A decentralized sewage treatment offers better opportunities for the development of circular solutions even for arable land, a European Environment Agency analysis says
By Matteo Cavallito
The use of new strategies in sewage treatment plants can foster the development of circular solutions that benefit both environment and soil, according to a report by EEA, the European Environment Agency. By moving beyond the classic linear approach – water remediation and pollutant disposal- to new recovery options, the agency explains, it is possible to turn plants into true resource hubs, providing recovered water, energy, nutrients and organic materials for reuse. And thus contribute to achieving the goals of the European Green Deal.
Sewage management, the study notes, carries high financial and environmental costs in terms of GHG emissions. This requires upstream efforts to ensure more efficient use of water while minimizing the level of contamination. And while large reclamation plants can provide significant efficiencies of scale, it is also evident that decentralized treatment can ensure circularity at local level.
The importance of decentralized solutions
“Decentralised waste water management,” the study says, “is used to treat and dispose of, at or near the source, relatively small volumes of waste water, originating from single households or groups of dwellings located in relatively close proximity” (less than c.3-5km) and not served by a central sewerage system.”
These modes of management also rely on the application of natural solutions that “can contribute to biodiversity and provide additional benefits, such as biomass production, carbon sequestration, flood mitigation, aesthetic value and opportunities for recreation.”
The decentralized approach relies on technological solutions based on source separation of the elements that make up sewage. Several studies, the researchers point out, show that the application of these technologies in different contexts- like separation toilets invented in Sweden in the 1990s or the on-site resource and energy recovery system in water cycle management in Hamburg, Germany – enables the treatment of concentrated, unmixed fractions. This is a more resource-efficient system than the management of highly diluted and combined volumes.
Sewage can be as valuable as biomass
The use of a circular system, the researchers further note, can offer new resources for soil health. The idea, in other words, is to integrate the circular process with agricultural chain management. It is a principle that is already finding several applications around the world.
“Owing to its high nutrient and organic matter content, and the energy content of dried sludge being comparable to that of woody biomass, sewage sludge is a prospective secondary resource that can contribute to Europe’s transition to a circular economy,” the study says.
Efficient recovery provides important resources to soil
The recovery process, the study warns, isn’t simple. During treatment, in fact, great care is required to prevent contamination of end products. Investing in these kinds of solutions, however, means betting on the strategy’s potential. Which looks very promising indeed.
“The estimated annual amount of nutrients that could be potentially recovered from sewage sludge produced in urban waste water treatment plants in the 27 EU Member States,” in fact, “ranges between 6,900 and 63,000t of phosphorus and between 12,400 and 87,500t of nitrogen.”
These amounts “correspond to 0.6‑6% of total phosphorus fertilisers and 0.1-1% of total nitrogen fertilisers used in the EU in 2018, respectively”, researchers conclude.