Within the 3.5 year ENREM project (Enhanced Nutrient REmoval in Membranebioreactors) in Berlin-Margaretenhöhe a novel and patented process was investigated to demonstrate the feasibility of a semi-decentralised solution reaching high effluent requirements set by the water authority of Berlin. This novel process could be a solution for suburban areas of Berlin which are not connected to central sewer system. The biological process combines enhanced biological phosphorus removal (EBPR) with post denitrification in MBR technology without dosing of any carbon sources. The process configuration of this demonstration plant enables advanced wastewater nutrients removal (C, P and N) and could be a promising option for wastewater treatment wherever high effluent qualities are required. A second prototype MBR system was operated in parallel, applying a different biological process, e.g. without biological phosphorus removal, enabling a comparison of these different technological approaches. The demonstration plant showed high elimination rates for COD (>95%), phosphorus (>99%) and nitrogen (up to 98%) when operated within the appropriate range of design conditions. The operational experience within the first years showed that there is a possibility for process stabilisation by changing the ratio of the process steps. For this reason the volume of the anoxic zone was enlarged by reducing the aerobic volume in Feb 2008. The positive effects could be seen on the basis of the effluent concentrations after a short period of adaptation. The membrane filtration performance was very reliable with a new cleaning strategy: Two membranes were operated alternating with an operational flux of 15 – 20 L/m²/h and a maintenance cleaning with low chemical concentration. Different cleaning agents were used in order to evaluate the cleaning efficiencies. An economical evaluation of the demonstration plant was performed in comparison to the existing wastewater treatment costs of app. 7 €/m3 by trucking away and the prototype MBR plant. Operated on the same site, the two MBR systems were used to calculate the actual costs, in relation to the effluent quality, and to perform a scale-up up to 5000 pe considering four different effluent quality classes. The results showed that the ENREM process applied in the demonstration plant is economically an alternative for plant sizes of 5000 pe and larger. For plant sizes smaller than 5000 pe, the prototype MBR system equipped with precipitation and a downstream adsorption filter for enhanced phosphorus removal proofed to be the more viable solution.

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).

MBR-technology is able to fulfil similar or even higher standard for nutrients removal than conventional activated sludge processes. This paper presents the optimisation of the membrane bioreactor technology, together with a low pressure sewer, to equip a remote and yet unsewered area of Berlin requiring high quality wastewater treatment. The hydraulic flow pattern of the entire system has to be studied carefully due to the small collection system (no time delay between wastewater discharge and treatment to minimise the daily profile). The pollutant concentrations in the wastewater exhibit also stronger variations. In order to flatten out the hydraulic and load profile, and therefore to reduce the size of the biological reactor and the membrane surface, an buffer tank was installed before the MBR-plant. A full analysis of the influent hydraulic flow and wastewater characterisation is provided for the demonstration MBR-plant.