Case Story Switzerland

Biowaste and sewage sludge recovery: separate digestion, common gas upgrading and heat supply, Switzerland

April 2014

The new biogas digester of the company Biogas Zürich AG started operation in July 2013. It is a thermophilic installation for biowaste, built on the former composting site close to the wastewater treatment plant “Werdhölzli” of the city of Zurich, which already had digesters for sewage sludge. The separation of the two waste streams – sewage sludge and biowaste – allows using the digestate of the new plant as fertiliser. In Switzerland sewage sludge must be incinerated. The proximity of the two biogas plants (Figure 1) creates various symbioses, which are fully utilised by Biogas Zürich AG together with ERZ Entsorgung + Recycling Zürich and lead to optimised energy management of both plants.

The shares of Biogas Zürich AG are owned by the city of Zurich, Limeco and Erdgas Zürich, which represent at the same time the key partners that procure and treat biowaste, as well as produce and sell biogas.