Different technologies for tertiary wastewater treatment are compared in their environmental impacts with life cycle assessment (LCA). Targeting very low phosphorus concentration (50–120 µg/L) and seasonal disinfection of wastewater treatment plant (WWTP) secondary effluent, this LCA compares high-rate sedimentation, microsieve, dual media filtration (all with UV disinfection), and polymer ultrafiltration or ceramic microfiltration membranes for upgrading the large WWTP Berlin-Ruhleben. Results of the LCA show that mean effluent quality of membranes is highest, but at the cost of high electricity and chemical demand and associated emissions of greenhouse gases or other air pollutants. In contrast, gravity-driven treatment processes require less electricity and chemicals, but can reach significant removal of phosphorus. In fact, dual media filter or microsieve cause substantially lower specific CO2 emissions per kg P removed from the secondary effluent (180 kg CO2-eq/kg P, including UV) than the membrane schemes (275 kg CO2-eq/kg P).

Within the project OXERAM state of the art membrane filtration was applied as a tertiary treatment step for advanced phosphorus removal in a municipal wastewater treatment plant. Two membrane types, ceramic and polymeric, were tested in pilot scale, using commercial membrane modules. Due to the drawback of membrane fouling, leading to comparably high investment and operating costs, pre-treatment with ozone was tested. Ozonation was expected to increase the sustainable flux for both membrane types. For both membranes types high filtrate quality was achieved. A mean total phosphorus concentration below 25 µg/L was achieved over two years. Additionally disinfection is reached and therefore the European bathing water standards were met. The effect of ozonation and coagulation on various water quality parameters were evaluated and are presented in this report. Ultrafiltration modules (0.02 µm) made of polyether sulfone (PES) were tested comparing different capillary diameters (0.9 vs. 1.5 mm) leading to different package densities (respectively 40 and 60 m2 per module). Both types were operated in parallel and the experience showed a more robust operation with 1.5 mm capillaries when applying high fluxes targeting high recoveries. Both evaluation parameters, total fouling rate and membrane regeneration by cleaning in place, suggested the 1.5 mm module for the application at the WWTP Ruhleben. Optimizing the operation set up and cleaning strategy proved that recoveries = 95 % could be achieved and therefore a second filtration unit treating the backwash water is obsolete. The design with max 75 L/(m2h), 60 minutes of filtration, and a backwash duration of 40 s is the proposed set up for WWTP Ruhleben. A daily acidic chemical enhanced backwash combined with a weekly caustic cleaning step proved to manage the fouling affinity and a cleaning in place interval of 1 – 3 months was demonstrated in a long term run. The usage of ozone did not improve the overall filtration performance, because the benefit of a higher filterability is compensated by a higher additional fouling resistance after each backwash. Therefore the mean trans-membrane pressure remains in the same range. These results were only collected with the combination of ozonation and PES ultrafiltration membranes. Lab scale tests conducted at the Chair of Water Quality, TU Berlin, confirm this outcome but showed different results for other membrane materials and pore sizes. The potential to reduce the total fouling rate combining ozonation with coagulation prior ceramic membrane filtration was shown. A microfiltration membrane (0.1 µm) consisting of Al2O3 and a surface of 25 m2 was tested in pilot scale. Applying a dose of 15 mgO3/L (z = 1.18 mgO3/mgDOC) could reduce the total fouling rate by half even when doubling the flux from 60 L/(m2h) to 120 L/(m2h). Critical flux experiments showed that the application of 7.5 mgO3/L (z = 0.7 mgO3/mgDOC) was sufficient to recognize the beneficial effect of pre-ozonation. Treating the secondary effluent of WWTP Ruhleben a sustainable flux around 130 – 140 L/(m2h) was identified when applying pre-ozonation of 7.5 mgO3/L (z = 0.7 mgO3/mgDOC) and 8 mgFe/L for coagulation. It was not possible to demonstrate this process set up in a long term run, due to technical malfunctions. An economic evaluation showed however that for the case of WWTP Ruhleben a sustainable flux > 500 L/(m2h) is required to be competitive against tertiary treatment with polymeric membranes without ozone. This high value can be explained by the high module cost for ceramic membranes and the high DOC content of the secondary effluent, leading to increased effort for ozonation.

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.

