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Sellin, Jessica, 2021. Comparison of mesophilic and thermophilic anaerobic sludge digestion at Hammarby Sjöstadsverk MBR pilot plant for wastewater treatment. Second cycle, A2E. Uppsala: SLU, Department of Molecular Sciences



Anaerobic digestion is a commonly used method for stabilisation of sewage sludge and production of biogas at municipal wastewater treatment plants (WWTPs). The hydraulic retention time for sludge in the digestion reactors is about 16 days at Henriksdal WWTP in Stockholm. As Henriksdal WWTP is being extended and rebuilt for increased capacity, the hydraulic retention time will be decreased to 14 days. The present study investigated to what extent further decrease in retention time is possible by evaluating data from stress tested anaerobic digestion processes. The study also investigated methods for analysis of volatile fatty acid (VFA) as well as estimation of methane production. The present pilot study, conducted at Hammarby Sjöstadsverk pilot facility, proves that anaerobic digestion can prevail at nine to four days retention time. A retention time of four days resulted, however, in a specific methane production which was 42-48% lower than at Henriksdal WWTP at thermophilic (55 °C) and mesophilic (37 °C) temperatures. The ratio between VFA and alkalinity stayed within normal levels during both stress tests, indicating stable processes. Unexpectedly, VFA did not increase substantially during the stress tests. This might be explained by low organic loading rate and low degradability of the substrate. Alkalinity, however, was one of the first parameters to decrease below normal levels, possibly due to lower nitrogen mineralisation. Although this study shows that it is possible to maintain a viable anaerobic digestion process at nine to four days retention time, the loss of buffering capacity and lower methane generation should discourage long term operation at short retention times. The present study also suggests spectrophotometric VFA analyses for detection of low VFA concentrations as well as methane production estimations based on reduction of fat, protein and carbohydrate.

Main title:Comparison of mesophilic and thermophilic anaerobic sludge digestion at Hammarby Sjöstadsverk MBR pilot plant for wastewater treatment
Authors:Sellin, Jessica
Supervisor:Schnürer, Anna
Examiner:Pell, Mikael
Series:Molecular Sciences
Volume/Sequential designation:2021:09
Year of Publication:2021
Level and depth descriptor:Second cycle, A2E
Student's programme affiliation:NM029 Soil, Water and Environment - Master's Programme, 120.0hp
Supervising department:(NL, NJ) > Department of Molecular Sciences
Keywords:Anaerobic digestion, sludge, wastewater treatment, thermophilic, mesophilic, stress test
Permanent URL:
Subject. Use of subject categories until 2023-04-30.:Energy resources management
Water resources and management
Deposited On:24 May 2021 10:17
Metadata Last Modified:27 May 2021 12:21

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