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.

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)).

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.

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.

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.

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.