Project coordinator Pedro Carvalho explains how NEUTRAL4GS combines nature-based solutions with advanced treatment for urban water.
Water is the resource through which almost every other development challenge is expressed. Where it is scarce, food systems falter, and economies stall; where it is contaminated, public health collapses long before the pollution is ever measured. By 2040, an estimated one in four children will be living in regions of extremely high water stress as a result of overuse, population growth, and climate change. That figure is often quoted, but it deserves to be read carefully: it describes a future in which water insecurity is not an exceptional emergency but an ordinary condition of childhood for hundreds of millions of people. The regions where this will be felt most acutely are those of the Global South, where rapid urbanisation and climate vulnerability meet infrastructure that was never designed for the populations it now serves.
NEUTRAL4GS was conceived as a direct response to that reality. Funded by the European Union’s Horizon Europe programme under the Marie Sklodowska-Curie Actions Staff Exchanges scheme, the project began on 1 January 2025 and runs for 48 months, with an EU contribution of EUR 740,600. It brings together eight partners from seven countries – six academic institutions, one innovative SME, and one water utility – around a single proposition: that solutions inspired by nature should be developed for and with the Global South, rather than exported to it. Aarhus University coordinates the consortium alongside Technicka Univerzita v Liberci in the Czech Republic, the Italian SME IRIDRA, the Universidade de Aveiro and the Portuguese water utility Aguas do Ribatejo, together with the Universidad Tecnologica de Pereira in Colombia, Universitas Muhammadiyah Pontianak in Indonesia and Rajamangala University of Technology Thanyaburi in Thailand.
Four places, four different problems
The project is anchored in four case studies, three in the Global South and one in Europe, and their diversity is deliberate. In Thailand, the uncontrolled discharge of untreated wastewater is the central challenge, with Pathum Thani province serving as the study area for identifying feasible treatment options. In Colombia, prolonged drought compounded by deteriorating water quality is restricting access for competing users, and the country’s coffee-producing region is the setting for exploring alternative water sources. In Indonesia, the work centres on the water quality, geography, socio-economic context, and management practices of the river system at Pontianak. In Portugal, Aguas do Ribatejo – a publicly owned utility serving seven municipalities – is assessing the challenges arising from the revised EU urban wastewater treatment directive and the technologies that might address them.
Setting these four alongside one another is the point. It prevents the project from converging on a single technological answer and forces every solution to prove itself against genuinely different constraints: tropical rainfall regimes, seasonal drought, dense informal urban settlement, and a European regulatory tightening. Technology design guidelines developed in the temperate Global North cannot simply be transposed to tropical climates, and the absence of local design and cost data is itself a barrier that deters decision-makers from adopting anything new.
Why nature-based solutions, and why they are not enough
Nature-based solutions are the backbone of our approach for good reasons. Constructed wetlands and related systems are robust, comparatively cheap to operate, tolerant of variable and intermittent loads, and buildable and maintainable with local skills and locally available materials. They also deliver co-benefits that engineered systems do not – habitat, cooling, amenity, and a visible presence in the urban fabric that helps communities understand what is being done with their water. Where skilled operators are scarce, spare parts arrive slowly, and power supply is unreliable, these are not soft advantages. They are frequently the difference between a system still working in year ten and one abandoned in year two.
It would be dishonest, though, to present them as sufficient on their own. Conventional nature-based systems were not designed for today’s contaminant profile: pharmaceutical residues, micropollutants, heavy metals and persistent compounds pass through many of them at concentrations that still matter for health and for reuse, and land availability in dense, fast-growing cities imposes hard limits on footprint. Circular urban water management therefore calls not only for nature-based solutions but for a range of supporting units alongside them.
