Tagus Estuary Clean-up Project
How Smart Wastewater Management leads to Urban Sustainability
Alexandra Serra
Aguas de Portugal Internacional
(Executive Board Member)

António Frazão
Águas do Tejo Atlântico
(President)

Pedro Póvoa
Águas do Tejo Atlântico
(Asset Management Department Director)

Tagus River covers the heart of two countries - Portugal and Spain, thus the river's basin contributes immensely to the economic development of both the countries. With almost 3 millions inhabitants, several important industries, and with an extensive administrative divisions comprising of 19 municipalities, it is the largest SOE(Standard Operating Environment) of Western Europe. With this context, this case-study has got international prominence for contributing to modern economic development of both the countries.

Importance of Tagus Estuary: Tagus River is the longest river of the Iberian Peninsula. It flows west across Spain and Portugal for 1,000 km to end into the Atlantic Ocean near Lisbon. It covers the heart of Portugal and Spain, and has been of vital importance to the modern economic development of the two nations.

Tagus estuary is the largest estuary in Western Europe with about 34,000 hectares (84,000 acres), and regularly hosts 50,000 wintering waterfowl. It is an important natural reserve and includes the largest wetland in Portugal and one of the most importants in Europe. The estuary is a sanctuary for fish, mollusks, crustaceans, and especially to birds that stop-over on their migration between Northern Europe and Africa.

Tagus estuary plays a fundamental role not only in terms of ecological value but also in economic development. Several important industries and extensive areas of agriculture are located near the estuary. Almost 3 million inhabitants are concentrated in the north and south bank of the estuary, the highest population concentration in Portugal.

Problem Statement: Back in 1998, estuarine ecosystems were affected by highly polluting activities receiving wastes from agricultural and industrial activities and from large urban centers. Trancãoriver, a tributary to Tagus estuary was the most polluted river in Europe. Some of the most beautiful beaches around Lisbon were heavily polluted. Constant and devastating floods due to functional failure of sewage network during storms provoked major losses in Lower Lisbon. Wastewater treatment facilities were unreliable; and untreated domestic and industrial wastewater were discharged in the estuary. In fact the concentration of densely urbanized areas and industrial clusters in the region has resulted in strong and growing environmental degradation that could only be curbed through combined efforts and integrated solutions.

This situation was common across Portugal. Water Supply and Wastewater Sector was lagging behind, faced with poor performance, fragmentation in service provision, and lack of financial sustainability. In many regions of the country, potable water did not reach minimum quality standards, the service was interrupted during summer due to vulnerable water sources, and information for the consumer was not available. Only 15 percent of the population was connected to wastewater treatment facilities; many rivers were heavily polluted and a large extension of coastal area bathing waters were contaminated.

Project Conceptualization: The Central State realized that it was not possible to maintain business as usual and decided to start a transformative institutional reform. The strategy defined at the political level was based on combined efforts of public and private entities with a strong commitment of the State and the Municipalities. It was conceived and implemented an innovative governance model involving the Central State, through Águas de Portugal, and the local authorities (the municipalities around the estuary) in a public-public partnership where Águas de Portugal and the municipalities are shareholders of the two Wastewater Utilities (Águas do Tejo Atlântico and SIMARSUL) in the north and south bank of the estuary. These utilities operate under a 30 concession contract with a full cost recovery approach.

An ambitious Rejuvenation Project was set up for Tagus Estuary, involving the integrated efforts of all key-stakeholders for the implementation of the following major actions:
  • Depollution of the waterlines(conception, construction, and O & M of high-tech STP for urban and industrial wastewater treatment by Águas de Portugal subsidiaries)
  • Requalification and reforestation of riverfronts by the municipalities
  • Sludge removal, treatment, and valorization by Aguas de Portugal subsidiaries
  • Fluvial regularization and flood control by the Central State through the national water authorities.
This integrated approach was also very important to gather the necessary skills together, to share management structures, to optimize investments, and to scale up the economies.

Implementation: The action plan implemented by Águas de Portugal subsidiaries (Águas do Tejo Atlântico and Simarsul) included an ambitious infrastructure investment plan of around 700 million Euro to expand and modernize sewerage systems for more than 3.8 million of inhabitants-equivalent. It was a high scale and technical complex intervention. The treatment level of the Sewerage Treatment Plants (secondary, tertiary, and tertiary with disinfection) was defined taking into account the discharge location and the quality requirements of estuary waters for specific uses and also the re-use of treated water. All technological solutions considered the integration of the infrastructures in the landscape with mitigation of environmental impacts, innovative systemic models, and smart asset management to optimize efficiency, quality, and resilience.

