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Nanofiltration and ultrafiltration membranes from end-of-life reverse osmosis membranes. A study of recycling
No full textReverse osmosis (RO) is the most employed technology for water desalination. However, membrane fouling is inevitable and one of the main reasons for a regular membrane replacement. Due to the continuous growth of this technology, end-of-life RO membrane management has created an economic and environmental concern. Therefore, alternative management routes need to be faced by the industry and academia. The overall aim of this study is to investigate the direct recycling process as a feasible alternative to produce nanofiltration (NF) and ultrafiltration (UF) recycled membranes.
In this study membrane fouling was characterized through thermo-gravimetric, spectrometric and microbiological techniques. Brackish and seawater RO membranes were subjected to the chemical attack of free chlorine. The main objective was altering their selective active layer of polyamide (PA). Recycling process was carried out by membrane passive immersion in sodium hypochlorite solutions, at room temperature with no pressure and no agitation. The TM720-400 BW membrane was selected as the case study at laboratory scale. It was investigated the effect of exposure time, pH solution and membrane storage (dry and wet) on the recycling process. It was observed that recycled membrane permeability values and rejection coefficients were affected by the storage condition. Indeed, 124 ppm free chlorine at basic pH solution during 50 h (equivalent to 6,200 ppm·h) were the initial selected conditions to transform RO membrane performance into NF membrane. In addition, longer exposure time (242 h) was chosen for obtaining UF membrane performance. Afterwards, the recycling method was optimized aiming at decreasing the aforementioned exposure time required. Therefore, the exposure dose concept (ppm·h) was evaluated, i.e. diverse solution concentrations and exposure times were combined to achieve fixed exposure doses (6,200; 30,000 y 300,000 ppm·h). The impact created on the membranes was evaluated in terms of permeability and rejection coefficients, during brackish water treatment. Some experiments were repeated using other end-of-life RO models to evaluate the reproducibility of the selected conditions. Moreover, results were compared with several pristine commercial membranes (RO, NF and UF). In fact, recycled membrane performance values were within the range values observed using NF90-400 and NF270-400 nanofiltration membrane models. Moreover, membranes exposed to high exposure level were also compared to a commercial UF membrane (10 KDa). Recycled membranes showed rejection coefficients similar or higher than the commercial one, when treating urban wastewater. The recycling process at pilot scale required analogous exposure doses (ppm·h) to those used at laboratory scale.
At both scales, membrane scaling affected significantly the recycling process. Membranes that were fouled by inorganic clay, organic and microbiological matter did not show difficulties in the recycling process. Surface characterization was conducted to confirm the degradation of the PA layer by the attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM). From 50,000 ppm·h exposure doses, ATR-FTIR spectra of recycled membranes were different than RO pristine membrane. SEM micrographs showed pores on the recycled membranes surfaces, with a Feret Diameter ranges from 8 to 14 nm (calculated by ImageJ software). Beside, the molecular weight cut off determined at laboratory scale ranges from 10,000 to 38,000 g/mol. Finally, a business model of end-of-life RO membranes of a hypothetical recycling membrane plant was developed identifying potential user, investors, technical drawback, market competition and social barriers.
This study demonstrates that direct passive recycling could be a feasible alternative that can further boost the RO membrane technology towards circular economy approach
Desafíos a la seguridad hídrica de las ciudades en América Latina y Europa: la mirada a largo plazo
No full textBiodegradation of microcystins by freshwater bacteria: new genetic and ecological perspectives Biodegradación de microcistinas mediante bacterias de agua dulce: nuevas perspectivas genéticas y ecológicas
No full textLas proliferaciones (o blooms) de cianobacterias en aguas dulces son un fenómeno frecuente que está aumentando a escala global y un tema de preocupación debido a los efectos nocivos que acarrean sobre el ecosistema y los usos del agua. Algunas cepas de cianobacterias formadoras de blooms también producen toxinas (cianotoxinas) que afectan negativamente a los humanos y otros animales. Entre estas cianotoxinas, las microcistinas (un grupo de potentes hepatotoxinas) son las más frecuentes y las más ampliamente distribuidas en los ecosistemas de agua dulce. Las microcistinas son moléculas estructuralmente estables y resistentes a procesos físicos y químicos, tanto a los que tienen lugar de manera natural en el medio ambiente como a los aplicados en tecnologías convencionales de tratamiento del agua. Por tanto, el estudio de las cianobacterias y cianotoxinas permite mejorar las estrategias de gestión del agua y los procesos para su eliminación en plantas de tratamiento.
