The idea of recycling sewage into drinking water would make the stomachs of many turn. It invokes imagery of a dystopian future, but it is by no means a new notion. It has been done before, and however drastic the measure sounds, the reality is a lot more logical and cleaner. Countries around the world have employed this tactic when dealing with a lack of fresh water supply and is a very efficient way of maintaining the municipal water supply.
As strains on water supply become more prevalent, the possibility of widespread wastewater recycling is becoming more of a reality.
How is wastewater recycled for consumption?
Although the idea of drinking recycled wastewater understandably makes some gag – the process of treating the water is extremely stringent, with many steps to ensure its purity before it hits the taps again. First, sediment is removed through a process of filtration and clarification. Then, bacteria is removed using UV sterilisation, and finally, one more stage of filtration removes the remaining micropollutants.
According to southern water, there is a four-stage process to filtering raw sewage:
Screening is the process of removing larger items that shouldn’t have made their way into the sewers, such as refuse like plastic bags and nappies. These are removed at this stage of the process, along with debris from the surface that washes into it.
The next stage is where heavy sediments are removed from the water. They are kept in sedimentation tanks where solid waste sinks to the bottom of the tank, separating from the water.
The remaining sludge is then processed for use as fertiliser, and the water is moved on to treat the microparticles.
This part of the process is where bacteria is added to the solution for the purpose of breaking down microparticles of dirt, rendering them harmless. This is then passed over a filter bed with waste-eating bacteria.
This is the final stage of the process, where the nearly clean water goes through a final stage of filtration to remove any remaining waste particles.
When processing water back into the drinking water supply, there is an extra stage where UV sterilisation gets rid of any unwanted bacteria or viruses.
Where has wastewater recycling been employed in the past?
Namibia has been supplying locals with water treated from wastewater for over 50 years now. On the outskirts of the capital, Windhoek, the processing plants turn huge vats of raw sewage into potable drinking water.
Namibia is one of the driest countries, with an average rainfall of 250mm per year (according to Veolia). The country relies on three dams for its water supply, so these schemes are essential to maintain it.
As of 2021, Singapore recycled 40% of their wastewater, with plans rolling out to increase this number coming since then. Due to a lack of natural water supplies in Singapore, they use wastewater recycling with desalination to ensure water is freely available.
The company responsible, NEWater, is on course so source up to 55% of the city-states water demands.
The rest of the world.
Namibia and Singapore are the only two locations in the world where recycled wastewater is directly pumped back into the municipal supply. For the rest of the world, wastewater is fed out into the sea through rivers or canals until it joins the global pool of freshwater supply again further down the line
Pumping the recycled water back into the municipal supply also reduces ocean pollution, therefore providing a sustainable answer to a big problem
It may be some time until we see the whole of the world following this practice if we ever do at all. As water scarcity becomes more of a problem, nations will take heed of the lessons learned from Namibia and Singapore.