The pilot trials at the Ruhleben wastewater treatment plant proved that the microsieve technology combined with chemical pre-treatment achieves good and reliable phosphorus removal with effluent values < 80 µg/L TP. The first three months of pilot operation confirmed the general process performance observed during the pre-trials in 2009 but also revealed a need for process optimization with regard to the removal of suspended solids and the reduction of coagulant breakthrough. An improved performance was achieved through change from ferric chloride (FeCl3) to polyaluminum chloride (PACl). In the presented case, PACl gave clearly better results for the removal of phosphorus and suspended solids than FeCl3. Additionally, the occurrence of coagulant residues could be noticeably reduced. In contrast to FeCl3, dosing PACl led to an improvement of the water transmittance simplifying disinfection with UV irradiation. Load proportional dosing of PACl and polymer was introduced in order to avoid under as well as over dosing of the chemicals. The dose of cationic polymer had a significant impact on water quality and backwash time: With the initial process configuration 1.5 to 2 mg/L cationic polymer were recommended for a safe and stable operation with adequate backwash time resulting in an average polymer dose of 1.7 mg/L. However, latest results showed that a polymer dose of only 0.6 mg/L is possible without losses in water quality and filtration performance when mixing conditions were optimized. During the constructional modifications the hydraulic retention time of the coagulation was reduced from 4 to 1 min at peak flow. Due to the installation of a TurbomixTM short-circuiting could be avoided. Furthermore, the turbulence in the flocculation tank was increased. Despite the noticeable reduction of the hydraulic retention time and the polymer dose the rebuild resulted in improved reduction of suspended solids (2.2 mg/L) and coagulant residues in the microsieve effluent. The operation regime of the chemical treatment prior to the microsieve filtration showed to be a trade-off between the energy demand for mixing and the polymer consumption. Due to the continuous operation over more than 20 months important operational experience was gained with regard to backwash behavior and cleaning intervals. The backwash time mainly correlates with the influent flow (1030 m3/h), the influent water characteristics and the properties of the formed flocs. Due to progressing fouling of the filter panels chemical cleaning was necessary every 4 to 7 weeks. A shorter cleaning interval (e.g. every 4 weeks) might be beneficial as the backwash time and thus the energy demand could be kept on a lower level. In this application the microsieve produced on average 1.8 % of backwash water. The backwash water showed excellent settling properties (SVI << 50 mL/g) and might be easily treated via returning to the primary clarifiers. The UV disinfection plant behind the microsieve was operated with a fluence of 730 J/m2. Good disinfection could be provided for a continuous operation of 7 months. During this period there were always less than 100 MPN/100 mL of E. coli and Enterococci in the effluent of the UV disinfection. Overall, the microsieve in combination with dosing of coagulant and polymer is a robust technology with low phosphorus effluent values (< 80 µg/L) and a low energy demand of about 21 Wh/m3 (+ site-specific energy demand for water lifting). Microsieving, together with UV disinfection, can be an option for applications targeting phosphorus removal and disinfection, e.g. effluent polishing for sensitive areas or landscape irrigation.

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.