Co-granulation of bio-ash with sewage sludge and lime for fertilizer use

This study investigated co-granulation of bio-ash with sewage sludge and lime. It measured compressive strengths, neutralizing values, and elemental concentrations of the granules. The concentrations of heavy metals (As, Cd, Cr, Cu, Pb, Ni, and Zn) in the granules were sufficiently low not to prevent their use in forest fertilizer use according to Finnish legislation. Overall, the concentrations of nutrients (Ca, K, and P) were reasonably high. The addition of lime improved the neutralizing capacity of the studied granules, and the addition of sewage sludge increased their nitrogen content. The addition of sewage sludge considerably lowered the compressive strength of the granules, and the addition of lime (slaked lime) did not improve the strength of the granules. From a technical point of view, the co-granulation was very successful.