Energy and resource recovery from municipal wastewater is a pre-requisite for an efficient and sustainable water management in cities of the future. However, a sound evaluation of available processes and pathways is required to identify opportunities and short-comings of the different options and reveal synergies and potentials for optimisation. For evaluating environmental impacts in a holistic view, the tool of Life Cycle Assessment (LCA, ISO 14040/44) is suitable to characterize and quantify the direct and indirect effects of new processes and concepts. This paper gives an overview of new processes and concepts for upgrading existing wastewater treatment plants towards energy positive and resource efficient wastewater treatment, based upon an evaluation with LCA using data from pilot and full-scale assessments of the considered processes.

Being a measure to counteract an increasing water scarcity in multiple regions of the world, water reuse is the subject of numerous investigations. The pan-European project DEMOWARE aims at tackling barriers related to water reuse to support further applications. At the project site of Braunschweig in Germany wastewater is reused historically to irrigate agricultural fields. Against the background of an ongoing debate in Germany to establish a legal basis for water reuse, options for a disinfection of secondary treated wastewater were tested at the wastewater treatment plant Steinhof. This thesis investigates the disinfection performance of two pilot scale plants (performic acid (PFA) dosage and UV irradiation) against the background of the compliance with wastewater-related standards, especially DIN 19650 and a WHO guideline regarding wastewater reuse. In order to meet recommendations of the latter, a noro- and rotavirus removal of 1.5 log was recommended by (1) for the site of Braunschweig. E. coli, intestinal enterococci (IE) and Clostridium perfringens were analyzed regarding their abundance and log removal concerning physicochemical properties. Serving as indicator organisms, they were related to the log removal of noro- and rotavirus. Differing doses were tested. The impact of the contact time was investigated for PFA by the presence or absence of sodium thiosulfate (STS) in the sampling bottles whereat the presence of STS terminates the disinfection process. The application of STS in the PFA sampling bottles caused a performance difference of 1.32 log for E. coli, 0.78 log for IE and 0.28 log for C. perfringens. Hence, the PFA reaction was not completed at the effluent sampling spot of the reactor (stirrer tank) and the determined minimum contact time of 3.5 min is not sufficient for PFA to develop its complete disinfection performance. The disinfection reactor did not provide the minimum recommended RT (10 min). Possibly, short circuits and zones with limited substance exchange occur. For full scale implementations, the PFA contact basins need to be designed carefully. A flow channel as used at full scale reference applications is preferable here. The PFA plant showed break-ins of the disinfection performance (to values < 0.5 log) for definable and indefinable reasons. Hence, its disinfection performance is not constant. Further investigations are necessary. Of the 3 doses per method deployed, a UV dose of 44 Wh/m³ and a PFA dose of 2 ppm (= 10 min, without STS) is proper to achieve quality class 3 of the DIN 19650 which is required for the present conditions and applications in Braunschweig. The requirements for a noro- and rotavirus removal of 1.5 log units according to the WHO guideline can be satisfied by a dose of 2 ppm of PFA and 35 Wh/m³, respectively, using an evaluation based on the mean value of the disinfection performance (both PFA and UV). By the application of a threshold-based evaluation the requirements are not satisfied for UV irradiation. Regarding PFA dosing, a dose of 2 ppm is sufficient as long as a sufficient contact time (= 10 min) is provided. The order of sensitivity against the disinfection methods was found for both UV irradiation and PFA dosage the same: E. coli > E. cocci > C. perfringens. Clostridium being used as an indicator for endospore-formers showed a remarkably lower sensitivity against both methods. A doseperformance-linearity can be suggested for the present range of dosage for E. coli and IE. C. perfringens does not show a correlation between the PFA/UV dose and the disinfection performance.

Commercialisation of nutrient recovery technologies are progressing across Europe, with a contract signed earlier this year to recycle phosphorus from 60,000 tons of sewage sludge ash. This article looks at progress and options from other companies against market barriers such as raw material prices and legal frameworks.

