Dietikon / Switzerland

Dietikon / Schweiz
Green Gas from Waste and Wastewater

Waste and Wastewater Treatment Efficiently Combined

The Power to Gas plant in Dietikon makes a pioneering contribution to efforts to remodel the Swiss energy system. Electricity generated from the treatment of waste and carbon dioxide (CO₂) from digester gas are used to create a new carrier of energy: synthetic methane. This lighthouse resource recycling project is the
first in Europe where a natural gas substitute for commercial use is produced on the basis of Hitachi Zosen Inova’s biological methanation technology.

Limeco, the Limmat Valley’s intermunicipal utility, had the ideal location for the first industrial Power to Gas facility in Switzerland. On its site in Dietikon it operates both a Waste to Energy (WtE) plant and a wastewater treatment (WWT) plant. This combination provided the ideal conditions for the Power to Gas plant, which was constructed in collaboration with eight Swiss energy utilities and the Swisspower municipal alliance, and went into operation in early 2022. It consists of an
electrolyser, the BiON® methanation reactor, a gas upgrading system and a unit for managing heat and cold. The green gas produced by the plant represents a reduction of around 5,000 tonnes of CO₂ emissions, as much as generated by around 2,000 households.

 

Optimum Combination of Processes
Achieving this involves an efficient combination of existing treatment and upgrading processes. The WtE plant treats more than 95,000 tonnes of household and industrial waste a year to produce regenerative electrical energy. Instead of being fed into the public grid, this electricity is used in the Power to Gas plant’s electrolysis unit to split potable water from the wastewater treatment plant into hydrogen (H2) and oxygen (O2). The hydrogen is used in the biological methanation process, where microorganisms convert it into methane by feeding in biogenic gas from the wastewater treatment unit containing CO₂. In the digestion towers of the wastewater treatment plant, anaerobic microorganisms first break down the sewage sludge into biogas, which consists of about twothirds methane and one-third carbon dioxide. It is compressed and fed into the bioreactor, which is three-fifths full of digested sewage sludge from the wastewater treatment plant. In the BiON® process developed by HZI Schmack, archaea metabolise the CO₂ with the hydrogen from the electrolysis unit under anaerobic conditions to produce additional methane. A multi-stage upgrading process brings the product gas from the methanation reactor to the required quality for feeding into the gas grid. This produces up to 18,000 MWh of natural gas substitute a year.
Robust and Flexible Technology
The BiON® anaerobic technology used in the process has key advantages over conventional technologies. Impurities in the raw gas do not affect the process. In addition, momentum is maintained in on-off operation: after a quick stop, the system starts up again just as reliably. This way production rates can always be flexibly controlled, from standby to full capacity. And since almost no energy is needed for slow start-up of the reactors or rinsing of the systems, BiON® also scores in terms of environmentally friendly operation. The technology is also easily scalable and available in various sizes.