At WWTP Kralingseveer, a lithium-based tracer test was conducted in the sludge digestion tanks to evaluate hydraulic performance, with a focus on mixing efficiency and potential short-circuiting. Understanding these dynamics is essential for optimizing digestion processes and minimizing methane emissions from biosolids post-digestion.

The tracer was introduced into the digesters under normal operating conditions, and its concentration was monitored at the outlet over time. The spread and timing of the lithium signal provided insight into flow characteristics and indicated whether the sludge was well-mixed or whether portions of the sludge moved too quickly through the system. A model-based interpretation of the tracer data was used to estimate the extent of short-circuiting.

By determining the portion of short-circuiting in the digesters, a more accurate estimate can be made of the residual methane potential in the sludge after digestion. This insight is valuable for improving energy recovery, minimizing greenhouse gas emissions, and assessing the overall environmental impact of the process. The findings underscore the importance of effective mixing and well-designed digestion systems to enhance treatment efficiency. Additionally, the analysis provides a basis for identifying operational or design improvements that can reduce methane emissions post-digestion.