Las proliferaciones masivas de cianobacterias coexisten e interaccionan con otros microorganismos presentes en el medio acuático. Un grupo de bacterias específicas capaces de degradar de manera eficiente microcistinas está frecuentemente asociado a las proliferaciones masivas de cianobacterias. A pesar de su relevancia en la eliminación de dichas toxinas del medio acuático, esta comunidad bacteriana está escasamente estudiada a nivel global y, muy especialmente, en la región mediterránea. Esta tesis evalúa, en primer lugar, la capacidad de biodegradación de microcistinas en un embalse situado en el centro de España y, posteriormente, profundiza en las características genéticas y ecológicas, así como en la diversidad bacteriana que está detrás de este proceso de biodegradación. Esta tesis se enfoca sobre las bacterias de agua dulce asociadas a los blooms de cianobacterias desde diferentes ángulos, utilizando varios métodos analíticos e incluyendo un estudio de tres años de muestreos en campo.
Tras la detección de actividad de biodegradación de microcistinas en el embalse de estudio, se desarrolló la siguiente secuencia de eventos: optimización de un método eficiente de aislamiento de bacterias degradadoras de microcistinas, aislamiento e identificación taxonómica de las cepas degradadoras y, posteriormente, detección de los genes responsables del proceso de degradación de microcistinas (genes mlr). Se identificaron, dentro de la comunidad bacteriana degradadora, dos genotipos diferentes de bacterias en base a la presencia o ausencia de los genes mlr (mlr+ y mlr−, respectivamente). Posteriormente se evaluaron las eficiencias de degradación de microcistinas de cada uno de los genotipos en presencia de otros compuestos de carbono y nitrógeno en el medio. La detección de una alta eficiencia de degradación de microcistinas, en presencia de un amplio rango de concentraciones de otros compuestos de carbono y nitrógeno en una de las bacterias aisladas, llevó al desarrollo y optimización de un método para un uso eficiente de dicha bacteria como herramienta biológica en la eliminación de microcistinas del agua.
La identificación de los dos genotipos (mlr+ y mlr−) de bacterias degradadoras de microcistinas coexistiendo en el medio acuático condujo al desarrollo de un estudio de diversidad sobre la comunidad bacteriana asociada a las proliferaciones de cianobacterias. Por último, se realizó un estudio de las dinámicas estacionales de las comunidades de cianobacterias productoras y bacterias degradadoras de microcistinas, así como la influencia de los factores fisicoquímicos más relevantes del medio acuático sobre ambas dinámicas estacionales. El desarrollo de estrategias adecuadas de gestión del agua para prevenir, frenar y reducir los episodios de blooms de cianobacterias y sus toxinas requiere, necesariamente, de un buen conocimiento de las dinámicas temporales de dichos blooms y de la comunidad bacteriana asociada capaz de degradar las microcistinas
Critical assessment of pendimethalin in terms of persistence, bioaccumulation, toxicity, and potential for long-range transport
No full textDiversity and temporal shifts of the bacterial community associated with a toxic cyanobacterial bloom: An interplay between microcystin producers and degraders
No full textThe biodegradation of microcystins (MCs) by bacteria constitutes an important process in freshwater ecosystems to prevent the accumulation of toxins. However, little is known about the diversity and the seasonal dynamics of the bacterial community composition (BCC) involved in the degradation of MCs in nature. To explore these BCC shifts, high-throughput sequencing was used to analyse the 16S rRNA, mcyE and mlrA genes during a year in a freshwater reservoir with a toxic cyanobacterial bloom episode. The analysis of the mcyE and mlrA genes from water samples revealed the coexistence of different MC-producing and MC-degrading genotypes, respectively. The patchy temporal distribution of the mlrA genotypes (from the families Sphingomonadaceae and Xanthomonadaceae) suggests their dissimilar response to environmental conditions and the influence of other factors besides the MCs that may control their presence and relative abundance. During the maximum toxic cyanobacterial biomass and cell lysis, other bacterial taxa that lack mlr genes increased their relative abundance. Among these bacteria, those with a recognized role in the degradation of xenobiotic and other complex organic compounds (e.g., orders Myxococcales, Ellin6067, Spirobacillales and Cytophagales) were the most representative and suggest their possible involvement in the removal of MCs in the environment
Treatment of reverse osmosis brine by direct contact membrane distillation: Chemical pretreatment approach
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Retos sociales y de gobernanza. Los derechos humanos al agua y el saneamiento en países desarrollados: cuando la cobertura no es el desafío
No full textScientific advice on Proposed EU minimum quality requirements for water reuse in agricultural irrigation and aquifer recharge
No full textFollowing a request from the Commission, the Scientific Committee on Health, Environmental and Emerging Risks (SCHEER) reviewed the report prepared by the European Commission Joint Research Centre on “Proposed EU minimum quality requirements for water reuse in agricultural irrigation and aquifer recharge". The SCHEER concludes that, while the methodology chosen is appropriate and the report considers many important elements, the document is deficient in key details. The SCHEER recommends that the description of the methodology be extended and detailed guidance be provided on how minimum quality requirements should be derived. The SCHEER is of the opinion that, in its current form, the minimum quality requirements proposed provide insufficient protection both to environmental and human health