Within the ambitious project SeaH2land a 1-gigawatt electrolyzer is currently planned by a group of companies (consisting of ArcelorMittal, Yara, Dow Benelux and Zeeland Refinery). By contrast, the largest electrolyzers to date have only achieved a capacity of around 10 MW (Trends of the Future, 2021). One more reason to take a closer look at this technology and investigate its potential applications in larger contexts. Great synergy effects can be achieved currently by using electrolyzers in combination with existing wastewater treatment plants (with a digestion step). The “waste product” of electrolysis, the oxygen, can be injected into the aeration basins, thereby significantly reducing the electricity demand of the WWTPs. The waste heat from the electrolyzer heats the digestion tower. CO2 in high concentration can be extracted from it to be used for methanation and further increase of the overall efficiency of the plant combination. In addition, the provision of load-frequency control energy is possible. However, the energy for operating the electrolyzer must be provided by renewable sources. Frequently, wastewater treatment plants are built nearby rivers and often have potential for generating electricity from hydropower. This article uses the example of the “City of Moosburg” to present a scenario in which all the above factors are fully considered. A potential analysis as well as an estimation of a possible transferability to other locations conclude the article.