Various tertiary treatment processes were compared in the OXERAM project, including a polymeric membrane and a microsieve pilot plant which were installed at the Ruhleben WWTP in Berlin and operated for almost two years. To increase the performance of both these processes, pre-treatments with ozonation, coagulation and/or flocculation were tested. In order to optimize the hybrid processes and to develop a control strategy, online monitoring was implemented. After a literature review and lab trials at the Technische Universität Berlin (TUB) during the project preparation phase, two instruments were recommended. An NS500 device by Nanosight was installed in the UF membrane pilot (pore diameter = 20 nm) influent with sampling every 15 minutes before and after the inline coagulation. The particles between 50 and 1000 nm were analysed to evaluate the impact of the ozonation / coagulation or the coagulation alone on the nanoparticles below 500 nm which are most responsible for fouling. For a better reproducibility and quality of the results, samples were pre-filtered by an online metallic 5 µm filter. Particle analysis by Nanoparticle Tracking Analysis (NTA) was obtained to give reliable and reproducible information about the concentration and size distributions of the colloidal fraction in the tested treated domestic wastewater. Correlation between the membrane reversible fouling measured with the help of the trans-membrane pressure (TMP) and the concentration of particles between 100 and 200 nm were detected. Online measurements at the pilot-scale indicate that colloid peak concentrations can be compensated for by coagulation with an optimum dose of 8 mg Fe3+/L. Furthermore, a comparison of FeCl3 and PACl demonstrated that the former is more effective in colloid removal in this treated domestic wastewater. Due to the combination of pre-ozonation and subsequent coagulation, a synergy effect was determined as the combined treatments lead to a better particle removal compared to the effect of the single treatments at same dosages of O3 and Fe3+. A combination of 0.5 mg O3/mg DOC0 and 8 mg Fe3+/L leads to a total reduction down to < 5 % of the initial colloid content1. However a direct prediction of irreversible fouling was not possible. This device should be further optimized for its potential to reduce operational costs and lower solid loads and thus fouling on the membrane. A Pamas particle counter device was installed in the microsieve effluent pipe bypass and this measured the particle size distribution continuously by light extinction at a wavelength of 635 nm at 25 mL/min. No pre-treatment was necessary and it was possible to automatically clean the instrument every hour with distilled water or another cleaning solution. Piping and sensor cell maintenance was crucial to improve the quality of the results due to the high potential of the effluent water to post-flocculate. For optimization of the coagulant and flocculant mixing velocity, the particle counter results were more accurate than the turbidity sensor which did not detect any changes in the effluent water quality. The monitoring tool detected the lowest particle concentration for the optimized mixing velocity. However, the particle counter did not provide better information than an online turbidity sensor for other parameters such as the coagulant types or doses. Therefore, while it is recommended to use an online particle counter during the microsieve plant (10 µm) start-up phase to optimize the coagulation and flocculation, for routine controls an online turbidity sensor is sufficient. Moreover turbidity sensors are less demanding in terms of maintenance effort. The project showed that using the turbidity signal to adapt the coagulant dose was very efficient.

Im Projekt OXERAM wurden verschiedene Technologien im Hinblick auf die Anforderungen an die 4. Reinigungsstufe, vor allem Phosphorentfernung, in Pilot- und Laborversuchen untersucht. Ferner wurden die Leistungsfähigkeit der Verfahren sowohl durch eine Ökobilanz als auch eine Kostenrechnung bewertet. Der vorliegende Bericht fasst diese Ergebnisse aus den Jahren 2010 bis 2013 zusammen. Die Vorgehensweise und eine ausführliche Ergebnisdiskussion sind in den Kapiteln 2 - 6 beschrieben.