Diffuse nitrate (NO3) contamination from intense agriculture adversely impacts freshwater ecosystems, and can also result in nitrate concentrations exceeding limits set in drinking water regulation, when receiving surface waters are used for drinking water production. Implementation of near-natural mitigation zones such as reactive swales or wetlands have been proven to be promising measures to reduce nitrate loads in agricultural drainage waters. However, the behavior of these systems at low temperatures and its dependence on systemdesign has not beenwell known until now. In this study, the behavior of a full-scale (length: 45 m) reactive swale treating drainage water from an agricultural watershed in Brittany (France), with high nitrate concentrations in the receiving river, was monitored for one season (6 months). As flow in this full-size field system is usually restricted to winter and spring months (December–May), it usually operates at lowwater temperatures of 5–10 WC. Tracer tests revealed shorter than designed retention times due to high inflows and preferential flow in the swale. Results show a correlation between residence time and nitrate reduction with low removal (<10%) for short residence times (<0.1 day), increasing to >25% at residence times >10 h (0.4 day). Performance was compared to results of two technical-scale reactive swales (length: 8 m) operated for 1.5 yearswith two different residence times (0.4 and 2.5 days), situated at a test site of the German Federal Environmental Agency in Berlin (Germany). Similar nitrate reduction was observed for comparable temperature and residence time, showing that up-scaling is a suitable approach to transferring knowledge gathered from technical-scale experiments to field conditions. For the design of new mitigation systems, one recommendation is to investigate carefully the expected inflow volumes in advance to ensure a sufficient residence time for effective nitrate reduction at low temperatures.

To cope with the occurrence of organic micropollutants (OMPs) in the urban water cycle, different technologies have been tested to upgrade wastewater treatment plants for OMP removal. Measures are either based on adsorption onto activated carbon or ozonation. To ensure an economic and effective operation of the OMP removal, an automatic control system, which adapts the dosage to the varying water quality of the secondary effluent, is necessary. An online OMP measurement is not possible because of the high analytical afford, thus other surrogates have to be used for control purposes instead. One promising surrogate is the reduction of the ultraviolet absorption at 254 nm (delta UVA254) at the ozonation stage, which correlates very well with the OMP removal. In this study, the results of the successful application of the delta UVA254 for a closed-loop control at an ozonation pilot plant for OMP removal are presented with a focus on implementation issues like coping with delay time and the choice of measurement points. OMP removal was assessed for three different delta UVA254 setpoints, of which two of them also were performed as an advanced ozone process. It could be shown that changes of the ozone demand, e.g. by a varying concentration of the dissolved organic carbon (DOC) or nitrite, can be detected and countered by an adaption of the applied ozone dose.

In den letzten Jahren wurde eine Vielzahl von Machbarkeitsstudien für die Aufrüstung von Kläranlagen mit einer weitergehenden Reinigungsstufe zur Reduzierung der Einleitung von organischen Spurenstoffen in Oberflächengewässer durchgeführt. Die eingesetzten technischen Maßnahmen basieren meistens auf der adsorptiven Wirkung von granulierter (GAK) bzw. pulverförmiger Aktivkohle (PAK) oder der Oxidation mittels Ozon. Während Spurenstoffe bei der Adsorption an die Aktivkohle physisch aus dem Wasser entfernt werden, so werden diese bei der Reaktion mit Ozon in andere Moleküle transformiert. Daher ist eine Spurenstoffelimination in diesem Zusammenhang als Primärelimination aufzufassen. Für einen ökonomischen und effizienten Betrieb dieser technischen Maßnahmen sind geeignete Steuer- und Regelungskonzepte erforderlich. Da eine Onlinemessung der Zielsubstanz(en) aufgrund des analytischen Aufwands nicht möglich ist, werden andere Indikatoren für die Dosisanpassung an eine variierende Wasserqualität benötigt. Ein häufig verwendeter Indikator zur Abschätzung der Spurenstoffelimination ist die auf den gelösten organischen Kohlenstoff (DOC) bezogene Ozonzehrung (mg O3 / mg DOC), die beispielsweise für eine frachtproportionale Steuerung verwendet werden kann. Diese Steuerung erlaubt jedoch keine direkte Prozesskontrolle und zur Berücksichtigung des stark ozonzehrenden Nitrits (3,4 mg O3 / mg-N) kann ein zusätzlicher Messaufwand nötig sein. Eine Alternative dazu bildet die relative Abnahme des spektralen Absorptionskoeffizienten SAK254 (delta SAK254), für welche in mehreren Studien wie z.B. [1-5] eine Korrelation mit der Spurenstoffeliminierung verschiedener Substanzen beschrieben wurde. Das erzielte delta SAK254 wird dabei von der effektiven Ozonzehrung im Wasser beeinflusst, so dass eine veränderte Wasserqualität entsprechend detektiert und durch eine Anpassung der Ozondosis ausgeglichen werden kann. Die Verwendung einer Regelung mit dem Ziel eine konstante SAK254 – Reduzierung und damit auch eine entsprechend konstante Spurenstoffelimination zu gewährleisten, bietet daher auch den Vorteil einer direkten Prozesskontrolle. Auf eine zusätzliche Onlinemessung des Nitrits kann ebenfalls verzichtet werden. Die Verwendung des delta SAK254 könnte auch für eine Pulveraktivkohledosierung interessant sein, da in den Arbeiten von [6; 7] ebenfalls ein Zusammenhang zwischen dem delta SAK254 und der Spurenstoffelimination gezeigt werden konnte.