The focus of this study investigation was laid on the plant-specific applicability of a NaOH and thermal pretreatment of activated sludge AS with following mesophilic digestion and the influence on the biomethane potential BMP. Firstly, the hydrolysis of activated sludge from the granular sludge process of the Nereda technology, which differs from conventional activated sludge in terms of sludge formation, sludge stabilization, and sludge age, was investigated for the first time. A higher dose of NaOH (0.02 - 0.08 g NaOH per gVS, 70 °C) raised the COD and phosphate degree of digestion and the digester gas yield by 22 - 47 %. Different hydrolysis temperatures (50 - 90 °C, 0.05 g NaOH per gVS) also increased the sludge parameters. However, the BMP only enhanced by 12 % at temperatures higher than 70 °C. With increasing hydrolysis temperature, the digestion time was reduced by 2 - 5 days. Despite the process-related differences between conventional AS (from the Stahnsdorf wastewater treatment plant) and AS from the granular sludge processing, comparable results were obtained in the BMP test, with and without pretreatment. Due to a lack of time, the experiments could only be carried out once or twice. As there are currently no further experience and references on this subject, additional attempts for achieving significant results will follow. In the second part, sludges from the Waßmannsdorf sewage treatment plant were used. Laboratory tests have shown that primary sludge has no influence on the digestion process. The calculated BMP of 176.5 NmL/gCSB deviates by 3% from the value of 181.9 NmL/gCSB measured in the laboratory test. It is directly related to the ratio of the used sludges. Hydrolysis according to PONDUS (70 °C; 2 h; 2.5 mL NaOH 50 % per L AS) at laboratory revealed a comparable influence on the sludge parameters as with hydrolysis on a pilot scale. During the BMP test, the laboratory sample achieved a maximum gas yield of 143 NmL/gCSB, which is a 9 % higher BMP in comparison to the pilot sample with 132 NmL/gCSB. The laboratory results can, therefore, be transferred to the pilot scale, so that the effects of changes in operation can be reliably assessed by cost, time and effort saving laboratory tests. This thesis was written within the framework of the project “Evaluation of process options for the reduction of energy consumption and greenhouse gas emissions of Berlin sewage treatment plants" at the Berlin Centre of Competence for Water.

The objective of this work was to determine the effects of thermal-pressure hydrolysis (TPH) on dewatered secondary sludge (5-7 % DR) from the wastewater treatment plant Waßmannsdorf with regard to solubilisation properties, biogas production and the formation of refractory substances. In laboratory tests, the impact of the treatment temperature on the sludge due to the TPH was investigated by varying the treatment temperatures within the range of 130-170 °C with a constant hydrolysing time of 30 minutes. Furthermore, the effect of TPH (TTH: 140-170 °C; tTH: 30 min) on digested mixed sludge was studied to quantify the total biogas production of the “Degradation-Lysis-Degradation”-process (DLD). With increasing treatment temperatures (130-170 °C), the COD solubilisation of the hydrolysates was increased linearly up to 45 % which caused higher a biogas production and improved organic matter reduction rates during the anaerobic batch tests. An average methane yield of 212 L·(kg VSS)-1 was produced by the untreated secondary sludge. TPH caused an enhancement of the methane production of additional 17-27 % with the highest surplus observed at treatment temperatures of 170 °C. The organic matter degradation of 46.6 % in the untreated secondary sludge was 2.6 to 36.5 % higher in the hydrolysed sludges and increased with higher temperatures. TPH treatment of the secondary sludge caused formation of refractory COD, that has been measured in the digested sludge filtrate after 28 days of the aerobic degradation test. The organic matter of the untreated secondary sludge was found to be transformed to refractory COD up to 3 %. For the hydrolysed sludges (130-170 °C), the transformation of the organic compounds to refractory COD amounted, temperature-dependent, to 3.9-8.4 %. Raising the TPH treatment temperature from 160 to 170 °C, showed a sharp increase in refractory COD. In order to achieve high biogas yields with moderate loads of refractory compounds in the sludge water, a TPH-temperature of 150-160 °C is recommended. Applying the TPH to the DLD-configuration, hydrolysed sludges showed 20-30 % greater methane yields as well as 16-27 % higher biodegradation rates compared to the untreated digested sludge. At a treatment temperature of 170 °C of the digested sludge, 372 L·(kg VSS)-1 methane were produced with a organic matter reduction of 67.6 %. Comparing the test results of TDH at 170 °C and the Thermo-alkaline Hydrolysis (TaH) of secondary sludge, dosing 0,08 g NaOH·(g DR)-1 at a treatment temperature of 70 °C, the highest achievable methane yields were in the same range of approx. 270 L·(kg VSS)-1. TaH caused a 50 % lower refractory compound formation than TDH. However, the enhanced dewaterability of TDH treated sludge, compared to TaH treatment, provides cost-saving potential.

