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Problems with emptying pit latrines

16 November 2018

Photographs from Sustainable Sanitation Alliance (SuSanA)

The recognised best practise way to empty the latrines is using a pump, usually a vacuum pump. A large bore hose is put down into the pit and sucks up the waste material into a vessel. Sounds easy? It is thwart with problems. Firstly, very often pit latrines allow the liquid to drain away leaving a solid mass that can not be pumped. In order to make it pumpable, liquid needs to be added to it and it mixed to make a slurry.

Once you have a slurry it can be pumped but into what? As the volume is relatively small compared to the volume a vacuum tanker can hold it is not economically feasible to use a vacuum tanker even if you could get one near to the latrine. So it is usually pumped into small containers to be taken for disposal (I’m not going to think about where it is disposed!).

So the problem we have been working on, in collaboration with the Red Cross, is what to do with the material in the stage between getting it out of the pit and disposing of it. The idea is simple enough. Pump it out into a small container, transport it to a larger hub container which takes the contents from a number of pit latrines, then, when you have enough for a full sized vacuum tank you can empty the hub container and move it onto a new location to start refilling with the contents from a new set of pit latrines. The proposal is to use bladder tanks as the hub containers as they can be rolled up when empty for easy moving to a new location. But the problems don’t stop there. As I said above pit latrines are often used as rubbish pits and even if they are not, items such as sticks, stones, leaves and corn cobs can be used for anal cleansing. These items, and other sharp objects, can cause problems for the pumps and the bladder tanks so SOWTech have been devising a robust filter mechanism that will remove unwanted items before they can do any damage.

A prototype filter has been built and, after preliminary trials at SOWTech, it is being sent to Malawi where the Red Cross will be testing it under real conditions. We look forward to hearing the results of the trials. I am sure that there will be teething troubles but we believe that the filter is robust and easy to use and easy to clean and will prove to be a big asset when emptying pit latrines.

One of the big problems with sanitation waste when you are not connected to a sewer system is how do you get rid of the waste. Even in the western world, if you are connected to a septic tank it still needs to be emptied periodically by a vacuum tanker. Imagine if you live in the Global South where you live in tightly packed slum areas or a refugee camp or a rural area with no reasonable roads where no large vacuum tanker can access. Add to that the fact that your toilet is a pit latrine, an ideal place to dispose of things you don’t want any more, rags, plastic and glass bottles even x-rays plates, and you can see that emptying your toilet is no easy matter.

So what do you do? If there is room you can close up that pit latrine and dig another one. Not good for the environment and not always possible. It’s a question that the aid and humanitarian agencies have been looking into. There are people who will empty your pit latrine for you. It normally involves them lowering a bucket into the pit or going into the pit themselves and shovelling it out by hand. And don’t forget they have no PPE if they are lucky they might be wearing shoes.

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At SOWTech our primary focus has always been on sanitation but one of the other things that has been concerning us is water -  or more precisely the lack of it. This was really brought home to John when he was in Uganda a few years ago. He was talking to a farmer about one of the problems of using anaerobic digesters to treat cattle manure. The problem was that the cattle manure was too dry to flow into the digester and it needed to be mixed with water. To get the water people had to walk to the bottom of the hill where there was a stream that they could collect it from. A familiar story in Africa but the irony of this account was that at the time it was pouring with rain. The rain was running down off the roofs straight into the ground and being lost.

John realised that in the UK, and elsewhere, this didn’t happen as we all have gutters on our roofs to collect the water. But at the farm none of the buildings had gutters and, as he travelled around, he realise this was the norm. All that water being lost that could be collected and used. On his return to the UK we began to look into this.

There were a number of issues that we identified. Firstly most of the roofs are made of congregated metal that overhang the building walls so conventional western style gutters wont work. Secondly there is the quantity of water to be stored. Rain water tanks are available in Africa but most only store a few hundred litres water at best which would soon be used up in the rainy season. To be of practical use the water storage tanks had to hold many thousand litres. The pattern of rainfall was another major issue. Typically in the rainy season there is a heavy deluge for about and hour then it stops. Any rainwater harvesting system would need to be able to cope with a lot of water falling in a short space of time.

So we at SOWTech have set about designing an inter-seasonal rainwater harvesting system. It has three main elements. The first is the guttering. We have devised a simple gutter that wraps around the edge of the roof using the troughs in the corrugated metal to collect and direct the rain landing on the roof into the gutter.

The second element is a series of buffer tanks under the end of the gutter. They are sized to be able to hold the amount of rain falling in 24 hours onto the roof area. This means that the water can have 24 hours to drain through small bore pipe to the main storage tank rather than using large more expensive drain pipes. It also has the advantage of giving debris from the roof to either settle and be trapped in the buffer tank or to float to be skimmed off.

The final piece of the jigsaw is a storage tank that can hold enough water to be of use throughout the dry season. The tank we have come up with can be sent “flat packed” for erection on site whilst being fully enclosed to stop ingress by insects etc. The roof of the tank is also designed to be a rain water collection surface.

The first prototype of our system has just been sent to a school in Zimbabwe sponsored by Africa Trust. They are going to test the system for us and we look forward to receiving their feedback.

Water, water everywhere and not a drop to drink

29 November 2018

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