October 2007
The WRC operates in terms of the Water
Research Act (Act 34 of 1971) and its mandate
is to support water research and development
POLICY Brief
as well as the building of a sustainable water
research capacity in South Africa.
Sanitation
Management of full pits poses complex challenges for users, local authorities
and policy-makers. Households with full, unusable pits are no better off
than those with no sanitation at all. The addition of commercial bacterial or
enzyme-additives has been promoted has a valuable option for enhancing
biological degradation of pit contents and extending the life of a VIP toilet.
The results of rigorous laboratory testing suggest that expenditure on
commercial additives should be approached with caution. The research
indicates that they offer no proven benefit in many situations.
Investigating the efficacy
of pit latrine additives
Biological degradation of
pit contents
These reactions only occur under certain conditions,
Human waste (faeces and urine) in a ventilated improved
necessary physical and chemical conditions are not met,
with the appropriate mix of temperature, water content,
pH, energy sources and nutrient co-factors.
the bacteria die back or go into a dormant state. Under
pit (VIP) toilet is a complex mixture of organic compounds,
bacteria and pathogens.
If the
these conditions, the pit will fill rapidly and foul-smelling
These compounds can be
by-products accumulate. Once full, the pit will need to
broken down by a complex combination of biological
be emptied or replaced.
and chemical reactions.
Feasibility of enhanced
biological degradation?
In physical terms, the masses of mixed bacterial
populations ‘feed’ on the waste, multiply, and thereby
decrease the amount of waste in the pit. (Materials such
as plastic, bottles or cans break down so slowly that they
It has been suggested that the addition of various
should be regarded as inert solid waste.)
combinations of chemicals, enzymes and bacteria to a
VIP can enhance the biological degradation of the pit
In ideal conditions, the by-products of these micro-
contents. A range of such compounds have been tested
biological reactions are gases (e.g. carbon dioxide and
by the Pollution Research Group at the University of
methane) or small water-soluble molecules (e.g. simple
KwaZulu-Natal in a project commissioned by the Water
sugars and fatty acids).
Research Commission.
These can escape into the
surrounding air, enter the adjacent soil to be utilized
further by soil bacteria, or be transported into the
Enhancing the biological activity opens up possibilities
groundwater.
for managing the accumulation of pit latrine sludge
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PO L I C Y B R I E F
SANITATION
through the application of a range of commercial pit
Research into the efficacy and action of additives on
latrine additives. These additives may be chemical,
pit latrine contents is ongoing. The research to date
microbiological or enzymatic in nature, and are marketed
indicates that -
on the basis of their ability to reduce, or even reverse, the
sludge accumulation rate in pit latrines. They are also
n
said to reduce potential fly and odour problems.
Pit latrine additives do not appear to have any effect
on pit latrine sludge under anaerobic conditions.
n
Pit latrine additive studies must be carefully designed
Anecdotal evidence suggests that they may well be
to distinguish between the effects of natural
effective, although independent scientific evidence of
(unenhanced) biological activity, the method of
their efficacy is scarce.
treatment (i.e. adding water or stirring the waste)
and the effect of the additives themselves on pit.
Conversely, a number of informal studies have suggested
n
There is a political and societal argument for field
that these additives perform no better than a placebo,
trials of pit latrine additives; however, these fields
such as plain water or an inert additive.
trials must be designed carefully to separate out
the effects of additives from other factors, through
Testing the efficacy of
commercial additives
the implementation of appropriate control and
reference experiments.
n
Reliable methods of assessing changes in pit
The biggest difficulty when testing commercial pit latrine
volumes must be developed to measure the effect
additives lies in creating a controlled environment. Field
of the treatments on pit latrines. Simple height
trials are subject to so many uncontrolled variables that
measurements have been found to be subjective
it would be prohibitively expensive to implement a full
and do not provide an accurate measure of the
volume changes in the pit.
scale trial that produced statistically significant and
n
scientifically defensible results.
Before pit latrine additives are implemented widely
as part of a pit management strategy, economic
A protocol was developed for testing the efficacy and
factors should be considered. In many instances,
functioning of commercial pit latrine additives in the
the cost of emptying a pit every 5 years may be
laboratory. It ensures test conditions that are consistent,
substantially less then regular treatment with a pit
controllable and replicable, and conform as closely as
latrine additive.
possible to conditions in a working pit latrine.
The results of this study suggest that expenditure
Findings
on bacterial or enzyme-based additives should be
Using this protocol, a range of pit latrine additives was
they are not a universal solution to full pits, as they offer
approached with caution. The research indicates that
no proven benefit in many situations.
tested. Under the conditions tested, the results indicate
that these additives do not correct the physical and
chemical conditions sufficiently to enhance biological
activity to any significantly extent.
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POLIC Y B R I E F
SANITATION