With the new sewage sludge ordinance from 2017, phosphorus recovery becomes obligatory for large sewage treatment plant operators. Within the last year, the interpretation of this ordinance due to the exact wording has changed. As an example, a process aiming to recover phosphorus within the sewage treatment plant from waste water or sludge before the sludge is legally understood as waste. Therefore, a benchmark of 20 g Phosphorus (P)/kg dry matter (DM) is foreseen. However, this benchmark is an obstacle to increasing energy efficiency and sludge reduction, since carbon and dry matter is transferred into biogas in anaerobic digestion. Normally, raw sludge has a phosphorus content around 20 g P/kg DM, while digested sludge has a phosphorus content of about 35 g P/kg DM. The paper shows estimations of different full-scale combinations targeting phosphorus and advanced energy recovery and the resulting phosphorus content in sewage sludge per kg DM. Furthermore, this paper discusses the legal framework regarding phosphorus recovery from ash based on the sewage sludge ordinance, the national fertilizer regulation, the European Union fertilizing product regulation and the European Union feed/fodder regulation. The author concludes, that the legal framework is not explained properly to sewage treatment plant operators, which leads to confusions. Several questionable paragraphs and their wording should be addressed in future regulation amendments. Finally, there should be a regulatory need to establish phosphorus recovery from demand side (fertilizer industry, farmers) and not only from supplier side (sewage treatment plants). Because otherwise products must be produced, whereby no actual market for these products is established.

The aim of this thesis is to investigate the effectiveness and economic feasibility of installing a biogas treatment plant and power-to-gas (PtG) technology at a wastewater treatment plant (WWTP) in Berlin. After extensive literary research, suitable technologies for the biogas treatment as well as the PtG technology were selected. The next step was to develop an energy tool to determine the best technological solution for the available biogas at the WWTP in question. Several scenarios were selected to be tested by the energy tool. In addition, the selected scenarios were analysed and evaluated from both economic and ecological standpoints. The results show that the use of a combined heat and power (CHP) plant along with a wind turbine or a biogas treatment plant is the best option for the selected WWTP. A biogas upgrading plant does not currently offer any environmental and economic benefits. However, the results of economic analysis also reveal that a biogas treatment plant is very cost-effective for digester gas. Compared to the current situation regarding the reference WWTP, the gas treatment technology requires approximately 75% less investment and approximately 85% lower operating costs. In addition, a biogas treatment can compete with a CHP plant if the 2017 CHP Act is considered and CHP subsidy is no longer granted. The results show that PtG technology is not an economically viable investment, since this technology is associated with very high investment costs and has no support scheme.

The last 60 years has seen unprecedented groundwater extraction and overdraft as well as development ofnew technologies for water treatment that together drive the advance in intentional groundwater replenishment known as managed aquifer recharge (MAR). This paper is the first known attempt to quantify the volume ofMAR at global scale, and to illustrate the advancement of all the major types ofMAR and relate these to research and regulatory advancements. Faced with changing climate and rising intensity ofclimate extremes, MAR is an increasingly important water management strategy, alongside demand management, to maintain, enhance and secure stressed groundwater systems and to protect and improve water quality. During this time, scientific research—on hydraulic design offacilities, tracer studies, managing clogging, recovery efficiency and water quality changes in aquifers—has underpinned practical improvements in MAR and has had broader benefits in hydrogeology. Recharge wells have greatly accelerated recharge, particularly in urban areas and for mine water management. In recent years, research into governance, operating practices, reliability, economics, risk assessment and public acceptance ofMAR has been undertaken. Since the 1960s, implementation of MAR has accelerated at a rate of 5%/year, but is not keeping pace with increasing groundwater extraction. Currently, MAR has reached an estimated 10 km3/year, ~2.4% of groundwater extraction in countries reporting MAR (or ~1.0% of global groundwater extraction). MAR is likely to exceed 10% of global extraction, based on experience where MAR is more advanced, to sustain quantity, reliability and quality ofwater supplies.

Die Erhöhung der Resilienz urbaner Wasserinfrastrukturen wird oft als wichtiges Ziel genannt. Eine Literaturstudie zeigt, dass dafür konkretisiert werden muss, um welche Infrastruktur es sich handelt, gegenüber welcher Störung sie resilient sein soll und an welcher Leistung sich die Resilienz zeigen soll. Hier wird darauf aufbauend ein quantitativer Ansatz der Resilienzmessung vorgeschlagen, der die Schwere des Leistungsausfalls gegenüber einem Grenzwert über die Zeit integriert und dieses Integral über das Zeitintervall und den gewählten Grenzwert normiert. Eine beispielhafte Anwendung für Stadtentwässerungsstrategien bei Starkregenereignissen zeigt, dass der vorgeschlagene Ansatz den Vorteil hat, dass Dauer und Ausmaß eines Leistungsausfalls in einem Resilienzwert berücksichtigt werden können. Zudem erlaubt der Ansatz eine Evaluation unterschiedlicher Störungen, beispielsweise durch Systemausfälle. Durch die Normierung wird ein Vergleich unterschiedlicher Leistungen von Wasserinfrastruktur ermöglicht. Allerdings ist die normierte Resilienz stark von der Wahl des Zeitintervalls und des festgelegten Grenzwertes abhängig und damit nicht ohne weiteres auf andere Systeme übertragbar.

For ensuring microbial safety, the current European bathing water directive (BWD) (76/160/EEC 2006) demands the implementation of reliable early warning systems for bathing waters, which are known to be subject to short-term pollution. However, the BWD does not provide clearly defined threshold levels above which an early warning system should start warning or informing the population. Statistical regression modelling is a commonly used method for predicting concentrations of fecal indicator bacteria. The present study proposes a methodology for implementing early warning systems based on multivariate regression modelling, which takes into account the probabilistic character of European bathing water legislation for both alert levels and model validation criteria. Our study derives the methodology, demonstrates its implementation based on information and data collected at a river bathing site in Berlin, Germany, and evaluates health impacts as well as methodological aspects in comparison to the current way of long-term classification as outlined in the BWD.