Human waste (excreta disposal) mechanisms

Scholarly notes for Environmental and Public Heath Learners in tertiary institutions.As recommended by Dr Tumwebaze Mathias PhD, Bishop Stuart University

1. Human waste (Excreta disposal) mechanisms Dr Tumwebaze Mathias BSU - MPH YR 11

2. Introduction Human waste (excreta) faeces & urine, contains organisms that cause disease . Safe disposal of human excreta is the primary barrier to transmission of excreta related diseases. Human faeces lead to contamination of ground water sources as well as being bleeding ground for flies and mosquitoes which cary infection.

3. Diseases spread by faeces Bacterial diseases: cholera,typhoid and bacillary dysentery. Viral diseases: Hepatitis A,poliomyelitis and viral diarrhoea . Protozoa diseases: amoebic dysentery and giardiasis . Helminth worm infestations:ascaris , hookworm, schistosomiasis and tape worm. Urine carries the infective ova of urinary bilharzias

4. Faecal oral route of excreta related diseases Fluids Flies Faeces Food Person Fingers Fields Main way of getting diseases from faeces . ( faecal oral route transmission

5. Selection criteria for excreta disposal Social political factors Social cultural Available space Ground conditions Water availability Anal cleansing materials Menstruation Time constraints Financial constraints Design life Human resource Operation and maintenance

6. Excreta disposal mechanisms Trench latrine's (shallow or deep) Bucket latrines Storage tank latrines Chemical toilets Open defecation Simple latrines VIP latrine Pour flush toilet Over hung latrine Borehole latrines Sewerage system Cat method San plat

7. Difficult conditions for simple latrine Where water table is high Where ground water source are likely to be contaminated easily Where there is hard rock Where the ground is so soft that pit walls may collapse In flooded areas

8. Options for difficult conditions Raised pit latrines Twin pit latrines Sand enveloped pit latrines Eco-San toilets (Anaerobic composting latrines) Septic tanks Aqua-privy

9. Siting latrines Not be more than 50 m away from dwelling house to be served At least 30 m away from water storage and treatment facilities At least 30m away surface water sources At least 30m horizontal distance from shallow ground water At least 50m away from communal food storage Close to hand washing facility Easily accessible to children and adults

10. VIP Latrine- standards VIP latrine is designed to minimize odour and flies A vent pipe is incorporated into the design to remove oduorous gases from pit It should be situated outside latrine interior & extend above roof by 50cm, be painted black to increase solar heating of air inside vent pipe Open end if fitted with gauze mesh /fly proof netting prevent flies entering and those leaving Inside superstructure should be dark, only a gap left above door to allow in fresh air Face the door towards prevailing wind It should declared full at 0.5m below the slab.

11. VIP Latrine

12. Mode of operation of VIP Latrine Flies are attracted to light through the vent pipe. In some VIP latrine the superstructure is not square or round but in the shape of a spiral. This spiral type of superstructure controls flies even though there is no door. Insect control: Vent pipe controls flies in VIP latrines in two ways Flies are attracted to the latrine by faecal odours . Almost all the flies will try to enter the pit via the top of the vent from which the odours emanate. The flies are prevented from entering by the fly screen.

13. Con’t operation of VIP Latrine 2. A few flies may enter through the squat hole and lay eggs in the pit. The emerging flies will try to escape in the direction of the brightest light. Will try to escape through the vent pipe but will be trapped by the vent screen. The vent pipe Diameter: should be 10cm minimum diameter Materials: Durable materials of plastic, metal, bricks, blocks and cement.

14. Cont VIP Vent pipe It traps flies, which are trying to escape through the vent pipe. Because it is screened, the flies are trapped and eventually die and fall back into the pit. Odour control: The principle of operation of a vent pipe Air movement across the top of the vent pipe i.e. wind, causes suction in the pipe which pulls air up the vent pipe, Air moving up also pulls air out of the pit. The air leaving the pit, pulls air down the squat hole into the pit a vicious cycle air suction is maintained

15. Ecological Sanitation – “ Ecosan ” A reuse cycle and closed-loop system for excreta Treats human excreta as a beneficial resource Excreta are confined and processed on site until they are free of pathogenic (disease-causing) organisms Sanitized excreta are then recycled by using them for agricultural purposes. Key features of ecosan : Prevent pollution and disease caused by human excreta Manage human excreta as a resource rather than as a waste product Recover and recycle water and nutrients

16. San plat The sanplat is the cheapest and most basic pit latrine. It is a small concrete platform (usually 60cm by 60cm or smaller), laid on top of logs or other supporting material traditionally used to cover the pit. The purpose of the sanplat is to provide a sanitary (san) platform (plat) which can be easily cleaned to limit the presence of helminths such as hookworm. Once the pit is full, the sanplat can easily be moved. However, the sanplat design does not overcome problems with odours or flies and may not be acceptable to some community members . The sanplat is best used when there is very little money for improving sanitation and where odours and flies will be tolerated.

