Microbial electrolysis for the energy-efficient treatment of wastewater from the hydrothermal carbonization of food waste on cruise ships

Large passenger and cruise ships generate significant amounts of food waste and biological sewage sludge every day. Until now, this waste has primarily been incinerated—an energy-intensive process associated with CO₂ emissions and air pollutants.

In collaboration with Environmental Systems GmbH, this project explores a sustainable alternative that can efficiently treat this organic waste while simultaneously converting it into valuable products.

The focus lies on hydrothermal carbonization (HTC), a process that converts wet waste into carbon-rich biochar under elevated pressure and temperature. This reduces waste volume and significantly lowers environmental impacts caused by emissions. However, the resulting HTC process water poses a major challenge, as its high organic load would overwhelm the ship’s wastewater treatment system.

Therefore, in this project, we are developing and evaluating a microbial electrolysis cell (MEC) that can treat the process water while recovering chemical energy. An MEC uses electroactive microorganisms to oxidize organic matter and transfer the released electrons to an electrode. The key question is whether this approach can operate reliably with the highly contaminated HTC process water.

At the same time, potential application pathways for the biochar produced are being evaluated, such as use as a fuel, filter material, or soil amendment.

The project follows an integrated approach: from waste treatment and wastewater treatment to the evaluation of biochar. It provides a scientific foundation for a well-founded assessment of the potential of HTC in combination with electroactive microorganisms—for more sustainable and energy-efficient waste management on board and, in the future, on land as well.