Analysis of a photobioreactor scaling up for tertiary wastewater treatment: denitrification, phosphorus removal, and microalgae production

The present work studies the removal of nutrients (nitrate and phosphate) from a synthetic wastewater simulating a secondary treatment effluent using the microalgae Chlorella vulgaris in autotrophic photobioreactors, together with an analysis of the critical points affecting the scaling-up process from laboratory to pilot scale. Laboratory experiments were done in open agitated 1-L photobioreactors under batch operation mode, while pilot-scale experiments were done using a 150-L closed tubular photobioreactor under continuous operation mode. In both scales, nitrate was the limiting substrate and the effect of its concentration on microalgae performance was studied. From laboratory experiments, an average microalgae productivity of 85 mgVSS L−1 day−1 and approximate maximum N-NO3− and P-PO43− removal rates of 8 mg N gVSS−1 day−1, and 2.6 mg P gVSS−1 day−1 were found. Regarding pilot scale, the average microalgae productivity slightly decreased (76 mgVSS L−1 day−1) while the approximate maximum N-NO3− and P-PO43− removal rates slightly were increased (11.7 mg N gVSS−1 day−1 and 3.04 mg P gVSS−1 day−1) with respect to the laboratory-scale results. The pilot-scale operation worked under lower levels of turbulence and higher dissolved oxygen concentration and light intensity than laboratory experiments; those parameters were difficult to control and they can be identified as the critical points in the differences found on both nutrient removal and microalgae production.El presente trabajo estudia la remoción de nutrientes (nitrato y fosfato) de un agua residual sintética simulando un efluente de tratamiento secundario utilizando la microalga Chlorella vulgaris en fotobiorreactores autótrofos, junto con un análisis de los puntos críticos que afectan el proceso de escalado de laboratorio a escala piloto. . Los experimentos de laboratorio se realizaron en fotobiorreactores abiertos agitados de 1 L en modo de operación por lotes, mientras que los experimentos a escala piloto se realizaron utilizando un fotobiorreactor tubular cerrado de 150 L en modo de operación continua. En ambas escalas, el nitrato fue el sustrato limitante y se estudió el efecto de su concentración sobre el comportamiento de las microalgas. A partir de experimentos de laboratorio, una productividad media de microalgas de 85 mg VSS L -1 día-1 y máximo aproximado N-NO 3 - y P-PO 4 3- tasas de eliminación de 8 mg N g VSS -1 día -1 , y 2,6 mg P g VSS -1 día -1 se encontraron. Con respecto a la escala piloto, la productividad promedio de microalgas disminuyó levemente (76 mg VSS L −1 día −1 ) mientras que las tasas máximas aproximadas de remoción de N-NO 3 - y P-PO 4 3− aumentaron levemente (11.7 mg N g VSS −1 día -1 y 3,04 mg P g VSS -1 día−1 ) con respecto a los resultados a escala de laboratorio. La operación a escala piloto funcionó bajo niveles más bajos de turbulencia y mayor concentración de oxígeno disuelto e intensidad de luz que los experimentos de laboratorio; esos parámetros fueron difíciles de controlar y pueden identificarse como los puntos críticos en las diferencias encontradas tanto en la eliminación de nutrientes como en la producción de microalgas

Towards the optimization of electro-bioremediation of soil polluted with 2,4-dichlorophenoxyacetic acid

The aim of this work is to study the optimization of electro-bioremediation (EBR) treatment of a 2,4-dichlorophenoxyacetic acid (2,4-D) polluted clay soil. The influence of two different variables were evaluated through batch experiments in a bench-scale electrokinetic setup using previously acclimated microbial cultures for 2,4-D biodegradation. First, it was studied the influence of the frequency applied in polarity reversal (PR): frequencies under study were 1, 2 and 6 d−1, i.e., polarity changed every 24, 12 and 4 h respectively. The duration of experiments were 14 days and the electric field applied was 1.0 V cm−1 (20 V) at room temperature. The second variable under study was the operation time, and based on the previous results, the selected frequency of PR was 2 d-1 and three additional EBR experiments were conducted using different operation times (3, 7 and 10 days). Experiments without electric current (only biological contribution) for each operation time were simultaneously performed under the same experimental conditions as reference tests to check the influence of electrokinetics. Removal of 2,4-D from polluted clay soil was completed in 10 days. It was observed that solubility of the pollutant is a critical factor to ensure high removal efficiencies. Moreover, polarity reversal contributed to the successful results by maintaining correct pH values and reducing the removal of electrolytes from soil. By comparing the EBR results with the reference tests (without the contribution of EK phenomena), it was proved that the combination of bioremediation and electrokinetics has positive effects in the remediation of low permeable polluted soil

