Promoting sustainability in education through the implementation of green walls for greywater treatment

This study describes the methodology followed to design, build and operate a pilot green wall treating greywater from a vocational training center. The study was carried out in the framework of a master thesis in Environmental Engineering carried out in collaboration with the vocational training center where the pilot system was built. The system consisted of several pots arranged in rows planted with different species of macrophytes. Results showed a successful removal efficiency of the main pollutants (total solids and organic matter), while further post-treatment would be needed to reduce turbidity and pathogens in order to fulfill water reuse standards. This work shows how teaching in certain engineering studies can focus on sustainability and perform a practical work involving younger students from a vocational training center

Optimization of multi-stage thickening of biomass in a demonstrative full–scale microalgae-based wastewater treatment system

This study gathers the results of the operation and optimization of the thickening of microalgal biomass produced at demonstrative scale in photobioreactors fed with agricultural runoff and domestic wastewater. The optimization was conducted during two months. The system consisted in two gravity thickeners connected in series in a multi-stage approach. The objective of thickening was to concentrate the microalgae grown in photobioreactors (total solids (TS) concentration of 0.1–1 g/L) into a biomass with 20 g/L of TS, which was considered optimal for the subsequent anaerobic digestion process. First, the utilization of one single thickener alone allowed to achieve a concentration factor (CF) of 1.9 and recovery efficiency (RE) of 28%. However, the final concentration of TS in the thickened biomass (6.4 g/L) was still much lower than the target concentration. The installation of the second thickener connected in series with the first one significantly improved the overall performance. Indeed, a TS concentration of 26.5 g/L was finally achieved, with an overall CF of 3.6. The results of the study suggest that the multi-stage thickening process is a suitable strategy and it is highly advisable to achieve a successful microalgal biomass thickening at full-scale. In addition, other three points have been identified as key factors to be taken into account for biomass tickening: proper adjustment of the purge flowrate, coordination between purges times and volumes in the different stages, and proper adjustment of the operation of the scrapers.The authors would like to thank the European Commission (INCOVER, GA 689242) and the Government of Catalonia (Consolidated Research Group 2017 SGR 1029) for their financial support. E. Uggetti and R. Díez-Montero would also like to thank the Spanish Ministry of Industry and Economy for their research grants (RYC2018-025514-I and IJC2019-042069-I, respectively).Peer ReviewedPostprint (published version

Model-based evaluation of a trickling filter facility upgrade to biological nutrient removal

This article presents the feasibility evaluation and preliminary design of a wastewater treatment plant upgrade supported by simulation. The existing facility was based on trickling filters, and the objective of the upgrade was to achieve nutrients removal. The proposed solution modifies the existing primary clarifier to host an anaerobic-anoxic suspended growth reactor, which is an alternative that, to our knowledge, has not been proposed or explored so far. The trickling filters would remain as aerobic reactors. In this study, the novel treatment scheme has been assessed for the first time, through model simulations. The modified treatment train was simulated, showing that the anoxic zone is able to denitrify satisfactorily achieving the required effluent nitrogen concentration. However, to promote biological phosphorus removal, an additional aerobic zone combined with a bypass of activated sludge from the anoxic zone to the first trickling filter is needed, in order to provide aerobic conditions to the phosphate accumulating organisms. Several combinations of additional aerobic volume and sludge bypass flowrate were found to successfully achieve both nitrogen and phosphorus removal, using the existing facilities without the need for new reactors neither implementing modifications that could put the trickling filters' physical integrity at risk. The novel treatment scheme could be applied in other cases with similar flowsheet in the same context.Peer ReviewedPostprint (author's final draft

Advanced biokinetic and hydrodynamic modelling to support and optimize the design of full-scale high rate algal ponds

High rate algal ponds (HRAP) are known for their suitability to treat wastewater and to produce microalgal biomass, which can be converted into bioproducts. However, full-scale application of HRAP is still limited to few cases, and design procedures are not consolidated or standardized. In this study, a demonstrative-scale HRAP system for secondary wastewater treatment to be implemented in India (treatment capacity of 50 m3·d-1) has been designed combining conventional dimensioning techniques and advanced modelling tools. The objective of the study was to assist, verify and optimize the conventional dimensioning of the secondary HRAP by means of simulations predicting the behaviour of the system in the specific local conditions under different configurations and operational strategies. Biokinetic modelling and hydrodynamic analysis using Computational Fluid Dynamics (CFD) were carried out. The simulations performed with the biokinetic model showed that the optimal hydraulic retention time to enhance nutrient removal and biomass production is 4 days. For the hydrodynamic modelling, a 3D model of the HRAP was built to simulate the hydrodynamic behaviour of 36 different designs. Simulations allowed quantifying the presence of low velocity zones as well as the land use efficiency of the different designs in terms of the useful area vs. the total occupied area. Two baffles and tear-shapes with a diameter equal to ¼ of the channel width was the most efficient configuration. Moreover, a technical–economic assessment of the system was carried out, resulting in an investment cost of 483 € per population equivalent and an operational cost of 0.19 € per m3 of treated wastewaterAuthors would like to thank the European Commission for the financial support (PAVITR project, GA 821410) and the Department of Sciences and Technology from Government of India for the financial support (GA DST/IMRCD/India-EU/Water Call2/PAVITR/2018). Authors are also grateful to the Government of Catalonia (Consolidated Research Group 2017 SGR 1029). E. Uggetti and R. Díez-Montero would also like to thank the Spanish Ministry of Industry and Economy for their research grants (RYC2018-025514-I and IJC2019-042069-I, respectively).Peer ReviewedPostprint (published version

