Methods to desludge trench latrines?
The Trench latrines in camp require de-sludging. There is no access for vacuum tankers so we will need a mobile system to access the latrines in camps. There is no water for anal cleansing so the pits are mostly solid. I need advice on the most appropriate pump and methodology for de-sludging.
The Vacutug was designed by me for Graham Alabaster of UN-Habitat United Nations Centre for Human Settlements in Nairobi Graham.email@example.com and is being manufactured in Bangladesh by the Mirpur Agricultural Workshop and Training Centre (MAWTS) in Mirpur, close to Dhaka.The "ex-works" cost was around US $ 5,000 last time I heard about two years ago. (Contact Hamidul Bari at firstname.lastname@example.org. You can also contact Harrison Kwach at UN-Habitat in Nairobi < Harrison.email@example.com who co-ordinates things in Nairobi. It is also planned to manufacture it in Mozambique, South Africa and Kenya.
It was designed specifically to reach into areas where other vehicles cannot reach and the initial trials were carried out in Kibera township, a peri urban settlement of around 800,000 people in an area of only 210 hectares on the outskirts of Nairobi. Its performance is limited to relatively short haul distances due to its small capacity (500 litres) and low travel speed (5 kph) but it can go where no other latrine emptying systems can reach.
The wastes in pit latrines decompose with time with the heavier inorganic wastes settling to the bottom of the pits so that after about two years sedimentation these wastes are virtually unsuckable by any vacuum system. The wastes at the bottom of the pit may have a density as high as SG. 2.0 with a high viscosity and high thixotropy. The fresher organic wastes at the top of the pit will have SG 1.0 with a low viscosity and are easier to suck. The height of the top of the tank above ground level will determine the total suction head so that it gets progressively harder to suck the wastes the fuller the tank, the deeper the pit and the longer the wastes have been decomposing.
However, you refer to "trench latrines" and presumably these are for emergency situations and refugee camps so that I assume that they will be quite shallow and the wastes will be relatively fresh. In situations such as this the Vacutug can be used effectively as a pump to push the wastes back up a pipe to a "mother" tanker" some distance away. This can be mounted on a truck or on an agricultural tractor trailer for transporting the wastes to the disposal area.
The Vacutug has a top inlet valve and a bottom discharge valve so that a short length of vacuum hose can be used to suck in 500.l of sludge through the inlet valve. This valve is then closed and the tank is pressurised to a pressure of around 1.0 bar to force the wastes out through the discharge valve and through the transfer pipe to the mother tanker. In this way the Vacutug can pump as much as 10 loads (5,000. l) per hour when used as a pump and the size of its tank is not relevant. (Typically each person will produce between 35 litres and 50 litres of ... (more)
Oxfam GB have a desludging pump in their equipment catalogue. The code is WSDP/6, which includes generator, pump, fittings, hoses and anti-dive plate. The pump has a rated delivery of 20m head, and can handle solids up to 30mm diameter. Cost is, in the OGB catalogue, 3238 GBP.
There is a risk of collapse when using the pump in unlined pits, so you need to consider health and safety issues fairly closely-fencing while desludging etc. If the pump cannot handle the solids then you will have to add water to make a manageable slurry. You can use 50 gallon drums to transport the water in a pickup. Add the water to the contents of the trench and use a chain drag to agitate and mix the slurry. You can then use the empty water drums to collect the slurry.
Another option, unfortunately widely practiced, is manual desludging. As obnoxious as this sounds it may be the only feasible technical option. This needs to be handled carefully and sensitively, as there are often significant social stigmas attached. In my experience it is often carried out at night as the guys doing it don't want their peers to know who it is. This is a filthy, disgusting and dangerous job, so if you go down this route pay the guys well and provide protective clothing, full face safety visors, breathing masks, gloves and bathing facilities.
From a public health perspective it is critical to ensure safe final disposal. If these activities are not supervised very closely there will be a tendency for the people doing the emptying to use the nearest convenient spot to discharge to. If you cannot ensure that this will be done correctly, and it will probably be quite a difficult and time consuming task in your current circumstances, then it might be safer (and probably less expensive) just to back fill the trenches, space allowing. There is a very real risk of protests from residents in the area if they feel that he job is not been carried out properly. I have heard of several cases of NGO's and staff being targeted with violence due to spillage and poorly planned final disposal, though not in Haiti.
A final option is the use of bio-digestion powders. These are added to the trenches and reduce the volume of sludge in the pit. I have heard mixed reviews on their effectiveness and have no direct experience of using them. If this is a route you would like to try let me know and I will dig up some information on suppliers and effectiveness on Monday.
Ideally, one would cover full trench latrines and move on but there probably isn't much space (we aren't sure exactly where this is). Many of these latrines were dug quickly and probably aren't lined in which case they may be unstable when de-sludged. Unfortunately, manual de-sludging sounds like your best option but could be dangerous.
You might be able to bring in a sludge pump but there could be large stones in the sludge so it would have to be a good one and there's the issue of no water.
Normal practice is not to desludge but to backfill and move the trench by a metre or more, depending on the soil.
Unsupported soil walls will usually not support de-sludging, but may collapse during the operation. Are the trenches lined?
If you really want to desludge, a honey-sucker will not shift solid material. You will have to add water to make the material soft enough for a desludging pump.
Digging out may be your best option. However, shifting the material will be unpleasant and may be a health problem.
This is the holy grail for on-site sanitation and nobody has really got the answer. Some are a lot further from a solution than others.
The key contact at UN HABITAT would be Graham Alabaster.
The other person to contact would be Steven Sugden at the London School of Hygiene and Tropical Medicine who has much more up to date knowledge and experience than I:
I would also recommend anybody wanting information about sanitation and hygiene to make their first port of call Duncan Mara’s website:
He has a load of stuff on pit emptying: http://www.personal.leeds.ac.uk/~cen6ddm/PitEmptying.html
One thing to consider when taking this approach is the soil stability. There is a danger that the trench sides will collapse if you suck the shit out. So even though it is an appalling job, a first pilot using hand methods (with appropriate H&S precautions) should be considered. It may well be that emptying will not be feasible and if there is no room for new trenches, a completely different approach will be needed.
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