Early in the Haiti emergency intervention there were large numbers of IDP’s in camps. The WASH cluster set a goal of building 11,000 latrines with an initial goal of one latrine for every 100 people. However, there were not enough pump trucks in country to properly maintain the latrines, nor was – or is – there a satisfactory method to dispose of the sludge when the latrines are cleaned.
Large bag digesters can help address this deficiency.
An anaerobic digester significantly reduces the volume of solids in human waste. They can be prefabricated as flexible bags and placed forward to accompany any disaster intervention that will result in IDP camps. They can be designed to easily connect to toilets so that no transport of sludge is required. Moreover, they can be relocated, if necessary. They are less effective in cold climates.
They produce a gas that can be used for cooking, heating, running a motor or lighting, although they are not very efficient at lighting.
The liquid effluent (supernatant) can be used as a fertilizer or for other purposes. The supernatant is not pathogen free and careful consideration should be given to its use in siteing the digester.
The solid component of the residual sludge requires removal several times a year.
Here is a website that shows the fabrication of a simple bag digester from 8 mil polyethylene sheet.
In many developing countries charcoal is used for cooking. To the extent that the biogas can be used to replace charcoal there are clear climate benefits. Charcoal emits black carbon, a major driver of climate change. Replacing charcoal will also preserve trees – a clear climate impact.
If the sludge is placed in pits for disposal, it will generate methane gas, a significant green house gas.