent community.
The actual management and operation of wastewater treatment
systems is a complex activity that can benefit from a risk
assessment approach that evaluates the chain of components
that together make up the system. Such assessments can
help ensure their proper functioning under expected levels of
efficiency, and highlight weak links in the chain that could cause
health and safety issues.
DATA AND INFORMATION NEEDS
Data on wastewater collection and treatment are sparse,
particularly (but not only) in developing countries. Only 55 out
of 181 analysed countries had reliable statistical information on
generation, treatment, and use of wastewater; 69 countries had
data on one or two aspects; and 57 countries had no information
at all.
Moreover, data from approximately two-thirds (63%) of the
countries were over five years old. The key challenge with data
collection relates to the need of generating data at the national
level that it is sufficiently detailed, consistent, and comparable with
other countries. PA
January 2018 Volume 23 I Number 11
January 2018 Volume 23 I Number 11