Eliminación de metales pesados en aguas mediante bioadsorción. Evaluación de materiales y modelación del proceso.

Una de las principales fuentes de contaminación de las aguas es el vertido de efluentes insuficientemente depurados, razón por la que el control de vertidos ha centrado gran parte de las actuaciones legislativas de las administraciones competentes en esta materia. Las técnicas convencionales de depuración de metales pesados presentan dificultades para lograr el cumplimiento de los límites de vertido siendo necesaria la búsqueda de técnicas alternativas para reducir estas emisiones. En este sentido, la investigación en bioadsorción ha mostrado en los últimos años el potencial de esta tecnología para el tratamiento de aguas contaminadas por metales pesados. El objetivo de la tesis doctoral es el estudio de la bioadsorción como tecnología para el tratamiento de aguas residuales industriales contaminadas con metales pesados utilizando Posidonia oceanica y turba como bioadsorbentes. Para ello se ha implementado una metodología dirigida al desarrollo de una herramienta de predicción del proceso de bioadsorción en lecho fijo y a la evaluación de la potencial aplicación del proceso a nivel industrial. La presentación de resultados se inicia con el estudio experimental dirigido a la evaluación del uso de la Posidonia oceanica y de la turba para la eliminación de cobre en aguas. Tras determinar las características físico-químicas de ambos bioadsorbentes, se han evaluado los mecanismos de interacción con el cobre. Se presenta la caracterización del equilibrio de adsorción tanto en discontinuo como en la operación dinámica en columnas de lecho fijo. El empleo de una técnica de estímulo-respuesta ha permitido determinar los valores del coeficiente de dispersión hidrodinámica y su variación con la velocidad intersticial del fluido en lechos de ambos bioadsorbentes. La presencia de agentes complejantes en las aguas residuales puede ocasionar interferencias en los tratamientos de depuración convencionales. Por ello, se analiza el efecto de la presencia de EDTA, seleccionado como agente complejante típico, sobre el rendimiento del proceso. Asimismo, se analiza la reutilización de los bioadsorbentes en ciclos consecutivos de adsorción-desorción. A continuación se presenta el modelo matemático desarrollado con el fin de obtener una herramienta para la simulación de la bioadsorción de metales pesados en columna de lecho fijo. La calibración del modelo se ha realizado utilizando los datos de los ensayos de bioadsorción de cobre en columna de lecho fijo sobre Posidonia oceanica y sobre la turba, y ha permitido la estimación del coeficiente de transferencia de materia interna en estos sistemas. Con la validación del modelo, realizada a partir de experimentos independientes a los utilizados en la fase de calibración, se corroboran las hipótesis del modelo. Asimismo, se incluye un análisis de sensibilidad del modelo mostrando la influencia del coeficiente de dispersión hidrodinámica y del coeficiente de transferencia de materia interna sobre los resultados de las predicciones del modelo. El trabajo se completa con ensayos realizados en el marco de un proyecto de investigación aplicada, financiado por el Instituto Tecnológico Metal-Mecánico (AIMME) para evaluar la aplicación de la tecnología en el sector de tratamiento de superficies. Se presenta un estudio comparativo del rendimiento de la operación sobre diversos materiales incluyendo la Posidonia oceanica y la turba, otros bioadsorbentes (chitosan y chitín) y dos carbones activados comerciales, utilizando cobre o níquel como metales pesados de referencia en las aguas residuales de este sector. El estudio incluye la evaluación de la bioadsorción para el tratamiento de aguas residuales aportadas por una empresa del sector de tratamiento de superficies metálicas. Por último, se analizan los resultados del estudio de una configuración de columnas en serie utilizando un lecho de bioadsorbente seguido de un lecho de carbón activado como alternativa para el tratamiento de aguas contaminadas con metales pesados en presencia de agentes complejantes.The objective of this doctoral thesis is to study biosorption technology for treatment of wastewater polluted with heavy metals using Posidonia oceanica and peat as biosorbents. For this purpose, a methodology has been implemented to develop a fixed-bed performance prediction tool and to evaluate the industrial application of biosorption technology. Posidonia oceanica and peat are tested for copper removal from wastewater. Physicochemical properties of both biosorbents and mechanisms involved in copper retention are evaluated. Equilibrium results in batch and dynamic conditions in fixed-bed columns are presented. Hydrodynamic characterisation of biosorbent beds has been achieved with a stimulus-response technique and consequently the hydrodynamic dispersion coefficient and its variation with fluid interstitial velocity have been obtained. The effect of the presence of EDTA in the feed solution of the column was investigated for both biosorbents from an industrial application perspective. Likewise, reutilisation of biosorbents was evaluated in adsorption−desorption cycles. A mathematical model has been developed as a simulation tool for heavy metal biosorption fixed-bed processes. Model calibration is carried out using experimental results of copper biosorption in fixed-bed columns, which allows the intraparticle mass transfer coefficient to be estimated. Experimental results obtained in independent biosorption experiments were used to model validation, corroborating model hypothesis. Finally, the influence of hydrodynamic dispersion coefficient and intraparticle mass transfer coefficient on simulation results is evaluated with a sensitivity analysis. The thesis is completed with a study carried out as a part of a research project focused on the industrial application of the technology. The experimental design was developed to evaluate biosorption technology to treat industrial wastewater from surface treatment facilities, whose main characteristic is the presence of complexing agents. The copper and nickel biosorption performance of Posidonia oceanica and peat is compared with those of other biosorbents (chitosan and chitin) and with two activated carbons. Sorbent performances were also checked using industrial wastewater of a representative facility of the surface treatment sector. A serial column configuration with a biosorbent bed of Posidonia oceanica or peat coupled with an activated carbon bed was evaluated as an alternative configuration for heavy metal with complexing agent wastewater treatment

