Pilot scale on-site demonstration and seasonality assessment of nitrogen recovery and water reclamation from pig's slurry liquid fraction.

Livestock slurry has gathered significant interest as a secondary raw material for fertilisers industry due to its content on macronutrients -nitrogen, phosphorous, and potassium- and organic carbon. In this study, the performance of an on-site pilot plant composed by microfiltration, membrane-assisted stripping, and reverse osmosis for selective recovery of nitrogen as fertiliser and water reclamation was demonstrated for 2 years in a pig farm, referenced to 8 batches for seasonal assessment. Microfiltration mitigated the seasonal variation in the composition of pig slurry leading to stable process efficiency in the following steps. Membrane-assisted stripping resulted in the recovery of up to 56% of nitrogen as high-purity ammonium sulphate, and up to 42% of reclaimed water as reverse osmosis permeate. The proposed train of technologies reported proper performance and robustness during the whole demonstration period as it resulted in the production of reclaimed water and ammonium sulphate with no significant quality variations. The energy cost for both products obtained in this study was found in the average of the previous works reviewed with 12.49 kWh kg-1 NH3 produced, and 0.37 kWh m-3 of reclaimed water. The environmental assessment showed that nitrogen losses could be reduced by up to 90 kg N ha-1 d-1 by replacing manure spreading with precise fertilisation techniques, enabled by the selective recovery of nitrogen from SLF. Finally, the financial study showed that the scaling up of the proposed train of technologies would result in benefits for farms with more than 1600 pig heads.

Influence of pH and ozone dose on sulfaquinoxaline ozonation.

Sulfaquinoxaline (SQX) is an antimicrobial of the sulfonamides class. Usually employed in veterinary medicine, this contaminant of emerging concern has been found in superficial and groundwater and its consequences for the environment and human health are not completely known. In this study, SQX (C0 = 500 µg L-1, 1 L) degradation by an ozonation process at pH 3, 7, and 11 was evaluated. Ozonation was effective in degrading SQX: efficiency exceeding 99% was obtained applying an ozone dose of 2.8 mg L-1 at pH 3. Assays were performed according to a 22 design of experiments (DOE) with star points and three central points for statistical validity. Minimum and maximum levels were set at 3 and 11 for pH, and 0 and 11.5 mg L-1 for applied ozone dose. There was no significant interaction between these variables, and the pH value played the most important role in terms of contaminant degradation. In relation to toxicity, samples ozonated at pH 3 did not inhibit the luminescence of the bacteria, even though different intermediates were formed and identified by mass spectra. At pH 7, inhibition of luminescence remained almost constant (at around 30%) according to ozonation time or ozone dose. However, the hydroxyl radical, the major oxidant at pH 11, was responsible for the formation of toxic intermediates.

Oxidative degradation of sulfathiazole by Fenton and photo-Fenton reactions.

This article presents experimental results on 47 µmol L(-1) sulfathiazole (STZ) degradation by Fenton and photo-Fenton reactions using multivariate analysis. The optimal experimental conditions for reactions were obtained by Response Surface Methodology (RSM). In the case of the Fenton reactions there were 192 µmol L(-1) ferrous ions (Fe(II)) and 1856 µmol L(-1) hydrogen peroxide (H2O2), as compared with 157 µmol L(-1) (Fe(II)) and 1219 µmol L(-1) (H2O2) for photo-Fenton reactions. Under these conditions, around 90% of STZ degradation were achieved after 8 minutes treatment by Fenton and photo-Fenton reactions, respectively. Moreover, a marked difference was observed in the total organic carbon (TOC) removal after 60-min treatment, achieving 30% and 75% for the Fenton and photo-Fenton reactions, respectively. Acetic, maleic, succinic and oxamic acids could be identified as main Fenton oxidation intermediates. A similar pattern was found in the case of photo-Fenton reaction, including the presence of oxalic acid and ammonia at short periods of irradiation with UV-A. The calculated values of Average Oxidation State (AOS) corroborate the formation of oxidized products from the initial steps of the reaction.

