Evaluating slow sand filtration for digestate post-treatment: A step toward safe agricultural reuse in rural communities in Colombia

The digestate from low-tech digesters may not be ready for a safe agricultural reuse due to the presence of pathogens and large amounts of potential contaminants for the environment, which calls for post-treatment processes to improve its quality. This study aimed to evaluate slow sand filters (SSFs) to treat the digestate from a low-tech digester and ensure its safe reuse in agriculture. The influence of the design and operational parameters of SSFs on the quality of the filtered digestate was also evaluated, i.e. the effect of sand diameter on the effluent quality was assessed. Solids, organic matter, nutrients, and pathogens removal were analyzed to define the optimum filter configuration. Among the different sand diameters, fine sand (D10 = 0.14 mm) showed the best performance in terms of solids, dissolved organic C, phosphate, and pathogens removal efficiency (up to 50, 55, 90, and 99 %, respectively). The effluent from SSF complied with most of the quality parameters established for its reuse in fertigation. Moreover, the partial replacement of synthetic fertilizers may allow for significant savings in small-scale farms (about 200 € year−1). Filtered digestate may be thus safely reclaimed in agriculture in partial substitution to mineral fertilizers, boosting the circular bioeconomy in rural communities.