Effect of the polarity reversal frequency in the electrokinetic-biological remediation of oxyfluorfen polluted soil. 2017, 177

This work studies the feasibility of the periodic polarity reversal strategy (PRS) in a combined electrokinetic-biological process for the remediation of clayey soil polluted with a herbicide. Five two-weeks duration electrobioremediation batch experiments were performed in a bench scale set-up using spiked clay soil polluted with oxyfluorfen (20 mg kg. Additionally, two complementary reference tests were done: single bioremediation and single electrokinetic. The microbial consortium used was obtained from an oil refinery wastewater treatment plant and acclimated to oxyfluorfen degradation. Main soil conditions (temperature, pH, moisture and conductivity) were correctly controlled using PRS. On the contrary, the electroosmotic flow clearly decreased as increased. The uniform soil microbial distribution at the end of the experiments indicated that the microbial activity remained in every parts of the soil after two weeks when applying PRS. Despite the adapted microbial culture was capable of degrade 100% of oxyfluorfen in water, the remediation efficiency in soil in a reference test, without the application of electric current, was negligible. However, under the low voltage gradients and polarity reversal, removal efficiencies between 5% and 15% were obtained, and it suggested that oxyfluorfen had difficulties to interact with the microbial culture or nutrients and that PRS promoted transport of species, which caused a positive influence on remediation. An optimalEste trabajo estudia la viabilidad de la estrategia de inversión periódica de polaridad (PRS) en un proceso combinado electrocinético-biológico para la remediación de suelos arcillosos contaminados con un herbicida. Se realizaron cinco experimentos por lotes de electrobiorremediación de dos semanas de duración en una instalación a escala de banco utilizando suelo arcilloso con púas contaminado con oxifluorfeno (20 mg kg. Adicionalmente, se realizaron dos pruebas complementarias de referencia: biorremediación simple y electrocinética simple . El consorcio microbiano utilizado fue obtenido de una planta de tratamiento de aguas residuales de una refinería de petróleo y aclimatado a la degradación del oxifluorfeno. Las principales condiciones del suelo (temperatura, pH, humedad y conductividad) se controlaron correctamente mediante PRS. Por el contrario, el flujo electroosmótico disminuyó claramente a medida que aumentado. La distribución microbiana uniforme del suelo al final de los experimentos indicó que la actividad microbiana permaneció en todas las partes del suelo después de dos semanas al aplicar PRS. A pesar de que el cultivo microbiano adaptado fue capaz de degradar el 100% del oxifluorfeno en el agua, la eficiencia de remediación en el suelo en una prueba de referencia, sin la aplicación de corriente eléctrica , fue insignificante. Sin embargo, bajo los gradientes de bajo voltaje y la inversión de polaridad, se obtuvieron eficiencias de remoción entre el 5% y el 15%, y sugirió que el oxifluorfeno tenía dificultades para interactuar con el cultivo microbiano o los nutrientes y que el PRS promovió el transporte de especies, lo que provocó una influencia positiva. sobre la remediación. Un óptim

Can electro-bioremediation perform as a self-sustainable process?

This work studies the effect of treatment period on remediation efficiency in an oxyfluorfen-polluted soil through electro-bioremediation technology. Five lab-scale experimental plants were started up simultaneously, operated under an electric field of 1.0 V cm−1 with a polarity reversal frequency of 2 day−1 and disconnected at different times (2, 4, 6, 11 and 24 weeks); these plants underwent post mortem characterization after their operation period. Various parameters were monitored in the electrolyte wells during the experiments. The obtained results indicate that despite the low reproducibility of pH and conductivity in the wells (not in soil), the main conclusions that can be drawn for the different plants are sound and hence have acceptable reproducibility. Polarity reversal allowed suitable conditions for microbial life in terms of pH, but nutrients were also depleted in the soil, which leads to a decrease in the total population of microorganisms during treatment. For treatment periods of less than 10 weeks, there was an appreciable population of microorganisms in the soil, which reached oxyfluorfen removal levels of up to 40%. Longer reaction times were ineffective, and this was related to the much lower concentration of microorganisms. In comparing these results to those obtained in conventional soil bioremediation technology, the application of polarity-reversed electric current led to an increase in the average removal of oxyfluorfen from 0.11 to 0.17 mg kg−1 day−1 but a much higher decrease in the active microorganism population from 88.0 ± 9.0 to 41.0 ± 6.0% of the initial seeded value

Influence of electric field on the remediation of polluted soil using a biobarrier assisted electro-bioremediation process

