Twelve years after the first full scale municipal application in Europe of the membrane bioreactor (MBR) technology, the process is now accepted as a technology of choice for wastewater treatment, and the market is showing sustained growth. However early misconceptions about the technology are persistent and false statements are commonly encountered in articles and conferences, generating unnecessary research efforts or even fuelling either fascination or scepticism with regards to the technology, which is ultimately detrimental to the perception of the process by water professionals. We try to provide some factual and rational clarifications on ten issues which are often wrongly reported about MBR technology.

The removal of trace organic compounds through membrane bioreactors (MBR) in comparison to a conventional wastewater treatment plant (WWTP) in a long term study was investigated. Two MBR pilot plants were operated in parallel to a full-scale WWTP, fed with the same municipal raw waste water. Bulk organic parameters such as COD and TOC, high polar compounds (phenazone-type pharmaceuticals, their metabolites and carbamazepine), and less polar estrogenic steroids (estradiol, estrone and ethinylestradiol) were quantified. The removal rate of phenazone, propyphenazone and formylaminoantipyrine by the conventional WWTP was below 15 %. Significant higher removal rates (60-70 %) started to be clearly monitored with the pilot plants after about 5 months. The removal of the drug metabolite acetylaminoantipyrine during conventional treatment was below 30 % and reached 70 % in both pilot plant. Higher removal rates coincided here with higher temperatures at the summer time. Carbamazepine was not removed during conventional and membrane activated sludge treatment.The conventional WWTP removed in average more than 90 % of the natural steroids estrone and estradiol and about 80 % of the synthetic ethinylestradiol. The elimination of estradiol and estrone by the MBR processes were of about 99 % and Ethinylestradiol was removed by about 95 %.

Two configurations of membrane bioreactors were identified to achieve enhanced biological phosphorus and nitrogen removal, and assessed over more than two years with two parallel pilot plants of 2m³ each. Both configurations included an anaerobic zone a head of the biological reactor, and differed by the position of the anoxic zone: standard pre-denitrification, or postdenitrification without dosing of carbon source. Both configurations achieved improved phosphorus removal. The goal of 50mgP/L in the effluent could be consistently achieved with two types of municipal waste water, the second site requiring a low dose of ferric salt ferric salt < 3mgFe/L. The full potential of biological phosphorus removal could be demonstrated during phosphate spiking trials, where up to 1mg of phosphorus was biologically eliminated for 10mg BOD5 in the influent. The postdenitrification configuration enabled a very good elimination of nitrogen. Daily nitrate concentration a slow as 1mg N/L could be monitored in the effluent in some periods. The denitrification rates, greater than those expected for endogenous denitrification, could be accounted for by the use of the glycogene pool, internally stored by the denitrifying microorganisms in the anaerobic zone. Pharmaceuticals residues and steroids were regularly monitored on the two parallel MBR pilot plants during the length of the trials, and compared with the performance of the Berlin-Ruhleben WWTP. Although some compounds such as carbamazepine were persistent through all the systems, most of the compounds could be better removed by the MBR plants. The influence of temperature, sludge age and compound concentration could be shown, as well as the significance of biological mechanisms in the removal of trace organic compounds.

Two configurations of membrane bioreactors were identified to achieve enhanced biological phosphorus and nitrogen removal, and assessed over more than two years with two parallel pilot plants of 2 m3 each. Both configurations included an anaerobic zone ahead of the biological reactor, and differed by the position of the anoxic zone: standard pre-denitrification, or postdenitrification without dosing of carbon source. Both configurations achieved improved phosphorus removal. The goal of 50µgP/L in the effluent could be consistently achieved with two types of municipal wastewater, the second site requiring in addition a low dose of ferric salt ferric salt < 3mgFe/L. The full potential of biological phosphorus removal could be demonstrated during phosphate spiking trials, where up to 1mg of phosphorus was biologically eliminated for 10mg BOD5 in the influent. The post-denitrification configuration enabled a very good elimination of nitrogen. Daily nitrate concentration as low as 1 mgN/L could be monitored in the effluent in some periods. The denitrification rates, greater than those expected for endogenous denitrification, could be accounted for by the use of the glycogene pool, internally stored by the denitrifying microorganisms in the anaerobic zone.

Im Berliner Stadtgebiet gibt es Siedlungsgebiete, die bisher nicht an ein Klärwerkangeschlossen sind, da eine zentrale Erschließung nicht wirtschaftlich ist. Für dieseGebiete könnte eine dezentrale Lösung mit dem Membranbelebungsverfahreneingesetzt werden. Dann würden die gleichen Überwachungsanforderungen wie inder Abwasserreinigung in Berlin bereits gültig, sicher erfüllt bzw. überschritten. FürPhosphor könnten sogar zukünftig zu erwartende strengere Überwachungswertebereits erreicht werden (50 µg/L). Das Membranbelebungsverfahren wird bereitsseit den 90er Jahren eingesetzt und hat den Stand der Technik erreicht. Für diePhosphorelimination wird in Membranbelebungen eine Simultanfällung durchgeführt,wodurch zuverlässig Ablaufwerte <1mg/L erreicht werden können. Die Fällung führtjedoch zu einer um ca. 25% erhöhten Schlammproduktion (für ß~1,5), einem hohenChemikalienbedarf und einer Aufsalzung des Vorfluters. Das Ziel des Forschungsprojektes ist es die vermehrte biologischePhosphorentfernung (Bio-P) im Membranbelebungsverfahren bei einemSchlammalter von 8 bis 26 Tagen zu untersuchen. Die Zielkonzentration fürGesamtphosphor wurde mit 50µgP/L festgelegt. Auch der Prozess der Stickstoffentfernung sollte optimiert werden. Dabei wird die vorgeschalteteDenitrifikation mit der nachgeschalteten Denitrifikation ohne Kohlenstoffdosierung Post-Denitrifikation) verglichen.

In den letzten Jahren hat die Untersuchung des Vorkommens und Verhaltens von Arzneistoffen und endokrin wirksamen Substanzen in der Umwelt zunehmend an Bedeutung gewonnen (Daughton and Ternes, 1999; Kümmerer, 2001; Heberer, 2002). Verschiedene Studien zeigten, dass abwasserbürtige Verbindungen zum Teil nicht oder nicht vollständig durch die Behandlung des Abwassers entfernt werden (Heberer, 2002; Ternes, 1998; Daughton and Ternes, 1999). Somit können unter anderem Humanpharmazeutika und deren Metabolite über Kläranlagenabläufe in die aquatische Umwelt gelangen. Da die Wirkschwelle solcher Verbindungen zum Teil schon in sehr geringer Konzentration erreicht wird (z.B. Ethinylestradiol - Purdom et al., 1994) oder die Datenlage hierzu unzureichend ist, gewinnt die Entfernung der Spurenstoffe während der Abwasserbehandlung immer mehr an Bedeutung. Membranbelebungsanlagen könnten hier einen verbesserten Rückhalt bewirken. Neben der biologischen Phosphor- und Stickstoffentfernung (Gnirss et al., 2003; Lesjean et al., 2002) war es Ziel dieses Forschungsprojektes, die Entfernung von ausgewählten organischen Spurenstoffen in zwei Membranbelebungsanlagen im Vergleich zu einem konventionellen Klärwerk zu untersuchen.