Fouling still is one of the major issues of membrane bioreactor (MBR) research. Most attention is currently paid to extracellular polymeric substances (EPS) in either bound or soluble/colloidal (soluble microbial products, SMP) form. While several trends or correlations were reported, the comparability of results is still limited by the numerous differences in plant set-up and analytical methods. The aim of this study is to compare polysaccharide concentrations and their respective fouling potential in different MBR operated under different conditions using the same analytical and evaluation tools and considering all relevant differences. Results are also compared to literature findings in an attempt to come to more generally valid conclusions. Results indicate that SMP influence fouling only under certain conditions such as low sludge age and large pore size.

Two membrane bioreactors were operated with biological phosphorus removal, carbon degradation and denitrification to check how comparable and representative they were compared to full-scale plants. One was fed with synthetic municipal wastewater and was switched from pre- to post-denitrification without carbon dosing. The influent of the second plant was drawn from a separate sewer. This plant worked the whole time with post-denitrification without carbon dosing. The synthetic wastewater was designed to achieve a realistic COD:TN:TP ratio and tested for long time biodegradability. The eliminations were >94% (COD) and >97% (TP) for both plants. This was within the range of commercial plants, as well as the TN elimination for the pre-denitrification of plant I (>75%). The eliminations of TN for post-denitrification were above 80% for both plants despite the high influent concentrations and the missing carbon source for post-DN. A calculation of the nitrification rates gave values similar to those found in literature (1–6 mgN/(gMLVSS h)). A comparison of the denitrification showed expected rates for pre-denitrification (7.5 mgN/(gMLVSS h)) for plant I. The values (on average 1.8 mgN/(gMLVSS h)) for post-denitrification in plant II were higher than endogenous denitrification rates which are commonly reported as 0.2–0.8 mgN/(gMLVSS h). The rates for post-denitrification in plant I were only slightly higher than endogenous ones (0.9 mgN/(gMLVSS h)).

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 widespread application of the membrane-assisted activated sludge process is restricted by membrane fouling, which increases investment and operating costs. Soluble microbial products (SMPs) are currently considered as the major cause of membrane fouling in membrane bioreactors (MBRs). This study aims at elucidating and quantifying the effects of varying environmental conditions on SMP elimination and rejection based on findings in a pilot MBR and in well-defined lab trials. Several factors are thought to influence the concentration ofSMP and their fouling propensity in one way or the other, but findings are often inconsistent or even contradictory. Here, SMP loading rate was found to have the greatest effect on SMP elimination and thus on concentration in the MBR. The degree of elimination decreased at very lowDO and low nitrate concentrations. On average, 75% of influent SMP were eliminated in both pilot and lab trials, with the elimination of polysaccharides (PS) mostly above 80%. Rejection of SMP components by the used membrane (PAN, 37nm) ranged mainly from 20% to 70% for proteins and from 75% to 100% for PS. Especially protein rejection decreased at higher temperatures and higher nitrification activity. The increased fouling rates at lower temperatures might therefore partly be explained by this increased rejection. Apparently, mainly the nitrite-oxidising community is responsible for the formation for smaller SMP molecules that can pass the membrane.

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.

The ENREM project aims at demonstrating a novel wastewater treatment process based on the technology of membrane bioreactor (MBR), set up in a configuration to enable enhanced biological elimination of nutrients. A new plant, and the related sewer system, was built in a unsewered periurban area of Berlin. The plant is to be operated over more than one year, and the process to be optimised. Performances and costs of the treatment system will be then assessed for the size 250 – 10,000pe, corresponding to semi-central schemes. The plant was started on 28 February 2006 with 8 month delay on the program identified in the LIFE proposal. As a consequence, a project extension request of 8 months will be lodged, in order to match the initial duration of 18 months for the optimisation, evaluation and dissemination phase. This delay incidentally caused also a 6 month delay for the preparation of this Interim Report. Despite these aspects, the management of the project has been achieved according to the organisation identified in the LIFE proposal. Annex 7.1 presents and discusses the key deliverables and milestones depending on the LIFE proposal and the current status. In relation to the technical content, Task 2 “Site and process definition” and Task 4 “Detailed design” were completed early 2005. Task 3 “Preliminary testing on representative site” was completed in September 2005 and enabled to validate the design, operation and start-up criteria of the MBR demonstration plant. The public tenders for the construction of the sewer network and the MBR container unit occurred during the first semester of 2005, and the construction of the scheme was completed by end 2006. In parallel, the required legal permits were acquired (for plant construction & operation, water discharge), as well as the parcel hosting the treatment unit. A relationship with the inhabitants of Margaretenhöhe was maintained in order to ensure a smooth construction phase, and a quick connection to the new sewer system. The dissemination activities covered several communication vectors (Tri-lingual website www.kompetenz-wasser.de, press-release and articles and bi-lingual KWB Newsletter, local press, scientific press, plant visits and inauguration, communication material etc). The project results will be widely communicated in the national and international medien, and a final project workshop will be organised in June 2007. The main task in 2006 will be the operation, optimisation and technical / economical evaluation of the low sewer system and the MBR demonstration plant. So far, the budget is generally in line with the expectations, or slightly below. The project finances allow the project extension of 8 months, required to achieve all announced technical outcomes of the project. After the 8 month extension the final project budget is expected to remain about 20% below the planned proposal, i.e. approx. € 600,000 savings on the total budget should be recorded, corresponding to a subvention reduction of approx. € 100,000 (also close to 20% reduction).

Extracellular polymeric substances (EPS) are considered as the major cause of membrane fouling in membranebioreactors. Recent studies have revealed a linear relationship between fouling rate (increase of filtration resistanceover time) and polysaccharide (PS) concentration [1]. Several factors like the type of wastewater, sludge loading rate, sludge age, MLSS concentration, and mechanical stress are known to influence the concentration of dissolved EPS. Also, unsteady states like intermittent feeding or shifts in the oxygen supply have been identified as additionalfactors leading to an increase in EPS formation or to a change in its fouling propensity. However, no systematicinvestigation to quantify such influences has been undertaken so far. This study is aimed at determining the influenceof discontinuous excess sludge withdrawal often applied in small decentralised plants and resulting unsteady loadingrates on EPS formation and filtration resistance. The general trend of increased fouling rate at higher PS concentrationsis confirmed but data show a larger scatter which could be due to a change in the PS structure and hence their fouling potential. The levels of dissolved oxygen and nitrate which also fluctuate more strongly in MBRs withirregular sludge wastage appear to have a profound impact on EPS uptake rate and thereby on EPS concentration.