In this work, it was carried out the study of the electro-bioremediation of soil polluted with diesel by means of combined electrokinetic soil flushing and biobarriers, using bench scale setups and fourteen days-long tests. Two different biobarriers were evaluated: one of them was developed in the laboratory, with a culture of diesel-degrading microorganisms supported on gravel particles (BB1); the other was obtained by mixing directly clay soil with activated sludge obtained in a municipal wastewater treatment plant (BB2). Biobarriers were placed in a central point of the soil section to be treated, to prevent the negative consequences of pH fronts on microorganisms viability. Potential difference of 0.5 and 1.0 V cm−1 were applied. For the promotion in the transport of the diesel to the biobarrier, a surfactant solution was used as electrolyte (flushing fluid). Results confirm that negative influence of the extreme pH fronts on the microbial viability can be prevented using this electro-bioremediation approach. In the same way, uniform diesel removal was obtained all over the soil by using the surfactant solution. After fourteen days of treatment, in the experiments using the BB1, 19.36% and 27.36% of the total amount of diesel present in the soil were removed applying 0.5 and 1.0 V cm−1, respectively. In the experiments using BB2, 23.33% and 29.10% referred to the total amount of diesel were removed after the fourteen days tests at 0.5 and 1.0 V cm−1, respectively, indicating that the non-specific barrier is slightly more efficient despite not containing an acclimated culture.En este trabajo se llevó a cabo el estudio de la electro-biorremediación de suelos contaminados con diésel mediante lavado electrocinético combinado de suelos y biobarreras, utilizando montajes a escala de banco y ensayos de catorce días de duración. Se evaluaron dos biobarreras diferentes: una de ellas desarrollada en laboratorio, con un cultivo de microorganismos degradadores de diesel soportado en partículas de grava (BB1); el otro se obtuvo mezclando directamente tierra arcillosa con lodos activados obtenidos en una estación depuradora de aguas residuales municipales (BB2). Se colocaron biobarreras en un punto central de la sección del suelo a tratar, para prevenir las consecuencias negativas de los frentes de pH sobre la viabilidad de los microorganismos. Diferencia de potencial de 0,5 y 1,0 V cm −1se aplicaron. Para la promoción en el transporte del diésel a la biobarrera se utilizó una solución de surfactante como electrolito (líquido de lavado). Los resultados confirman que la influencia negativa de los frentes de pH extremos en la viabilidad microbiana se puede prevenir utilizando este enfoque de electro-biorremediación. De igual forma se obtuvo una remoción uniforme de diesel en todo el suelo al utilizar la solución de surfactante. Después de catorce días de tratamiento, en los experimentos con BB1, se eliminó el 19,36% y el 27,36% de la cantidad total de diésel presente en el suelo aplicando 0,5 y 1,0 V cm - 1 , respectivamente. En los experimentos con BB2, el 23,33 % y 29,10 % referido a la cantidad total de diésel se eliminó después de los catorce días de pruebas a 0,5 y 1,0 V cm −1, respectivamente, indicando que la barrera no específica es ligeramente más eficiente a pesar de no contener un cultivo aclimatado

Biostimulation versus bioaugmentation for the electro-bioremediation of 2,4 dichlorophenoxyacetic acid polluted soils

The aim of this work is to compare three biological strategies for the in situ remediation of a 2,4-dichlorophenoxyacetic acid (2,4-D) polluted clayey soil by coupling electrokinetics (EK) and bioremediation (technology named as electrobioremediation, EBR). The first option (i) is EK-biostimulation, in which the activity of microorganisms already present in soil is enhanced by EK phenomena. The second and third options are EK-bioaugmentation, which consist of addition of microorganisms to soil through the inclusion of permeable biological barriers: (ii) using a microbial fixed biofilm reactor as biobarrier (BB1), and (iii) using a mixture of clean soil and a microbial suspension as biobarrier (BB2). Thus, three batch experiments at bench scale were conducted under a constant electric field of 1 V cm−1, and electrode polarity was periodically reversed every 12 h (2 d−1). The duration of each test was 10 days. Two additional tests using only biodegradation or only EK were performed as auxiliary reference tests. A microbial consortium acclimated to 2,4-D biodegradation was employed. Results showed that EK-biostimulation strategy offered the best pollutant removal efficiency (reaching up almost 100%) while biobarriers offered pollutant removal rates between 75 and 85%. Permeable biobarriers allowed the introduction of microorganism but caused a decrease in the electro-osmotic flow which, in turn, reduced the mobilization and contact between microorganisms and pollutants. These results can contribute to the knowledge and understanding of electrobioremediation of polluted soil and to the feasibility of delivering microorganism to the soil by using biobarriers. Despite biostimulation was found to be the best option, results show that permeable reactive biobarriers may result in a successful alternative for in-situ EK-bioaugmentation when acclimated microbial population is not already present in soil