Fouling characterisation in PVDF membrane contactors for dissolved methane recovery from anaerobic effluents: effect of surface organofluorosilanisation

Characterisation of the fouling attached to PVDF membranes treating an anaerobic effluent for dissolved CH4 recovery was carried out. A commercial flat-sheet PVDF membrane and a PVDF functionalised by grafting of organofluorosilanes (mPVDF) that increased its hydrophobicity were subjected to a continuous flux of an anaerobic reactor effluent in long-term operation tests (> 800 h). The fouling cakes were studied by the membrane autopsy after these tests, combining a staining technique, FTIR, and FESEM-EDX, and the fouling extraction with water and NaOH solutions. Both organic and inorganic fouling were observed, and the main foulants were proteins, polysaccharides, and different calcium and phosphate salts. Also, a significant amount of live cells was detected on the fouling cake (especially on the non-modified PVDF). Although the fouling cake composition was quite heterogeneous, a stratification was observed, with the inorganic fouling mainly in the bulk centre of the cake and the organic fouling mainly located in the lower and upper surfaces of the cake. The mPVDF suffered a more severe fouling, likely owing to a stronger hydrophobic-hydrophobic interaction with the foulants. Irreversible fouling remained on both membranes after the extraction, although a higher irreversible fouling was detected in the mPVDF; however, a complete polysaccharide removal was observed. Regarding the operation performance, PVDF showed a lower stability and suffered a severe degradation, resulting in a lower thickness and perforations. Finally, the decrease in the methane recovery performance of both membranes was associated with the fouling depositions

Demethanization of aqueous anaerobic effluents using a polydimethylsiloxane membrane module: Mass transfer, fouling and feasibility

The performance, fouling and feasibility of a polydimethylsiloxane hollow fibre membrane module for in situ methane degasification from the effluent of an Expanded Granular Sludge Bed anaerobic reactor has been investigated. Experiments at different operational conditions were carried out (liquid flow, sweep gas flow and vacuum pressure) with maximum removal efficiency (77%) at lowest flow-rate (0.4 L h-1), highest vacuum gauge pressure (-800 mbar) and liquid flowing in lumen side. Mass transport analysis denoted a considerably higher methane transfer than that predicted (attributed to liquid over- saturation). An enhancement factor for liquid phase has been proposed to correlate the experimental results. Long-term experiments were also performed in order to determine the possible influence of fouling on the module performance, and it showed that relatively frequent cleaning with water might be carried out to ensure preservation of the membrane efficiency. Characterization of water quality before and after membrane module was carried out to elucidate fouling causes. Energy balance analysis evidenced that energy production exceeded the system energy requirements. A substantial reduction of CO2 equivalent emissions showed the positive environmental impact of this technology

