Sewage sludge is often perceived as gross because it contains waste and faeces from sewage treatment plants. Nevertheless, sewage sludge can play a role in the energy transition as it can potentially be used to generate energy and recover valuable resources such as phosphorus.
Various types of energy can be obtained from sewage sludge. Here are some of the common methods:
Biogas production: Sewage sludge contains organic substances that can be converted into biogas through anaerobic digestion. In this process, microorganisms are used to break down the sludge and produce methane (the main component of biogas). The biogas can be used to produce electricity and heat. Thermal utilization: Sewage sludge can be incinerated in special incinerators to generate thermal energy. This heat can be used to generate steam, which in turn drives a turbine to generate electricity. The resulting waste heat can also be used for heating purposes. Pyrolysis: During pyrolysis, the sewage sludge is heated at high temperatures in the absence of oxygen. This creates liquid and gaseous products as well as a solid residue. The resulting gas can be used as fuel to generate heat or electricity. Hydrothermal carbonization: In hydrothermal carbonization, the sewage sludge is converted in a pressure vessel at high temperatures and pressures. This creates a carbon-rich solid fuel that can be used like lignite to generate heat or electricity.
It is important to note that energy recovery from sewage sludge also has other aspects to consider, such as residue disposal and contaminant treatment. In addition, the specific technologies and the efficiency of energy generation can vary depending on the location and size of the plant.