Enhancing the agronomic value of dry faecal sludge for agricultural soil amendment by adding natural phosphate rock and other local substrates in Burkina Faso

Raw dry faecal sludge in Burkina Faso is commonly used for agricultural soil amendment. Due to its acidity, this application may lead to various forms of soil degradation. The current study aimed to investigate rapid and sustainable agricultural valorization of dry fecal sludge in farming systems through different formulations of dry sludge-based manure. For this purpose, we prepared composite samples of dry faecal sludge from the Dogona station in western Burkina and seven formulations of dry faecal sludge-based manures. Dry faecal sludge amended with natural phosphates, montmorillonite, slaked lime and zinc ore were analyzed for their physicochemical, biochemical, pathogenetic and toxicological properties to evaluate their suitability as agricultural amendment. The results outlined that dry faecal sludge, although having a high organic matter content (25.34 ± 0.09 to 40.97 ± 9.99%), adversely affected soil structural stability because of its low pH (4.58), a low C/N ratio (10.03) and a very high COD/BOD5 ratio of 5.00. However, their content in trace metal elements (Cu, Zn, Cd, Pb, Cr and Ni) and pathogens (helminth eggs, coliforms and fecal streptococci) were in a range favorable for being used as manure. The different formulations of manures proved to be better organo-mineral amendments compared to raw sludge due to improved properties. The pH was significantly higher (between 7.24 and 7.72), the C/N ratio increased (ranging from 9.40 to 10.09) and the biodegradability indicator COD/BOD5 was significantly lower as well (r2.39 to 2.71). Our results showed that dry faecal sludge amended with local substrates gives new prospects for using these formulations as fertilizers in sustainable soil fertility management while contributing to waste recycling and environmental protection.