Building waste sludge as nutrient adsorbents for improving soil quality
Abstract
This study investigates the potential use of waste building sludge (WBS) as soil improvement additives after enrichment with nutritionally attractive ions (NH4+ and PO43− ). Two types of sludge were tested: (i) the concrete sludge (B) and, (ii) the sludge from the production of artificial stone (TS), both enriched with NH4+ and PO43− by adsorption from amodel solution. The enriched sludge (Bsorb. and TSsorb.) were then incorporated into two soils with different characteristics: (i) sandy-loam soil (2.1), and (ii) clay-loam soil (6S). Subsequently, leaching experiments were performed to determine the release behavior of adsorbed ions and to assess the overall impact of the enriched sludges on the nutrient content of the soils. In the enrichment step, B showed a high adsorption efficiency of PO43− (≈99 %), which mainly resulted from the precipitation of poorly soluble calcium phosphate rather than true adsorption. This indicates limited availability of PO43− to plants. In contrast, TS released PO43− into the solution and acted as a secondary nutrient source. In the case of NH4+ enrichment, TS showed a higher NH4+ adsorption efficiency (approaching 60 %) than B, where the high alkalinity limited NH4+ adsorption. Leaching test showed that TSsorb. increased PO43− and NH+4 content in both soils, with higher effect in soil 2.1, whereas Bsorb. improved only 2.1 soil. Overall, the results show that enriched WBS, particularly TSsorb., have potential to enhance the quality of nutrient-deficient soils.