WRC study proves that pit additives are not effective
There are currently dozens of pit additives being marketed in South Africa with claims that they will prevent pit toilets from filling up, or will at least reduce the rate at which they fill. Findings from studies by the Water Research Commission (WRC) concluded that pit additives have no significant effect on pit filling rates. Studies undertaken by Partners in Development and the Pollution Research Group at the University of Kwa-Zulu Natal, with funding from the WRC tested 20 different pit additives currently on the market in South Africa and none of these products have been found to have a statistically significant effect on the degradation of sludge.
“A fifth of South African municipalities indicate that they purchase additives as part of their sanitation management programme” says Mr Jay Bhagwan, WRC Director, who managed the study. “A typical additive treatment costs in the region of R20-30/month per pit. Multiplied by tens of thousands of pits, this represents a great deal of fruitless expenditure”.
Mechanical or manual emptying typically costs between R500 and R1 500, and is required every 5 to 10 years. Alternative designs such as movable pre-cast top structures or toilets designed to work with alternating pits are effective methods to make the operation and maintenance of basic sanitation more sustainable.
In controlled laboratory experiments developed during research, additives were tested on samples of VIP (Ventilated Improved Latrine) sludges. The samples were taken from the surface of the pit beneath the pit pedestal and placed in 300 mℓ jars. The samples were dosed at the rate indicated by the manufacturer, with tests performed in three or five replicates for each additive and two control treatments: one in which only water was added, and one in which nothing was added. The jars were incubated for 30 days at approximately constant temperature and the mass of each jar was recorded periodically to determine the rate of mass loss as a result of biological activity in the jar. While mass loss rates varied considerably there was no significant difference between the rate of mass loss for each of the four treatments and the controls. Four to six month long field trials on a further five products failed to find any difference in filling rates between pits where the additives were used and those where they were not.
An individual produces between 0.12 and 0.40 litres of faeces and 0.6 and 1.5 litres of urine per day. This amounts to roughly 110 litres of faeces – about 30% of which is bacteria -- and 440 litres of urine per person per year. Added to this volume is anal cleansing material – toilet paper, newspaper or other materials. What happens in a pit is that as material accumulates, micro-organisms from the sludge and the soil multiply and begin to break the sludge down into gases, liquids and inorganic matter. The gases escape from the pit into the air and liquid leaches into the surrounding soil, transporting dissolved particles with it. Where oxygen is present in the pit (usually on the sludge surface and sometimes on the sides of the pit, if the pit is not lined and there is contact with the soil) micro-organisms which use aerobic processes multiply rapidly, increasing their mass from 30% of the fresh sludge to 65%. While they break down sludge quickly, converting about 75% of the original mass to carbon dioxide, after they die some of their own biomass remains as organic unbiodegradable material which cannot break down. This represents about 10% of the original mass of the sludge, and along with the inorganic component of the sludge which has been unable to break down, remains as about 25.5% of the original mass, unable to leave the pit.
Bhagwan adds that there is no standard for testing additives and South Africa does not yet have an independent standards board for testing new additives that come on the market. This means that when a manufacturer puts a product on the market which claims to reduce pit contents, this claim has not been verified. An independent standards board with a standardised laboratory test protocol is needed in South Africa in order to assess each new pit additives that come onto the market to to determine whether it has any effect on pit contents ,how great an effect is neededin order to actually have some benefit, and what conditions are required for the product to achieve optimal effect. Legislation is also needed to prevent sellers of pit additives from making unsubstantiated claims about their products.
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