The CONCLUSION project (CO2 reduction on industrial composting plants using GNSS-based cooperative localisation) pursued UN Sustainable Development Goal 13: Climate action. The aim of the project was to use GNSS to reduce the carbon footprint throughout the entire composting process.

Composting of organic waste plays a significant role in climate protection. However, not every aspect of commercial composting is climate-friendly. In windrow composting, which is used by most domestic composting companies, the material to be decomposed is piled up in long, triangular rows. The material must be turned at regular intervals using compost turning machines. These compost turning machines are often diesel-powered and manually controlled – not automated. In addition, turning the material releases climate-damaging greenhouse gases such as carbon dioxide (CO2) and methane (CH4). The less frequently the material is turned, the higher the emissions.

The CONCLUSION project aimed to reduce climate-damaging emissions in commercial composting and builds on the predecessor projects ANTON and ANDREA, in which a GNSS-based navigation module was developed for an autonomous, electrically powered compost turner (research laboratory eWender). CONCLUSION relies on three innovative developments to reduce emissions.

The first development is an innovative concept for GNSS-based cooperative localisation of several electrically powered, autonomous compost turners (eWenders). The idea behind this is that turning the compost more frequently with climate-friendly eWenders will reduce the formation of climate-damaging greenhouse gases during decomposition. The original mobile research laboratory eWender from the preliminary projects was equipped with an expensive GNSS receiver. The concept developed in CONCLUSION is based on only one eWender being equipped with expensive equipment and serving as a mobile GNSS reference station; the remaining machines are equipped with low-cost GNSS receivers and low-cost inertial measurement units (IMUs). All receivers measure code and phase measurements. Using double-differenced carrier phases, the baselines between the eWender with a high-end GNSS receiver and the mobile low-cost rovers can be determined with high accuracy. In addition, IMU measurements are integrated to bridge short-term GNSS failures in the low-cost receivers. All observations are processed centrally using factor graph optimisation to determine the state vectors of all moving machines. The concept has been successfully tested in laboratory operations at the composting plant.

The second innovation was the development of a sharing concept for work machines using an innovative model-based systems engineering (MBSE) approach. The idea was that several composting plants would share autonomous eWenders in order to save resources. The eWenders are equipped with GNSS receivers and are transported from distribution centres (hubs) to the respective composting plants. This allows even small composting plants to compost in an environmentally friendly manner without having to resort to diesel-powered equipment. The sharing concept was designed systemically and also implemented technically. Model-Based Systems Engineering (MBSE) was used to create a clear system architecture with stakeholder models and detailed flowcharts. The technical implementation consisted of location planning, route optimisation and agent-based simulation (ABS), which realistically mapped dynamic scenarios. Highlights included efficient route planning in conjunction with a user-friendly booking system: users of the sharing system can select the time slot for which a device is to be booked. The routing algorithm then calculates the optimal round trip. The sharing system ensures flexibility for users while optimising route guidance. The agent-based simulation enabled robust testing in dynamic scenarios.

The third innovation was the development of an emission model using a coupled computational fluid dynamics (CFD) discrete element method (DEM) simulation. The aim was to investigate how CO₂ and CH₄ are released during the compost turning process. The approach maps particle-air interactions and quantifies velocity fields, which were integrated into a multiphase CFD model to map the transport and dispersion of CO₂ and CH₄. Calibration was based on DEM parameters from the predecessor project ANDREA and experimental measurements of air flow and gas concentrations from two measurement campaigns. The model reproduces the distribution of emissions during turning and thus represents a validated simulation model of the emission process. The experimental results showed that CO₂ and CH₄ concentrations increase during turning, but the additional emissions compared to the resting phase are not so large that an active capture system appears economically viable. Nevertheless, the CFD–DEM simulation model was used to demonstrate in principle how such a system could work. For this purpose, a conceptual capture system was implemented in the simulation model. By introducing an enclosure and guided extraction behind the eWender, the model was able to show that emission plumes can be effectively captured.

Finally, the project examined the climate-related effects of the electrically powered eWender in comparison to a conventional diesel turner as part of a partial life cycle assessment. The emissions during the usage phase were considered, taking into account the annual operating times and the documented energy and material consumption. The eWender produced a total of 686 kgCO2e per year, while the diesel turner produced 14,375 kgCO2e per year. This means that significant amounts of CO2 can be saved by using several eWenders at a composting plant or by implementing a sharing concept that allows eWenders to be shared between composting plants. The capture system can further reduce emissions.