Unveiling amending properties of biosolids from constructed wetland systems: a comparative study

Climate change and intensive farming have caused soil degradation and decreased organic carbon stocks. Current research focuses on restoring soil fertility, often through organic amendments. Biosolids stabilized in constructed wetlands (CWs) may serve as an applicable organic amendment, although limited literature exists on their properties. This study evaluated the effectiveness of biosolids as an organic amendment and compared them with other amendments such as biochar, compost, microalgae, and digestate. Over six months, a microcosm experiment with clay-loamy soil examined soil organic matter (SOM) dynamics, organic carbon and nitrogen distribution in pools, and microbial activity. Results indicated that biosolids positively affected SOM dynamics, with a low carbon mineralization rate (k: 0.006 d^-1). Biosolids significantly increased total organic carbon and total nitrogen stocks in the soil, reaching up to 18.1 Mg·ha^-1 and 1.8 Mg·ha^-1, respectively. They also enhanced stable and recalcitrant organic carbon fractions by up to 48 % and 57 %. Furthermore, biosolids improved soil biological fertility by boosting total enzymatic activity and microbial biomass carbon, which increased by 76 % compared to the unamended control at the end of the incubation. Overall, biosolids stabilized in CWs can be effective organic amendments, producing results comparable to other amendments.