Wastewater treatment (WWT) is obligatory for the protection of ecosystems and human health but also produces the greenhouse gases (GHGs) nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2 ) along the process chain. According to the IPCC (2018) anthropogenic CO2 and carbon emissions must decline by 45% worldwide from 2010 levels by 2030 to keep temperatures from rising beyond 1.5 ° degrees. Currently the sector of WWT contributes about 0.11 % to the total carbon emissions in Germany and was responsible for about 5 % of global non-CO2 GHG emissions in 2005. N2O emissions in particular play the major role here. Aerobic granular sludge (AGS) for biological WWT has gained increasing interest mainly due to higher process efficiency compared to conventional activated sludge (CAS). Studies show a reduction potential of 20 – 25 % in operation costs, 23 – 40 % in electricity use and 50 –75 % in space requirements. AGS processes are implemented as sequencing batch reactor (SBR). SBRs with a small temporal and spatial variability for biological metabolism are likely to generate process conditions promoting N2O formation. A 1% increase in direct N2O emissions could already result in a 30 % increase of the carbon footprint of a WWTP. In this thesis direct GHG emissions from AGS treating domestic wastewater are studied. It was part of the project E-VENT where an AGS Nereda® pilot-plant has been operated at Stahnsdorf WWTP, Berlin (Germany). The reactor was fully-covered and GHG emissions have been monitored online over a 3 months period. A conservative approach for off-gas flow determination has been chosen to not over-estimate GHG loads. The plant was operated with domestic wastewater extracted after the primary clarifiers. At stable operating conditions maximum removal rates of 96 % chemical oxygen demand, 90 % nitrogen and 87 % phosphorous were achieved. Determined emission factors (EF) for N2O and CH4 over the complete measurement period were 2.86 % and 0.18 % respectively. Rising process temperatures from 13 – 20 °C showed a positive correlation with EFs and higher TN loads during the day lead to higher N2O complementing literature review on N2O EFs. The CO2 EFs showed that determined values for AGS are in accordance with 2.8 % ± 1.2 % found in a comparable study by Guimarães et al. (2017). Findings conclude that N2O contributes to about 95 % to total direct carbon emissions of the Nereda® plant and is a main factor for the climate impact of AGS.

Fecal indicator organisms such as Escherichia coli, enterococci, and coliphages are important to assess, monitor, and predict microbial water quality in natural freshwater ecosystems. To improve predictive modelling of fecal indicators in surface waters, it is vital to assess the influence of autochthonous and allochthonous environmental factors on microbial water quality in riverine systems. To better understand how environmental conditions influence the fate of fecal indicators under varying weather conditions, the interdependencies of environmental parameters and concentrations of E. coli, intestinal enterococci, and somatic coliphages were studied at two rivers (Rhine and Moselle in Rhineland-Palatinate, Germany) over a period of 2 years that exhibited contrasting hydrological conditions. Both riverine sampling sites were subject to similar meteorological conditions based on spatial proximity, but differed in hydrodynamics and hydrochemistry, thus providing further insight into the role of river-specific determinants on fecal indicator concentrations. Furthermore, a Bayesian multiple linear regression approach that complies with the European Bathing Water Directive was applied to both rivers’ datasets to test model transferability and the validity of microbial water quality predictions in riverine systems under varying flow regimes. According to multivariate statistical analyses, rainfall events and high water discharge favored the input and dissemination of fecal indicators in both rivers. As expected, concentrations declined with rising global solar irradiance, water temperature, and pH. While variations in coliphage concentrations were predominantly driven by hydro-meteorological factors, bacterial indicator concentrations were strongly influenced by autochthonous biotic factors related to primary production. This was more pronounced under low flow conditions accompanied by strong phytoplankton blooms. Strong seasonal variations pointed towards bacterial indicator losses due to grazing activities. The Bayesian linear regression approach provided appropriate water quality predictions at the Rhine sampling site based on discharge, global solar irradiance, and rainfall as fecal indicator distributions were predominantly driven by hydro-meteorological factors. Assessment of microbial water quality predictions implied that rivers characterized by strong hydrodynamics qualify for multiple linear regression models using readily measurable hydro-meteorological parameters. In rivers where trophic interactions exceed hydrodynamic influences, such as the Moselle, viral indicators may pose a more reliable response variable in statistical models.

This paper presents the assessment of a planned scheme of indirect potable reuse (IPR) in the Vende´e region of France 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 (LCA) are used to characterize the risk associated with the use of reclaimed water for IPR, but also the environmental benefits compared with other options for additional drinking water supply. The LCA results show that IPR is competitive with other options of water supply in its energy demand and greenhouse gas emissions. Pathogens as the main health hazard are controlled effectively by existing and planned preventive measures. For chemicals the number of potentially relevant substances could be reduced substantially by the assessment.

Upgrading wastewater treatment plants (WWTPs) with advanced technologies is one key strategy to reduce micropollutant emissions. Given the complex chemical composition of wastewater, toxicity removal is an integral parameter to assess the performance of WWTPs. Thus, the goal of this systematic review is to evaluate how effectively ozonation and activated carbon remove in vitro and in vivo toxicity. Out of 2464 publications, we extracted 46 relevant studies conducted at 22 pilot or full-scale WWTPs. We performed a quantitative and qualitative evaluation of in vitro (100 assays) and in vivo data (20 species), respectively. Data is more abundant on ozonation (573 data points) than on an activated carbon treatment (162 data points), and certain in vitro end points (especially estrogenicity) and in vivo models (e.g., daphnids) dominate. The literature shows that while a conventional treatment effectively reduces toxicity, residual effects in the effluents may represent a risk to the receiving ecosystem on the basis of effect-based trigger values. In general, an upgrade to ozonation or activated carbon treatment will significantly increase toxicity removal with similar performance. Nevertheless, ozonation generates toxic transformation products that can be removed by a post-treatment. By assessing the growing body of effect-based studies, we identify sensitive and underrepresented end points and species and provide guidance for future research.

Phosphorus (P) recovery through struvite is already both technically and economically feasible. This has been proved by more than 40 large-scale plants worldwide. However, when designing and implementing these P-recovery technologies, the environmental effects need to be considered. Therefore, a comparative environmental life cycle assessment of phosphorus recovery with different generations of the AirPrex® reactors at WWTP Wassmannsdorf and Amsterdam West was carried out in this study. Results show that both AirPrex® configurations with 1 reactor and 3 reactor have positive energy benefits and better environmental credits for the global warming potential (GWP), freshwater eutrophication potential, and marine eutrophication potential. The 3-reactor configuration shows better results in cumulative energy demand with 35% improvement of energy surplus, 36% reduction of GWP and less eutrophication potential. These improvements are mainly due to optimized struvite precipitation and harvesting and show that technology can be developed further, especially in plant operation and not only in the laboratory or pilot plant.