Green Technology Feature: Cleaning Water with Microbes

2021-10-19

 |  Biodiversity/Conservation

For many in developing countries, clean drinking water is a luxury, not a right. The issues surrounding access to clean water range from water scarcity, to poor sanitation infrastructure, and even contamination of drinking water sources with harmful chemicals or microbes. With over one billion people around the world lacking access to clean drinking water, methods to filter and clean existing contaminated water are extremely beneficial. Some of the most common methods of water treatment in developing countries include UV water purification, membrane filters, and slow sand filtration. 

To be useful and practical in a developing country, a water treatment system should be low cost, low maintenance, and easily accessible. Slow sand filtration checks all these boxes. Slow sand filtration is highly reliable and has been used for hundreds of years since its first operation in 1804, where it was employed to reduce cholera cases in Scottish waters. The slow sand filtration method filters water by using a complex biological film (or biofilm) on the top of sand. The biofilm is often made up of microorganisms such as bacteria, fungi, protozoa, or aquatic insect larvae. When water passes through the biofilm, particles of foreign and organic material in the water are either caught by the biofilm, or absorbed, while clean water exits. 

It may be hard to believe that simply adding a layer of microbes on top of sand could offer a solution to producing clean water; however, the slow sand filtration system has a slew of benefits. For example, it is a simple model, requiring few resources to set-up. Once set up, this filtration method requires little maintenance or expertise to continue working. In addition, compared to other filtration methods, slow sand filtration does not need large amounts of chemicals or electricity to operate well. Nevertheless, despite these benefits, it should be noted that this system has a low filtration rate, meaning it is best suited for small populations. 

Many studies prove that slow sand filters have improved public health. For example, the International Journal of Environmental Health Research published a study looking at the efficiency of slow sand filters in Egypt. A system made of four slow sand filters and a roughing filter (to remove larger contaminants) was introduced into the Sandoop Compact Water Treatment Plant in El‐Mansoura City. Raw water was obtained from the El‐Bahr El‐Saghier Canal, a branch of the River Nile, and was unloaded onto the filters. In total, 10000 cercariae (the larval form of the Trematode parasite) units were present in each litre of the water. After filtration using the slow sand system, there was no evidence of parasites in the final effluent.

More recently, these slow sand filters have been the root cause of a rise in economic growth in developing countries. It was projected by The World Health Organization that every $1 put into clean water technology will have a profit of approximately $3 (region dependent). It was also reported that developing countries with improved access to filtered water and sanitation experienced an average economic annual growth of 3.7%. These results make it clear that by employing water filtration technologies like slow sand filtration, developing countries can see long-term benefits beyond immediate health and sanitation improvements. 

Slow sand filtration is a prime example of the incredible work microbes can do. If you are interested in learning more about the science behind slow sand filtration, there are countless studies that dive deeper into the biological aspect of the biofilm and the specific organisms involved. On the other hand, if you are keen to get involved in water-related issues, there are many organizations, such as the Samaritan Purse, Pure Water for the World, and Clean Water for Haiti, that will build a filter, deliver it, install it, and monitor it for a year. Overall, these filters cost approximately $100 USD each and are built by local workers who help educate their community on water education and sustainability. These programs provide long-term access to water and job opportunities in communities, exactly where they are needed most.