Im Rahmen eines Planspiels wurden für ein Stadtquartier Kombinationen der Regenwasserbewirtschaftung erstellt und wissenschaftlich bewertet. Die verwendete Methode kombiniert dazu lokale Bedingungen (Problemlage, Machbarkeit von Maßnahmen und lokale Ziele) mit einer Bewertung von 27 Einzelmaßnahmen hinsichtlich ihrer vielfältigen Effekte. Die Ergebnisse zeigen zunächst, dass eine skalenübergreifende Kombination von Maßnahmen vom Gebäude bis zum Kanaleinzugsgebiet ein großes Potenzial für die Verbesserung der städtischen Umwelt (Gewässer und Biodiversität) und Lebensqualität (Stadtklima, Freiraumqualität, Nutzen auf Gebäudeebene) hat. Die verwendete Methode erwies sich als gut geeignet für die Auswahl effektorientierter (und machbarer) Maßnahmen und für deren gezielte Platzierung in Problemräumen. Die Erfahrungen zeigen aber auch, dass die Methode optimiert werden muss, um eine bestimmte Zielerreichung (z.B. Kostenrahmen oder Einleitbeschränkung) während der Planung zu berücksichtigen.

This report describes different options for tertiary treatment of secondary effluent from municipal wastewater treatment plants for the purpose of water reuse. For each of the treatment trains, associated environmental impact (represented by energy demand and related global warming potential) and risk reduction potential (i.e. removal of chemical and microbial contaminants) are described based on the results of the DEMOWARE case studies. This should inform water professionals about impacts and benefits of different options for producing reclaimed water, enabling an informed decision on an adequate treatment train depending on the water quality targets for the respective reuse purpose.

This report presents the assessment of the planned water reuse scheme at Le Jaunay reservoir (Vendée) in its potential risks for human health and ecosystems, and also in its overall environmental impacts. Methods of risk assessment (quantitative microbial and chemical risk assessment) and Life Cycle Assessment are used to characterize the potential hazards associated with the use of reclaimed water, but also the environmental benefits compared to other options for additional drinking water supply. The assessments show that water reuse can be operated without unacceptable risks for humans and the environment, and that it is competitive to other options of water supply in its energy demand and greenhouse gas emissions. Data quality should be improved in a demonstrator phase to validate the outcomes of this first assessment.

The recovery of phosphorus (P) from sewage sludge, sludge liquor, or ash from monoincineration can be realized with different processes which have been developed, tested or already realized in full-scale in recent years. However, these pathways and processes differ in their amount of P that can be recovered in relation to the total P content in sludge, in the quality of the recovered P product, and in their efforts in energy, chemicals, fuels, and infrastructure required for P recovery. This study analyses selected processes for P recovery from sludge, liquor, or ash in their potential environmental impacts, following the method of Life Cycle Assessment (LCA, ISO 14040/44). Based on available process data from technology providers and end users, these processes are implemented in a hypothetical reference system for sludge digestion, dewatering and disposal in mono-incineration, including potential side-effects on mainstream wastewater treatment with the return load from sludge dewatering. Recovered products (e.g. P or N fertilizer, electricity, district heating) are accounted as credits for substituting equivalent industrial products. Depending on the maturity of the investigated process, collected process data of process efficiency, product quality, and energy and material demand originates from full-scale plants, pilot trials, or prospective modeling (status in 2014). This data is validated with the technology providers, transferred to the reference system and evaluated with a set of environmental indicators for energy demand, global warming, acidification, abiotic resource depletion, eutrophication, and human and ecotoxicity. Results show that pathways and processes for P recovery differ heavily in their amount of recovered P, but also in energy and related environmental impacts (e.g. greenhouse gas emissions). As direct struvite precipitation in sludge or liquor relies on the dissolved amount of P in digested sludge, these processes are only applicable in wastewater treatment plants with biological P removal. Here, they can recover 4-18% of total P in sludge with a relatively low effort in energy and chemicals, reducing return load to the mainstream process and eventually improving sludge dewaterability in case of direct precipitation in sludge. Acidic leaching of P from digested sludge can yield up to 48% of P for recovery, but requires a significant amount of chemicals for control of pH (leaching and precipitation) and for minimizing heavy metal transfer into the product. The quality of products from sludge and liquor is good with low content on heavy metals, leading to a low potential toxicity for humans and ecosystems. Leaching of monoincineration ash with sulphuric acid yields 70% P with moderate chemical demand, but the leached ash and co-precipitated materials have to be disposed, and the product contains some heavy metals. Complete digestion of ash in phosphoric acid and multi-stage cleaning with ion exchangers yields high recovery of 97% P in a high-quality product (H3PO4) and several coproducts, having an overall low environmental impact. Thermo-chemical treatment of ash can recover up to 98% P with moderate energy input in case of integration into an existing monoincineration facility, but the product still contains high amounts of selected heavy metals (Cu, Zn). Metallurgic treatment of dried sludge or ash can also recover up to 81% of P, but the process has still to be tested in continuous pilot trials to validate product quality, energy demand, and energy recovery options. Sensitivity analysis shows that other pathways of sludge disposal (e.g. co-incineration combined with upstream P extraction, direct application in agriculture) may also be reasonable from an environmental point of view depending on local boundary conditions and political targets. In general, the use of life-cycle based tools is strongly recommended to evaluate and select suitable strategies for regional or national concepts of P recovery from sewage sludge.