Effects of Minimalist Footwear and Foot Strike Patterns on Plantar Pressure during a Prolonged Running

The use of minimalist shoes (MS) in running involves changes in running mechanics com pared to conventional shoes (CS), but there is still little research analysing the effects of this footwear on plantar pressure, which could help to understand some risk injury factors. Moreover, there are no studies examining the effects of a prolonged running and foot strike patterns on baropodometric variables in MS. Therefore, the aim of this study was to analyse the changes produced using MS on plantar pressure during a prolonged running, as well as its interaction with the time and foot strike pattern. Twenty-one experienced minimalist runners (age 38 ± 10 years, MS running experience 2 ± 1 years) ran with MS and CS for 30 min at 80% of their maximal aerobic speed, and mean pres sure, peak pressure, contact time, centre of pressure velocity, relative force and contact area were analysed using a pressure platform. Foot strike pattern and time were also considered as factors. The multivariable linear regression mixed models showed that the use of MS induced, at the end of a prolonged running, higher peak pressure (p = 0.008), lower contact time (p = 0.004) and lower contact area (p < 0.001) than using CS. Also, runners with forefoot strike pattern using MS, compared to midfoot and rearfoot patterns, showed higher mean and peak pressure (p < 0.001) and lower contact time and area (p < 0.05). These results should be considered when planning training for runners using MS, as higher peak pressure values when using this type of footwear could be a risk factor for the development of some foot injuries

Performance and feasibility of biotrickling filtration in the control of styrene industrial air emissions

The performance and feasibility of a pilot unit of biotrickling filter (BTF) for the treatment of industrial emissions polluted by styrene was investigated for one year at a fiber reinforced plastic industrial site. The pilot unit was packed with a structured material with a volume of 0.6 m3. Monitoring results have shown successful treatment of the industrial styrene emissions working at empty bed residence times (EBRT) between 31 and 66 s. The best performance was obtained after 300 days when a more stable biofilm had been developed, obtaining the highest elimination capacity of 18.8 g m−3 h−1 (removal efficiency of 75.6%) working at 31 s of EBRT. In addition, a photocatalytic reactor was evaluated as pretreatment of the biological process, but results have shown very low capacity for improving the BTF performance due to catalyst deactivation. The economic feasibility of the BTF was evaluated. The total direct cost, excluding capital recovery, of the biotrickling filter technology was estimated in 0.71 year−1 per Nm3 h−1 of treated air whereas 2.27 year−1 per Nm3 h−1 was obtained for the regenerative catalytic oxidizer equipped with a zeolite pre-concentrator. Results show that this technology is economically and environmentally competitive in comparison with thermal treatment

Observación de muestras biológicas al microscopio óptico

La observación microscópica de muestras de aguas de los reactores biológicos de una Estación Depuradora de Aguas Residuales proporciona información cualitativa sobre la calidad de la población microbiana y del estado de los flóculos. En este vídeo, se muestra la utilización de un microscopio óptico para la observación de muestras de agua de un reactor de fangos activados. Data: 2013

Observació de mostres biològiques al microscopi òptic

L'observació microscòpica de mostres d'aigues dels reactors biològics d'una Estació Depuradora d'Aigues Residuals proporciona informació qualitativa sobre la qualitat de la població microbiana i de l'estat dels flòculs. En aquest vídeo, es mostra la utilització d'un microscopi òptic per a l'observació de mostres d'aigua d'un reactor de fangs activats. Data: 2013

Observació de mostres biològiques al microscopi òptic

L'observació microscòpica de mostres d'aigues dels reactors biològics d'una Estació Depuradora d'Aigues Residuals proporciona informació qualitativa sobre la qualitat de la població microbiana i de l'estat dels flòculs. En aquest vídeo, es mostra la utilització d'un microscopi òptic per a l'observació de mostres d'aigua d'un reactor de fangs activats. Data: 2013

Observación de muestras biológicas al microscopio óptico

La observación microscópica de muestras de aguas de los reactores biológicos de una Estación Depuradora de Aguas Residuales proporciona información cualitativa sobre la calidad de la población microbiana y del estado de los flóculos. En este vídeo, se muestra la utilización de un microscopio óptico para la observación de muestras de agua de un reactor de fangos activados. Data: 2013