Strategies for the electrobioremediation of oxyfluorfen polluted soils

This work compares three strategies for the in-situ remediation of oxyfluorfen polluted clay soil, based on the combination of biological processes and electrokinetics (EK): (i) EK-biostimulation, in which the action of microorganisms contained in soil is promoted without the use of biological permeable barriers, (ii) EK-bioaugmentation with fixed culture of microorganisms (BB1), which enhanced the natural bioremediation by including a microbial fixed biofilm reactor as permeable biobarrier, and (iii) EK-bioaugmentation with suspended culture of microorganisms (BB2), which improves the natural remediation by including a mixture of soil and a microbial suspension as permeable biobarrier. To do this, two-week batch electro-bioremediation tests were carried out using bench scale set-ups. In each case, a constant electric field (1 V cm−1) was applied, and electrode polarity was reversed periodically, every 12 h. In addition, a microbial consortium acclimated to oxyfluorfen biodegradation was used. The best oxyfluorfen removal efficiency (15%) was obtained using the option (i). Permeable biobarriers allowed the introduction of microorganism and nutrients into the soil, and the biological activity reached the whole soil positions. However, the insertion of these biobarriers caused an excessive decrease in the electro-osmotic flow (approximately 80%) which, in turn reduced the mobilization of the pollutants. Despite of that, results show that permeable reactive biobarriers may result in a successful alternative for in-situ EK-bioaugmentation, although higher retention times would be needed to obtain higher removal efficiencies

Effect of electric field on the performance of soil electro-bioremediation with a periodic polarity reversal strategy

In this work, it is studied the effect of the electric fields (within the range 0.0–1.5 V cm−1) on the performance of electrobioremediation with polarity reversal, using a bench scale plant with diesel-spiked kaolinite with 14-d long tests. Results obtained show that the periodic changes in the polarity of the electric field results in a more efficient treatment as compared with the single electro-bioremediation process, and it does not require the addition of a buffer to keep the pH within a suitable range. The soil heating was not very important and it did not cause a change in the temperature of the soil up to values incompatible with the life of microorganisms. Low values of water transported by the electro-osmosis process were attained with this strategy. After only 14 d of treatment, by using the highest electric field studied in this work (1.5 V cm−1), up to 35.40% of the diesel added at the beginning of the test was removed, value much higher than the 10.5% obtained by the single bioremediation technology in the same period.En este trabajo se estudia el efecto de los campos eléctricos (en el rango 0,0–1,5 V cm −1) sobre el desempeño de la electrobiorremediación con inversión de polaridad, utilizando una planta a escala de banco con caolinita enriquecida con diesel con pruebas largas de 14 días. Los resultados obtenidos muestran que los cambios periódicos en la polaridad del campo eléctrico dan como resultado un tratamiento más eficiente en comparación con el proceso único de electrobiorremediación, y no requiere la adición de un tampón para mantener el pH dentro de un rango adecuado. El calentamiento del suelo no fue muy importante y no provocó un cambio en la temperatura del suelo hasta valores incompatibles con la vida de los microorganismos. Con esta estrategia se lograron valores bajos de agua transportada por el proceso de electroósmosis. Después de solo 14 d de tratamiento, usando el campo eléctrico más alto estudiado en este trabajo (1.5 V cm −1), se eliminó hasta un 35,40% del diesel agregado al inicio de la prueba, valor muy superior al 10,5% obtenido por la tecnología de biorremediación sola en el mismo período

Electrokinetic remediation of soil polluted with insoluble organics using biological permeable reactive barriers: Effect of periodic polarity reversal and voltage gradient

