Removal of emerging pollutants by a 3-step system: Hybrid digester, vertical flow constructed wetland and photodegradation post-treatments

• Published in: The Science of the total environment Vol. 842; p. 156750
• Main Authors: Sánchez, M., Ramos, D.R., Fernández, M.I., Aguilar, S., Ruiz, I., Canle, M., Soto, M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10.10.2022
• Subjects: Advanced oxidation process; Constructed wetland; Emerging pollutant; Hybrid digester; Municipal wastewater; Hybrid digester; Constructed wetland; Emerging pollutant; Advanced oxidation process; Municipal wastewater
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.156750

The removal of emerging pollutants from municipal wastewater was studied for the first time using a three-step pilot-scale system: 1) hybrid digester (HD) as first step, 2) subsurface vertical flow constructed wetland (VF) as second step, and 3) photodegradation (PD) unit as third step or post-treatment. The HD and VF units were built and operated in series with effluent recirculation at pilot scale. For the PD post-treatment, three alternatives were studied at lab-scale, i) UVC irradiation at 254 nm (0.5 h exposure time), ii) UVA irradiation at 365 nm using a TiO2-based photocatalyst and iii) sunlight irradiation using a TiO2-based photocatalyst, the last two for 1 and 2 h. Alternative iii) was also tested at pilot-scale. Degradation of nine compounds was evaluated: acetaminophen (ACE), caffeine (CAF), carbamazepine (CBZ), ketoprofen (KET), ibuprofen (IBU), diclofenac (DCL), clofibric acid (ACB), bisphenol A (BPA), and sotalol (SOT). Overall, the HD-VF-UVC system completely removed (>99.5 %) ACE, CAF, KET, IBU, DCL and ACB, and to a lesser extent SOT (98 %), BPA (83 %) and CBZ (51 %). On the other hand, the HD-VF-UVA/TiO2 system (at 2 h) achieved >99.5 % removal of ACE, CAF, KET, IBU and DCL while ACB, BPA, CBZ and SOT were degraded by 83 %, 81 %, 78 % and 68 %, respectively. Working also at 2 h of exposure time, in summer conditions, the HD-VF-Sol/TiO2 system achieved >99.5 % removal of ACE, CAF, KET, IBU, DCL and ACB, and to a minor extent BPA (80 %), SOT (74 %) and CBZ (69 %). Similar results, although slightly lower for SOT (60 %) and CBZ (59 %), were obtained in the pilot sunlight plus TiO2 catalyst unit. However, the use of sunlight irradiation with a TiO2-based photocatalyst clearly showed lower removal efficiency in autumn conditions (i.e., 47 % SOT, 31 % CBZ). [Display omitted] •The removal of nine persistent pollutants was evaluated using a 3-step system.•Over 99 % removal of four drugs and caffeine was done in biological steps.•Photodegradation was effective for some biologically refractory compounds.•Photodegradation with sunlight and TiO2 resulted in a promising post-treatment.•Bisphenol A removal was 80 % in biological steps but not completed by photodegradation.