Influence of liquid-to-biogas ratio and alkalinity on the biogas upgrading performance in a demo scale algal-bacterial photobioreactor

The influence of the liquid-to-biogas ratio (L/G) and alkalinity on methane quality was evaluated in a 11.7 m3 outdoors horizontal semi-closed tubular photobioreactor interconnected to a 45-L absorption column (AC). CO2 concentrations in the upgraded methane ranged from <0.1 to 9.6% at L/G of 2.0 and 0.5, respectively, with maximum CH4 concentrations of 89.7% at a L/G of 1.0. Moreover, an enhanced CO2 removal (mediating a decrease in CO2 concentration from 9.6 to 1.2%) and therefore higher CH4 contents (increasing from 88.0 to 93.2%) were observed when increasing the alkalinity of the AC cultivation broth from 42 ± 1 mg L−1 to 996 ± 42 mg L−1. H2S was completely removed regardless of the L/G or the alkalinity in AC. The continuous operation of the photobioreactor with optimized operating parameters resulted in contents of CO2 (<0.1%–1.4%), H2S (<0.7 mg m−3) and CH4 (94.1%–98.8%) complying with international regulations for methane injection into natural gas grids.Peer ReviewedPostprint (published version

Feasibility assessment of energy-neutral microalgae-based wastewater treatment plants under Spanish climatic conditions

The energy balance of a hypothetical microalgae-based wastewater treatment plant (WWTP) has been performed for thirteen geographic locations covering the whole range of latitudes, longitudes and climate conditions of the different Spanish regions. The proposed WWTP includes high rate algae ponds (HRAPs) for secondary treatment and nitrogen removal, anaerobic codigestion of primary sludge and the biomass grown in the HRAPs, and a combined heat and power unit for electricity and heat production. The operation of the HRAPs was optimized using the BIO_ALGAE model, which also predicted the biomass production of the HRAPs under the different climate conditions. Under the assumptions of this study, the electrical energy balance resulted neutral or even positive in all the locations during the whole year, in spite of the climatic conditions variations. However, the heat balance resulted closer to the neutral footprint. The most favorable locations (Almeria and Seville, south of Spain) were analyzed in detail, confirming the feasibility of a positive electrical energy balance, while the heat balance resulted slightly negative in the cold season. Along with the solar radiation, the air temperature and its variation during the year are determinant to predict the feasibility of the heat balance in the proposed WWTP scheme.Peer ReviewedPostprint (author's final draft

CFD simulation of a novel anaerobic-anoxic reactor for biological nutrient removal: model construction, validation and hydrodynamic analysis based on OpenFOAM®

AnoxAn is a novel multi-environment reactor for biological nutrient removal (BNR) from wastewater. Although its biological efficacy has been demonstrated on a pilot scale, hydrodynamics is observed to significantly affect the performance of AnoxAn. To study its complex hydraulic behaviour, a model based on Computational Fluid Dynamics 3D (CFD) is constructed using the OpenFOAM® open source toolbox and validated by experimental tests of Residence Time Distribution (RTD). Reactor elements represent a key factor in the modelling process. In this sense, the impeller of the anoxic zone is modelled as a flat disk, and the baffle after the anoxic zone as a porous media. According to CFD model simulations, stagnant, short-circuit zones and mixing quality are established and quantified. Finally, the influence on the hydrodynamics of reactor elements is also evaluated. The results of this detailed hydrodynamic analysis will form the basis for the design and optimization of scalable AnoxAn configurations.Peer ReviewedPostprint (author's final draft

Sludge treatment wetland for treating microalgae digestate grown in agricultural runoff: a technical, economic, and environmental assessment

