Publicaciones

2025

Elimination of faecal indicator microorganisms from wastewater by combining constructed wetlands and heterogeneous photocatalysis: from laboratory to pilot-scale implementation

Frontiers of Environmental Science and Engineering — Article — Open Access — 2025 — DOI: 10.1007/s11783-025-2094-4

Sánchez, M., Torres, E., Ramos, D.R., Aguilar, S.D., Fernández, M.I., Ruiz, I., Canle, M., Soto, M. 

Abstract: A combined system comprising a hybrid anaerobic digester (HD), a vertical subsurface flow constructed wetland (VF), and a heterogeneous photocatalysis unit was evaluated at pilot-scale for the elimination of faecal indicator microorganisms—total coliforms, Escherichia coli and Clostridium perfringens. The VF effluent was subjected to laboratory-scale experiments using different photodegradation post-treatments: UVC photolysis, heterogeneous photocatalysis with ultraviolet light (UVA/TiO₂), and sunlight-driven heterogeneous photocatalysis (Sol/TiO₂). Subsequently, the Sol/TiO₂ system was scaled up and implemented at pilot-scale (p.Sol/TiO₂). The total footprint of the combined HD+VF+p.Sol/TiO₂ system was 4.4 m². Under continuous operation, the combined HD+VF system was able to remove approximately 1.0, 1.3 and 1.1 log units for total coliforms, E. coli and C. perfringens, respectively, with the VF unit accounting for more than 80% of the overall elimination during biological treatment. Laboratory-scale experiments showed high removal efficiency, following the order UVC< UVA/TiO₂ > Sol/TiO₂. In contrast, the p.Sol/TiO₂ post-treatment (after 2 h of exposure) achieved lower removals of approximately 0.5, 1.2 and 0.1 log units for total coliforms, E. coli and C. perfringens, respectively. To our knowledge, this is the first study on the combination of VF constructed wetlands and photodegradation processes with the aim of improving the quality of reclaimed water for potential reuse. As a general conclusion, the photocatalysis pond employed in the present study improved the quality of the VF effluent, widening the possibilities for reuse of the reclaimed water.

2024

The use of constructed wetlands to treat effluents for water reuse

Environments - MDPI — Review — Open Access — 2024 — DOI: 10.3390/environments11020035

de Campos, Sandro Xavier; Soto, Manuel

Abstract: Constructed wetland systems (CWs) are technologies based on natural processes for pollutant removal and have been more and more accepted in the treatment of domestic and industrial wastewater. This study selected and reviewed articles published in the last six years involving the use of different CW conceptions and their association with other technologies to treat different effluents and evaluated the quality of the effluents for reuse. From a total of 81 articles reviewed, 41 presented quantitative data on the quality of the treated effluent in relation to the requirements of the reuse regulations in different countries of the world. CWs can be used to treat gray water and runoff water, as well as domestic and industrial effluents with the purpose of reusing them. While studies on the removal of new chemical and biological substances have increased, challenges are associated with the optimization of CWs to improve the removal of pathogens and new contaminants that have appeared more recently. The potential for the improved removal of those pollutants lies in the association of CWs with conventional and advanced technologies in new configurations. We concluded that studies related to the reuse of effluents using CWs are in constant evolution, with experiments at different scales. The perspectives are promising since CWs are an economic, environmentally friendly, and efficient technology to help in the mitigation of water scarcity problems imposed by climate changes.

Horizontal flow aerated constructed wetlands for municipal wastewater treatment: The influence of bed Depth

Science of the Total Environment — Article — Open Access — 2024 — DOI: 10.1016/j.scitotenv.2023.168257

Pascual, A., Álvarez, J.A., de la Varga, D., Arias, C.A., Van Oirschot, D., Kilian, R., Soto, M.