This study investigated the remediation of clay soil polluted with low-solubility organics (diesel hydrocarbons) using a combined electrochemical-biological technology. Electrokinetic soil flushing was used, coupled with a biological permeable reactive barrier, which was placed into soil away from electrodes to prevent the negative effects of the acidic and basic fronts on the viability of microorganisms. Three two-week long batch experiments were performed in a lab-scale installation specifically designed to evaluate the remediation of polluted soil. The primary variable under study was the electric field applied to the soil (0.5, 1.0 and 1.5 V cm−1), and the experimental procedure included daily polarity reversal of the electrodes and the addition of anionic surfactant in the electrode wells. The polarity reversal was observed to be a key strategy, which allowed adequate experimental conditions to be maintained in the soil (especially temperature and pH) for the success of the organic biodegradation process. The surfactant was evenly distributed across the soil, which helped the pollutant be transported. The biological activity was not limited to the barrier area but extended to the entire soil portion due to the microbial transport and growth far from the central barrier position. The voltage gradient did not have a strong influence on the measured experimental conditions (soil temperature, pH and moisture) but affected the electroosmotic flow. A higher diesel removal efficiency (36%) was observed when using the higher voltage gradient (1.5 V cm−1) after two weeks, which demonstrates a promising performance of the studied technology for a future real in-situ application.Este estudio investigó la remediación de suelos arcillosos contaminados con compuestos orgánicos de baja solubilidad (hidrocarburos diesel) utilizando una tecnología combinada electroquímica-biológica. Se utilizó lavado electrocinético del suelo, junto con una barrera reactiva permeable biológica, que se colocó en el suelo lejos de los electrodos para evitar los efectos negativos de los frentes ácido y básico sobre la viabilidad de los microorganismos. Se realizaron tres experimentos por lotes de dos semanas de duración en una instalación a escala de laboratorio diseñada específicamente para evaluar la remediación de suelos contaminados. La variable primaria en estudio fue el campo eléctrico aplicado al suelo (0.5, 1.0 y 1.5 V cm −1), y el procedimiento experimental incluyó la inversión diaria de polaridad de los electrodos y la adición de surfactante aniónico en los pozos de los electrodos. Se observó que la inversión de polaridad era una estrategia clave, que permitía mantener las condiciones experimentales adecuadas en el suelo (especialmente temperatura y pH) para el éxito del proceso de biodegradación orgánica. El surfactante se distribuyó uniformemente por el suelo, lo que ayudó a transportar el contaminante. La actividad biológica no se limitó al área de la barrera sino que se extendió a toda la porción del suelo debido al transporte y crecimiento microbiano lejos de la posición central de la barrera. El gradiente de voltaje no tuvo una fuerte influencia en las condiciones experimentales medidas (temperatura del suelo, pH y humedad) pero afectó el flujo electroosmótico. V cm −1 ) después de dos semanas, lo que demuestra un rendimiento prometedor de la tecnología estudiada para una futura aplicación real in situ

Kinetic modelling of a diesel-polluted clayey soil bioremediation process

A mathematical model is proposed to describe a diesel-polluted clayey soil bioremediation process. The reaction system under study was considered a completely mixed closed batch reactor, which initially contacted a soil matrix polluted with diesel hydrocarbons, an aqueous liquid-specific culture medium and a microbial inoculation. The model coupled the mass transfer phenomena and the distribution of hydrocarbons among four phases (solid, S; water, A; non-aqueous liquid, NAPL; and air, V) with Monod kinetics. In the first step, the model simulating abiotic conditions was used to estimate only the mass transfer coefficients. In the second step, the model including both mass transfer and biodegradation phenomena was used to estimate the biological kinetic and stoichiometric parameters. In both situations, the model predictions were validated with experimental data that corresponded to previous research by the same authors. A correct fit between the model predictions and the experimental data was observed because the modelling curves captured the major trends for the diesel distribution in each phase. The model parameters were compared to different previously reported values found in the literature. Pearson correlation coefficients were used to show the reproducibility level of the model.Se propone un modelo matemático para describir un proceso de biorremediación de suelos arcillosos contaminados con diesel. El sistema de reacción en estudio se consideró un reactor discontinuo cerrado completamente mixto, que inicialmente entró en contacto con una matriz de suelo contaminada con hidrocarburos diesel, un medio de cultivo específico líquido acuoso y una inoculación microbiana. El modelo acopló los fenómenos de transferencia de masa y la distribución de hidrocarburos entre cuatro fases (sólido, S; agua, A; líquido no acuoso, NAPL; y aire, V) con la cinética de Monod. En el primer paso, se utilizó el modelo que simula las condiciones abióticas para estimar solo los coeficientes de transferencia de masa. En el segundo paso, se utilizó el modelo que incluía tanto la transferencia de masa como los fenómenos de biodegradación para estimar los parámetros biológicos cinéticos y estequiométricos. En ambas situaciones, las predicciones del modelo fueron validadas con datos experimentales que correspondían a investigaciones previas de los mismos autores. Se observó un ajuste correcto entre las predicciones del modelo y los datos experimentales porque las curvas de modelado capturaron las principales tendencias para la distribución del diesel en cada fase. Los parámetros del modelo se compararon con diferentes valores reportados previamente encontrados en la literatura. Se utilizaron coeficientes de correlación de Pearson para mostrar el nivel de reproducibilidad del modelo