García-Pacheco, R. (2017) Nanofiltration and ultrafiltration membranes from end-of-life reverse osmosis membranes. A study of recycling. PhD thesis, University of Alcalá.
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Abstract
Reverse 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.
| Item Type: | Thesis (PhD) |
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| Additional Information: | Autor/a Garcia Pacheco, Raquel Departamento Química I Director/a García Calvo, Eloy Codirector/a Landaburu Aguirre, Junkal Fecha de defensa 11/05/2017 Calificación Sobresaliente Cum Laude Programa Doctorado en Hidrología y Gestión de los Recursos Hídricos (RD 1393/2007) Mención internacional No |
| Subjects: | Q Science > QD Chemistry T Technology > TD Environmental technology. Sanitary engineering |
| Divisions: | Faculty of Engineering, Science and Mathematics > School of Civil Engineering and the Environment |
| Depositing User: | José Ángel Gómez Martín |
| Date Deposited: | 25 May 2017 11:30 |
| Last Modified: | 18 Apr 2023 15:55 |
| URI: | http://eprints.imdea-agua.org:13000/id/eprint/768 |
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