and the Efficacy of Pit Latrine Additives - Water Research Commission

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1 INTRODUCTION Ventilated improved pit latrines (VIP) are an accepted basic sanitation delivery option and are the regulated minimum acceptable level of sanitation in South Africa. These systems are being installed without a quantitative scientific knowledge of their operation under South African conditions. 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 (Figure 1.1). Management of full pits poses 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. Figure 1.1: Photograph of a poorly maintained, overflowing pit latrine, filled with non-biodegradable material. One of the solutions proposed for management/disposal of pit latrine sludge is the use of 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 a vast body of anecdotal evidence that suggests that they have the ability to significantly reduce 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 1
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 additives. 1.1 Construction of a VIP For a pit latrine to qualify as a VIP, it must comply with certain requirements; it must (i) provide hygienic separation of human waste from contact with people, (ii) have a vent pipe fitted with a fly-screen to minimise odour and flies; (iii) be built on a secure slab that will resist collapse of the superstructure; and (iv) provide privacy and dignity for the user. Fly-screen Vent pipe Superstructure Pedestal with lid Door Slab Collar Pit Figure 1.2: Basic structure of a VIP A typical VIP consists of the following basic features (Figure 1.2): Pit, collar, slab, superstructure with a closing door, vent pipe with fly-screen and a pedestal with a lid. 1.1.1 The pit The pit allows for the collection of faeces and anal cleansing material, which may then undergo a degree of stabilisation through natural biological processes. The pit may be either a single pit or an alternating twin pit lined with open-joint brickwork or block work. The lining prevents the walls of the pit from collapsing during emptying operations or during heavy rains, while the open vertical joints allow liquid to soak out of the pit into the surrounding soil (Mara, 1984). The pit can be circular or rectangular (Bester and Austen, 2000) and may be built up above the surrounding ground to provide extra depth if the pit is located in an area with shallow bedrock (Bester and Austen, 2000). 1.1.2 Cover slab This is usually made up of reinforced concrete which covers the pit and has two holes; one for the pedestal, and one for the vent pipe (Mara, 1984). The cover slab serves to support the superstructure and the vent 2
Page 1 and 2: Scientific Support for the Design a
Page 3 and 4: Obtainable from Water Research Comm
Page 6 and 7: EXECUTIVE SUMMARY 1 Introduction Ve
Page 8 and 9: A number of studies in which pit la
Page 10 and 11: in this study were undertaken on pi
Page 12 and 13: from samples were considerable lowe
Page 14: ACKNOWLEDGMENTS This report was com
Page 17 and 18: 3.5 Effect of additional moisture a
Page 19 and 20: LIST OF FIGURES Figure 1.1: Photogr
Page 24 and 25: pipe and also prevent the exposure
Page 26 and 27: 2 REVIEW OF EXISTING KNOWLEDGE ON T
Page 28 and 29: 2.1.2 Overview of aerobic degradati
Page 30: faeces entering in the prescribed f
Page 33 and 34: occur in the absence of oxygen, tak
Page 35 and 36: (a) (b) Figure 3.2: (a) photograph
Page 37 and 38: Aerobic degradation: In the presenc
Page 39 and 40: This section presents data from stu
Page 41 and 42: A practical definition was used to
Page 43 and 44: excess water ingress (e.g. due to h
Page 45 and 46: 3.4.4.1 Summary of results obtained
Page 47 and 48: A homogenous sample was collected f
Page 49 and 50: of this work is that a pit emptier
Page 51 and 52: esults from Study B indicate that b
Page 53 and 54: 300 T3 - faeces + inoculum + Gas pr
Page 55 and 56: the variation observed in the data
Page 57 and 58: conditions. The gas production rate
Page 59 and 60: conditions. Some additives in this
Page 61 and 62: their ability to metabolise mixed o
Page 63 and 64: Table 4.3: Results of field pit add
Page 65 and 66: change in actual volume of pit cont
Page 67 and 68: inwards leaving the pits and their
Page 69 and 70: 4.4 Laboratory-scale testing of pit
Page 71 and 72:
Anaerobic units were closed, limiti
Page 73 and 74:
The average rate of mass loss in ae
Page 75 and 76:
Further, the moisture loss may in f
Page 77 and 78:
These results confirm the findings
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In a programme of pit latrine empty
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The new understanding of processes
Page 83 and 84:
5.4.1.1 Performance of standard VIP
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A further observation was that pede
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5.5.4 Maintenance It was observed t
Page 89 and 90:
This study has not elucidated the m
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REFERENCES APHA, ed. (1998). Standa
Page 94 and 95:
APPENDIX A: PHOTOGRAPHIC DIARY This
Page 96 and 97:
Walls of pit during emptying. This
Page 98 and 99:
Workers engaged in spraying solids
Page 100 and 101:
APPENDIX B: STUDY INTO EFFECT OF MO
Page 102 and 103:
2.2 Gas production from each experi
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NaHCO 3 improved the rate of gas pr
Page 106 and 107:
moisture have a beneficial effect o
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Complete chemical characterisation
Page 110:
Finally, it may also be concluded t
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APPENDIX D: PROTOCOL FOR TESTING PI
Page 116:
4.2 Chemical analyses In addition t
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