Application of aerobic granular sludge for municipal wastewater treatment - Process performance and microbial community dynamics under fluctuating conditions
Doctoral thesis, 2023
Pressures of growing cities, competition for use of urban areas and higher influent loads, are pushing for innovative technologies for wastewater treatment with low demands for land footprint and costs. Furthermore, wastewater treatment is needed to move towards a circular economy by harvest of valuable resources such as nutrients and energy. Aerobic granular sludge (AGS) is a biofilm process without a carrier material for wastewater treatment, exhibiting efficient treatment performance, excellent settleability, high biomass retention, tolerance to toxicity and high loads of organic matter. In this thesis, the first implementation of the AGS process in the Nordic countries was studied to assess the treatment performance, microbial community structure, energy usage, land footprint, and volume needs. The results in this project suggested that selective sludge withdrawal, retaining long solids retention time, sufficient substrate availability, and operational flexibility are important factors for granulation. Both the AGS and parallel conventional activated sludge (CAS) process achieved stable organic matter, nitrogen, and phosphorus removal with low average effluent concentrations. Seasonal variations and environmental factors were identified as important for microbial community succession. The granular biofilm demonstrated higher biomass concentration, diversity, and lower seasonal fluctuations in community composition than the flocculent sludge. A one-year energy comparison resulted in lower specific energy usages (kWh m-3 and kWh reduced P.E.-1) and land footprint for the AGS compared to the CAS process. However, a potential for decreased energy usage was recognised for both systems, leading to the conclusion that operational optimisation and process design might be as important as the type of technology. Additionally, the influence of decreasing temperature on AGS was studied in lab-scale reactors, revealing different responses of the functional groups in the microbial community, and even various response of ASVs at the genus level. In conclusion, the AGS technology for municipal wastewater treatment under fluctuating conditions achieved low average effluent concentrations, was more compact and energy efficient compared to the CAS.
energy usage
aerobic granular sludge
sequencing batch reactors
granulation
municipal wastewater treatment
nutrient removal
start-up
microbial community dynamics
full-scale operation
low temperature
activated sludge
Föreläsningssal EC, Hörsalsvägen 11
Opponent: Prof. Anuska Mosquera Corral, University of Santiago de Compostela, Spain
Author
Jennifer Ekholm
Chalmers, Architecture and Civil Engineering, Water Environment Technology
Full-scale aerobic granular sludge for municipal wastewater treatment - granule formation, microbial succession, and process performance
Environmental Science: Water Research and Technology,;Vol. In Press(2022)
Journal article
Ekholm, J., de Blois, M., Persson, F., Gustavsson, D.J. Bengtsson, S., van Erp, T., and Wilén, B.M. Case study of aerobic granular sludge and activated sludge – energy, footprint and nutrient removal
Ekholm, J., Burzio, C., Saeid Mohammadi, A., Modin, O., Persson, F., Gustavsson, D.J., de Blois, M., and Wilén, B.M. Influence of decreasing temperature on aerobic granular sludge: microbial community dynamics and treatment performance
Ekholm, J., Persson, F., de Blois, M., Modin, O., Gustavsson, D.J., Pronk, M., van Loosdrecht, M.C., and Wilén, B.M. Comparison of microbial community structure and function in parallel full-scale granular sludge and activated sludge processes
Wastewater should be cleaned as energy efficiently as possible, on a small piece of land, and result in minimal pollution. Is the answer aerobic granular sludge?
Contamination of surface waters from discharged wastewater can lead to eutrophication, algal blooms, dead sea bottoms and loss of biodiversity, and result in long-term ecological damage. With stricter environmental regulations, societies ask for excellent wastewater treatment which is also sustainable. However, advanced treatment methods, such as biofilm systems, can be highly energy-demanding. Less advanced treatment processes, such as activated sludge, might be spacious and slow. In Aerobic Granular Sludge (AGS), nutrients and organic matter can be removed simultaneously, and the fast settling takes place in the same reactor for the separation of the treated water and the biological sludge. This enables an efficient, compact treatment, which also had lower energy usage and land footprint compared to activated sludge. However, full-scale studies of AGS are few and do not cover a variety of environmental conditions. Furthermore, little is known about microbial ecology in full-scale AGS reactors.
In this thesis, the treatment performance, and microbial community structure were investigated in the first full-scale AGS process in Sweden. The microbes responsible for the removal of contaminants were detected with varying abundance, and they removed contaminants well since the observed average effluent concentrations were low. Selection of “the right” microbes for granulation was likely achieved by measures such as bottom-feeding, feast-famine operation, selective sludge discharge, substrate availability, and a long biomass residence time. The microbial community in the AGS was following a seasonal periodicity and was little influenced by the microorganisms in the influent wastewater. The activated sludge process at the same plant had low settleability, and a different microbial community, yet produced comparably low effluent concentrations. The AGS had a 70% lower land footprint, and 15-38% lower energy usage compared to the activated sludge process. This confirms that AGS can be compact without increased energy usage. This research gives new insights into the challenges of the treatment of municipal wastewater with AGS under fluctuating conditions.
Contamination of surface waters from discharged wastewater can lead to eutrophication, algal blooms, dead sea bottoms and loss of biodiversity, and result in long-term ecological damage. With stricter environmental regulations, societies ask for excellent wastewater treatment which is also sustainable. However, advanced treatment methods, such as biofilm systems, can be highly energy-demanding. Less advanced treatment processes, such as activated sludge, might be spacious and slow. In Aerobic Granular Sludge (AGS), nutrients and organic matter can be removed simultaneously, and the fast settling takes place in the same reactor for the separation of the treated water and the biological sludge. This enables an efficient, compact treatment, which also had lower energy usage and land footprint compared to activated sludge. However, full-scale studies of AGS are few and do not cover a variety of environmental conditions. Furthermore, little is known about microbial ecology in full-scale AGS reactors.
In this thesis, the treatment performance, and microbial community structure were investigated in the first full-scale AGS process in Sweden. The microbes responsible for the removal of contaminants were detected with varying abundance, and they removed contaminants well since the observed average effluent concentrations were low. Selection of “the right” microbes for granulation was likely achieved by measures such as bottom-feeding, feast-famine operation, selective sludge discharge, substrate availability, and a long biomass residence time. The microbial community in the AGS was following a seasonal periodicity and was little influenced by the microorganisms in the influent wastewater. The activated sludge process at the same plant had low settleability, and a different microbial community, yet produced comparably low effluent concentrations. The AGS had a 70% lower land footprint, and 15-38% lower energy usage compared to the activated sludge process. This confirms that AGS can be compact without increased energy usage. This research gives new insights into the challenges of the treatment of municipal wastewater with AGS under fluctuating conditions.
Implementering av aerobt granulärt slam i Sverige - en fullskalestudie (AGNES II)
The Swedish Water & Wastewater Association (500521AgnesII), 2018-01-01 -- 2020-06-15.
Driving Forces
Sustainable development
Subject Categories
Civil Engineering
Environmental Engineering
Water Engineering
Water Treatment
Environmental Biotechnology
ISBN
978-91-7905-868-5
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5334
Publisher
Chalmers
Föreläsningssal EC, Hörsalsvägen 11
Opponent: Prof. Anuska Mosquera Corral, University of Santiago de Compostela, Spain