Sewage additives do not extend pit latrine life

Pit latrine additives claim to slow the filling rate of pit toilets, but scientific studies refute this claim, says the WRC.

The Water Research Commission (WRC) concluded that pit additives have no significant effect on pit filling rates. Studies by Partners in Development and Pollution Research Group at the University of Kwa-Zulu Natal, funded by the WRC, tested 20 different pit toilet additives.

“None of the 20 tested products were found to have a statistically significant effect on degradation of sewage sludge, while 20% of South African municipalities buy additives as part of their sanitation management programme,” says Jay Bhagwan, WRC director, who managed the study.

“A typical additive treatment costs R25 per month per pit. Multiplied by tens of thousands of pits, this represents a great deal of fruitless cost”.

Mechanical or manual emptying typically costs between R500 and R1 500, and is required every five 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.

Additives were tested on samples of VIP (Ventilated Improved Latrine) sludges. Samples were taken from the surface of the pit beneath the pit pedestal and placed in 300 mℓ jars.

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.

Test 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 additives were used, and those where they were not used.

Sewage components and volumes

Every person produces between 0.12 and 0.40 litres of faeces and 0.6 and 1.5 litres of urine per day. This amounts to 110 litres of faeces, about 30% of which is bacteria, and 440 litres of urine per person per year.

Sewage breakdown process

Added to this volume is cleansing material like toilet paper or newspaper. As material accumulates, micro-organisms from sewage sludge and soil multiply and begin to break the sludge down into gases, liquids and inorganic matter.

Gases escape from the pit into the air and liquid leaches into 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) micro-organisms which use aerobic processes multiply rapidly, increasing their mass from 30% of fresh sludge to 65%.

Sewage residues volumes

They break down sludge quickly, converting about 75% of 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 original mass, unable to leave the pit.

Bhagwan explains that there is no standard for testing additives and South Africa does not yet have an independent standards body for testing additives. Product claims are not verified.

An independent standards board or laboratory test protocol is needed to assess sewage additives, and advise on conditions required for optimal effect from additives.

Legislation is also needed to prevent sellers of pit additives from making unsubstantiated claims about their products.

PHOTO; A typical ventilated pit (VIP) latrine, where expensive biological breakdown, or bio-remediation additives are used without benefit.

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