17. Aqua-privies An aquaprivy is similar to a septic tank; it can be connected to flush toilets and take most household wastewater. It consists of a large tank with a water seal formed by a simple down pipe into the tank to prevent odour and fly problems . Its drawback is that water must be added each day to maintain the water seal, and this is often difficult to do unless water is piped into the home. The tank is connected to a soakaway to dispose of effluent. Unlike a septic tank , the aquaprivy tank is located directly below the house, but it, too , requires periodic emptying and must be accessible to a vacuum tanker. Aquaprivies are expensive and do not offer any real advantages over pour–flush latrines.

18. Determining the required size of a pit The liquids in the pit will normally infiltrate into the soil, and excreta and anal cleansing material will decompose over time. What stays behind in the pit are decomposed solids. To determine what volume a pit will have to be, we have to know how much of these solids (sludge) will accumulate during its period of use. Table below presents estimates on how much solids will accumulate in pits used under different circumstances. These are the sludge accumulation rates

19. Sizing pits for pit latrine Anal cleansing material Wet pit (a) Dry pit (b) Water 40 l/p/y (0.04 m3/p/y) 60 l/p/y (0.06 m3/p/y) Solid material (e.g. stones, corncobs 60 l/p/y (0.06 m3/p/y) 90 l/p/y (0.09 m3/p/y) (a) : a pit in which the excreta are in the ground)water (b) : a pit in which the excreta are not in liquid l/p/y : litres per person per year m3/p/y : cubic metres per person per year

20. SIZING PITS FOR PIT LATRINES It takes time for the solids to decompose, and the sludge will accumulate at a higher rate over the short term. The volume of the sludge that will accumulate over the design life (i.e. the total time over which the pit will be used) can be calculated with the formula Vs = R x P x N Note term: The term waste retained in water applied to a pit latrine means:- waste are in a section of the pit that is below the water table

21. SIZING PITS FOR PIT LATRINES Vs : approximate volume of sludge that will be produced (in m3) R : estimated sludge accumulation rate per person ( in m3/p/y)) P : the average number of people using the latrine over the design life N : the design life of the pit (in years) A family of 6, who would build a latrine with a dry pit, and who would use water for anal cleansing , would accumulate over a period of 15 years a volume of around (0.06 x 6 x15 ) = 5.4 m3.

22. Sizing pit Three additional things have to be taken into account when sizing the pit that has to be dug: i) The pit should be taken out of use when the level of the sludge in the pit has reached 0.5 meters below the slab if the pit needs to be lined, the lining may take an important volume affecting internal size Anal cleansing materials

23. Example 1 Thus, if in our example a rectangular pit would be dug of 1.6 x 1.4 metres , and it would have to be lined from the bottom to the top1 with blocks 0.1 metres wide, the pit would only have an effective size of around 1.4 x 1.2 metres (we lose the width of the blocks on two sides). The horizontal surface of the pit would be (1.4 m x 1.2 m) = 1.68 m2. To be able to contain 5.4 m3 of sludge, the pit would need to be (5.4 m3/1.68 m2) = 3.2 metres deep. As the top 0.5 metres of the pit can not be used, the total depth of the pit should be (3.2 m + 0.5 m =) 3.7 metres .

24. More simple examples for Pit Latrine size Assume SAR is = 0.05 m3 / person/ year 1 Size of one household = 9 persons Number of years before emptying = 3 years Volume for 9 persons for 3 years=(0.05 m3 / person/ year)*(9 persons)*(3 years)=1.35 m3 Pit area = (1.25 m) * (1.25 m) = 1.56 m2 Depth = Volume / Area = (1.35 m3)/ (1.56 m2 ) = 0.87 m The depth of the pit should be designed 0.20 m deeper from the surface to prevent wastes from coming too near to the surface after the designated time. T Thus, Pit Depth = 0.87 m + 0.20 m = 1.07 m = 1.1 m In summary, the pit dimension is 1.25 m long * 1.25 m wide * 1.1 m deep

25. More examples Volume of pit,v = (NXSXD) + 0.5A. Equation 1 Where N= Number of users , S= sludge accumulation rate (l/p/y), D= design life (years) A= pit base area

26. Practice A dry pit latrine of solid accumulation rate of 60l/year is to be used by 20 people for a period of 2 years and degradable corncobs are to be used for anal cleansing . The base of the pit is to be 1m by 1m sq Determine the volume of the pit? Determine the effective depth of the pit ?. Determine the full depth of the pit ?.

27. Emptying pits Use of mechanical pumps- use of a vacum tanker (sludge gulper) Its a truck with a large tank fitted with mechanical pump After suction of faeces the tank is driven to dispose off excreta in sewarage treatment work or pit. This is only good for liquid excreta otherwise dry pits with solids stones , sticks, plastics rags

28. Emptying pits Hand operated pumps Manual emptying Sludge reduction – use of bio-additives