A MBBR before an advanced sedimentation step was operated as new wastewater process scheme for maximum COD extraction. The objective of this biological reactor was to modify the soluble COD ratio in primary wastewater. At high loads, the MBBR is able to consume the soluble COD for bacteria activity with very little oxidation. This process changes the soluble COD into particulate COD which is better separate from the wastewater during the following step with coagulation, flocculation and micro sieve filtration. Goals were 95% removal of suspended solids and 80% of COD extracted through separation. To check these new scheme performances, a pilot plant (0.5 to 3 m³/h) was operated at the Stahnsdorf WWTP in the south of Berlin. First results showed that a HRT of 20-30 min and a load 40-60 g CODf /(m2*d) can be recommended for maximum accumulation and minimum oxidation and that the 80% of COD extraction can be achieved (at low oxygen concentration below 1 mg/L). However the performance difference between the scheme with or without MBBR did not exceed 8 %

The study aims at assessing in long-term trials a gravity-driven ultrafiltration pilot plant designed for a capacity of 5 m3/d. The unit was operated in South Africa with Ogunjini surface water and was run with restricted chemical intervention or maintenance (no backflush, no aeration, no crossflow and no chemical). Under South African environmental conditions and with direct filtration of the river water and only one manual drainage of the membrane reactor every weekday, the unit could fulfil the design specification in terms of water production (5 m3/d) as long as the turbidity of the raw water remained in a reasonable level (up to 160 NTU), with a filtration flux typically 4 to 6 L/h.m² (corrected at 20°C). This value was in the same range as the lab results and was consistent with the first phase results (around 5-7 L/h.m² after biosand filtration). However, the flux dropped significantly to a range of 2 to 4 L/h.m² after a rain event resulting in a turbidity peak over several days up to > 600 NTU. This demonstrated that for variable raw water types with expected turbidity peaks above 100 NTU, a pre-treatment would be required for the system (biosand filter or other). The performance of microbiological tests confirmed the integrity of the membrane and the ability of the system to achieve advanced 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.

In this study the applicability of the microsieve technology together with coagulation and flocculation for advanced phosphorus removal was investigated. A pilot unit including a microsieve with 10 µm mesh size is operated continuously with secondary effluent. By applying a pretreatment of 0.07-0.09 mmol/L coagulant and 1.5-2 mg/L cationic polymer total phosphorus values below 80 µg/L were achieved. Coagulation with polyalumium chloride (PACl) produced better effluent quality compared to FeCl3 as less suspended solids and less residual coagulant were found in the microsieve effluent. Also the transmittance of UV radiation through the water is improved by using PACl. The amount of backwash water was very low (< 3 %). Results after rebuilding the chemical pre-treatment showed that under optimized mixing conditions polymer doses << 1 mg/L are possible without losses in water quality and filtration performance. In total microsieving with chemical pretreatment is a viable option for high quality effluent polishing.

Pre-treatments minimizing membrane fouling are extensively studied, to extend membrane life span and decrease the operating costs. In this study, the effect of several pre-treatment options before tertiary membrane treatment was investigated with a submicron particle counter from Nanosight (UK). This device using the Nanoparticle Tracking Analysis method is able to measure the particle size distribution and the absolute particle concentration of particles between 50 and 1000 nm in secondary effluent. The goal of this study is to enhance the understanding of MF/UF membrane fouling by monitoring the submicron particle fraction in the water. Experiments were carried out at lab-scale. Reliability and reproducibility of the device were determined as well as the impact of the pre-filtration on the measurements. The impact of ozonation (0-15 mg O3/L) and/or coagulation (0-12 mg Fe3+/L) on particle size distribution and on the filtration performance was studied on a polyethersulfone ultrafiltration membrane. Results showed a clear relationship between the amount of nanoparticles below 200 nm and the filtration behavior. Lower particle concentrations in this size range resulted in lower flux decline due to reversible fouling. Coagulation and ozonation pre-treatment decreased the particle concentration below 200 nm. The combination of ozonation/coagulation shows synergistic effects and leads to an additional decrease of submicron particle content and further improvement of the filtration performance. Long term impact on hydraulic irreversible fouling still needs to be clarified.