Soil-based filter bricks clean up water for Moroccan farmers

A home-made filter system using layers of soil and gravel cleans domestic waste water well enough to make it suitable for irrigation, a research team in Morocco has found.

Waste water. Image credit: Nigel Wylie/Wikipedia (PD)

The filter prototype, tested in Al Haouz, a rural district about 40 kilometres from Marrakech, removed a large amount of waste such as solid particles, organic pollution, nitrogen and fertiliser residue. The system was also successful at killing off coliform bacteria and other pathogens in the water including faecal matter, E.coli and streptococci bacteria.

The filter system consists of a two-stage process that can be easily assembled with local material in water barrels. The researchers created filter ‘bricks’ from sandy soil, charcoal, sawdust and iron scraps, and packed these into the barrels with gravel. While running through the barrel, the water is filtered alternatively by the bricks and the gravel.

The soil bricks on their own were good enough to filter organic waste and nutrients from the water. But when combined with the gravel, the two-stage system became effective enough to tackle pathogens.

The system could provide cheap and low-tech water filtration to rural, arid areas, such as the North African and Asian deserts, where water preservation is crucial for farmers and expensive, industrial water purification is not available.

It also has benefits such as simple maintenance, no frequent clogging and no energy requirements. The expected lifetime of each filter system, if correctly maintained, is about 20 years.

The system removed around 90 per cent of pollutants, including around 95 per cent of nitrogen, a fertiliser residue. The filtered water was not safe to drink, but was usable for agricultural irrigation and household chores. It could be made potable with additional treatment, such as chlorination or UV light.

However, the system would struggle with dangerous chemical pollution, like heavy metals and the more resistant waterborne pathogens such as cholera and salmonella

The filter media should be backwashed or changed after some time, because any biofilm that forms will cause clogging, but the size and surface of the gravel into which the filter bricks are laid could reduce the growth of algae. (SciDev.Net)

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