Effect of design and operational factors on the removal of emerging organic contaminants in constructed wetlands for wastewater treatment
- Autores: Cristina Ávila Martín
- Directores de la Tesis: Josep Maria Bayona Termens (dir. tes.), Joan García Serrano (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2013
- Idioma: inglés
- Tribunal Calificador de la Tesis: José Luis Cortina Pallás (presid.), Teresa Vicent i Huguet (secret.), Jaime Nivala (voc.), Jaume Puigagut Juárez (voc.), Isabel Martín García (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Water of quality constitutes a scarce and essential resource for life and public health, and its sustainable management is of crucial importance. Thus, wastewater treatment, reuse and reclamation represent a key practice in that approach. Nevertheless, there is a generalized concern about the occurrence and possible adverse effects of emerging organic contaminants such as pharmaceutical and personal care products in the environment, which are often not well removed in conventional wastewater treatment plants. Constructed wetlands have shown promise in their ability to remove a variety of these contaminants, and represent a good alternative for wastewater treatment in small communities, having low operational and maintenance expenses. However, there is a need in increasing the knowledge about the conditions that promote the removal of these compounds within this ecotechnology. This thesis aims at evaluating the capacity of different wetland configurations (vertical subsurface flow, horizontal subsurface flow and free water surface), as well as the effect of various design and operational factors (primary treatment, operation strategy, loading frequency, grain size, use of active aeration, hydraulic loading rate) on the removal of a variety of emerging organic contaminants, including three non-steroidal anti-inflammatory drugs (ibuprofen, diclofenac and acetaminophen), three personal care products (tonalide, triclosan and oxybenzone) and two endocrine disrupting compounds (ethinylestradiol and bisphenol A). Assays were carried out at experimental and pilot scale in constructed wetland systems in Spain and Germany. In order to achieve approximate steady state conditions of the influent concentrations of the target emerging organic contaminants and to obtain a more reliable estimate of the removal efficiency of the systems, continuous injection experiments were performed at experimental-scale systems. The performance of horizontal subsurface flow wetlands exhibited a seasonal pattern. The use of a hydrolitic upflow sludge blanket reactor -as opposed to a conventional settler- for the primary treatment of wastewater resulted in reduced performance. Conversely, operating the horizontal wetlands in batch, alternating cycles of saturation and unsaturation, promoted the existence of higher redox conditions, enhancing the removal of target compounds. The identification of an intermediate product of bisphenol A (promoted by the operation in batch) suggests that aerobic biodegradation could constitute a principal removal mechanism of this substance when a higher redox status prevail. In VF wetlands, a higher loading frequency (bi-hourly vs. hourly) showed to perform significantly worse on the removal of some EOCs. The occurrence of gravel (4-8 mm) as opposed to sand (1-3 mm) in this type of systems exhibited a significantly lower treatment performance. Conversely, the use of active aeration in a saturated vertical flow wetland did not show to enhance contaminant removal in respect to the typical unsaturated vertical wetland. A hybrid treatment system based on a vertical wetland stage and a horizontal subsurface flow and free water surface wetlands in series has proved to be a very robust technology for wastewater treatment in small communities, producing a final effluent suitable for its reuse in various applications. Overall removal efficiency of emerging contaminants was very high (90 ± 11%), even under high hydraulic loads, presumaby due to the combination of various abiotic/biotic removal mechanisms (e.g. biodegradation, sorption, volatilization, hydrolysis, photodegradation). Toxicological assays performed together with the injection of antibiotics at high hydraulic loading rates showed that general toxicity, estrogenicity and dioxin-like activities were well removed along the different units of the treatment system.
