Sanitation and Vector Control - Biological and Environmental Control of Disease Vectors - page 155

diethylcarbamazine (DEC). Over a 5 year period,
a progressive decline was observed in micro-
fi larial rate from 49% to 3%. A nearby town,
where people had only been treated with DEC,
showed a progressive increase in microfi larial
rate over a 3-6 year period, suggesting the large
impact on vector control by using the polystyrene
beads (Maxwell et al ., 1999). Although the
authors cautioned that the costs of reducing the
mosquito population by 65% might not be of set
by its impact on fi lariasis, the reduction of
nuisance mosquitoes resulted in widespread
support for the programme.
The polystyrene beads are therefore an
ef ective way to reduce mosquito populations in
wet-pit latrines, cesspits and septic tanks. For
ease of transport, the beads are not expanded
until just before being applied. This is done by
boiling them for 5 min in a sui ciently large
vessel while the mixture is frequently stirred,
during which they expand 30-fold (Sivagnaname
et al ., 2005). The ease of application makes them
a suitable intervention. Beads are non-
biodegradable and this, together with the
suggested high implementation cost, could be a
serious drawback of the intervention. Every pit
latrine will eventually fi ll up and may need to be
emptied. If the collected sludge needs to be
treated at a local waste treatment plant, it will be
impossible to separate beads from sludge before
they enter the treatment plant with conventional
treatment technology, hence they will most
probably end up polluting the environment.
The use of oil in wet-pit latrines has been
implemented based on similar objectives as the
polystyrene beads, but was found to be of a
limited ef ect as the layers never completely
sealed and rapidly deteriorated due to bacterial
activity within the pit (Curtis, 1994).
The placement of a mosquito trap on the
squat hole was found to be ef ective and well
accepted by the users of the facilities in a short-
term experiment (Curtis, 1994). However, no
study so far has investigated the long-term
acceptability of using a mosquito trap on the
squat hole. A possible future approach is the
application of coated material or paint products
containing organophosphates to reduce the
survival of fl ies, cockroaches and mosquitoes in
the domestic environment and in latrines
(Mosqueira et al ., 2010). The slab or the wall of
the latrine could be treated with insecticidal paint

containing organophosphates or pyrethroids
that reduce the lifespan or increase mortality of
adult mosquitoes.

8.3.3 Off-site sanitation

Water-borne sewerage

Water-borne sewerage represents the top rung
of the sanitation ladder, and is the form of
sanitation most users aspire to. It is convenient,
situated within the household, does not require
emptying, and disposes waste with a single fl ush
never to be seen, or smelt, again. However,
water-borne sewerage requires major
investments in infrastructure, a minimum water
use of 60 l per capita per day, a good solid waste
collection system and responsible users. The
absence of a reliable solid waste collection
system will result in solid waste being fl ushed
through the toilet, causing obstructions and
blockages of the sewer pipes and drains. The
fl ow within sewerage systems is determined by
gravity and a minimum amount of water needs
to be used by each household in order for the
system to function properly. Thus, water-borne
sewerage systems are constructed only in those
areas where households have a reliable piped
water system with household connection.
Sewerage systems in low-income countries are
therefore usually found only in the better-of
neighbourhoods and in areas of economic
importance.
All the wastewater produced by the
household, and often also storm water from the
same neighbourhood, is collected by sewerage
systems and transported through an intricate
network from the household connections via
street, main and collector drains to a wastewater
treatment plant, or to the sea, river or another
surface water-body. Depending on income levels,
some sewerage systems might still have open
drains to collected sewerage at the household or
street level. Sewer pipes and drains are connected
to each other and, at regular intervals, manholes
are inserted along sewerage lines to allow
inspection for maintenance and cleaning.
The quality of wastewater within a water-
borne sewerage system will depend on the
amount of water used per capita per day and the
amount of rainfall discharged per day by the