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This paper aims to provide a holistic analysis of the role of hydrogen for achieving greenhouse gas neutrality in Germany. For that purpose, we apply an integrated energy system model which includes all demand sectors of the German energy system and optimizes the transformation pathway from today's energy system to a future cost-optimal energy system. We show that 412 TWh of hydrogen are needed in the year 2045, mostly in the industry and transport sector. Particularly, the use of about 267 TWh of hydrogen in industry is essential as there are no cost-effective alternatives for the required emission reduction in the chemical industry or in steel production. Furthermore, we illustrate that the German hydrogen supply in the year 2045 requires both an expansion of domestic electrolyzer capacity to 71 GW H2 and hydrogen imports from other European countries and Northern Africa of about 196 TWh. Moreover, flexible operation of electrolyzers is cost-optimal and crucial for balancing the intermittent nature of volatile renewable energy sources. Additionally, a conducted sensitivity analysis shows that full domestic hydrogen supply in Germany is possible but requires an electrolyzer capacity of 111 GW H2. • 412 TWh of hydrogen demand in a greenhouse gas neutral Germany in the year 2045. • Hydrogen usage is crucial for defossilization of chemical and steel industry. • 47% of hydrogen is imported from other European countries and Northern Africa. • 71 GW H2 of electrolyzer capacity in Germany with flexible operation. • 35 TWh of hydrogen storage in salt caverns for security of supply. [ABSTRACT FROM AUTHOR]

• Cr(VI) removal below 0.5 µg L−1 with RCF combined with biological iron removal (RCbF). • RCbF is robust against variations of pH, filtration velocity or Cr(VI) concentration. • Fe(II) dosage is the key parameter for low target Cr(VI) concentrations. • Chromium is strongly immobilized as co-precipitated Cr(III) solid solution. • The technical effort for RCbF is considerably decreased compared to conventional RCF. Cr(VI) is identified as highly toxic, therefore a far-reaching limitation of total chromium or Cr(VI) in drinking water was proposed by the Germany Environment Agency. There is a lack in efficient treatment processes to reach Cr(VI) concentrations below 1 µg L−1. In this study, the combination of chemical reduction, coagulation and filtration (RCF) was further developed by adding biological iron removal as filtration step (RCbF). The aim of this enhancement was to reach lower effluent concentrations and a higher robustness regarding process parameters. The effectiveness of Cr(VI) removal was investigated using two-stage pilot-scale waterworks. RCbF reaches Cr(VI) effluent concentrations below 0.5 µg L−1 despite variations of pH, filtration velocity, or Cr(VI) influent concentrations. Fe(II) dosage and hence molar excess of Fe(II) over Cr(VI) was identified as the key parameter for Cr(VI) removal. Low oxygen dosage for biological iron removal improved the efficiency of RCbF compared to RCF. The co-precipitation of Cr(III) and Fe(III) as solid solution in the supernatant of the filter bed was promoted by low oxygen concentrations making Cr(VI) the preferred oxidant. RCbF was shown to be a suitable treatment process for reaching a low limit value for total chromium or Cr(VI) concerning technical feasibility. [ABSTRACT FROM AUTHOR]