Degradation of sulphamethazine by means of an improved photo-Fenton process involving a hydrogen peroxide systematic dosage.

Despite being acknowledged as an emerging contaminant, sulphamethazine (SMT) degradation has received scarce attention in the advanced oxidation processes field. Thus, this work addresses the degradation of SMT in water solutions (12 L of 25mgL-1 samples) by means of a photo-Fenton process and a systematic H202 dosage protocol that enhances its performance. A conventional photo-Fenton process led to 86% mineralization after 120 min treatment when adding the Fenton reactants at once (initial concentrations were 10mgL-1 Fe(II) and 200mgL-1 H2O2). Conversely, the process achieved the total mineralization of the samples in less than 75 min when the same amount of H202 was continuously dosed according to a conveniently tuned dosage protocol. In both cases, total SMT degradation was achieved within 10 min. Hence, this work's aim is to determine the efficient dosage conditions of H2O2. The results show that a significant improvement of the photo-Fenton mineralization of SMT solutions is possible by adjusting the dosage of H2O2.

Forest bathing and hiking benefits for mental health during the COVID-19 pandemic in Mediterranean regions.

Forest bathing (FB) has evidenced positive effects on individuals' mental health and well-being, but its benefits have mainly been studied in Asian biomes. The present study aimed to evaluate whether its benefits are also generalisable to other forests and biomes of the world, such as the Mediterranean. Eighty-six healthy adults of the general population were assessed before and after a FB near Barcelona (Spain) during the COVID-19 pandemic. A control-hiking group of participants was also analysed to contrast the FB effects on anxiety, affect, mood states and mindfulness. Results show that the guided practice of FB in Mediterranean-Catalan forests increases mindfulness states and positive affect and reduces anxiety and negative affect, with effect sizes being large to very large. Hiking also induced significant changes in all variables tested, but FB showed higher effect sizes. An exploratory analysis also revealed a different profile of the FB participants compared to the hiking practitioners, being highly educated women living in urban areas and with lower basal levels of psychological well-being. Accordingly, it is concluded that both Mediterranean FB and hiking (to a lesser degree) might be cost-effective strategies to promote and restore psychological well-being after the COVID-19 pandemic and to promote sustainable tourism in Mediterranean biomes of the European forested and protected areas.

Nutrient recovery and valorisation from pig slurry liquid fraction with membrane technologies.

Livestock slurry has been reported to be a potential secondary raw material as it contains macronutrients ­nitrogen, phosphorus and potassium-, which could be valorised as high-quality fertilizers if proper separation and concentration of valuable compounds is performed. In this work, pig slurry liquid fraction was assessed for nutrient recovery and valorisation as fertilizer. Some indicators were used to evaluate the performance of proposed train of technologies within the framework of circular economy. As ammonium and potassium species are highly soluble at the whole pH range, a study based on phosphate speciation at pH from 4 to 8 was assessed to improve the macronutrients recovery from the slurry, resulting in two different treatment trains at acidic and alkaline conditions. The acidic treatment system based on centrifugation, microfiltration and forward osmosis was applied to obtain a nutrient-rich liquid organic fertilizer containing 1.3 % N, 1.3 % P2O5 and 1.5 % K2O. The alkaline path of valorisation was composed by centrifugation and stripping by using membrane contactors to produce an organic solid fertilizer -7.7 % N, 8,0 % P2O5 and 2.3 % K2O-, ammonium sulphate solution -1.4 % N- and irrigation water. In terms of circularity indicators, 45.8 % of the initial water content and <50 % of contained nutrients were recovered - 28.3 % N, 43.5 % P2O5 and 46.6 % K2O - in the acidic treatment resulting in 68.68 g fertilizer per kg of treated slurry. 75.1 % of water was recovered as irrigation water and 80.6 % N, 99.9 % P2O5, 83.4 % K2O was valorised in the alkaline treatment, as 219.60 g fertilizer per kg of treated slurry. Treatment paths at acidic and alkaline conditions yield promising results for nutrients recovery and valorisation as the obtained products (nutrient rich organic fertilizer, solid soil amendment and ammonium sulphate solution) fulfil the European Regulation for fertilizers to be potentially used in crop fields.