Abstract: The influence of bed depth on the performance of aerated horizontal constructed wetlands was investigated at the pilot plant scale. Two horizontal flow subsurface constructed wetlands (HF) intensified units of different bed depth (HF1: 0.90 m and HF2: 0.55 m, 0.8 m and 0.5 m water level, respectively) were fitted with forced aeration, while a third one (HFc, 0.55 m bed depth, 0.5 m water level) was used as control and not aerated. The three HF units were operated in parallel, receiving the same municipal wastewater pre-treated in a hydrolytic up-flow sludge blanket anaerobic digester. Applied surface loading rates (SLR) ranged from 20 to 80 g biochemical oxygen demand (BOD₅)/m²·d and from 3.7 to 6.7 g total nitrogen (TN)/m²·d, while it ranges from 6 to 23 g BOD₅/m²·d and from 1.1 to 1.7 g TN/m²·d in the control unit. Removal of total suspended solids (TSS) and BOD₅ was usually close to a 100 % in all units, whilst chemical oxygen demand (COD) removal was higher for the HF1 unit (97 % on average, range of 96–99 %) than for HF2 (92 %, 82–98 %) and HFc (94 %, 86–99 %). TN removal reached on average 33 % (16–43 %) in HFc, 37 % (10–76 %) in HF2 and 51 % (21–79 %) in HF1. High TN removal required a longer aeration time for nitrification and higher effluent recirculation ratio to enhance denitrification. The results indicate that artificial aeration and a high bed depth allows to increase the SLR by a factor of 4 in HF1 but only by a factor of 2 in HF2.

2023

Sustainable wastewater treatment using a new combined hybrid digester – Constructed wetland system

Journal of Environmental Chemical Engineering — Article — 2023 — DOI: 10.1016/j.jece.2023.110861

Sánchez M.; Ruiz I.; Soto M.

Abstract: Constructed wetlands are one of the most promising decentralised wastewater treatment technologies for single-family homes, rural or peri-urban areas as well as for low-income areas. The present work reports for the first time the combination of a new hybrid anaerobic/anoxic digester (HD) as pre-treatment for a vertical subsurface constructed wetland (VF). Part of the nitrified VF effluent was recirculated to the HD to favour the simultaneous removal of organic matter and nitrogen, intensifying both the HD denitrification and VF nitrification processes. The results indicate that HD was the main responsible for the removal of suspended solids and organic matter, which was completed in the VF up to values always below the discharge limits. Nitrate removal ranged from 64 % to 94 % and ammonium removal from 64 % to 89 %, the former occurring mainly in the HD and the latter in the VF. The combined HD-VF system achieved high overall removal efficiency, reaching 98 % TSS, 94 % COD, 97 % BOD₅, 86 % NH₄⁺-N and 43 % TIN on average. Methane emissions were lower than those reported in the literature for CWs. The VF showed no signs of clogging. The system was operated in a sustained manner during a continuous period of 266 days with an average overall surface loading rate of 43.6 g BOD₅ /m²•d (range of 29–83 g BOD₅ /m²•d). The total surface area required was 1.4 m²/equivalent inhabitant.

Combining constructed wetlands and UV photolysis for the advanced removal of organic matter, nitrogen, and emerging pollutants from wastewater

Environments - MDPI — Article — Open Access — 2023 — DOI: 10.3390/environments10030035

Sánchez, M.; Fernández, M. I.; Ruiz, I.; Canle, M.; Soto, M.

Abstract: This study reports the performance of a three-step lab-scale system including a hybrid digester (HD), a vertical flow (VF) constructed wetland, and a photodegradation (PD) lamp, with two different arrangements regarding the position of the recirculation point. In addition to total suspended solids (TSS), chemical oxygen demand (COD), and nitrogen compounds, removal of the following pollutants was investigated: paracetamol (ACE), ofloxacin (OFL), caffeine (CAF), ketoprofen (KET), ibuprofen (IBU), clofibric acid (ACB), bisphenol A (BPA), and sotalol (SOT). An excellent performance of HD was achieved on the elimination of TSS (82.2 ± 18.5% on average) and COD (63.9 ± 4.1%). TSS and COD removal increased to 91.2 ± 0.4% and 83.4 ± 2.9%, respectively, for the combined HD–VF system. Ammonia removal was 57.0 ± 7.8% in the VF unit while significant denitrification occurred in the HD. The overall HD–VF–PD system achieved mean removals of 100% for OFL, KET, SOT, and IBU, 98 ± 2% for ACE, 87 ± 8% for CAF, 81 ± 38% for ACB and 26 ± 9% for BPA. The removal of ACE, OFL, CAF, and IBU was mostly by biodegradation in the HD and VF units while the PD unit was responsible for the removal of KET, ACB, and SOT.

2022

2021

2020

2015-2010

D. de la Varga, M.A. Díaz, I. Ruiz, M. Soto. Avoiding clogging in constructed wetlands by using anaerobic digesters as pre‐treatment. Ecological Engineering 52 (2013) 262– 269.

