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

An international review of the market, current practices and R&D projects on the topic of rainwater harvesting management was performed. The review highlighted leading countries in different regions of the world, but also the variety of practices and acceptance. Current R&D issues and further research needs are identified and discussed. The application of RWHM techniques at household level seems to be mature, but sanitary risks exist when rainwater is used inside homes and also reserve on economical an environmental aspects can be drawn when drinking water supply is available. Promising concepts are being developed and demonstrated at larger scale such as industrial or commercial buildings or even urban catchments where the use of rainwater and the operation of the systems are under full control. For schemes of this scale, the integration and optimization of several beneficial aspects such as –traditionally- additional water supply and stormwater management, but also urban planning with water and green spaces, energy compensation in buildings and in the cities or ecological enhancement seems to be promising. Specific expertise will be required to best plan these schemes according to the local conditions and targets and to operate, maintain and upgrade them over their entire life time.

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.

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).

Membrane processes stand as a promising technology to ensure a safe water supply at the community and the household levels. As the price of membranes has notably decreased over the last years, the market of membrane-based systems for decentralised applications has developed and diversified. In order to have a view of what the current market offers, 204 water companies were contacted and asked to characterise their Point-of-use (POU) or small-scale membrane systems, with a focus set on operation and maintenance, costs and energy requirements. Such study was not performed previously. With a 15% reply rate, the survey enables to identify the different market niches. That includes ceramic POU, organic POU, organic point-of-entries (POE), modular treatment units and emergency systems, whose technical characterization is further detailed in the Annex. Besides, the review of the marketed membrane modules reveals that ultrafiltration is the most available process. The survey also shows that the pre-treatment is a key parameter when considering options for decentralised water supply. As needs for sustainable solutions for small water supply are established, the membrane market is expected to grow and more standardised products to appear. The market evaluation can be summarized in Figure 1. Depending on the product niche, the membrane material and the filtration type, different degrees toward the market maturity are then highlighted. Such systems would be broadly applied in developed countries, but they represent also great potential for transition and developing countries. However, few systems designed for long-term operation with low-energy and low-chemical requirements exist yet. Therefore, the R&D identified within Techneau matches a non-fulfilled yet requirement.

For small membrane bioreactor (MBR) plants, in order to save investment for infrastructure, it could be beneficial not to withdraw excess sludge on a daily basis, but to store it in the biological reactor and only withdraw it every 2 to 4 weeks. This study aimed at investigating the effect of such an excess sludge removal strategy on the performance of an MBR plant in terms of permeate quality, nutrients removal rates and fouling. An MBR pilot plant, fed with domestic waste water from a remote area, was operated with enhanced biological phosphorus removal and post-denitrification without carbon dosing. 50% of the reactor volume was withdrawn when around 13 g l-1 TS was reached in the membrane reactor. This sludge removal strategy did not lead to failure of neither the biological phosphorus removal, nor the post-denitrification. Higher specific denitrification rates (DNR) were observed during higher organic loading of the anaerobic zone. The average DNR at 20°C was 1.5 mgN(gVSS h)-1. Nitrification was influenced by the discontinuous excess sludge removal. During that period the nitrification rate varied in a wide range between 1.8 and 5 mgN(gVSS h)-1, with a trend to lower rates right after a sludge removal. Fouling was not effected by the excess sludge removal strategy. For both withdrawal strategies the fouling rate was around 5*1010(md)-1. The EPS concentration did not affect the fouling behaviour.

The Berlin Centre of Competence for Water organised, together with the International Water Association, the 2nd National Young Water Professionals Conference in Germany. This event was held on 4-5 June 2007 in Berlin and was following up on the first NYWP conference organised in Aachen in October 2005. It provided a forum for young researchers and professionals working in the membrane sector of the wastewater industry to present their work and meet their peers. The conference consisted on formal presentation of papers and posters, and an exchange with water industry professionals providing information on water career opportunities in Germany. This event was an initiative of “MBR-Network”, the European cluster on the membrane bioreactor technology, gathering about 50 European and international companies and institutions within the four FP6 projects Amedeus, Eurombra, MBR-Train and Puratreat (more info at www.mbrnetwork.eu). The technical program of the conference consisted mainly of contributions from German and international young water professionals including students, recent graduates and other professionals under the age of 35. This book contains most of the papers and posters which were presented at the Conference.