Modelling of the photo-Fenton process with flexible hydrogen peroxide dosage: Sensitivity analysis and experimental validation.

The supply of hydrogen peroxide (H2O2) controlling the amount of highly oxidant hydroxyl radicals is the most critical operational issue for the photo-Fenton process. Accordingly, this study addresses the development of a model for photo-Fenton processes including a flexible H2O2 supply given as a function of time. The model is aimed at its future exploitation in treatment optimization and the determination of the optimal profile for H2O2 supply. The work has adopted a photo Fenton model previously reported that includes the inlet flow (fed-batch) and describes the system dynamics under a flexible dosage. Thus, model global sensitivity analysis (GSA) and parameter estimation were performed using Simulink® to examine the behavior of the model under flexible H2O2 dosage. GSA was carried out using partial rank correlation methods and the Latin hypercube sampling to assess to which extent variations of the model parameters affect each measured response (H2O2, total organic carbon, TOC, and dissolved oxygen, O2 -the experimentally available information). Hence, the model is discussed in regard of its hypothesis and chances for reducing its complexity. This resulted in the rejection of two reactions of the initial model. Next, a set of 12 kinetic, stoichiometric and operative parameters was estimated through the fitting of H2O2, TOC, and O2 profiles. Discussion on model fitting includes computational issues, the role of initial values for the estimation process, the goodness of fit criteria, and the sampling method. The model was fit to experimental data with assorted H2O2 supply profiles and validated, and Root Mean Square Error (RMSE) below 0.009 mM, 0.42 mM, and 0.127 mM were obtained for TOC, H2O2 and O2, respectively. Therefore, this work contributes a practical model aimed at providing model-based optimization for the H2O2 dosage profile of the photo-Fenton process.

Towards an Efficient Generalization of the Online Dosage of Hydrogen Peroxide in Photo-Fenton Process to Treat Industrial Wastewater.

This work addresses the dosage of H2O2 in photo-Fenton processes and the monitoring of Dissolved oxygen (DO) that can be used to drive the dosage of H2O2. The objective of this work is to show that a smarter monitoring of a process variable such as DO (for which on-line measurement can be inexpensively obtained) enables the proposal and implementation of efficient dosage strategies. The work explores the application of a recent proposed strategy consisting of: (i) initial H2O2 addition, (ii) continuous H2O2 addition until a DO set up is reached, and (iii) automatic H2O2 addition by an on-off control system based on DO slope monitoring, and applies it to the treatment of different individual contaminants and their mixtures (paracetamol and sulfamethazine). The assays performed following this dosage strategy showed improved values of TOC removed per H2O2 consumed. For the case of sulfamethazine, this improvement increased up to 25-35% with respect to the efficiency obtained without dosage. Furthermore, a deeper analysis of the results allowed detecting and assessing the opportunity to redesign the dosage scheme and reduce its complexity and the number of control parameters. The promising results obtained are discussed in regard of future research into further increasing the simplicity and robustness of this generalized control strategy that improves the applicability of the photo-Fenton process by reducing its operating costs and increasing automation.

Manufacturing and Application of 3D Printed Photo Fenton Reactors for Wastewater Treatment.