The main operational problem of subsurface flow constructed wetlands (CWs) is clogging of granular medium, a phenomenon related to the accumulation of different types of solids that lead to a reduction of the infiltration capacity of the gravel bed. It is generally accepted that the application of a good wastewater pretreatment is essential for the long‐term operation of subsurface flow CW. Anaerobic digesters (ADs) could help to the aim of clogging prevention. Two combined AD‐CW treating either municipal or winery wastewater were designed and monitored for trough performance and efficiency parameters, solids accumulation and hydraulic conductivity, over a long term period. CW operated at high organic loading rates in terms of TCOD and BOD5 while suspended solids loading rates and solids accumulation in CW were lower. In turn, CW maintained an adequate hydraulic conductivity and low rates of solids accumulation.

D. de la Varga, M.A. Díaz, I. Ruiz, M. Soto. Heavy metal removal in an UASB‐CW system treating municipal wastewater. Chemosphere 93 (2013) 1317–1323.

The objective of the present study was to investigate for the first time the long‐term removal of heavy metals (HMs) in a combined UASB‐CW system treating municipal wastewater. The research was carried out in a field pilot plant constituted for an upflow anaerobic sludge bed (UASB) digester as a pretreatment, followed by a surface flow constructed wetland (CW) and finally by a subsurface flow CW. While the UASB showed (pseudo) steady state operational conditions and generated a periodical purge of sludge, CWs were characterised by the progressive accumulation and mineralisation of retained solids. This paper analyses the evolution of HM removal from the water stream over time (over a period of 4.7 year of operation) and the accumulation of HMs in UASB sludge and CW sediments at two horizons of 2.7 and 4.0 year of operation. High removal efficiencies were found for some metals in the following order: Sn > Cr > Cu > Pb > Zn > Fe (63–94%). Medium removal efficiencies were registered for Ni (49%), Hg (42%), and Ag (40%), and finally Mn and As showed negative percentage removals. Removal efficiencies of total HMs were higher in UASB and SF units and lower in the last SSF unit.

M. A. Vázquez, D. de la Varga, R. Plana, M. Soto. Integrating liquid fraction of pig manure in the composting process for nutrient recovery and water re‐use. Journal of Cleaner Production. Available online 13 May 2015.

Composting of solid fraction of swine manure is a usual practice in most farms in order to obtain a fertilizer of better quality. Due to the negative hydric balance of the composting process, watering the composting material is necessary, what may be carried out with liquid fraction of pig manure. In this way, substantial amounts of liquid fraction can be treated by composting, allowing the recovering the nutrients and reducing the volumes to be transported to the more distant crop fields or subjected to further treatment. Thus, the main objective of this research was to study the treatment of liquid fraction of pig manure by co‐composting with solid fraction of pig manure and other solid biowaste generated in rural areas. The present research is part of a project to find an integral solution for pig manure consisting of nutrient recovery through compost production and water re‐use after biological purification in constructed wetlands. In accordance with the European waste management hierarchy, sustainable and low cost cleaner technologies aiming at resource recovery must be developed as an alternative to conventional technologies applied to the treatment of pig manure. This paper presents the results of composting of liquid fraction of fresh manure, which is conceived at the same time as a pig wastewater pre‐treatment, wastewater volume reduction and a nutrient recovery system. Two 30 m3 turned windrows were constituted with solid fraction of pig manure and Populus sp. wood chips as bulking material at volume ratios of 1:1 and 1:2 and watered intensely with liquid fraction whilst thermophilic temperatures were maintained. Subsequently, both windrows were divided and the new windrows each received the same quantity of a different organic waste (solid fraction of pig manure, sawdust and grape bagasse), being watered with liquid fraction for a further 30 days. Stabilised composts with a nitrogen content ranging from 1.8 to 2.0% and a carbon to nitrogen ratio from 14.0 to 18.8 were obtained. Water balances showed evaporation rates ranging from 14 to 76 L/t total solids∙d and overall evaporation ratios from 1‐2.7 m3/t total solids, referred to dry matter of solid waste. While the reduction of liquid fraction volume ranged from 58 to 88% (depending on the watering rate), mass reduction of pollutants reached approximately 90% of total Kjeldahl nitrogen, ammonium and suspended solids. In comparison with traditional composting processes of solid fraction, our results show that huge amounts of liquid fraction can be treated by co‐composting with solid fraction and other solid wastes. Integrating the liquid fraction of pig manure in the composting process has improved the compost quality and has reduced the pollutant load in the remaining liquid fraction, which makes possible an advanced treatment in constructed wetlands in order to reach the necessary water quality to be recycled or even to discharge in natural water bodies. In this way, both composting and constructed wetland systems can offer an integral solution for the recovery of water and fertilizer elements contained in pig manure and diverse locally generated solid wastes. However, in spite of these benefits, more research focusing on nitrogen balances, ammonia volatilisation and greenhouse emissions will be of great interest.