In the north bank, Alcantara STP treats urban wastewater collected from approximately 900,000 households in Lisbon and its outskirts. The sewerage system comprises of the Alcantara STP, 13 pumping stations, and 26 km of main sewers. The intervention included the WWTP expansion and the upgrade of its treatment standards (to secondary treatment and disinfection), reducing odors, and improving the landscaping. For the preliminary treatment, Multiflo and Actiflo technologies were used in the upgradation of Alcantara STP, the latter being only used under wet conditions, when the tributary flows exceed the capacity of the Multiflo lines (3.3 m³/s). Subsequent biological treatment is carried out by biofiltration using Biostyr technology. The legal requirements for the quality of discharged waters are the followings: BOD < 25 mg O2/l; COD < 125 mg O2/l, SS < 35 mg/l and E.Coli : < 2000 Un/1000 ml. The plant is equally equipped with a deodorizing system with the capacity to treat 160,000 m3/ h of polluted air. After biological treatment, the wastewater undergoes ultraviolet disinfection and is finally discharged on the Tagus River under safe environmental conditions.

This STP is considered one of the best environmental engineering works in Portugal and it even features in international guides to the best industrial architecture to be visited. The existence of this STP may, however, go by unnoticed as it is unique in its carefully planned suspended gardens, making it perfectly integrated in the urban landscape. This eco-design also protects the facilities from extreme sunlight, sudden downpours, helps improve air quality, and promote urban biodiversity.

The intervention included complex civil works in the old downtown of Lisbon, for the construction of 2 interception chambers (with tidal valves) in the old 18th century drainage pipes, and the construction of interceptors and wastewater pumping stations for the routing of the flow to the ALCANTARA WWTP.


Figure 1 - ALCANTARA STP. Aerial view of the rooftop.

The GUIA STP is the second largest STP of the Great Lisbon region. It treats the sewerage of 800,000 people in a top touristic area in the coastal area near Lisbon: Costa do Estoril and Cascais. Costa do Estoril is a residential and tourist area, with 720 thousand people equivalent, being one of the most attractive areas in Lisbon surroundings, due to its sandy beaches and appealing landscape. In the fifties, Costa do Estoril population was less than 200 thousand inhabitants, living in small agglomerations located mainly along the coastline, with independent sewer systems, including sometimes short submarine outfalls. In the sixties, these agglomerations experienced a rapid growth and new cities were born further inland, contaminating local streams and through them the coastal waters. Then water quality started to deteriorate and, in the eighties, most of Costa do Estoril beaches had incompliant and heavily polluted bathing water. An old STP was built in the 90's just for wastewater screening. Integrated in the Tagus Clean Up Project , in the first decade of 2000, a new plant was built.

Due to the sensitivity of the urban and environmental surroundings, the liquid phase of the new plant is fully underground. It is prepared to switch to different treatment levels in winter and in summer due to the bathing water quality requirements. The solid phase of the GUIA STP is located 5 km from the liquid phase and the sludge is pumped through a pressure conduit. A biogas energy production is incorporated in the solid phase. Presently GUIA STP is selfsufficient in terms of energy.


Other smaller STP were built and are being operated in both the banks of Tagus Estuary. In parallel, a comprehensive program was implemented to eradicate the wastewater discharges along the small rivers and channels.

R & D aspect of the project: Tagus cleanup project was also an opportunity for R & D. An integrated decision support system was created - Aquasafe. Aquasafe is an Operational Decision Support System (ODSS), awarded by International Water Association (IWA).It was designed by wastewater experts with the support of Lisbon University; it connects complex mathematical modelling and several data acquisition system (excel, SCADA, SQL BD, Web services). It covers the Big Data of the urban water cycle from real time weather dataflow and energy to forecast the environmental effects of the discharge impact in the estuary and to support operational measures during flood events.

Conclusion: Tagus cleanup project is an international case study by its complexity and excellent results. In the last decade, it was possible to reduce the pollutant discharges significantly to assure biodiversity conservation and habitat restoration; and also to have a significant increase in the number of Blue Flags' beaches, an European award to high quality European beaches. These results were made possible due to an enabling institutional environment fostered by a sound governance system, diversified, and robust management models involving public (central and local) and private companies, clear regulatory standards, and state-of-the art engineering.