Additive manufacturing (AM) or 3D printing offers a new paradigm for designing and developing chemical reactors, in particular, prototypes. The use of 3D printers has been increasing, their performance has been improving, and their price has been reducing. While the general trend is clear, particular applications need to be assessed for their practicality. This study develops and follows a systematic approach to the prototyping of Advanced Oxidation Processes (AOP) reactors. Specifically, this work evaluates and discusses different printable materials in terms of mechanical and chemical resistance to photo-Fenton reactants. Metallic and ceramic materials are shown to be impracticable due to their high printing cost. Polymeric and composite materials are sieved according to criteria such as biodegradability, chemical, thermal, and mechanical resistance. Finally, 3D-printed prototypes are produced and tested in terms of leakage and resistance to the photo-Fenton reacting environment. Polylactic acid (PLA) and wood-PLA composite (Timberfill®) were selected, and lab-scale raceway pond reactors (RPR) were printed accordingly. They were next exposed to H2O2/Fe(II) solutions at pH = 3 ± 0.2 and UV radiation. After 48 h reaction tests, results revealed that the Timberfill® reactor produced higher Total Organic Carbon (TOC) concentrations (9.6 mg·L-1) than that obtained for the PLA reactor (5.5 mg·L-1) and Pyrex® reactor (5.2 mg·L-1), which suggests the interference of Timberfill® with the reaction. The work also considers and discusses further chemical and mechanical criteria that also favor PLA for 3D-printing Fenton and photo-Fenton reactors. Finally, the work also provides a detailed explanation of the printing parameters used and guidelines for preparing prototypes.

Sulfaquinoxaline Oxidation and Toxicity Reduction by Photo-Fenton Process.

Sulfaquinoxaline (SQX) has been detected in environmental water samples, where its side effects are still unknown. To the best of our knowledge, its oxidation by Fenton and photo-Fenton processes has not been previously reported. In this study, SQX oxidation, mineralization, and toxicity (Escherichia coli and Staphylococcus aureus bacteria) were evaluated at two different setups: laboratory bench (2 L) and pilot plant (15 L). The experimental design was used to assess the influence of the presence or absence of radiation source, as well as different H2O2 concentrations (94.1 to 261.9 mg L-1). The experimental conditions of both setups were: SQX = 25 mg L-1, Fe(II) = 10 mg L-1, pH 2.8 ± 0.1. Fenton and photo-Fenton were suitable for SQX oxidation and experiments resulted in higher SQX mineralization than reported in the literature. For both setups, the best process was the photo-Fenton (178.0 mg L-1 H2O2), for which over 90% of SQX was removed, over 50% mineralization, and bacterial growth inhibition less than 13%. In both set-ups, the presence or absence of radiation was equally important for sulfaquinoxaline oxidation; however, the degradation rates at the pilot plant were between two to four times higher than the obtained at the laboratory bench.

An experimental approach to the optimization of the dosage of hydrogen peroxide for Fenton and photo-Fenton processes.

The determination of the hydrogen peroxide dosage scheme that minimizes hydrogen peroxide consumption while meeting the specified treatment outcome is crucial for Fenton and photo-Fenton processes. The challenge is building a methodology that provides the optimal dosage profile. However, the lack of detailed dynamic models prevents exploiting model-based optimization methods that have proved successful in other applications. Thus, this work addresses this challenge by providing a problem formulation identifying and discussing objectives and constraints, and the nature of the optimal solution. From this point, the work presents a novel dosage model and a consequent methodology aimed at experimentally optimizing the dosage profile along a discretized time horizon following recipe optimization concepts. The approach is parallel to the numerical solution of the model-based optimization problem posed by hydrogen peroxide dosage. The proposed methodology is validated in the remediation of a Paracetamol (PCT) solution, and the obtained results are assessed and discussed in regard of the evolution of the concentration of hydrogen peroxide, the contaminant (PCT), and Total Organic Carbon (TOC). The concentration of dissolved oxygen (DO), which is also monitored, allows providing a more comprehensive explanation of the nature of the process.

A novel modeling approach for a generalizable photo-Fenton-based degradation of organic compounds.