The management and disposal of wastewater treatment sludge can be a costly and resource-intensive process. To provide a cost-effective and sustainable alternative, Sludge Treatment Wetlands (STW) have emerged as a viable solution for enhancing sludge quality through dewatering and biodegradation. In this study, the effectiveness of a full-scale STW for stabilizing and dewatering digested microalgal biomass from a domestic and agricultural wastewater treatment system was evaluated. The properties of the treated digestate in the STW were assessed after 35 weeks of operation and a resting period of 4 weeks. The dry matter content was found to be 12.8%, and the average macronutrient content was K: 3.8 mg/g DW, P: 4.9 mg/g DW, and Ca: 95 mg/g DW. The highest contents of micronutrients were for Fe: 7.8 mg/g DW and Mg: 7.6 mg/g DW, while heavy metals and pathogen contents were below the EC limits for sewage sludge reuse in agriculture. The STW was found to be a cost-effective and environmentally friendly option for treating mixed wastewater-based sludge for land application. The STW outperformed reference systems using centrifuge dewatering techniques, particularly in terms of eutrophication potential and acidification potential. However, the STW’s economic performance was slightly worse than that of the dewatering system in terms of unit production cost. This study is the first in the literature to investigate the use of STW for treating digested microalgae and its possible reuse in arable land, suggesting that STW infrastructures have great potential for the development of sustainable and eco-friendly sludge treatment technologies.This research was funded by the European Commission (H2020 project INCOVER, GA 689242). E. Gonzalez-Flo would like to thank the European Union-Next Generation EU, Ministry of Universities and Recovery, Transformation and Resilience Plan for her research grant [2021UPF-MS12]. A. Ortiz would like to thank the European Union Next-Generation EU, Ministry of Universities and Recovery, Transformation and Resilience Plan for his research grant [2022UPC-MSC-94120].Peer ReviewedBy Eva Gonzalez-Flo 1 , Antonio Ortiz 2, Carlos A. Arias 3, Rubén Díez-Montero 2,4, Norbert Kohlheb 5, Ulf-Henning Schauser 6, Joan García 2 and Peder K. S. Gregersen 7. 1 GEMMA-Group of Environmental Engineering and Microbiology, Department of Civil and Environmental Engineering, Escola d’Enginyeria de Barcelona Est (EEBE), Universitat Politècnica de Catalunya-BarcelonaTech, Av. Eduard Maristany 16, Building C5.1, E-08019 Barcelona, Spain 2 GEMMA-Group of Environmental Engineering and Microbiology, Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya-BarcelonaTech, c/Jordi Girona 1-3, Building D1, E-08034 Barcelona, Spain 3 Department of Biology, Aarhus University, 8000 Aarhus, Denmark 4 GIA-Group of Environmental Engineering, Department of Water and Environmental Sciences and Technologies, Universidad de Cantabria, Avda. Los Castros s/n, 39005 Santander, Spain 5 Helmholtz-Zentrum Fuer Umveltforschung GMBH–UFZ (“UFZ”), 04318 Leipzig, Germany 6 N.A.T., Ingenieurökologisches Planungsbüro, 24340 Eckernförde, Germany 7 Center for Recirkulering v/Peder S, 6870 Gregersen Ölgod, DenmarkPostprint (published version

Inorganic carbon stimulates the metabolic routes related to the polyhydroxybutyrate production in a Synechocystis sp. strain (cyanobacteria) isolated from wastewater

Cyanobacteria are capable of transforming CO2 into polyhydroxybutyrate (PHB). In this study, different inorganic carbon concentrations (0–2 gC L−1) were evaluated for a Synechocystis sp. strain isolated from wastewater. Quantitative RT-qPCR was also performed to decipher the links between inorganic carbon and PHB and glycogen metabolism. 2 gC L−1 of bicarbonate stimulated cell growth, nutrients consumption and production of PHB. Using this concentration, a 14%dcw of PHB and an average productivity of 2.45 mgPHB L−1 d−1 were obtained. Gene expression analysis revelated that these conditions caused the overexpression of genes related to glycogen and PHB synthesis. Moreover, a positive correlation between the genes codifying for the glycogen phosphorylase, the acetyl-CoA reductase and the poly(3-hydroxyalkanoate) polymerase was found, meaning that PHB synthesis and glycogen catabolism are strongly related. These results provide an exhaustive evaluation of the effect of carbon on the PHB production and cyanobacterial metabolism

Polyhydroxybutyrate and glycogen production in photobioreactors inoculated with wastewater borne cyanobacteria monocultures

The aim of this study was to investigate the PHB and glycogen accumulation dynamics in two photobioreactors inoculated with different monocultures of wastewater-borne cyanobacteria, using a three-stage feeding strategy (growth phase, feast-famine phase and feast phase). Two cyanobacterial monocultures containing members of Synechocystis sp. or Synechococcus sp. were collected from treated wastewater and inoculated in lab-scale photobioreactors to evaluate the PHB and glycogen accumulation. A third photobioreactor with a complex microbial community grown in real wastewater was also set up. During each experimental phase different concentrations of inorganic carbon were applied to the cultures, these shifts allowed to discern the accumulation mechanism of carbon storage polymers (PHB and glycogen) in cyanobacteria. Conversion of one into the other was directly related to the carbon content. The highest PHB and glycogen contents (5.04%dcw and 69%dcw, respectively) were achieved for Synechocystis sp