The digestate from low-tech digesters may not be ready for safe agricultural reuse due to an incomplete removal of contaminants, which calls for post-treatment processes to improve its quality. In this study, slow sand filters (SSFs) were used to treat the digestate from a low-tech digester and ensure its safe reuse in agriculture. The sand filters design was firstly optimized in terms of supernatant water level, and then the effect of sand diameter on the effluent quality was evaluated. Solids, organic matter, nutrients, and pathogens removal were analysed to define the optimum filter configuration. Results of filter design optimization showed that a supernatant water level of 5 cm allowed for the highest pathogen removal, likely due to the aerobic conditions prevailing in the biological layer. Among the different sand diameters, fine sand (D10=0.14 mm) showed the best performance in terms of total solids, dissolved organic C, phosphate, and pathogens removal efficiency (up to 50, 55, 90 and 99%, respectively). Conversely, SSFs should be further optimized to enhance ammonium-N and biodegradable organic matter removal and avoid clogging