M.A. Vázquez, D. de la Varga, R. Plana, M. Soto. Vertical flow constructed wetland treating high strength wastewater from swine slurry composting. Ecological Engineering, 50, 37‐43.

An integral solution for the recovery of fertilizer elements contained in swine farm slurry is the joint com‐posting of diverse solid wastes generated in the installation and surroundings, in which the composting material was watered with swine slurry. In such a system, a high percentage of the water contained in the slurry is evaporated while nutrients are, in part, retained in the compost produced. This paper presents the results of a pilot vertical flow constructed wetland (VFCW) treating the high strength leachate generated from the compost piles. The VFCW was provided with effluent recycling in order to deal with high influent concentrations of nitrogen compounds, which reached up to 459 mg NH3‐N/L and 904 mg TKN/L without the need for dilution with clean water. After start‐up, and operating at 10 C with surface loading rates (SLRs) of 9.2, 17.9, 4.8 and 1.9 g/m2 d of TSS, TCOD, BOD5 and TN, respectively, the VFCW reduced the concentration of all these parameters by more than 93%. Effluent concentration of nitrate was high during the two first months of operation (178 mg NO3‐N/L), but afterwards simultaneous nitrification and denitrification developed, reaching total nitrogen removal of 93% and low effluent nitrogen concentration (16 mg NH3‐N/L and 10 mg NO3‐N/L). Furthermore, options to avoid clogging or to facilitate the application of higher SLR are discussed.

Serrano L., de la Varga D., Ruiz I. & Soto M. (2011). Winery Wastewater Treatment in a Hybrid Constructed Wetland. Ecological Engineering 37, 744‐753.

A full‐scale hybrid constructed wetland (CW) was built to treat mixed effluent derived from a winery and tourist establishment. The treatment system consisted of a hydrolytic upflow sludge bed (HUSB) digester for suspended‐solids removal, a vertical‐flow constructed wetland (VF) and three parallel subsurface horizontal‐flow constructed wetlands (HF). The HUSB reduced TSS loads to 72‐172 mg L‐1, helping to prevent clogging, while organic loads for the wastewater entering the VF ranged from 422 to 2178 mg COD L‐1 and from 216 to 1379 mg BOD5 L‐1. At an average hydraulic loading rate (HLR) of 19.5 mm d‐1 and average surface loading rates (SLR)
of 30.4 g COD m‐2 d‐1 and 18.4 g BOD5 m‐2 d‐1, the overall VF+HF CW system reached average removal efficiencies of 86.8% of TSS, 73.3% of COD, and 74.2% of BOD5. The system also removed 52.4% of total Kjeldhal nitrogen (TKN), 55.4% of NH3‐N and 17.4% of phosphates. While the VF unit showed high removal rates, the HF unit operated at lower removal rates than those previously reported. The CW units showed rapid adaptation to low pH values. A linear‐regression analysis indicated that the independent variables SLR and temperature determined more than 95% of the variation in performance and efficiency of the CW system and offered simple mathematical models for design and system‐description purposes.

D. de la Varga, I. Ruiz, M. Soto. Winery Wastewater Treatment in Subsurface Constructed Wetlands with Different Bed Depths. Water Air Soil Pollution. 224:1485.

A comparative long‐term study of three subsurface horizontal‐flow (HF) constructed wetlands (CW) treating winery wastewater was carried out. The water depth for HF1 was 0.3 m, while the depth for HF2 and HF3 was 0.6 m, respectively. Hydraulic loading rate ranged from 7 to 93 mm/d, while surface loading rates fell into the following ranges: 4–85 g COD/m2∙d, 2–49 g BOD5/m2∙d and 0.5–6 g TSS/m2∙d. The percentage of biological oxygen demand (BOD5) removal clearly decreased when influent concentration increased, while surface removal rate increased and reached a maximum of approximately 8 g BOD5/m2∙d removed in the range of 10–20 g
BOD5/m2∙d fed, depending on the CW depth. HF1 showed a worse performance than the other units, appearing to be more affected by high influent concentrations. Solids accumulation on gravel media, hydraulic conductivity and gas emissions were monitored over the 2.8 years of operation.