Extended Sludge Retention Time (EXRT) technique for increased biogas production


The Wastewater treatment plant Himmerfjärdsverket cleans the water of some 300 000 people equivalents in the southern municipalities of Stockholm, Sweden. The plant is operated by SYVAB, a company owned by the surrounding municipalities Botkyrka, Nykvarn, Salem, Södertälje (through Telge AB) and Stockholm Water. As a part of the WWTP’s sludge management three continuously stirred reactors are run in parallel in a mesophilic anaerobic co-digestion process together with food and other organic waste. The biogas was initially used for internal purposes but since 2010, most of the gas produced is sold as biofuel after upgrading. Together with IVL Swedish Environmental Research Institute and financial support from the Swedish Water & Wastewater Association, SYVAB is now testing out a technique based on sludge recirculation that was developed at IVL/KTH´s R&D-facility Hammarby Sjöstadsverk. The process is called Extended Sludge Retention Time (EXRT) and has had some very promising results in pilot scale in terms of efficient use of existing digestion volumes. The full scale tests will be run in one of the three digesters where one of the other reactors will be used as reference. In addition to comparison of standard digestion benchmarking key figures like degree of digestion and specific gas production, an analysis of how the EXRT process affects the digester microbial populations compared to the reference reactor will be done. At the time of the presentation, trials have been running long enough to present some hopefully interesting preliminary results and experiences of the start-up phase.

Medarbetare: Jesper Karlsson

Nyckelord: Sludge management, biogas, biofuel, Extended Sludge Retention Time (EXRT), digestion

Typ: Proceedings/konferensbidrag

År: 2013

Rapportnummer: A2073

Författare: Maximilian Lüdtke, Lars Bengtsson, Stridh S., Berg M., Jesper Karlsson, Baresel C

Publicerad i: Presented at the NordIWA 2013, Malmö