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The water quality deteriorated in the middle of the 1970s in the Albufera lake, a shallow Mediterranean coastal lagoon in the east coast of Spain. In few years, the water changed from an oligotrophic status to hypereutrophic as the lagoon received sewage and agrochemicals, lacking adequate sanitation facilities. For more than 40 years, the lake was used as a wastewater treatment plant given the urban development in the surrounding area. It was not until the early 1990s, 20 years after the hypereutrophic state was reached, when the first sanitation facility protecting the lake was implemented: a perimeter intercepting sewer carrying out the sewage to a waste water treatment plant. This paper describes the different engineering solutions and tools implemented to improve the water quality in the Albufera lagoon. We describe the measures and their effects on the water quality as well as their limits. Those are sanitation solutions as sewers, wastewaters treatment plants, stormwater detention tanks, and nature based solutions as constructed wetlands that have been used in these years. In addition, the role of agricultural activity in the water balance (quantity and quality), the importance of sediments management and the use of water quality models in environmental engineering have been assessed. Evidences of the improvement of environmental quality are the decrease of mean clorophyll a concentration from 800 μg Chl a l−1 in 1980s to less than 100 μg Chl a l−1 currently observed, the increase of water transparency and the recovery of macrophytes within the lake or the presence of winterbirds which disappeared years ago. • Restoration of eutrophic lakes combines grey and green infrastructures. • Restoration of the Albufera lake is ongoing but it is a long term process. • Constructed wetlands treating eutrophic waters reduce nutrients improve biodiversity. • Flushing is a measure to be considered if water resources are available. • Natural monitoring recovery for sediments is recommended for l'Albufera. [ABSTRACT FROM AUTHOR]

Abstract: Three free water surface constructed wetlands (FWSCWs) have been built in the border of the Lake L’Albufera de Valencia (Valencia, Spain). This lake is the emblematic element of one of the most important wetlands in Spain, L’Albufera de Valencia Natural Park, and it is highly eutrophicated. The function of the set of CWs (9ha) is treating the eutrophic water from the lake with the objective of reducing the phytoplankton population and nutrients. The treatment wetlands named as FG and fp are comprised of three basins in a series, while the last, F4, consists of a single cell. During the first 2 years of operation, the inflow from lake was gradually increased from 0.01m3 s−1 (April 2009) to 0.13m3 s−1 (December 2010) with the goal of establishing the maximum hydraulic loading rate (HLR) and finding the highest removal efficiency. Input concentrations of different water quality variables studied showed a high variability. The inflow contained 8.80–94mgl−1 TSS, 0.16–1.13mgl−1 TP, 1–17.30mgl−1 TN, 0.13–13.10mg Nl−1 DIN, 0.10–11.50mg NO3 −-Nl−1, and 3.34–257.03μgl−1 Chl a. The best removal results for these parameters were obtained in the FG wetland, where the average mass removal efficiencies were 75% TSS, 65% TP, 52% TN, 61% DIN, 58% NO3 −-N, and 46% Chl a. In the set of constructed wetlands the removal rates increased with the hydraulic load rate for TSS and TP but neither for nitrogen species nor Chl a; for these variables the input concentrations are a key factor in removal. For instance, mean removal rate for nitrate is 101mg Nm−2 d−1 but values higher than 400mg Nm−2 d−1 were obtained when input concentrations were about 7mg NO3 −-Nl−1. Values of first-order constant aerial rate (k A) have been obtained for all variables. The corresponding values for nitrogen species and total phosphorus are higher than obtained in previous studies but the value k A value for TSS is low (94.9myear−1) owing to the eutrophic characteristics of water and a k A value for phytoplankton-Chl a of 65.1myear−1 is introduced. The management of CWs implies the harvest of vegetation, not for remove nitrogen because nitrification–denitrification processes reduce the 83.3% of TN that enters, but for the phosphorus, limiting nutrient in the Lake L’Albufera, that now is accumulated in plants and soils but could be sent back in several years. [Copyright &y& Elsevier]

In this article, a mechanistic biokinetic model for nitrogen removal in free water surface constructed wetlands treating eutrophic water was developed, including organic matter performance due to its importance in nitrogen removal by denitrification. Ten components and fourteen processes were introduced in order to simulate the forms of nitrogen and organic matter, the mechanisms of autotrophic and heterotrophic microorganisms in both aerobic and anoxic conditions, as well as macrophytes nitrogen uptake and release. Dissolved oxygen was introduced as an input variable with a time step of 0.5 days for mimicking eutrophic environments: aerobic conditions were assigned during daylight hours and anoxic conditions during the night. The sensitivity analysis showed that the most influential parameters were those related to the growth of heterotrophic and autotrophic microorganisms. The model was properly calibrated and validated in two full scale systems working in real conditions for treating eutrophic water from Lake L'Albufera (València). In the studied systems, ammonium was mainly removed by the growth of autotrophic microorganisms (nitrification) whereas nitrate was removed by the anoxic growth of heterotrophic microorganisms (denitrification). Macrophyte uptake removed between 9 and 19% of the ammonium entering to the systems, although degradation of dead standing macrophytes returned a significant part to water column. [ABSTRACT FROM AUTHOR]