This work aims at proposing and validating a model that can be exploited for the future development of industrial applications (e.g., process design and control) of Fenton and photo-Fenton processes. Hence, a compromise modeling solution has been developed between the non-generalizable accuracy of the first principles models (FPMs) and the oversimplification of the empirical models (EMs). The work presents a novel model of moderate complexity that is simplified enough to be generalizable and computationally affordable, while retaining physical meaning. The methodology is based on a general degradation mechanism that can be algorithmically generated from the carbon number of the target compound, as well as from the knowledge of two kinetic parameters, one for the faster initial rate and the other one for the subsequent degradation steps. The contaminant degradation mechanism has been combined with an appropriately simplified implementation of the well-known Fenton and photo-Fenton kinetics. This model describes the degradation not only of the target compound and of the oxidant, but also of total organic carbon (TOC), which is used to define the overall quality of the water. Experimental design techniques were used along with a non-conventional modeling methodology of programmable process structures (PPS). This novel modeling approach was applied and validated on the degradation of three model compounds. A successful prediction of the evolution of the contaminants H2O2 and TOC was confirmed and assessed by the root mean square error (RMSE).

Systematic optimization approach for the efficient management of the photo-Fenton treatment process.

The photo-Fenton process is a photochemical process that has proved to be highly efficient in degrading new potentially harmful contaminants. Despite of this, scarce attention has been paid to the development of systematic procedures and optimisation strategies to efficiently operate such a process. The present work aims at investigating the effectiveness of a model-based approach in carrying out the dynamic optimisation of the recipe of a photo-Fenton process, performed in fed-batch mode (reactant dosage). This work has addressed and solved multiple optimisation problems, searching for the optimal hydrogen peroxide (H2O2) dosage profile, and Pareto frontiers have been built accordingly in order to point out the interaction between three main process efficiency parameters, such as processing time, total amount of H2O2 used, and Total Organic Carbon (TOC) removal. Such a study allows mapping the best operating conditions and provides a decision-making oriented overview of the process. An economic study has also been carried out with the aim of finding out the optimal H2O2 dosage profile that guarantees the minimum operating cost under a varying set of operational and environmental constraints, such as TOC removal. This work has adopted and properly adapted the model by Cabrera Reina et al. (2012) in order to describe the evolution of the system under a flexible reactant dosage. Cabrera Reina et al. (2012) proposed a semi-empirical kinetic model to track paracetamol degradation using the photo-Fenton process and experimentally validated this model for a pollutant load range between 4 and 25 mmol L-1 of TOC (e.g. industrial wastewaters). Dynamic optimisation has been addressed applying a direct simultaneous optimisation method using this extended model. Results have been presented and discussed in regard of optimal H2O2 dosage under both economic and environmental constraints. The model-based optimisation approach has allowed a fast practical recipe adjustment with reduced experimental work.

Removal of Paracetamol Using Effective Advanced Oxidation Processes.

Fenton, photo-Fenton, and photo-induced oxidation, were investigated and compared for the treatment of 0.26 mmol L-1 of paracetamol (PCT) in a deionised water matrix, during a reaction span of 120.0 min. Low and high Fenton reagent loads were studied. Particularly, the initial concentration of Fe2+ was varied between 0.09 and 0.18 mmol L-1 while the initial concentration of H2O2 was varied between 2.78 and 11.12 mmol L-1. The quantitative performance of these treatments was evaluated by: (i) measuring PCT concentration; (ii) measuring and modelling TOC conversion, as a means characterizing sample mineralization; and (iii) measuring cytotoxicity to assess the safe application of each treatment. In all cases, organic matter mineralization was always partial, but PCT concentration fell below the detection limit within 2.5 and 20.0 min. The adopted semi-empirical model revealed that photo induced oxidation is the only treatment attaining total organic matter mineralization ( ξ MAX = 100% in 200.0 min) at the expense of the lowest kinetic constant (k = 0.007 min-1). Conversely, photo-Fenton treatment using high Fenton reagent loads gave a compromise solution ( ξ MAX = 73% and k = 0.032 min-1). Finally, cytotoxicity assays proved the safe application of photo-induced oxidation and of photo-Fenton treatments using high concentrations of Fenton reagents.