This is where the core scientific ambition of NEUTRAL4GS sits – not in choosing between nature-based and advanced treatment, but in combining them intelligently. The project pairs nature-based systems with membranes, nanofiber biomass carriers, graphene-based nanocomposites, photocatalysis and lightweight porous media, organised as a division of labour. The nature-based component absorbs hydraulic and organic load, buffers variability and supplies the resilience and low running costs that make long-term operation realistic. The advanced unit is deployed selectively, on the fraction of the flow and the subset of compounds where wetland processes are demonstrably insufficient: as a polishing step, as a targeted barrier ahead of reuse, or as an intensification measure where space is constrained. Configured this way, the advanced unit extends what the nature-based system can achieve without importing the fragility of a high-technology plant into a low-resource setting.
The work is organised accordingly. Stormwater is being addressed by cataloguing nature-based applications across geographical contexts and by developing membrane technology combined with sorbents, moving stormwater management from peak-flow control towards harvesting and reuse. Greywater – lightly polluted and the easiest stream to recover – is being tackled through vertical systems and green walls at building and neighbourhood scale, which requires new lightweight porous media that support biofilm and plant growth without overloading existing structures. Wastewater work spans nanofiber and microfiber membranes produced from natural materials, biodegradable nanofibrous composites targeting micropollutants, sorption post-treatment using macroalgae and carbon-based nanostructures, solar-driven photocatalysis, and the priming of microbial communities for enhanced micropollutant removal. Across all of it, the commitment is to customise technologies to local realities using sustainable and locally available materials – because a treatment train dependent on a proprietary consumable shipped from Europe is not a solution for a mid-sized city in Southeast Asia or the Andes, however impressive its removal efficiencies in a laboratory.
Running through everything is a holistic evaluation layer combining life cycle assessment, techno-economic modelling, and socio-economic analysis. This is a deliberate corrective to a familiar failure in our field, where a technology is optimised for removal efficiency and only afterwards examined for cost, energy demand, maintenance burden and public acceptability – by which point the answer is already fixed. Assessing in parallel lets us discard configurations that would never be adopted and concentrate where performance, affordability, and acceptability are all credible.
What the first year delivered
As a staff exchange action, the project’s central mechanism is the movement of people, and that is where our first year went. 25 researchers completed 33 person-months of mobility during 2025, and every partner and associated partner hosted at least one secondment. Those exchanges were not ceremonial: they carried the case study characterisation, the first laboratory work and a substantial training programme, including LC-MS/MS and high-resolution mass spectrometry training for visiting staff at Aarhus, courses on nanofiber membranes and biotechnology in water treatment delivered at Thanyaburi, and training on water quality and nature-based solutions delivered in Pontianak. A kick-off meeting at Aarhus in April 2025 established the working structures; the consortium then presented across Europe and at the IWA Water and Development Congress in Bangkok in December 2025. One partner has already filed a patent application on a membrane solution.
We do not yet have consolidated performance results, and I will not pretend otherwise. What we do have is arguably harder to build: harmonised protocols and a shared analytical vocabulary across seven countries, four characterised case studies, laboratory testing of technology combinations under way, and an experimental programme designed jointly rather than assigned. In collaborative research of this kind, that alignment is the precondition for results that mean anything when they arrive.
A two-way exchange
The framing of expertise flowing from Europe outwards captures only half of what is happening. Europe faces intensifying drought and water scarcity of its own, and the questions our partners have long confronted – how to deliver acceptable quality with constrained capital, how to operate reliably without dense technical support, how to secure genuine community ownership of infrastructure – are becoming European questions. Several of the innovations being developed here have clear application in the EU, and I regard that as a realistic expectation rather than a diplomatic formulation.
Co-creation is the method. Communities of Practice in each case study region bring local stakeholders, authorities and residents into defining the problem and selecting the solution, and the project will cycle its findings back to them before it closes. A technically excellent system that no institution owns and no community trusts is a stranded asset. Clean water should be a right rather than a privilege, and delivering it at the pace urbanisation and climate change demand will require systems that are resilient, affordable, and capable at once. NEUTRAL4GS exists to establish how well nature and advanced treatment work together – and to make sure the answer is useful to the cities that need it most.
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