Enhanced nutrients removal in membrane bioreactors (ENREM) combines enhanced biological phosphorus removal (EBPR), post-denitrification without additional carbon supply, and membrane filtration in a relatively compact wastewater treatment process [Gnirss et al. 2003]. Since 2006, a demonstration plant of 10 m³ is serving a peripheral area of Berlin to treat the wastewater of about 250 people, following an anaerobic – aerobic – anoxic process scheme [Gnirss et al. 2008]. Post-denitrification without additional carbon supply is quite uncommon because the lack of carbon as electron donor usually results in low endogenous denitrification rates (DNR) below 0.6 mgNO3-N/(goTS h), leading to larger reactor volumes and thus higher investment costs [Kujawa & Klapwijk 1999]. In contrast to that, the ENREM process showed enhanced denitrification rates of 1-2 mgNO3-N/(goTS h), raising the question which carbon source is used to obtain these rates [Adam 2004; Lesjean et al. 2005; Vocks et al. 2005]. To address this question, several batch experiments were conducted using acetate as reactor feed, which is completely consumed by the biomass within the anaerobic phase. These experiments ruled out soluble carbon sources such as extracellular polymeric substances (EPS), lysis/hydrolysis products, or adsorption of acetate [Vocks et al. 2005; Bracklow et al. 2007]. The analysis of polyhydroxyalkanoates (PHAs) and glycogen as intracellular carbon storage compounds typical for EBPR systems showed no clear trend for the anoxic phase. Furthermore, the results showed a carbon recovery rate for the anaerobic phase of only 50-70 %, accounting for PHAs, glycogen, carbon dioxide, soluble COD, and acetate. The experiments also showed that the DNR can be increased by adding higher acetate dosages at the beginning of the process [Nicke 2005; Baumer 2006; Stüber 2007]. These observations led to the assumption that an unknown intracellular carbon storage compound might be formed during the anaerobic phase which serves as carbon source for enhanced denitrification [Lesjean et al. 2008; Vocks 2008]. This study was conducted to prove the theory of an unknown intracellular carbon storage compound used for enhanced denitrification and to identify this compound. In-vivo nuclear magnetic resonance spectroscopy (NMR) has proven to be an adequate tool to analyse metabolic pathways of microorganisms and to identify also unknown compounds [Pereira et al. 1996; Maurer et al. 1997; Jeon & Park 2000; Lemos et al. 2003]. However, NMR requires the use of a single carbon source (monosubstrate) which can be labelled by 13C isotopes. Hence, this study included the adaption of the ENREM process to acetate as monosubstrate in lab scale. A 6 L sequencing batch membrane bioreactor (SBMBR) was inoculated with sludge from the ENREM demonstration plant and stepwise adapted to acetate as single carbon source. The reactor was operated successfully for a period of 190 days and showed phosphorus and nitrogen dynamics typical for the ENREM process. Furthermore, carbon mass balances showed the same recovery rates of 50-70 % like in previous studies, and fluorescence in-situ hybridisation (FISH) showed a high abundance of phosphorus accumulating organisms (PAOs), thus indicating a successful adaption of all ENREM process characteristics to monosubstrate. The continuous long-term operation with a readily biodegradable monosubstrate rules out the presence of slowly biodegradable COD (sbCOD) as carbon source for denitrification.

Für die steigenden Anforderungen an die Ablaufqualität von Abwasserreinigungsanlagen sind Membranbelebungsanlagen (MBR-Anlagen) durch ihre hohen Reinigungsleistungen bezüglich den Nährstoffen wie Phosphor und Stickstoff sowie die Zurückhaltung von Bakterien eine geeignete Lösung. Ziel dieser Untersuchung war es, auf der Grundlage zweier in Berlin mit kommunalem Abwasser betriebenen MBR-Anlagen die Kosten semizentraler MBRAnlagen in Abhängigkeit von ihrer Größe und ihrer Reinigungsleistung zu vergleichen. Es handelt sich bei diesen Anlagen um eine Demonstrationsanlage für 130 EW und eine Pilotanlage für 50 EW, wobei sich die Technisierungsgrade und Reinigungsziele der beiden Anlagen stark unterscheiden. Ein Upscaling machte den Vergleich zwischen MBR-Anlagen mit Größen von 50 bis 5.000 EW möglich. Die Investitionskosten wurden anhand der einzelnen Anlagenteile aufgegliedert und für größere Anlagen mit Hilfe der Kapazitätsmethode abgeschätzt. In die Betrachtung der Betriebskosten gingen Personal-, Schlammentsorgungs-, Energie- und Chemikalienkosten sowie die Kosten für Wartung und Instandhaltung und die Abwasserabgabe ein. Aus den ermittelten Investitions- und Betriebskosten wurden mit einer dynamischen Kostenvergleichsrechnung die durchschnittlichen Jahreskosten berechnet. Um die Reinigungsleistung zu bewerten, wurde eine Einteilung in Reinigungsklassen mit unterschiedlichen Eliminationsraten für den chemischen Sauerstoffbedarf, Stickstoff und Phosphor vorgenommen, in die die MBR-Anlagen eingeordnet wurden. Die Untersuchung ergab, dass die vergleichsweise hohen spezifischen Kosten der betriebenen Anlagen mit zunehmender Anlagengröße stark abfallen. Sie sinken bei einer Anlagengröße von 1.000 EW auf ca. 2 €/m³. Die Erreichung einer hohen Ablaufgüte kann durch unterschiedliche Technologien erzielt werden. Es ist dafür bei den untersuchten MBR-Anlagen ein hoher Chemikalienaufwand oder ein hoher Energieaufwand nötig.