A kinetic study for the Fenton and photo-Fenton paracetamol degradation in an annular photoreactor.

A kinetic model describing Fenton and photo-Fenton degradation of paracetamol (PCT) and consumption of hydrogen peroxide (H2O2) was proposed. A set of Fenton and photo-Fenton experiments (18 runs in total) was performed by fixing the initial concentration of PCT to 40 mg L-1 and varying the initial concentrations of H2O2 and ferrous ion, Fe2+. The experimental set-up was a well-stirred annular photoreactor equipped with an actinic BL TL-DK 36 W/10 1SL lamp. Experimental results highlighted that PCT is no more detected by HPLC analysis within a minimum reaction time of 2.5 and a maximum reaction time of 15.0 min. Besides, a maximum conversion of total organic carbon (TOC) of 68.5% was observed after 75 min of reaction in case of using UV radiation and the highest concentrations of the Fenton reagents. The experimental data were used to fit the kinetic model. The radiation field inside the reactor was taken into account through the local volumetric rate of photon absorption, evaluated by assuming a line source model with spherical and isotropic emission. The kinetic parameters were estimated by using a non-linear least-squares regression procedure and root mean square errors (RMSE) were calculated in order to validate the feasibility of the proposed model. A good agreement between experimental and predicted data was observed and the lowest values of RMSE resulted in 5.84 and 9.59% for PCT and H2O2 normalized concentrations, respectively.

Experimental design of Fenton and photo-Fenton reactions for the treatment of ampicillin solutions.

This paper discusses the degradation of the antibiotic ampicillin (AMP) by Fenton and photo-Fenton reactions. The influence of the three main variables that govern the degradation kinetic (pH, H(2)O(2) and Fe(II) concentrations) was evaluated with a circumscribed central composite (CCC) model and a response surface methodology (RSM). The optimal conditions for Fenton and photo-Fenton reactions are very similar: pH 3.5, around 400 micromol L(-1) H(2)O(2) and 87 micromol L(-1) Fe(II). Under such optimized conditions, the complete AMP removal was reached after 10 min and 3 min for Fenton and photo-Fenton reactions, respectively. A very similar removal profile in the first 2 min of reaction was observed for both systems with a high degree of degradation (close to 90%). After a 2-min treatment, the Fenton reaction became slower, and the IR product analysis suggests the formation of different oxidation intermediates. This observation was confirmed by the COD and TOC evolution during the reactions. The oxidation degree, measured as Average Oxidation State (AOS), indicates that the photo-Fenton reaction produces faster most of the oxidation intermediates. The antibacterial activity (AA) of the oxidized samples was determined using the inhibition halo methodology on agar plates cultured with Staphylococcus aureus bacteria. The course of AA is concomitant with the AMP removal, which indicates that the long-term intermediates do not present antibiotic properties.

Characterization of the degradation performance of the sulfamethazine antibiotic by photo-Fenton process.

The present study provides results describing the degradation performance of the Sulfamethazine (SMT) antibiotic via photo-Fenton treatment. Experiments were carried out using 1 L solution samples of SMT (50 mg L(-1)) under different conditions. HPLC results reveal that both Fenton and photo-Fenton reactions were able to completely remove SMT antibiotic from the studied samples in less than 2 min treatment. Half-life times and kinetic parameters (assuming a pseudo-first-order kinetics at reaction initial stage, far from the equilibrium) for SMT degradation were determined and discussed. Hence, appropriate Fenton reagent loads are given to attain different targets proposed. TOC and HPLC data also revealed the presence of reaction intermediates; thus toxicity assays were performed regarding bacterial growth rate. The toxicity of an SMT solution was shown to increase during its degradation by means of photo-Fenton reactions.