Management of sewage sludge is a crucial part of wastewater treatment operations. In Latvia, biological treatment of sludge such as composting and anaerobic digestion is encouraged. Out of all the sludge produced in Latvia in 2024, 11% was composted and 33% was digested, contributing to the local circular economy and a reduction in waste generation.

However, 51% of the produced sludge that year was in temporary storage, awaiting further treatment. During storage, where the environment is anoxic or anaerobic, sludge emits strong odours because of interactions between microorganisms and organic matter. Odour pollution is not only unpleasant for the WWTP staff and nearby residents but can also negatively impact human health and air quality. Therefore, odour reduction measures are facilitated. Some of the approaches can be chemical scrubbing, biofiltration or adsorption. Furthermore, odour control in the wastewater sector is a necessary part of complying with the Industrial Emissions Directive.

In this study, several odour reduction methods were tested in lab-scale experiments using sewage sludge from the largest WWTP in Latvia. Odour emissions over the course of 30 days were characterized by gas measurements and organoleptic tests. The most promising treatment strategies were the application of activated charcoal, biomass (leaves) and lactic acid bacteria. Following the lab experiments, a GIS-based odour impact assessment was performed. The results from sludge chemical profiling were included to model the areas impacted by odour emissions coming from sludge storage sites in Latvia. Overall, our work identified the most feasible sludge odour reduction methods as well as examined the possible decrease in sludge odour annoyance in the case of Latvia.