Scientific support for the design and operation of VIPS

Funded by: Water Research Commission
2005 - 2008

Partner organisations: Partners in Development, eThekwini Water and Sanitation

Project description
Ventilated improved pit latrines (VIP) are an accepted basic sanitation delivery option and are the regulated minimum acceptable level of sanitation in South Africa. For a pit latrine to qualify as a VIP, it must comply with certain requirements; it must
  1. provide hygienic separation of human waste from contact with people, 
  2. have a vent pipe fitted with a fly-screen to minimize odor and flies; 
  3. be built on a secure slab that will resist collapse of the superstructure; and 
  4. provide privacy and dignity for the user.
The basic processes occurring in a VIP are filling (with faecal, water and other material), water transfer into and out of the pit, biological transformation and pathogen deactivation. In general, the rate of filling of the pits as a function of local conditions is not well known; neither is there a good understanding (at least at a policy-making level) of what the condition of the material in the pits will be when the pits become full.

In principle the rate of degradation or leaching of the material in a pit should be similar to the rate of filling thus providing a long service life for the pit. In practice, it is often observed that pits may fill rapidly, particularly if a significant portion of the material added to the pit is non-degradable. Management of full pits pose a number of complex challenges to policy-makers, local authorities and householders since households or communities with full pits are no better off than those with no sanitation at all.

One of the solutions proposed for management/disposal of pit latrine sludges are a range of commercial products hereafter referred to as pit latrine additives. These may be chemical, microbiological or enzymatic in nature and are marketed on their ability to reduce (or even reverse) the accumulation rate in pit latrines, and reduce potential fly or smell problems. Independent scientific investigations into their efficacy are limited and ambiguous, although there is anecdotal evidence that suggests that they have the ability to significantly reduce the mass or volume of pit contents, fly and odour problems. Equally, a number of informal studies have suggested that there is no significant benefit to the use of these additives over the addition of water or some essentially inert additive (in effect, a placebo). In many instances, municipalities and other service providers are hesitant to sanction the use of pit latrine additives as they have no scientific basis for choosing one product over another, and are concerned that trials with these products may lead to an expectation among communities that the products will be used forthwith. This in turn could lead to a situation where political pressure results in the application of expensive products that may or may not have any significant benefit. It is generally felt that a scientific explanation of the mechanism of pit latrine additives, and proof of their efficacy would provide the authorities with the ability to rationally assess the cost-effectiveness of implementing programmes for treating pits with commercial pit latrine additive products.

This project proposed to undertake field and laboratory investigations of VIPs and their contents in and around the eThekwini Municipal area in order to understand the conditions found in the pits and to propose design and operating practice that will extend the life of pits. The study concentrate on three main areas of interest:
  • Water balance in pits under different hydro-geological conditions (water draining into the pit, water draining out of the pit, no water transfer in or out of the pit)
  • Stabilisation rates in pits (organic, pathogens)
  • Efficacy and action of additives on pit processes