Membrane bioreactor for the removal of emerging contaminants from municipal wastewater and its viability of integrating advanced oxidation processes
Gurung, Khum (2019-10-01)
Väitöskirja
Gurung, Khum
01.10.2019
Lappeenranta-Lahti University of Technology LUT
Acta Universitatis Lappeenrantaensis
School of Engineering Science
School of Engineering Science, Kemiantekniikka
Kaikki oikeudet pidätetään.
Julkaisun pysyvä osoite on
https://urn.fi/URN:ISBN:978-952-335-411-1
https://urn.fi/URN:ISBN:978-952-335-411-1
Tiivistelmä
Water scarcity is undoubtedly a global concern due to exacerbated population growth, economic development, climate change, and rapid urbanization. This has necessitated the need for establishing more sustainable and well-functioning natural ecosystems by transforming current water industries based on smart technologies and management approaches. Municipal wastewater reclamation is one of the promising approaches to relieve growing pressure on global water resources. However, adequate and efficient treatment is always essential to achieve high quality reclaimed water, ensuring no potential risks to human health and aquatic environment due to the presence of emerging contaminants (ECs), for which legislations are being stricter with time. Since conventional wastewater treatment plants are not designed to remove ECs, the capabilities of advanced wastewater treatment technologies, for enhancing the removal of ECs before releasing the treated effluent into the environment or reclamation, such as membrane bioreactor (MBR) and its integration with advanced oxidation processes, are emerging topics of research worldwide.
This dissertation presents a comprehensive practical study on the applicability of the MBR system for treating municipal wastewater in terms of its performance on the removal of diverse ECs, such as pharmaceutically active compounds, steroid hormones, and endocrine disrupting compounds, under different operating conditions, including Nordic cold environment and varying solid retention times. Additionally, a potential viability of integrating MBR with two emerging advanced oxidation processes (AOP) technologies, such as electrochemical oxidation (ECO) and photocatalytic oxidation (PCO), were studied in batch modes to further enhancing the removal of ECs and to produce high quality reclaimed water.
A significant membrane fouling, accompanying with about 75% permeability drop, was observed when process temperature in MBR was below 10 °C, indicating high deterioration of membrane performance. However, relatively consistent removal efficiency of human enteric viruses, such as norovirus GI, norovirus GII, and adenovirus, heavy metals, and selected ECs, was achieved Similarly, the removal and fate of 23 diverse ECs was studied at varying solid retention times (60 and 21 days). It was observed that at long solid retention time, ECs removal majorly enhanced, while biopolymers concentrations decreased. Moreover, diverse removal efficiencies of the selected ECs were observed, which were explained based on their physicochemical properties and other process operating parameters. The electrochemical oxidation of carbamazepine, which is one of the highly recalcitrant EC, was studied in batch mode using Ti/Ta2O5- SnO2 anode. The main operating parameters effecting the removal of carbamazepine, including current density, initial substrate concentration, pH, and temperature, were studied. A complete removal (>99.9 %) of carbamazepine, with concentration close to environmental level (10 μg L-1), in real MBR effluent was observed when electrolyzed under the optimized conditions (current density: 9 mA cm-2, pH: 6, and temperature: 30 °C) in synthetic solutions. Subsequently, the removal of ECs (carbamazepine and diclofenac) was studied by heterogeneous photochemical oxidation using 5% Ag2O/P-25 photocatalyst under UV irradiation. The matrix effect, i.e., ECs in deionized water and MBR effluent, was studied along with the catalyst dosage and initial ECs concentration. The optimal removal of carbamazepine and diclofenac reached 89.1% and 93.5%, respectively at catalyst dosage of 0.4 g L-1 in deionized water matrix, and further revealed that optimal catalyst dosage for ECs removal in MBR effluent matrix increased by 1.5 to 2 fold to achieve the similar removal efficiency as deionized water matrix. High reusability of 5% Ag2O/P-25 photocatalyst was observed for both ECs. Moreover, various intermediates of carbamazepine generated during photochemical oxidation were analyzed and identified, and a possible degradation pathway was proposed.
The current study has expanded the knowledge on the applicability and efficiency of MBR operation in unique Nordic environment and integration possibilities of MBR with selected innovative advanced oxidation processes. It has also revealed the need of many other important related topics for further investigations.
This dissertation presents a comprehensive practical study on the applicability of the MBR system for treating municipal wastewater in terms of its performance on the removal of diverse ECs, such as pharmaceutically active compounds, steroid hormones, and endocrine disrupting compounds, under different operating conditions, including Nordic cold environment and varying solid retention times. Additionally, a potential viability of integrating MBR with two emerging advanced oxidation processes (AOP) technologies, such as electrochemical oxidation (ECO) and photocatalytic oxidation (PCO), were studied in batch modes to further enhancing the removal of ECs and to produce high quality reclaimed water.
A significant membrane fouling, accompanying with about 75% permeability drop, was observed when process temperature in MBR was below 10 °C, indicating high deterioration of membrane performance. However, relatively consistent removal efficiency of human enteric viruses, such as norovirus GI, norovirus GII, and adenovirus, heavy metals, and selected ECs, was achieved Similarly, the removal and fate of 23 diverse ECs was studied at varying solid retention times (60 and 21 days). It was observed that at long solid retention time, ECs removal majorly enhanced, while biopolymers concentrations decreased. Moreover, diverse removal efficiencies of the selected ECs were observed, which were explained based on their physicochemical properties and other process operating parameters. The electrochemical oxidation of carbamazepine, which is one of the highly recalcitrant EC, was studied in batch mode using Ti/Ta2O5- SnO2 anode. The main operating parameters effecting the removal of carbamazepine, including current density, initial substrate concentration, pH, and temperature, were studied. A complete removal (>99.9 %) of carbamazepine, with concentration close to environmental level (10 μg L-1), in real MBR effluent was observed when electrolyzed under the optimized conditions (current density: 9 mA cm-2, pH: 6, and temperature: 30 °C) in synthetic solutions. Subsequently, the removal of ECs (carbamazepine and diclofenac) was studied by heterogeneous photochemical oxidation using 5% Ag2O/P-25 photocatalyst under UV irradiation. The matrix effect, i.e., ECs in deionized water and MBR effluent, was studied along with the catalyst dosage and initial ECs concentration. The optimal removal of carbamazepine and diclofenac reached 89.1% and 93.5%, respectively at catalyst dosage of 0.4 g L-1 in deionized water matrix, and further revealed that optimal catalyst dosage for ECs removal in MBR effluent matrix increased by 1.5 to 2 fold to achieve the similar removal efficiency as deionized water matrix. High reusability of 5% Ag2O/P-25 photocatalyst was observed for both ECs. Moreover, various intermediates of carbamazepine generated during photochemical oxidation were analyzed and identified, and a possible degradation pathway was proposed.
The current study has expanded the knowledge on the applicability and efficiency of MBR operation in unique Nordic environment and integration possibilities of MBR with selected innovative advanced oxidation processes. It has also revealed the need of many other important related topics for further investigations.
Kokoelmat
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