Dieser Beitrag vermittelt einen Überblick über die im Rahmen des EU Projektes P-REX erzielten Ergebnisse und Schlussfolgerungen. Neben der Bewertung von praxisrelevanten Verfahren zur Phosphorrückgewinnung aus dem Abwasserpfad und den jeweiligen Recyclaten geht es vor allem auch um Aspekte zur flächendeckenden Implementierung und Marktentwicklung. Vor allem integrative Ansätze, die auf eine bessere Ausnutzung der bereits vorhandenen Infrastruktur zur Optimierung des Phosphorrecyclings abzielen, bieten vielversprechende und vor allem kurzfristig umsetzbare Lösungen. Um jedoch Anreize für deren Umsetzung zu schaffen, bedarf es Entscheidungen und verlässlicher politischer Weichenstellungen. Für den Fall des Phosphorrecycling haben Goethes Worte „Wissen ist nicht genug, wir müssen auch anwenden! Wollen ist nicht genug, wir müssen auch tun!“ höchste Aktualität.

The implementation of tertiary treatment at large wastewater treatment plants (WWTP) may be required in many WWTPs in Germany due to water quality targets defined in the Water Framework Directive (EU-WFD) and Bathing Water Directive (EU-BWD) of the European Union. Furthermore, potential environmental risks of organic micropollutants (OMP) from anthropogenic sources (i.a. pharmaceuticals, sweeteners) could require additional treatment steps for tertiary treatment in future. EU-WFD requires a “good ecological status” of all water bodies, which can lead to a need of enhanced phosphorus removal at large WWTP (>100’000 pe), targeting an effluent quality <100µg/L TP. Moreover, if a WWTP discharges upstream of bathing water, EU-BWD requirements have to be met. Hence implementing a disinfection step might be necessary. Different options for enhanced P-removal and disinfection have already been analyzed in their economic and environmental impacts (KWB 2013). Based on these results, both targets can be adequately met by coagulation with subsequent dual media filtration (DMF) and UV-disinfection (UV). On this basis, the present study focusses on the additional integration of a process for OMP-removal into a tertiary treatment scheme. Considered technologies for OMP-removal are oxidation by ozonation and adsorption by activated carbon (AC) either by dosing powdered activated carbon (PAC) or using filtration units with granulated activated carbon (GAC), respectively. These technologies increase the additional demand of energy and chemicals for tertiary wastewater treatment. WWTPs are already one of the major contributors of electricity demand at municipality level (UBA 2008), and further treatment steps may add up significantly in this environmental impact. In the present study, different options and process configurations for OMP-removal are integrated in a tertiary treatment with advanced P-removal and UV-disinfection, and the entire tertiary treatment train is then analysed in its environmental impacts using the methodology of Life Cycle Assessment (LCA). The goal of the LCA is to reveal the trade-off between local environmental benefits by higher effluent quality and global environmental impacts, e.g. an increasing CO2-footprint. With the methodology of LCA different tertiary treatment schemes are analysed in a holistic approach “from cradle to grave” (ISO 2006), which includes direct effects at water bodies through discharge, and indirect effects resulting from infrastructure, chemical and electricity demand by tertiary treatment and additional sludge treatment. The baseline scenario is defined as treatment of secondary effluent of an existing WWTP located in Berlin, Germany (1’500’000 pe) by DMF with coagulation and UV (Figure 1.1). Sludge from backwash of filtration units is considered in the LCA by a simplified model for sludge treatment and mono-incineration (SMIP). For integration of OMP-removal into tertiary treatment, 7 possible scenarios are compared in their environmental impacts (Figure 1.2): (1) Ozone+DMF+UV, (2) PAC-dosing+DMF+UV, (3) PAC-cycle+DMF+UV, (4) DMF+GAC-filter+UV, (5) DMF w/ GAC-layer+UV, (6) Ozone+DMF w/ GAC-layer+UV, or (7) parallel treatment by ozonation and PAC+DMF+UV, respectively. Each scenario is analysed with a low, medium, and high dosage of ozone or AC, displaying the whole range of economic feasibility and effluent quality targets (Table 1.1). The specific dosage of ozone and PAC are referred to DOC-concentration of the secondary effluent (12.8mg/l DOC). Data used for advanced P-removal and UV-disinfection are based on a previous study (Remy et al. 2014) using planning data from the WWTP operator considering process efficiency, infrastructure, energy and chemical demand. Data for OMP-removal technology are based on pilot plants and planning data from WWTP operator. For LCA, impact categories of ReCiPe Midpoint method are taken into account (Goedkopp et al. 2008), e.g. global warming potential (GWP) or freshwater eutrophication potential (FEP), and cumulative energy demand (CED) of fossil and nuclear resources (VDI 2012), and USEtox indicators (Rosenbaum et al. 2008) freshwater ecotoxicity (ETP) and human toxicity potential (HTP). Environmental benefits of tertiary treatment scenarios on the global scale can be seen in the FEP and ETP indicators. TP from secondary effluent is reduced from 320µg/l to 55µg/l TP after tertiary treatment. The global USEtox indicator ETP includes preliminary impact factors for seven measured OMPs (6 pharmaceuticals, 1 herbicide), neglecting potential toxic effects of metabolites or transformation products as limitation of the multi-fate model. Removal of OMP has a positive effect on ETP in all scenarios. However, background processes and heavy metal loads play a major role in the contribution to the global ecotoxicity indicator. On the contrary, a higher energy and chemical consumption lead to a significant increase of CED and GWP due to OMP-removal (Figure 1.3). Comparing baseline scenario (DMF+UV) with the gross GWP of a large WWTP, the CO2-footprint will increase by +11% (82g CO2-eq/m³). Ozonation increases the GWP by 23% to 37% depending on ozone dosage. Main contributors for GWP are electricity and liquid oxygen demand for ozonation. Highest effects on GWP are detected for the scenario “PAC-cycle+DMF+UV” with an additional CO2-footprint of 36% or 110%, respectively, which is mainly caused by emissions during production of AC. In summary, OMP-removal can double the GWP of an existing large WWTP in the worst case and thus contributes significantly to global environmental effects. Production of AC is a crucial parameter for scenarios using GAC or PAC. Hence, a sensitivity analysis is performed changing raw materials for AC production. AC production is modelled according to available data from Bayer et al. (2005) using 3kg of hard coal as resource for activation process and generating 1kg of virgin AC. Other possible resources for AC production can be lignite or coconut shells. Varying the type of resource reveals a high uncertainty in GWP. Considering scenario “PAC+DMF+UV” a possible reduction of -23% of net GWP using coconut shells or even an increase of net GWP by +32% using lignite is possible. Since specific discharge limits for OMP removal are not defined yet, a direct comparison between the considered scenarios is not possible, as they lead to different effluent qualities in OMP concentration. Thus, in theory a low dosage of PAC (1.0g/gDOC) may be sufficient to achieve certain effluent targets, whereas ozonation could require a high dosage (1.0g/gDOC) for the same quality, or vice versa.