The United Nations Environment Programme (UNEP) and the Stockholm Environment Institute (SEI) published a report in October on the challenges and stakes involved with recovering domestic wastewater. Based on the observation that nearly 330 km3 of municipal wastewater is produced globally each year, the study looks at the various processes for recovering and reusing this potential resource. Credit: Thinkstock – hxdyl
A wide range of potential resources!
Credit: Thinkstock – hxdyl
If this volume was treated or recycled, it would be enough to irrigate 40 million hectares of farmland or generate enough sludge biogas to supply 130 million households with energy! For instance, this would represent 15% of current irrigation requirements worldwide. Vientiane, the capital of Laos, could produce enough biogas with its wastewater to drive a bus 10,000 km. The possibilities for creating value from a city’s wastewater are not restricted to just recycling or biogas production, as highlighted in the report: wastewater treatment sludge also contains various components that are used in most fertilisers and could supply 25% of the nitrogen and 15% of the phosphorus used for this. In other words, a city with 10 million inhabitants produces a volume of wastewater each year that could fertilise 500,000 hectares of farmland. So, waste also has an economic value! For instance, the UNEP-SEI study estimates the value of wastewater produced by Indian coastal cities each day at 17 million dollars.
Economic and cultural issues
A deficient or undeveloped wastewater treatment network can therefore have major health and economic impacts. In India for example, improving the sanitation system would make it possible to cut the costs of healthcare and water provision by 54 billion dollars. The research presents a selection of best practices and solutions to capture the value available with these resources, in addition to setting out the prerequisites for efficient recovery: a good sanitation system must not only be economically viable and technically reliable, it must also be aligned with local cultural practices and institutional frameworks, as well as regional natural risks.
For instance, in Hölö, Sweden, low population-density has made centralized wastewater treatment financially unfeasible. Local stakeholders have chosen to set up a collection process where wastewater is transported by truck to storage units, which convert it into fertiliser for local farms. The study includes other examples of similar practices in Burkina Faso or Bolivia for instance.
Lastly, the report presents other solutions: making use of the purification capacity of plants, such as duckweed, to treat wastewater stored in lagoons; using residual sludge for construction materials in Sweden; or even using sludge as nutrients for rearing insects (which eat it) for animal feed, in line with the approach adopted by the French start-up Ynsect.