In work package 4 the influence of different treatments (ozonation, coagulation) on macromolecular organic substances (biopolymers) in secondary effluent and the effects on subsequent ultrafiltration were investigated at lab-scale. Furthermore, fouling mechanisms were intensively investigated and an analytical method was developed to observe the formation of ozonation by-products. Analyses with LC-OCD showed a significant reduction of major organic foulants (biopolymers) for coagulation while ozonation appears to transform macromolecules into compounds smaller than approx. 50 nm. With ultrafiltration tests (PES membranes) it could be shown that coagulation is capable to reduce total fouling resistance to some extent and additional ozonation can further enhance the membrane filtration process. However ozonation as a pretreatment step caused more irreversible fouling. The lowest irreversible fouling was achieved with coagulation. LC-OCD analyses showed that the transformation of organic matter by ozonation is mainly responsible for the observed increased irreversible fouling of ultrafiltration membranes. Tests with different membranes showed comparable results for pretreated secondary effluent concerning total fouling resistance. Total fouling resistance was reduced with additional ozonation compared to coagulation without ozonation. In contrast to the observations with all tested UF membranes, for the tested microfiltration membranes irreversible fouling was reduced with additional ozonation. In general, the pore size seems to be strongly influencing irreversible fouling if ozonation is used for pretreatment of membrane filtration. Intensive investigations of fouling mechanisms using filtration laws identified cake filtration as the dominant filtration process for coagulation while additional ozonation leads to increased pore blocking/in pore fouling. Experiments with secondary effluents from different sewage treatment plants in Berlin showed comparable fouling behavior for all observed pretreatments. Thus membrane filtration results generated with samples from WWTP Ruhleben seem to be transferable to other WWTPs in Berlin. MALDI-TOF-MS analyses of secondary effluent were not suitable to identify major organic foulants, neither in solution nor on top of the membrane after filtration. Consequently, MALDI-TOF-MS was primarily used for investigations of theoretical aspects of fouling by using model fouling substances. An analytical procedure for bromate was successfully developed with LC-MS/MS at TUB. With the procedure it was possible to quantify samples up to a limit of quantification of 0.5 µg bromate per liter. Higher concentrations of bromate (> 10 µg/L) were produced only at specific ozone consumptions higher than 0.9 mgO3/mgDOC0.

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.

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.

For a future upgrade of the wastewater treatment plant (WWTP) Ruhleben targeting advanced removal of total phosphorus (TP) (< 50-120 µg/L TP) and seasonal disinfection, various technological options for tertiary treatment of secondary effluent are suitable to fulfill these goals. This study applies the holistic methods of Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) to assess and compare those options for tertiary treatment at WWTP Ruhleben in their environmental and economic impacts, including all relevant direct and indirect processes and effects of the WWTP upgrade. Options for tertiary treatment include gravity-driven processess such as dual media filtration (DMF), microsieve filtration (MSF), or high-rate sedimentation (HRS), and membrane-based processes such as ultrafiltration with polymer membranes (Polymer UF) or microfiltration with ceramic membranes (Ceramic MF). For disinfection in the summer period, gravity-driven processes are complemented by downstream UV disinfection, which is only applied in rain weather bypass for membrane processes. Process data for operational parameters and infrastructure design are based on longterm pilot trials at technical scale (DMF, MSF, Polymer UF, Ceramic MF) or process modelling based on supplier information (HRS). LCA shows that the existing phosphorus load in secondary effluent of WWTP Ruhleben (28 t/a TP) can be reduced substantially by all processes, eliminating 19-25 t/a TP (6790%) depending on the process. A minor side-benefit for effluent quality is also expected from the further elimination of heavy metals adsorbed to particulate matter in secondary effluent. At the same time, tertiary treatment schemes will increase energy demand and related emissions of greenhouse gases (carbon footprint) of the existing WWTP process by an estimated 12-21% and 7-13%, respectively. Gravity-driven processes with low coagulant dosing (DMF, MSF, HRS) have a considerably lower energy demand and carbon footprint than membrane-based processes with high electricity demand for feed pumps and higher coagulant dose. At the same time, low-energy treatment processes do not reach the exceptional high effluent quality of membrane-based processes. Consequently, a certain trade-off between energy demand/carbon footprint and effluent quality can be quantified. In analogy to the environmental assessment and effluent quality, LCC results show that total annual costs are lowest for HRS (5.1 Mio €/a) and comparable between DMF and MSF (5.7 Mio €/a), followed by Polymer UF (10.2 Mio €/a) and Ceramic MF (12.2 Mio €/a). In comparison to gravity-driven processes, membrane-based processes are characterized by both higher investment costs (factor 1.5 – 3x) and higher operational costs (factor 2 – 2.5x), mainly due to high costs of membranes, machinery, electricity, and coagulants. Comparing the relative resource efficiency for selected environmental and economic parameters related to the total load of eliminated phosphorus, DMF and MSF are the most efficient of the assessed technologies for tertiary treatment, spending ~ 250 €/kg Pelim and causing 180 kg CO2-eq/kg Pelim (both with UV disinfection as post-treatment). HRS + UV has higher relative costs (270 €/kg Pelim) and higher carbon footprint (235 kg CO2-eq/kg Pelim) due to the lower effluent quality of the process (= less reduction in TP loads). Membrane-based processes have the highest relative costs for P removal (400475 €/kg Pelim) and the highest carbon footprint (275 kg CO2-eq/kg Pelim): even though their superior effluent quality leads to the highest total reduction in TP loads, the high energy demand and costs of membrane processes yield higher relative spending of resources related to the final goal.

Different technologies for tertiary wastewater treatment are compared in their environmental impacts with Life Cycle Assessment (LCA). Targeting low phosphorus concentration (50-120 µg/L) and disinfection of WWTP secondary effluent, this LCA compares high-rate sedimentation, microsieve, dual media filtration (all with UV disinfection), and polymer ultrafiltration or ceramic microfiltration membranes for upgrading the large-scale wastewater treatment plant Berlin-Ruhleben. Results show that mean effluent quality of membranes is highest, but at the cost of high electricity and chemicals demand and associated emissions of greenhouse gases (GHG) or other air pollutants. In contrast, gravity-driven treatment processes require less electricity and chemicals, but can reach significant removal of phosphorus. In fact, the latter options will only lead to a minor increase of GHG emissions and energy demand compared to the existing pumping station or UV treatment.