Three different methods for fi ltration characterization in Membrane Bioreactor (MBR) systems were compared. These were the Delft Filtration Characterization Method (DFCm), the Berlin Filtration Method (BFM) and an ex situ side-stream fi ltration test cell for the determination of the critical fl ux. The ex situ fi ltration test cell and the DFCm fi lter activated sludge from a tank, while the BFM works in situ with a test cell directly submerged into the biological tank at similar operational conditions to a typical MBR plant. The mixed liquor of four different MBR units was characterised several times with the three fi ltration methods. The three tested methods seemed to agree in the classifi cation of the tested mixed liquors in terms of fi lterability except for one of the tested activated sludges. Additionally, three critical fl ux protocols were studied using the BFM fi ltration test cell. The fi rst consisted in the classical fl ux-step method, the second included relaxation between fi ltration steps and in the third protocol, 2 min fi ltration at a fi xed fl ux were performed before every fi ltration step. The last protocol was selected as the most representative of full scale MBR operation and the most interesting one for giving valuable information about the irreversibility of the fouling.

Due to their compact design and their high quality and reliable treatment, package or containerised membrane bioreactor (MBR) units are used for decentralised and semi-decentralised wastewater treatment plants. The operational availability, performance and economical viability of these MBR systems depend on the fi ltration performance of the membrane modules. Current chemical cleaning strategies of MBR modules, based on regular (weekly) maintenance cleanings and/or occasional (quarterly to biannual) intensive cleanings proved not to be adapted to semi-central MBR applications (100 up to 1000 p.e.): regular maintenance cleanings require automation and lead to too much care and personnel requirement. Occasional intensive cleanings increase the operational risk of membrane fouling and low cleaning recovery. In addition, semi-central MBR applications are often designed with at least two redundant fi ltration lines. An alternative chemical cleaning strategy was therefore proposed, implemented and assessed in a containerised MBR unit serving a population of about 250 p.e.: at a given time, only one fi ltration line is in operation while the other one soaks in a low-grade chemical solution. The modules are switched alternately on a monthly basis. To identify a cleaning strategy and an agent showing a good recovery, one of the modules was cleaned with H2O2, while the other was cleaned with NaOCl. A cleaning step with citric acid is added when necessary. These cleanings were tested over 16 months with the goal to minimise maintenance effort and chemicals used.

Demonstrationsprojekt Berlin-Margaretenhöhe: Dezentrale Klärtechnik vor Ort erprobt und auf Wirtschaftlichkeit geprüft.

The MBR technology is able to fulfil similar or even higher standard for nutrients removal than conventional activated sludge processes. This paper presents the results of a scheme constructed in a remote and yet unsewered area of Berlin requiring high quality wastewater treatment, and consisting of one containerised MBR unit together with a low pressure sewer. The process includes enhanced biological phosphorus removal and post-denitrification. In order to flatten out the hydraulic and load profile, and therefore to reduce the size of the biological reactor and the membrane surface, a buffer tank was installed before the MBR-plant. The full-scale MBR demonstration plant in Berlin-Margaretenhöhe or 250 p.e.(person equivalent) could be operated continuously by remote control and could fulfil high quality treatment for both disinfection and enhanced biological phosphorus and nitrogen removal, matching under design load conditions the effluent criteria of TP < 0.1 mgP/L and TN < 10 mgN/L ( 99% P- and 90% N-elimination).

Two membrane bioreactor (MBR) plants were operated with a process which combines enhanced biological phosphorus removal (EBPR) and post-denitrification without external carbon dosing in the anoxic zone. An enhanced post-denitrification with denitrification rates (DNR) twice as high as the expected endogenous rate was observed. Batch tests revealed a linear correlation between the anaerobic acetate loading and the postDNR which is remarkable since the aerobic phase was located in-between the anaerobic and anoxic phase. An anaerobic build up of a carbon storage compound which can outlast the aerobic phase is postulated. Measurements showed that neither polyhydroxyalkanoates (PHAs) nor glycogen are used as carbon source for the enhanced post-denitrification. A carbon mass balance in the anaerobic phase strongly indicates the formation of a different so far unknown storage compound. This assumption is supported by literature data which show carbon recovery ratios of known storage compounds (PHAs and glycogen) in the anaerobic phase of EBPR systems often below 1 down to 0.3, in particular for trials performed with real wastewater. The potential of enhanced post-denitrification in conventional UCT systems is also demonstrated in full-scale non-MBR wastewater plants. When implemented in MBR process, enhanced nutrients elimination could be biologically achieved with 99% TP-removal and 90% TN-removal. A small full-scale unit is in operation in Berlin since March 2006 to demonstrate the process in real operation conditions with domestic wastewater.