The usage of membranes in wastewater treatment often leads to problems with scaling and fouling, which results in an irreversible loss of membrane permeability. Various pretreatments as well as mechanical and chemical cleaning possibilities are described and evaluated in order to ensure continuous operation. The cleaning has been performed by a sequential backwash with filtrate. In addition, the membrane was cleaned chemically to restore the flux to an acceptable level. The effect of chemically enhanced backwash (CEB) and cleaning in place (CIP) has been considered in more detail. The UF membranes are typically cleaned by soaking in alkali, acids and/or oxidizing solutions. Sodium hydroxide (NaOH), sodium hypochlorite (NaOCl) and acid sulphur (H2SO4) were used as cleaning agents. Furthermore, the impact of pre-treatment by pre-ozonation and subsequent coagulation on the performance of a polyether sulphone ultrafiltration membrane has been investigated in a pilot plant. Ozone is used in water treatment for the oxidation of organic substances, which leads to a reduction of organic fouling. A subsequent coagulation is applied to form stable aggregates out of biopolymers, which are most relevant for membrane fouling in order to backwash them easily from the surface and the membrane pores. Both pre-treatments have an influence on an improved filtration performance. The scope of the current paper is to critically evaluate the impact on the hydraulic and chemical treatment of an organic membrane and to find out which cleaning strategy is the best against membrane fouling.

Within this research project different treatments (ozonation, coagulation) of secondary effluent and the fouling behavior during subsequent ultrafiltration were investigated at labscale. Coagulation with 4 mg Fe3+/L leads to a significant removal of fouling resistance and moreover pre-ozonation up to a dosage of 15 mg O3/L can clearly enhance the filtration process. In contrast rising ozone dosages produce more hydraulically irreversible fouling. The subsequent coagulation can only compensate ozone-induced stronger irreversible fouling to some extent.

The total phosphorus concentration (TP) in Berlin’s surface waters has to be decreased to 6090 µg/L to achieve good ecological conditions. Furthermore, securing the bathing water quality of surface waters gains more attention. The wastewater treatment plant (WWTP) in Ruhleben should be upgraded by tertiary treatment to reduce the TP concentration (< 80 µg/L) and the pathogen germ concentration in the WWTP effluent. The project OXERAM compares different filtration technologies with regard to their efficiency and applicability as tertiary treatment. In this thesis the combination of microsieve filtration and UV-disinfection has been investigated. Before this trial the microsieve was rebuilt after a one year operation period. The volume of the coagulation tank was reduced to 26 % (0.56 m³) of its initial volume. The coagulation stirrer was exchanged by a Turbomix TM, applying a constant G·t-value of 25 000. Additionally, the angle of the blades of the flocculation stirrer was changed, almost doubling the G-value (154 1/s.) Long term trials have shown that an average TP effluent concentration of 60 µg/L can be achieved through microsieve filtration (10 µm) with chemical pretreatment (2.0 mg Al/L PACl and 0.61 mg/L cationic polymer). 80 % of the grab samples had a TP concentration = 73 µg/L. An average effluent suspended solid concentration of 2.2 mg/L was achieved. The average residual Aluminum concentration was 0.35 mg/L. The increase of the G-value during coagulation and flocculation after the rebuild led to an increased energy demand of both stirrers. However, through the new hydraulic conditions, the average polymer dose was reduced by 65 % in comparison to the dynamic operation in summer 2011 and the hydraulic retention time during coagulation could be reduced to 1 minute at peak flow. Furthermore, the impact of applied energy during coagulation and flocculation was investigated. A reduction of the G·t-value during coagulation led to a higher SS effluent concentration of 25 % (2.8 mg/L). During flocculation a high G-value (153 1/s) was favorable for the microsieve performance. A lower backwash time and effluent turbidity were observed. As a result, the increased energy demand of the stirrers can be justified, alongside to the polymer and hydraulic retention time reduction, with an improved effluent water quality and a lower energy demand for the backwash. The UV-disinfection operated reliably after the microsieve filtration. The UV effluent concentration of Enterococci and E.Coli were always under the limit of quantification (15-38 MPN/100 mL), even at a fluence of 361 J/m². Coliphages (= 7 PFU/100 mL) were detected in the effluent of the UVdisinfection, when the calculated fluence was lower than 549 J/m². In this study it was demonstrated that the microsieve filtration with chemical pretreatment and a subsequent UV-disinfection represents an alternative as tertiary treatment. TP effluent values lower than 80 µg/L were reliably achieved. An excellent water quality accordingly to the EG Bathing Water Quality Framework Directive was attained through the subsequent UV-disinfection.

Niederdruckmembranen (Mikro- und Ultrafiltrationsmembranen) stellen eine leistungsfähige Technik zur weitergehenden Behandlung kommunaler Abwässer dar. Neben den Vorteilen eines kleinen Flächenbedarfs und eines verlässlichen Betriebes, birgt vor allem die hohe Ablaufqualität das Potential, die aufnehmenden Gewässer zu entlasten. Ein großes Problem beim Einsatz solcher Membranen ist das Membranfouling. Dieses führt zur raschen Abnahme der Filtrationsleistung, zur Erhöhung der Reinigungsfrequenz und des Chemikalieneinsatzes, was insgesamt hohe Betriebskosten verursacht. Sowohl gelöste organische Stoffe, als auch kolloidale und partikuläre Wasserinhaltsstoffe wurden als Hauptverursacher des Foulings von Niederdruckmembranen identifiziert. Durch gezielte Vorbehandlungen des Wassers kann das Membranfouling deutlich reduziert werden. Verschiedene Studien zeigen, dass eine vorgeschaltete Flockung zur Ausbildung eines porösen, hydraulisch gut rückspülbaren Filterkuchens führt. Weiterhin konnte gezeigt werden, dass eine Kombination aus Ozonung und Flockung durch den Effekt der Mikroflockung eine Bildung größerer, stabilerer Flocken bewirkt und somit eine verbesserte Filtrierbarkeit des Wassers erreicht werden kann. Bisher fehlt jedoch die Möglichkeit, verlässliche Vorhersagen über das Foulingpotential von gereinigtem Abwasser zu treffen. Das Ziel dieser Studie ist es, auf Grundlage von Partikelgrößenanalysen im nm-Bereich, Abschätzungen über das Foulingverhalten von Kläranlagenablauf zu treffen. Darauf aufbauend soll die Vorbehandlung aus Ozonung und anschließender Flockung für die Minimierung des Foulingpotenzials der im Wasser enthaltenen Substanzen optimiert werden.

Der Einsatz von Niederdruckmembranen (Mikro- und Ultrafiltration) zur Aufbereitung von biologisch behandeltem Abwasser ermöglicht eine weitergehende Entfernung von Mikroorganismen und damit eine verbesserte hygienische Ablaufqualität. Membranfouling, also die Ablagerung von Wasserinhaltsstoffen auf oder in der Membran und eine damit verbundene Verringerung der Membranpermeabilität gelten dabei als ein wesentliches Problem. Gerade das irreversible Fouling verhindert einen vermehrten Einsatz dieser Aufbereitungstechnik. Untersuchungen zeigen, dass organische Makromoleküle in erheblichem Maße für das Fouling verantwortlich sind. Mittels Fluoreszenzanalytik und Größenausschlusschromatographie konnten Proteine hierbei als stark foulingverursachende Fraktion identifiziert werden. Filtrationsversuche mit Standard-Proteinlösungen über Niederdruckmembranen bestätigen deren Foulingpotenzial. Dies wird auf elektrostatische und hydrophobe Wechselwirkungen zwischen Membran und Protein (Porenverblockung /einschnürung) zurückgeführt bzw. mit intermolekularen Wechselwirkungen zwischen den Proteinen erklärt (Deckschichtbildung). Weiterhin hat der pH-Wert einer Proteinlösung starken Einfluss auf die Filtrierbarkeit. Bisherige Untersuchungen zeigen hier jedoch unterschiedliche Ergebnisse. Während Koehler et al. (1997) in Fouling-Maximum im Bereich des isoelektrischen Punktes (IEP) feststellen, zeigt Salgin (2007) ein stärkeres Fouling bei pH<IEP. Die genaue Ursache ist unklar und wird von verschiedenen Autoren in unterschiedlichem Maße den oben genannten Wechselwirkungen zugeschrieben. Der überwiegende Teil der Untersuchungen ist für die Membranfiltration in der Abwasseraufbereitung nur in beschränktem Maße relevant, da die eingesetzten Proteinkonzentrationen mit >100mg/L deutlich über dem Bereich des Klarlaufs einer kommunalen Kläranlage liegen. Im Rahmen dieser Arbeit wurde der Einfluss unterschiedlicher Faktoren (pH-Wert, Hintergrundmatrix) auf die Filtrationseigenschaften und das Proteinfouling im geringeren Konzentrationsbereich (5 mg/L) untersucht. Bei der Untersuchung kam auch erstmals ein hochmodernes MALDI-TOF-MS mit zusätzlichem HighMassDetektor für die direkte Analyse der verwendeten Membranen zum Einsatz.

In order to meet the requirements of the European framework directive on water, authored by the European parliament, measures have to be taken to enhance the situation of the bodies of water in Berlin. The discharge of treated wastewater is an important source of phosphor into the bodies of water of Berlin. The OXERAM project investigates different possible technologies to decrease these entries of phosphor and the conditional growth of algae. Pilot plants for these technologies are being operated at Sewage Treatment Plant Ruhleben (STP Ruhleben). Installed are a microsieve plant and two membrane plants. In previous tests, it was possible to proof the functionality of the microsieve plant under static influent flow and volume proportional chemical dosing. Effluent concentrations of < 80 µg/L were reliably achieved. The goal of this thesis is to evaluate the functionality of the pilot plant under dynamic operating conditions and load proportional chemical dosing. Therefore several tests were conducted. In a first step the pilot plant was operated with an artificial daily flow pattern, which was calculated regarding the daily flow variations in the influent of the STP Ruhleben. Tests under volume proportional dosing, and under load proportional chemical dosing, were conducted. The dosing of the coagulant was thereby varied according to the ortho phosphate concentration in the influent of the pilot. In a third step the influent flow was directly correlated to the influent flow of STP Ruhleben, in combination with load proportional dosing. During all conducted tests, sufficiently low total phosphorus concentrations in the effluent of the pilot plant could be achieved. By using load proportional dosing, savings of 11 % for the coagulant and 14 % for the polymer could be achieved. In addition several tests concerning the optimization of the whole process were conducted e.g. different reaction times for the flocculation and different polymer concentrations were tested. At the end an estimation of the operating costs for a microsieve plant of the size that would be required for the STP Ruhleben was made. Thereby the costs for Energy, Coagulant and Polymer and repair/ maintenance were discovered as main parts of the operating costs. The specific operating costs would be ca. 3.1 Cent/m³. To be able to compare the investigated technology with the other processes further tests of the pilot plant in combination with a UV plant as disinfection step of the effluent water from the microsieve have to be conducted.